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.

Pseudomonas is a genus of bacteria commonly found in contaminated raw milk. This bacterial genus can form a biofilm on equipment surfaces during the production of dairy products which causes equipment corrosion and is difficult to remove. The biofilm formed by Pseudomonas not only promotes the secretion of heat-resistant peptidases but also provides a substrate for the growth of pathogenic bacteria, posing a great risk to the safety of dairy products. This article outlines recent progress in understanding the mechanisms for the regulation of Pseudomonas biofilm formation and the environmental factors affecting Pseudomonas biofilm formation, which is helpful for the prevention and control of Pseudomonas bioflim.

Psychrotrophic bacteria and their heat-resistant enzymes are common contaminants in raw milk,leading to dairy product spoilage.The biodiversity of psychrotrophic bacteria isolated from raw milk in Shanghai was investigated by 16S rRNA sequencing and the individual isolates were evaluated for protease and lipase activities by plate culture.All isolates were classified into 33 genera in 9 classes,with Pseudomonas (55％),Acinetobacter (10％) and Flavobacterium (5％) being predominant,and the remaining 30 genera accounting for 30％ of the total number of isolates.Most isolates had the ability to produce protease or lipase,and different genera had different enzymatic profiles.Pseudomonas and Flavobacterium exhibited considerable protease activity,whereas Klebsiella showed strong lipase activity.On the other hand,most Acinetobacter isolates could produced neither protease nor lipase.

Microwave is a technology that enables fast heating. In this review, the recent progress in the application of microwave in the dairy industry with respect to its effect on milk quality and its use in the detection of dairy products and the degradation of dairy wastes. It is showed that microwave has broad prospects for application in the dairy industry.

This article summarizes the current progress in understanding the characteristics of mixed culture fermentation and interaction mechanism of Lactobacillus bulgaricus and Streptococcus thermophilus as well as the influences of mixed culture fermentation on the synthesis of exopolysaccharides and flavor substances. The aim of this review is to provide useful information for researchers to apply them and screen starter cultures.

The major free middle-chain fatty acids (hexanoic acid, octanoic acid, decanoic acid) in raw milk and dairy products are regarded as important compounds that affect liquid milk quality and safety due to their strong flavor characteristics. This article provides an analytical method using headspace solid phase microextraction and gas chromatography-mass spectrometry (HS-SPME-GC-MS) with an internal standard for the quantitative determination of free middle-chain fatty acids in liquid milk. The method was verified as an approach with high accuracy, simple operation and high extraction efficiency.

In this study, the recombinant Lactobacillus casei LC2W were constructed for overexpressing four bsh genes from L. plantarum ST-III and the Bile salt hydrolase (BSH) enzyme activities were determined. It was shown that the four recombinant strains all showed a lower enzyme activity than the host, indicating that the bsh gene overexpression could not achieve the goal of enhancing the hydrolysis of the bile salts.

Biochip serves as a novel microanalysis and high-throughput detection technique, and it has been gradually introduced in biological research, food, medicinal and agricultural fields. This paper summarizes the basic principle, classification and manufacturing process of biochip with special emphasis on its application in the field of food safety. Problems encountered in the development of biochip technology and future trends are also briefly described.

Pseudomonas is highlighted as predominant psychrotrophic spoilage bacteria in milk and dairy products. Its extracellular proteases are heat-resistant, and have residual activity even after ultra high temperature sterilization (UHT) treatment leading to short life of UHT milk. The current article summarizes recent studies on extracellular proteases of psychrotrophic Pseudomonas in milk, with special emphasis on their catalytic mechanisms as well as the application of protease genes including apr X to identify Pseudomonas. At last, the further research directions in this area are discussed.

Lactic acid is a valuable organic acid widely used in the food, pharmaceutical, cosmetic, and chemical industries, which is also the major end product of carbohydrate fermentation by homofermentative lactic acid bacteria. This paper summarizes the current status of studies on the species distribution of the microbial genus, and the biosynthesis pathway and metabolic regulation of lactic acid. Future prospects in this area are also discussed.

Staphylococcus aureus (S. aureus) is a Gram positive bacterium that is carried by about one third of the general population and is responsible for common and serious diseases. These diseases include food poisoning and toxic shock syndrome, which are caused by exotoxins produced by S. aureus. Among the more than 20 staphylococcal enterotoxins (SEs), SEA and SEB are the best characterized and are also regarded as superantigens because of their ability to bind to class II MHC molecules on antigen presenting cells and stimulate large populations of T cells that share variable regions on the β chain of the T cell receptor. This article provides a detailed elaboration of the pathogenicity and underlying mechanism of SEs as well as the methods used to detect the exotoxins, which has a guiding significance for clinical treatment and food safety monitoring. Owing to the occurrence of multiple resistant strains of S. aureus, the health harm of S. aureus in food has become more and more serious, so we have to minimize the microbial load of this bacterium in food, and prevent cross contamination in food.

The safety of dairy products has increasingly become the focus of both social and scientific attention. This article provides an overview of the concepts of dairy product safety and microbial risk assessment. From the point of view of the hazard factors affecting the safety of dairy products, a comprehensive review is executed with respect to the sources of microbial hazards and the current status of microbial risk assessment at home and abroad. And differences between microbial risk assessment and chemical hazard risk assessment are pointed out. Finally, a perspective outlook is proposed to expect the future direction of microbial risk assessment of dairy products in China.