Effect of pectin oligosaccharide on quality control of quick-frozen pumpkin puree

In this work, pectin oligosaccharide (POS) was prepared by an enzymatic method and was used to protect pumpkin puree during frozen storage. The changes in structure and properties of the pumpkin puree during frozen storage were investigated. The results showed that the addition of POS can minimise changes in syneresis rate, total soluble solids, particle size and zeta potential of pumpkin puree during frozen storage. The results of Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) showed that the addition of POS significantly decreased the cavities produced by sublimation of ice crystals and enhanced the continuity of the internal structure of pumpkin puree. Confocal Laser Scanning Microscope (CLSM) results showed that the macromolecules in the quick-frozen pumpkin puree tended to be uniformly distributed during frozen storage with POS added compared with the control sample. In addition, texture was well protected, which allowed the pumpkin puree to maintain a good taste. POS was shown to serve as an antifreeze agent to protect the internal structure of the pumpkin puree during freezing. The optimum concentration to achieve the best anti-freeze effect was 2% POS, which is similar with that of 2% trehalose.