Abstract:
The salted fish industry is now facing tremendous problem in controlling its product quality, mainlythe amount of salt in the fish. Therefore, the rate of transport of salt into fish was studied in terms ofthe diffusion coefficient. The research was divided into three parts. The first part was the study ofmethods for estimating the diffusion coefficient, i.e., the sorption kinetics method and thepermeation method. In the second part, the effects of fat content and the freshness of fish skin andfish flesh were studied. The results were then used as criteria for controlling the raw materials usedin the subsequent section. In the final part, the effect of brine concentration on the diffusioncoefficient of salt was investigated.The results revealed that the permeation method was most suitable for the determination of thediffusion coefficient of salt in this research since the diffusion coefficient of salt obtained from thismethod is in the same order of magnitude as that obtained from the literature. For the result of thesecond part of the study it was found that the fish skin and fish flesh containing the total volatilebase nitrogen 25 mgN1100 g sample and the fat content between 0.17-0.30 and 0.01-0.15 glg drysample were most suitable as the raw material. At 28 k 1 'C and 95 percent confidence, thediffusion coefficient of salt in fish skin did not depend on the brine concentration while thediffusion coefficient of salt in fish flesh decreased when the brine concentration increased from 13to 20, 28 and 36 percent (wlv). When the brine concentration was higher than 20 percent (wlv)the diffision coefficients of salt in fish flesh were not significant different at differentconcentrations but at the brine concentration below 20 percent (w/v) the diffusion coefficients ofsalt in fish flesh were higher. The relationship between the diffision coefficient of salt in fish fleshand the brine concentration was explained by the linear equation, DnCSh~=8 .33~10~~~)-(0.13~10-~~~)where D,,, is the diffusion coefficient of salt in fish flesh ( d s ) and C is the brine ccncentration(kg/m3).