Durian (Durio zibethinus L.): Nutritional Composition, Pharmacological Implications, Value-Added Products, and Omics-Based Investigations

Abstract

Durian (Durio zibethinus L.), a tropical fruit celebrated in Southeast Asia for its distinct flavor, is the focus of this comprehensive review. The fruit’s pulp is rich in high-value bioactive compounds, including gamma-glutamylcysteine, a precursor to the essential antioxidant glutathione. With durian cultivation gaining prominence in Southeast Asia due to its economic potential through cultivar enhancement, an in-depth examination of durian-related research becomes crucial. This review explores the health benefits of durian, analyzing the nutritional compositions and bioactive compounds present in the pulp, peel, and seed. It also underscores durian-based food products and the potential for valorizing durian waste. This review encapsulates the significant advancements made in omics-based research, aimed at deciphering the molecular complexities of durian fruit post-harvest ripening and the metabolic shifts impacting its sensory attributes. It is the first to summarize studies across genome, transcriptome, and metabolome levels. Future research should prioritize the development of molecular markers to accelerate the breeding of elite cultivars with preferred traits. It also proposes the exploration of durian waste valorization, including underexplored parts like flowers and leaves for their bioactive compounds, to promote a sustainable bioeconomy. Finally, it suggests the development of innovative durian products catering to the tastes of health-conscious consumers.

1. Introduction

Durian (Durio zibethinus L.), a significant tropical fruit crop in Southeast Asia, is revered as the “King of Fruit”. It is distinguished by its potent and unique aroma, formidable spiny husk, and intense flavor. Native to Southeast Asia, durian’s diversity center is located on the island of Borneo in Indonesia. Despite its origin, durian has been introduced to numerous countries within tropical Asia [1]. The scientific classification of D. zibethinus L. is taken from Brown [2].

• Kingdom: Plantae
• Clade: Tracheophytes
• Clade: Angiosperms
• Clade: Eudicots
• Clade: Rosids
• Order: Malvales
• Family: Malvaceae
• Genus: Durio
• Species: D. zibethinus L.

The Durio genus comprises approximately 28 species, with Borneo being the native habitat for 19 of them, indicating it as the likely center of diversity. Malaysia is home to 23 reported species [3], while the Philippines and Thailand host four [4] and six [5] species, respectively. In addition to D. zibethinus, seven other species, including D. testudinarium Becc, D. graveolens Becc, D. grandiflorus Kosterm. and Soegeng, D. dulcis Becc, D. oxleyanus Griff, D. kutejensis Hassk. and Becc, and D. lowianus Scort. ex King, yield edible fruit. These species, which vary in fruit size and pulp color, are typically found in the wild across Southeast Asia rather than in domestic cultivation. D. zibethinus, the primary cultivated durian species, is commercially grown in extensive orchards throughout Southeast Asia [6].

Thailand, home to over 200 durian varieties, is the global leader in durian exports. With annual production exceeding 600,000 tons, the export revenue in 2022 reached an impressive USD 3.3 billion, as reported by the Food and Agriculture Organization of the United Nations (FAO) [7]. The diverse durian varieties display a range of sensory traits, including variations in fruit pulp colors, textures, flavors, and post-harvest ripening periods. Global preferences vary, with Malaysia, Indonesia, and Singapore favoring pungent and bitter varieties, while Thailand prefers sweeter cultivars with a milder aroma. The global demand for durian is on the rise due to its unique tropical flavors and perceived health benefits. To meet this demand sustainably, it is essential to breed new cultivars with enhanced sensory characteristics, vibrant pulp colors, improved nutritional content, and extended shelf lives.

Durian-related research has seen a significant surge in recent years, with a particular focus on metabolic profiling. The fruit pulp, the primary organ of interest, is rich in bioactive compounds. It is a potent source of vitamins such as thiamin (vitamin B1), riboflavin (vitamin B2), A, C, and E, and minerals like calcium, phosphorus, potassium, and iron [8]. The durian fruit’s high antioxidant property, primarily attributed to its rich polyphenol content [9], adds to its nutritional value. Caffeic acid and quercetin are the dominant polyphenolic compounds in ripe durian pulp [10]. The pulp also contains carotenoids (mainly beta- and alpha-carotene) [11] and sugars. As the fruit ripens, the levels of reducing sugars (glucose and fructose) and nonreducing sugars (sucrose) increase rapidly. Nonreducing sugars, which account for 70%–80% of the total sugars, primarily contribute to the fruit pulp’s sweetness [12,13]. Among the bioactive compounds in durian fruit pulp, sulfur-containing metabolites like glutathione (GSH) and its precursor gamma-glutamylcysteine (γ-EC) [14,15] are of significant interest for human consumption.

Durian cultivation in Southeast Asia showcases unique harvesting methodologies. In Thailand, growers harvest mature fruit based on specific indices, including days after anthesis, color, spine disposition [6], and dry matter percentage [16], extending the fruit’s shelf life to 5–10 days. Conversely, in Malaysia and Indonesia, durian fruit is allowed to ripen naturally on the tree, optimizing quality and appearance. This involves collecting naturally abscised fruit multiple times daily from beneath the trees, although these naturally ripened fruits have a shorter shelf life of two to three days [6]. Existing literature reveals diverse datasets across different durian cultivars from Thailand, Indonesia, and Malaysia, particularly at the ripe stage. This variability is attributed to distinct sampling and harvesting behaviors, leading to disparate nutritional compositions. An intriguing question remains regarding the sensory characteristics and nutritional composition of naturally detached durian fruit compared to artificially ripened ones.

Modern agriculture, driven by population growth and market demands, relies on large-scale production systems that generate significant amounts of organic agricultural waste (OAW). This waste, including rejected or inedible plant tissues and food processing by-products, traditionally accumulates in landfills, causing environmental harm. Notably, fruit pulp, a major OAW component, is a by-product of fruit juice production and the rejection of climacteric fruits due to post-harvest losses. Plants, with their extensive metabolic diversity and over 200,000 structurally distinct metabolites [17], offer a wide array of health benefits [18,19]. This diversity is mirrored in OAW, making it a valuable bioactive compound source. The biocircular-green economic model (BCG) views OAW biomass as a sustainable resource rather than waste. OAW valorization allows the recovered bioactive compounds to be reintegrated into the production chain, offering potential applications in functional foods, food and feed additives, and nutraceutical and cosmeceutical products, while mitigating the adverse effects of OAW accumulation in landfills. This model aids developing nations in achieving the United Nations (UN) Sustainable Development Goal (SDG) 12, which promotes sustainable consumption and production patterns. In Southeast Asia, particularly in durian orchards, a substantial amount of OAW is generated annually, reaching approximately one million tons in 2020 in Thailand alone, as reported by FAOSTAT [20] in Khaksar et al. [21]. A diverse range of value-added products have been developed in the food, pharmaceutical, cosmetic, and nutraceutical industries by reintegrating high-value compounds from durian fruit waste back into the production chain.

