Next Article in Journal
Theoretical Description of Attosecond X-ray Absorption Spectroscopy of Frenkel Exciton Dynamics
Next Article in Special Issue
Evaluation of Antioxidant Activities from a Sustainable Source of Okara Protein Hydrolysate Using Enzymatic Reaction
Previous Article in Journal
Various Energetic Metabolism of Microglia in Response to Different Stimulations
Previous Article in Special Issue
Effects of Oat β-Glucan on the Textural and Sensory Properties of Low-Fat Set Type Pea Protein Yogurt
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 28
Issue 11
10.3390/molecules28114503
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Effect of Chemical Refining on the Reduction of β-Carboline Content in Sesame Seed Oil

by
Lili Shi
1,
Ziyu Cui
1 and
Wei Liu
1,2,*
1
College of Food Science and Technology, Henan University of Technology, Lianhua Street 100, Zhengzhou 450001, China
2
National Engineering Laboratory for Wheat & Corn Further Processing, Henan University of Technology, Lianhua Street 100, Zhengzhou 450001, China
*
Author to whom correspondence should be addressed.
Molecules 2023, 28(11), 4503; https://doi.org/10.3390/molecules28114503
Submission received: 6 May 2023 / Revised: 30 May 2023 / Accepted: 31 May 2023 / Published: 1 June 2023
(This article belongs to the Special Issue Extraction, Modification, Functionality and Bioactivity of Plant Proteins for a Healthy and Sustainable Food System)
Browse Figures
Versions Notes

Abstract

:
β-carbolines (harman and norharman) are potentially mutagenic and have been reported in some vegetable oils. Sesame seed oil is obtained from roasted sesame seeds. During sesame oil processing, roasting is the key procedure to aroma enhancement, in which β-carbolines are produced. Pressed sesame seed oils cover most market share, while leaching solvents are used to extract oils from the pressed sesame cake to improve the utilization of the raw materials. β-carbolines are nonpolar heterocyclic aromatic amines with good solubility in leaching solvents (n-hexane); therefore, the β-carbolines in sesame cake migrated to the leaching sesame seed oil. The refining procedures are indispensable for leaching sesame seed oil, in which some small molecules can be reduced. Thus, the critical aim is to evaluate the changes in β-carboline content during the refining of leaching sesame seed oil and the key process steps for the removal of β-carbolines. In this work, the levels of β-carbolines (harman and norharman) in sesame seed oil during chemical refining processes (degumming, deacidification, bleaching and deodorization) have been determined using solid phase extraction and high performance liquid chromatography-mass spectrometry (LC-MS). The results indicated that in the entire refining process, the levels of total β-carbolines greatly decreased, and the adsorption decolorization was the most effective process in reducing β-carbolines, which might be related to the adsorbent used in the decolorization process. In addition, the effects of adsorbent type, adsorbent dosage and blended adsorbent on β-carbolines in sesame seed oil during the decolorization process were investigated. It was concluded that oil refining can not only improve the quality of sesame seed oil, but also reduce most of the harmful β-carbolines.

1. Introduction

Heterocyclic aromatic amines (HAAs) are a class of polycyclic aromatic compound containing N-heterocycles, which are produced by the reaction of free amino acids, sarcosine, creatinine and sugars under high temperature. HAAs have carcinogenic and mutagenic activities [1]. So far, more than 30 HAAs have been identified in various foods [2]. β-carbolines, mainly including harman (1-methyl-9H-pyrido[3,4-b]indole) and norharman (9H-pyrido[3,4-b]indole), are very easy to generate in thermal food processing, such as baking and roasting. These two substances are not mutagenic by themselves, but when coexisting with aniline, o-toluidine or other HAAs, they will cause strong carcinogenicity [3]. Animal studies have also shown that harman and norharman affected the physiological behavior of animals, mainly because they bind to certain sites in the liver and brain of mice [4,5]. In addition, harman and norharman can poison some nerves and inhibit some key enzymes.
Over the past few decades, β-carbolines (harman and norharman) have been detected in many processed foods, including thermally processed meats (e.g., pork), coffee products and tobacco smoke [6,7,8]. At present, more attention has been paid to HAAs in foods of animal origin, but relatively less to HAAs in foods of plant origin. Wojtowicz et al. revealed that the β-carboline contents in chicory coffee increased rapidly (up to 25-fold) after roasting at 160 °C [9]. Theoretically, plant-protein-based foods can also produce HAAs after roasting at high temperatures. Coffee beans contain only about 13% protein, but high-temperature roasting can produce HAAs. Because of the roasting process of oil seeds (e.g., sesame seed, peanut), some vegetable oils (e.g., sesame seed oil) may be considered as the main contributor to β-carboline compounds. There are limited reports on the levels of β-carbolines (harman and norharman) in edible oils, especially in sesame seed oil and other flavored vegetable oils. Recently, Chang et al. showed that the levels of harman and norharman in sesame seed oils were 168 μg/kg and 162 μg/kg, respectively, while HAAs were not detected in other vegetable oils (e.g., linseed oil, soybean oil) [10]. In addition, Zhang et al. reported that the levels of harman and norharman in sesame seed oils were 453 μg/kg and 276 μg/kg, respectively, which were much higher than those in sunflower oil, canola oil and peanut oil [11]. Our group has analyzed commercial sesame seed oils (pressed fragrant sesame oils, ground fragrant sesame oils, cold-pressed sesame oils) produced by different processes and found that most of sesame oil samples contained both harman and norharman [12].
Sesame seed oil (sesamum indicum) is a traditional edible oil in China and other Asian regions. There are four kinds of sesame seed oils in China, including pressed fragrant sesame seed oil, ground fragrant sesame seed oil, cold-pressed sesame seed oil and refined sesame seed oil. Pressed fragrant sesame oil is generally produced using mechanical pressing after high-temperature roasting. The production of pressed fragrant sesame seed oil leads to a large amount of sesame meal, which can be used to produce refined sesame seed oil though solvent extraction and the subsequent refining process (Figure 1). Whereas β-carbolines (harman and norharman) are non-polar HAAs with good solubility in leaching solvents (e.g., hexane), the β-carbolines in sesame meal migrate into the leached sesame oil. It has been shown that chemical refining can reduce most of the minor components of vegetable oils (e.g., soybean oil) such as free fatty acids, vitamin E, phytosterols and other small molecule compounds [13,14,15]. Therefore, it is meaningful to investigate the level of HAAs (β-carbolines) in the refining process of sesame seed oil.
Oil refining usually consists of degumming, deacidification, decolorization and deodorization steps, of which decolorization is one of the important processes in edible oil refining. Some studies have reported that solid adsorbents (e.g., clay and activated carbon) used in the decolorization process can bind to small molecules (e.g., pigments) in oils via physical adsorption [16,17]. Recently, it has been shown that decolorization is a key process to reduce some harmful compounds (e.g., BaP) [18,19,20]. Thus, the effect of sorbents on the level of HAAs (β-carbolines) in the oil-refining process can also provide a possible method for the removal of HAAs. In this work, the level of β-carbolines (harman and norharman) in crude sesame oil and oils during refining processes (degumming, deacidification, bleaching and deodorization) has been studied and the effect of the chemical refining process on the level of harman and norharman in sesame seed oils has been discussed. Importantly, the effect of adsorbent type, adsorbent dosage and composite adsorbent on the removal of β-carbolines from sesame seed oil during the decolorization process was investigated as well. This work will provide new insight into the removal of HAAs (β-carbolines) from edible oils.

