High-heat treatments are most effective in releasing antioxidants into blueberry juice.

The importance of blueberries as a major source of antioxidants is well known. For example, USDA research has shown that polyphenolic compounds in blueberries can extend life spans in whole organisms under certain conditions, possibly by protecting cells against dysfunction due to heat stress during aging. The health benefits of blueberries have led processors to seek more effective ways of maintaining levels of antioxidants in processed blueberry products. With the availability of new processing techniques, such as the microwave, it is important to determine the most effective techniques for optimizing antioxidants and product quality.

Scientists at North Carolina State University wanted to determine the effects of various process technologies on antioxidants and the quality of blueberries. They found that rapid heating techniques may be more effective in protecting the antioxidant content of juices without causing changes in the quality of the product.

In tests, two Rabitteye varieties--Tifblue and Powder Blue--along with cultivars of Highbush blueberries were obtained from a university research farm and frozen at -20 C. The researchers thawed and processed the blueberries into juices using four different processing methods: the microwave, cold processing, hot processing and pasteurization. Samples were liquidified. Scientists added pectinase and processed the samples into juices.

After processing the samples, the investigators measured the antioxidant activity and the quality of the juices by determining total phenol (TP), oxygen radical absorbance capacity (ORAC) and total anthocyanin levels immediately and after the products were placed in chilled storage at 3 C for 30 days.

The Rabitteye varieties contained a higher level of antioxidants than any of the Highbush varieties. The higher heat treatments, such as pasteurization followed by microwaving, were most effective in releasing antioxidants into the juices. The investigators observed this trend in juices and their wines in which Powder Blue followed by Tifblue Blue, Croatian, Reveille, Premiere and Pender showed decreasing levels of antioxidants. The refrigerated storage of juices over a period of 30 days caused no major decreases in antioxidant activity or changes in anthocyanin levels.

The research on blueberries is continuing, as is research on muscadine. Scientists are examining the effects of processing on antioxidant retention in the two commodities.

Further information. Leon Boyd, Department of Food Science, North Carolina State University, Schaub Hall, Box 7624, Raleigh, NC 27695; phone: [phone]; fax: [phone]; email: [e-mail].