Structural characteristics of purified beta-conglycinin from soybeans stored under four conditions

Tracking protein aggregation behaviour and emulsifying properties induced by structural alterations in common carp (Cyprinus carpio) myofibrillar protein during long-term frozen storage

The effect of ultrasound-assisted immersion freezing (UIF), air freezing (AF), and immersion freezing (IF) on the protein structure, aggregation, and emulsifying properties of common carp (Cyprinus carpio) myofibrillar protein during frozen storage were evaluated in the present study. The result showed that, compared with AF and IF samples, UIF sample had higher reactive/total sulfhydryl, protein solubility, and lower protein turbidity (P < 0.05), indicating that UIF was beneficial to inhibit protein oxidation and aggregation induced by frozen storage. UIF inhibited the alteration of secondary structure and tertiary structure during frozen storage. Meanwhile, UIF sample had higher emulsifying activity index, and smaller emulsion droplet diameter than AF and IF samples (P < 0.05), suggesting that UIF was beneficial for maintaining the emulsifying properties of protein during storage. In general, UIF is a potential and effective method to suppress the decrease in protein emulsifying properties during long-term frozen storage.

Controlling the assembly of soy β-conglycinin to fabricate heat-stable particles for high protein liquid systems

BACKGROUND

Recently, there is a growing interest in developing protein-fortified liquid systems, which are formulated to provide special nutrient combinations to those with special dietary needs. The fabrication of heat-stable protein for protein-fortified liquid systems relies heavily on precise control of the edible protein-building process.

RESULTS

Results suggested that heat-stable 7S protein particles (7SPPs) could be obtained by preheating at 100 °C for an extended time, whereas 7S proteins with better gelling properties were discovered after preheating at lower temperatures. According to the findings of the protein conformational and morphological characterization, the 7SPPs showed rather stable tertiary and secondary structures as well as size distributions, which might be responsible for their heat stability. Additionally, during the reheating test, suspensions of 7SPPs showed no signs of gelation and had a low viscosity even though the protein content was as high as 120 mg mL^-1 . However, 7S proteins with improved gelling properties were found to show rising aggregate size, higher susceptibility and larger conformational structure changing rates upon reheating treatment.

CONCLUSION

Soy β-conglycinin (7S) proteins with tunable heat stability were successfully prepared by preheating 10 mg mL^-1 protein dispersions at various temperatures (80-120 °C) and durations (15-120 min). These findings provide fundamental insights for developing 7S-based protein-fortified systems. © 2023 Society of Chemical Industry.

Influence mechanism of polysaccharides induced Maillard reaction on plant proteins structure and functional properties: A review

Plant proteins have high nutritional value, a wide range of sources and low cost. However, it is easily affected by the environmental factors of processing and lead the problem of poor functionality. These problems of plant proteins can be improved by the polysaccharides induced Maillard reaction. The interaction between proteins and polysaccharides through Maillard reaction can change the structure of proteins as well as improve the functional properties and biological activity. The products of Maillard reaction, such as reductone intermediates, heterocyclic compounds and melanoidins have certain antioxidant, antibacterial and other biological activities. However, heterocyclic amines, acrylamide, and products generated in the advanced stage of the Maillard reaction also have a negative impact, which may increase cytotoxicity and be associated with chronic diseases. Therefore, it is necessary to effectively control the process of Maillard reaction. This review focuses on the modification of plant proteins by polysaccharide-induced Maillard reaction and the effects of Maillard reaction on protein structure, functional properties and biological activity. It also points out how to accurately reflect the changes of protein structure in Maillard reaction. In addition, it also points out the application ways of plant protein-polysaccharide complexes in the food industry, for example, emulsifiers, delivery carriers of functional substances, and natural antioxidants due to their improved solubility, emulsifying, gelling and antioxidant properties. This review provides theoretical support for controlling Maillard reaction based on protein structure.

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.

