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Article

Comparative Evaluation of Structural Characteristics of Starch from 10 Varieties of Lotus Root

by
Fei Wang
1,
Minghui Xu
1,
Yaying Jiang
1,
Bei Zhang
1,
Yuyang Shao
1,
Jun Liu
1,
Juan Kan
1,
Man Zhang
1,
Lixia Xiao
1,
Xiaohua Qi
2,
Liangjun Li
2,
Shuping Zhao
2 and
Chunlu Qian
1,*
1
Department of Food Science and Engineering, School of Food Science and Engineering, Yangzhou University, Yangzhou 225127, China
2
Department of Horticulture, College of Horticulture and Landscape Architecture, Yangzhou University, Yangzhou 225009, China
*
Author to whom correspondence should be addressed.
Horticulturae 2024, 10(11), 1200; https://doi.org/10.3390/horticulturae10111200
Submission received: 29 September 2024 / Revised: 8 November 2024 / Accepted: 12 November 2024 / Published: 14 November 2024
Browse Figures
Versions Notes

Abstract

:
Starch extracted from ten lotus root varieties (Yeyong, MRHZ, Zhonghua, Suiningbaiou, Zaohua, Meirenhong, E9:11, Huchengyeou, Peixianyeou, Xin No. 5) from Jiangsu Province, China, were studied. The structural characteristics of lotus root starch were analyzed based on its physical and chemical properties, particle structure, crystal structure, layered structure, thermal properties and gel properties. The lotus root starches were generally milky white, with a starch content ranging from 81.72 to 99.54%, amylose content ranging from 15.44 to 23.54%, light transmittance between 15.30 and 26.90%, and swelling power and solubility at 22.15–29.72% and 2.00–6.00%, respectively. Among the varieties, “Suiningbaiou” had the whitest starch, while “Meirenhong” and “Suiningbaiou” had higher starch contents. “Huchengyeou” had the lowest amylose content, and “Zhonghua” showed the highest light transmittance. “Yeyong” and “Zaohua” had higher solubility, whereas “Zhonghua” had the highest swelling power. An optical, polarizing and scanning electron microscope revealed that most of the lotus starch was oval. However, starch from “Zhonghua”, “E9:11”, “Peixianyeou” and “Zaohua” was longer, whereas starch from “Meirenhong”, “MRHZ”, “Huchengyeou”, “Yeyong”, “Suiningbaiou” and “Xin No.5” was shorter. The X-ray powder diffraction patterns and 13C NMR spectroscopy indicated that “Zaohua” starch exhibited type A crystallization, while starch from the other varieties displayed type CA crystallization, with a relative crystallinity between 18.27 and 22.10%; “Huchengyeou” and “Yeyong” had higher crystallinity. Infrared spectroscopy and small-angle X diffraction analysis showed similar results for short-range order and lamella spacing. The thermal and gel properties of starch from the ten lotus root varieties also varied. The enthalpy change values of “Xin No.5” and “Yeyong” were higher, and starch from “Yeyong” and “Huchengyeou” showed a greater gel strength. Finally, factor score analysis ranked the starch quality of the top four lotus root varieties in Jiangsu as “Suiningbaiou”, “Yeyong”, “Huchengyeou”, and “Zaohua”.

1. Introduction

Lotus (Nelumbo nucifera Gaertn) is an aquatic vegetable widely cultivated in China, Japan, India and Australia, with a nearly 1000-year planting history in China [1]. As China’s most widely cultivated aquatic vegetable, approximately 12 million tons are lotus is produced annually, making it a high-value cash crop [2]. During its growing season, lotus roots develop underground, forming multiple joints. These joints, typically 10–20 cm long, are milky white or yellowish-brown with a smooth color or brown spotted surface [3]. Lotus roots produce and store a variety of nutrients, including starch and amino acids, and contain bioactive compounds like polyphenols, polysaccharides and flavonoids [4]. These active substances possess antioxidant properties, enhancing immunity and metabolism, which makes lotus root and its processed forms popular functional foods in Asia [5].
Starch, a macromolecular carbohydrate, consists of glucose molecules arranged and polymerized into amylose and amylopectin [6]. Naturally, starch is a polycrystalline polymer with both crystalline and amorphous regions. The dense crystalline region consists of amylopectin, while the sparse amorphous region is composed of amylose. The amylopectin’s outer chain interacts with water, folding into a double helix and forming microcrystals [7]. Starch is abundant, renewable, degradable and inexpensive, and has diverse applications [8].
Lotus root is highly nutritious, with a fresh weight starch content of 10~20%. Lotus root starch is considered an ideal nutritional food with therapeutic value in traditional Chinese medicine. In Jiangsu Province, China, lotus cultivation is extensive, yielding many varieties with different starch contents and structural characteristics, resulting in varying functional and physicochemical properties. Starch characteristics are essential for assessing lotus root’s storage and processing quality [9]. However, there are limited studies on the structural differences between varieties of lotus root starch. Therefore, this study selected 10 lotus root varieties from Jiangsu Province to prepare starch samples and systematically examined their physicochemical and structural characteristics. By comparing these varieties, we aim to identify the most suitable types for specific applications, maximizing their economic value. This research provides a theoretical basis for the processing and utilization of lotus root starch.

2. Materials and Methods

2.1. Plant Materials

In total, 10 varieties of fresh lotus root, namely “Yeyong”, “MRHZ”, “Zhonghua”, “Suiningbaiou”, “Zaohua”, “Meirenhong”, “E9:11”, “Huchengyeou”, “Peixianyeou” and “Xin No. 5”, were harvested from the aquatic vegetable resource nursery at Yangzhou University (Table 1).
Table 1 shows the epidermis, length and starch content of these lotus root varieties, highlighting their distinct features. Among the varieties, six (“MRHZ”, “Zhonghua”, “Suiningbaiou”, “Meirenhong”, “Huchengyeou” and “Xin No. 5”) had smooth skin and a bright yellow color, making them suitable for high-quality appearance products. “Zaohua”, “E9:11” and “Peixianyeou” are longer in length, with a higher starch content. “Yeyong” and “Suiningbaiou”, known for their powdery lotus roots, also had a higher starch content, which contributes to greater industrial value.

