Effect of fuzzy-controlled slow freezing on pumpkin (Cucurbita Moschata Duch) cell disintegration and phenolics

Abstract

Freezing has been widely used to preserve vegetables including seasonal pumpkins. This work aimed to investigate the effects of freezing on pumpkin cell disintegration and phenolics. A fuzzy logic control (FLC) system was built to obtain better temperature control of the freezing system. Changes in cellular disintegration, electrical conductivity and phenolics content were evaluated. The angle measure technique and principal component analysis were used to delineate the surface texture changes of the frozen pumpkin cells. The results showed that FLC offered reliable temperature control performance. Freezing at -18 °C for 7 h caused the highest cell degradation of 0.467 on the disintegration scale. Decomposition was also indicated by an almost double increase in electrical conductivity. The changes in texture were accurately reflected in the mean angle spectra and 81.3% and 7.4% of the variability due to treatments could be explained by two principal components respectively. Freezing pumpkin at -18 °C for 6 h correlated to the maximum increase in total phenolics of 70.44%. The increased phenolics were dominated by caffeic acid, chlorogenic acid and p-coumaric acid. In conclusion, as the freezing system exhibits positive effects on the phenolics content of pumpkin, it may be employed to process seasonal pumpkin to obtain higher value from the produce.