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Article

A Study of Application and Comparison of Thermal Drying and Freeze Drying of Fresh Edamame Seeds in the Analysis of Seed Composition

by
Guo-Liang Jiang
*,
William Townsend
,
Edward Sismour
and
Yixiang Xu
Agricultural Research Station, Virginia State University, P.O. Box 9061, Petersburg, VA 23806, USA
*
Author to whom correspondence should be addressed.
Agronomy 2022, 12(9), 1993; https://doi.org/10.3390/agronomy12091993
Submission received: 10 August 2022 / Revised: 21 August 2022 / Accepted: 22 August 2022 / Published: 24 August 2022
Browse Figure
Review Reports Versions Notes

Abstract

:
Edamame is a vegetable soybean (Glycine max) with high nutritional and market value. It is mainly grown in Asia and has expanded to North America and Africa. Freeze and low- and high-heat drying methods were used to dry fresh edamame seeds of 20 soybean lines and cultivars for analysis of their composition using near-infrared reflectance (NIR) technology. The results indicated that significant differences existed between years of samplings for all seed composition traits investigated. Differences between drying methods were significant for all the traits with whole-seed samples, while they were not significant in protein, raffinose and linoleic acid for flour samples. Ground flour and whole-seed samples were similar or comparable in most cases for freeze and low-heat drying methods, but differences in seed composition between sample types were observed for high-heat drying. Among the traits investigated, protein content was the most consistent for all three drying methods, with an over 91% estimate of repeatability, showing high stability during drying. Oil content also showed a repeatability estimate of over 86% for all three drying methods. Low-heat drying generated results more comparable to freeze drying, while high-heat drying exhibited larger differences in most cases. Estimates of repeatability and correlation coefficients further confirmed that, low-heat drying, similar to freeze drying, was appropriate for drying fresh edamame seeds, but high-heat drying was not. Therefore, low-heat drying is a suitable method for drying fresh edamame and rapid analysis of seed composition, and it can be used as an alternative of freeze-drying method.

1. Introduction

Edamame, a Japanese term and also known as maodou in China, is a vegetable soybean (Glycine max (L.) Merr.) and is a consumable specialty crop. Uniquely, edamame is harvested at the R6 growth stage [1], i.e., when the pods and seeds are still green, while the commercial soybean is harvested after full maturity (R8 growth stage). Edamame has been grown for many centuries, mainly in China, Japan and Korea [2,3]. It has a relatively high market value compared with commercial soybeans and thus is regarded as a new alternative or niche crop in the North America [4,5] and a superfood crop in Africa [6,7]. Edamame can be used in different diets, such as vegetable dishes or snacks. Edamame products include boiled or steamed pods, shelled or unshelled beans, fresh or frozen seeds, and fried or roasted beans. Attention to and interest in edamame have been increasing due to its high nutritional value and other unique features [8,9,10]. These features include larger seed size, higher sugar and protein contents, and appealing taste compared with commercial soybeans.
Because of a relatively small production scale, research on edamame is limited, especially in North America [11,12,13,14,15]. Most edamame cultivars grown in North America were developed in Asia and usually exhibit poor adaptability to local eco-economic conditions and/or cropping management practices [5,9]. Many edamame cultivars are characterized by a very short plant structure with low bottom-pod position that results in an increased loss of pods or decreased harvest efficiency by mechanical harvesting. On the other hand, excessively tall plants may also negatively impact harvest efficiency [16]. Additionally, seed shattering, especially in association with mechanical harvesting for seed production, is a common problem for edamame cultivars, which leads to seed yield loss and increased production costs. Plant breeding is one of the most effective approaches to address the challenges facing edamame producers.
Seed composition is an important determinant of edamame quality and market or consumer acceptability. However, a large-scale analysis of seed nutritional composition is a great challenge, because hundreds and/or thousands of breeding materials need a timely phenotypic screening. There is a realistic need to develop a rapid evaluation of nutrient profiles in fresh seeds for edamame breeding and related research [17,18]. Although traditional wet chemistry techniques provide accurate measurements [19,20,21,22,23], these techniques require a trained technician and cannot achieve simultaneous multiple-trait measurements for a single sample. Additionally, wet chemistry techniques need a high labor input, and can be highly time consuming and cost inefficient, in addition to concerns with chemical residues [23,24,25]. Near-infrared reflectance (NIR) technology provides an optimal alternative solution that has been used in soybean research [24,26,27,28,29,30]. However, the current NIR calibrations used for soybean analysis are not appropriate for fresh edamame because fresh edamame contains approximately 65% moisture [5,31,32]. This level is far beyond the range of 4–20% moisture in mature soybean seeds that were used to develop the calibrations (Perten Instrument AB). Therefore, drying fresh edamame samples to reduce moisture is a prerequisite prior to the evaluation of nutrient profiles by NIR analysis. However, little research on the methods and effects of edamame drying has been reported [32,33] and, therefore, it is important to develop a suitable method for drying fresh edamame [18,34].
Jiang et al. used two different oven-drying methods to dry fresh edamame seeds and analyzed the seed composition traits using NIR spectroscopy to generate information useful for edamame research and breeding [18]. However, heating might influence seed composition during drying [35,36]. Freeze drying is the best drying method for fruits and vegetables because it maintains high product quality and minimizes impacts on nutrient composition [35,36,37]. In this regard, we attempted to use freeze and heat drying methods to dry fresh edamame, to explore if the thermal drying method is suitable for drying fresh edamame seeds in rapid NIR evaluation of their nutritional profiles. The objectives of this study were (1) to analyze the major seed composition traits (protein, oil, sugars, and fatty acids) in edamame, and (2) to compare differences between edamame seeds dried using different methods, i.e., freeze drying, and low- and high-heat frying.