Impact of soybean aging conditions on tofu sensory characteristics and acceptance

BACKGROUND

Tofu from aged soybeans is of poor quality, mainly with respect to texture. Texture defects described in the literature are contradictory. No study has investigated all sensory properties simultaneously. The objective of the present study was to evaluate the effect of soybean aging conditions [natural: ambient temperature and RH, 18 months, and accelerated: 30 °C, 84% relative humidity (RH), 6 months] on all of the sensory characteristics and the acceptance of tofu. Texture and color were also evaluated via an instrumental method. The control condition was -20 °C and 47% RH. Coodetec 214 and BRS 267 cultivars were studied.

RESULTS

The effect of soybean accelerated aging on tofu sensory characteristics and acceptance was more pronounced compared to the natural condition. The two cultivars had a similar behavior. Tofu control exhibited a light, uniform and bright color, cohesive appearance, sweet aroma and flavor, as well as a firm and elastic texture. Tofu made from both aged cultivars showed a gray color with dark spots, a rough appearance, fermented aroma, rancid flavor, an astringent and bitter taste, a fracturable texture and adherence to the oral cavity after chewing. These characteristics of tofu from aged soybeans implied a low acceptance by consumers.

CONCLUSION

Tofu from natural and accelerated aged soybeans has sensory attributes of appearance, as well as aroma, flavor and damaged texture, that are unacceptable by consumers. © 2017 Society of Chemical Industry.

Drying Damage on Physiological Properties of Rice Seed Associated with Ultrastructure Changes

The aim of the present study was to investigate the alterations of the physiological properties associated with the ultrastructure changes of rice seed after drying at different temperatures. The drying process was accomplished at 30, 45, 60, 75 and 90°C and at 29.3%, 13.0%, 6.4%, 3.2%, and 1.8% relative humidity, respectively. As a result, the germination percentage of the rice seeds was reduced as the increasing of the drying temperature and the highest value of vigor index was recorded at 45°C due to the dormancy breakage. There were no changes in the color of the raw rice seed dried at different temperatures; however, the yellowness of the brown rice and the electrical conductivity increased with the increasing drying temperature. The starch granules of the rice endosperm dried at 45°C were wrinkled and wilted and this damage occurred with high intensity after drying at temperatures above 60°C. The structure of the starch granules eventually became rupture when the drying temperature reached to 90°C. The cells of the rice embryo presented a contraction of their volumes drying at temperatures above 45°C due to the degradation of the middle lamella. The form of the oil drops was also altered after drying. At temperature above 75°C, the drops broke up and coalesced. It was concluded that the physiological quality of rice seed was closely associated with the alterations of cell structure during drying process.

Effect of soy flour on nutritional, physicochemical, and sensory characteristics of gluten-free bread

The aim of this study was to assess the effect of soy flour on nutritional, physicochemical, and sensory characteristics of gluten‐free (GF) bread. In this study, corn flour was replaced with soy flour at different levels 5%, 10%, and 15% to produce a more nutritionally balanced GF bread. Physical and chemical properties, sensory evaluation and crust and crumb color were measured in bread samples. The results of evaluations showed that protein content of soy flour‐supplemented GF bread significantly increased from 9.8% to 12.9% as compared to control along with an increased in fat (3.3%–4.1%), fiber (0.29%– 0.38%), and ash (1.7%–2.2%) content. Moisture (27.9%–26.5%) and carbohydrate (58.3–52.3) content decreased with the incremental addition of soybean flour. The highest total score of sensory evaluation was for the bread sample containing 15% soybean flour. The evaluation of crust and crumb showed that bread samples with 15% soy flour were significantly darker than the other bread samples. In conclusion, adding higher levels of soybean flour into GF bread can improve bread quality, sensory characteristics, and nutritional properties of bread. Nutritional status in patients with celiac disease (CD) can be improved through the produce GF bread in this way.

