Abstract
Milk is generally very rich in nutrients and this may lead it to be an ideal growth environment for many microorganisms, including pathogens, so effective measurements aiming to ensure total microbiological safety of milk and minimize the risk to human health are needed. Milk heat treatments are the most common practices carried out to inhibit the microbial growth; therefore it is necessary to have analytical procedures that are more and more up-to-date and capable of detecting the effectiveness of the heat treatments. Most of the reference and official methods to assess heat treatment in milk are based on the evaluation of the modifications of some milk components following the thermal process, such as the determination of enzyme activities (alkaline phosphatase and lactoperoxidase), whey proteins, Maillard reaction compounds (generally furosine), and lactulose. Besides the most common techniques (liquid and gas chromatography, capillary electrophoresis, or spectroscopy) used for the detection of single thermal indicators, new approaches, such as chemometric studies or more recent techniques, including size-exclusion chromatography with online electrospray mass spectrometry or stable isotope ratio mass spectrometry, are discussed in this review in order to evaluate heat treatment in milk.
Highlights
Milk is a food item rich in nutrients; it is source of essential amino acids and has significant amounts of vitamins and minerals, calcium
Ultra High Temperature (UHT) treatment must be carried out: (i) involving a continuous flow of heat at a high temperature for a short time, so that no viable microorganisms or spores are capable of growing in the UHT food when it is stored in an aseptic closed container at room temperature and (ii) in order to ensure a microbiological stability of the food after incubating for 15 days at 30∘C in closed containers or for 7 days at 55∘C in closed containers or after any other method demonstrating that the heat treatment has been successful
The main conclusions of this study showed that heat treatment damage occurring in milk can be evaluated through several closely related indexes: in particular, β-LG is a good index for mild treatments, which resulted in the formation of low amounts of lactulose and HMF
Summary
Milk is a food item rich in nutrients; it is source of essential amino acids and has significant amounts of vitamins and minerals, calcium. Due to this high nutrient content and its low acidity, milk is an ideal growth environment for many microorganisms, resulting in a perishable and very spoiling commodity. Pasteurization must be carried out by (i) a high temperature for a short time (at least 72∘C for 15 seconds); (ii) a low temperature for a long time (at least 63∘C for 30 minutes); or (iii) any other combination of time-temperature conditions to obtain an equivalent effect, such that foods show negative reaction to alkaline phosphatase immediately after the heat treatment. Ultra High Temperature (UHT) treatment must be carried out: (i) involving a continuous flow of heat at a high temperature for a short time (not less than 135∘C in combination with a suitable holding time), so that no viable microorganisms or spores are capable of growing in the UHT food when it is stored in an aseptic closed container at room temperature and (ii) in order to ensure a microbiological stability of the food after incubating for 15 days at 30∘C in closed containers or for 7 days at 55∘C in closed containers or after any other method demonstrating that the heat treatment has been successful
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