The recent reduction in the cost of high-throughput next-generation sequencing platforms, coupled with the unveiling of the durian draft genome by Teh et al. [22], has led to a significant increase in durian-related research. These studies, employing single- and multi-omics-based approaches, focus on various aspects such as the identification of ripening-related transcription factor (TF) families and biosynthetic genes across genome, transcriptome, and metabolome scales. The insights derived from these investigations provide valuable information for the development of molecular markers, thereby accelerating the breeding of new cultivars with desirable traits. These findings also form the foundation for a comprehensive genome and metabolome database that includes a diverse range of durian varieties. This database serves as a crucial resource for ongoing research aimed at enhancing fruit quality and promoting sustainable agricultural practices. The collective efforts in durian-related research not only contribute to our understanding of the durian genome but also facilitate advancements in breeding techniques, ultimately benefiting the agricultural industry.

In response to the growing significance of durian cultivation in Southeast Asia and recognizing the economic potential of cultivar enhancement, this comprehensive review endeavors to expedite the breeding of superior durian varieties, standardize durian-based product development, and augment the nutritional profile of durian fruit. Our meticulous examination extends to the health benefits of durian, encompassing the pulp, peel, and seed. We focus on nutritional composition and functional properties, delving into bioactive compounds and antioxidant capacity. Moreover, we synthesize research findings on post-harvest ripening-related metabolic shifts that contribute to the distinct sensory attributes of durian fruit. By delving into the molecular mechanisms governing post-harvest ripening, we are able to provide valuable insights. Additionally, we offer an overview of durian-derived food products and explore the valorization of durian waste, enhancing its value across diverse industries, including food, pharmaceuticals, cosmetics, and nutraceuticals. In conclusion, we advocate for future research endeavors in the realm of the durian fruit, emphasizing the development of molecular markers to expedite the breeding of elite cultivars with desirable traits. Our proposal also encourages the identification and/or rediscovery of bioactive compounds from underexplored durian agricultural waste, including flowers and leaves. Finally, we indicate innovative durian product development tailored to the preferences of the new health-conscious generation. To the best of our knowledge, this review stands as the inaugural report summarizing studies on the molecular mechanisms underlying post-harvest ripening and the associated metabolic shifts in durian fruit.

2. Methodology of the Review

This study relies on an extensive literature review sourced from diverse databases such as Web of Science, PubMed, MEDLINE, Scopus, Science Direct, and Google Scholar. The search strategy focused on specific keywords and phrases, including “durian”, “durian fruit”, “durian nutritional composition”, “Durio zibethinus”, “durian bioactive compounds”, “plant-based food from durian”, “durian agricultural waste”, and “durian fruit post-harvest ripening”.

3. Durian Fruit

The durian fruit encompasses a weight average derived from all its components, including the pulp, peel, and seed (Figure 1).

Renowned for its substantial size, potent aroma, and formidable spiky husk, the durian fruit can weigh over 10 kg. The fruit exhibits varying shapes, such as globose, ovoid, or oblong, with pericarp colors ranging from green to brownish. The fleshy aril, constituting the edible part of the fruit, emerges from the funiculus, the point of attachment of the seed to the carpel. Aril development commences approximately four weeks after pollination. Notably, the pulp showcases distinct sensory characteristics among different cultivars, differing in flavor, color, texture, and thickness [23]. Edible cultivars present arils in various colors, including yellow, white, and golden-yellow [24]. Typically large, the seeds of durian fruits range from one to four per locule. Each seed is entirely encased in a fleshy aril that becomes edible, attaining a custard-like texture upon full ripening. The thickness and content of the aril can vary, offering a spectrum of flavors from deliciously sweet to relatively plain. When comparing cultivated varieties to their wild counterparts, cultivated durians stand out with exceptionally thick, juicy, and flavorful arils [25].

Morphological variations, such as spine shape, can help to distinguish different durian varieties to some extent, as noted by Hiranpradit et al. [26] for Thai durian varieties. The fruit’s shape is influenced by the presence of seeds, with locules containing unfertilized ovules leading to unevenly shaped fruits. Understanding pollination and its impact on durian fruit development is crucial, as fruit shape significantly influences marketability [6]. The durian husk’s color typically varies from green to brown, depending on the specific cultivar [27].

The durian fruit is abundant in bioactive compounds, particularly in the fruit pulp, which is the primary focus of this study due to its high concentration of these beneficial substances. We first summarize the existing literature reporting information on the pulp, including nutritional and bioactive compounds. We will then discuss the available information on the other parts of the fruit, namely the peel and seed.

3.1. Durian Pulp

3.1.1. Nutritional Value

The energy content of durian pulp, as documented for several durian cultivars [10,28], ranges from 84 to 185 kcal per 100 g on a fresh weight (FW) basis. The Thai durian cultivar ‘Kradum’ has the highest energy content at 185 kcal/100 g FW, while the Indonesian durian cultivar ‘Hejo’ has the lowest at 84 kcal/100 g FW [28]. This fluctuation in energy content is primarily due to differences in carbohydrate content, which varies from 15.65 to 34.65 g/100 g FW across different durian cultivars [28,29]. Compared to other tropical fruits like mango, jackfruit, and pineapple, durian has a higher energy content (United States Department of Agriculture (USDA) Food Composition Data) [30]. The protein content in various durian cultivars ranges from 1.40 to 3.50 g/100 g FW [28,29]. Durian is also rich in fat, with amounts ranging from 1.59 to 5.39 g/100 g FW [28,29,31]. In comparison to ripe olives, durian’s fat content is approximately one-third (USDA Food Composition Data) [30]. The total sugar content in different durian cultivars ranges from 3.10 to 19.97 g/100 g FW. Among the sugars present in durian pulp, sucrose is the most abundant, ranging from 5.57 to 17.89 g/100 g FW, followed by glucose, fructose, and maltose [32]. According to Ho and Bhat [24], Devalaraja et al. [33], Voon et al. [34], and Gorinstein et al. [35], the nutritional composition of durian fruit pulp includes significant amounts of water, carbohydrates, lipids, fibers, and proteins, as detailed in

Table 1. Nutritional and quality parameters of durian fruit pulp.

Compound	Proximate Amount (g/100 g on a Fresh Weight Basis)
Water (moisture)	61.43–64.99
Carbohydrates	26.11–27.09
Total lipids	5.07–5.33
Fibers	2.87–3.08
Proteins	1.02–1.47
Ash	1.01–1.12
Parameter
pH	6.88–7.60
Titratable acidity	0.09–0.26
Total soluble solids (%)	32.00–41.00

Reference: [24,33,34,35].

.

Previous studies have investigated the fatty acid compositions in the pulps of various durian cultivars. In a study conducted by Haruenkit et al. [36], it was noted that the primary unsaturated fatty acids in durian pulp cv. ‘Monthong’ were oleic and linoleic acids. The principal saturated fatty acids present in durian included capric, myristic, palmitic, arachidic, and stearic acids. In a separate study by Phutdhawong et al. [37], the main fatty acids identified in the pulp cv. ‘Monthong’ were linoleic acid (2.20%), myristic acid (2.52%), oleic acid (4.68%), 10-octadecenoic acid (4.86%), palmitoleic acid (9.50%), palmitic acid (32.91%), and stearic acid (35.93%). The presence of unsaturated fatty acids, including omega-3 fatty acids (polyunsaturated fatty acids), can offer numerous health benefits, such as reducing blood pressure, inflammation, plasma triacyclglycerols, and platelet aggregation. These associations have been highlighted in studies by Breslow [38] and Rodriguez et al. [39].

