Kinetics of quality changes of pumpkin (Curcurbita maxima L.) stored under isothermal and non-isothermal frozen conditions

The effects of freezing process and frozen storage at isothermal (-7, -15 and -25 °C) and non-isothermal (accelerated life testing with step-stress methodology; temperature range from -30 to -5 °C) conditions on pumpkin quality were investigated. Storage temperature conditions were selected to embrace the limits practiced in the cold chain. Quality changes, such as texture, colour CIE Lab and vitamin C (ascorbic acid) content, were evaluated for both frozen storage regimes. The freezing process (that included a pre-blanching step) and subsequent frozen storage had significant impacts on all quality parameters analysed. A fractional conversion kinetic model was adequate in colour, texture and vitamin C data fits. The storage temperature effect was successfully described by the Arrhenius law. This study shows that non-isothermal frozen storage has a marked effect on pumpkin quality.