2. Materials and Methods

2.1. Plant Materials and Sampling

In view of variability existing in crop varieties, a set of genotypes with a range of variation in seed size and other traits were selected and multiple lots of samples taken from different years were analyzed in order that the results could be referred under different conditions. A total of 20 soybean genotypes, i.e., cultivars and lines with a large range of variation in seed size and composition traits (Table 1), were used in this study and grown at the Virginia State University Randolph Farm in 2018–2020. The experimental field is located at 37°14′34″ N and 77°25′32″ W, south of Chesterfield County in Virginia, with a type of sandy soil (series–Bourne, and family–fine, silty mixed thermic). Four-row or two-row plots, 3.8 m long and 0.76 m row-spacing, were planted at a rate of 85 seeds per row using a research-plot planter (Almaco, Nevada, IA, USA). General cropping management was followed but no fertilizer was applied. At R6 stage before yellowing [1], sample plants were cut from the stem bottom and threshed using a KE-6S-N1 stationary edamame thresher (Mitsuwa & Co., Ltd., Nagoya City, Aichi, Japan). One batch of samplings, i.e., all genotypes were sampled at once, was conducted in 2018 and 2019, while two batches of samplings were made in 2020. In total, four batches of samplings were done in three years. The sample pods were then shelled using a peeling machine (Jiaozuo Zhiyou Machinery Co., Ltd., Jiaozuo, Henan, China) to collect fresh seed samples. Fresh edamame samples from each genotype were divided into three subsamples, each weighing about 40 g seeds in 2018 and 75–90 g seeds in 2019 and 2020, for different drying treatments. To maximize the homogeneity or similarity of samples within the groups for each batch of samplings, the subsamples were randomly taken and assigned to each of the three drying treatments. The fresh weight of each subsample was determined on an electronic scale. The subsamples were stored in a −20 °C freezer pending drying treatment. The subsamples were dried separately using freeze, low-heat or high-heat method.

2.2. Edamame Drying

For freeze drying, the frozen seed samples were dried using a FreeZone® Stoppering Tray Dryer (Labconco Corporation, Kansas City, MO, USA) in 2018 and 2019 or VirTis Freezemobile 25EL Freeze Dryer (SP Scientific, Gardiner, NY, USA) in 2020 for about 5 days, following the manufacturer’s instructions. The conditions of freeze drying were set as −6 °C for operating temperature in the sample chamber and −80 °C for operating temperature in the collector chamber, and less than 1 mbar for vacuum pressure. In thermal drying of vegetables and fruits, a temperature of 60–66 °C is recommended, especially for oven drying [38,39,40,41]. Higher temperatures were also used in some cases to shorten the drying time [18,39,42]. Referred to the previous reports and based on our experience [18], in this study, the drying temperature and processing time were set as follows. For low-heat drying, the samples were dried at 65 °C using a Thelco 6M double-door incubator (Thermo Electron Corporation, Marietta, OH, USA) in 2018 and 2019 or Blue M gravity oven (Thermal Product Solutions, LLC., New Columbia, PA, USA) in 2020 for about 2.5 days. For high-heat drying, the samples were dried at 105 °C also using a Thermo Scientific convection oven (Thermo Fisher Scientific, Waltham, MA, USA) for about 2 days. After the seeds were fully dried, i.e., no obvious change of weight was observed during 2–3 h, the samples were weighed immediately to determine moisture content in fresh seeds as
Fresh moisture = [(fresh weight − dried weight)/fresh weight] × 100%.
The seeds in each sample were counted to calculate fresh and dried 100-seed weights. The dried seed samples were stored for three to four weeks under ambient conditions until seed composition analysis.

2.3. Seed Composition Analysis

Dried samples were analyzed for seed composition using DA 7250 NIR analyzer (Perten Instrument AB, Hagersten, Sweden). In light of possible effects of differences in seed appearance feature between drying methods on the analysis [34], two types of samples were adopted, i.e., whole seed and ground/flour samples. Seed composition analysis was conducted first using whole seeds and repeated three times for each subsample. The seeds were then ground into flours using an IKA A11 Basic Analytical Mill (IKA Works, Inc., Wilmington, NC, USA) and were reanalyzed as before. Seed composition was quantified as mg g−1 (dry weight basis) for protein, oil, dietary fiber, ash and sugars, percentage of oil content for fatty acids, and percentage of dry seed weight for acid detergent fiber (ADF) and neutral detergent fiber (NDF). Average data derived from three replicate analyses for subsamples was used in statistical analysis.

2.4. Statistical Analysis

Data processing and Pearson correlation analysis were conducted using Microsoft Excel 2016. Analysis of variance (ANOVA) [43] was computed using PROC GLM in SAS version 9.4 (SAS Institute Inc., Gary, NC, USA). Years or batches of samplings were regarded as replications and random effects, while drying methods, genotypes and sample types were treated as fixed effects. ANOVA was performed separately for different considerations. First, an overall analysis was conducted by combining all the data from three years or four batches, three drying methods and two sample types. Second, analysis for each sample type with all three drying methods over three years was performed to test the significance of difference between drying methods. Finally, analysis for individual drying methods with a single sample type over three years was conducted to estimate the repeatability for a single method. According to the ANOVAs for the last two situations, i.e., analysis for a single sample type and analysis for a single drying method, repeatability was estimated based on genotype means as follows:
R = VG/[VG + VGM/n + VE/(nr)]
and
R = VG/(VG + VE/r)
where VG = genotype variance, VGM = genotype x method interaction variance, VE = error variance, n = number of methods, and r = number of batches of samplings.

