Effects of Blanching on Browning Enzyme Inactivation and Color of Pumpkins (Cucurbita moschata D.)

Abstract

The presence of polyphenol oxidase (PPO) impairs the quality of prepared fruits and vegetables and limits their commercialization in the market. Therefore, this study investigated effects of conventional blanching at 80-90 °C for 60-240 s on PPO inactivation and color of pumpkin sticks and slices. Fresh pumpkin was rich in nutrition (9.70±0.48 % protein, 0.14±0.01 % fat, 4.13±0.04 % ash, 7.68±0.38 % crude fiber, 78.35±0.82 % carbohydrate and 117.42±1.70 mg/100 g carotenoid); however, the intense PPO activity (62.54±3.09 U/g dry matter) implied it was prone to browning reactions. The results demonstrated that PPO activity from pumpkins decreased with the increasing blanching temperature and time. PPO inactivation kinetics followed the first-order model with large determination coefficients (R2 = 0.81-0.97) and recorded kinetic parameters at 90 °C were k = 130.49±21.28x10-4 s-1, D = 179±27 s, Ea = 152±33 kJ.mol-1, and z = 13.61±0.76 °C (pumpkin sticks); or k = 142.82±17.84x10-4 s-1, D = 163±22 s, Ea = 91±22 kJ.mol-1, and z = 10.84±0.88 °C (pumpkin slices). These findings indicated that pumpkin slices were more sensitive to temperature increase than pumpkin sticks; however, the D values showed no significant differences (p > 0.05). The surface color of pumpkins was also reduced significantly during blanching, with a higher color retain in pumpkin slices (L* = 84 %, a = 61 %, and b = 74 % of its initial values).