Numerous studies have highlighted the mineral compositions of durian pulp across different cultivars, showcasing a rich potassium content that ranges from 70.00 to 601.00 mg/100 g on a FW basis [29,31]. This potassium concentration is comparable to other potassium-rich fruits, such as bananas, which contain approximately 358.00 mg/100 g FW (USDA Food Composition Data) [30]. The phosphorus, magnesium, and sodium content in durian ranges from 25.79–44.00, 19.28–30.00, and 1.00–40.00 mg/100 g FW, respectively. Durian also serves as a source of iron, copper, and zinc [32].

Durian pulp serves as a rich source of various vitamins, each playing a crucial role in maintaining overall health and well-being. On a 100 g FW basis, durian pulp contains the following vitamins (in mg): vitamin C (19.7); thiamine (vitamin B1) (0.374); riboflavin (vitamin B2) (0.2); niacin (vitamin B3) (1.074); pantothenic acid (vitamin B5) (0.23); and vitamin A (44) [33,34,35]. Folates, also known as vitamin B9, are essential nutrients that the human body cannot synthesize independently. Therefore, it is vital to ensure an adequate supply through dietary sources or supplements. Striegel et al. [40] found that durian pulp is an exceptionally rich natural source of folates, containing 0.175–0.44 mg/100 g on a FW basis. Given that the recommended daily intake of folate is 0.3 mg, individuals with a penchant for durian in Southeast Asia may effortlessly meet or exceed their daily folate requirements by consuming more than 200 g of durian per day.

3.1.2. Bioactive Compounds

Regular consumption of fresh fruits is essential due to their abundant content of health-enhancing bioactive compounds, including polyphenols and vitamins. These bioactive compounds, renowned for their antioxidant properties, play a vital role in neutralizing free radicals, thereby reducing levels of oxidative stress. Consequently, processes detrimental to the development of chronic diseases, such as cancer and coronary heart disease, can be mitigated. Recent reports highlight that durian pulp boasts a diverse array of bioactive compounds, encompassing polyphenols, such as tannins, phenolic acids, and flavonoids, and carotenoids (

Table 2. Profile of bioactive compounds present in durian fruit pulp.

Group	Class	Identified Compound(s)	Reference
Polyphenols
	Tannins	-	[36,41]
	Hydroxycinnamic acids	Caffeic acid, p-coumaric acid, ferulic acid, p-anisic acid	[41]
	Hydroxybenzoic acids	Gallic acid	[10]
	Flavanols	Morin, quercetin, rutin, kaempferol, myricetin	[42]
	Flavanones	Hesperetin, hesperidin	[42]
	Flavones	Luteolin, apigenin	[42]
	Anthocyanins	-	[9,10]
Carotenoids		β-carotene, α-carotene, β-cryptoxanthin, lycopene, lutein, zeaxanthin	[11]

- indicates that no compounds were reported in the provided references.

).

Notably, total phenolic content of durian pulp ranges from 21.44 to 374.30 mg gallic acid equivalent (GAE)/100 g FW [10,43,44], whereas its total flavonoid content varies from 1.90 to 93.90 mg catechin equivalent (CE)/100 g FW [10,42,43].

Phenolic acids identified in durians fall into two categories: hydroxycinnamic acids, including caffeic acid (31.08–490.00), p-coumaric acid (29.22–600.00), ferulic acid (158.67–414.40), and p-anisic acid (1.48) on a μg/100 g FW basis [41], and hydroxybenzoic acids, such as gallic and vanillic acid derivatives [10]. Additionally, durian pulp contains three primary flavonoids: flavonols like morin, quercetin, rutin, kaempferol, and myricetin; flavanones like hesperetin and hesperidin; and flavones like luteolin and apigenin [42]. Total carotenoid content of durian pulp varies from 5.13 to 8.22 μg β-carotene equivalent per 100 g FW [11]. The carotenoid profile of durian pulp includes β-carotene, α-carotene, β-cryptoxanthin, lycopene, lutein, and zeaxanthin [11], as outlined in Table 2. Notably, according to Wisutiamonkul et al. [45], the durian pulp gradually turns yellow due to the accumulation of carotenoids, primarily β-carotene and α-carotene, along with minor amounts of zeaxanthin and lutein. Moreover, the anthocyanin content in the durian pulp is at 0.32–633.44 cyanidin-3-glucoside equivalent per 100 g FW [9,10]. The content of bioactive compounds significantly varies based on factors such as cultivars and ripening stages.

A study conducted by Toledo et al. [10] examined the bioactive compound content in the pulp of various Thai durian cultivars, including ‘Monthong’, ‘Chanee’, ‘Kan Yao’, ‘Phungmanee’, and ‘Kradum’. Among these, ‘Monthong’ exhibited the highest levels of total phenolic content (361.4 mg GAE/100 g) and flavonoid content (93.9 mg CE/100 g) based on FW measurements. In another study by Ashraf et al. [43], various Malaysian durian cultivars, including ‘Chaer Phoy’, ‘Yah Kang’, ‘D11’, and ‘Ang Jin’, were analyzed for their phenolic, flavonoid, carotenoid, and vitamin C contents. The durian pulp of the cultivar ‘Ang Jin’ exhibited the highest concentrations of total phenolics and flavonoids. However, the carotenoid content was relatively low. In terms of vitamin C content, the pulp of the cultivar ‘D11′ had the highest amount, while ‘Ang Jin’ had the lowest.

Arancibia-Avila et al. [9] conducted a study to investigate the content of bioactive compounds in the pulp of the ‘Monthong’ cultivar of durian at various stages of ripening. They found that the ripe pulp had significantly higher levels of total phenolic and flavonoid contents compared to the mature and overripe stages. Interestingly, hydrolyzed forms of polyphenols and flavonoids were more prevalent than their free forms. The primary antioxidant compounds identified in the ripe durian pulp were caffeic acid and quercetin. In contrast, a study by Haruenkit et al. [36] reported that the overripe pulp of the ‘Monthong’ durian cultivar exhibited the highest level of polyphenols, with a measurement of 4.3 mg GAE/g dry weight (DW). However, the ripe durian was found to have a higher concentration of flavonoids, measuring 2.2 mg CE/g DW. Furthermore, Paśko et al. [46] reported that the ripe and overripe fruit of the ‘Monthong’ cultivar had the highest contents of polyphenols, flavonoids, flavanols, tannins, and vitamin C. They also found that these stages of the fruit had the highest antioxidant capacities, as measured by radical scavenging assays.

In summary, durian pulp contains a diverse array of bioactive compounds, including polyphenols and carotenoids. However, the concentrations of these bioactive compounds can vary due to factors such as differences in cultivars and stages of ripening.

Durian pulp is rich in bioactive polyphenols, imparting significant antioxidant capabilities. The antioxidant capacity of durian pulps from numerous cultivars has been assessed using diverse methods, including 1-diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH), ferric ion reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), 2,2-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS), and cupric reducing antioxidant capacity (CUPRAC) assays. The reported values for each assay are presented in

Table 3. Evaluation of antioxidant properties in durian fruit pulp across various Thai cultivars.

Cultivar	DPPH	FRAP	ORAC	ABTS	CUPRAC	Reference
Monthong, Chanee, Kradum, Kan Yao, Phuangmanee	97.93–1366.16	71.84–749.08	1903.40–2793.90	265.86–2352.70	427.65–1075.60	[10,29,31,36,47]

Values are presented as μM trolox equivalent per 100 g fresh weight. 1-diphenyl-2-picrylhydrazyl radical scavenging activity (DPPH), ferric ion reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC), 2,2-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS), cupric reducing antioxidant capacity (CUPRAC).

