Analysis of the Moisture Sorption Isothermic Characteristics of Dried Salted Glossogobius giuris

Abstract

Glossogobius giuris, commonly known as white goby or biyang puti, is a local fish species in Laguna de Bay, Philippines, commonly sun-dried for selling. Traditional sun-drying of salted white goby has been a prevailing practice, but no initiatives were accounted to study in detail and improve its drying, storing, and packaging process. This study then identifies the water activity (a_w) and equilibrium moisture content (EMC) of dried white goby using different salt proportions, storage temperatures, and packaging mechanisms which were used to model its moisture sorption isotherm. Modelling its moisture sorption isotherm will aid in designing and optimizing the drying process, storage techniques, and packaging mechanism. Modelling techniques, like Oswin, Smith, Halsey, and Henderson models, as well as Langmuir, Brunauer-Emmett-Teller (BET), and Guggenheim-Anderson-de Boer (GAB) equations, were considered and analyzed to characterize the moisture sorption isotherm of these dried salted white goby. The best fit among these models was tested using root mean square error (RMSE), mean relative percentage difference (RPD), and coefficient of determination (R²). Analysis was done at temperatures of 15 °C, 25 °C, 35 °C and 40 °C that correspond to water activity (a_w) ranging from 0.10 to 0.80, which varied by different salt saturation, with and without packaging conditions. Among the models utilized and tested, the GAB model best projected the EMC of the salted white goby both with and without packaging with the highest R² greater than 0.94 and lowest RMSE of less than 0.020, which will lead to the detail description of moisture sorption characteristics of dried salted goby necessary for the improvement of the drying process. T-tests for independent samples were also employed and found that statistically, there was no significant difference between the a_w and EMC with a p-value of 0.96 and 0.91 for dried goby with and without packaging, suggesting further improvement can be made upon the packaging mechanism to increase its efficacy.