Abstract
Psychrotrophic microorganisms, especially Pseudomonas spp., are present in the microbiota of refrigerated milk as they can grow at refrigeration temperatures irrespective of their optimal growth temperature. Psychrotrophic counts ranging from 105 to 108 CFU/mL in refrigerated raw milk effect cheese quality, since the synthesized thermoresistant enzymes affect the nutritional value, sensory properties, and texture. Cheese is the dairy product with the highest growth rate in the food industry in Brazil in recent years and meets the current consumption trends of nutritious and practical foods. The objective of this review was to address the importance and influence of the psychrotrophic raw milk microbiota on the quality and sensory properties of cheese. The enzymes produced by psychrotrophic microorganisms lead to taste changes, undesirable clotting times, increased concentrations of free fatty acids and free amino acids, and a reduced shelf-life, in addition to negatively affecting cheese yields. Proteases from psychrotrophs are also associated with slicing problems and progressive loss of the elasticity of cheese, a bitter taste, and increased clotting times of cheese produced with pasteurized milk. On the other hand, their lipases increase the clotting time and have a negative effect on the sensory properties by providing a rancid, soap, metallic, or oxidized smell and taste. The control of the psychrotrophic population found in refrigerated raw milk contributes to better cheese production yields and desirable texture and sensory properties, which extends the shelf-life of cheese and improves consumer acceptance.
Highlights
Milk is a secretory product of mammary glands and a homogeneous aqueous mixture of compounds, such as proteins, carbohydrates, lipids, minerals, vitamins, and enzymes
Milk composition varies among animal species and breeds, but other factors can affect the chemical composition of milk, such as age, lactation stage, genetics, diet, and health (Ordonez-Pereda et al, 2005; Walstra et al, 2006)
Milk is sterile following synthesis and secretion in the alveoli of mammary glands (Tolle, 1980) but can be contaminated by microorganisms found in the mammary gland, external surface of the udder and teats, and surface of milking equipment and utensils and expansion tanks (Bramley & McKinnon, 1980)
Summary
Milk is a secretory product of mammary glands and a homogeneous aqueous mixture of compounds, such as proteins, carbohydrates, lipids, minerals, vitamins, and enzymes. Milk is an excellent growth medium for microorganisms since it has a pH close to neutral, high water activity, and rich nutrient content. The larger the population of microorganisms in raw milk, the lower the physical, chemical, microbiological, and sensory qualities of processed fluid milk and dairy products (Singh et al, 2011). Considering the dairy industry in Brazil, the cheese market has shown the highest growth rate in recent years, with an emphasis on mozzarella, Prato, Minas Frescal, and curd cheese. In 2019, the production of cheese in Brazil was to amount to 770 thousand metric tons (Mendoza, 2020) and the average per capita consumption stands at 5.1 kg in 2020, including a wide variety of types, flavors, and sizes (Statista, 2020)
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