3. Results and Discussion

3.1. Fresh Seed Moisture and Seed Weight

Both genotype and year or sampling batch effects were significant for fresh seed moisture, fresh 100-seed weight and dried 100-seed weight. The average performances of 20 genotypes in the moisture and 100-seed weight of fresh seed as well as seed composition in dried seed are presented in Table 1. The differences between the three subsamples used for different drying methods were insignificant, indicating that there was a high homogeneity in the samples between different groups of drying treatment. In other words, the three sets of subsamples were highly similar or comparable to each other. Table 2 presents the means and ranges of variation of traits in edamame for each drying method across three years. Overall, the moisture of fresh edamame seeds averaged 66.0% (58.3–72.0%), and the fresh 100-seed weight averaged 46.4 g (23.7–87.5 g). The average of dried 100-seeds was 15.9 g (7.8–32.8 g). There was a very large variation in seed size or 100-seed weight among the genotypes (Table 1), although the variation of fresh seed moisture was relatively small over the genotypes and three years.

3.2. Comparison of Sample Types

By combining all data across three drying methods and two types of samples, an overall ANOVA indicated that the differences between years were significant for all seed composition traits. There was no significant difference between whole seed and flour samples for seed ash, sucrose, stearic, oleic, linoleic and linolenic acids (data not shown). Differences in other seed composition traits were significant between sample types, which might be due to the differences in physical features between whole seed and flour. However, the absolute values of differences between sample types were relatively small, less than 5% of the ground sample averages for most of the traits (Table 3). Stachyose content varied the most, followed by raffinose and total sugar. Additional investigations are needed to explain this phenomenon. The differences between drying methods were also significant except linolenic acid over combined two types of samples. Significant sample type x drying method interactions were observed for all constituents except ash and palmitic acid. These differences may be associated with factors that influence sample reflectance and, therefore, detection by the NIR analyzer, such as appearance, solidities, structures and unit weight or relative density. For instance, freeze dried seeds were light and crispy and had lower unit weight, while the high-heat dried seeds were solid and hard and had higher unit weight (Figure 1). However, the exact reasons are unclear. Further investigations will help explicate the effects of different types of samples on NIR analysis.
To more accurately elucidate the results, ANOVAs were conducted separately for whole seed and flour samples. Using all data for the three drying methods, the ANOVA results of ground seeds were similar to those of whole seed samples in most cases (Table 4). The differences between drying methods using whole seeds were significant for all traits. However, the differences between drying methods using flours were not significant for protein, raffinose and linoleic acid, although they were significant for other traits. In addition, genotypic differences were not significant among flour samples for ash and palmitic and stearic acids, and only raffinose was not significant among whole seed samples. Estimates of repeatability based on genotype means were also comparable between the two sample types for most traits (Table 3). Whole seeds showed higher repeatability estimates for fatty acids than those of ground samples, but flours exhibited higher repeatability for most other traits.
Pearson correlation coefficients comparing flour and whole-seed samples were significant for all traits for both freeze and low-heat drying (Table 5). Correlations between flour and whole-seed samples subjected to high-heat drying were significant for all traits except ash, raffinose, total sugar, and stearic and linolenic acids, indicating that high-heat drying was less consistent compared with freeze and low-heat drying. In addition, differences between whole seeds and flours treated using low heat were very small, with a relative percent of difference (RPD) of 0.21–4.43%, except for sugars and dietary fiber, and were smaller than those for the samples treated using high heat in most cases. It was also noticed that, compared to other traits, stachyose and sucrose contents exhibited more obvious differences between sample types for both freeze and low-heat drying. These results suggested that it would be more appropriate to use specific calibrations established for different types of samples for NIR analysis of seed sugar contents.

3.3. Comparison of Edamame Drying Methods

As discussed above, the composition of whole seed and flour samples treated using freeze and low-heat drying methods was comparable for most traits but varied when samples were dried using high heat. Given that whole seeds were less uniform than ground samples in terms of physical features as discussed above, the subsequent discussion will mainly focus on ground samples unless otherwise specified.
As shown in Table 4, the differences between drying methods were significant for most of the seed composition traits except protein, raffinose and linoleic acid for ground samples. Genotypic differences were also significant except for ash, palmitic acid and stearic acid. No significant method x genotype interaction was found for all traits investigated. We also conducted a separate ANOVA for each drying method. The results showed that genotype effects were significant for all traits except stachyose and linolenic acid by freeze drying and stachyose by low-heat drying. However, no significant difference among genotypes was revealed by high-heat drying for seed ash, total sugar, stearic and linolenic acid. Therefore, we would suspect that high-heat drying might have larger influences on seed composition than low-heat drying and/or freeze drying [41], and thus interrupted detection of genotypic variations.
Freeze drying demonstrated minimum impact on seed nutritional composition [35,36,37]. Thus, this method was used as the reference in the present study. Table 6 presents the trait means and ranges of variation for the three edamame drying methods. Overall, low-heat drying produced results comparable to freeze drying more so than did high-heat drying. The average RPD between low-heat drying and freeze drying was 3.91% (Table 6), and RPD for individual traits varied from 0.19–7.36% relative to the reference and most were lower than 5%. For high-heat drying, the average RPD was 7.90% and ranged 0.35–29.84% for individual traits. The results indicated that low-heat drying was more appropriate than high-heat drying for NIR determination of seed composition in fresh edamame, especially for sucrose, total sugar, and fatty acids.
Protein content demonstrated high stability and was the most consistent of the traits evaluated among the three drying methods (Table 6). Under low-heat drying, the RPDs when compared to freeze drying were insignificant or <5% for most traits except linolenic acid, ADF and NDF. However, under high-heat drying, the RPDs were significant for most traits. By high-heat drying, sucrose exhibited the largest difference from the freeze drying, followed by linolenic acid and total sugar contents.

