Thermal processing affecting phytochemical contents and total antioxidant capacity in broccoli (Brassica oleraceaL.)

Abstract

Broccoli is increasing consumed with phytochemicals level. Thermal processing may alter food antioxidant properties by initiating destruction, release or transformation of antioxidant components. Effects of thermal processing methods (boiling, steaming, stir-frying, microwaving, and baking) and duration on antioxidants and total antioxidant capacity (TAC) in broccoli florets have been estimated. Boiling 2 min, steaming 4 min, stir-frying 6 min, microwaving 2 min, and baking 25 min were optimized according to sensory quality evaluation and total ascorbic acids (TAA) retention. Stir-frying resulted in highest total phenolic content (TPC) and total flavonoid content (TFC) with increasing by 47.56 and 67.93%, respectively, followed by boiling (increasing by 28.25 and 44.93%, respectively) and steaming (increasing by 24.90 and 27.49%, respectively). Boiling, steaming, and stir-frying significantly elevated TAC values. Strong positive correlations between TAC and TPC and TFC were found. TAA drastically deteriorated regardless of processing methods. Microwaving and baking displayed destructive effect on broccoli quality. Practical applications Most vegetables have to be thermal processed before eating. It is important to optimize processing methods and duration to promote beneficial effects and to counteract, to the best possible, undesired effects. This study has optimized five common thermal processing methods (boiling, steaming, stir-frying, microwaving, and baking) and duration of broccoli florets. Meanwhile, the effect of these thermal processing methods at defined duration on antioxidants and total antioxidant capacity was estimated. Data obtained are expected to offer both modern food industry and consumers optimum conventional processing methods with the highest nutrients retention in vegetables.