Change in texture improvement of low-fat tofu by means of low-fat soymilk protein denaturation

Storage stability and shelf-life of soymilk obtained via repeated boiling and filtering: A predictive model

This study investigated the effects of different processing methods on the quality and nutrition of soymilk, as well as the changes in storage stability (centrifugal sedimentation rate (CSR), viscosity, and particle size) and shelf-life of soymilk at different storage temperatures (25°C, 35°C, 45°C, and 55°C). Results showed that soymilk processed via the repeated boiling-to-filtering method (RBFM) exhibited the highest protein content (3.89 g/100 g), carbohydrate content (1.27 g/100 g), and stability coefficient (0.950). The CSR and particle size of RBFM soymilk increased gradually during storage at different temperatures, while the viscosity and sensory score decreased. The correlation between the CSR and the sensory score of RBFM soymilk was the highest (R 2 = .9868). The CSR was selected as the key indicator to predict the shelf-life of RBFM soymilk. The average residual variation in RBFM soymilk shelf-life based on the predictive model was 10.78%, indicating the strong accuracy of the model for predicting the shelf-life of RBFM soymilk stored at temperatures ranging from 25-45°C. This study provides a theoretical basis and technological support for the development, transportation, and storage of soymilk and soymilk beverage products.

Mechanism of the glucono-δ-lactone induced soymilk gelation: Enthalpy and entropy transformation in the cross-linking of protein molecules

This study aimed to explore new techniques to regulate the quality of soy products. The glucono-δ-lactone (GDL) induced soymilk gelation process and the gel network structure characteristic were compared as a matter of temperature, and the role of reaction kinetics was discussed. Results showed that there were similarities in the development of G' curves under different temperatures, whereas the gel network structures and the energy requirements of cross-linking reactions were different. In the high-temperature region (70 °C-95 °C), the exposure and binding of reactive groups were promoted. The activation enthalpy (ΔH*) required by protein aggregates decreased and the effect of entropy reduction (-TΔS*) was enhanced, which led to shorten the preaggregation time (t_g) and increase the gelation rate (k), resulting in the formation of rough, porous gel network with high stiffness. By contrast, in the low-temperature region (40 °C-70 °C), high enthalpy contributions and low entropy changes were required, then a fine, soft, and tender gel network formed. Besides, a funnel-shaped model of the enthalpy-entropy energy transformation mechanism of soymilk gelation was proposed. The results of this study revealed that adjusting the enthalpy-entropy energy requirements of the protein cross-linking reaction could be utilized to the regulation of the network structure and quality of soymilk gels, which could enrich the reaction kinetics theory and provide innovative ideas for food quality control technology from the perspective of energy requirement and energy input.

Synergism of selective thermal denaturation and glycosylation improves quality characteristics of green soybean tofu

BACKGROUND

Tofu is rich in nutrients and contains high-quality protein. However, commercial tofu products usually have weak gel strength and low water holding capacity (WHC). In the present study, the effects of selective thermal denaturation (STD) time (0-20 min, 5-min interval; 85 °C) and glycosylation (100 °C; 0, 10 and 20 g kg-1 glucose) on the quality characteristics of green soybean tofu were studied through by the evaluation method of the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) model for the best synergism condition of STD and glycosylation.

RESULTS

Compared to STD or glycosylation, combination treatment of STD and glycosylation improved hardness, WHC, yield, protein and fat contents of green soybean tofu. Furthermore, the gel strength, WHC, yield, protein and fat contents of tofu was increased by 135.21%, 20.18%, 12.21%, 24.91%, 44.15% compared to untreated tofu. Meanwhile, synergistic treatment of STD and glycosylation significantly improved microstructure network structure of green soybean tofu and made it more homogeneous and denser. However, the green soybean tofu was faded and turned yellow under the combination of the STD and glycosylation.

CONCLUSION

The results obtained through TOPSIS showed that the combination of thermal treatment (85 °C for 15 min) and glycosylation (20 g kg-1 glucose at 100 °C) had the greatest improvement in the characteristics of green soybean tofu. Hence, the combination treatment of STD and glycosylation should be useful for improving the quality characteristics of green soybean tofu and providing the technical references for industrial processing of tofu. © 2022 Society of Chemical Industry.

Effects of the Marinating Process on the Quality Characteristics and Bacterial Community of Leisure Dried Tofu

Leisure dried tofu (LD-tofu) was prepared using two different marinating processes: the repeated heating method (RHM) and the vacuum pulse method (VPM). The quality characteristics and bacterial community succession of LD-tofu and the marinade were evaluated. The results showed that the nutrients in LD-tofu were easily dissolved into the marinade during the marinating process, while the protein and moisture content of RHM LD-tofu changed most dramatically. With the increase in marinade recycling times, the springiness, chewiness and hardness of VPM LD-tofu increased significantly. The total viable count (TVC) of the VPM LD-tofu decreased from the initial value of 4.41 lg cfu/g to 2.51-2.67 lg cfu/g as a result of the marinating process, which had a significant inhibitory effect. Additionally, 26, 167 and 356 communities in the LD-tofu and marinade were detected at the phylum, family and genus levels, respectively. Pearson correlation analysis showed that Pseudomonadaceae, Thermaceae and Lactobacillaceae were closely related to the quality characteristics of LD-tofu, whereas Caulobacteriaceae, Bacillaceae and Enterobacteriae were closely related to the marinade. The present work provides a theoretical basis for the screening of functional strains and quality control in LD-tofu and marinade.

