Degradation of Polyphenolic Antioxidants in Blueberry Nectar Aseptically Filled in PET

Kajetan Trošt, Alenka Golc-Wondra,* Mirko Prošek

Laboratory for Food Chemistry, National Institute of Chemistry, Slovenia, Hajdrihova 19, 1001 Ljubljana, Slovenia
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One of the conservation processes for blueberry preservation is aseptic filling of blueberry nectar in PET packaging. As virgin PET exhibits a low oxygen barrier, oxygen scavengers can be added to multi-layer bottles that sandwich a barrier plastic between layers of PET or simply mixed with PET to add barrier properties. As polyphenolic antioxidants are known to positively influence human health, stability determination is crucial. This study shows changes in total polyphenol oncentrations and total and individual anthocyanin concentrations showing antioxidant activity. A stability scale for individual anthocyanins was made. Since oxygen can destroy the antioxidant ability of polyphenols, various methods of protecting against oxidation were used and characterized by a gradient HPLC-Vis technique. Total polyphenol analyses and antioxidant activity analyses were carried out using spectrophotometric measurements. During 9 months of blueberry nectar storage there was a 3–9.9% decrease in polyphenol concentrations and antioxidant activity decreased by 20.9–24.2%. The biggest drop was seen among anthocyanins, whose concentration decreased by 78–84% of total anthocyanins. Among the quantified anthocyanins, cyanidin 3-glucoside and cyanidin 3-galactoside were the most stable, while malvidin 3-arabinoside was the least stable. The packaging that offered the least protection was the virgin PET bottle without oxygen protection. Antioxidant activity analyses suggest that a three-layer multilayer bottle is the packaging that gives the best protection to the product.

Keywords: Blueberry nectar, antioxidants, barrier PET, anthocyanins, HPLC-VIS