Macadamia Drying Characteristics And Mechanical Properties Studies

With the economy and people's living standard develop rapidly, people pay more and more attention and favor to healthy foods like nuts. Macadamia nut is a newly emerging nuts food with high-protein and high fat. Long-term consumption leads to a very good result of prevention cardiovascular and cerebrovascular disease as well as lowering cholesterol. In recent years, macadamia nut products emerge one after another, and they are greatly favored by domestic and foreign consumers. Macadamia nut industry in China has achieved great improvement after ten years'development. However, the relative backwardness of the nut-drying technology becomes a largest shackles to constraint the development of macadamia nut industry.At present, there are three problems in the production and processing of nut materials: first, nut products are greatly impacted by drying temperature. Second, it is difficult to break the shell and to take the kernels. Third, the processing equipments are imperfect and the processing technology is immature. Therefore, macadamia nuts which has high economic value as a research object are taken in this paper, combining the unique resources of Yunnan Province to study the drying characteristics and mechanical characteristics of the macadamia nuts, aiming to provide a reference for the practical production and processing of it.Firstly, the nuts moisture content and drying rate were taken as the experimental index to study the drying characteristics of macadamia nuts in this paper. Analyzes drying characteristics of the shells, kernels and nuts in natural drying conditions and different hot air temperatures. And the mutual influence in the drying process of shells and kernels were analyzed, the regression analysis of the test data were made by using SPSS statistical software, the drying mathematical model of shells, kernels and nuts under natural drying and hot air conditions were built. Secondly, the effective diffusion coefficients of the shells, kernels and nuts were calculated in the hot air drying process, and the relationship equations between effective diffusion coefficient and air temperature of the shells, kernels and nuts were set up. After hot air drying, the 3-directions shrinkage was calculated in this paper. Subsequently, the impact of the moisture content of shells on the cracked force in natural drying conditions and in hot air drying conditions are analyzed, compressing position of the macadamia nuts on the cracked force after hot air drying;a relationship equation between the shells moisture content and the cracked force in 3 directions was built. Comparing of the broken load after natural drying and hot air drying. The relation between the moisture content of kernels and the whole kernel rate in the hot air drying conditions were studied by using the mechanical index of breaking loads and the auxiliary index of whole kernel rate.The experimental results show that in natural drying conditions, the decline in moisture content of macadamia nuts is mainly caused by the decline in moisture content of kernels. When the moisture content of nuts falls to 10g/100g,the natural drying is very difficult to reduce the moisture content of nuts further. At this stage, other drying methods are required to assist to reduce the nut moisture content. Lewis model has the best simulation effect of macadamia nuts drying process in natural drying conditions. Hot air temperature has the most significant effect on drying characteristics of macadamia nuts. The higher the air temperature is, the faster the drying rate is, the less time is required for drying. The whole hot air drying process of macadamia nuts contains only the falling rate period, the water diffusion form of nuts in the drying process is closer to that of shells. Diffusion is the main form of water movement. In the initial of hot air drying period, the moisture content decline of nuts is mainly caused by water evaporation of shells. When the shell cracks, the water evaporation of nuts causes a decline in moisture content of macadamia nuts. Lewis model has the best simulation effect on the hot air drying process of shells, kernels and nuts. The shrinkage of the width direction is the most significant, the thickness is second, shrinkage of the hilum is the least obvious.In natural drying conditions, the cracked force does not so significantly change in accordance with the shells moisture content change. The maximum of the force is required to break in the hilum, width direction at the second, and the thickness direction requires the minimum. In the natural drying conditions, the nuts closely adheres the shells, the whole kernel rate is almost 0. After hot air drying, the shell cracks apparently, and cracked force decreases significantly as the moisture content drops in the shells. The largest force is required to break in the width of the nuts with that in the hilum following behind it, and that in the thickness directions at the smallest. When the decline in water content of macadamia nuts causes a clearance between kernels and shells, the whole kernel rate increases significantly, and when the moisture content of the nuts fall to a certain degree, the whole kernel rate begin to decrease. With the drying process going on, the gap appears between the shells and the kernels. The gap in the hilum is the most obvious, but the increase of the gap in the thickness is the least obvious. Compared to natural drying, the cracked force decline and the whole kernel rate increase sharply under hot air drying.In the production and processing, macadamia nuts which can not be dried timely by hot air drying, could be dried by natural drying until the moisture content falls to about 10g/100g(db), and then dry the nuts by hot air. When the moisture content falls to 5.4g/100g, the breaking load is smaller and the whole kernel rate is larger to break nuts in the thickness direction.