In vitro digestion of tofu with different textures using an artificial gastric digestive system

Two kinds of tofu with obvious differences in texture ["GDL" and "CaSO₄", standing for tofus made with the application of either glucono-δ-lactone (GDL) or calcium sulfate, with measured hardness 23.1 ± 3.3 g and 105.2 ± 25.1 g, respectively] were used as to investigate the in vitro progress and extent of tofu digestion, using an independently-developed artificial gastric digestion system (AGDS). The particle size distributions of both CaSO₄ and GDL tofu shifted towards smaller particles as the digestion time increased, while the viscosity of the gastric digesta also increased. Tofu proteins were hydrolyzed in the simulated stomach, with GDL tofu showing a higher hydrolysis rate, based on the temporal evolution of SDS-PAGE bands, and had a higher amino acids accumulation than CaSO₄ tofu at the end of gastric digestion. In the absence of peptic enzymes, the protein was acidically-hydrolyzed, but the degree of hydrolysis was much lower than in the presence of enzymes; these findings are in accord with the changes in microstructure observed by scanning electron microscopy. The results indicated that the in vitro extent of tofu digestion is related to its hardness, which is in turn related to its microstructure; they also indicated the potential of our developed in vitro dynamic stomach in studying semi-solid foods.

Processing technology optimization for tofu curded by fermented yellow whey using response surface methodology

The technological applications utilized for tofu processing are diverse and complex, resulting in different yields and quality characteristics of tofu. The current study investigated the gel-forming principle of soybean protein coagulated using fermented yellow whey (FYW) to produce tofu. The effects of several processing parameters (soybean-to-water ratio, boiling temperature, boiling time, and FYW content) on the yield and protein content of tofu produced by the boiling-to-filtering method (BFM) were studied and optimized using response surface methodology. Results indicated significant differences in yield and protein content of tofu using different processing parameters, with FYW content being the most significant (p < .05). Optimum processing parameters of the BFM were found to be: soybean-to-water ratio of 1:5 (kg:kg), boiling time 6.1 min, boiling temperature 105°C, and FYW content of 26%. Under optimum conditions, tofu's yield and protein content were 235.17 g/100 g and 10.60%, respectively, and these were 47.93 g/100 g and 4.16% higher than those before optimization. This study provides practical technical support and a theoretical basis for the standardized industrial production of high-yield and high-protein tofu.

Effect of high-intensity ultrasound soymilk pretreatment on the physicochemical properties of microbial transglutaminase-catalyzed tofu gel

Tofu prepared by conventional methods often has a bitter taste and poor water-holding capacity (WHC). To improve the quality of the product, alternative processes must be developed. Herein, the effect of ultrasound pretreatment on the properties of soymilk and tofu gel derived thereof were investigated. Treatment of soymilk with ultrasound gave rise to a reduction in the particle size and an enhancement in the surface hydrophobicity, whereby optimum values were obtained after 15 min treatment. Subsequently, microbial transglutaminase (MTG) was added to ultrasound-treated soymilk to promote the soy protein crosslinking. The gel strength, WHC, and nonfreezable water content of MTG-catalyzed tofu gel obtained from treated soymilk increased with the extension of the ultrasound pretreatment time, whereas the free sulfhydryl content decreased because of the formation of disulfide bonds. Fourier transform infrared spectroscopy demonstrated variations in the secondary structure of MTG-catalyzed tofu gel. Furthermore, soymilk's exposure to high-intensity ultrasound pretreatment led to a tofu gel with a dense, homogenous, and stable network structure, as evidenced by scanning electron microscopy. Therefore, this study answers for the theoretical support of the industrial production of MTG-catalyzed tofu gel from ultrasound-treated soymilk. PRACTICAL APPLICATION: High-intensity ultrasound pretreatment improved the texture properties of MTG-catalyzed tofu gel. The resulting MTG-catalyzed tofu gel has potential application in industrial production.

