Abstract
Fruits and vegetables are fresh products that are highly perishable and refrigeration is widely applied to extend food shelf-life under postharvest conditions. The main phenomena associated with the refrigeration process are heat and mass transfer, which directly influence food decay. For this reason, the objective of this research is to evaluate the thermal and mass profiles of fresh strawberry and lettuce, under refrigeration. Strawberry and lettuce samples were harvested from a hydroponic system and stored at 5 ± 1 °C for 5 days under low relative humidity conditions (50-60 %). In order to correlate the two main phenomena, the mass transfer and cooling kinetics parameters were quantified. The mass loss results demonstrated a greater reduction for lettuce (21.7 %) than for strawberry (16.7 %) samples, which is related to the larger surface to mass ratio of lettuce. The strawberry transpiration rate presented a stable behavior after the first day of storage (1.31 g kg-1 h-1), which provides a linear reduction in the strawberry mass, while lettuce had a higher transpiration rate at the beginning (4.25 g kg-1 h-1) and showed a gradual reduction during cold storage until reaching 1.81 g kg-1 h-1. Water loss in food occurs through evaporative heat from respiration and a reduction in the water content leads to an increase in the internal food temperature. A gradual increase in the food temperatures was observed for both lettuce and strawberry (by 0.5 °C and 0.1 °C, respectively) during storage due to vegetable physiology. Based on the thermal history, a faster thermal response was observed for lettuce. Also, the cooling rate was higher for lettuce (8.7 °C h-1) than for strawberry (6.9 °C h-1) and the half-cooling times were 0.2 h and 0.3 h for the lettuce and strawberry samples, respectively. These findings aid a better understanding of postharvest food behavior and could lead to novel preservation technologies.
