G. S. Chauhan

Relative changes in tocopherols, isoflavones, total phenolic content, and antioxidative activity in soybean seeds at different reproductive stages.

Immature seeds of soybean are becoming increasingly popular as a snack/vegetable to harness the health benefits of soybean. They are shelled from the immature pods picked from the mother plant at different reproductive stages. Information concerning changes in antioxidant constituents and antioxidant capacity during reproductive phases of soybean seeds is scarce. The aim of the present study was to determine whether immature seeds picked at different reproductive stages differ in tocopherol, isoflavone, total phenolic contents, free radical scavenging activity, and total antioxidative capacity. Seeds shelled from the soybean pods picked at three reproductive stages (R5, R6, and R7) as well as at full maturity were subjected to high-performance liquid chromatography analyses for tocopherol and isoflavone contents. Significantly higher values (P<0.05) were observed for tocopherols and isoflavones in immature seeds picked at late reproductive stages. At the first reproductive stage, that is, R5 stage, delta-tocopherol was the predominant form of tocopherol, whereas in subsequent reproductive stages as well as at complete maturity stage, the gamma-isomer contributed maximum proportion to the total tocopherol content. Genistein was, in general, the major form of isoflavone at all reproductive stages. Reduction in free radical scavenging activity, total antioxidant capacity, and total phenolic content in late-picked seeds concomitant with increased concentration of tocopherol and isoflavone isomers was observed. The results show that bioactive constituents other than isoflavones and tocopherols may decline with the advancement of maturity.

Evaluation of Vegetable-Type Soybean for Sucrose, Taste-Related Amino Acids, and Isoflavones Contents

Vegetable soybean differs from the conventional soybean in its distinct taste. Genetic variability has been scarcely investigated in vegetable soybean for taste-related compounds viz. sucrose, aspartic acid, glutamic acid, glycine, alanine, and isoflavones. In the present study, analysis of green seeds of 12 vegetable-type genotypes, between reproductive stages of R6 and R7 (i.e., when the pods were completely filled but the seeds and pods shell not yet turned yellow), revealed ranges of 1.28–7.12, 0.37–1.51, 0.64–2.82, 0.17–0.72, 0.11–0.51 g/100 g for sucrose, aspartic acid, glutamic acid, glycine, alanine content, respectively, while a range of 8.64–33.19 mg/100 g was observed for total isoflavones content. Genotypes with high levels of sucrose, aspartic acid, glutamic acid and alanine scored high for taste. Results did not indicate any significant relationship between isoflavones content and the taste score.

Physico-Chemical Properties of Immature Pods of Japanese Soybean Cultivars

Twelve Japanese cultivars and JS335, the most popular soybean cultivar in India, were grown in the field. Days to arrival of R6 stage (when pods are still green, immature, and tight with fully developed immature green seeds) of these cultivars were recorded. Pods picked at this stage were evaluated for pod yield per plant, pod characteristics (width, presence of hairs) fresh green seed weight and percent moisture content. Fresh green seeds were analyzed for compositional traits viz. protein content, trypsin inhibitor lipoxygenase isozymes, oil content, and polyunsaturated fatty acids (essential fatty acids). Japanese cultivars showed higher fresh green seed weight and pod yield than JS335. On a fresh weight basis, Japanese cultivars exhibited lower protein content but higher oil content than JS335. Most of the Japanese cultivars showed lower trypsin inhibitor content and a varying level of lipoxygenase-I, as well as lipoxygenase-II + III when compared to JS335. Total polyunsaturated fatty acids content in JS335 was higher than some of the Japanese cultivars. The number of pods per plant showed a positive correlation (r = 0.863, p < 0.001) with pod yield per plant. Some of the Japanese cultivars offer great potential for consumption at the green pod stage or as a source for desirable traits.

Identification of SSR markers associated with seed coat permeability and electrolyte leaching in soybean

Seed coat permeability and electrolyte leaching are the important traits that have been negatively associated with seed longevity in soybean. The objective of this study was to use SSR markers to identify genomic regions significantly associated with QTLs controlling seed coat permeability and electrolyte leaching in a segregating F2 population derived from a cross of Birsa soya-1 x JS 71-05. Parental polymorphism survey using 145 SSR markers identified 21 polymorphic ones, which were used to genotype 153 F2 individuals. Four independent markers (Satt434, Satt538, Satt281 and Satt598) were significantly (P=0.05) associated with seed coat permeability. One of these markers (Satt 281) also showed significant association with electrolyte leaching that partly supported the observed positive correlation (r = 0.425) between the two traits. Markers for seed coat permeability individually explained 3.9% to 4.5% of the total phenotypic variation, while the marker linked with electrolyte leaching explained 5.6% of the total variation.

COMPOSITIONAL TRAITS OF SOYBEAN SEEDS AS INFLUENCED BY PLANTING DATE IN INDIA

Information on the influence of date of planting on protein, oil and fatty acid composition of soybean seeds is meagre, whilst similar studies on lipoxygenase isozymes and trypsin inhibitor contents are lacking. A field experiment was conducted with nine Indian genotypes and three planting dates (spread over 23 days) to study the influence of planting dates on these seed traits. Results based upon a one-year study indicated that oil content declined with delays in planting. Oleic acid content increased from the first to third planting, while the reverse trend was observed for linolenic acid. Lipoxygenase-1 activity was reduced by delayed plantings. Protein content was the lowest and trypsin inhibitor content was the highest for the second planting. However, no differences were observed for protein and trypsin inhibitor contents between the first and third planting. Significant interactions. observed between genotype and planting date for most of the seed compositional characters suggest that the influence of late planting is genotype-dependent.