Effect of transglutaminase and acidification temperature on the gelation of reconstituted skim milk

Fermentation Characteristics, Antinutritional Factor Level and Flavor Compounds of Soybean Whey Yogurt

Soybean whey contains high levels of off-flavors and anti-nutritional factors and is generally considered unsuitable for direct application in the food industry. In this work, to reduce beany off-flavors and anti-nutritional factors, and to improve its fermentation characteristics, soybean whey was treated with electrodialysis desalination, vacuum concentration and lactic acid bacteria (LAB) fermentation. The results showed that electrodialysis desalination increased the fermentation rate and the number of viable lactic acid bacteria of soybean whey yogurt. More than 90% of the antinutritional factor level (urease and trypsin inhibitory activity) was removed due to high-temperature denaturation inactivation and LAB degradation. Concentrated desalted soybean whey yogurt (CDSWY) possessed larger values for firmness and consistency, and a denser network microstructure compared with undesalted yogurt. Over 90% of off-flavors including hexanal, 1-octen-3-ol and 1-octen-3-one were removed after electrodialysis desalination and concentration treatment. Meanwhile, the newly generated β-damascenone through carotenoid degradation and 2,3-butanedione improved the pleasant flavor and sensory quality of CDSWY, while the salty taste of CSWY lowered its sensory quality. This study provided a theoretical basis for better utilization of soybean whey to develop a plant-based yogurt like dairy yogurt.

Comparison of physicochemical properties and volatile flavor compounds of plant-based yoghurt and dairy yoghurt

The aim of this study was to investigate and compare the physicochemical characteristics and volatile flavor compounds of three kinds of yoghurt made from reconstituted milk, soy drink and oat drink. The results showed that with the same fermentation ending pH of 4.5, reconstituted yoghurt had the highest titratable acidity mainly due to the highest buffering capacity and microbial counts (LAB). The textural and water holding capacity (WHC) parameters revealed that soy-based yoghurt had the highest firmness, consistency and WHC, indicating more rigid gel was formed. Meanwhile, rheological analysis showed soy-based yoghurt owned higher G' and G'' values and higher stability against external stress, demonstrating that more and stronger interactions between soy proteins were built during fermentation. The confocal laser scanning microscopy (CLSM) image witnessed that soy-based yoghurt had the densest and finest network, while oat-based yoghurt had much coarser and looser structure, which was consistent with the lowest firmness and G' value for oat-based yoghurt. In terms of color, reconstituted yoghurt was the lightest and oat-based yoghurt showed more reddish and yellowish. The main volatile flavor compounds in all yoghurts were ketones, while aldehydes contributed more in soy and oat yoghurt. PCA plot showed that volatile flavor compounds of reconstituted yoghurt and oat-based yoghurt were relatively similar, while soy-based yoghurt was much more different with high OAVs of hexanal, 1-octen-3-one, 1-octen-3-ol and 2-octenal. This study supplied a theoretical basis and an improvement direction for the better development of healthier plant-based yoghurt similar to dairy yoghurt.

Rheological and textural properties of goat's milk set-type yoghurt as affected by heat treatment, transglutaminase addition and storage

BACKGROUND

Production of goat's milk set-style yoghurt encounters challenges in achieving the texture characteristic for this type of product, primarily due to protein composition of this milk. This study evaluated the effects of using microbial transglutaminase (mTGase) concomitantly with starter culture in the production of goat's milk yoghurt - a method that has not been employed with this milk type until now- indicating the potential of the enzyme to change yoghurt's textural properties. Goat's milk set yoghurts were produced from milk heated at 72 °C/30 s and 90 °C/5 min, without (G72 and G90) and with mTGase (G72TG and G90TG) and starter culture addition. Protein profiles of goat's milks and yoghurts were also examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Yoghurts were evaluated for rheological properties, texture, microbiological and sensory profile over 2 weeks to study the influence of mTGase, pasteurization and storage.

RESULTS

The enzyme caused significant increases of storage moduli at the end of fermentation: 8.32 ± 0.27 Pa (G90TG) and 2.89 ± 0.18 Pa (G72TG) vs. 6.13 ± 0.07 Pa (G90) and 1.27 ± 0.18 Pa (G72) without enzyme. Lower loss tangent values indicated the enhanced elastic character of the gels with enzyme. Enzyme increased yoghurt's firmness from 49.69 ± 2.61 g (G90) to 60.81 ± 5.29 g (G90TG) after 1 day and from 58.21 ± 0.53 g (G90) to 80.45 ± 0.59 g (G90TG) after 15 days' storage. Enzyme improved starter bacteria survivability during storage of G72TG yoghurt.

CONCLUSION

mTGase can be used simultaneously with the starter culture to improve the rheological properties and texture of goat's milk yoghurt, without deteriorating effect on its flavour. © 2021 Society of Chemical Industry.