Water Sorption Isotherms and Crispness of Fried Yam Chips in the Temperature Range from 293K to 313K

Abstract

Water sorption isotherms of fried yam chips were determined using a static gravimetric method with saturated salt solutions in the range of water activity between 0.22 and 0.85 at 293, 303 and 313K. Four sorption models namely GAB, Peleg, modified Mizrahi, and BET were fitted with the sorption data generated. The GAB model followed by Peleg and modified Mizrahi models were found to best represent the experimental data in the a w range of 0.22-0.85. However, the BET model was more applicable between a w range of 0.22-0.55. The adsorption isotherm of fried yam chips clearly showed the influence of temperature, decreasing the moisture content at a fixed water activity value with higher temperature. The net isosteric heats of sorption of water were estimated by applying the Clausius-clapeyron equation to the adsorption isotherms at different temperatures. The net isosteric heat of sorption was observed to be decreasing as moisture content increases. Samples stored in desiccators of 0.44 and 0.55 a w at 303 and 313K, respectively, were rated higher in terms of textural properties investigated.

Experimental and Mathematical Description of Sorption Isotherms and Thermodynamic Properties of Salted and Dried African Catfish (Clarias gariepinus)

“…Equilibrium was considered to be reached when the change in weight did not exceed 0.001g (about 28 days). Similar method had been reported by Konopacka et al (2002); Akanbi et al (2006); Sobukola et al (2007); Hadrich et al (2008) and Boudhrioua et al (2008).…”

“…Experiments were performed using known mass of about 2 -4g of the samples for all temperatures in the water activity range from 0.33 to 0.85 as earlier reported (Bellagha et al, 2007;Sobukola et al, 2007). The saturated salt solutions were prepared by dissolving in a jar, an appropriate quantity of salt in distilled water.…”

“…However, for high salt concentration food, a different shape was observed for sorption isotherm (Doe et al, 1982). A common method to find experimental water sorption data is equilibration of samples over saturated salt solutions filled in insulated jars at a constant temperature and gravimetric measurement of the steady state water content (Bellagha et al, 2005;Sobukola et al, 2007;Hadrich et al, 2008;Toujani et al, 20011). Relative humidity for various salt solutions at different temperatures may be obtained from literature (Labuza et al, 1985).…”

Designing experiments to differentiate between adsorption isotherms using T-optimal designs

“…60 6 b 3 6 0.99. However, there were some materials for which the model parameters fell well outside these ranges, including rice , maize flour (Oyelade et al, 2008), walnut kernels (Togrul and Arslan, 2007), freeze dried blueberries (Syamaladevi et al, 2009), freeze dried plantain (Johnson and Brennan, 2000), sorghum malt (Aviara et al, 2006), morel mushrooms (Mulet et al, 2002), cocoa beans (Sandoval and Barreiro, 2002) and yam chips (Sobukola et al, 2007). The range of model parameters selected above is slightly different from that recommended by Lewicki (1997), Blahovec (2004) based on theoretical considerations.…”

“…This review included grains and seeds Arslan, 2006, 2007;Oyelade et al, 2008;Mohamad Saad et al, 2009;Resio et al, 1999;Peng et al, 2007;Chen, 2003;Pagano and Mascheroni, 2003), dried fruits and berries (Goula et al, 2008;Syamaladevi et al, 2009), tubers (IkhuOmoregbe, 2006Viollaz and Rovedo, 1999), and other foodstuffs (Rahman and Al-Belushi, 2006;Kaymak-Ertekin and Sultanoglu, 2001;Arslan and Togrul, 2006;Johnson and Brennan, 2000;Aviara et al, 2006;Mulet et al, 2002;Sandoval and Barreiro, 2002;Sobukola et al, 2007). Based on this review, we selected the following ranges of the model parameters as encompassing most of the reported values: 1 6 b 1 6 20,1 6 b 2 6 15,0.…”