3.4. Repeatability and Correlations

Repeatability measures the consistency or stability of a method when comparing multiple genotypes. According to the ANOVA results, we further estimated the repeatability on entry or genotype means for each drying method. As shown in Table 7, protein and oil contents exhibited higher estimates of repeatability than other seed constituents, which is consistent with previous reports [18,30,44]. The estimates of repeatability for protein and oil contents were 91.19–93.91% and 86.84–91.84%, respectively, for all three drying methods. Freeze and low-heat drying methods exhibited comparable repeatability estimates, which were moderate to high for most traits but lower for stachyose and linolinic acid. Under high-heat drying, most traits showed lower repeatability estimates, i.e., less than 60%, compared to freeze drying. These results suggest that high-heat drying would result in a greater impact to the nutritional composition of edamame [41].
Correlation analysis helps understand the relationship or association between two or more variables. In this study, correlation coefficients between low-heat drying and freeze drying were significant at p < 0.01 for all the traits, varying from 0.622 to 0.975 (Table 7). The coefficients of correlation between high-heat drying and freeze drying varied largely with traits, and insignificant for ash, palmitic, stearic and linolenic acid, suggesting that the data for these traits was less comparable between high-heating and freeze drying. Comparably, the correlations of freeze drying with low-heat drying were higher than those with high-heat drying for most of the traits. These results further confirmed that low-heat drying could be used as an alternative of freeze drying and thus was appropriate for drying fresh edamame seeds, but high-heat drying was not.

3.5. Application

In fruit and vegetable drying for production of commercial goods [35,45], a large amount but single source of material was usually treated, and thus the drying treatment is relatively simple and there is no need to consider contamination among samples. In scientific research, especially for plant breeding and genetics studies, however, a large number of samples each of a small amount should be handled in general. It is important to avoid contamination among the samples. Limited studies on edamame drying methods have been reported so far [18,33]. In edamame drying for home-made snacks, a temperature as high as 375 °C can be used [42,46,47]. However, these protocols are not applicable to agricultural and food research, because the high temperature may negatively affect the nutritional and physical quality of products [36,41]. The present study was an attempt to explore simple and suitable drying methods and demonstrated that low-heat drying at 65 °C had the results comparable to freeze drying and could be used for rapid and large-scale evaluation of seed nutritional compounds in edamame breeding and research. No study has reported such a systematic comparison between freeze drying and thermal drying methods based on as many as 20 genotypes and multiple years or batches of samplings. It is expected that this study would provide useful information and a reference to related work in the research area.
Freeze drying was referred as an optimal method in vegetable and fruit drying because it can minimize the reverse impact of drying on the nutrients and maintain the product quality at maximum [45,48,49,50]. However, a higher cost and specific requirements for the equipment and facilities hinder its application. In the present study, the process of freeze drying also was complicated and lasted a longer time, compared with heat drying. Relatively, thermal drying is simple and easy to conduct, and more cost-efficient [38,45,50]. In thermal drying of fruits and vegetables, the higher temperature is used and the longer drying is conducted, the harder the products will be and the more impact will arise to the product quality [41]. Mercer indicated that the temperature should not exceed 66 °C to avoid quality loss [41]. This study confirmed that low-heat drying at 65 °C could produce a result comparable to freeze drying. In other words, the impact of thermal drying at such a low temperature could be ignorable for most of seed composition traits. However, high-heat drying at 105 °C was not appropriate for edamame drying. The impact of high-heat drying was observed as harder seeds, somewhat burning and reduced seed size (Figure 1), although no significant differences were observed in 100-seed weight (Table 2).
Current calibrations used in NIR analysis of soybean seed composition were established using samples with 4–20% moisture. For this study all samples were dried fully to determine the fresh seed moistures. In terms of energy savings, drying efficiency and maintenance of product quality, it is appropriate and good enough to have the samples dried to 12–15% moisture for analysis, i.e., the hardiness is similar to mature beans combined from field trials. In this way, the drying time could be decreased by half to one day compared to complete drying, depending on drying method and sample sizes. The duration of drying will vary depending on a multitude of factors in addition to the drying method, including but not limited to sample placement in the drying unit, sample container volume and shape, and number of samples to be dried simultaneously. Approaches to increase the exposed surface area of seeds in the sample, using open or mesh containers, and separately placing samples could facilitate moisture removal. These approaches help shorten drying time and thus improve drying efficiency.
The present study suggests that milling might produce improved NIR estimates of seed composition by reducing the effects of uneven drying of whole seeds. The trade-off, however, is the additional expense of time and effort to grind seeds. Whole seed samples dried under a low-heat condition exhibited results comparable to milled samples (Table 5), and their physical features also are similar to the mature dry seeds that are generally used in the NIR analysis [34]. Whole samples treated using freeze drying also showed a result comparable to ground samples (Table 5), although differences in physical features, e.g., being light and crispy and lower unit weight, were noticed compared with regular mature seeds (Figure 1). These results suggest that both flour samples and whole seeds from freeze drying and low-heat drying are suitable for analysis. It may deserve to study if the physical differences influence the detectability by NIR. For a specific nutrient compound like sugars, calibrations with higher prediction accuracy should be established for a given drying method or sample type with a large number of samples.

4. Conclusions

Three methods, freeze drying, low-heat drying (65 °C) and high-heat drying (105 °C), were used to dry fresh edamame seeds harvested from 20 soybean lines and/or cultivars and evaluate the effect of drying method on NIR estimates of nutrient composition in three consecutive years. Significant differences were identified between years or batches of samplings for all seed composition traits. Differences between ground- and whole-seed samples varied among traits. They were insignificant for ash, sucrose, stearic acid, oleic acid, linoleic acid and linolenic acids but were significant for other constituents. The differences between drying methods were significant for all the traits with whole-seed samples, but they were not significant in protein, raffinose and linoleic acid for ground samples. The results of ground and whole samples were comparable across traits in most cases for freeze and low-heat drying methods but varied with traits for high-heat drying. It is indicated that both ground samples and whole seeds by either freeze drying or low-heat drying are suitable for analysis of seed composition in edamame. However, high-heat drying exhibited larger differences from freeze drying in most traits, in addition to insignificant correlation or inconsistency between ground and whole samples for ash, raffinose, total sugar, stearic acid and linolenic acid. Thus, high-heat drying should not be an appropriate choice for edamame drying.
Among the composition traits investigated, protein was the most consistent across methods, showing a high stability during drying, followed by oil content. Sucrose, oleic and linoleic acids also exhibited a relatively high stability. Overall, low-heat drying generated more comparable results to freeze drying than high-heat drying. Estimates of repeatability and coefficients of correlation further confirmed that low-heat drying was appropriate for drying fresh edamame seeds, but high-heat drying was not. Therefore, low-heat drying is recommended as the preferred method of drying fresh edamame for rapid NIR analysis of seed composition. Low-heat drying also can be used as an alternative of freeze drying method in case where the latter is unavailable.

