Pressure processing retains ‘fresh’ milk taste, extends shelf life

December 13, 2006

CORVALLIS, Ore. – New processing techniques for dairy milk are resulting in a “fresher” taste and a shelf life that outlasts conventional processing by more than 30 days. If commercialized, the technique could help local dairies find larger markets for their product while maintaining their high quality standards.

Researchers in Oregon State University’s Department of Food Science and Technology are using an emerging high-pressure technology to process milk at lower temperatures while still maintaining the safety of heat-pasteurized milk. The result is safe milk that tastes fresher and has a longer shelf life than conventionally processed milk.

A recent report on the flavor impact of high hydrostatic pressure processing combined with low to moderate heat appeared in the Journal of Agricultural and Food Chemistry.

The use of high or ultra-high temperature pasteurization to kill microbes in milk results in a safe product, but also a heat-damaged product, said Michael Qian, one of the primary researchers on the project. Using high pressure to kill bacteria requires less heat and results in a less-processed flavor that is similar to farm-fresh milk.

“The flavor of milk is a product of its chemical properties,” said Qian. “Under ultra-high temperature pasteurization the chemical composition changes, sometimes resulting in a cooked or burned flavor that may be unappealing to some consumers.”

This cooked flavor is representative of most milk processed and sold in other countries, but its cooked flavor has been largely unpopular in the U.S., said Qian. Even milk pasteurized at a moderate temperature can undergo a flavor change.

“A lot of the time consumers don’t realize what they are tasting is a result of the processing technique, not the milk itself,” he said. “The level of heat used during processing is one of the reasons different brands of milk taste differently.”

Many of the brands of milk sold in stores today are labeled as ultra-pasteurized meaning they’ve been heated at higher temperatures or for longer periods of time in order to kill bacteria, said J. Antonio Torres, a food scientist in OSU’s College of Agricultural Sciences.

“Ultra is not better, it’s worse,” he said. “More vitamins are destroyed and more taste is lost the longer the milk is held at excessively high temperatures.”

There is an inverse relationship between pressure and temperature in milk processing, Torres added, with greater pressure levels using less heat during processing. This discovery has led to a request for federal funds to demonstrate the technology’s use with other foods.

The success of high pressure in killing microbes has been extensively studied, but the OSU researchers, including Pedro Vazquez-Landaverde, are some of the first scientists to study the technology’s effect on flavor, said Qian.

Conventionally pasteurized milk can usually stay under refrigerated conditions for about 15-20 days before spoiling. Pressure processing can result in a refrigerated shelf life of more than 45 days, possibly resulting in new business opportunities.

“Around the nation there are certain milk producing regions that produce a surplus of milk,” said Torres. “This technology could help dairies that have a low-cost of milk production get their product to areas that are unable to produce the needed volume of milk. A dairy in California could ship its milk to New York.”

Organic dairies are areas of the industry that could see some of the greatest benefit from the technology, said Torres. Organic milk is one of the fastest growing divisions of the dairy industry, but consumers who favor the product remain fairly wide spread. If organic milk can be processed using pressure at a price that is economically feasible, dairies could significantly grow their markets.

Milk processed under pressure could be commercially available within 3-5 years if it’s made cost-effective for the industry, said Torres. The technique is already being used with other products and in other industries as a means of microbial control.

The research was paid for through funds collected from milk producers and distributed by Dairy Management Inc.

Author: Aimee Brown
Source: Michael Qian, Antonio Torres