Effect of Cooking on Moisture Sorption Isotherms of Shea Nut (Vitellaria paradoxa Gaertn.) Kernels Part II: Modelling and Properties of Sorbed Water

An investigation was undertaken in this work to model the sorption isotherms of cooked and raw shea nut kernels determined by the standard static gravimetric method. The GAB, Halsey and Caurie models were validated and used in describing the sorption behaviour of the kernels. The monolayer moisture contents derived from Caurie’s equation for the desorption of cooked and raw kernels at 40, 50 and 60 °C were 5.49, 4.40 and 2.65 % and 5.22, 3.68 and 2.47 %, respectively. Monolayer moisture contents obtained from the GAB model showed a similar variation. As the temperature of sorption increased from 40 to 60 °C, the number of adsorbed monolayers (N), the surface area of adsorbent (A) and the percent bound water decreased significantly (p?<?0.05). It is suggested that the sorption process at all temperatures is multilayered. Desorption isosteric heats were lower for cooked kernels than the raw ones, while the reverse phenomenon was obtained for the adsorption process. It was established that, during storage, cooked kernels adsorbed moisture more slowly, suggesting that they could be stored for a longer period compared to the raw ones.     

Optimisation of the Cooking Process of Sheanut Kernels (Vitellaria paradoxa Gaertn.) Using the Doehlert Experimental Design

The response surface method employing Doehlert’s experimental design was used to optimise the cooking of sheanuts to strike a balance between the advantages and disadvantages usually offered by the process. The independent factors investigated were cooking time, cooking temperature and nut size while the responses were moisture content of the kernels, amount of oil extracted, acid and peroxide values of the butter. Second order polynomial models were generated to describe the process for the responses studied. The validity of the models was tested and it was found that they could be used to explain respectively 83%, 99% and 95% of the variation of moisture content, acid value and peroxide value. The cooking process greatly reduced the free fatty acid values of the butter (<6%) but increased its peroxide value (up to 20 meq/kg). The cooking process was significantly influenced by all three independent factors investigated. The optimum conditions defined for the cooking process were: cooking time (95–120 min), cooking temperature (75–90 °C) and nut size (40–45 mm). These optimal conditions gave the following responses: moisture content 51.97% w.b., amount of oil extracted 47.47%, acid value (as FFA) 2.76% and peroxide value 3.87 meq/kg. The parameters of the cooking conditions could be set to appropriate values to give butter of either category 1, 2 or 3 in terms of acid and peroxide values.     

液压逻辑控制原理

液压开关回路及电液控制系统的实质是实现对执行元件工作压力信号的逻辑控制，单通道液压开关是实现此控制的基本元件．本文建立了液压逻辑控制的规则．     

Effect of Cooking on Moisture Sorption Isotherms of Sheanut (Vitellaria paradoxa Gaertn.) Kernels: Evidence from Light and Scanning Electron Microscopy

The standard static gravimetric method was used to determine moisture sorption isotherms of both raw and cooked sheanut kernels at 40, 50 and 60 °C in the water activity range 0.11–0.96 in order to evaluate the influence of cooking on the moisture sorption capacity of the kernels. Preliminary analysis showed that the kernels lost a significant quantity of its proteins and carbohydrate during the cooking process. Results of analysis of the moisture sorption isotherms revealed that cooked kernels generally had significantly (p?<?0.05) lower equilibrium moisture contents (EMC) than the raw ones for both desorption and adsorption processes. The effect of temperature on the sorption processes as portrayed by the desorption isotherms revealed that EMC decreased steadily with increase in temperature within the water activity range 0.10–0.8 a_w but increased rapidly with increase in temperature above 0.8 a_w resulting in the overlap of isotherms for all sorption processes. This crossing over of isotherms was attributed to the dissolution of sugars at higher water activities. The protein matrix in the kernel was observed using light microscopy and was found to have been disorientated after cooking. Studies using light and scanning electron microscopy revealed that the reduced ability of cooked kernels to sorb water could be linked to changes in the structure of the kernels brought about by the cooking of the kernels. It is concluded that cooking had a very significant effect on the amount of water sorbed by sheanut kernels.