. The antioxidant potential of the pulp exhibits significant variability based on the ripening stage.

Significant variations in antioxidant capacity levels during the pulp ripening stages have been documented in several studies. In the study by Arancibia-Avila et al. [9], investigating the impact of different ripening stages on the antioxidant properties of the durian pulp cv. ‘Monthong’, ripe durian extracts demonstrated higher antioxidant capacity, as assessed by FRAP and CUPRAC, compared to extracts from overripe durian fruits. Similarly, Leontowicz et al. [48] reported that the antioxidant capacity of extracts from the ripe durian pulp cv. ‘Monthong’ surpassed that of mature and overripe fruit, based on the results from the DPPH and ABTS assays.

Durian fruit pulp is recognized for its rich array of high-value bioactive compounds, among which γ-EC, the direct precursor to GSH, is particularly noteworthy for human consumption. Durian fruit pulp serves as a substantial natural source of both GSH and γ-EC [14,15], containing approximately 2.6 and 14 mg/g DW, respectively [49]. Interestingly, the levels of GSH and γ-EC in ripe durian pulp significantly exceed those found in various other fruits and vegetables [49]. GSH, an important endogenous antioxidant, is the most abundant low-molecular-weight thiol found in mammalian cells. It plays a crucial role in maintaining and regulating the thiol-redox status of the cell. Beyond its roles as a reducing agent and a major antioxidant [50], GSH is involved in numerous physiological functions [51]. The effective operation of our immune system depends on maintaining a finely tuned intermediate level of GSH within lymphoid cells. Even slight changes in intracellular GSH levels can adversely affect the functions of lymphocytes [52]. Cellular GSH depletion often results from the downregulation of expression or reduction of the specific activities of the first biosynthetic enzyme, glutamate-cysteine ligase [53]. GSH levels have been shown to decrease with aging and in several age-related degenerative diseases, particularly Alzheimer’s disease—the most common form of dementia affecting the elderly [54]. Interestingly, it has been suggested in the literature that the supply of γ-EC may become limiting for maintaining cellular GSH at normal levels, which is required to efficiently protect against oxidative stress and potential physiological damages. A study by Zarka and Bridge [55] found that oral administration of γ-EC (a single 2-g dose) significantly enhanced intracellular GSH levels above homeostasis. Furthermore, Braidy et al. [56] documented the beneficial effects of increased GSH levels by γ-EC, which can decrease apoptosis, oxidative stress, and inflammation in human astrocytes. These studies collectively identify a potential therapeutic strategy.

Given that durian fruit pulp is considered a rich source of γ-EC, breeding new varieties with enhanced levels of γ-EC and other bioactive compounds could pave the way for biofortifying durian fruit as functional foods. This is especially relevant in an era when human health is being dramatically threatened by pathogen outbreaks, such as the coronavirus disease of 2019 (COVID-19).

3.1.3. Polar Metabolite Profiling

In recent decades, metabolomics has seen widespread application across diverse scientific disciplines, propelled by advancements in analytical instrumentation and data-analytics platforms [57]. Multiple studies have delved into the metabolic profiling of durian fruit pulp, both during post-harvest ripening and at the ripe stage.

Pinsorn et al. [14], utilizing capillary electrophoresis-time of flight/mass spectrometry (CE-TOF/MS), identified cultivar-specific metabolite markers associated with durian fruit quality traits. These traits spanned nutritional aspects, exemplified by the presence of pyridoxamine, and sensory characteristics, including odor-related compounds such as cysteine and leucine. Furthermore, markers linked to the ripening process, represented by aminocyclopropane carboxylic acid, were discerned. Notably, a significant accumulation of metabolites associated with sulfur metabolism was observed in the fruit pulp. In a subsequent study by Sangpong et al. [13], a thorough examination of durian pulp at both unripe and ripe stages revealed 94 metabolites intricately associated with the ripening process. During ripening, there was a discernible increase in sucrose content. This study, for the first time, reported changes in raffinose-family oligosaccharides. Concurrently, the malate and succinate contents increased, while citrate, an abundant organic acid, remained unchanged. Intriguingly, there was an overall elevation in most amino acids, including isoleucine, leucine, and valine, whereas aspartate decreased and glutamate remained unchanged.

These studies significantly enhance our understanding of the dynamic metabolic transformations that occur in durian fruit during post-harvest ripening. They shed light on cultivar-specific markers, providing valuable insights into nutritional aspects, odor development, and the overall ripening process. Despite these advancements, a comprehensive metabolome database that encompasses diverse durian varieties with distinct sensory characteristics is still lacking. In the wake of domestication and enhancement efforts by breeders, various types of durian fruit have emerged. These are tailored to human preferences, usage patterns, and local climates. However, the metabolic alterations that accompany these guided evolutionary processes in durian fruit remain largely unexplored. Investigating how human breeding programs have influenced the durian fruit metabolome is crucial. This is key to establishing a knowledge base to enhance fruit quality and providing a valuable resource for future studies in plant metabolic biology. To address this gap, future studies should incorporate multi-omics analyses. Notably, biological systems are intricate, with various components working together synergistically. The integration of multi-omics approaches can help address gaps or uncertainties present in single-omics datasets. This will help to discern the impact of appearance- and taste-oriented breeding programs on the metabolic profile of durian. This approach will not only contribute to our understanding of the molecular underpinnings of durian diversity but also serve as a foundation for continued research. The aim is to improve fruit quality and foster sustainable agricultural practices.

3.1.4. Volatile Components

Fruits produce a range of volatile compounds that vary in concentration. These compounds give each fruit its own unique aroma and significantly influence its flavor. The primary volatile compounds include aldehydes, alcohols, terpenes, and other substances. These compounds play a significant role in the creation of various products, such as bakery foods, beverages, and cosmetics. From an organoleptic perspective, these volatile compounds are crucial, as they can influence consumers’ acceptance of a product. In fact, the flavor of a product can be a harmonious blend of different volatile molecules. The pulps of different durian cultivars are known for their unique and robust aromas. These aromas are characterized by their abundant ester and volatile sulfur compound (VSC) contents. Esters play a pivotal role in imparting a sweeter, fruitier fragrance. On the other hand, VSCs, such as thiols, disulfide, and trisulfides, contribute to the distinctive roast and onion-like odor associated with durian [58,59]. Notably, methionine γ-lyase (MGL) was identified as the main enzyme associated with the production of VSCs [22].

