Evaluation of MENAQUINONE‐7 and fat‐soluble vitamin production by starter cultures during fermentation in dairy products using RPLC method

Vitamin K2, also known as menaquinone, has become a significant research focus, particularly in fermented products. This study aims to investigate the content of menaquinone-7 (MK-7), an essential form of vitamin K, and other fat-soluble vitamins (A, D, E) during the fermentation of various fermented milk products. The vitamin contents of six fermented milk products were analyzed: two yogurt samples (produced with commercial starter and probiotic starter), two kefir samples (produced with commercial starter and kefir grain), and milk fermented with <i>Lactobacillus acidophilus</i> or <i>Bifidobacterium bifidum</i>. Throughout the fermentation process, continuous pH monitoring was conducted, and fermentation was terminated based on pH levels. Fat-soluble vitamins and vitamins K1, K2 were extracted from samples taken at specific fermentation periods and quantitatively determined using the reverse phase liquid chromatography (RPLC) method. The developed method was validated according to ICH guidelines. Simultaneously, the microbial content of the samples was analyzed. Among the fermented dairy products analyzed, the highest MK-7 content (4.82 μg/100 g) was found in the kefir sample produced with kefir grain (KG). The diverse microorganisms in kefir grains necessitated detailed research to explain their role in this complex mechanism. In yogurt samples, the presence of <i>L. acidophilus</i> in the YB sample suggests that this bacterium may be responsible for the observed differences. This is supported by the LA sample, where production with <i>L. acidophilus</i> strain showed an increase from 0.97 to 1.70 at the 20th hour of fermentation. It was noted that the concentration of menaquinone-7 increased throughout the fermentation period. Given the critical health effects of essential fat-soluble vitamins and MKs, determining their content in commonly consumed fermented dairy products and understanding the influence of starter cultures, which are potential probiotics, on vitamin production underscores the importance of this research. It is important to highlight the potential of fermented products in nutritional recommendations.