DEVELOPMENT OF MATHEMATICAL MODEL FOR TRANSPIRATION RATE OF FRESH-CUT LETTUCE

During postharvest handling and storage, fresh fruits and vegetables continue to lose water through the process of transpiration which is a physiological process of water loss from fresh products. This process is influenced by factors such as temperature, relative humidity, respiration rate, surface area and air movement; an excessive weight loss causes change in texture, a favourable environment for microbial growth and leads to unsalable loss of market value, during retail marketing and to a direct financial loss. Iceberg lettuce is a highly perishable product with a short shelf life (7 days at 7°C) due to the influence of minimal processing unit operations, such as cutting and shredding that causes disruptions of cells, which induces an increase in respiration rate, transpiration and enzymatic activities after harvest. The aim of this work was to quantify the transpiration rate (TR) of fresh cut lettuce under different storage condition. Experiments were conducted by conditioning the sample at 2, 6 and 10°C and 76, 86, 96 and 100% RH and TR was recorded during 7 days of storage. The results showed that both temperature and relative humidity affected transpiration rate: TR increased by increasing temperature and by decreasing RH; TR ranged from 0.49 to 1.26 (g kg-1h-1) over all the combinations of temperature and RH tested. A mathematical model was developed to predict TR as a function of temperature and humidity.