Author Contributions

Conceptualization, G.-L.J.; Data curation, G.-L.J. and W.T.; Formal analysis, G.-L.J.; Funding acquisition, G.-L.J.; Methodology, G.-L.J.; Project administration, G.-L.J.; Resources, G.-L.J., W.T., E.S. and Y.X.; Writing – original draft, G.-L.J.; Writing – review & editing, G.-L.J., W.T., E.S. and Y.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by USDA National Institute of Food and Agriculture grant number 2017-38821-26413.

Acknowledgments

This study was supported in part by the USDA-NIFA Evans-Allen Research Program and the USDA-NIFA Capacity Building Grant (CBG) Program (funding awarded to G-L Jiang). Dennis Katuuramu, Yuet Hah Cheung and Sadal Hwang provided assistance in the field trials and sampling. David Lipston, Haley Berry and Kyle Epps, the undergraduate students of Virginia State University, participated in the project. This article is a contribution of the Virginia State University, Agricultural Research Station (Journal Series No. 384).

Conflicts of Interest

The authors declare no conflict of interest.

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Agronomy 12 01993 g001 550
Figure 1. Dried edamame seeds of line VS15-6021. (A) fresh seed dried by freeze drying, (B) fresh seed dried by low-heat drying, and (C) fresh seed dried by high-heat drying.
Figure 1. Dried edamame seeds of line VS15-6021. (A) fresh seed dried by freeze drying, (B) fresh seed dried by low-heat drying, and (C) fresh seed dried by high-heat drying.
Agronomy 12 01993 g001
Table
Table 1. Average performance of 20 edamame cultivars and lines in seed size and composition traits across three years (2018–2020). Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively.
Table 1. Average performance of 20 edamame cultivars and lines in seed size and composition traits across three years (2018–2020). Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively.
GenotypeFresh Moisture (%)Fresh 100-Seed Wt (g)Dried 100-Seed Wt (g)ProteinOilFiberAshSucroseStachyose
Asmara66.0 ± 0.948.3 ± 1.316.4 ± 0.9440.8 ± 13.2207.3 ± 14.146.9 ± 2.458.7 ± 0.961.2 ± 7.541.1 ± 4.5
Moon Cake67.9 ± 4.338.2 ± 5.212.3 ± 2.4434.4 ± 13.4205.4 ± 16.948.8 ± 1.059.9 ± 1.162.8 ± 8.544.4 ± 4.0
N6202-863.8 ± 2.546.7 ± 1.716.9 ± 1.8467.9 ± 21.2200.7 ± 13.644.0 ± 2.357.9 ± 0.752.9 ± 2.239.3 ± 5.9
NC 34662.9 ± 0.444.3 ± 5.616.4 ± 1.9442.5 ± 17.5216.8 ± 13.546.5 ± 3.657.9 ± 1.150.8 ± 17.152.3 ± 13.9
NC Green64.4 ± 2.161.7 ± 3.821.9 ± 1.2454.8 ± 12.8207.9 ± 8.348.6 ± 2.258.8 ± 2.745.8 ± 14.549.1 ± 9.4
NC Raleigh64.8 ± 3.427.4 ± 2.89.6 ± 0.2393.9 ± 19.7231.9 ± 22.752.0 ± 1.657.6 ± 1.866.5 ± 7.943.3 ± 7.8
Randolph66.5 ± 2.735.7 ± 6.712.0 ± 3.0446.9 ± 16.0194.7 ± 16.748.1 ± 4.259.6 ± 0.861.1 ± 14.848.3 ± 8.6
VS11-002267.8 ± 1.762.7 ± 3.120.1 ± 1.1451.2 ± 10.6203.2 ± 12.545.1 ± 3.961.0 ± 0.649.1 ± 11.542.4 ± 6.3
VS11-011266.5 ± 3.144.6 ± 3.015.0 ± 1.9434.1 ± 12.9205.4 ± 18.047.9 ± 1.759.4 ± 1.565.7 ± 8.339.7 ± 3.3
VS11-013767.2 ± 2.444.1 ± 2.314.5 ± 1.8430.8 ± 14.0199.2 ± 18.245.8 ± 2.259.3 ± 1.766.2 ± 12.139.0 ± 4.8
VS12-002168.6 ± 2.376.9 ± 6.724.2 ± 3.4437.8 ± 11.3205.7 ± 13.946.5 ± 1.959.3 ± 1.063.4 ± 7.538.7 ± 7.2
VS12-016168.2 ± 2.044.1 ± 2.414.0 ± 1.3439.4 ± 21.7188.4 ± 15.550.4 ± 1.460.0 ± 1.567.5 ± 8.544.8 ± 3.5
VS15-400767.6 ± 3.050.7 ± 4.416.4 ± 1.1442.2 ± 6.9209.2 ± 9.848.7 ± 2.959.3 ± 1.759.6 ± 18.141.0 ± 4.7
VS15-404963.8 ± 3.326.6 ± 1.89.7 ± 1.5431.8 ± 15.4212.3 ± 15.451.2 ± 2.757.5 ± 1.860.4 ± 7.941.9 ± 2.9
VS15-514864.9 ± 3.362.0 ± 6.121.7 ± 1.5453.6 ± 8.2204.5 ± 14.144.9 ± 2.059.5 ± 1.353.5 ± 8.241.8 ± 7.3
VS15-600566.4 ± 1.933.0 ± 3.911.0 ± 1.0428.1 ± 16.8207.7 ± 6.450.1 ± 2.658.8 ± 0.963.6 ± 8.742.8 ± 10.8
VS15-607765.4 ± 1.442.0 ± 2.514.5 ± 1.1439.7 ± 15.4199.8 ± 17.548.0 ± 2.458.7 ± 1.161.0 ± 14.341.8 ± 5.4
