Influence of ginger addition on the microbiological shelf life and sensory attributes of soy–cow milk yoghurt blends

Abstract

This study evaluated the effect of ginger addition on the sensory microbial shelf-life and attributes of soy–cow milk yoghurt during storage. Yoghurt samples were prepared using three milk formulations (100:0, 75:25 and 50:50 of cow milk to soymilk ratio, respectively), fermented with Lactobacillus bulgaricus and Streptococcus thermophilus then, varying concentrations of ginger extract (0%, 5%, and 10%) added to each blend and stored at 25°C for 96 h. Microbiological analyses, including total bacterial count, lactic acid bacteria enumeration, and fungal count, were conducted using standard plate count techniques during a 96 h storage period. Sensory evaluation by semi-trained panelists was conducted using a 9-point hedonic scale. Then statistically analyzed using ANOVA. Results showed that bacterial populations in all samples ranged from 1.9 × 10⁸ to 7.9 × 10⁸ CFU/mL initially and increased during storage, indicating continued metabolic activity of lactic acid bacteria. Fungal counts remained within acceptable limits throughout the storage period. The increase in LAB counts suggests ongoing probiotic activity, although the stability of fungal counts indicates no spoilage. Sensory evaluation revealed that sample AQ (100% cow milk with 5% ginger) received the highest overall acceptability score (8.74 ± 0.012), with the highest ratings for sweetness, flavor and thickness. Samples with higher proportions of soy milk received significantly lower overall acceptability scores, with CH (50:50% cow milk with 10% ginger) scoring lowest (1.50 ± 0.002). These findings suggest that moderate ginger addition enhances sensory appeal in dairy-dominant yoghurts, but formulation adjustments may be needed to improve the acceptability of soy-rich variants.