Studies On The Effects And Mechanisms Of High Pressure Inert Gas Treatments On The Shelf-life Of Fresh-cut Pineapple And Apple During Cold Storage

Quick rhythm and high-quality lifestyles of modern consumers, along with the desire for health, have been responsible for the current rise of production and consumption of fresh-cut fruits and vegetables. These fruits and vegetables combine their fresh-like and healthy characteristics with a minimal time of preparation before consumption both at the consumer and catering levels. However, it is difficult to preserve the quality of fresh-cut fruits and vegetables. The fresh-cut process heightens respiration rate and wound-induced C2H4 production and activates more enzymatic reactions, which accelerate ripeness, senescence and deterioration of fresh-cut products. The process also increases the exposure of surface area per unit volume to external factors and the release of nutrients leading to microbial growth. Many common method of preserving food are not effective in improve the quality of fresh-cut products at storage. Studying novel methods of extending the shelf life of fresh-cut products is necessary for industrial development of fresh-cut products. In this study, fresh-cut pineapples and apples were treated by pressurized inert gas such as argon, xenon and nitrogen. The effect of these treatments on physiological and physical aspects, the quality parameters and microbial growth of fresh-cut pineapples and apples are investigated for further research and application of the novel technique.Fresh-cut pineapples and apples were treated by high pressure (HP) argon (Ar), nitrogen (N) and their mix (Ar+ N). The effects of the treatments on changes in respiration rate, ethylene production, browning, the activities of enzyme, nutrient ingredient, sensory attributies and microbial growth of these fresh-cut fruits were investigated. Respiration rate and ethylene production of fresh-cut apples treated by the HP Ar, N and (Ar+ N) were lower apparently in comparison with those untreated. HP Ar, N and (Ar+ N) treatments inhibited the activity of PAL, PPO and POD enzyme and delayed browning and microbial growth of these fresh-cut fruits. They did not affect the content of titrated acidity and soluble solids, effectively reduced the loss of total phenol and ascorbic acid and maintained antioxidant capacity. HP Ar treatments had greater effects than HP N or HP (Ar+ N) treatments. It is because argon has better water solubility than nitrogen and more argon gas hydrate was formed during HP operation. However, HP operation have caused the negative effects on the firmness to some degree.The effects of treatment temperature, time and pressure on the efficiency of pressurized Ar treatment for fresh-cut pineapples was studied to determine the optimum conditions. The application of HP Ar treatment under 1.6-2.2 MPa at 2-6℃for 43-65 min was found to offer optimum processing conditions for fresh-cut pineapples. Samples treated at optimum condition were stored at 4℃for 20 days to evaluate the effect of HP Ar treatment on nutritional components, microbial growth, sensory quality, membrane permeability and microstructure. HP Ar treatment effectively maintained the quality of pineapple slices and delayed the microbial growth. An extension of shelf life by 6 days during cold storage was achieved by applying HP Ar treatment. Fresh-cut apples were treated by ultra HP (150 MPa) Ar. The efficiency of ultra HP Ar treatment for preserving fresh-cut apples was investigated. Ultra HP Ar treatment effectively delayed browning and microbial growth of fresh-cut apples at cold storage. However, ultra HP operation have caused the negative effects on the color and firmness to some degree. The combination treatment between ultra HP Ar and dipping in solutions (0.5% ascorbic acid, 0.5% citric acid and 0.5% calcium chloride) showed a better alternative and remained good sensory attributes of fresh-cut apples for 12 days at 4°C.Fresh-cut apples and pineapples were treated by HP Xe or HP Ar and Xe (Ar:Xe = 2:9 partial pressure) mixture (Ar+ Xe). The effects and mechanisms involved in HP Ar and Xe mixed treatment on wound healing ability in fresh-cut apples and pineapples were investigated. Results showed that the HP Xe or HP (Ar+ Xe) treatment promoted the wound-healing response and enhanced resistance against the infection of E. coli or S. cerevisiae in fresh-cut apples and pineapples. The enhanced wound healing ability in fruit pieces subjected to HP Xe or HP (Ar+ Xe) treatment is found to be associated with the increase in H2O2 production and the accumulation of phenolics and lignin during storage after treatment.