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Title: Enzymatic antioxidants in potato (Solanum tuberosum L.): Determination of Polyphenol oxidase and Peroxidase activities in different organs
Authors: Kaur, Hardeep
Supervisor: Das, N.
Keywords: Potato (Solanum tuberosum L.) cultivars;Enzymatic antioxidants;Polyphenol oxidase;Peroxidase;Three phase partitioning
Issue Date: 7-Sep-2019
Abstract: Potato is very nutritious and a major non-grain food crop consumed worldwide. It contains biologically active substances that affect the human health positively and reduce degenerative chronic disorders. Although, cutting and peeling of potato induces black or brown pigments of damaged tissues, results from enzymatic browning. This reaction is a result of catalytic conversion of phenolic compounds into quinones by the enzymes namely, polyphenol oxidase (PPO) and peroxidase (POD). PPO uses molecular oxygen (O2) whereas POD uses hydrogen peroxide (H2O2) for oxidation. Both PPO and POD are involved in the ROS defence mechanism and are the crucial part of enzymatic antioxidants. The objectives of the study were a) extraction and estimation of PPO and POD in different organs of potato cultivars at different stages of growth under field conditions along with different storage conditions of the harvested tubers; b) to purify both the enzymes conveniently by simple and rapid three phase partitioning (TPP). The specific activity of PPO and POD was notably higher in mature leaves, stem and tuber in comparison to young leaves, stem and tuber. The specific activities of PPO and POD showed a considerable increasing trend during the storage for 60 days at low temperatures. Prolonged storage at 20ºC was associated with more accumulation of the enzymes as compared to 4ºC and room temperature. Facile TPP method was adopted for purification of the enzymes. The focus was on mainly two parameters such as ammonium sulphate concentrations and crude to t-butanol ratios. 40% ammonium sulphate concentration and 1:1 crude to t-butanol ratio worked effectively for PPO where, the enzyme was purified up to 1.64 fold (with 96% recovery) and 2.73 fold (with 86% recovery) for the cultivars CS-1 and DE, respectively. Whereas 50% ammonium sulphate concentration and 1:0.67 crude to t-butanol ratio worked well for POD. In this case, the enzyme was purified up to 3.21 fold (with 95% recovery) and 1.98 fold (with 134% recovery) for the cultivars CS-1 and DE, respectively. Molecular weight of the TPP-purified PPO and POD subunits were found to be in the range of 20-25 kDa as revealed by SDS-PAGE
Description: MSc Biochemistry thesis
Appears in Collections:Masters Theses@SCBC

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