2.2. Separation of Lotus Root Starch

Lotus root starch was extracted using a method adapted from [10]. The lotus roots were rinsed, peeled, sliced and homogenized. The slurry was filtered, and the filtrate was collected in a transparent plastic bucket. After 12 h of precipitation, the supernatant was discarded, and the sediment was rinsed with distilled water. This step was repeated 3 times until the supernatant became clear. The sediment was then soaked in a 0.05% NaOH solution for 1 h, rinsed with 85% ethanol three times for degreasing and deproteinizing, and dried in an oven at 40 °C for 24 h. The dried starch was ground and sieved through a 100-mesh screen, yielding the final lotus root starch. The extraction yield of starch from the ten lotus root varieties ranged from 10.13% to 12.11%.

2.3. Color Measurement

The color of lotus root starch was measured using a handheld colorimeter. Before the determination, a white board was used as a control. L* = 100 represented white, L* = 0 represented black. Measurements were taken 3 times in parallel.

2.4. Starch and Amylose Content Measurement

The starch and amylose content were determined using a kit from Beijing Solarbio Tech Co., Ltd., Beijing, China.

2.5. Light Transmittance Measurement

The light transmittance was measured according to Sun [11], with slight modifications. First, 0.05 g lotus starch sample was used to prepare a starch paste with a mass fraction of 1%, which was then heated in a water bath at 90 °C for 15 min, cooled, and measured at 620 nm.

2.6. Swelling Power and Solubility

The swelling power and solubility were determined based on Dudu’s method [12], with slight modifications. A 0.1 g starch sample was mixed with 10 mL of distilled water and then heated in a water bath at 95 °C for 30 min. After cooling, it was centrifuged at 5000 r/min for 10 min. The supernatant was dried at 105 °C to a constant weight, which was recorded as the soluble starch mass. The remaining starch in the centrifuge tube was recorded as the expanded starch. The calculations used were as follows:
Swelling power (SP%) = P/(W − A)
Solubility (S%) = (A/W) × 100
where W is the weight of the starch (g); A is the weight of the soluble starch (g); and P is the weight of the expanded starch (g).

2.7. Morphology Observation of Lotus Root Starch

A small starch sample was mixed with 1 mL of distilled water, shook well, dropped onto the center of a slide, covered with a cover slide, and put on the loading platform; then, a polarizing microscope (BA310Pol, Motic China Group Co., Ltd., Xiamen, China) was used at a magnification of 40 × 10 times to observe the optical and polarizing microscopic images of starch.

2.8. Scanning Electron Microscope (SEM) Analysis

The SEM analysis was conducted with the Carl Zeiss Gemini SEM 300 scanning electron microscope (GeminiSEM 300, Carl Zeiss AG, Oberkochen, Baden-Württemberg, Germany). Samples were fixed on an aluminum platform, coated with gold in a vacuum, and viewed at 15 kV with 800× magnification. Three images were captured for each sample.

2.9. X-Ray Powder Diffractometry (XRD) Analysis

The crystal structure of lotus root starch was examined with a Bruker D8 Advance X-ray powder diffractometer (D8 Advance, Bruker Corporation, Billerica, MA, USA). The operating current was 40 mA at 40 kV, with a scanning range of 3–40° (2θ), at a rate of 0.3°/min. The relative crystallinity was calculated using Miao’s method [13].

2.10. 13C Solid-State NMR Analysis

13C Solid-state NMR analysis was conducted on an Avance III 400 MHz WB spectrometer (Avance III 400WB, Bruker Corporation, Billerica, MA, USA) following Man’s method [14].

2.11. ATR-FTIR Analysis

Using Yong’s method [15], the infrared spectrum was measured with a Cary 610/670 ATR—FTIR spectrometer (Cary 610/670, Varian Medical Systems Inc., Palo Alto, CA, USA). After baseline correction and deconvolution, the spectral intensity ratios at 1047/1022 cm−1 and 1022/995 cm−1 were calculated and compared.

2.12. Thermal Performance Analysis

Following Wei’s method [16], 3 mg of starch was weighed in an aluminum pot and 9 μL of distilled water was added. The pot was sealed and balanced at room temperature overnight. A DSC 8500 differential scanning calorimeter (DSC 8500, PerkinElmer Inc., Waltham, MA, USA) was used, with a heating temperature ranging from 25 °C to 100 °C and a heating rate of 10 °C/min.

2.13. Lamellar Structure

Following Yuryev’s method [17] with slight modifications, starch was mixed with distilled water to form a 50% solution. The lamellar structure of lotus root starch was analyzed using the NanoSTAR small-angle X-ray scatterer (NanoSTAR, Bruker Corporation, Billerica, MA, USA).

2.14. Gel Texture Analysis

Adjustments were made to Ali’s method [18]. A 6% starch suspension was prepared and heated in a 95 °C water bath for 30 min to fully gelatinize the starch. The mixture was transferred to a mold, covered with plastic wrap to prevent water loss, stored at 4 °C for 24 h to solidify, and brought to room temperature for 2 h before testing. The texture analyzer (TA. TOUCH, Bosin Tech Co., Ltd., Shanghai, China) parameters were as follows: probe TA/75, test speed of 1.0 mm/s, trigger force of 5.0 gf, compression ratio of 50%, and holding time of 5.0 s; this was followed by a second compression, with measurements repeated three times.

2.15. Statistical Analysis of Data

Microsoft Office Excel 2021 and Origin 2021 were used for statistical analysis and the experimental results were drawn. SPSS 25.0 software was used for variance analysis and Duncan test (p < 0.05).

