Moisture Sorption Isotherms and Mathematical Model Selection for Dried Sandfish (Holothuria scabra)

Abstract

Dried sandfish (Holothuria scabra) is often poorly dried by artisanal fishers in the Philippines, resulting in downgrading of the product. To establish recommended moisture content (MC) for a stable product, this study aimed to develop moisture sorption isotherms (MSI) at 30, 45 and 60°C at ten levels of water activity (a_w) using an isopiestic method based on saturated salt solutions. MSI data was fitted to six mathematical models by non-linear regression analysis. Water vapor transmission rate (WVTR) of low-density polyethylene (PE) and polypropylene (OPP) film was measured at 30 and 35^oC. A mass-balance model was used to predict shelf life and moisture content during storage based on MSI and WVTR data. MSI of H. scabra followed a Type III curve, which was best fitted to a Peleg model. For a stable product, the recommended range for MC during storage was 0.12-0.18 g g^-1 dry matter to avoid over- or under-drying; this corresponded to a_w of 04-0.6. Predicted shelf life for PE and OPP film packs at 30^oC reached 114 d and 372 d, respectively; at 35^oC, predicted shelf life was 83 d and 141 d, respectively.