Baldry et al. [60] conducted a study on durian fruits, identifying 26 distinct volatile compounds in the distilled samples. These compounds were primarily categorized into one aromatic compound, two aldehydes, four alcohols, seven sulfur compounds, and twelve aliphatic esters. In a separate study, Chin et al. [58] examined three Malaysian durian varieties, namely ‘D2’, ‘D24’, and ‘D101’, and reported the presence of 39 volatile compounds. Similarly, an analysis of Indonesian durian varieties, including ‘Ajimah’, ‘Hejo’, ‘Matahari’, and ‘Sukarno’, revealed the identification of 44 volatile compounds [61]. Sulfur was identified as the primary volatile component found in durian, with ethanethiol, propanethiol, diethyl disulfide, ethyl propyl disulfide, and diethyl trisulfide being the most abundant sulfur compounds detected in the Malaysian durian variety. A comprehensive summary by A Aziz and Mhd Jalil [32] presented the mean relative amounts of volatiles identified in different durian cultivars from Malaysia and Indonesia. Furthermore, Li et al. [62] utilized aroma extract dilution analysis to discover 44 different odor compounds present in Thai durian pulp cv. ‘Monthong’. Interestingly, 24 of these compounds were previously unidentified. The study also revealed the presence of unique compounds like 1-(propylsulphanyl) ethanethiol in a natural product for the first time. Aschariyaphotha et al. [63] compared the volatile profiles of three Thai commercial cultivars, including ‘Kanyao’, ‘Chanee’, and ‘Monthong’. Out of 41 volatile compounds detected in ripe durian pulp, 33 were esters. In a study by Xiao et al. [64], a total of 27, 36, and 38 volatile compounds were detected in ‘Black Thorn’, ‘Musang King’, and ‘Monthong’ cultivars, respectively, among which some aroma-active substances were identified.

Harvesting methods significantly impact the aroma and overall flavor of durian fruit. Durians that naturally detach from the tree (natural fall) exhibit a more pronounced aroma than those that are artificially ripened [65].

While the studies mentioned above have provided valuable insights into the volatile compound profiling of durian fruit pulp, there are still significant areas that warrant further research. These areas pertain to the realm of volatile and aromatic compounds in durian fruit pulp and include:

• Elucidation of the kinetic scheme of aroma formation:

Investigating the dynamic process of aroma induction and formation at different stages of fruit maturity, including developmental and post-harvest ripening stages. The goal is to gain a better understanding of the kinetic scheme involved in aroma formation.

2.

Role of environmental conditions in aroma induction and formation:

Determining the specific role played by environmental conditions in inducing aroma in durian fruits by exploring factors such as temperature, humidity, and atmospheric composition.

3.

Comparative analysis of volatile compounds in raw and processed durian fruit products:

Conducting a comprehensive comparison of volatile compounds in raw durian fruits versus those in processed durian fruit products can help to identify changes in aroma profiles during processing.

Addressing these research gaps can lead to a deeper understanding of the complex interplay of factors influencing the flavor and aroma of durian fruits. This knowledge can contribute to enhancing the quality control, post-harvest management, and processing techniques of durian fruit pulp. Ultimately, this could benefit consumers and the durian industry by improving the overall quality and appeal of durian products.

3.2. Durian Peel

Nutritional Value

Durian peel constitutes approximately 60% of the entire fruit. A compilation of previous studies outlining the chemical composition of durian peel is presented in

Table 4. Composition of durian fruit peel.

Tissue/Cultivar	Identified Compounds	Reference
White inner sac and the outer shell/unknown	Phenolic acids and phenolic glycosides, coumarin, triterpenoids, simple glycosides	[66,67]
Peel/unknown	Pectin	[68]
Shell/Monti, Malik, and Malon (Indonesian)	Flavonoids	[69]
White inner and green outer rinds/Monthong (Thai)	Crude protein, crude lipid, crude fiber, moisture, ash, minerals	[70]
Peel/Unknown (Thai)	Insoluble and soluble dietary fiber	[71]
Hull powder/Unknown	Moisture, glucose, ash	[72]

.

The peel contains polysaccharides, such as pectin [68], triterpenoids, phenolics, glycoside esters [66,67], and flavonoids [69]. Additionally, a study by Wang and Li [73] sheds light on the polyphenol content of durian peel, reporting a methanolic extract containing approximately 33.77 mg GAE/g in terms of total polyphenols. The antioxidant activity of durian peel has also been investigated. According to Wang and Li [73], methanolic extracts from durian peel exhibited various IC50 values in different assays. Specifically, the values were 280.79, 154.67, 324.63, 770.52, 4.45, 102.37, and 19.50 g/mL for activities including reducing power (Fe³⁺), reducing power (Cu²⁺), hydroxyl radical scavenging, superoxide anion radical scavenging, anti-lipid peroxidation, DPPH, and ABTS, respectively.

3.3. Durian Seed

Nutritional Value

Durian seeds, which make up approximately 20% of the whole fruit, have been the subject of several studies investigating their nutritional composition. Srianta et al. [74] found that fresh durian seeds are composed of 54.90% moisture, 3.40% protein, 1.58% ash, 1.32% fat, and 18.92% starch. In another study, Amin and Arshad [75] analyzed the composition of whole durian seed flour and found it to contain 6.5% water, 6.0% protein, 3.1% ash, 0.4% fat, 10.1% crude fiber, and 73.9% carbohydrates. Deng et al. [76] reported that durian seed extracts have a total polyphenol content of approximately 3.67 mg GAE/g. They also found that the fat- and water-soluble fractions of the seed exhibited antioxidant capacity, as demonstrated by the ABTS assay.

4. Development of Plant-Based Foods (PBFs) from Durian Fruit

Recent reports underscore the untapped potential of both edible and nonedible components of the durian fruit in terms of their nutritional value. Traditionally, durian fruit pulp is enjoyed on its own or paired with sticky rice, a starch-rich companion. Additionally, it serves as a key ingredient in various bakery products, such as durian cake. The production of PBFs derived from both durian pulp and seeds is summarized in

Table 5. Plant-based foods (PBFs) developed from durian fruit pulp and seed.

Tissue/Food Product	Preparation Method	Country of Origin	Reference
Pulp
Tempoyak	Combining durian pulp with salt and lactic acid bacteria (LAB) which has undergone anaerobic fermentation at an ambient temperature	Malaysia, Indonesia	[77]
Lempok	Boiling durian flesh with coarse sugar	Malaysia, Indonesia	[77]
Dodol	Cooking pulp with sugar	Malaysia, Indonesia	[78]
Durian paste (durian kuan)	Pulp cooked with flour and sugar	Malaysia, Indonesia, Thailand	[78,79]
Durian juice	Durian pulp was processed by treating with pectinase enzyme at different concentrations	Malaysia	[80]
Durian jam, candy, toffees, ice cream, wine, and milkshakes	Durian pulp undergoes the general manufacturing process	Southeast Asia and international market	[24]
Dried fruit powder	Freeze-drying and spray-drying the pulp	-	[81]
Seed
Angkak	Solid-state fermentation technique is employed (durian seed as a substrate for Monascus sp.)	Indonesia, China, Philippines, and Thailand	[74]
Vegan mayonnaise	Durian seed gum serves as the emulsifying agent instead of the conventional egg yolk	-	[82]
Candy	Seeds are roasted, cut into slices, and coated with sugar	Indonesia	[24]
Dish	Seeds are fried in spicy coconut oil and consumed as a dish with rice	Indonesia	[24]
Serawa (sweet sauce)	Boiling pulp and seeds along with brown sugar and coconut milk	Malaysia	[83]
Snack	Seeds are often roasted or boiled and eaten as a snack	Southeast Asia	[84,85]

.