2. Results and Discussion

2.1. Effects of Sesame Seed Oil Refining Process on the Content of β-Carboline Compounds

To explore the changes in HAA content during the refining process of sesame seed oil, the level of HAAs in sesame crude oil and oils during refining processes (degumming, deacidification, bleaching and deodorization) have been detected using LC-MS. A flow chart of the refining process of sesame seed oil is shown in Figure 1. The chemical structures of the 14 heterocyclic aromatic amines are shown in Figure 2.
The levels of HAAs in sesame crude oil, degumming oil, deacidification oil, bleached oil and deodorized oil were determined, respectively. The results showed that the HAAs in crude sesame seed oil were mainly β-carbolines (harman and norharman) [10,12] (Table 1). The levels of total β-carbolines (harman and norharman) decreased from 552.34 μg/kg to 502.69 μg/kg and 418.50 μg/kg during degumming and deacidification of sesame seed oil, respectively (Figure 3). This may be due to the formation of colloids in the hydration degumming process. The soap formed in the deacidification process adsorbed some small molecule compounds (e.g., harman and norharman) in sesame seed oil, but the ability to remove β-carbolines was limited [21,22]. Notably, the bleaching step could significantly reduce β-carbolines (harman and norharman) in sesame seed oil from 418.50 μg/kg to 1.64 μg/kg, which might be attributed to the absorbents (e.g., activated clay and activated carbon) used in this step [23]. Some studies reported that solid adsorbents (e.g., activated clay and activated carbon) could bind to small molecules (e.g., pigmented substances) in oils via physical adsorption [24], which also contributed to the removal of β-carboline compounds. Decolorization is one of the important processes in the refining of edible oils. In addition to removing pigments and improving the appearance of the oil, it can also decrease the content of free fatty acids, phospholipids, peroxides, carbonyl compounds and other small molecular compounds (e.g., polycyclic aromatic hydrocarbons) in oils [23]. Thus, the decolorization process is a key step for the effective reduction of harman and norharman content in sesame seed oil.

2.2. Effect of Different Types of Adsorbents on the Removal of β-Carbolines from Sesame Seed Oil

To investigate the effect of adsorbent type on the removal of the β-carbolines (harman and norharman) in sesame seed oil, different kinds of decolorizers, including silica gel, attapulgite, activated carbon and clay, were used in adsorption decolorization experiments. The results showed that the four adsorbents were all effective in the removal of β-carbolines (harman and norharman) from sesame seed oil (Figure 4). When the adsorbents silica gel, attapulgite, activated carbon and clay were added to the sesame deacidification oil for decolorization, respectively, the content of β-carbolines decreased from 418.50 μg/kg to 162.64 μg/kg, 50.04 μg/kg, 4.43 μg/kg and 7.16 μg/kg, respectively.
In general, activated carbon and clay were more effective for the removal of β-carbolines (harman and norharman). The reason may be that activated carbons have hydrophobic graphene layers, which can interact readily with non-polar compounds (e.g., harman and norharman) [25]. Clay had a large specific surface area, high activity and strong adsorption capacity for minor compounds (e.g., harman and norharman) in sesame seed oil [26]. However, the adsorption capacity of attapulgite and silica gel for harman and norharman was relatively inferior. The possible reason was that many adsorption active points on the pore surface of attapulgite preferentially adsorbed polar substances and adsorbed non-polar compounds less (e.g., harman and norharman) [27]. Silica gel was a strong polar adsorbent, which was favorable for adsorbing high polar compounds [28].

2.3. Effect of Adsorbent Dosage on the Removal of β-Carbolines from Sesame Seed Oil

The removal effect of β-carbolines (harman and norharman) in the decolorization process of sesame seed oil was also related to the amount of adsorbents. To investigate the effect of adsorbent dosage on β-carbolines in sesame seed oil, the decolorization of sesame seed oil was carried out at different adsorbent dosages (1%, 3%, 5%). The results showed that the total β-carbolines (harman and norharman) in sesame seed oil gradually decreased as the amount of adsorbents (silica gel, attapulgite, activated carbon and clay) increased from 1% to 5% (Figure 5). When the bleaching agents were silica gel, attapulgite, activated carbon and clay, with the dosage increasing from 1% to 5%, the total β-carbolines (harman and norharman) in bleached oil decreased from 162.64 μg/kg to 29.76 μg/kg, 50.04 μg/kg to 3.78 μg/kg, 4.43 μg/kg to 1.10 μg/kg and 7.16 μg/kg to 1.24 μg/kg, respectively (Figure 5). The above results suggested that 5% clay and 5% activated carbon were more effective in decreasing the content of harman and norharman in sesame seed oil. Among them, when activated carbon and clay were added at 5% of oil weight, the contents of harman in decolorized oil were 0.55 μg/kg and 0.72 μg/kg, respectively, and the contents of norharman were 0.55 μg/kg and 0.52 μg/kg, respectively (Figure 5C,D).

