The hydrostatic pressure processing developed by researcher Michael Qianand his team at Oregon State Universityalso does not introduce any off-flavors in the milk, they claim. The studycould providemanufacturers with a substitute technique for thermal processing, the mainmethod used by processors to achieve microbial safety and shelf-lifestability of milk.
Although high-temperature-short-time (HTST) pasteurization is typicallyused commercially to process milk, the product shelf life is only 20 days atrefrigeration temperatures.Meanwhile ultrahigh-temperature pasteurization allows milk to stay fresh atroom temperature for six months -- but also leaves a "cooked" flavorbehind.
By contrast the team's hydrostatic method gives milk a shelf life atrefrigerated temperature of at least 45days, Qian claims.
High hydrostatic pressure processing (HPP), can destroymicroorganisms by high hydrostatic pressure without heat.The technology has been gaining commercial acceptance in the manufacture offood products with "fresh" flavor that are not possible with otherpreservation technologies,they say.
"Milk processed at a pressure of about 85,000 pounds per square inchfor five minutes, and lower temperatures than used in commercialpasteurization,causes minimal production of chemical compounds responsible for the cookedflavor," the researchersreported in a paper to be published in the November 29 issue of the Journalof Agricultural and Food Chemistry.
They noted that HPP has been reported to change some properties of thefoods. HPP can reduce the size of casein micelles in milk at pressures above230 MPa, resulting in a decrease in whiteness and turbidity and an increasein the viscosity of milk.
High pressure can also affect the crystallization properties of milkfat. The crystallization behavior of milk fat can be altered because thehigh pressure will shift the phase transition temperature.
The objective of their study was to investigate volatile generation inmilk under high pressure and moderate temperature and to compare thevolatile formation with that formed under atmospheric pressure conditions atcomparable temperature.
Other new technologies are being developed to process milk withoutcompromising its flavor, theynoted. Several nonthermal processing technologies have been explored toachieve microbial safety and minimize off-flavor formation.
Microfiltration using cross-flow membrane separation has showedpromising results in eliminating bacteria from milk and increasing shelflife without the development of off-flavors. However, high levels of milkfat could foul the membrane and place some restrictions on the use ofmicrofiltration as an alternative technique for milk processing.