Impacts of milk processing and fermentation on microRNA levels in cow’s milk

Recent evidence suggests that milk-derived microRNAs (miRNAs) are bioactive components of milk that can influence host cells through cross-kingdom miRNA transfer mechanisms. Therefore, it is essential to assess the content and stability of these miRNAs in drinking milk and milk products to explore their potential roles in human health. Here, we examined the small RNAs and microRNA levels in raw and processed milk samples, including plain and prebiotic-rich kefir. Total RNA was isolated from milk samples processed with different heat treatments and fermentation. The effects of milk processing on specific miRNAs were investigated by RT-qPCR, which evaluated the quantities of four miRNAs related to human diseases. We found that miR-21 and miR-125b could resist harsh conditions applied in milk processing plants. However, no detectable amounts of the tested miRNAs were found in kefir samples by qPCR. Our study highlights the miRNA-specific effects of milk processing methods on milk miRNA content. Future studies focusing on total small RNA content in kefir and other milk products may offer valuable insights into the functional role of milk-derived miRNA. Overall, miRNAs in drinking milk warrant further attention for their potential importance for public health.