Processing Effects on the Antioxidant Activities of Blueberry Juices

Abstract

The inverse relationship between antioxidant intake and many disease states has been seen repeatedly. The importance of antioxidants has led blueberry processors and other food processors to look for ways to modify processing techniques to optimize the antioxidant levels in the final product. With the availability of new processing methods such as microwaving, it is important to determine the effects emerging process technologies have on antioxidant retention and product quality. The goal of this research was to determine the best processing method available to produce blueberry juice with the highest antioxidant activity.

One experiment examined the effect of cold (22°C) versus hot processing (43°C) of seven cultivars of blueberries using the oxygen radical absorbance capacity (ORAC) and total phenols assays. The results showed that hot processing yielded, on average, a product with 50% more total phenols and antioxidant capacity. A second experiment used ORAC and total phenols to evaluate the effect of cold (22°C), hot (47°C), and pasteurization (90°C) of blended blueberries heated in a steam-jacketed kettle versus microwave heated (85°C, 92.5°C, and 95°C) blended blueberries. The results showed that pasteurization had the highest total phenols and ORAC values, and that the hot processed and microwaved juices had similar values, with the cold processed blueberries having the lowest total phenol and ORAC values. The final study used ORAC, total phenols, and total anthocyanins to evaluate a one month refrigerated (3-5°C) time study on pasteurized (90°C) and microwaved blueberry juices (85°C, 92.5°C, and 95°C). The results again showed that pasteurization was equal to or better than the microwaved treatments. The results also showed that the pasteurized and microwaved samples had stable ORAC and total phenol values, as well as a slight increase in total anthocyanin levels. The implication of this research was that the addition of heat increased the levels of total phenols and ORAC of juices. Addition heat, without sustained boiling, resulted in even higher levels of total phenols and ORAC in blueberry juices.