Studies on Polyphenol Oxidase Activity of Heat Stabilized Whole Wheat Flour and its Chapatti Making Quality

Abstract

Studies were conducted to evaluate the effect of heat treatment on polyphenol oxidase (PPO) activity of whole-wheat flour (WWF) as well as its chapatti making quality. Whole wheat flour samples were heat treated through various means such as (i) dipping in boiling water (BW) for 20, 30, 40, 50, and 60 min; (ii) inpack heating under pressure (PH) at 0.352 kg/cm2 for 4, 6, 8, 10, and 12 min; (iii) microwave heat treatment (MW) at 900 Watt, 2450 MHz for 20, 40, 60, 80, and 100 s. Studies showed that the heat treatment effectively reduced PPO level in whole wheat flour; although, it had adverse effect on the dough-making quality. Based on textural analysis of dough and chapatti as well as sensory scores of chapatti, the conditions for each of the treatments were optimized, i.e., (i) Dipping in boiling water (BW) for 30 min; (ii) inpack heating under pressure (PH) at 0.352 kg/cm2 for 10 min; and (iii) microwave heating (MW) for 80 s. A maximum reduction (71.2%) in PPO activity of WWF using microwave treatment could be achieved followed by PH (56.9%) and BW (38.3%). The changes in colour of unbaked chapattis (flattened circular dough, diameter 150.0 mm and thickness 2.0 mm) and changes in quality of baked chapattis were measured to assess the effectiveness of the heat treatment. The L-value (lightness) decreased from 65.2 to 55.8, 65.7 to 58.3, 65.9 to 61.4, and 64.8 to 49.1 in case of BW, PH, MW treated, and control samples, respectively during the 72 h of storage under refrigeration temperature (5–6°C).