Effect of whey protein isolate-pullulan edible coatings on the quality and shelf life of freshly roasted and freeze-dried Chinese chestnut

Harvested chestnut is characterized by a short shelf life, exposing many Chinese producers to a storage problem as product losses are very high. The objective of this study was to develop a suitable technology to extent the shelf life of harvested chestnut fruits for commercial use. The effect of whey protein isolate-pullulan (WPI-Pul) coating on fresh-roasted chestnut (FRC) and roasted freeze-dried chestnut (RFDC) quality and shelf life was studied under 2 different storage temperature (4 and 20 degrees C) conditions. Coatings were formed directly onto the surface of the fruits by dipping them into a film solution. SEM micrographs showed homogeneous WPI-Pul to cover the whole surface of chestnut with good adherence and perfect integrity. Moisture loss or gain, fruit quality, and shelf life were evaluated by weight loss or gain, surface color development, and visible decay during the storage period of 15 to 120 d at 4 and 20 degrees C, respectively. WPI-Pul coating had a low, yet significant effect on reducing moisture loss and decay incidence of FRC, hence delaying changes in their external color. The results were satisfactory when the coating was done with freeze-drying at low temperature storage, thus improving the quality and increasing the shelf life. This provides an alternative strategy to minimize the significant losses in harvested chestnut.