2.4. Effects of Different Types of Activated Carbons on the Removal of β-Carbolines from Sesame Seed Oil

Activated carbon is made from a wide range of raw materials, generally from coal, peat, wood powder, coke from coconut shells and other raw materials through carbonization and activation processing [26]. Thus, different types of activated carbons (wood powder, coconut shell powder, coconut shell particles, coal, etc.) were carried out for the adsorption and decolorization process of sesame oil. Since the capacity of activated carbon is affected by its specific surface area, pore structure and surface functional groups, etc. [29], different types of activated carbons had different adsorption capacities for β-carbolines (harman and norharman) in sesame seed oil. Figure 6 shows the contents of β-carbolines in sesame seed oil after decolorization by different types of activated carbons (GC, PC, AP, F10 and PW). PW significantly decreased the harman and norharman levels in sesame seed oil compared with those of the control (418.50 μg/kg) to 1.10 μg/kg, followed by F10 (2.88 μg/kg), AP (3.10 μg/kg), PC (3.24 μg/kg) and GC (22.52 μg/kg). Among the activated carbons, GC was less effective in the removal of β-carbolines from sesame seed oil, probably because it is a granular activated carbon and had relatively less contact area with sesame seed oil during decolorization. The surface properties of activated carbon such as porosity and specific surface area differ based on the raw materials used [30]. Lee et al. demonstrated that powdered activated carbon made from wood had a larger specific surface area than powdered activated carbon made from other raw materials [31]. Thus, the powdered activated carbon PW was more effective in reducing the β-carboline level of the sesame seed oil compared with activated carbon F10, AP and PC.

2.5. Removal of β-Carbolines from Sesame Seed Oil Using Blended Decolorizers

In general, in the process of oil decolorization, too much clay results in the acid value rising and an earthy smell, while too much activated carbon causes large oil loss. In the present study, activated carbon compounded with a clay mixture was usually used for decolorization in the grease decolorization process [19,32]. It not only improved the decolorization capacity and reduced the risky substances (e.g., harman and norharman), but also decreased the adsorbent dosage and loss of oil. Therefore, the adsorption decolorization experiments were carried out by using a blended decolorizer of white clay and activated carbon (PW) with a mass ratio of 1:1, and the amount of decolorizer added was 1% and 3% of the oil weight, respectively. The results showed that when adding 1% and 3% blended decolorizer for the decolorization process, respectively, the contents of β-carboline compounds decreased from 418.50 μg/kg to 1.05 μg/kg and 0.80 μg/kg, respectively (Figure 7). The blended decolorizer was more capable of removing heterocyclic aromatic amines (HAAs) than a single type of adsorbent. Meanwhile, the introduction of activated carbon (PW) could improve the decolorization performance of clay for edible oils and also effectively reduce the content of risk substances (e.g., harman and norharman). A possible reason was that clay preferentially removed impurities (e.g., pigments) from sesame seed oil, preserving the adsorption capacity for the removal of β-carbolines by activated carbon (PW). Thus, a blended decolorizer consisting of activated carbon and clay could effectively remove HAAs from sesame seed oil while meeting the process requirements for the decolorization of edible oils.

2.6. Changes in Basic Physicochemical Properties of Sesame Seed Oil Refining Process

To evaluate the changes in physicochemical indexes during the refining process of sesame seed oil, the acid value (AV), peroxide value (POV) and color of sesame seed oil were determined (Table 2 and Table 3).Therein, the AV and POV are important indicators of basic edible oil quality, which are closely related to oil stability. The AV and POV of the leached sesame seed oil (crude oil) were 1.72 mg/g and 0.037 mmol/kg, respectively. The AV of sesame seed oil decreased continuously in the process of chemical refining, probably due to the adsorption of small amounts of free fatty acids by the oil soap horns during the deacidification process. The AV and POV in the final refined sesame seed oil were 0.28 mg/g and 0.003 mmol/kg, respectively, which reached the quality index of first-grade refined sesame seed oil. The deodorization process removes most of the small molecules and unstable compounds (e.g., peroxide compounds). Therefore, except for improving the quality of sesame seed oil, refining could reduce most of the harmful substances as well.
Changes to the color of sesame seed oil during the refining process were investigated. L*, a* and b* denote the chromaticity value of the object color, where any color has a unique coordinate value for the color space coordinates. L* denotes brightness (black and white), a* denotes green to red and b* denotes blue to yellow. Crude sesame oil exhibited lower L* and a* values and higher b* values (Table 3, Figure 8). This meant that crude sesame oil was darker, greener and more yellow than the refined sesame seed oil. The color formation in sesame seed oil was probably due to nonenzymatic browning (Maillard reaction), which occurred during the roasting of sesame seeds [33]. Some studies have demonstrated that roasting increased the color of dark and yellow units as well as caused the production of green pigments, especially chlorophyll [34,35,36]. In contrast, pigments could be removed during the degumming, deacidification and decolorization processes, so that the color of sesame seed oil was clear and transparent with less green and yellow during refining (L* and a* values gradually increase, while b* values gradually decrease). Notably, compared with other decolorizers, the color of sesame seed oil after decolorization with 3% blended decolorizer was clear and transparent with less yellow (L*: 89.58; a*: 1.72; b*: −4.47). This means that the removal of pigments from sesame seed oil is related to the adsorbent type and dosage.