Protein structural changes during processing of vegetable feed ingredients used in swine diets: implications for nutritional value

Protein structure influences the accessibility of enzymes for digestion. The proportion of intramolecular β-sheets in the secondary structure of native proteins has been related to a decrease in protein digestibility. Changes to proteins that can be considered positive (for example, denaturation and random coil formation) or negative (for example, aggregation and Maillard reactions) for protein digestibility can occur simultaneously during processing. The final result of these changes on digestibility seems to be a counterbalance of the occurrence of each phenomenon. Occurrence of each phenomenon depends on the conditions applied, but also on the source and type of the protein that is processed. The correlation between denaturation enthalpy after processing and protein digestibility seems to be dependent on the protein source. Heat seems to be the processing parameter with the largest influence on changes in the structure of proteins. The effect of moisture is usually limited to the simultaneous application of heat, but increasing level of moisture during processing usually increases structural changes in proteins. The effect of shear on protein structure is commonly studied using extrusion, although the multifactorial essence of this technology does not allow disentanglement of the separate effects of each processing parameter (for example, heat, shear, moisture). Although most of the available literature on the processing of feed ingredients reports effects on protein digestibility, the mechanisms that explain these effects are usually lacking. Clarifying these mechanisms could aid in the prediction of the nutritional consequences of processing conditions.

Effect of soybean aging on the quality of soymilk, firmness of tofu and optimum coagulant concentration

This study investigated the influence of soybean aging (cultivars Coodetec 214 and BRS 267) on the physicochemical properties of soymilk and tofu. Two aging conditions were adopted: accelerated aging (84% relative humidity and 30 °C, up to 9 months) and natural aging (ambient temperature and relative humidity, up to 18 months) and a control condition (47% relative humidity, -20 °C). Tofu was coagulated with MgSO4. Optimum coagulant concentration (OCC) decreased with increasing coagulation temperature and soybean aging time. OCC showed positive correlation with total solids, protein, ash, Ca, Mg and P contents of soymilk. The products showed, in general, reduced color parameters (L(∗) and h°), proteins, lipids, carbohydrates, ash, Ca, Mg, P and total solids (except in the tofu) and firmness (tofu) with increasing aging time. Tofu yields decreased with accelerated aging time.

Structural and Gel Textural Properties of Soy Protein Isolate When Subjected to Extreme Acid pH-Shifting and Mild Heating Processes

Changes in the structural and gel textural properties were investigated in soy protein isolate (SPI) that was subjected to extreme acid pH-shifting and mild heating processes. The SPI was incubated up to 5 h in pH 1.5 solutions at room temperature or in a heated water bath (50 or 60 °C) to lead to protein structural unfolding, followed by refolding at pH 7.0 for 1 h. The combination of pH-shifting and heating treatments resulted in drastic increases in the SPI gel penetration force (p < 0.05). These treatments also significantly enforced the conversion of sulphydryl groups into disulfides, increased the particle size and hydrophobicity values, reduced the protein solubility (p < 0.05), and strengthened the disulfide-mediated aggregation of SPI. The intrinsic fluorescence spectroscopy results indicated structural unravelling when protein was subjected to acidic pH-shifting in combination with heating processes. The slight loss of secondary structure was observed by circular dichroism. These results suggested that pH-shifting combined with heating treatments provide great potential for the production of functionality-improved SPI, with the improved gelling property highly related to changes in the protein structure and hydrophobic aggregation.

Analysis using fluorescence labeling and mass spectrometry of disulfide-mediated interactions of soy protein when heated

It is well-known that disulfide-mediated interactions are important when soy protein is heated, in which soy proteins are dissociated and rearranged to some new forms. In this study, the disulfide bond (SS) linked polymer, which was composed of the acidic (A) polypeptides of glycinin, basic (B) polypeptides of glycinin, and a small amount of α' and α of β-conglycinin, was formed as the major product, accompanied by the formation of SS-linked dimer of B and monomer of A as minor products. The role of sulfhydryl (SH) of different subunits/polypeptides for forming intermolecular SS was investigated. The SH of B in glycinin (Cys298 of G1, Cys289 of G2, Cys440 of G4) was transformed into SS in polymer identified by mass spectrometry analysis. The SH content of polymer was lower than that of glycinin and β-conglycinin subunits when heated. The SH content of B in polymer was lower than that in glycinin subunit, and both of them were decreased by heating. The SH content of A in polymer was increased and higher than that of B in polymer and A in glycinin subunit when heated. These results indicated that the SH of B in glycinin subunit was subjected to not only SH oxidation but also SH-SS exchange (with SS of A) for forming intermolecular SS of polymer. The SH oxidation and SH-SS exchange were proven by the change of SH content for the first time. The SH of B was suggested to be reactive for forming intermolecular SS of polymer.

