# Accelerating the coagulation of germinated soymilk by glucono-δ-lactone using different physical treatments and quality assessment of separated soybean whey

## TL;DR

This study shows that microwave and ultrasound treatments speed up soy protein coagulation and improve tofu texture when using germinated soybeans.

## Contribution

The study introduces microwave and ultrasound as effective methods to enhance coagulation and tofu quality from germinated soybeans.

## Key findings

- Microwave and ultrasound treatments accelerated coagulation 5.4–8.7 times faster than steaming.
- Microwave treatment increased tofu hardness and β-sheet content while reducing α-helix content.
- Germination increased amino acids Arg, Glu, and Asp in soybean whey.

## Abstract

This investigation was undertaken to assess the efficacy of glucono-δ-lactone coupled with thermal (steaming and microwave) and non-thermal (ultrasound) treatment in the coagulation of soy protein from germinated soybean seeds. The findings indicated that both microwave and ultrasonic treatments significantly accelerated coagulation of soy protein (5.4–8.7 times faster) compared to conventional steaming treatment. Regarding textural properties, soybean curd obtained from germinated soymilk displayed increased hardness values (122.0 to 277.3 g) and microwave treatment further augmented this textural attribute, except for the sonicated samples. FTIR data also confirmed that the microwave treatment was found to elevate the β-sheet content while concurrently diminishing the α-helix content within the soybean curd. Concerning the soybean whey isolated from soybean curd, the germination was shown to amplify the concentrations of the amino acids Arg, Glu, and Asp. Although the phenolic content in the whey fraction of the germinated samples was higher than that of the non-germinated samples, the FRAP activity of the microwave- and ultrasound-treated samples followed the opposite trend. Overall, microwave treatment reduced processing time while improving texture of tofu, suggesting that microwave treatment can serve as an effective processing intervention to improve both efficiency and structural properties in tofu manufacturing.

•Microwave and ultrasound accelerated coagulation by 5.4–8.7 times than steaming.•Tofu from germinated soybean seeds had higher hardness than non-germinated seeds.•Microwave improved the hardness of tofu coagulated with GDL.•Microwave increased the β-sheet while decreased the α-helix content of soybean curd.•Germination intensified the Arg, Glu and Asp amino acids content in soybean whey.

Microwave and ultrasound accelerated coagulation by 5.4–8.7 times than steaming.

Tofu from germinated soybean seeds had higher hardness than non-germinated seeds.

Microwave improved the hardness of tofu coagulated with GDL.

Microwave increased the β-sheet while decreased the α-helix content of soybean curd.

Germination intensified the Arg, Glu and Asp amino acids content in soybean whey.