3. Materials and Methods

3.1. Materials

White sesame seed was purchased from a local supermarket. The five adsorbents of activated carbons used in the present study were as follows: powdered type activated carbon made from peat (AP, F10), powdered type activated carbon made from wood (PW), powdered type activated carbon made from coconut shell (PC) and granular type activated carbon made from coconut shell (GC). F10, PW, PC and GC were purchased from Xin Sen Carbon Co., Ltd. (Nanping, China). AP was obtained from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Acetonitrile (HPLC grade) was purchased from Thermo Fisher Scientific (Shanghai, China). Ammonium hydroxide and hydrochloric acid (HPLC grade) were obtained from Kemiou Chemical Reagent Co., Ltd. (Tianjin, China). Methyl alcohol, acetic acid and n-hexane were of HPLC grade, and other chemicals were of analytical reagent grade. Oasis MCX solid-phase extraction cartridge (150 mg, 6 mL) was purchased from Waters (Milford, CT, USA). Additionally, the water used was Wahaha purified water purchased from a local supermarket. The standards AαC, MeAαC, DMIP, Trp-P-1, Trp-P-2, Glu-P-2, MeIQ, MeIQx, IQ, PhIP, 4,8-DiMeIQx, 7,8-DiMeIQx were purchased from Toronto Research Chemicals (Toronto, ON, Canada). Harman, Norharman and 4,7,8-TriMeIQx were purchased from Alta scientific (Tianjin, China).

3.2. Methods

3.2.1. Roasting Treatment and Extraction of Oil from Sesame Seeds

The sesame seeds were roasted using an oven at 220 °C for 20–30 min. The roasted sesame seeds were cooled naturally at room temperature and then fed into an oil press to obtain sesame seed oil and sesame cake. The sesame cake was extracted with n-hexane three times. The obtained mixture (oil–hexane) was processed under reduced pressure to remove the solvent (n-hexane), and the leached sesame seed oil for the following experiments was afforded.

3.2.2. Hydration Degumming

The above-prepared oil sample was stirred in a water bath at 60 °C for 30–40 min. The distilled water was heated to the oil temperature and added to the above oil sample. The water should be sprayed evenly, and the added water was 2~3 times the phosphorus content. At the end of hydration, a reduction in stirring speed was beneficial for flocculation separation. After hydration, the degummed oil was obtained via centrifugation.

3.2.3. Alkali Refining Deacidification

The specified concentration of NaOH was added to the obtained oil sample to neutralize the free fatty acids and additional NaOH was infused to ensure the complete formation of soaps. This process was initially carried out at 30 °C with stirring. Once the NaOH was added, the temperature was immediately raised to the specified temperature, maintaining the temperature for the required time. Then, the soaps were separated via centrifugation at 5000 r/min. To remove the remnants of the soap and reagents dissolved in the treated oil, the oil obtained in the previous stages was washed with 90 °C pure water three times successively. Finally, the deacidified oil was obtained by heating under reduced pressure to remove the washing water.

3.2.4. Adsorption Decolorization

The removal of HAAs using the oil bleaching procedure was conducted using different adsorbents. The different amounts of adsorbent (1%, 3%, 5%) adopted were added to the prepared oil sample, and the mixture was kept at 80 °C for 30 min by stirring in a vacuum atmosphere. Then, the adsorbent was removed under filtration and the bleached oil was obtained.

3.2.5. Distillation Deodorization

The deodorization was a type of distillation process to remove volatile compounds and heat-instable pigments. Deodorization parameters were set as follows: 240 °C of deodorization temperature, 80 Pa of deodorization pressure and 60 min of deodorization time. Then, the oil samples was cooled down to room temperature and the deodorized oil was obtained.

3.2.6. Extraction and Purification of HAAs

The extraction of HAAs from oil samples was according to the reference with slight modification [37]. Approximately 2 g of oil samples was placed into a 50 mL centrifuge tube. Then, 10 μL 5 mg/L internal standard working solution (4,7, 8-TriMeIQx) and 10 mL acetonitrile solution containing 1% (volume fraction) acetic acid were added. The mixture was homogenized for 1 min, followed by ultrasound for 10 min and cryogenic centrifugation at −4 °C (10,000 r/min, 10 min). The supernatant was collected into a 50 mL centrifuge tube. The above acetonitrile extraction operation was repeated twice. All extracts were collected together.
The solid phase extraction column Oasis MCX cartridges (150 mg/6 mL) were pre-activated with 10 mL methanol and 10 mL 0.1 mol/L hydrochloric acid/methanol (80:20, v/v). All extracts were transferred to the MCX column for enrichment and purification. Then, 10 mL water, 10 mL methanol and 10 mL methanol/ammonia/water (25:5:75, v/v/v) were added to the MCX column successively for washing and purification. Finally, 10 mL methanol/ammonia mixed solution (95:5, v/v) was used for elution and collection. All eluent was collected and dried with nitrogen. A mixture of 10 mL 5% formic acid/acetonitrile (95:5, v/v) was added to the blow-dried sample and then filtered through a 0.45 μm microporous filter for LC/MS analysis.