3. Results and Discussion

3.1. Color of Lotus Root Starch

Color is an important indicator for evaluating starch quality. The L* value indicates brightness, and a higher L* value means a whiter starch color. The a* value represents the red–green spectrum, where a positive value indicates redness and a negative value indicates greenness. The b* value represents the yellow–blue spectrum, where a positive value indicates yellowness and a negative value indicates blueness. As shown in Table 2, the brightness of “Suiningbaiou” was significantly (p < 0.05) higher than that of other starch, while “Xin No.5” had a significantly (p < 0.05) lower brightness. Among the 10 lotus starch varieties, “Huchengyeou” showed higher redness and yellowness, significantly (p < 0.05) more than the other starches. Therefore, “Suiningbaiou” is suitable for processing products that require a high starch color quality. Due to its iron content, lotus root starch gradually oxidizes to a slightly reddish color upon exposure to air. While this color difference does not affect its nutritional value, pure white starch has an improved product appearance and greater commercial appeal.

3.2. Starch Content of Lotus Root

The basic information of ten lotus root varieties is shown in Table 2. The total starch content of these varieties ranged from 81.72 and 99.54% (dry weight), with “Yeyong” having the lowest content and “Meirenhong” the highest. The amylopectin content was calculated by subtracting the amylose content from the total starch and ranged from 64.25% to 83.84%. The variation in starch content among the varieties may be attributed to differences in growth conditions. “Meirenhong” had the highest total starch content (99.54%), indicating high starch purity, and a brighter white color; however, it had a relatively low starch extraction rate of 10.13%, making it suitable for pure starch products. “Suiningbaiou” also had a high starch content (97.02%), with the whitest color and a higher extraction rate of 11.47%, indicating a better quality starch than “Meirenhong” and greater processability.
The amylose content affects the gelatinization and aging, swelling force and viscosity of starch, and also impacts the product’s texture, which is a key quality factor for product application [19]. There were significant (p < 0.05) differences in amylose content in the 10 varieties of lotus root, ranging from 15.44 to 23.54%. Among the varieties, “Suiningbaiou” had the highest amylose content, while “Huchengyeou” had the lowest. The amylose content of lotus root starch is generally reported to be between 25 and 35%, though the results in this study are slightly lower, possibly due to differences in lotus root varieties, planting areas, culture conditions, harvesting time, and region [20]. Varieties are likely the primary determinant. A high amylose ratio would lead to cooked rice with a hard texture and poor taste, while a high amylopectin content would lead to soft rice with a good taste [21]. The high amylose content in “Suiningbaiou” may lead to faster aging, lower cold-water solubility, and thermal instability, limiting its functionality. In contrast, the low amylose content in “Huchengyeou” may result in a softer texture and improved taste after processing.

3.3. Light Transmittance of Lotus Root Starch

Light transmittance significantly impacts the appearance and sensory evaluation of starch-based products. As shown in Figure 1, there were significant (p < 0.05) differences in light transmittance among the 10 varieties. “Zhonghua” had the highest light transmittance, while “Suiningbaiou” had the lowest. A high amylose content can reduce starch light transmittance, as smaller amylose molecules evenly disperse in solution, causing more light scattering and reflection through the starch paste. These results suggest that starch from “Zhonghua” is more suitable for products requiring high light transmittance.

3.4. Swelling Power and Solubility of Lotus Root Starch

Swelling power and solubility describe the expansion and disintegration of starch particles when heated in excess water [22]. As shown in Figure 2, the swelling power of lotus root starch ranged from 22.15 to 29.72%, while its solubility ranged from 2.00 to 6.00%. Amylose diffuses from expanded particles and binds molecules through entanglement, inhibiting expansion [23]. Therefore, the amylose content was inversely correlated with the swelling power, consistent with the findings of Sun [11]. Swelling power differences are influenced by starch granule surface characteristics, the amylopectin and amylose content, and minor components. These results suggest that “Yeyong” and “Zaohua” are more suitable for products requiring high solubility.

3.5. Observation of Starch Particle Morphology

The appearance and morphology of starch particles were observed using optical, polarizing and scanning electron microscopes. The morphology images directly reflect the surface structure of starch particles. As shown in Figure 3, starch particles from 10 lotus root varieties exhibited a similar morphology under an optical microscope, being mostly short rod-like with some elliptical or spherical particles. The umbilical point of the oval grains was located at one end, while in round grains it was located in the middle of the grain, with visible lamination on the starch grain surface. Under the polarizing microscope, starch from all 10 varieties showed obvious polarizing characteristics, indicating the crystal structure of the molecular chains within the particles. If the molecular crystal structure is disrupted, the polarizing cross disappears [24]. The surface of the lotus root starch particles was smooth, without cracks, and with some irregularly broken particles, likely due to starch particle breakage during the separation. The grain size of lotus root starch from the 10 varieties ranged from 53.33 to 75.15 μm. Starch from “Zhonghua”, “E9:11”, “Peixianyeou” and “Zaohua” had larger grain sizes, while “Meirenhong” had smaller grains. “Meirenhong”, “E9:11” and “Huchengyeou” exhibited more broken particles, while “Zhonghua” and “Zaohua” had fewer. These morphological differences may be due to the biological origin and physiological characteristics of each plant. The size of starch particles and the degree of breakage affect the gelatinization speed and degree, swelling and solubility, and then affect the starch products’ quality [25].

3.6. 13C CP-MAS NMR Analysis of Starch

13C NMR spectroscopy can reveal the crystalline morphology of starch, often used in conjunction with XRD [26]. In nuclear magnetic resonance, starch produces four regions with distinct signal intensities: the 96–106 ppm range corresponds to the C-1 region, 79–83 ppm corresponds to the C-4 region, and the overlapping signal with 68–78 ppm corresponds to the C-2, C-3 and C-5 regions. The 59–62 ppm signal corresponds to the C6 region [27]. The C-1 region represents the double helix crystal structure of starch, while the C-4 region represents the amorphous structure [28]. Type A starch shows triplet peaks at 102, 101 and 100 ppm in C-1; type B starch shows a binary state at 101 and 100 ppm in C-1, and Type C starch is a mixed type with characteristics of both A and B. As shown in Figure 4, the C1 resonance of the 10 samples displayed triple peaks at 101.6, 100.3 and 99.7 ppm, indicating a crystallization type similar to type A. This result aligns with the XRD findings, confirming that the starch from the ten lotus root varieties is CA type.

