Thermodynamic Analysis of Moisture Adsorption Isotherms of Raw and Blanched Almonds

Abstract

The equilibrium moisture content of raw and blanched almonds of California grown “Carmel” variety was determined by using static gravimetric method at 25, 35 and 45C over a range of water activities (Aw) from 0.11 to 0.97. The sorption data were fitted to the Guggenheim–Anderson–de Boer (GAB) model. The goodness of fit of the model was evaluated by standard error of estimate, mean relative percentage deviation modulus and randomness of residual, which showed good fit of the GAB equation to the experimental data. The moisture adsorption isotherms of almonds exhibited type II sigmoid shape. Thermodynamic properties such as differential enthalpy and entropy were determined from moisture adsorption data by using the Clausius–Clapeyron equation. The results showed that enthalpy–entropy compensation theory was applicable for the moisture adsorption phenomena of raw and blanched almonds. The adsorption process of almond was enthalpy‐controlled. PRACTICAL APPLICATIONS Over 80% of the world almond production is grown in California and shipped to over 90 countries around the world. When exported to distant markets in the tropical regions, the physical, chemical and microbiological changes in almonds could cause the deterioration of food products due to environmental factors. Despite the large‐scale production and export of almonds, very little information on the sorption characteristics of almond varieties grown in California can be found in the literature. Reliable information on sorption isotherms is critical to designing optimum storage and shipping conditions to ensure desired levels of almond quality at consumption. This paper presents results from a comprehensive study of the sorption characteristics of one of the most important almond varieties grown in California, namely “Carmel.”

Moisture sorption isotherms and thermodynamic properties of whole black peppercorns (Piper nigrum L.)

“…5, the net isosteric heat of sorption is highly dependent on the EMC; with the energy required for sorption increasing at low MC and after reaching a maximum value decreasing exponentially with increasing EMC. Similar trend has been observed in previous studies (Taitano et al, 2012;Toğrul and Arslan, 2007).…”

“…At higher EMC the active sites on the surface could be occupied by the water molecules hence had less capacity for sorption thus reducing the entropy. Similar trends in sorption entropy has been previously reported in potatoes (McMinn and Magee, 2003), dried casein (Sawhney, 2011), almonds (Taitano et al, 2012), whey protein concentrate from buffalo milk (Sawhney et al, 2013) and in sorghum (Bonner and Kenney, 2013). Moreover, the plot of enthalpy (H) versus entropy (S) shows a linear relationship for adsorption (R 2 0.9998) and for desorption (R 2 0.993), which indicates the existence of the enthalpy-entropy compensation.…”

“…An increase in a w equivalent to an increase of M 0 by 0.1 units decreases the shelf life of a food product by a factor of 2-3 (Labuza, 1984). It is therefore an important quality parameter with regards to the designing optimal storage conditions for food products (Taitano et al, 2012). Therefore the M 0 values reported in this study represent the optimal MC for the storage of whole black peppercorns.…”

“…It is clear that the (-G) decreases exponentially with increasing EMC. High G indicates that there is high freedom of water adsorption due to hydrophilic properties in a food material (Taitano et al, 2012). Moreover, the (-G) at a specific moisture content was lower the higher the incubation temperature.…”

“…Above 5% EMC the difference in free energy change was not significant between adsorption and desorption isotherm at any temperature (22°C, p=0.619; 30°C, p=0.284; 37°C, p=0.307). According to Taitano et al (2012), the influence of MC on the (-G) is more pronounced when the MC is less than the M 0 .…”