Durian pulp finds versatile applications in Southeast Asian culinary delights, including dodo (pulp cooked with sugar) and durian paste (durian kuan) (pulp cooked with flour and sugar). These products are gaining global popularity, as evidenced by their recent distribution beyond the Southeast Asian region (Table 5). Significantly, efforts have been directed toward commercializing processed durian pulp, leading to the production of dried fruit powder using freeze-drying and spray-drying techniques [81]. It is crucial to emphasize that the nutritional integrity of durian fruit pulp may undergo degradation during the processing phase. As elucidated by Singcha et al. [49], the substantial reduction in GSH and γ-EC levels in durian chips and pastes, compared to the unprocessed pulp, indicates a detrimental impact attributed to the processing, particularly the application of heat.

In addition to the pulp, durian seeds offer a promising opportunity for the development of PBFs. Angkak, also known as monascus-fermented rice, is a traditional food popular in Indonesia, China, the Philippines, and Thailand. Traditionally, Angkak is produced through solid-state fermentation, using rice as a substrate for Monascus sp. However, a study by Srianta et al. [74] demonstrated that durian seeds can also serve as a novel substrate for Monascus sp. in the production of Angkak. Another typical example is the production of vegan mayonnaise wherein durian seed gum serves as the emulsifying agent instead of the conventional egg yolk [82].

In conclusion, the exploration of durian fruit components, both pulp and seed, has resulted in the development of various PBFs with significant culinary and nutritional implications. The global distribution of durian-based products and the inventive use of durian seeds in traditional foods like “Angkak” highlight the expanding potential of this unique fruit in the food industry. Further research should concentrate on creating innovative food products from durian fruit tailored for the new generation of health-conscious consumers, including options like probiotic-fortified durian juice.

5. Valorization of Agricultural Waste from Durian Plants: Development of Value-Added Products in a Circular Economic Model

Transitioning to a systemic and circular approach, emphasizing “reuse, recycle, and regenerate”, is pivotal for advancing a sustainable agricultural sector and achieving UN SDG 12. In this context, OAW is a valuable reservoir of bioactive compounds, including phenolic compounds and secondary metabolites, known for their diverse health benefits. Harnessing OAW as a material for extracting and uncovering novel functional compounds offers an opportunity to reintegrate these discoveries into the production system. This strategy not only addresses the negative environmental repercussions associated with OAW accumulation in landfills but also enhances value across various industries, including food, pharmaceuticals, cosmetics, and nutraceuticals.

According to data from FAOSTAT [20], as reported in Khaksar et al. [21], durian peel, pulp, and seed collectively contributed to a substantial amount of OAW, reaching 1,111,928 tons in Thailand in 2020. In food, pharmaceutical, cosmetic, and nutraceutical industries, several value-added products have been developed by reintegrating high-value compounds from durian fruit waste back into the production chain. Noteworthy examples of this practice are summarized in

Table 6. Value-added products from durian organic agricultural waste.

Waste	Value-Added Product	Application	Typical Example	Reference
Seed	Gum	Thickening, gelling, stabilizing, and suspending agents in foods	Emulsifier in vegan mayonnaise	[82,83]
Seed	Flour (starch)	Food applications (thickening agent)	-	[83,85]
Seed	Enzyme β-galactosidase	Food application	Application in pasteurized milk to produce ice milk	[86,87]
Peel and seed	Extract (antioxidant and antibacterial agent)	Food preservative	Shelf-life enhancement of preserved meat	[88]
Peel	Polysaccharide gel	Dressing film	Wound healing in pig skin	[89]
Peel	Polysaccharide gel	Feed supplement	Stimulating immune response and lowering cholesterol levels in the chicken	[90]
Peel	Polysaccharide gel	Skin moisturizer	Application showed significant effect on skin capacitance and significantly increased skin firmness	[91]
Peel	Polysaccharide gel	Pharmaceutical application	Inhibiting cartilage degradation enzymes (matrix metalloproteinase groups (MMPs))	[92]
Peel	Polysaccharide gel	Pharmaceutical application	Antimicrobial activity (in vitro)	[93]
Peel	Organohydrogel	Antimicrobial wound dressing in medical supplies	Wound dressing on pig skin	[94]
Peel	Extract	Pharmaceutical application	Anti-inflammatory agent	[67]
Peel	Flour	Food industry	Wheat flour is replaced by durian peel flour for the development of gluten-free biscuits	[95]
Peel	Extract	Pharmaceutical application	H2O2-induced oxidative damage in HepG2 cells was reduced	[96]
Peel	Crude polysaccharide extract	Pharmaceutical application	Effect in treating functional constipation and regulating intestinal flora in rats	[97]
Peel	Hydrolysate	Bioenergy	Bioconversion of peel hydrolysate into biodiesel	[98]
Peel	Pelletized biochar	Bioenergy	-	[99]
Peel, seed, and pulp	Flour	Food industry	-	[100]
Peel, seed, and pulp	Crude and polysaccharide extract	Cosmetics	A gel formulation containing the extract was prepared by a cold process. It had a good stability, with no skin irritation reported by the volunteers	[101]
Peel (white inner part)	Ground powder	Feed supplement	Disease resistance in Red Tilapia fish	[70]
Early immature durian fruit	Crude extract	Cosmetics	It is used in various types of cosmetic products in Thailand as anti-premature skin aging	[102]
Pulp	Extract	Pharmaceutical application	Antiproliferative activities on human cancer cell lines	[36,46,103,104,105]
Pulp	Extract	Pharmaceutical application	Antidiabetic effect (regulating the expression of glycolysis regulatory genes) on HepG2 cell line	[46]
Pulp	Extract	Pharmaceutical application	Neuroprotective effect on human neuroblastoma cell line (SH-SY5Y)	[106]
Pulp	Extract	Pharmaceutical application	Anti-mutagenic and chemopreventive effects	[107]
Pulp	Extract	Pharmaceutical application	In vitro studies on the interaction of extracted durian polyphenols with human serum proteins (HSP)	[108]

, while Figure 2 illustrates the value-added products derived from durian fruit waste.

5.1. Valorization of the Seed

Several studies have explored the potential of utilizing durian seeds as a starting material for valorization. Significant value-added products derived from these seeds include seed gum and flour, widely acknowledged for their extensive use as thickening agents in the food industry. This popularity is attributed to the abundant presence of starch and other hydrocolloids in durian seeds (Table 6) (Figure 2).

5.2. Valorization of the Peel

The durian peel, comprising about 60% of the whole fruit, stands out as the predominant source of OAW accumulation in durian orchards across Southeast Asia. Substantial evidence underscores the significant potential of durian peel as an ideal feedstock for valorization. This acknowledgment has stimulated the creation of diverse value-added products spanning various industries. These include flour for the food industry, organohydrogel in pharmaceuticals, polysaccharide gel for skin moisturizers in cosmetics, and pelletized biochar for bioenergy applications (Table 6) (Figure 2).

5.3. Valorization of the Pulp

Durian pulp, renowned for its abundant bioactive profile, constitutes a significant portion of OAW. Mitigating post-harvest losses, especially for perishable fruits like durian with a short shelf life, is imperative. The valorization of durian pulp has resulted in the creation of various value-added products, particularly in the pharmaceutical industry (Table 6). Encouragingly, exploring the use of durian pulp extract as a functional dietary supplement is justified due to its nutritional composition and pharmacological impacts. These encompass antiproliferative effects [36,46,103,104,105], neuroprotective properties [106], and antidiabetic activities [46] on human cell lines. Furthermore, environmentally friendly extraction from waste material adds to its prestige.

