Enhancing the flavour of bio-yogurt by supplementation with various concentrations of threonine

Aim: The objective of this study is to enhance the flavor of bio-yogurt through the addition of threonine at various concentrations, and to evaluate its influence on the physicochemical, microbiological, and sensory characteristics of the product. Methods: To prepare bio-yogurt from cow’s milk, a probiotic starter culture comprising Bifidobacterium bifidum (Bb-12), Lactobacillus acidophilus (La-5), and Streptococcus thermophilus (ST) was used, both with and without the addition of the amino acid threonine at three concentrations: 1, 5, and 10 mg/100 mL milk. The bio-yogurt samples were then subjected to various physical, chemical, microbiological, and sensory analyses, and compared against a threonine-free control sample. Results: On the first day, the logarithmic counts of the probiotic starter cultures were 8.55–8.58, 8.33–8.34, and 8.53–8.57 log CFU/g for Bb-12, La-5, and ST, respectively; these values decreased to 7.01–7.03, 7.52–7.56, and 7.82–7.89 log CFU/g after 21 days. The concentrations of volatile compounds (acetaldehyde, acetoin, and diacetyl) in the threonine-enriched bio-yogurt ranged from 42.12 µg/kg to 49.40 µg/kg, 25.11 µg/kg to 29.02 µg/kg, and 3.09 µg/kg to 3.97 µg/kg, respectively, compared to the control sample, which exhibited concentrations of 38.23 µg/kg, 22.50 µg/kg, and 2.55 µg/kg, respectively. Sensory evaluation results indicated that the sample supplemented with 10 mg of threonine received the highest scores compared to the other samples. Conclusions: Our findings provide evidence of the value of supplementing bio-yogurt with threonine, as it does not alter its physicochemical properties. Furthermore, it does not adversely affect the total viable counts of probiotic bacteria but significantly improves the flavor profile and enhances consumer acceptability.