Abstract
Soybean processing, e.g., by soaking, heating, and fermentation, typically results in diverse metabolic changes. Herein, multivariate analysis-based metabolic profiling was employed to investigate the effects of fermentation by Aspergillus oryzae or Bacillus subtilis on soybean substrates extracted at 4, 25, or 55 °C. As metabolic changes for both A. oryzae and B. subtilis were most pronounced for substrates extracted at 55 °C, this temperature was selected to compare the two microbial fermentation strategies, which were shown to be markedly different. Specifically, fermentation by A. oryzae increased the levels of most organic acids, γ-aminobutyric acid, and glutamine, which were ascribed to carbohydrate metabolism and conversion of glutamic acid into GABA and glutamine. In contrast, fermentation by B. subtilis increased the levels of most amino acids and isoflavones, which indicated the high activity of proteases and β-glucosidase. Overall, the obtained results were concluded to be useful for the optimization of processing steps in terms of nutritional preferences.
Highlights
IntroductionMerill) contain numerous functional components such as proteins, isoflavones, fatty acids, vitamins, and essential amino acids, their direct use is hindered by indigestion caused by the presence of anti-nutrients such as oligosaccharides and trypsin inhibitors [1]
Metabolic Profiling and Multivariate Analysis of Fermented Soybeans. Primary metabolites such as amino acids, organic acids, sugars, and fatty acids are variously assembled as end-products of fermentations and interrelated with secondary metabolites as precursors [24]
This study evaluated the metabolic differences between A. oryzae (AO)- and Bacillus subtilis (BS)-fermented soybeans extracted at 4, 25, or 55 ◦ C
Summary
Merill) contain numerous functional components such as proteins, isoflavones, fatty acids, vitamins, and essential amino acids, their direct use is hindered by indigestion caused by the presence of anti-nutrients such as oligosaccharides and trypsin inhibitors [1]. Generally used as the initial step of soybean curd, soy sauce, and soy milk production, increases the levels of amino acids and vitamins [2] and releases functional proteins and isoflavones into soybean exudates, when high water temperatures are employed [3]. The soybean residues remaining after extraction still contained some valuable nutrients. The contained nutrients can be negatively affected by the use of excessively high temperatures and long extraction times, e.g., boiling reduces the levels of some vitamins and essential amino acids [7]. An appropriate extraction temperature is important for efficiently using soybean residues as functional resources as well as extracting exudates from soybeans
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