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

Monitoring of carbon dioxide and equilibrium moisture content for early detection of physicochemical and morphological changes in soybeans stored in vertical silos

In the context of grain storage, impurities and soybeans defects in soybeans can significantly impact the equilibrium moisture content. This, cause moisture migration and heating of the stored product, leading to increased respiratory activity. Furthermore, temperature measurements within stored grain mass do not provide sufficient information for effective grain quality monitoring, primarily due to the grains excellent thermal insulating properties. To address this issue, we propose a different approach: monitoring the equilibrium moisture content and CO2 concentration as indicators of soybean respiration within the intergranular spaces of the stored grain mass. This study propose monitoring the CO2 concentration in the intergranular air along with environmental variables for early detection of physicochemical and morphological changes in soybeans stored in vertical silos using near infrared spectroscopy, X-ray diffraction and scanning electron microscopy. Thermogravimetry and spectrometry analyses revealed that the interrelationships among variables had a direct impact on soybean quality attributes. Specifically, the presence of soybeans with 5.2 % impurities led to an increased in respiration rates, resulting in a CO2 concentration of up to 5000 ppm and the consumption of up to 3.6 % of dry matter. Consequently, there were changes in the percentage of ash, proteins, fibers, and oils compositions. These findings highlight the potential for indirect assessments, enabling the prediction of physicochemical quality and contamination of soybeans stored in vertical silos through continuous monitoring of CO2 concentration and equilibrium moisture content.

Effect of Oxidation on Quality of Chiba Tofu Produced by Soy Isolate Protein When Subjected to Storage

Chiba tofu is a new type of vegetarian food prepared with soy protein isolate (SPI). According to factory feedback, the SPI stored in the factory storeroom in summer undergoes reactive oxidation, which changes the structure of SPI and further affects the quality of Chiba tofu. Consequently, the main objective of this study was to prepare Chiba tofu with SPI with different storage periods and evaluate the effect of different degrees of oxidation on structural characteristics of SPI and rheology, texture, microstructure and sensory properties of Chiba tofu. The carbonyl content and turbidity of SPI significantly increased, and the contents of free sulfhydryl (SH) and disulfide bond (S-S) simultaneously decreased with storage time. The oxidation changes the SPI conformation, leading to a transition of α-helix and β-turn to β-sheet and random coil during the storage periods. In the SDS–PAGE analysis, oxidation promoted the SPI molecules crosslinked and aggregated, which affected the quality of Chiba tofu. In short storage periods (0–12 days), SPI was relatively moderately oxidized when the carbonyl content was between 4.14 and 6.87 mmol/g. The storage and loss modulus of Chiba tofu both increased, the network was compact, and the hardness and springiness of Chiba tofu showed an increasing trend. Moreover, in longer storage periods (12–30 days), the SPI was relatively severely oxidized when the carbonyl content was between 7.24 and 9.14 mmol/g, which had an adverse effect on Chiba tofu rheological and texture properties, microstructure, and sensory properties. In sensory evaluation, Chiba tofu stored 12 days had the highest overall quality score than that stored on other days. This study is expected to provide an argument for the better industrial production of Chiba tofu.

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.

Recent update on methodologies for extraction and analysis of soybean seed proteins

Soybean is one of the best sources of plant protein. Development of improved soybean cultivars through classical breeding and new biotech approaches is important to meet the growing global demand for soybeans. There is a critical need to investigate changes in protein content and profiles to ensure the safety and nutritional quality of new soybean varieties and their food products. A proteomics study begins with an optimal combination of extraction, separation and detection approaches. This review attempts to provide a summary of current updates in the methodologies used for extraction, separation and detection of protein from soybean, the basic foundations for good proteomic research. This information can be effectively used to investigate modifications in protein content and profiles in new varieties of soybeans and other crops. © 2018 Society of Chemical Industry.

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.

Effects of moisture and temperature during grain storage on the functional properties and isoflavone profile of soy protein concentrate

The objective of this study was evaluate the effects of moisture and temperature during grain storage on the functional properties and isoflavone profile of soy protein concentrate. The protein concentrate was extracted from soybeans on the first day of storage and after 12months of storage, at 12 and 15% moisture and at temperatures of 11, 18, 25, and 32°C. The protein concentrate obtained from grains stored at 32°C showed decreased extraction yield (51.6% with 15% of moisture) and protein solubility (24.8% with 15% of moisture) with increased emulsifying capacity (52.2% with 12% of moisture) and foam formation, compared with sample obtained at the start of the storage period. The isoflavone profile showed a decrease in the concentrations of glycosylated, malonyl, and acetyl isoflavones and a corresponding increase in the concentrations of aglycone isoflavones, with the magnitude of these changes increasing with increasing storage temperature and moisture content.

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.

Changes in the Bioactive Compounds Content of Soybean as a Function of Grain Moisture Content and Temperature during Long-Term Storage

Soybean is a rich source of bioactive compounds, such as phenolic acids, flavonoids, isoflavones, carotenoids, and tocopherols. The amount of bioactive compounds in freshly harvested soybeans and their derived products has been determined; however, when they are used in the food industry, soybeans are generally stored prior to being processed. This study aimed to evaluate the effects of soybean moisture content (12%, 15%, and 18%) and storage temperature (11, 18, 25, and 32 °C) on the free phenolic, total flavonoid, vanillic acid, total carotenoid, and δ- and γ-tocopherol content of soybeans stored for 12 mo. Moreover, the ABTS and DPPH radical scavenging activities of phenolic extracts were determined. There was an increase in free phenolics and total flavonoids in the stored grains compared with the grains on the 1st d of storage. Vanillic acid showed a decrease in soybeans stored at 15% and 18% moisture content and 25 or 32 °C, which indicated some degradation into other metabolites. Total carotenoid content decreased as a function of storage temperature and showed some temperature-dependent degradation. The δ- and γ-tocopherol content also tended to decrease in grains stored at 15% or 18% moisture content or 25 or 32 °C, regardless of the moisture content studied.