Effects of preheat treatment and syringic acid modification on the structure, functional properties, and stability of black soybean protein isolate.

This study investigated preheated (25-100°C) black soybean protein isolate (BSPI) conjugated with syringic acid (SA) (25 and 50 µmol/g protein) under alkaline conditions, focusing on the structure, functional properties, and storage stability. The results revealed that the SA binding equivalent and binding rate on BSPI increased continuously as the preheat temperature increased. Additionally, preheating positively impacted the surface hydrophobicity (H0) of BSPI, with further enhancement observed upon SA binding. Preheating and SA binding altered the secondary and tertiary structure of BSPI, resulting in protein unfolding and increased molecular flexibility. The improvement in BSPI functional properties was closely associated with both preheating temperature and SA binding. Specifically, preheating decreased the solubility of BSPI but enhanced the emulsifying activity index (EAI) and foaming capacity (FC) of BSPI. Conversely, SA binding increased the solubility of BSPI with an accompanying increase in EAI, FC, foaming stability, and antioxidant activity. Notably, the BSPI100-SA50 exhibited the most significant improvement in functional properties, particularly in solubility, emulsifying, and foaming attributes. Moreover, the BSPI-SA conjugates demonstrated good stability of SA during storage, which positively correlated with the preheating temperature. This study proposes a novel BSPI-SA conjugate with enhanced essential functional properties, underscoring the potential of preheated BSPI-SA conjugates to improve SA storage stability. PRACTICAL APPLICATION: Preheated BSPI-SA conjugates can be used as functional ingredients in food or health products. In addition, preheated BSPI shows potential as a candidate for encapsulating and delivering hydrophobic bioactive compounds.

Changes in phenolic compounds and antioxidant activities of "nine steaming nine sun-drying" black soybeans before and after in vitro simulated gastrointestinal digestion.

Black soybean (Glycine max (L.) Merr.) is rich in phenolic compounds, and processing technology has a significant effect on the content and activity of phenolic compounds. However, the mechanism of nine steaming and nine sun-drying processing technique is not fully understood. This paper presents the changes of phenolics content, phenolic acids composition and their influence on antioxidant activity before and after in vitro simulated gastrointestinal digestion of black soybeans (BS) under the process of nine steaming nine sun-drying. Results showed that the total phenolic content (TPC) and total flavonoids content (TFC) in BS were reduced by the heat treatment method, and exhibited a decreasing trend with more steaming and sun-drying cycle. During in vitro digestion, the contents and bioaccessibility of 12 phenolic acids (PA-12) in BS were highest in the stomach, followed by mouth and the intestine. The bioaccessibility of PA-12 in steamed and sun-dried BS was higher than that of raw black soybeans (S0D0) after digestion. It reached maximum after digestion at the third steaming and sun-drying cycle (i.e. S3D3), wherein the phenolic acids with the highest bioaccessibility were syringic acid, gallic acid, ferulic acid and chlorogenic acid. Syringic acid, in particular, increased significantly during digestion compared with that before digestion, which also increased during processing. The antioxidant activity of in vitro digested BS products with appropriate steaming and sun-drying degree increased compared with S0D0. Principal component analysis (PCA) showed that the in vitro digestion-induced properties of steamed and sun-dried BS could be well distinguished. The results confirm that the phenolic compounds and bioaccessibility of nine steamed nine sun-dried BS must be taken into account when assessing the improvement of human health.

Effect of selenium biofortification on bioactive compounds and antioxidant activity in germinated black soybean.

Biofortification using inorganic selenium has become an effective strategy to enhance selenium content in crops. In the present study, the effects of selenium biofortification on the chemical composition and antioxidant capacity of black soybean (BS) during germination were studied. The contents of selenium, total sugar, vitamin C, γ-aminobutyric acid, total polyphenols, and total flavonoids in selenium biofortified germinated black soybeans (GBS-Se) significantly increased compared to germinated black soybeans (GBS). However, the contents of soluble protein, fat, and reducing sugar were decreased, while fatty acid composition was not significantly different between GBS and BS. HPLC analysis showed that 12 phenolic acids of all samples, which mainly existed in free forms. Their contents increased at low concentration of selenium and decreased along with the rise of selenium concentrations. The antioxidant activity of GBS-Se as analyzed by Pearson correlation analysis positively correlated with the accumulation of phenolic substances. Principal component analysis (PCA) showed that GBS and GBS-Se were significantly different from BS. Moreover, the physicochemical indexes of GBS showed regularly changes with increasing selenium content, and those of GBS-Se50 and GBS-Se75 were significantly different from GBS. The results provide a systematic evaluation on the effect of selenium fortification on the germination of seeds and useful information for the development of Se-enriched functional foods. PRACTICAL APPLICATION: The organic selenium black soybean (BS) produced by the germination method can be directly processed and eaten to improve human health. In addition, complexes of organic selenium, vitamin C, and γ-aminobutyric acid of germinated BS can be developed into functional substances and applied to food or health products as functional ingredient and/or natural antioxidant supplements.