39B-3

J. M. LEE¹, R. E. Wrolstad, and R. W. Durst. (1) Food Science and Technology, Oregon State University, 100 Wiegand Hall, Corvallis, OR 97331-6602

JUSTIFICATION: There is intense interest in the possible health benefits of blueberries and blueberry products, because of their high antioxidant capacity, which is related to anthocyanin and polyphenolic content. While there has been considerable effort in measuring the antioxidant capacity of many Vaccinium species, less attention has been given to compositional changes from processing. Due to native polyphenoloxidase (PPO), anthocyanins and polyphenolics undergo significant degradation when the fruit is processed into juice concentrate.

OBJECTIVES: The objective of this study was to compare the effectiveness of heat and sulfur dioxide (SO₂), in the inactivation of native PPO in pasteurized juice and concentrate.

METHODS: Frozen blueberries (Vaccinium corymbosum, v. Rubel) were pilot-plant processed into juice, and concentrate, by two treatments and a control. Control fruits were thawed, crushed, depectinized, pressed, filtered, pasteurized, and concentrated. Heat treatment procedure differed only in that the thawed blueberries were immediately heated to 95C and cooled to 38C. SO₂ treatment differed by additions of SO₂ during thawing and crushing (total of 100ppm). All three trials were replicated. Samples were taken from each step of juice processing after crushing for analysis. Anthocyanins and polyphenolics were separated by reverse-phase HPLC. Determination of total monomeric anthocyanin content, % polymeric, and color measurements (CIEL*a*b*) were also performed.

RESULTS: Pressed juice yield ranged from 74 to 83% (w/w), but only 15-29% of the frozen blueberry anthocyanins were recovered in the pasteurized juice. Measurements of total and individual anthocyanins and polyphenolics in samples showed a great loss after the thawing, crushing, and depectinization steps of the three trials. Heat and SO₂ treated samples were higher in anthocyanins and polyphenolics. A substantial amount of anthocyanins were present in the presscake (>40% of anthocyanin of fresh fruit).

SIGNIFICANCE: The findings will be useful to processors wishing to improve the final yield of flavonoids in their blueberry products.