Changes in protein characteristics during soybean storage under adverse conditions as related to tofu making

Soybeans stored under adverse conditions decrease in protein recovery (content) in the soymilk and tofu yield. This study investigated how protein structural changes contributed to the decrease in tofu yield. Soymilks were produced from original soybeans (Proto and IA2032 cultivars) and adversely stored soybeans, respectively, and soymilk protein contents were adjusted to the same level before making into tofu. Tofu yield was compared with that made from soybeans without protein content adjustment. For understanding protein structural changes, soy proteins were extracted from Proto soybean by using different solvents, including distilled water, sodium dodecyl sulfate (SDS), and 2-mercaptoethanol. The proteins in the extracts were analyzed by using SDS-PAGE and gel filtration. Results showed that tofu yield was more significantly affected by protein structural characteristics than the protein content in soymilk. Different levels of aggregations among 7S and 11S proteins during adverse storage were responsible for decreasing protein recovery in the soymilk.

Role of β-conglycinin and glycinin subunits in the pH-shifting-induced structural and physicochemical changes of soy protein isolate

Soy β-conglycinin (7S) and glycinin (11S) were incubated up to 4 h in acidic (pH 1.5 to 3.5) or alkaline (pH 10 to 12) solutions to induce protein structural unfolding followed by refolding 1 h at pH 7.0, a process known as pH-shifting. The pH-shifting markedly increased (P < 0.05) emulsifying activity of 11S and to a lesser extent 7S; the former also produced more uniform oil droplets. The emulsifying activity improvements were accompanied by a significant rise in protein surface hydrophobicity, slight loss of the secondary structure (circular dichroism), and substantial dissociation of disulfide-linked basic and acidic 11S subunits. The findings suggested that 11S globulins of soy protein isolate (SPI) were more responsive to pH-shifting treatments than were 7S globulins, and the resulting emulsifying activity enhancements of 11S, in parallel with that of SPI, were indicative of its determinant role in the overall emulsifying properties of pH-shifting-treated SPI.

PRACTICAL APPLICATION

Extreme alkaline (pH 12) and acidic (pH 1.5) medium treatments can significantly modify the structure and enhance the emulsifying properties of both β-conglycinin and glycinin components of SPI. The functionality improvement by the pH processes is more remarkable for the glycinin protein fraction. Therefore, SPI enriched with glycinin seems to be particularly suitable for extreme acidic or alkaline processes to produce surface-active functional ingredients for food applications.

Changes of soybean quality during storage as related to soymilk and tofu making

Soybeans are stored and transported under various humidity and temperature conditions. Soymilk and tofu are two of the most important foods made from whole soybeans. The objective of this study was to investigate the influence of storage conditions on soybean quality as related to soymilk and tofu-making properties. Soybeans of 3 different genotypes (Proto, IA2032, and Vinton 81) were stored in varying conditions: temperature ranging from 4 to 50 degrees C, relative humidity from 55% to 80%, initial moisture content from 6% to 14%, and storage time up to 15 mo depending upon storage conditions. The effects of different storage conditions on soybean color, solids and protein extractability, soymilk pH, tofu yield, tofu solids and protein contents, tofu color, and texture were investigated. While no significant changes occurred for the soybeans stored at 4 degrees C, the soybeans stored at high temperatures (30 to 50 degrees C) exhibited significant quality loss (P < 0.05). The degradation of soybean lightness (Hunter L), color difference (Delta E), and solid extractability exhibited a linear relationship with time. Soak weight decreased at high temperature and relative humidity, but increased at mild storage conditions. Several combinations of storage conditions at temperatures exceeding 30 degrees C produced a drastic loss in tofu yield. Storage also affected the tofu making process by reducing optimum mixing time to produce the highest tofu yield. Varietal difference in soybean storability was observed. The results provided useful information for the soybean processing industry to store soybeans using the optimal storage conditions and to estimate soybean quality after storage.