It has been suggested that immune senescence contributes to the aging of solid organs and that blocking immune senescence can alleviate the aging of organs. Aging is a systemic physiological change. It is currently difficult to achieve the goal of long-term delaying aging through drugs. Improving immunity and delaying aging through probiotics is a feasible research direction. Here, we first screened for a strain of Lactobacillus kefiri Fanghua (L. kefiri-FH) derived from Tibetan kefir and confirmed its function in restoring immunosuppression. Spleen weight, thymus weight, and whole blood cells were restored. The expression of programmed cell death-ligand 1 (PD-1), P16^ink4a, and senescence-associated secretory phenotype (SASP)-related genes in the spleen and thymus was decreased. Second, we further confirmed the phenotype of L. kefiri-FH in improving solid organ function in 16-month-old mice as well as prolonging the lifespan of Caenorhabditis elegans. Mechanistically, whole genome sequencing and metabolomic analysis indicated that L. kefiri-FH contained three genes related to bile acid metabolism and increased lithocholic acid (LCA) in the intestine. We also confirmed that LCA increased G-protein-coupled bile acid receptor (Gpbar5 or TGR5) gene expression in dendritic cells (DCs) and inhibited the induction of T helper (Th) 1 and Th17 cells. Overall, our findings establish a causal relationship between the intestinal microenvironment, immune senescence, and solid organ aging, suggesting a way to regulate the intestinal microenvironment through diet, which thereby improves immune senescence and subsequently reduces solid organ aging.

Steroid hormones, small lipophilic substances, are often illegally used as growth-promoting agents in the animal husbandry and breeding industry. Residual hormones in dairy products can enter the human body through the food chain causing a series of health hazards. Residues of steroid hormones in dairy products have become the focus of worldwide concern about veterinary drug residues. Regulations have been issued to limit the content of steroid hormones in dairy products in China. This paper discusses the structure, classification and functions of steroid hormones, and summarizes the maximum residue limits, detection methods, contents and health risks of steroid hormones in dairy products, aiming to provide a reference for further research of steroid hormones in dairy products.

Psychrotrophs and thermoduric bacteria are the major contaminating microorganisms in dairy products, which affect the quality and safety of dairy products. Therefore, it is particularly important to study the relationship among contaminating microbial communities, trace the pathways and sources of contamination, and reduce the hazards of contamination. Typing and identification technologies provide strong support for the precise identification and classification of contaminating microorganisms. This paper focuses on recent progress in the development of typing and identification methods for psychrotroph and thermoduric bacteria in dairy products from three aspects: phenotyping, molecular biology typing, and mass spectrometry typing. The principle, application, advantages and disadvantages of each technology are outlined, and the problems with the existing typing and identification methods are discussed. Finally, this review concludes with an outlook on future development directions. It aims at providing a scientific basis for the selection of suitable methods for the typing and identification of psychrotrophs and thermoduric bacteria in dairy products for more accurate and efficient identification and control of contaminating microorganisms in dairy products, thereby guaranteeing their quality and safety.