Effect of Kombucha Starter Culture on the Gelation Process, Microstructure and Rheological Properties during Milk Fermentation

This study is concerned with the effect of kombucha starter culture on the rheological properties, texture and microstructure as well as on the protein fractions in different phases of milk fermentation. The results were compared with those obtained for the samples prepared with yoghurt and probiotic starters. Quality parameters in the course of fermentation at 42C were measured at the pH values of 5.4, 5.1, 4.8 and 4.6. The viscosity values measured at pH 5.4 indicate similarity of the gelation processes taking place in the samples involving kombucha and probiotics. The sample produced with kombucha had the highest value of complex modulus, which resulted in better rheological characteristics of the final product. The earlier onset of the gelation process induced significant differences among the samples in the microstructure at pH 5.4. The analysis of the protein profile revealed better stability of α and β casein fractions compared with the other protein fractions in particular phases of milk fermentation. PRACTICAL APPLICATIONS: Although the method of scanning electron microscopy (SEM) has been already used to study the properties of the final product, the studies of the microstructural changes occurring in the course of yoghurt production are still lacking. As the application of kombucha in milk fermentation is still an attractive research topic, the authors found it interesting to include SEM into the set of methods for studying milk fermentation. Therefore, the objective of this research was to investigate the changes in the viscosity and texture during milk fermentation by a nonconventional starter – kombucha inoculum – and to establish the correlation of examined properties and the microstructure of the gel. The presented results represent a significant contribution to the understanding of the process of milk fermentation using different starter cultures related to the rheological characteristics of the gel. These characteristics and their changes are of significant practical importance for the process optimization and quality enhancement of new fermented milk product obtained by kombucha application.