3.7. XRD Analysis of Starch

X-ray diffraction can detect the crystalline structure of natural starch, determine its crystal type, and analyze its crystal structure and characteristics [29]. Based on the XRD diffraction pattern, natural starch crystals can be classified into type A, type B and type C. A-type starches have distinct diffraction peaks around 15° and 23°2θ, along with unsegregated double peaks around 17° and 18°2θ. B-type starches have diffraction peaks around 5.6°2θ, distinct diffraction peaks around 17°2θ, and weak peaks around 15°, 22° and 24°2θ. Type C crystalline starch is composed of A and B crystals, with distinct peaks around 17° and 18°2θ, and smaller peaks around 5.6° and 15°2θ. Depending on the proportion of type A and type B polycrystalline, type C can be further divided into type CA (has A-type crystal characteristics), type C and type CB (has b-type crystal characteristics) [30]. As shown in Figure 5, starch from “Zaohua” exhibited A-type crystallization, while the other varieties showed CA-type crystallization. The crystal type of lotus root starch has been a topic of debate. for example, Chandak [31] and Sukhija [32] reported lotus root starch crystallized in type A, while Zhong [33] and Gani [34] reported type B, and Lin [35] and Man [23] reported type C. These discrepancies suggest that the crystal type of lotus root starch may be influenced by factors such as the growth conditions, harvest maturity, amylose and amylopectin, and biological origin [36].
The crystallinity of starch is a key property that affects the characteristics and applications of starch-products [37]. As shown in Table 3, the relative crystallinity of starch from the 10 lotus root varieties ranged from 18.27 to 22.10%. Among these, starch from “Huchengyeou”, “Yeyong” and “MRHZ” exhibited higher relative crystallinity compared to other varieties, while starch from “Suiningbaiou” and “E9:11” showed lower crystallinity. Previous studies have shown that the crystallinity of natural starch particles typically falls between 15% and 45% [38]. This variation in crystallinity may be attributed to differences in crop genetics and growth conditions. The crystallinity od starch from “Huchengyeou” and “Yeyong” was higher, indicating that the order of the molecular chains within their structures was higher, with stronger intermolecular interactions, and more stable crystals, contributing to the better shape stability and texture of the starch-based products.

3.8. ATR-FTIR Analysis of Starch

FTIR can be used to determine the short-range ordered structure of starch and analyze the outer structure of starch particles [39]. The typical vibration absorption peaks are at 1047 cm−1 and 1022 cm−1. The absorption peak near 1047 cm−1 is related to starch in the crystalline zone, while the peak near 1022 cm−1 is related to starch in the amorphous zone. Therefore, the ratio of these two absorption peaks can represent the degree of ordered versus disordered [40]. As shown in Figure 6, the infrared spectra of lotus root starch from the 10 varieties were similar. A higher 1022/995 cm−1 value in “E9:11” and “Xin No.5” starch indicated a higher degree of disorder, while a higher 1047/1022 cm−1 value in “Zhonghua” and “MRHZ” starch indicated a higher degree of order. This short-range degree of ordering usually helps starch form a stable crystal structure, improving the physical and functional applications of starch.

3.9. DSC Analysis of Starch

Natural starch particles are a type of polycrystalline system. When starch particles are dispersed in water and a certain temperature is reached, they absorb water, expand, and split to form a uniform paste, accompanied by energy changes. This process is called starch gelatinization [41]. Differential scanning calorimetry (DSC) is often used to measure the thermal performance of starch, including the initial, peak and end gelatinization temperatures (T0, TP, TC) and gelatinization heat enthalpy values (ΔH) (Table 4). The T0, TP and TC of starch from the 10 lotus root varieties ranged from 58.28 to 66.21 °C, 64.41 to 70.84 °C and 69.05 to 77.23 °C, respectively. Amylose can limit starch gelatinization and expansion, resulting in higher gelatinization temperatures. Similar results were observed in studies on rice varieties with different amylose levels [42].
The enthalpy changes in starch from 10 lotus root varieties ranged from 7.10 to 15.22 J/g, with “Meirenhong” starch having the lowest value and “Xin No.5” the highest. The enthalpy change reflects the heat energy required to disrupt the crystal structure of starch during thermal gelatinization [43], indicating that the double helix structure of “Xin No. 5” starch was more resistant to gelatinization. The enthalpy change value of “Huchengyeou” starch was also high, indicating that the high crystallinity made its structure stable and resistant to damage. Studies on rice varieties with different amylose levels have shown that the ΔH of low-amylose varieties is higher [21], demonstrating that ΔH is inversely correlated with amylose content [44]. ΔH is influenced by factors such as the starch particle size, relative crystallinity, amylose content, and the fine structure of amylopectin [36].

3.10. SAXS Analysis of Starch

The small-angle X-ray scattering technique (SAXS) is widely used to analyze the layered structure of starch and can efficiently and quantitatively examine the lamellar structure composed of semi-crystalline growth rings in starch particles [45]. As shown in Figure 7, starch from the 10 varieties of lotus root showed similar SAXS profiles, with distinct scattering peaks (Smax) at a scattering vector of 0.584 to 0.612 nm−1. This nanoscale aggregation structure consists of a layered arrangement of amylopectin and amylose molecules, with a lamellar repeat distance of 9 to 10 nm, or Bragg spacing (2π/Smax) [29]. As shown in Table 3, the lamellar repeat distances of starch from the 10 lotus root varieties ranged from 10.267 to 10.759 nm. The results indicate that the lamellar repeat distance did not vary significantly among the varieties, suggesting that the lamellar structure of starch is largely independent of lotus root varieties. Additionally, the intensity of the scattering peaks reflects the degree of molecular order [46]. The scattering peak intensity of starch from the 10 lotus root varieties ranged from 62.999 to 97.696. The varieties with a more compact starch structure were “Yeyong”, “MRHZ”, “Peixianyeou”, “Huchengyeou” and “Meirenhong”, whereas the starch structure of “Zhonghua”, “E9:11”, “Xin No. 5” and “Suiningbaiou” were comparatively looser (Table 3).

