Psychrotrophic bacteria in milk and their negative effects on dairy products quality: A review

Abstract

The autochthonous microbiota of raw milk immediately after milking generallycomprises lactic acid bacteria such as Lactococcus, Lactobacillus, Streptococcus,and Leuconostocspecies, which are technologically important for the dairy industry. Raw milk is usually stored at coldtemperatures (about 4°C) before processing to reduce the growth of most bacteria.However, psychrotrophic bacteria can proliferate and contribute to spoilage of ultrahigh temperature (UHT) treated and sterilized milk and other dairy products during cold storage, due to their ability to produce extracellular heat resistant enzymes such aspeptidases and lipase these enzymes are responsible of spoilage caused by visible or non-visible defects and lead to significant food waste and economic losses. Psychrotrophic bacteria have developed diverse ways of adaptation to cold environment, from cell envelope and enzyme adaptation, to cryoprotectant and chaperone production, and novel metabolic capabilities. Several methods are implemented to prevent and control such contaminations. Prevention methods include good manufacturing and hygiene practices, air filtration, and decontamination systems, while control methods include inactivation treatments, temperature control, biopreservation and refrigeration.