High-pressure processing causes changes in raw milk.

The interest in using high-pressure processing (HPP) on dairy products has recently increased. Many advantages to using this technology have been demonstrated by scientists, including its ability to preserve nutrients and improve shelflife and the functional performance of the end product.

However, additional information on color, flavor and any rheological changes that might occur would be beneficial in expanding potential applications of HPP. The goals of scientists at the University of Florida were to measure the reduction in microbial numbers in raw milk after processing the milk under different HPP conditions. They also wanted to evaluate changes in the color, smell and rheology of the product that might occur as a result of HPP processing, and compare HP-processed milk with pasteurized milk.

The researchers obtained raw milk from the Dairy Research Unit at the university. They vacuum-packed 300 ml of raw milk, which was pressurized at 100, 350 and 600 MPa for 5 minutes in a commercial system. The investigators checked the samples for total plate counts. Images of the samples were taken with a machine vision system before and after they were processed. A white reference tile was included in the images for calibration purposes.

Colors were analyzed and average color values were calculated. Aroma profile analysis was conducted using a commercial electronic nose. Discriminant analysis was performed with commercial software. Large deformation mechanical rheology was also conducted.

The researchers found that HPP caused several changes in the milk. Color values decreased as pressure increased. Differences in aroma profiles were demonstrated by discriminant function analysis. Rheological analysis revealed an increase in the viscosity of the milk. Total plate counts showed 2 CFUs at 600 MPa. Such information regarding changes in color, flavor profile and texture, caused by applying high pressure, could help us take greater advantage of HPP as a nonthermal processing technique.

Further information. Murat O. Balaban, Department of Food Science and Human Nutrition, Aquatic Foods Pilot Plant, Room 216, P.O. Box 110370, University of Florida, Gainesville, FL 32611; phone: 352-392-1991; fax: 352-392-4273; email: mobalaban@ifas.ufl.edu.