Prediction of Equilibrium Moisture Contents of Black Grape Seeds (Siah Sardasht cultivar) at Various Temperatures and Relative Humidity: Shelf-Life Criteria

Background and Objectives: Food wastes are sometimes valuable; of which, seeds are significantly important. Grape seeds, as byproduct of grape processing, contain valuable substances for the production of advanced oils as well as feeds. Therefore, the major aim of this study was to assess moisture sorption isotherms of black grape seeds at various conditions. Materials and Methods: Moisture sorption isotherms of black grape seeds (Siah Sardasht cultivar) were measured using static gravimetric method with saturated salt solutions at five various temperatures of 20, 30, 40, 50 and 60 ˚C. Water activity ranged 0.1–0.9. Five mathematical models of Guggenheim, Anderson and De Boer (three-parameter), Brunauer-Emmett-Teller (two-parameter), D’Arcy-Watt (five-parameter), Henderson (two-parameter) and Halsey (two-parameter) were used to fit data using non-linear regression analysis method. Results: Results showed that the moisture sorption behavior of grape seed was temperature dependent as indicated by increases in equilibrium moisture contents at all levels of water activity with decreasing temperature. The best fit with experimental data in all water activities and temperatures were linked to Guggenheim, Anderson and De Boer model. D’Arcy-Watt model at 40, 50 and 60˚C was adjusted well. The net isosteric heat of sorption was achieved using Clausius-Clapeyron equation and showed the maximum value (754.3 kJ/kg) at a moisture content of 0.1 (%d.b). Conclusions: Rapid spoilage of grape seeds may occur at a water activity of 0.3 or greater for 20 ˚C and that of 0.6 for other temperatures. The Guggenheim, Anderson and De Boer model presented the best fitting. At highlighted temperatures, net isosteric heat increased significantly with decreases in moisture contents.