3.11. Gel Texture Analysis of Starch

After gelatinization, starch forms a gel system consisting of a mixture of solid and liquid phases, which creates a three-dimensional network structure with a specific strength and elasticity. This structures reflects the internal structure, molecular spacing, molecular weight, and other properties of starch molecules [47]. The hardness of the gel reflects the intermolecular forces present. The greater the gel hardness, the stronger the intermolecular force [48]. As shown in Table 5, the gel hardness of starch from the 10 lotus root varieties ranged from 182.84 to 218.68 gf, with the starch from “Peixianyeou” having the lowest hardness and that from “Yeyong” having the highest. Gel elasticity reflects the ability of a gel to recover from deformation after being thoroughly compressed [49]. The starch gel elasticity of the ten lotus root varieties ranged from 0.7218 to 0.7218 mm, with “Zhonghua” having the lowest elasticity and “Yeyong” having the highest. The chewability of the starch gels from the ten varieties ranged from 116.07 to 158.74 gf, with “Xin No. 5” having the lowest chewability and “Yeyong” having the highest. Cohesion measures the internal adhesion of the sample. The greater the cohesion, the stronger the interaction between molecules within the sample, which contributes to better gel stability. The cohesiveness of the starch from the ten varieties ranged from 0.8118 to 0.8876, with “Zhonghua” showing the lowest and “Huchengyeou” showing the highest. The adhesiveness of the starch gels ranged from 155.77 to 186.33 gf, with “Xin No. 5” having the lowest and “Yeyong” having the highest. In summary, the starch gels from “Yeyong”, “Huchengyeou”, “E9:11”, “MRHZ”, and “Suiningbaiou” exhibited a higher gel strength, making these varieties suitable for processing into products with high elasticity requirements, a strong sense of stiffness, and good chewability. Factors such as the temperature, gel concentration, and amylose content can affect the gel texture of starch, and, consequently, the taste of the product.

3.12. Analysis of Starch Quality Indexes Correlation in 10 Varieties of Lotus Root

Figure 8 analyzes the correlation between the structure quality indexes of starch from different varieties of lotus root. Amylose exhibited a negative correlation with crystallinity. Amylose forms an amorphous region, and when the amylose content is high, the crystalline region formed by amylopectin is disrupted, resulting in low starch crystallinity [50]. This finding is consistent with the conclusion of Lin [51,52]. Amylose showed a positive correlation with the gelatinization temperature: as the amylose content increases, its linear structure enhances intermolecular forces, requiring higher temperatures for gelatinization to occur. There was a significant (p < 0.05) negative correlation between light transmittance and the amylose content, indicating that a higher amylose content reduced the light transmittance of starch paste. Solubility was significantly (p < 0.05) positively correlated with chewability and adhesiveness, suggesting that starch particles with high solubility had better dispersion in solution and formed a better quality gel system. Additionally, there was a significant (p < 0.05) negative correlation between the expansion degree and cohesiveness, as well as a very significant (p < 0.01) negative correlation between the expansion degree and peak temperature. Gel strength was positively and significantly (p < 0.01) correlated with elasticity, mastication, cohesiveness and adhesiveness.

3.13. Principal Component Analysis of Starch Indexes in 10 Varieties of Lotus Root

For the dimensionality reduction analysis of factor scores, the following conditions should be met: KMO > 0.6 and Bartlett’s Test of Sphericity < 0.05. Indicators with poor correlations were excluded. Seven evaluation indexes, namely amylose, light transmission, starting temperature, ending temperature, elasticity, adhesiveness, and gel strength, were selected as variables to perform principal component analysis on the quality of starch from 10 different lotus root varieties. The results are shown in Table 6. The cumulative variance contribution rate of the first three factors reached 89.218%, so three factors were extracted for calculation.
Table 7 showed the load matrix for each index, with the load value indicating the proportion of each index in the principal component. The first principal component has a higher load on gel strength, elasticity, TP and amylose. The second principal component has a higher load on adhesiveness. The third principal component has a higher load on T0 and light transmittance.

3.14. Establishment of Evaluation Methods of Starch Quality from 10 Varieties of Lotus Root

According to the scoring coefficient matrix of each factor in Table 8, the scoring expression of each common factor can be obtained:
F1 = −0.033X1 + 0.015X2 + …… + 0.374X6 + 0.375X7
F2 = 0.442X1 − 0.523X2 + ……− 0.054X6 + 0.083X7
F3 = −0.03X1 + 0.198X2 + ……− 0.147X6 − 0.056X7
Using the above expression, the score and ranking of different lotus root varieties and starch indexes for each common factor can be calculated. The comprehensive score is the sum of the scores of each factor and the corresponding weight. The weight refers to the contribution rate of variance for each factor divided by the cumulative variance contribution rate. The following calculation formula is obtained:
Ft = 0.401F1 + 0.322F2 + 0.277F3
According to the above expression, a higher score for a variety indicates better quality. The comprehensive scores and rankings of the 10 different lotus root varieties are shown in Table 9. The top four varieties are “Suiningbaiou”, “Yeyong”, “Huchengyeou” and “Zaohua”.

4. Conclusions

There were significant differences in the physicochemical, structural and functional properties of starch extracted from the 10 different varieties of lotus root. The results showed that the lotus root variety had a major influence on the color, light transmittance, amylose content, expansion, solubility, particle size, relative crystallinity and gel properties of the starch. Except for the A-type crystal structure of “Zaohua” starch, other varieties exhibited CA type crystals, with a relative crystallinity ranging from 18.27 to 22.10%. There were no obvious differences in the short-range order or lamellar spacing among the 10 varieties. The thermal performances and gel properties of the starches also varied across the varieties. Finally, using factor score analysis, the top four starch qualities among the 10 lotus root varieties in Jiangsu were from “Suiningbaiou”, “Yeyong”, “Huchengyeou”, and “Zaohua”. Among them, “Suiningbaiou” starch, with its white color, is suitable for products requiring high color quality; “Huchengyeou” has a low amylose content and better taste after processing; “Zhonghua” has the highest transparency; “Yeyong” and “Zaohua” have higher solubility; and “Huchengyeou” has the highest crystallinity and enthalpy value, indicating a compact structure with thermal stability. Additionally, “Yeyong” has the highest gel strength, making it suitable for gel product processing. This conclusion provides a theoretical basis for the processing and utilization of various lotus root starch varieties, potentially adding economic value to its application. Further research is warranted to investigate the influence of the fine structure of amylose and amylopectin on the starch characteristics of different lotus root varieties.

