Abstract: Alpha-lactalbumin (α-LA) is an important immune protein in breast milk. In addition to providing various nutrients such as essential amino acids for infants, α-LA may also regulate intestinal flora. Infant formula contains a lower concentration of α-LA relative to breast milk. Therefore, it is important to explore the effects of different concentrations of α-LA on the diversity and structure of intestinal flora and to determine the appropriate amount of α-LA science added in infant formula. In this experiment, 4 groups of SD rats were orally administered respectively with an equal volume of normal saline (control group), α-LA at high, medium and low concentrations (200, 100 and 20 mg/kg), and colonic feces were aseptically taken after 14 and 28 days of administration. The V3-V4 region of the 16S rRNA gene of the intestinal flora was amplified. Alpha diversity, Beta diversity, and intestinal flora composition at the phylum and genus levels were analyzed by high-throughput sequencing. The results showed that α-LA at high and medium doses improved the species richness, diversity and structure of intestinal microbiota, and the effect was similar to that of breast milk. At the genus level, the high concentration of α-LA reduced the relative abundance of Lactobacillus, Blautia and Akkermansia, while the opposite effect was observed at medium and low concentrations. α-LA at all concentrations decreased the relative abundance of Prevotella and Bacteroides, and the effect was more pronounced with the decrease in its concentration. Moreover, α-LA at all concentrations increased the relative abundance of Eubacterium xylanophilum and maintained the relative abundance of Ruminococcaceae, Clostridium sensu stricto_1 and unknown Lachnospiraceae genera at a constant level. The medium concentration of α-LA enhanced intestinal microbial diversity, and increased or maintained the relative abundance of intestinal probiotics while reducing the abundance of intestinal harmful bacteria, suggesting α-LA at this concentration was optimal to regulate intestinal microbiota. The results of this study provide experimental data for improving infant feeding, and ultimately provide theoretical support for the supplementation of α-LA in infant formula.

Key words: α-lactalbumin, 16S rRNA, infant, intestinal flora, SD Rat