3.2.7. LC/MS Analysis of HAAs

The determination of HAAs was performed on an Agilent ZORBAX Eclipse XDB-C18 column (3.5 μm, 150 mm × 2.1 mm) at 35 °C. The gradient elution was carried out with 5% formic acid/5 mM ammonium formate aqueous solution (A) and 5% formic acid/5 mM ammonium formate methanol solution (B) as binary mobile phases at a flow rate of 0.4 mL/min. The gradient elution program was as follows: 0–0.01 min, 5%B; 0.01–1.00 min, 5%B; 1.00–1.10 min, 5–60%B; 1.10–5.00 min, 60–80%B; 5.00–6.00 min, 80–95%B; 6.00–8.00 min, 95%B; 8.00–8.10 min, 95–5%B; 8.10–8.20 min, 5%B; 8.20–10.00 min, adjusting mobile phase balance to initial state. The injection volume was 5 μL. The internal standard method was used to quantify the samples, and the results were analyzed under the standard curve established with 14 HAAs (gradient dilution to 0.10, 0.50, 1.00, 2.50, 5.00, 10.00, 20.00, 25.00 ng/mL).
Mass spectrometry was analyzed using positive electrospray ionization (ESI+). The multiple reaction monitoring conditions were automatically optimized. The capillary voltage was 5.5 kV, and the ion source temperature was 550 °C. The qualitative and quantitative characteristic ions and optimized mass spectrometry parameters of 14 heterocyclic aromatic amines (HAAs) and internal standards are shown in Table 4. The chromatograms of harman and norharman in sesame seed oil samples are shown in Figure 9.

3.2.8. Physicochemical Properties of Sesame Seed Oil

The peroxide value (POV) of sesame seed oil was characterized according to GB 5009.229-2016, while the acid value (AV) was analyzed based on the methods described in GB 5009.229-2016. Briefly, for POV, 2.0 g oil sample was titrated with 0.01 mol/L sodium thiosulfate standard solution and POV was expressed as reactive oxygen in mmol/kg of oil. For AV, 2.0 g oil sample was titrated with 0.01 mol/L KOH standard solution and AV was expressed as KOH in mg/g of oil. The sample color was measured using a Chroma Meter CR-400 and the L* value (lightness), a* value (red-green intensity) and b* value (yellow-blue intensity) were measured.

3.2.9. Statistical Analysis

All experiments were carried out in triplicate, and the data were expressed as mean ± standard deviation. Multi Quant software was used for heterocyclic aromatic amines data analysis. Origin Pro software (Origin Lab Co., Northampton, MA, US) was used for charting. The difference between groups was tested using ANOVA and Duncan’s multiple range tests. Means were compared and were considered significant when p < 0.05.

4. Conclusions

In this paper, the levels of β-carbolines (harman and norharman) in sesame seed oil during the refining process were investigated systematically. The results showed that the levels of the total β-carbolines (harman and norharman) in refined sesame seed oils were much lower than those in pressed fragrant sesame seed oils. Adsorption decolorization was the most effective process to reduce the content of β-carboline compounds, which was related to the adsorbent used in the decolorization process. Three percent blended decolorizer consisting of activated carbon and clay achieved the best results for removing β-carbolines. After refining, the basic physicochemical indexes of sesame seed oil, such as AV, POV and color, reached the quality index of first-grade refined sesame seed oil. It was concluded that oil refining could not only improve the quality of sesame seed oil, but also reduce most of the harmful substances (e.g., β-carbolines). This study will be meaningful to prove that decolorizers are effective to remove small molecule compounds (e.g., nonpolar heterocyclic aromatic amines harman and norharman) in edible oils.

Author Contributions

Conceptualization, W.L.; methodology, L.S.; software, L.S.; formal analysis, L.S.; investigation, L.S. and Z.C.; data curation, L.S.; writing—original draft preparation, L.S.; writing—review and editing, W.L.; supervision, W.L.; project administration, W.L.; funding acquisition, W.L. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Key Scientific and Technological Projects of Henan Province (222103810061) and the Project of Henan University of Technology Excellent Young Teachers (2014003).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples are available from Wei Liu on valid request.