Author Contributions

F.W. and L.L.: Conceptualization, Methodology; M.X. and Y.J.: Investigation, Writing—Original Draft; B.Z. and Y.S.: Validation, Investigation; J.L. and S.Z.: Validation, Visualization; J.K.: Investigation; L.X. and M.Z.: Conceptualization; X.Q. and C.Q.: Conceptualization, Writing—Review and Editing, Funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the National Natural Science Foundation of China (32472765), China Agriculture Research System (CARS-24), Jiangsu Seed Industry Revitali-zation ‘Jie Bang Gua Shuai’ project (JBGS [2021]017), Modern Agriculture Development Project of Jiangsu Province (2020-SJ-003-YD15), Jiangsu Provincial Key R & D Programme-Modern Agriculture (BE2022339), 2024 Jiangsu Graduate Research and Practice Innovation Program (SJCX24-2370), Qing Lan Project of Yangzhou University, China.

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Light transmittance of starch from different varieties of lotus root. Note: Different letters such as abcd indicate that there are significant differences among different varieties (p < 0.05).
Figure 1. Light transmittance of starch from different varieties of lotus root. Note: Different letters such as abcd indicate that there are significant differences among different varieties (p < 0.05).
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Horticulturae 10 01200 g002
Figure 2. Swelling power and solubility of starch from different varieties of lotus root. Note: Different letters such as abcd indicate that there are significant differences among different varieties (p < 0.05).
Figure 2. Swelling power and solubility of starch from different varieties of lotus root. Note: Different letters such as abcd indicate that there are significant differences among different varieties (p < 0.05).
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Horticulturae 10 01200 g003
Figure 3. Optical microscope (1) (10 × 40×), polarizing microscope (2) (10 × 40×) and scanning electron microscope images (3) (800×) of starch from different varieties of lotus root. (a1,a2,a3) Yeyong, (b1,b2,b3) MRHZ, (c1,c2,c3) Zhonghua, (d1,d2,d3) Suiningbaioum, (e1,e2,e3) Zaohua, (f1,f2,f3) Meirenhong, (g1,g2,g3) E9:11, (h1,h2,h3) Huchengyeou, (i1,i2,i3) Peixianyeou, (j1,j2,j3) Xin No.5.
Figure 3. Optical microscope (1) (10 × 40×), polarizing microscope (2) (10 × 40×) and scanning electron microscope images (3) (800×) of starch from different varieties of lotus root. (a1,a2,a3) Yeyong, (b1,b2,b3) MRHZ, (c1,c2,c3) Zhonghua, (d1,d2,d3) Suiningbaioum, (e1,e2,e3) Zaohua, (f1,f2,f3) Meirenhong, (g1,g2,g3) E9:11, (h1,h2,h3) Huchengyeou, (i1,i2,i3) Peixianyeou, (j1,j2,j3) Xin No.5.
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Horticulturae 10 01200 g004
Figure 4. 13C CP-MAS NMR spectra of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
Figure 4. 13C CP-MAS NMR spectra of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
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Horticulturae 10 01200 g005
Figure 5. XRD patterns of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
Figure 5. XRD patterns of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
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Horticulturae 10 01200 g006
Figure 6. FTIR spectrum of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
Figure 6. FTIR spectrum of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
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Horticulturae 10 01200 g007
Figure 7. SAXS patterns of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
Figure 7. SAXS patterns of starch from different varieties of lotus root. (a) Yeyong, (b) MRHZ, (c) Zhonghua, (d) Suiningbaiou, (e) Zaohua, (f) Meirenhong, (g) E9:11, (h) Huchengyeou, (i) Peixianyeou, (j) Xin No.5.
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Horticulturae 10 01200 g008
Figure 8. Pearson correlation analysis of quality indexes of starch from different varieties of lotus root. AC, amylose content; L*, starch light; T, light transmittance; S, solubility; SP, swelling power; RC, Relative crystallization; IR1, 1047/1022 cm−1; IR2, 1022/995 cm−1; Imax, intensity of scattering peak. * indicates significance at the 0.05 level; ** indicates significance at the 0.01 level.
Figure 8. Pearson correlation analysis of quality indexes of starch from different varieties of lotus root. AC, amylose content; L*, starch light; T, light transmittance; S, solubility; SP, swelling power; RC, Relative crystallization; IR1, 1047/1022 cm−1; IR2, 1022/995 cm−1; Imax, intensity of scattering peak. * indicates significance at the 0.05 level; ** indicates significance at the 0.01 level.
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Table 1. Information about the 10 varieties of lotus root.