VS15-401864.0 ± 0.249.5 ± 0.817.8 ± 0.2462.5 ± 16.1190.8 ± 15.247.6 ± 1.959.6 ± 1.135.4 ± 6.554.3 ± 15.9
VS15-602166.9 ± 0.561.6 ± 1.920.4 ± 0.8448.1 ± 2.5198.2 ± 14.245.3 ± 4.059.7 ± 1.352.1 ± 9.844.9 ± 8.3
VS15-602366.4 ± 1.150.0 ± 1.316.8 ± 0.2432.7 ± 13.5198.7 ± 11.448.0 ± 2.959.4 ± 1.161.2 ± 6.049.2 ± 5.2
GenotypeRaffinoseTotal SugarPalmitic acidStearic acidOleic acidLinoleic acidLinolenic acidADFNDF
Asmara15.0 ± 1.4117.3 ± 5.511.7 ± 0.55.2 ± 0.629.0 ± 1.540.5 ± 4.37.4 ± 2.615.1 ± 2.415.5 ± 0.8
Moon Cake14.8 ± 1.5122.0 ± 12.911.6 ± 1.15.0 ± 0.427.2 ± 2.643.6 ± 4.57.7 ± 2.014.9 ± 2.015.9 ± 0.9
N6202-813.5 ± 1.9105.7 ± 6.311.2 ± 0.75.0 ± 0.629.7 ± 1.842.3 ± 5.07.3 ± 3.714.8 ± 2.015.3 ± 0.7
NC 34612.8 ± 3.6115.9 ± 17.611.5 ± 1.04.5 ± 0.627.1 ± 2.443.7 ± 4.69.2 ± 4.415.2 ± 1.815.8 ± 1.0
NC Green12.6 ± 3.3107.5 ± 9.611.3 ± 0.94.9 ± 0.827.6 ± 1.742.9 ± 5.48.8 ± 3.715.8 ± 2.415.7 ± 1.0
NC Raleigh15.3 ± 1.1125.1 ± 13.111.6 ± 0.64.8 ± 0.426.8 ± 3.245.5 ± 3.86.8 ± 1.915.2 ± 0.816.8 ± 0.6
Randolph14.5 ± 2.3123.9 ± 18.811.8 ± 0.64.9 ± 0.429.2 ± 2.040.7 ± 5.48.6 ± 4.214.2 ± 1.515.4 ± 1.1
VS11-002215.0 ± 1.7106.5 ± 10.811.3 ± 0.85.4 ± 0.333.4 ± 2.637.3 ± 4.06.9 ± 2.514.7 ± 1.315.9 ± 1.0
VS11-011215.4 ± 1.7120.8 ± 10.711.4 ± 0.65.0 ± 0.430.2 ± 3.940.3 ± 8.27.6 ± 3.013.8 ± 1.115.5 ± 1.0
VS11-013715.5 ± 1.6120.7 ± 13.211.5 ± 0.65.0 ± 0.429.8 ± 1.941.5 ± 3.97.2 ± 2.414.1 ± 1.415.5 ± 1.0
VS12-002114.8 ± 0.5116.8 ± 13.211.1 ± 0.55.6 ± 0.628.7 ± 2.141.0 ± 5.38.5 ± 3.215.1 ± 1.016.4 ± 0.9
VS12-016115.5 ± 1.6127.8 ± 11.111.6 ± 0.55.2 ± 0.628.4 ± 3.640.8 ± 5.48.1 ± 3.914.1 ± 0.815.3 ± 0.5
VS15-400715.7 ± 2.1116.3 ± 22.911.8 ± 0.95.1 ± 0.627.0 ± 3.142.5 ± 5.77.9 ± 3.014.6 ± 1.715.8 ± 1.1
VS15-404914.9 ± 0.6117.2 ± 10.211.5 ± 0.34.9 ± 0.423.6 ± 2.248.2 ± 3.57.7 ± 2.414.8 ± 1.016.1 ± 0.7
VS15-514813.9 ± 2.1109.2 ± 8.011.1 ± 0.65.0 ± 0.533.3 ± 2.936.7 ± 7.28.2 ± 3.914.3 ± 1.715.4 ± 0.6
VS15-600514.8 ± 1.2121.3 ± 9.311.7 ± 0.84.8 ± 0.426.5 ± 2.043.4 ± 4.68.7 ± 2.914.7 ± 0.816.1 ± 0.3
VS15-607714.1 ± 2.4116.8 ± 15.511.3 ± 0.64.9 ± 0.529.4 ± 1.942.5 ± 3.07.3 ± 3.314.6 ± 1.715.7 ± 1.3
VS15-401811.3 ± 2.1101.0 ± 8.111.2 ± 0.34.8 ± 0.730.5 ± 0.638.4 ± 4.610.8 ± 5.215.7 ± 1.416.0 ± 0.4
VS15-602113.6 ± 0.8110.6 ± 16.111.2 ± 0.24.9 ± 0.735.2 ± 1.935.1 ± 1.78.4 ± 3.613.7 ± 0.915.1 ± 0.4
VS15-602313.8 ± 1.7124.1 ± 9.211.6 ± 0.24.9 ± 0.827.9 ± 3.440.8 ± 1.09.6 ± 3.614.6 ± 1.115.5 ± 0.3
Table
Table 2. Means (±sd) and ranges of variation of 100-seed weight and seed moisture of 20 soybean genotypes across three years (2018–2020).
Table 2. Means (±sd) and ranges of variation of 100-seed weight and seed moisture of 20 soybean genotypes across three years (2018–2020).
TraitFreeze DryingLow-Heat DryingHigh-Heat Drying
MeanRangeMeanRangeMeanRange
Fresh 100-seed weight (g)46.5 ± 13.224.4–87.547.3 ± 13.124.2–84.345.4 ± 13.123.7–85.2
Fresh moisture (%)65.7 ± 2.959.6–71.266.0 ± 2.760.3–71.766.2 ± 2.858.3–72.0
Dried 100-seed weight (g)15.9 ± 4.48.3–31.616.0 ± 4.38.2–29.215.8 ± 4.57.8–32.8
Dried moisture (%)10.3 ± 0.58.4–11.610.6 ± 0.89.1–12.49.9 ± 0.98.1–11.9
Table
Table 3. Means (±sd), differences and repeatability of seed composition traits for whole and ground edamame seed all over three drying methods and three years (2018–2020).
Table 3. Means (±sd), differences and repeatability of seed composition traits for whole and ground edamame seed all over three drying methods and three years (2018–2020).
Trait aMean DifferenceRepeatability (%)
Ground SamplesWhole Seed SamplesValue% of Ground SamplesGround SamplesWhole Samples
Protein440.0 ± 19.6441.8 ± 19.51.8 *0.4198.9098.35
Oil201.8 ± 16.5199.8 ± 16.6−2.0 *−1.0097.4596.45
Fiber49.3 ± 4.145.9 ± 6.5−3.4 *−6.8591.7989.77
Ash58.3 ± 2.458.9 ± 8.30.6 NS1.0477.9984.35