References

  1. Turesky, R.J.; Le Marchand, L. Metabolism and biomarkers of heterocyclic aromatic amines in molecular epidemiology studies: Lessons learned from aromatic amines. Chem. Res. Toxicol. 2011, 24, 1169–1214. [Google Scholar] [CrossRef] [PubMed]
  2. Zamora, R.; Hidalgo, F.J. Formation of heterocyclic aromatic amines with the structure of aminoimidazoazarenes in food products. Food Chem. 2020, 313, 126128. [Google Scholar] [CrossRef] [PubMed]
  3. Wakabayashi, K.; Sugimura, T. Heterocyclic amines formed in the diet: Carcinogenicity and its modulation by dietary factors. J. Nutr. Biochem. 1998, 9, 604–612. [Google Scholar] [CrossRef]
  4. Ergene, E.; Schoener, E.P. Effects of harmane (1-methyl-beta-carboline) on neurons in the nucleus accumbens of the rat. Pharmacol. Biochem. Behav. 1993, 44, 951–957. [Google Scholar] [CrossRef] [PubMed]
  5. Adell, A.; Biggs, A.; Myers, D. Action of Harman (1-methyl-beta-carboline) on the brain: Body temperature and in vivo efflux of 5-HT from hippocampus of the rat. Neuropharmacology 1996, 8, 1101–1107. [Google Scholar] [CrossRef]
  6. Aaslyng, M.D.; Duedahl-Olesen, L.; Jensen, K.; Meinert, L. Content of heterocyclic amines and polycyclic aromatic hydrocarbons in pork, beef and chicken barbecued at home by Danish consumers. Meat Sci. 2013, 93, 85–91. [Google Scholar] [CrossRef]
  7. Alves, R.C.; Casal, S.; Oliveira, B.P.P. Factors influencing the norharman and harman contents in espresso coffee. J. Agric. Food Chem. 2007, 55, 1832–1838. [Google Scholar] [CrossRef]
  8. Herraiz, T. Relative exposure to β-carbolines norharman and harman from foods and tobacco smoke. Food Addit. Contam. 2004, 21, 1041–1050. [Google Scholar] [CrossRef]
  9. Wojtowicz, E.; Zawirska-Wojtasiak, R.; Przygoński, K.; Mildner-Szkudlarz, S. Bioactive β-carbolines norharman and harman in traditional and novel raw materials for chicory coffee. Food Chem. 2015, 175, 280–283. [Google Scholar] [CrossRef]
  10. Chang, C.C.; Zhang, D.Q.; Wang, Z.Y.; Chen, B.H. Simultaneous determination of twenty heterocyclic amines in cooking oil using dispersive solid phase extraction (QuEChERS) and high performance liquid chromatography–electrospray-tandem mass spectrometry. J. Chromatogr. A 2019, 1585, 82–91. [Google Scholar] [CrossRef]
  11. Zhang, C.X.; Xi, J.; Zhao, T.P.; Ma, Y.X.; Wang, X.D. β-carbolines norharman and harman in vegetable oils in China. Food Addit. Contam. Part B 2020, 13, 193–199. [Google Scholar] [CrossRef]
  12. Liu, W.; Yang, Z.Y.; Shi, L.; Li, Y. Bioactive β-Carbolines Harman and Norharman in Sesame Seed Oils in China. Molecules 2022, 27, 402. [Google Scholar] [CrossRef] [PubMed]
  13. Gomez-Coca, R.B.; Alassi, M.; Moreda, W.; Perez-Camino, M.D. Pyropheophytina in Soft Deodorized Olive Oils. Foods 2020, 9, 978. [Google Scholar] [CrossRef] [PubMed]
  14. Abdel-Razek, A.G.; Abo-Elwafa, G.A.; Al-Amrousi, E.F.; Badr, A.N.; Hassanein, M.M.; Qian, Y.; Siger, A.; Grygier, A.; Radziejewska-Kubzdela, E.; Rudzińska, M. Effect of Refining and Fractionation Processes on Minor Components, Fatty Acids, Antioxidant and Antimicrobial Activities of Shea Butter. Foods 2023, 12, 1626. [Google Scholar] [CrossRef]
  15. Golimowski, W.; Teleszko, M.; Zając, A.; Kmiecik, D.; Grygier, A. Effect of the Bleaching Process on Changes in the Fatty Acid Profile of Raw Hemp Seed Oil (Cannabis sativa). Molecules 2023, 28, 769. [Google Scholar] [CrossRef] [PubMed]
  16. Chakroun, S.; Sghaier, D.; Gaied, M.E. Decolorization of soybean oil by acid-activated Ca-Bentonite (EL Gnater, Central Tunisia). Environ. Prog. Sustain. Energy 2023, 42, e14015. [Google Scholar] [CrossRef]
  17. Choi, S.K.; Choe, S.B.; Kang, S.T. Reduction of benzo(a)pyrene content in sesame seed oil by using adsorbents. J Korean Soc Food Sci Nutr. 2014, 43, 564–569. [Google Scholar] [CrossRef]
  18. Liu, X.; Zhang, Z.; Shen, M.; Wu, Y.; He, X.; Liang, L.; Zhang, J.; Xu, X.; Liu, G. Optimization of the Refining Process for Removing Benzo (a) pyrene and Improving the Quality of Tea Seed Oil. Eur. J. Lipid Sci. Technol. 2022, 124, 2100143. [Google Scholar] [CrossRef]
  19. Ma, Y.; Shi, L.; Liu, Y.; Lu, Q. Effects of Neutralization, Decoloration, and Deodorization on Polycyclic Aromatic Hydrocarbons during Laboratory-Scale Oil Refining Process. J. Chem. 2017, 2017, 7824761. [Google Scholar] [CrossRef]
  20. Kim, D.Y.; Kim, B.; Shin, H.S. Reduction of polycyclic aromatic hydrocarbons (PAHs) in sesame oil using cellulosic aerogel. Foods 2021, 10, 644. [Google Scholar] [CrossRef]
  21. Yang, B.; Wang, Y.H.; Yang, J.G. Optimization of enzymatic degumming process for rapeseed oil. J. Am. Oil Chem. Soc. 2006, 83, 653–658. [Google Scholar] [CrossRef]
  22. Cejpek, K.; Hajslova, J.; Kocourek, V.; Tomaniova, M.; Cmolik, J. Changes in PAH levels during production of rapeseed oil. Food Addit. Contam. 1998, 15, 563–574. [Google Scholar] [CrossRef]
  23. Xie, D.; Zhou, H.; Jiang, X. Effect of chemical refining on the levels of bioactive components and hazardous substances in soybean oil. J. Food Meas. Charact. 2019, 13, 1423–1430. [Google Scholar] [CrossRef]
  24. Silva, S.M.; Sampaio, K.A.; Ceriani, R.; Verhé, R.; Stevens, C.; De Greyt, W.; Meirelles, A.J. Effect of type of bleaching earth on the final color of refined palm oil. LWT-Food Sci. Technol. 2014, 59, 1258–1264. [Google Scholar] [CrossRef]
  25. Al-Ghouti, M.; Khraisheh, M.; Allen, S.; Ahmad, M. The removal of dyes fromtextile wastewater: A study of the physical characteristics and adsorptionmechanisms of diatomaceous earth. J. Ofenvironmentalmanag. 2003, 69, 229–238. [Google Scholar]
  26. Zschau, W. Bleaching of edible fats and oils. Eur. J. Lipid Sci. Technol. 2001, 103, 505–551. [Google Scholar] [CrossRef]
