Processing-Associated Taxonomic Profiles of Microbiota in Liquid and Powdered Horse Milk Revealed by Full-Length 16S rRNA Sequencing

Horse milk contains diverse microbial communities whose composition may be altered by processing and the addition of carrier ingredients. This study evaluated the effects of milk form and dextrin supplementation on the microbiota of horse milk prepared as pasteurized liquid milk (SKC), powdered milk supplemented with 15% dextrin (SKD), and powdered milk without dextrin (SKT). Microbial diversity and composition were analyzed using full-length 16S rRNA gene sequencing covering the V1-V9 regions. SKT showed the highest microbial richness, with 1185 observed taxa and a Shannon index of 3.43 ± 0.23, compared with 963 taxa and 2.40 ± 0.99 in SKD and 190 taxa and 2.02 ± 0.06 in SKC. SKC and SKD were dominated by lactic acid bacteria, particularly Lactobacillus gallinarum and Lactobacillus helveticus, whereas SKT contained higher proportions of stress-tolerant and spore-forming taxa such as Brevibacillus parabrevis (26%), Thalassoporum komareki (12%), and Lysinibacillus boronitolerans (10%). Sankey diagrams and principal component analysis further demonstrated distinct microbial community structures among the treatments. Overall, dextrin supplementation appeared to act as a protective carrier during drying, helping maintain the predominance of lactic acid bacteria, whereas powdered milk produced without dextrin was associated with a broader microbial profile.