Peroxidase as indicator enzyme of blanching in bottle gourd ( Lagenaria siceraria ): Changes in enzyme activity, color, and morphological properties during blanching

Abstract

This study investigated the effect of ohmic and conventional blanching on different characteristics of bottle gourd. The varying temperature–time combinations (60–90°C for 1–5 min) were used and optimum temperature–time of blanching was selected according to peroxidase activity and color retention. Residual peroxidase activity reached a level of no detection at 80°C for 4 min in ohmic blanching and 90°C for 5 min in conventional blanching. Ohmic blanching (80°C—4 min) was more effective than conventional blanching (90°C—5 min) at lesser temperature–time combinations. The temperature dependence of enzyme inactivation followed first-order reaction with R2 ranging from 0.955 to 0.997 in all temperature ranges. Increase in blanching temperature led to increase in rate constant, k from 0.26 to 2.6 at 60 to 90○C in conventional blanching and 0.30–1.6 at 60 to 80○C, respectively, in ohmic blanching. Color of blanched samples was well retained in both conventional and ohmic blanched samples as compared to control sample. Hue angle (h○) and (−a*) values of blanched samples increased with increasing temperature and time of blanching. Minimum browning index was observed in ohmically blanched (BO) samples. Microstructural and textural study of bottle gourd cubes blanched under optimized conditions (80°C—4 min; 90°C—5 min) were studied. Ohmic blanching was found more pronounced in faster degradation of residual enzyme activity and retention of color. Laser diffraction analysis of BO samples of bottle gourd showed highest decrease in particle size. Losses in functional properties were more pronounced in conventional blanched samples. Practical applications Consumer demand for bottle gourd juice (BGJ) owing to its high nutritional value and pharmacological benefits has led emphasis on improving its quality and market value. However, due to high enzymatic activity BGJ turn brown that appears to be unacceptable and leads to loss of market value. Peroxidases being high heat-resistant enzymes can act as potential trace markers for complete enzyme inactivation. Moreover, retention of color without much degradation to nutritional quality need to be assessed for increasing benefits and maximum returns.