Coacervation of β-conglycinin, glycinin and isoflavones induced by propylene glycol alginate in heated soymilk

Effects of Sodium Alginate on the Physical Properties and Storage Stability of Freeze-Dried Tofu Coagulated with Crab Shell Extract

The amount of processed by-products such as crab shells is increasing, but industrial utilization is insufficient. In our previous study, crab shell extract (CSE) acted as a coagulant for tofu manufacturing. This study aimed to reduce freeze-dried (FD) tofu breakdown by improving its physical properties through adding sodium alginate (SA). FD state in tofu helps increase storage and availability, but FD tofu frequently fractures during processing, which is a concern for manufacturers. Tofu samples were prepared with either crab shell extract (CSE) or MgCl2, and SA, and freeze-dried. In the yields of FD tofu samples, there were no significant differences (p < 0.05). The brokenness of FD tofu samples was lower in CSE than in MgCl2 and was significantly reduced by SA in both tofu samples, which was affected by hardness. The water-holding capacity decreased after freeze-drying, and CSE reduced this decrease, regardless of SA addition. The microstructures differed depending on the coagulant and were dense upon SA addition. The FD tofu was packed into a multilayer film and stored at 25 °C or 45 °C for 6 months to investigate storage stability. During the storage, brokenness was unchanged in all tofu samples, indicating that they maintained their original structure. There were no significant differences in the volatile base nitrogen and thiobarbituric acid values according to the coagulant type and SA addition (p < 0.05). In conclusion, SA reduced FD tofu breakdown by improving the network structure, which may help increase FD tofu quality and decrease economic loss.

Improvement of enzymatic cross-linking of ovalbumin and ovotransferrin induced by transglutaminase with heat and reducing agent pretreatment

The effects of transglutaminase (TGase, 1.0 unit/mL) with heat (95 °C, 5 min), 2-mercaptoethanol (2-ME, 0.83 %), and l-cysteine (l-Cys, 50 mM) pretreatment on the cross-linking of ovalbumin (OVA) and ovotransferrin (OVT) were investigated. SDS-PAGE revealed that although the polymerization of OVA and OVT did not occur after 3 h of incubation at 40 °C with TGase, OVA polymerized into high molecular weight polymers following TGase with 2-ME and heat pretreatment after 3 h of incubation. The surface hydrophobicity and reactive sulfhydryl (SH) groups of OVA samples significantly increased from 4065.7 ± 136.7 and 89.3 ± 1.2 SH groups (μmol/g) to 31483.6 ± 342.7 and 119.5 ± 3.7 SH groups (μmol/g), respectively. Similar results were obtained for OVT with TGase and l-Cys pretreatment and a 3-h incubation at 40 °C. The use of TGase, a reducing agent, and/or heat pretreatment can be used for the polymerization of OVA and OVT.

Effects of lactic acid bacteria fermented yellow whey on the protein coagulation and isoflavones distribution in soymilk

This study investigated the soymilk coagulation induced by fermented yellow whey (FYW), which is extensively used as a natural tofu coagulant in China. The aggregations involving proteins and isoflavone particles caused by FYW were analyzed using the proteomic technology and high-performance liquid chromatography, respectively. As indicated, the FYW-induced coagulation of soy proteins mainly occurred at pH 5.80-5.90. When the pH of soymilk decreased, the 7S β, 11S A3 and some of 11S A1a subunits and SBP, Bd, lectin and TA aggregated the earliest, and later did the 11S A4, other 11S A1a, 11S A2 and 11S A1b subunits. The 7S α and α' subunits and TB showed an obvious delay in aggregation. Moreover, isoflavones in the form of aglycones were more likely to coprecipitate with proteins, compared with glycosides. These results could provide an important reference and assistance for future research on the development of traditional FYW-tofu.

Research progress in tofu processing: From raw materials to processing conditions

As a traditional soybean product with good quality and a healthy food with many functional components, tofu is increasingly consumed in people's daily life. Traditional tofu processing consists of numerous steps, including the soaking and grinding of soybean seeds, heating of the soybean slurry, filtering, and addition of coagulants, and others. The properties of soybean seeds, processing scale, soaking and heating conditions, type and concentration of coagulant, and other factors collectively impact the processing steps and the final tofu quality. The generation of whole soybean tofu with more nutritive value comparing with traditional tofu has been successfully reported by several studies. As one of the most important functional component, isoflavones and their presence in tofu are also influenced by the above-mentioned factors, which influence the nutritive value of tofu. Research investigating the influence of tofu processing conditions on the quality and isoflavone profiles of tofu are the subject of this review. Issues that should be further studied to investigate the influence of processing conditions on the quality and nutritive value of tofu are also introduced.

Complex Coacervation of Soy Proteins, Isoflavones and Chitosan

In this study, the chitosan-induced coacervation of soy protein-isoflavone complexes in soymilk was investigated. Most of the soymilk proteins, including β-conglycinin (7S), glycinin (11S), and isoflavones, were found to coacervate into the soymilk pellet fraction (SPF) following the addition of 0.5% chitosan. The total protein in the soymilk supernatant fraction (SSF) decreased from 18.1 ± 0.3 mg/mL to 1.6 ± 0.1 mg/mL, and the pH values decreased slightly, from 6.6 ± 0.0 to 6.0 ± 0.0. The results of SDS-PAGE revealed that the 7S α’, 7S α, 7S β, 11S A3, and 11S acidic subunits, as well as the 11S basic proteins in the SSF, decreased to 0.7 ± 0.5%, 0.2 ± 0.1%, 0.1 ± 0.0%, 0.2 ± 0.2%, 0.2 ± 0.2% and 0.3 ± 0.2%, respectively. We also found that isoflavones in the SSF, including daidzein, glycitein, and genistein, decreased to 9.6 ± 2.3%, 5.7 ± 0.9% and 5.9 ± 1.5%, respectively. HPLC analysis indicated that isoflavones mixed with soy proteins formed soy protein-isoflavone complexes and were precipitated into the SPF by 0.5% chitosan.

Aggregation of soy protein-isoflavone complexes and gel formation induced by glucono-δ-lactone in soymilk

This study investigated the glucono-δ-lactone (GDL)-induced aggregation of isoflavones and soy proteins in soymilk. High-performance liquid chromatography (HPLC) analysis indicated that isoflavones mixed with β-conglycinin (7S) and glycinin (11S) proteins formed 7S-isoflavone and 11S-isoflavone complexes in soymilk supernatant fraction (SSF). Most of the soy protein-isoflavone complexes then precipitated into the soymilk pellet fraction (SPF) following the addition of 4 mM GDL, whereupon the pH value of the soymilk dropped from 6.6 to 5.9. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and HPLC analysis suggest that the addition of 4 mM GDL induced the aggregation of most 7S (α’, α and β subunits), 11S acidic and 11S basic proteins as well as isoflavones, including most aglycones, including daidzein, glycitein, genistein and a portion of glucosides, including daidzin, glycitin, genistin, malonyldaidzin and malonylgenistin. These results provide an important reference pertaining to the effects of GDL on the aggregation of soy protein-isoflavone complexes and could benefit future research regarding the production of tofu from soymilk.

An update on hypoallergenicity of peanut and soybean: where are we now?

Legumes are one of the major sources of proteins and positively correlate with the development of modern society. At the same time, unfortunately, they significantly contribute to the rising prevalence of food allergy.