UHT Sterilized Milks

ABSTRACT

UHT processing of milk consists of treating the milk at 138–145°C for 2–10s. The process allows attaining commercial sterility with a very minimal impact on the product's nutritional value. The quality, stability, acceptability, and sensorial properties of the products are affected by the combined influence of the quality of the raw milk, processing details, and storage conditions. Detailed information about the mechanisms that govern the evolution and severity of physicochemical instabilities in the final product, such as enzymatic- and non-enzymatic age gelation, sedimentation, and creaming has been established. This understanding highlights the adverse effects of residual activities of heat-stable proteases from psychrotrophic bacteria and plasmin on the quality and stability of UHT milk. These activities, along with the effects of heat treatment and storage temperature on the physicochemical properties, composition, and distribution of milk proteins, as well as the influence of pH and ionic composition, govern the manifestation of the afore-stated instabilities in UHT milk. Ensuring the quality and stability of UHT milk calls for utilizing milk with as low as possible somatic cell counts, maintaining the psychrotrophic bacteria counts of milk as low as possible as well as understanding the effects of the stage in lactation and seasonality of the properties of the raw milk. The sensorial quality of UHT milk reflects the accumulation of different volatile and non-volatile flavor and aroma impacting compounds that originate from the effects of heat treatment and storage conditions on the proteins, carbohydrates, and lipid constituents of milk. It can be also argued that the availability of high-quality and stable UHT milk products is of special importance during the time of disrupted supply chain, such as that during the COVID-19 pandemic of 2020.