USA - Pressure processing improves milk, say researchers
Published:November 21, 2006
Source :Dairy Reporter
A high pressure processing technique retains a fresh taste while at the same time killing bacteria and extending shelf life in products such as milk, say US researchers.
The hydrostatic pressure processing developed by researcher Michael Qian and his team at Oregon State University also does not introduce any off-flavors in the milk, they claim. The study could provide manufacturers with a substitute technique for thermal processing, the main method used by processors to achieve microbial safety and shelf-life stability of milk.
Although high-temperature-short-time (HTST) pasteurization is typically used commercially to process milk, the product shelf life is only 20 days at refrigeration temperatures. Meanwhile ultrahigh-temperature pasteurization allows milk to stay fresh at room temperature for six months -- but also leaves a "cooked" flavor behind.
By contrast the team's hydrostatic method gives milk a shelf life at refrigerated temperature of at least 45 days, Qian claims.
High hydrostatic pressure processing (HPP), can destroy microorganisms by high hydrostatic pressure without heat. The technology has been gaining commercial acceptance in the manufacture of food products with "fresh" flavor that are not possible with other preservation technologies, they say.
"Milk processed at a pressure of about 85,000 pounds per square inch for five minutes, and lower temperatures than used in commercial pasteurization, causes minimal production of chemical compounds responsible for the cooked flavor," the researchers reported in a paper to be published in the November 29 issue of the Journal of Agricultural and Food Chemistry.
They noted that HPP has been reported to change some properties of the foods. HPP can reduce the size of casein micelles in milk at pressures above 230 MPa, resulting in a decrease in whiteness and turbidity and an increase in the viscosity of milk.
High pressure can also affect the crystallization properties of milk fat. The crystallization behavior of milk fat can be altered because the high pressure will shift the phase transition temperature.
The objective of their study was to investigate volatile generation in milk under high pressure and moderate temperature and to compare the volatile formation with that formed under atmospheric pressure conditions at comparable temperature.
Other new technologies are being developed to process milk without compromising its flavor, they noted. Several nonthermal processing technologies have been explored to achieve microbial safety and minimize off-flavor formation.
Microfiltration using cross-flow membrane separation has showed promising results in eliminating bacteria from milk and increasing shelf life without the development of off-flavors. However, high levels of milk fat could foul the membrane and place some restrictions on the use of microfiltration as an alternative technique for milk processing.