Effects of fat content on the textural and in vivo buccal breakdown properties of soy yogurt

This study aimed to evaluate the effects of fat content on the textural and in vivo buccal breakdown properties of soy yogurt (SY) at different pH (5.4, 5.0, and 4.6). The microbial analysis, textural and rheological properties, and interfacial protein composition of all the samples were monitored. Microbial results suggested that the increased fat content in SY-5.0 and SY-4.6 resulted in significantly high viable cell counts of lactic acid bacteria (LAB). Textural studies demonstrated that the presence of a low fat content (1-3%) significantly reduced the hardness, springiness, and gumminess of the sample, but this effect was negligible with the addition of fat content (4-5%). The apparent viscosity and thixotropy of the SY-4.6 sample increased as the fat content increased. in vivo buccal digestion showed that a high fat content (2-4%) reduced the number of chews and chewing durations, which might be correlated with high oil droplet release (%) after mastication.

Tofu products: A review of their raw materials, processing conditions, and packaging

Tofu is a traditional product made mainly from soybeans, which has become globally popular because of its inclusion in vegetarian, vegan, and hypocaloric diets. However, with both commercial production of tofu and scientific research, it remains a challenge to produce tofu with high quality, high nutrition, and excellent flavor. This is because tofu production involves multiple complicated steps, such as soybean selection, utilization of appropriate coagulants, and tofu packaging. To make high-quality tofu product, it is important to systematically understand critical factors that influence tofu quality. This article reviews the current research status of tofu production. The diversity of soybean seeds (the raw material), protein composition, structural properties, and nutritional values are reviewed. Then, selection of tofu coagulants is reviewed to provide insights on its role in tofu quality, where the focus is on the usage of mix coagulants and recent developments with new coagulants. Moreover, a comprehensive summary is provided on recent development in making high-fiber tofu using Okara (the major by-product during tofu production), which has a number of potential applications in the food industry. To help encourage automatic, environmental friendly, and high-efficient tofu production, new developments and applications in production technology, such as ultrasound and high-pressure process, are reviewed. Tofu packaging, including packaging materials and techniques, is evaluated as it has been found to have a positive impact on extending the shelf life and improving the quality of tofu products. Finally, the future research directions and potential areas for new developments are discussed.

Effect of microbial transglutaminase cross-linking on the quality characteristics and potential allergenicity of tofu

Microbial transglutaminase (MTGase) has been developed as a new tofu coagulant in recent years due to its good hydrophilicity, high catalytic activity, and strong thermal stability. This study aimed to investigate the effect of MTGase on the physicochemical properties and immunoreactivity of tofu relative to conventional coagulants [brine and glucono-δ-lactone (GDL)]. Structural changes of the MTGase cross-linked soymilk protein were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD) spectroscopy, ultraviolet (UV) absorption spectroscopy, and fluorescence spectroscopy. The IgE-binding capacity of MTGase cross-linked proteins was tested by enzyme-linked immunosorbent assay (ELISA). The physicochemical properties, quality characteristics, and surface microstructures of five different types of tofu were determined by the Kjeldahl nitrogen method, texture analysis, and scanning electron microscopy (SEM). The digestibility of tofu was evaluated in vitro by simulated gastrointestinal (GIS) digestion. A cell sensitization experiment was performed in vitro to evaluate the capability of tofu digestion products to induce the release of bioactive mediators from human basophil leukemia (KU812) cells. Results indicated that MTGase significantly changed the advanced structure of the soymilk protein. Compared with tofu without MTGase, the composite coagulant tofu containing MTGase exhibited better quality. MTGase improved the water-holding capacity (WHC) of the internal mesh structure and increased the yield of tofu. The digestion products of the composite coagulant tofu, especially the GDL plus MTGase tofu, induced KU812 cells to release fewer bioactive mediators compared with those of MTGase-free tofu. MTGase can not only improve the quality of conventional coagulant tofu but also reduce the potential allergenicity of tofu to a certain extent.

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.

HPMC (hydroxypropyl methylcellulose) as a fat replacer improves the physical properties of low-fat tofu

BACKGROUND

The effect of the addition of hydroxypropyl methylcellulose (HPMC) on the textural properties of low-fat tofu was investigated. Three fat levels (240, 100 and 30 g kg^-1 ) were used to make tofu, which were identified as C (full-fat tofu), L1 and L2. HPMC (5 g kg^-1 ) was added to soymilk to prepare control and low-fat tofu, designated as CH, L1H and L2H.

RESULTS

Soymilk with a lower fat level had a lower viscosity: 143 (C), 100 (L1) and 42 (L2) cP. The addition of HPMC increased the viscosity of all types of soymilk, particularly in L2H (107 cP). With fat reduction, tofu syneresis increased from 19% (C) to 29% (L2), although syneresis of L2H recovered to 19%, which is similar to high-fat control tofu. Decreased fat resulted in a lower firmness in L2 (0.67 N) compared to control (0.78 N). Firmness increased to 1.08 N in L2H tofu, whereas the firmness of CH tofu was 0.63 N. All types of tofu showed a denser, well-connected and cross-linking structure when HPMC was added, especially in L2H tofu.

CONCLUSION

HPMC improved the texture of the low-fat tofu by creating a harder texture and reducing syneresis. HPMC is an effective fat replacer for lower fat soymilk. © 2017 Society of Chemical Industry.