Table 1. Information about the 10 varieties of lotus root.
PhotoEpidermisLengthStarch
YeyongHorticulturae 10 01200 i001Dark yellow with a rough surfaceThe main lotus root is about 40 cm long, while the lotus root section is about 10 cm long and slender11.88%;
Powdery lotus root
MRHZHorticulturae 10 01200 i002Yellow with a smooth surfaceThe main lotus root is about 36 cm long, while the lotus root section is about 18 cm long and slender10.28%;
Powdery lotus root
ZhonghuaHorticulturae 10 01200 i003Yellow with a slightly rough surfaceThe main lotus root is about 45 cm long, while the lotus root section is about 13 cm long and slender10.54%;
Crispy lotus root
SuiningbaiouHorticulturae 10 01200 i004Bright yellow with a smooth surfaceThe main lotus root is about 40 cm long, while the lotus root section is about 13 cm long and elliptical11.47%;
Powdery lotus root
ZaohuaHorticulturae 10 01200 i005Milky white with a rough and uneven surfaceThe main lotus root is about 50 cm long, while the lotus root section is about 14 cm long and elliptical11.84%;
Powdery lotus root
MeirenhongHorticulturae 10 01200 i006Pale yellow with a smooth surfaceThe main lotus root is about 32 cm long, while the lotus root section is about 10 cm long and slender10.13%;
Crispy lotus root
E9:11Horticulturae 10 01200 i007Milky white with a slightly rough surfaceThe main lotus root is about 48 cm long, while the lotus root section is about 13 cm long and slender12.11%;
Powdery lotus root
HuchengyeouHorticulturae 10 01200 i008Pale yellow with a smooth surfaceThe main lotus root is about 47 cm long, while the lotus root section is about 12 cm long, and slender10.54%;
Crispy lotus root
PeixianyeouHorticulturae 10 01200 i009Yellow with a slightly rough surfaceThe main lotus root is about 46 cm long, while the lotus root section is about 10 cm long and elliptical10.78%;
Crispy lotus root
Xin No.5Horticulturae 10 01200 i010Mmilky white with a smooth surfaceThe main lotus root is about 40 cm long, while the lotus root section is about 13 cm long and elliptical11.03%;
Crispy lotus root
Table 2. Color values and basic composition of starch from ten lotus root varieties.
Table 2. Color values and basic composition of starch from ten lotus root varieties.
L*a*b*Starch Content %Amylose Content %Amylopectin Content %
Yeyong78.92 ± 0.03 g2.96 ± 0.06 ef15.84 ± 0.14 cd81.72 ± 3.87 h17.47 ± 0.63 bc64.25
MRHZ81.08 ± 0.15 b2.63 ± 0.12 g14.90 ± 0.17 ef95.78 ± 3.15 c20.25 ± 0.26 ab75.53
Zhonghua80.34 ± 0.15 cd3.21 ± 0.14 cd15.59 ± 0.11 d92.78 ± 4.22 e15.53 ± 0.69 c77.25
Suiningbaiou81.41 ± 0.32 a2.41 ± 0.10 h14.43 ± 0.15 g97.02 ± 2.16 b23.54 ± 0.37 a73.48
Zaohua79.86 ± 0.11 e3.02 ± 0.05 de15.19 ± 0.17 e87.61 ± 3.45 f18.73 ± 0.70 bc68.88
Meirenhong80.60 ± 0.10 c2.79 ± 0.12 fg14.71 ± 0.21 fg99.54 ± 1.34 a15.70 ± 0.72 c83.84
E9:1179.55 ± 0.04 f3.00 ± 0.10 def15.56 ± 0.05 d84.76 ± 2.68 g17.81 ± 0.19 bc66.95
Huchengyeou76.24 ± 0.08 h4.62 ± 0.17 a17.53 ± 0.32 a94.38 ± 3.01 d15.44 ± 0.09 c78.94
Peixianyeou80.08 ± 0.04 de3.31 ± 0.10 c16.08 ± 0.05 bc92.74 ± 4.61 e16.37 ± 0.46 c76.37
Xin No. 577.69 ± 0.06 i3.60 ± 0.06 b16.38 ± 0.19 b84.57 ± 3.42 g15.95 ± 0.30 c68.62
Note: Different letters such as abcdefghi indicate that there are significant differences among different varieties (p < 0.05).
Table 3. The FTIR ratio, relative crystallinity and SAXS parameters of starch from ten varieties of lotus root.
Table 3. The FTIR ratio, relative crystallinity and SAXS parameters of starch from ten varieties of lotus root.
FTIR RatioRelative Crystallization %SAXS Parameters
1047/1022 (cm−1)1022/995 (cm−1)Smax (nm−1)d (nm)Imax
Yeyong0.6520.84521.43 ± 0.55 ab0.59810.50797.696
MRHZ0.6580.86121.07 ± 1.18 ab0.59810.50782.701
Zhonghua0.6620.83720.87 ± 1.12 ab0.59810.50772.158
Suiningbaiou0.6510.84918.27 ± 0.15 c0.59810.50762.999
Zaohua0.6560.85318.73 ± 0.47 c0.59810.50769.786
Meirenhong0.6520.85319.93 ± 0.61 bc0.59810.50777.421
E9:110.6490.86318.43 ± 0.40 c0.61210.26768.123
Huchengyeou0.6480.86222.10 ± 1.31 a0.58410.75980.054
Peixianyeou0.6510.85619.77 ± 0.96 bc0.61210.26781.398
Xin No. 50.6410.86320.73 ± 1.66 ab0.59810.50764.347
Note: Different letters such as abc indicate that there are significant differences among different varieties (p < 0.05).
Table 4. Thermal performance of starch in ten varieties of lotus root.
Table 4. Thermal performance of starch in ten varieties of lotus root.
T0 (°C)TP (°C)TC (°C)ΔH (J/g)
Yeyong59.82 ± 0.30 ab65.36 ± 0.85 ef 69.82 ± 2.36 c 12.06 ± 0.06 ab
MRHZ62.50 ± 4.66 ab70.84 ± 0.05 a 74.24 ± 0.09 ab 13.00 ± 1.66 ab
Zhonghua60.67 ± 0.59 ab64.85 ± 0.03 ef 70.02 ± 0.09 c 12.64 ± 0.86 ab
Suiningbaiou61.96 ± 4.30 ab65.71 ± 1.17 def 77.23 ± 0.68 a 11.41 ± 3.68 ab
Zaohua66.21 ± 2.69 a67.52 ± 0.49 bcd 74.16 ± 0.81 ab 10.80 ± 1.82 ab