Collectively, durian fruit waste exhibits promising nutraceutical value, substantiated by robust scientific evidence regarding its rich content of bioactive compounds (Figure 3). However, further research is crucial to elucidate the specific functional properties of value-added products derived from durian fruit waste, aiming to determine their suitability as functional food ingredients. Additionally, a comprehensive investigation into the bioactivity and safety profiles of the extracted compounds is essential for an accurate assessment of the true potential of these phytochemicals. For nonedible durian wastes, such as peels and seeds, there is a pressing need for more studies, including toxicity tests and/or animal model studies, to ensure their safety for potential applications. Exploring the use of durian seeds in pharmaceutical applications is also an area worthy of investigation. Moreover, additional research is warranted to explore the potential uses of durian flowers and leaves as organic agricultural waste for the development of value-added products. Addressing the potential risks associated with the waste valorization process, including the presence of contaminants from chemicals in crop residues due to the excessive use of pesticides and synthetic fertilizers, is crucial. This factor should be meticulously considered in research and development efforts. Overall, a comprehensive and multidisciplinary approach is essential to unlock the full potential of durian fruit waste in various applications, ensuring both efficacy and safety.

6. Toward Molecular Marker Development to Accelerate the Breeding of Novel Elite Cultivars with Desirable Traits

The global market is currently experiencing an increased demand for exotic fruits, with durian gaining significant attention as consumers worldwide actively seek novel taste experiences and potential health benefits. To address these demands sustainably, it becomes imperative to prioritize the development of new durian cultivars. These cultivars should feature enhanced sensory characteristics, including enticing aromas and flavors, vibrant pulp colors, improved nutritional values, and an extended shelf life. Meeting these criteria is paramount to satisfying the diverse preferences of consumers worldwide.

Durian breeding programs in Thailand traditionally employ a combination of outcrossing and selection methods to generate new cultivars. Many small-scale farmers rely on seedlings sourced from seeds harvested on their own farms or from clonal material resulting from hybridization and selection initiatives. The breeding strategy involves identifying and selecting promising maternal trees, assessing their adaptability over time and across different locations. The selection process prioritizes key characteristics such as fruit shape, size, aroma, color, texture, taste, and tree growth habits. However, durian breeding faces challenges such as prolonged juvenile periods, recurring growth cycles, substantial tree size, polyploidy, and inherent genetic diversity [6,109]. Conventional breeding methods are also known for being time-consuming, labor-intensive, and requiring extensive land resources. The overarching goal of breeding is to achieve genetic gains in desirable traits into crop genomes in a time- and cost-efficient manner. Hence, the development of molecular markers is crucial to accelerating the breeding of novel elite cultivars with desirable traits. To achieve this objective, enhancing our understanding of the molecular mechanisms driving the ripening process in durian fruit is imperative.

Integrated multi-omics strategies have been extensively employed to deepen our understanding of the molecular mechanisms governing various plant functions in economically valuable crops. Despite the crucial role of durian cultivation in the Southeast Asian region and its significant economic value in terms of cultivar enhancement, there is a notable gap in extensive research utilizing omics-based approaches for durian. In this context, we present an overview of research exploring the molecular mechanisms involved in the post-harvest ripening process of durian fruit, including the identification and characterization of ripening-related TF families (

Table 7. Ripening-related transcription factor families during post-harvest ripening of durian fruit.

Name	Ripening-Associated Role	Function	Target Gene(s)	Reference
Dof2.2	Regulation of auxin biosynthesis	Activator	TAA, YUCCA4	[110]
ARF2A	Regulation of ethylene biosynthesis	Activator	ACS, ACO	[111]
ERF6	Regulation of ethylene biosynthesis	Putative repressor	ACS, ACO	[112]
ERF9	Regulation of ethylene biosynthesis	Putative activator	ACS, ACO	[112]
CAMTA3, CAMTA8	Ethylene-mediated signaling	Putative activator	-	[113]
HD-ZIP1.8	Regulation of volatile sulphur compound production	Activator	MGL	[114]

DNA binding with one finger (Dof), L-tryptophan aminotransferase 1 (TAA1), Indole-3-pyruvate monooxygenase (YUCCA4), Auxin response factor (ARF), 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS), ACC oxidase (ACO), Ethylene response factor (ERF), Calmodulin-binding transcription activator (CAMTA), Homeodomain-leucine zipper (HD-ZIP), Methionine γ-lyase (MGL).

).

Additionally, we discuss studies that have focused on ripening-associated biosynthetic genes. These investigations contribute to our understanding of the transcriptional regulatory systems implicated in the ripening of durian fruit, shedding light on ripening-associated genes during this process. The insights gained from these studies can serve as valuable information for molecular marker development, thereby accelerating the breeding of new cultivars with desirable traits.

6.1. Identification of Ripening-Related TF Families during the Post-Harvest Ripening of Durian Fruit

The preliminary release of the durian draft genome by Teh et al. [22] has facilitated subsequent in-depth studies focused on identifying TFs governing fruit ripening on a genome-wide scale. Subsequently, Khaksar et al. [110] conducted an exhaustive genome-wide investigation, culminating in the identification of 24 durian Dofs (DzDofs), 15 of which were expressed in the fruit pulp. Through a thorough analysis of gene expression, they revealed distinct patterns in the expression of DzDofs during the ripening process in both the ‘Monthong’ and ‘Chanee’ durian cultivars. Comparing the expression levels of fruit pulp-expressed DzDofs between these two cultivars pinpointed DzDof2.2 as a potential cultivar-dependent factor. The transient expression of DzDof2.2 in Nicotiana benthamiana leaves significantly elevated the expression levels of auxin biosynthetic genes, implying a plausible role of DzDof2.2 in post-harvest ripening through the transcriptional regulation of auxin biosynthesis. Recognizing the potential ripening-associated role of auxin in durian fruit ripening and the significant role of the auxin response factor (ARF) TFs in auxin signaling, Khaksar and Sirikantaramas [111] identified 15 ARF members in durian (DzARFs), with 12 expressed in the fruit pulp. While most of these DzARFs exhibited differential expression, DzARF2A displayed a pronounced ripening-associated expression pattern during post-harvest ripening in the ‘Monthong’ cultivar. Transient expression and dual luciferase reporter assays indicated that DzARF2A functions as a ripening activator through the transcriptional regulation of ethylene biosynthesis. In a separate study, a comprehensive transcriptome analysis and expression profiling identified 63 ERFs in durian pulps, designated as DzERF1–DzERF63. Out of these, 34 displayed ripening-associated expression patterns during the fruit ripening process in the ‘Monthong’ cultivar. Correlation network analysis of these 34 ripening-associated DzERFs with potential target genes revealed a robust correlation between candidate ERFs (DzERF6 and DzERF9) and ethylene biosynthetic genes, indicating potential ethylene-mediated roles of DzERF6 and DzERF9 during fruit ripening, possibly through the transcriptional regulation of ethylene biosynthetic genes [112]. In a study by Iqbal et al. [113], a thorough examination of the calmodulin-binding transcription activator (CAMTA) gene family in durian identified ten CAMTAs with conserved domains. Through phylogenetic analysis, they positioned DzCAMTA3 alongside its validated counterpart in tomatoes, known for its confirmed role in fruit ripening through ethylene-mediated signaling. Furthermore, a transcriptome-wide assessment revealed DzCAMTA3 and DzCAMTA8 as the most highly expressed CAMTA genes in durian. These two specific DzCAMTAs exhibited a unique expression pattern associated with ripening during post-harvest stages in durian fruit cv. ‘Monthong’. In a study conducted by Pinsorn et al. [114], it was disclosed that a member of the homeodomain-leucine zipper (HD-ZIP) TF family found in durian, DzHD-ZIP1.8, acts as a transcriptional activator of durian MGL (DzMGL) during the post-harvest ripening of the fruit. This research provides valuable insights into the molecular regulation of the key gene (MGL) responsible for the production of VSCs during the ripening process. Beyond investigations into molecular mechanisms during fruit post-harvest ripening, a few studies undertook a reanalysis of durian genomic data [115,116,117].