Sucrose53.8 ± 16.353.6 ± 16.3−0.1 NS−0.2687.7983.30
Stachyose45.9 ± 8.954.9 ± 10.89.0 *19.5891.2684.79
Raffinose14.6 ± 2.215.7 ± 2.01.1 *7.3691.9547.60
Total Sugar114.3 ± 15.4124.2 ± 15.99.9 *8.6983.6868.39
Palmitic acid11.3 ± 1.111.6 ± 0.80.3 *3.0863.2867.60
Stearic acid4.9 ± 0.64.9 ± 0.40.0 NS0.2858.5284.26
Oleic acid29.5 ± 6.329.3 ± 6.3−0.2 NS−0.5682.9895.67
Linoleic acid42.2 ± 8.041.7 ± 8.2−0.5 NS−1.1679.4194.06
Linolenic acid8.1 ± 3.57.9 ± 2.5−0.2 NS−1.9755.7684.32
ADF14.4 ± 1.815.0 ± 1.90.6 *4.1879.4773.45
NDF15.6 ± 1.315.9 ± 1.90.3 *1.9686.0683.73
* and NS represent significant and not significant difference between the means of ground and whole samples at p = 0.05, respectively, based on t tests (LSD) from ANOVA. a Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively.
Table
Table 4. Mean squares from ANOVA of seed composition traits in edamame with ground and whole seed samples by combined data of freeze, low-heat and high-heat drying methods.
Table 4. Mean squares from ANOVA of seed composition traits in edamame with ground and whole seed samples by combined data of freeze, low-heat and high-heat drying methods.
Trait aGround SamplesWhole Seed Samples
MSY bMSMMSGMSMGMSYMSMMSGMSMG
Protein10435.00 **44.602315.83 **25.455183.18 **1176.93 **2715.85 **44.82
Oil9724.18 **1185.00 **940.31 **24.00536.27 **14232.00 **998.40 **35.45
Fiber359.91 **168.68 **46.58 **3.821430.33 **584.76 **65.86 **6.74
Ash5.15185.44 **5.741.264712.69 **441.16 **7.61 **1.19
Sucrose1236.46 **7408.47 **486.24 **59.38835.36 **19797.00 **294.82 **49.23
Stachyose517.80 **327.68 **222.93 **19.485409.63 **2020.87 **71.65 **10.90
Raffinose190.92 **3.638.15 **0.669.85 **73.30 **4.992.61
Total Sugar674.13 *5440.94 **328.61 *53.622653.27 **12203.00 **283.97 **89.78
Palmitic acid34.93 **33.70 **0.530.2020.41 **21.26 **0.48 **0.16
Stearic acid16.14 **5.63 **0.230.091.97 **1.38 **0.31 **0.05
Oleic acid901.29 **62.88 *115.23 **19.61958.69 **759.32 **108.74 **4.71
Linoleic acid2398.41 **31.94114.25 **23.522677.52 **1244.39 **111.32 **6.62
Linolenic acid771.53 **24.16 **3.52 *1.56345.17 **29.95 **4.78 **0.75
ADF118.05 **32.58 **3.51 **0.7232.22 **253.38 **2.68 **0.71
NDF12.38 **54.89 **2.48 **0.353.94 **289.54 **3.75 **0.61
* and **, Significant at p = 0.05 and 0.01, respectively, based on F tests. a Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively. b MSY, MSM, MSG, and MSMG represent the mean squares of year, drying method, genotype and method x genotype interaction effects, respectively.
Table
Table 5. Correlation coefficients between ground and whole seed samples.
Table 5. Correlation coefficients between ground and whole seed samples.
Trait aFreeze DryingLow-Heat DryingHigh-Heat Drying
Protein0.960 **0.972 **0.953 **
Oil0.968 **0.945 **0.886 **
Fiber0.776 **0.758 **0.817 **
Ash0.598 **0.675 **−0.368
Sucrose0.924 **0.753 **0.873 **
Stachyose0.445 *0.555 *0.558 *
Raffinose0.523 *0.624 **0.359
Total Sugar0.668 **0.672 **0.416
Palmitic acid0.582 **0.795 **0.545 *
Stearic acid0.820 **0.826 **0.030
Oleic acid0.841 **0.961 **0.819 **
Linoleic acid0.873 **0.957 **0.752 **
Linolenic acid0.789 **0.562 **−0.136
ADF0.557 *0.554 *0.609 **
NDF0.761 **0.668 **0.699 **
* and **, Significant at p = 0.05 and 0.01, respectively, based on t tests. a Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively.
Table
Table 6. Means (±sd) and ranges of variation of seed composition traits in ground samples of edamame dried by freeze, low-heat and high-heat drying methods and over three years (2018–2020).
Table 6. Means (±sd) and ranges of variation of seed composition traits in ground samples of edamame dried by freeze, low-heat and high-heat drying methods and over three years (2018–2020).
