Effects of processing parameters on moisture sorption isotherms of dehydrated catfish (Clarias gariepinus)

Abstract

Effects of processing parameters on moisture sorption isotherms of dehydrated catfish (Clarias gariepinus) at 25°C and 30°C and water activity ranged 0.1-0.85 were determined using the static gravimetric method. The interaction of processing variables, regarded as treatment was done using response surface methodology. Three best treatments selected through preliminary sensory evaluation falls within the parameters’ range (brine concentrations (6% and 9%), brining time (60 and 90 min) and drying temperatures (90°C and 110°C) ) and used in the production of the dehydrated catfish. Two un-brined samples, dried at each temperature were used as the control. The moisture sorption isotherm curves were fitted with Oswin, Smith, GAB and BET models. The constants of the equations used in fitting the curves were determined by non-linear regression analysis while the models were compared using the coefficient of determination, root mean square error and reduced Chi-square; and average grade ranking. Microbial qualities of the samples were determined. Sorption isotherms exhibited type II characteristics of BET classification. The equilibrium moisture content of the dehydrated catfish in all treatments decreased with increasing temperature and increased with increasing water activity at the same temperature. Oswin model ranked first in all the treatments and the set of temperature, indicating the best fit for the curves. However, treatment: 9%, 90 min and 90°C provided the lowest monolayer moisture content (0.298373 g water 100 g-1 dry matter) of GAB at 30°C which could aid the product stability. Total viable counts of the product samples ranged from 1.0×103 -1.6×104 cfu g-1 and fungi from 1.0×103 -2.0×103 cfu g-1 TVC. No pathogenic organism detected; indicating safety for consumption. Information and data useful in designing equipment for commercial processing of catfish with simple dehydration technique and the optimum conditions are provided which could boost the economic importance of catfish.