6.2. Ripening-Associated Biosynthetic Genes during the Post-Harvest Ripening of Durian Fruit

Wisutiamonkul et al. [45] delved into the influence of ethylene on carotenoid biosynthesis during fruit ripening, noting that 1-methylcyclopropene (1-MCP) induced a delay in the elevation of beta-carotene, alpha-carotene, and zeaxanthin levels while leaving lutein unaffected. The expression patterns of crucial carotenoid biosynthetic genes, including zeta-carotene desaturase (ZDS), lycopene beta-cyclase (LCYB), chromoplast-specific lycopene beta-cyclase (CYCB), and beta-carotene hydroxylase (BCH), exhibited a robust correlation with carotenoid content and pulp color. Notably, the application of 1-MCP significantly downregulated these key genes. Panpetch and Sirikantaramas [118] identified a novel leucylaminopeptidase with cysteinylglycine dipeptidase activity in durian, proposing its involvement in glutathione recycling during durian fruit ripening. In their metabolome and transcriptome analyses, Sangpong et al. [13] pinpointed key genes associated with the biosynthetic pathways of flavor-related metabolites during durian fruit ripening, particularly in sugar and amino acid metabolism. Suntichaikamolkul et al. [119] focused on cytochrome P450, an extensive enzyme family crucial for regulating various pathways in plant metabolite and phytohormone production. Through a comprehensive analysis of the durian genome and transcriptome libraries, they identified all P450 enzymes likely involved in the ripening process of durian fruit. In addition to identifying specific expression patterns linked to the fruit pulp and ripening stages, they highlighted certain P450 enzymes associated with phytohormone metabolism, particularly noting that the expressions of CYP72, CYP83, CYP88, CYP94, CYP707, and CYP714 were significantly influenced by external treatment with ripening regulators. This suggests a potential interplay between different phytohormones in orchestrating the intricate process of fruit ripening. Pinsorn et al. [15] focused on unraveling the functional characteristics of durian MGL (DzMGL), a key enzyme responsible for producing VSCs. Their analyses of genes and metabolites unveiled increased activity in sulfur metabolism as the durian fruit ripens. They observed that DzMGL is more efficient in utilizing L-cysteine compared to Arabidopsis MGL, leading to varying levels of VSCs and differences in aroma intensity between the two main Thai durian cultivars, ‘Chanee’ and ‘Monthong’. Notably, their findings underscored that γ-EC serves as the preferred sulfur storage form in durian pulp. The presence of a potential recycling mechanism generating intermediates suggests a pathway directing methionine toward ethylene synthesis and the production of VSCs. In a comprehensive genome-wide analysis, Tantisuwanichkul and Sirikantaramas [120] explored the carotenoid cleavage oxygenase (CCO) family in durian, uncovering 14 members. Notably, among these, nine were cis-epoxycarotenoid dioxygenases (NCEDs), known for their involvement in abscisic acid (ABA) production. A remarkable discovery was the identification of ripening-associated DzNCED5a, exhibiting the highest expression during the ripe stage, surpassing other CCO family members. Subsequent transient expression experiments involving DzNCED5a in N. benthamiana leaves provided conclusive evidence supporting its role in ABA biosynthesis. Aschariyaphotha et al. [121] conducted an analysis of ester profiles and the characteristics of alcohol acetyltransferase (AAT) in ripe durian pulp. Key esters responsible for aromatic compounds in durian were identified as ethyl-2-methyl butanoate, ethyl hexanoate, and ethyl octanoate. The effectiveness of AAT in catalyzing the synthesis of acetate esters through the reaction between acetyl CoA and various alcohols was assessed. AAT enzymes isolated from durian pulp displayed a notable preference for 3-methyl-1-butanol and hexanol as alcohol substrates. Propanol and butanol exhibited moderate activity as AAT substrates, while methanol and ethanol showed the least activity.

These inquiries have unveiled pivotal insights into the roles played by ripening-associated TFs and genes, significantly augmenting our understanding of the intricate molecular processes propelling durian fruit ripening. However, the dearth of an exhaustive genomic resource has hindered the exploration of durian historical evolution and current trait enhancement, a critical facet for the development of molecular markers. The evolution of durian’s biology during domestication brought about noteworthy changes, manifesting in a myriad of varieties with diverse pulp colors, aromas, and tastes. Without extensive genomic variation data spanning a diverse spectrum of durian varieties, including wild species, the identification of novel genes contributing to pivotal domestication traits on a global scale remains elusive. Noteworthy case studies in the existing literature have delved into genome resequencing in grapevine [122] and durian [117]. The latter study encompassed the whole-genome resequencing of three popular durian cultivars, unveiling genetic variations among them. Nevertheless, the restricted number of varieties in this study hampers the execution of a genome-wide association study to pinpoint potential genes associated with specific phenotypes. Therefore, forthcoming investigations should prioritize the comprehensive capture of whole-genome genetic variations at single-base resolution across a broad spectrum of durian varieties. Such studies are imperative for advancing our comprehension of durian biology, propelling trait improvement, and establishing the foundation for identifying genes pivotal to durian domestication on a global scale.

7. Future Perspective

Research has brought to light the multifaceted functional attributes of the durian fruit, spanning its pulp, peel, and seeds, showing promising potential for various health benefits. However, further investigations are imperative to pinpoint and isolate the specific chemical constituents responsible for the therapeutic effects linked to durian, particularly within its peel and seeds. A profound understanding of the physiological and molecular mechanisms underpinning these biological and pharmacological activities is essential. Moreover, there is a critical need for a comprehensive assessment of the bioactivity and safety profiles of extracted compounds. This entails rigorous pharmacokinetic evaluations to ascertain the bioavailability of specific compounds and toxicity tests, potentially involving studies with animal models. Additionally, researchers must give meticulous attention to the stability of extracted phytochemicals and the conditions necessary for maintaining cell cultures during in vitro studies, as oversights in these areas may compromise the reliability and relevance of the obtained results. To thoroughly explore the health benefits of integrating durian into functional foods, human interventional studies are warranted. These studies provide valuable insights into the practical applications and effects of durian-based dietary interventions on human health. Furthermore, expanding research to scrutinize the functional properties of other parts of the durian tree, such as its leaves and flowers, is crucial. These components may also harbor valuable bioactive compounds, and adopting a holistic approach to studying the various facets of the durian tree can contribute to a more comprehensive understanding of its potential contributions to human health. Finally, the significance of molecular markers for expediting elite cultivar breeding should be emphasized. This approach, coupled with advocating for a circular bioeconomy through waste valorization, can contribute to sustainable practices and maximize the potential benefits derived from the durian tree.