Sorption characteristics of red lentils as affected by postharvest conditions.

Abstract

Adsorption and desorption characteristics of three varieties of red lentils in commercial production (Robin, Blaze, and Redberry) were measured in a dynamic set-up where: (i) freshly harvested lentils of different initial moisture content, (ii) lentils that were exposed to successive rewetting and drying cycles, and (iii) lentils exposed to successive freeze/thaw cycles were placed on a set of stacked trays in air tight systems. The experiments were conducted for the air temperature range between 5 and 30°C (with a step of 5°C) and five relative humidity (RH) values to represent a typical storage range. The Modified Halsey equation was found most suitable for the description of lentil moisture relationships and a non-linear regression procedure was performed on both the adsorption and desorption data collected for each variety and treatment combination. The coefficient of determination for non-linear regression (R2) ranged between 0.952 and 0.982, while the standard error of the estimated relative humidity value was within 2.8 to 4.2%. Successive wetting and drying of lentils had little or no effect on the EMC-ERH (equilibrium moisture content - equilibrium relative humidity) characteristics of CDC Robin varieties and a significant change in EMC-ERH was observed for CDC Redberry and CDC Blaze above 60% RH. There was a significant difference between the fresh and freeze/thaw EMC samples for all three red lentil varieties studied. For each lentil variety, the predicted EMC value for the freeze/thaw treated lentils was lower than the predicted EMC value for freshly harvested lentils at a given ERH. The difference in EMC values between the two treatments was most significant at high RH levels.