Effect of acetic acid treatment on isoflavones and carbohydrates in pickled soybean

Proteolysis and lipolysis induced by acidification of sesame seeds

Vinegar-soaked seeds can be consumed as functional foods, and the acidification of vacuoles during seed germination is key for protein mobilization. Inspired by these, sesame seeds, containing proteases with peak activity at pH 4.5, were soaked in a 2 % acetic acid solution at 25 °C. Transmission electron microscopy showed that the acidic sesame proteases localized in protein storage vacuoles (PSVs), while liquid chromatography tandem mass spectrometry identified nine lipases. The seeds were acidified to pH 4.5 within 9 h, and the proteases were fully activated to hydrolyze the storage proteins and tonoplast of PSVs. The proteases were released and attacked almost all organelles. Oil body membrane proteins were degraded, causing the inner oil accessible to lipases. By 7 days of soaking, the protein components in the soaking system consisted of 39 % small peptides and 31 % free amino acids, while the oil was hydrolyzed into 26 % free fatty acids and 13 % diacylglycerols.

Evaluation of cooking, nutritional, and quality characteristics of fresh-cut potato slice pretreated with acetic acid

Fresh-cut potato slices are very popular in the service of hot-pots. However, the gelatinized starch easily escaping from the potato cells during cooking causes the thickening of beef tallow or soup in the hot-pot. Thus, acetic acid is considered for solving the problem of potato slices. Besides, the nutritional and quality characteristics of potato slices are also evaluated in this study. Results show that 1.0%-1.5% (v/v) acetic acid treatment can decrease mass loss and starch digestion rate, and delay the degradation of ascorbic acid and deterioration of color and texture of potato slices. Such treatment also inhibits membrane oxidation and PPO activity, and increase the total phenolic accumulation of potato slice in 7-day storage. The cell wall integrity of the potato slice is strengthened by acetic acid treatment, providing a strategy for the improvement of the boiling resistance of potato slice, and endowing potato slice with the digesting resistance. PRACTICAL APPLICATION: Acid pretreatment would cause the intensification of potato cell wall, which finally decrease the in vitro digestibility through decrease of leakage of gelatinized starch from potato cell and the contact between gelatinized starch and digesting enzyme. This observation proved that the integrity of cell structure in vegetable is important for their processing quality improvement (especially for their hardness improvement after heating or fermentation).

Endopeptidases, exopeptidases, and glutamate decarboxylase in soybean water extract and their in vitro activity

The proteolytic activity of some soybean endogenous proteases have been clarified in the previous studies, but the information concerning the roles of these proteases and some other unknown ones during soybean processing are scarce. Herein, 16 endopeptidases, 13 exopeptidases, 24 inhibitors (two serpin-ZX and one subtilisin inhibitor firstly identified), and one glutamate decarboxylase were identified in the soybean water extract by the liquid chromatography tandem mass spectrometry analysis. Amongst the identified endopeptidases, just the aspartic endopeptidases (optimal at pH 2.5-3 and 35-45 °C) showed the detectable proteolytic activity by the tricine-sodium dodecyl sulphate-polyacrylamide gel electrophoresis and protease inhibitor assay analyses, whereas serine, cysteine, and metallo- endopeptidases (except P34 probable thiol protease) did not. Free amino acid analysis showed that the exopeptidases and glutamate decarboxylase were optimal at pH 6 and 45 °C, and by 6 h incubation, the free amino acids and γ-aminobutyric acid almost doubled.

Comparative study of phenolic compounds, vitamin E, and fatty acids compositional profiles in black seed-coated soybeans (Glycine Max (L.) Merrill) depending on pickling period in brewed vinegar

BACKGROUND

Pickled soybeans or vinegar beans have long been used as a folk remedy and also a supplemental nutritional source in Korea. In general the pickling process in vinegar improves the digestibility of soybeans as well as increases the availability of various (non-)nutrients in soybeans. However, detailed information about the changes in functional substances such as (poly)phenolic compounds, vitamin E, and fatty acids (FAs) in soybeans during the pickling process is quite limited. Therefore, this study aims to investigate the changes in the selected phenolic compounds, vitamin E, and FAs in soybeans as a function of the pickling time.

RESULTS

The sum of the total phenolics in both the pickled soybeans and the pickling solutions increased by as much as 47% after pickling. Naringenin, vanillin, and catechin were the major phenolics observed in the pickled soybeans and pickling solutions. The total vitamin E content in the pickled soybeans decreased by 23% after pickling, although no vitamin E molecules were found in the pickling solution. γ-Tocopherol was abundant in the untreated soybeans, but decreased by ~29% after pickling. Both the total and major FA contents varied by less than 1% during the pickling period. In this study, a 10-20 day pickling period may be considered suitable in terms of retention of functional substances in the pickled soybeans, such as selected phenolics, vitamin E, and FAs.

CONCLUSIONS

Our findings provide basic information and insight into the production of functional compounds in soybeans upon immersing in brewed vinegar, and also may be helpful toward improving the health-functionality of soybean-based foods in the food industry. Graphical abstract How to change bioactive compounds during the pickling process?

Time course effects of fermentation on fatty acid and volatile compound profiles of Cheonggukjang using new soybean cultivars

In this study, we investigated the effects of the potential probiotic Bacillus subtilis CSY191 on the fatty acid profiles of Cheonggukjang, a fermented soybean paste, prepared using new Korean brown soybean cultivars, protein-rich cultivar (Saedanbaek), and oil-rich cultivar (Neulchan). Twelve fatty acids were identified in the sample set-myristic, palmitic, palmitoleic, stearic, oleic, vaccenic, linoleic, α-linolenic, arachidic, gondoic, behenic, and lignoceric acids-yet, no specific changes driven by fermentation were noted in the fatty acid profiles. To further explore the effects of fermentation of B. subtilis CSY191, complete profiles of volatiles were monitored. In total, 121, 136, and 127 volatile compounds were detected in the Saedanbaek, Daewon (control cultivar), and Neulchan samples, respectively. Interestingly, the content of pyrazines-compounds responsible for pungent and unpleasant Cheonggukjang flavors-was significantly higher in Neulchan compared to that in Saedanbaek. Although the fermentation period was not a strong factor affecting the observed changes in fatty acid profiles, we noted that profiles of volatiles in Cheonggukjang changed significantly over time, and different cultivars represented specific volatile profiles. Thus, further sensory evaluation might be needed to determine if such differences influence consumers' preferences. Furthermore, additional studies to elucidate the associations between B. subtilis CSY191 fermentation and other nutritional components (e.g., amino acids) and their health-promoting potential are warranted.