Trait cFreeze DryingLow-Heat DryingHigh-Heat DryingRelative Difference (%) d
MeanRangeMeanRangeMeanRangeLow-HeatHigh-Heat
Protein439.0 ± 18.9380.0–475.1440.4 ± 19.8373.4–485.0440.6 ± 20.4369.7–491.20.310.35
Oil197.3 ± 19.0160.5–250.7204.7 ± 15.9173.4–256.4203.5 ± 13.3181.2–259.33.78 a3.16 a
Fiber49.3 ± 4.937.3–60.347.8 ± 3.140.5–54.750.8 ± 3.641.2–58.33.18 b2.98 a
Ash56.5 ± 1.651.8–59.859.1 ± 1.555.1–62.259.4 ± 2.854.8–68.24.54 a5.04 a
Sucrose60.6 ± 14.133.7–81.558.3 ± 12.229.3–84.042.5 ± 18.98.0–83.23.6829.84 a
Stachyose46.2 ± 9.126.8–65.943.8 ± 7.832.1–64.947.8 ± 9.433.4–71.55.133.64
Raffinose14.8 ± 2.59.7–19.814.4 ± 2.09.0–18.014.5 ± 2.09.8–19.02.812.17
Total Sugar121.5 ± 9.8102.7–142.8116.5 ± 13.291.9–149.5104.8 ± 17.276.4–143.84.13 a13.75 b
Palmitic acid11.8 ± 0.510.4–13.011.5 ± 0.610.3–13.110.5 ± 1.57.9–13.03.25 a10.95 b
Stearic acid5.2 ± 0.64.0–6.05.0 ± 0.54.0–6.14.6 ± 0.73.3–5.93.48 a10.47 b
Oleic acid29.0 ± 3.619.9–37.028.9 ± 3.421.3–37.230.4 ± 9.813.1–49.40.194.95 a
Linoleic acid42.7 ± 5.332.4–53.641.5 ± 5.128.9–53.342.3 ± 11.719.4–63.12.861.04
Linolenic acid7.6 ± 3.12.9–12.98.1 ± 3.03.3–13.98.6 ± 4.22.2–16.26.95 a14.35 b
ADF13.7 ± 1.410.0–15.914.7 ± 1.412.1–18.014.9 ± 2.39.6–18.17.36 a8.80 a
NDF14.7 ± 0.812.6–16.715.7 ± 0.813.9–17.616.4 ± 1.612.7–18.86.98 a11.40 b
Average 3.917.90
a or b represents significant difference from freeze drying based on t tests (LSD0.05) from ANOVA. c Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively. d Compared to freeze drying.
Table
Table 7. Estimates of repeatability of edamame drying methods and correlations between heat drying and freeze drying with ground samples.
Table 7. Estimates of repeatability of edamame drying methods and correlations between heat drying and freeze drying with ground samples.
Trait aRepeatability (%)Correlation with Freeze Drying
Freeze DryingLow-Heat DryingHigh-Heat DryingLow-Heat DryingHigh-Heat Drying
Protein93.9192.0491.190.975 **0.961 **
Oil91.8486.8490.470.917 **0.946 **
Fiber56.5069.6575.350.705 **0.790 **
Ash52.8056.276.330.660 **0.373
Sucrose86.3474.8257.940.841 **0.591 **
Stachyose39.1339.2244.510.741 **0.680 **
Raffinose75.1270.4553.950.933 **0.793 **
Total Sugar62.0072.23−0.320.851 **0.508 *
Palmitic acid83.8044.9854.310.683 **0.330
Stearic acid66.9570.491.460.712 **0.072
Oleic acid84.3887.3469.700.914 **0.714 **
Linoleic acid82.6485.8966.460.916 **0.659 **
Linolenic acid42.9949.665.070.731 **0.436
ADF71.4627.4364.740.653 **0.635 **
NDF73.6562.6264.140.622 **0.869 **
* and **, Significant at p = 0.05 and 0.01, respectively, based on t tests. a Protein, oil, fiber, ash and sugars are presented as mg g−1 on dry weight basis; fatty acids are presented as percentage of oil (total fatty acid); and acid detergent fiber (ADF) and neutral detergent fiber (NDF) are shown as percentage of dry seed weight, respectively.
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Jiang, G.-L.; Townsend, W.; Sismour, E.; Xu, Y. A Study of Application and Comparison of Thermal Drying and Freeze Drying of Fresh Edamame Seeds in the Analysis of Seed Composition. Agronomy 2022, 12, 1993. https://doi.org/10.3390/agronomy12091993

AMA Style

Jiang G-L, Townsend W, Sismour E, Xu Y. A Study of Application and Comparison of Thermal Drying and Freeze Drying of Fresh Edamame Seeds in the Analysis of Seed Composition. Agronomy. 2022; 12(9):1993. https://doi.org/10.3390/agronomy12091993

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Jiang, Guo-Liang, William Townsend, Edward Sismour, and Yixiang Xu. 2022. "A Study of Application and Comparison of Thermal Drying and Freeze Drying of Fresh Edamame Seeds in the Analysis of Seed Composition" Agronomy 12, no. 9: 1993. https://doi.org/10.3390/agronomy12091993

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