Abstract
Cassava roots are susceptible to deterioration with 24 hrs of harvest; it needs processing into a more stable material such as dried cassava chips to extend its shelf life for long storage. However, improper knowledge of the effect of atmospheric relative humidity on these dried chips during storage makes it mouldy and unacceptable. This work aimed at studying the effect of sorption isotherms on the dried cassava chips. In this study, adsorption and desorption isotherm were carried out using static gravimetric method and data for equilibrium moisture content (EMC) were generated at five (5) temperatures (53, 60, 70, 80, 86oC). These were fitted into four (4) isotherm-models [Oswin, Peleg, the Modified Oswin and GAB]. The statistical criteria to test the models were coefficient of determination (R2 ), reduced chi-square (χ 2 ), root mean square error (RMSE) and mean bias error (MBE). The values of EMC ranged from 7.21-12.44% wb. The values of R2 ranged from 0.95-0.99; χ 2 ranged from 0.008-0.14; RMSE values ranged from 0.06-0.254 while MBE values ranged from -0.0004-1.1E-5. The values of isosteric heat of sorption calculated from the isosteres recorded a range from 6.579 to 67.829 kJ/mole. The Pelegmodel gave the best fit in the relative humidity range of 10 to 80%. The values of EMC show that the chips can have a stable shelf life without spoilage.
Highlights
IntroductionNigeria is the world’s largest producer of cassava (FAO-STAT, 2012; MAFAP, 2013) and has a defined national policy to aggressively expand its production and processing for the economic development of the country
Each desiccator was maintained at one relative humidity value between 10 and 80%
Equilibrium moisture content (EMC) values were found by calculation (Igbeka et al, 1975; Oyelade et al, 2001; Falade et al, 2003)
Summary
Nigeria is the world’s largest producer of cassava (FAO-STAT, 2012; MAFAP, 2013) and has a defined national policy to aggressively expand its production and processing for the economic development of the country. The life span of cassava chips is adjudged to be six months and the long-distance covered during exportation of these chips is a crucial factor as large part of the export turns mouldy on the high sea. This is because cassava chip is hygroscopic and gains moisture over time. It is important to consider and study the water activity of the chips This is a determinant factor of stability of the chips in long term storage because there is a possibility that the chips experience increase in moisture (adsorption) or decrease in moisture (desorption) due to fluctuations in relative humidity. Study of adsorption and desorption isotherm or their models which define the relationship between water activity and equilibrium moisture content (EMC) at different temperatures are important for three reasons: (a) to define the extent of free water removable in hot air drying of the chips which is all the moisture above the EMC, (b) to define the water activity at EMC and ensure it is low enough to ensure long term stability in storage and (c), to provide a basis for calculating the energy (isosteric heat) profile required for drying in a
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