Biochemical and proteomic analysis of soybean sprouts at different germination temperatures

Soybean sprouts are available throughout the year and have gained popularity as a functional food owing to their high nutritional value. In the present study, soybean seeds were germinated at different temperatures and the effects on growth characteristics, nutrient composition, and secondary metabolites were investigated. Sprout qualities such as whole length and hypocotyl length were observed to increase at a higher temperature of germination (25 vs. 20 °C). The total protein content of the sprouts increased, whereas the total fatty acid content decreased upon germination at 25 °C. The total phenolic content was higher in soybean sprouts than in soybean seeds. Additionally, antioxidant activity increased in a temperature-dependent manner. Both DPPH and ABTS activity were higher at 25 °C than at 20 °C. Proteomic analysis was conducted to generate temperature responsive protein profiles of soybean sprouts. Using 2D gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, 33 differentially expressed spots were identified. Further analysis of these spots revealed potential function in protein storage and modification. Upon germination at 25 °C, 16 spots increased significantly, whereas 17 protein spots were observed to decrease. Interestingly, a trypsin inhibitor was highly expressed at 25 °C. Semi-quantitative RT-PCR analysis showed that mRNA expression level of most of genes encoding the identified proteins correlated well with their protein abundance, suggesting their temperature-dependent transcriptional regulation in soybean sprouts. In summary, our results clearly indicate an effect of temperature on growth of and secondary metabolite production in soybean sprouts.