  27. Wang, Y.Q.; Feng, Y.; Jiang, J.L.; Yao, J. Designing of recyclable attapulgite for wastewater treatments: A review. ACS Sustain. Chem. Eng. 2019, 7, 1855–1869. [Google Scholar] [CrossRef]
  28. Gun’ko, V.M.; Matkovsky, A.K.; Charmas, B.; Skubiszewska-Zięba, J.; Pasieczna-Patkowska, S. Carbon-silica gel adsorbents. J. Therm. Anal. Calorim. 2017, 128, 1683–1697. [Google Scholar] [CrossRef]
  29. Mastral, A.; García, T.; Callén, M.; Murillo, R.; Navarro, M.; López, J. Sorbentcharacteristics influence on the adsorption of PAC: I. PAH adsorption with thesame number of rings. Fuel Process. Technol. 2002, 77, 373–379. [Google Scholar] [CrossRef]
  30. Liu, Z.S. Control of PAHs from incineration by activated carbon fibers. J. Environ. Eng. 2006, 132, 463–469. [Google Scholar] [CrossRef]
  31. Lee, S.M.; Jeong, J.-Y.; Lee, J.-G.; Kim, Y.-S. Effects of the absorbent types on changes in benzo [a] pyrene and volatile compounds in sesame oil. Appl. Biol. Chem. 2021, 64, 84. [Google Scholar] [CrossRef]
  32. Kiralan, S.S.; Toptancı, İ.; Tekin, A. Further evidence on the removal of polycyclic aromatic hydrocarbons (PAHs) during refining of olive pomace oil. Eur. J. Lipid Sci. Technol. 2019, 121, 1800381. [Google Scholar] [CrossRef]
  33. Yoshida, H.; Takagi, S. Effect of roasting temperature and time on the quality characteristics of sesame (Sesame indicum) oil. J. Sci. Food Agric. 1997, 75, 19–26. [Google Scholar] [CrossRef]
  34. Li, T.; Guo, Q.; Qu, Y.; Li, Y.; Liu, H.; Liu, L.; Zhang, Y.; Jiang, Y.; Wang, Q. Solubility and physicochemical properties of resveratrol in peanut oil. Food Chem. 2022, 368, 130687. [Google Scholar] [CrossRef]
  35. Oomah, B.D.; Busson, M.; Godfrey, D.V.; Drover, J.C.G. Characteristics of hemp (Cannabis sativa L.) seed oil. Food Chem. 2002, 76, 33–43. [Google Scholar] [CrossRef]
  36. Elleuch, M.; Besbes, S.; Roiseux, O.; Blecker, C.; Attia, H. Quality characteristics of sesame seeds and by-products. Food Chem. 2007, 103, 641–650. [Google Scholar] [CrossRef]
  37. Barceló-Barrachina, E.; Moyano, E.; Galceran, M.T.; Lliberia, J.L.; Bagó, B.; Cortes, M.A. Ultra-performance liquid chromatography–tandem mass spectrometry for the analysis of heterocyclic amines in food. J. Chromatogr. A 2006, 1125, 195–203. [Google Scholar] [CrossRef]
Molecules 28 04503 g001 550
Figure 1. The processing procedure of sesame seed oils.
Figure 1. The processing procedure of sesame seed oils.
Molecules 28 04503 g001
Molecules 28 04503 g002 550
Figure 2. The chemical structure of 14 heterocyclic aromatic amines.
Figure 2. The chemical structure of 14 heterocyclic aromatic amines.
Molecules 28 04503 g002
Molecules 28 04503 g003 550
Figure 3. Changes in β-carboline content during the refining of sesame seed oil. Note: The decolorizer used in the decolorization process was clay (3% of oil weight). Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Figure 3. Changes in β-carboline content during the refining of sesame seed oil. Note: The decolorizer used in the decolorization process was clay (3% of oil weight). Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Molecules 28 04503 g003
Molecules 28 04503 g004 550
Figure 4. Effects of different types of decolorizing agents on the removal of β-carbolines in sesame seed oil. Note: The control group was deacidified oil, and the dosage of decolorizers was 1% of the oil weight. Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Figure 4. Effects of different types of decolorizing agents on the removal of β-carbolines in sesame seed oil. Note: The control group was deacidified oil, and the dosage of decolorizers was 1% of the oil weight. Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Molecules 28 04503 g004
Molecules 28 04503 g005 550
Figure 5. Effect of adsorbent dosage on the removal of β-carbolines from sesame seed oil. Note: (A–D) represent the adsorbents used were silica gel, attapulgite, activated carbon and clay respectively. The control group was deacidified oil, and the dosage of decolorizers was the mass fraction of the oil weight. Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Figure 5. Effect of adsorbent dosage on the removal of β-carbolines from sesame seed oil. Note: (A–D) represent the adsorbents used were silica gel, attapulgite, activated carbon and clay respectively. The control group was deacidified oil, and the dosage of decolorizers was the mass fraction of the oil weight. Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Molecules 28 04503 g005
Molecules 28 04503 g006 550
Figure 6. Effects of different types of activated carbons for the removal of β-carbolines from sesame seed oil. Note: The control group was deacidified oil, and amount of activated carbons was 1% of the oil weight. The symbols for each activated carbon are as follows: GC, granular type activated carbon made from coconut shell; PC, powdered type activated carbon made from coconut shell; AP, F10, powdered type activated carbon made from peat; PW, powdered type activated carbon made from wood. Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Figure 6. Effects of different types of activated carbons for the removal of β-carbolines from sesame seed oil. Note: The control group was deacidified oil, and amount of activated carbons was 1% of the oil weight. The symbols for each activated carbon are as follows: GC, granular type activated carbon made from coconut shell; PC, powdered type activated carbon made from coconut shell; AP, F10, powdered type activated carbon made from peat; PW, powdered type activated carbon made from wood. Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Molecules 28 04503 g006
