Changes occurring in stabilized ultra-high-temperature-treated whole milk during storage

Area of Science:

• Dairy Science
• Food Chemistry
• Microbiology

Background:

• Ultra-high temperature (UHT) treatment extends milk shelf-life but can impact milk components.
• Casein and free fatty acids (FFAs) are key components affecting UHT milk quality during storage.
• Understanding the degradation rates of these components is crucial for predicting shelf-life and quality.

Purpose of the Study:

• To investigate the relationship between casein, FFAs, and storage time in UHT whole milk.
• To estimate the daily rate of casein degradation in UHT whole milk.
• To determine the total time for complete casein degradation.

Main Methods:

• Samples of UHT whole milk were collected over a 120-day period.
• Raw milk quality was assessed via total mesophilic (TMC), psychrotrophic (TPC), and somatic cell counts (SCC).
• UHT milk composition was analyzed for fat, sialic acid, casein, and FFA content.

Main Results:

• A significant negative correlation was found between casein content and storage time (r = -0.991).
• A significant positive correlation was observed between FFA content and storage time (r = 0.962).
• The estimated daily rate of casein hydrolysis was 0.021 g/100 g, with complete degradation predicted by day 560.

Conclusions:

• Microbiological quality and SCC of raw milk are critical factors influencing casein and lipid integrity in UHT milk.
• The degradation of casein and the increase in FFAs are directly linked to the storage duration of UHT milk.
• These findings contribute to a better understanding of UHT milk stability and shelf-life prediction.