Method for Determining the Respiration Rate of Horticultural Produce Under Hyperbaric Treatment

A method was developed to determine the metabolic respiration rate (RR_m) of fresh produce during the transient period at the beginning of a hyperbaric treatment. This method allowed for the correction in the apparent respiration rate (RR_ap) by considering the dilution effect of flushing the system and the error associated with gas solubilisation as the gas partial pressure varied. The dilution process was simulated by using the general equation for exhaust ventilation, thus allowing for the elimination of the dilution effect during the calculation of the net respiration rate (RR_N). The error associated with the CO₂ solubilisation in the flesh of the produce was solved by measuring the CO₂ solubility in the tissues of tomato at various CO₂ partial pressures and using this value to generate a mass balance of CO₂ within the system. The RR_m was estimated by incorporating the initial respiration rate (RR_i) of untreated fruits with the respiration rate at equilibrium (RR_e). The kinetic of the RR_m was proposed to follow a negative exponential equation. The constant value (k) of the RR_m model was found to decrease exponentially with the partial pressure of CO₂ at equilibrium which affected the amount of gas solubilised and the time to reach equilibrium. The developed method should be validated for the RR_m of other produce during the transient period at the beginning of a hyperbaric treatment.     

Effect of hyperbaric pressure and temperature on respiration rates and quality attributes of Boston lettuce

A study was conducted to determine whether hyperbaric treatment has an effect on the shelf life of lettuce during short‐term storage. Lettuce was treated with different pressure and temperature conditions (100–850 kPa at 20 °C and 100 kPa at 4 °C). A preliminary experiment was performed with different treatment periods, that is, 3, 5 and 7 days. Hyperbaric treatment of lettuces at 20 °C caused noticeable changes in sensory quality, but the product was still marketable after 3 days. On the other hand, the cold‐stored lettuce showed little degradation even after 7 days of treatment, at which time all the lettuce treated at 20 °C was unmarketable. At 5 days of treatment, the respiration rate of hyperbaric‐treated lettuces at 625 and 850 kPa remained fairly stable, while that of the lower‐pressure‐treated lettuce began to increase, indicating the initiation of decay. The 850‐kPa hyperbaric treatment showed better quality results than the 100 kPa, 20 °C treatment. Overall, hyperbaric treatment has the potential of being used as an alternative technique for short‐term storage of lettuce without refrigeration.     

Effect of Hyperbaric Pressure Treatment on the Growth and Physiology of Bacteria that Cause Decay in Fruit and Vegetables

The response of bacteria to hyperbaric pressure treatment was investigated. Three selected bacteria which cause fruit and vegetable decay (i.e., Pseudomonas cichorii, Pectobacterium carotovorum, and Pseudomonas marginalis) were inoculated onto BIOLOG microplates and subjected to different pressure and temperature conditions including 100, 200, 400, 625, and 850 kPa at 20 °C and 100 kPa at 4 °C. Changes in microplate color, which corresponds to carbon source utilization of bacteria or their growth, were monitored every 24 h for 7 days. Results showed that the bacterial growth was affected by both hyperbaric pressure and temperature. As hyperbaric pressure increased, the bacterial growth significantly decreased and the extent was dependent on bacterial species. The 850-kPa pressure treatment reduced maximum growth by 71, 56, and 43 % for Pseudomonas cichorii, Pectobacterium carotovorum, and Pseudomonas marginalis, respectively. Among these bacteria, Pseudomonas cichorii was the most pressure-sensitive, while the most temperature-sensitive was Pectobacterium carotovorum. In general, an increase in hyperbaric pressure caused bacteria to utilize carbon sources similar to those when they were exposed to low temperature. Overall, hyperbaric treatment has the potential to directly reduce bacterial growth in fruit and vegetables after harvest.     

A Comparative Study on the Effects of Microwave and High Electric Field Pretreatments on Drying Kinetics and Quality of Mushrooms

This research evaluated the effects of microwave and high-voltage pretreatments on convective freeze drying of mushrooms (Agaricus bisporus) independently. The effect of the microwave (5 W/g for 5 min) and high electric field (HEF; 430 kV/m for 15 min) as pretreatments on enhancement of the drying rates during subsequent drying and the value addition due to the above pretreatments on the quality of the final dehydrated products were investigated. An exponential mathematical model was developed by fitting the drying kinetics to the Page equation to predict the effects of the pretreatments on the drying kinetics of the mushrooms. The parameters considered for the evaluation of product quality project included color, texture, shrinkage properties, and rehydration ratio of the dried mushrooms. The drying rate of HEF-pretreated mushrooms was found to be unaffected overall when compared to the control and the HEF pretreatment resulted in better quality product and less overall shrinkage. Freeze drying of the pretreated mushrooms was found to result in slower drying rate but better overall quality and rehydration ratio.