Molecules 28 04503 g007 550
Figure 7. Effects of blended decolorizer on the removal of β-carbolines from sesame seed oil. Note: The control group was deacidified oil, and the dosage of blended decolorizer was the mass fraction of the oil weight. The blended decolorizer was a 1:1 mass ratio of clay and activated carbon (PW). Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Figure 7. Effects of blended decolorizer on the removal of β-carbolines from sesame seed oil. Note: The control group was deacidified oil, and the dosage of blended decolorizer was the mass fraction of the oil weight. The blended decolorizer was a 1:1 mass ratio of clay and activated carbon (PW). Means (n = 3) across all samples without a common letter differ significantly (p < 0.05).
Molecules 28 04503 g007
Molecules 28 04503 g008 550
Figure 8. The color of sesame seed oil after decolorization with different decolorizers. Note: The dosage of decolorizers was 3% of the oil weight. PW, powdered type activated carbon made from peat. The blended decolorizer was a 1:1 mass ratio of clay and activated carbon (PW).
Figure 8. The color of sesame seed oil after decolorization with different decolorizers. Note: The dosage of decolorizers was 3% of the oil weight. PW, powdered type activated carbon made from peat. The blended decolorizer was a 1:1 mass ratio of clay and activated carbon (PW).
Molecules 28 04503 g008
Molecules 28 04503 g009 550
Figure 9. The chromatogram of sample with high content of harman and norharman (a,b); the chromatogram of sample with low content of harman and norharman (c,d).
Figure 9. The chromatogram of sample with high content of harman and norharman (a,b); the chromatogram of sample with low content of harman and norharman (c,d).
Molecules 28 04503 g009
Table
Table 1. The contents of 14 HAAs were determined during the refining of sesame seed oil (μg/kg) a.
Table 1. The contents of 14 HAAs were determined during the refining of sesame seed oil (μg/kg) a.
HAA (μg/kg)Crude OilDegummedDeacidifiedBleachedDeodorized
AαCND bNDNDNDND
MeAαCNDNDNDNDND
Trp-P-1NDNDNDNDND
DMIPNDNDNDNDND
Glu-P-2NDNDNDNDND
MeIQNDNDNDNDND
MeIQxNDNDNDNDND
IQNDNDNDNDND
PhIPNDNDNDNDND
4,8-DiMeIQxNDNDNDNDND
7,8-DiMeIQxNDNDNDNDND
Harman301 ± 3274 ± 2242 ± 41.2 ± 0.30.52 ± 0.04
Norharman251 ± 3229 ± 1176 ± 40.45 ± 0.070.35 ± 0.02
Trp-P-2NDNDNDNDND
a Note: heterocyclic aromatic amines (HAAs) were detected using LC-MS. b Not detected (ND).
Table
Table 2. Changes in basic physical and chemical indexes of sesame seed oil refining process.
Table 2. Changes in basic physical and chemical indexes of sesame seed oil refining process.
Oil SampleAcid ValuePeroxide Value
(mg/g)(mmol/kg)
Crude oil1.7 ± 0.0 a0.037 ± 0.00 b
Degummed oil1.6 ± 0.0 b0.069 ± 0.00 a
Deacidified oil0.24 ± 0.02 c0.024 ± 0.00 c
Bleached (3% blended decolorizer) oil0.29 ± 0.04 c0.037 ± 0.00 b
Deodorized oil0.28 ± 0.04 c0.003 ± 0.00 d
Note: The letters a, b, c and d represent the differences among crude, degummed, deacidified, bleached and deodorized oils; the same letter indicates no significant difference (p > 0.05), different letters indicate a significant difference (p < 0.05).
Table
Table 3. Changes in color of sesame seed oil during the refining process.
Table 3. Changes in color of sesame seed oil during the refining process.
Oil SampleL*a*b*
Crude oil84.64 ± 0.02 a−9.29 ± 0.22 a16.55 ± 0.03 a
Deacidified oil86.20 ± 0.01 b−6.42 ± 0.02 c8.24 ± 0.03 c
Deacidified oil86.20 ± 0.01 b−6.42 ± 0.02 c8.24 ± 0.03 c
Bleached (3% blended decolorizer)89.68 ± 0.02 c1.69 ± 0.01 d−3.88 ± 0.06 d
Deodorized oil88.77 ± 0.01 c1.72 ± 0.02 d−4.47 ± 0.01 d
Note: The letters a, b, c and d represent the differences among crude, degummed, deacidified, bleached and deodorized oils; the same letter indicates no significant difference (p > 0.05), different letters indicate a significant difference (p < 0.05).
Table
Table 4. Qualitative and quantitative characterization of 14 HAAs with internal standard and optimized mass spectrum parameters.
Table 4. Qualitative and quantitative characterization of 14 HAAs with internal standard and optimized mass spectrum parameters.
HAAsPrecursor Ion [M + H]+ (m/z)Diagnostic
Productions (m/z)		Cone Voltage (V)Collision Voltage (eV)Dwell Time (ms)
AαC184.0167.21083230
140.010832
MeAαC198.2154.11044030
127.110445
Trp-P-1212.0168.0803030
195.28040
DMIP162.9147.3904530
105.09045
Glu-P-2185.2131.1804030
78.28040
MeIQ213.1198.01003530
144.010060
MeIQx214.1199.01004030
131.010055
IQ199.1184.01004030
157.010050
PhIP225.3210.21204530
183.212050
4,8-DiMeIQx228.1211.81004530
160.010040
7,8-DiMeIQx228.0131.31005530
213.210040
4,7,8-DiMeIQx242.0227.11204030
145.012050
Harman183.0115.01205030
168.312040
Norharman169.2115.01004530
142.010040
Trp-P-2198.0154.0604030
128.06040
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Shi, L.; Cui, Z.; Liu, W. Effect of Chemical Refining on the Reduction of β-Carboline Content in Sesame Seed Oil. Molecules 2023, 28, 4503. https://doi.org/10.3390/molecules28114503

AMA Style

Shi L, Cui Z, Liu W. Effect of Chemical Refining on the Reduction of β-Carboline Content in Sesame Seed Oil. Molecules. 2023; 28(11):4503. https://doi.org/10.3390/molecules28114503

Chicago/Turabian Style

Shi, Lili, Ziyu Cui, and Wei Liu. 2023. "Effect of Chemical Refining on the Reduction of β-Carboline Content in Sesame Seed Oil" Molecules 28, no. 11: 4503. https://doi.org/10.3390/molecules28114503

APA Style

Shi, L., Cui, Z., & Liu, W. (2023). Effect of Chemical Refining on the Reduction of β-Carboline Content in Sesame Seed Oil. Molecules, 28(11), 4503. https://doi.org/10.3390/molecules28114503

Article Metrics

Back to TopTop