Adsorption isotherms and heat of sorption of fresh and preosmosed oven-dried bananas

Author: K. O. Falade ^* and O. O. Awoyele

Received 18 July 2004, acepted 15 November 2004.

Abstract

Three banana varieties (Omini Red, Cavendish and Cooking banana) were transversely cut into 10 mm slices, pretreated in sucrose solution of 52, 60 and 68°B and maintained at 25°C for 12 hours. Both fresh and preosmosed banana slices were subsequently oven-dried at 60°C for 72 hours. Adsorption isotherms of fresh and preosmosed oven-dried banana slices were determined at 20 and 40°C using gravimetric–static method. Suitability of eight sorption models in describing the adsorption data was tested. Moreover, isosteric heat of sorption of both fresh and preosmosed oven-dried bananas was determined using Clausius–Clapeyron equation. Adsorption isotherms of fresh and preosmosed oven-dried banana slices gave type I (J–shaped) isotherms. Isotherms were affected by temperature and pretreatment sucrose solution concentration. Crossing of isotherms occurred at a_w~0.55-0.70. Among the eight models, tested, Guggenheim-Anderson-de Boer (GAB) model gave the best fit. Calculated GAB monolayer moisture (M_m) content (9.80–20.8% d.b.) decreased with increase in temperature. Generally GAB M_m content increased with increase in total solids (%) content of preosmosed banana slices. Isosteric heat of sorption increased with decreased moisture content in banana slices.