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Subpasteurization Heat Treatment to Inactivate Lipase and Control Bacterial Growth in Raw Milk.

G F Senyk1, R R Zall1, W F Shipe1

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Heat treating raw milk significantly reduces lipase activity and bacterial growth. Even mild heat treatments inhibit milk lipase and lower standard plate and psychrotrophic bacteria counts during storage.

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Area of Science:

  • Food Science
  • Dairy Microbiology
  • Food Preservation

Background:

  • Raw milk contains lipase enzymes and bacteria that can proliferate during storage.
  • These factors affect milk quality and shelf-life.
  • Understanding the impact of heat treatment is crucial for dairy processing.

Purpose of the Study:

  • To evaluate the effect of subpasteurization and suprapasteurization heat treatments on raw milk lipase activity.
  • To assess the impact of heat treatment on bacterial growth (Standard Plate Count and Psychrotrophic Bacteria Count) in raw milk during refrigerated storage.
  • To determine the efficacy of different heat treatment conditions in controlling microbial load and enzymatic activity.

Main Methods:

  • Raw milk was subjected to various heat treatments (57.2°C to 82.2°C for 10 seconds).
  • Milk lipase activity and bacterial counts (Standard Plate Count, Psychrotrophic Bacteria Count) were measured before and after heat treatment.
  • Samples were stored at 4.4°C and 6.7°C for up to 72 hours to monitor changes.

Main Results:

  • Heat treatments ranging from 57.2°C to 73.9°C for 10 seconds inhibited milk lipase activity by 42% to 98%.
  • Standard Plate Counts after 72 hours at 6.7°C were significantly reduced in heat-treated milk compared to unheated milk.
  • Psychrotrophic Bacteria Counts were also substantially lower in heated milk samples after 72 hours of storage.

Conclusions:

  • Heat treatment of raw milk effectively limits milk lipase activity.
  • Heat treatment significantly reduces the growth of bacteria, including psychrotrophic bacteria, during refrigerated storage.
  • Implementing heat treatment for raw milk supplies can enhance milk quality and extend shelf-life by controlling enzymatic and microbial spoilage.