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Application of thermal inactivation of enzymes during vitamin C analysis to study the influence of acidification, crushing and blanching on vitamin C stability in Broccoli (Brassica oleracea L var. italica)

Munyaka, Ann Wambui, Oey, Indrawati, Van Loey, Ann, Hendrickx, Marc
Food chemistry 2010 v.120 no.2 pp. 591-598
ascorbic acid, enzyme inactivation, food analysis, food composition, heat inactivation, broccoli, acidification, crushing, blanching, ascorbate oxidase, extraction, pH, florets, stems, dehydroascorbic acid, temperature, food nutrient losses, food matrix
The effectiveness of heat inactivation of oxidative enzymes e.g., ascorbic acid oxidase (AAO) to stabilise vitamin C during extraction and analysis was evaluated. The influence of different sequences of performing treatments including acidification (pH 4.3 vs. pH 6.5), crushing, high temperature short time (90°C/4min-HTST) and low temperature long time (60°C/40min-LTLT)) blanching on vitamin C stability in broccoli florets and stalks was also investigated. Heat inactivation of enzymes prior to matrix disruption resulted in higher vitamin C values mainly in L-ascorbic acid (L-AA) form, while lack of enzyme inactivation resulted in high vitamin C losses resulting from conversion of L-AA to dehydroascorbic acid. Various treatments and their sequence of application influenced vitamin C stability as follows: (i) crushing prior to blanching reduced vitamin C stability and (ii) in the absence of heating, acidification increased vitamin C stability (iii) blanching prior to crushing resulted in higher vitamin C retention, with HTST blanching retaining more vitamin C than LTLT blanching.