Meirenhong62.28 ± 0.74 ab66.61 ± 0.28 cde 72.18 ± 2.91 bc 7.10 ± 3.35 b
E9:1158.28 ± 0.49 b64.41 ± 0.01 f 69.05 ± 0.03 c 11.77 ± 0.07 ab
Huchengyeou62.52 ± 1.48 ab69.27 ± 0.62 ab74.10 ± 1.13 ab 13.57 ± 1.09 a
Peixianyeou61.95 ± 1.12 ab68.13 ± 0.50 bc 74.59 ± 0.76 ab 12.19 ± 0.32 ab
Xin No. 559.90 ± 0.86 ab65.46 ± 1.92 ef 69.59 ± 0.82 c 15.22 ± 3.84 a
Note: Different letters such as abcdef indicate that there are significant differences among different varieties (p < 0.05). T0, initial gelatinization temperatures; TP, peak gelatinization temperatures; TC, end gelatinization temperatures; ΔH, gelatinization heat enthalpy values.
Table 5. Gel texture of starch from different varieties of lotus root.
Table 5. Gel texture of starch from different varieties of lotus root.
Hardness/gfElasticityChewiness/gfCohesionAdhesiveness/gfGel Strength/g·cm
Yeyong218.68 ± 4.07 a0.8518 ± 0.00 a158.74 ± 5.52 a0.8789 ± 0.01 ab186.33 ± 10.77 a 147.74 ± 4.08 a
MRHZ198.08 ± 7.27 bcd0.7719 ± 0.03 cd130.44 ± 6.38 bc0.8533 ± 0.01 abc169.06 ± 8.34 ab 132.72 ± 4.87 abc
Zhonghua200.42 ± 11.40 abcd0.7218 ± 0.04 e117.68 ± 7.85 c0.8118 ± 0.03 d162.68 ± 10.93 ab 112.24 ± 7.36 c
Suiningbaiou193.60 ± 10.89 cd0.7787 ± 0.03 bcd128.10 ± 5.68 bc0.8508 ± 0.02 abc164.55 ± 5.49 ab 132.67 ± 4.97 abc
Zaohua196.06 ± 8.50 cd0.8221 ± 0.01 ab139.49 ± 5.78 abc0.8655 ± 0.01 abc169.72 ± 8.14 ab 132.07 ± 7.70 abc
Meirenhong198.69 ± 11.67 abcd0.7677 ± 0.01 cde128.50 ± 7.81 bc0.8434 ± 0.01 bcd167.50 ± 12.59 ab 128.52 ± 3.38 abc
E9:11212.48 ± 3.13 abc0.7684 ± 0.03 cde135.66 ± 5.84 abc0.8301 ± 0.01 cd176.40 ± 5.56 ab 133.18 ± 5.11 abc
Huchengyeou216.82 ± 4.56 ab0.8241 ± 0.02 ab147.40 ± 5.38 ab0.8876 ± 0.02 a178.37 ± 10.87 ab 141.86 ± 4.38 ab
Peixianyeou182.84 ± 11.78 d0.8123 ± 0.01 abc128.22 ± 6.51 bc0.8636 ± 0.01 abc157.77 ± 9.43 b 130.66 ± 6.22 abc
Xin No. 5183.83 ± 8.37 d0.7442 ± 0.01 de116.07 ± 6.44 c0.8474 ± 0.02 bcd155.77 ± 8.42 b 123.60 ± 5.64 bc
Note: Different letters such as abcde indicate that there are significant differences among different varieties (p < 0.05).
Table 6. Total variance explained.
Table 6. Total variance explained.
Principal ComponentCharacteristic ValueContribution Rate of Variance %Cumulative Variance Contribution Rate %
12.84735.75335.753
22.13128.72364.477
31.26724.74189.218
Table 7. The load matrix of each quality index in the principal component analysis.
Table 7. The load matrix of each quality index in the principal component analysis.
IndexComponent
123
Gel strength 0.8330.510
Elasticity0.798
Amylose content0.588−0.541
Adhesiveness0.5070.761
TP0.656−0.66
T0 0.773
Light transmittance−0.553 0.610
Table 8. Factor scoring coefficient matrix.
Table 8. Factor scoring coefficient matrix.
IndexFactor
123
Amylose content−0.0330.442−0.03
Light transmittance0.015−0.5230.198
T0−0.012−0.1930.627
TP−0.0440.1810.387
Elasticity0.352−0.0970.189
Adhesiveness0.374−0.054−0.147
Gel strength0.3750.083−0.056
Table 9. Comprehensive scores and rankings of different varieties of lotus root starch.
Table 9. Comprehensive scores and rankings of different varieties of lotus root starch.
SampleF1F2F3FtReorder
Suiningbaiou−0.379172.583440.245720.751
Yeyong1.95755−0.09887−0.978230.482
Huchengyeou1.11050−0.330990.452690.463
Zaohua0.31421−0.590551.856010.454
MRHZ−0.134010.445880.421350.215
Peixianyeou−0.25569−0.0331450.784550.016
Meirenhong−0.30503−0.445670.14486−0.237
E9:110.28874−0.15502−1.56573−0.378
Xin No. 5−1.125210.07265−0.94611−0.699
Zhonghua−1.47188−1.14941−0.41511−1.0710
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Wang, F.; Xu, M.; Jiang, Y.; Zhang, B.; Shao, Y.; Liu, J.; Kan, J.; Zhang, M.; Xiao, L.; Qi, X.; et al. Comparative Evaluation of Structural Characteristics of Starch from 10 Varieties of Lotus Root. Horticulturae 2024, 10, 1200. https://doi.org/10.3390/horticulturae10111200

AMA Style

Wang F, Xu M, Jiang Y, Zhang B, Shao Y, Liu J, Kan J, Zhang M, Xiao L, Qi X, et al. Comparative Evaluation of Structural Characteristics of Starch from 10 Varieties of Lotus Root. Horticulturae. 2024; 10(11):1200. https://doi.org/10.3390/horticulturae10111200

Chicago/Turabian Style

Wang, Fei, Minghui Xu, Yaying Jiang, Bei Zhang, Yuyang Shao, Jun Liu, Juan Kan, Man Zhang, Lixia Xiao, Xiaohua Qi, and et al. 2024. "Comparative Evaluation of Structural Characteristics of Starch from 10 Varieties of Lotus Root" Horticulturae 10, no. 11: 1200. https://doi.org/10.3390/horticulturae10111200

APA Style

Wang, F., Xu, M., Jiang, Y., Zhang, B., Shao, Y., Liu, J., Kan, J., Zhang, M., Xiao, L., Qi, X., Li, L., Zhao, S., & Qian, C. (2024). Comparative Evaluation of Structural Characteristics of Starch from 10 Varieties of Lotus Root. Horticulturae, 10(11), 1200. https://doi.org/10.3390/horticulturae10111200

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