Optimization of the prebiotic & probiotic concentration and incubation temperature for the preparation of synbiotic soy yoghurt using response surface methodology

•Synbiotic soy yoghurt was prepared using optimized formulation and process condition.•FOS and probiotic culture combinations (ST-LA) interaction improved the quality of soy yoghurt.•FOS improves textural characteristics with fast acidification.

This research work aimed to develop synbiotic soy yoghurt with improved product characteristics and consumer acceptability. Response surface methodology was employed to investigate the combined effects of FOS concentration (2-10 % w/v), ST-LA inoculum size (2-4% v/v), and fermentation temperature (37-42 °C) on fermentation time (h), hardness (g), whey separation (%) and overall acceptability on 9 point hedonic scale of synbiotic soy yoghurt. A second-order polynomial response surface equation and response surface graph revealed that the experimental variables significantly affected the studied responses. Determination coefficients (R2) were higher than 87% which showed that the developed models were well fitted to the experimental data. Synbiotic soy yoghurt was prepared using optimized FOS concentration (8.1% w/v), culture combination ST-LA with inoculum size 3.6% v/v, 1:1 ratio and incubated at temperature 41 °C for 5.25 h. The optimized product was well set with very less whey separation (1.14%). The developed product showed good nutritional, textual and sensory characteristics.