Improved stability of blueberry juice anthocyanins by acidification and refrigeration

Abstract

BACKGROUND: Blueberry anthocyanins are susceptible to degradation during juice processing and storage of juice at ambient temperature. Methods are needed to stabilize the health-promoting anthocyanins in blueberry and other anthocyanin-rich berry juices. OBJECTIVE: In this study we determined the effect of acidification (pH 2.1, 2.5 and 2.9) of blueberry juice on changes in anthocyanins and percent polymeric color in response to juice processing and during eight months of storage at ambient and refrigerated temperatures. METHODS: Three subsamples of non-pasteurized blueberry juice were adjusted to three pH levels: 2.9 (control, no pH adjustment), 2.5, and 2.1. After pH adjustment, juices were pasteurized and placed in storage at 4 and 25°C. Samples were analyzed before (non-pasteurized) and after pasteurization, and after 2, 4, 6, and 8 months of storage at each temperature (4 and 25°C) for anthocyanin composition by HPLC and percent polymeric color. RESULTS: Blueberry juice acidified to pH 2.1 retained higher levels of total anthocyanins and had lower percent polymeric color values than juice acidified to pH 2.5 and control juice (pH 2.9) following pasteurization. Anthocyanin arabinosides were more susceptible to thermal degradation than glucosides, galactosides and acetylated derivatives. Levels of total anthocyanins declined markedly over 8 months of storage, but juices stored at 4°C had on average 56 higher levels of total anthocyanins than juices stored at 25°C. Juice acidified to pH 2.1 had on average 12 and 26 higher levels of total anthocyanins than pH 2.5 and control juices, respectively. After 8 months of storage, juice acidified to pH 2.1 had 11 and 22 higher levels of total anthocyanins than pH 2.5 and control juices stored at 4°C, and 26 and 59 higher levels of total anthocyanins than pH 2.5 and control juices stored at 25°C. Acetylated derivatives were more prone to losses during storage than glycosides, especially in acidified juices. CONCLUSIONS: Acidification of blueberry juice coupled with refrigerated storage are effective treatments to retain health-promoting anthocyanins.