Because of technological improves for the heat controllers and you can operating handle techniques, it’s become you can to help you feature drying heavens temperature handle steps (nonisothermal drying out), making it possible to pursue sinusoidal trend users (Profile 1a), square wave or package function pages (Profile 1b), broadening and you can p users, saw-tooth revolution pages, and you may trapezoidal wave users (Shape 1c), among others. Nonisothermal drying out has made they possible to find affairs regarding highest high quality and also reduced drying moments compared to https://datingranking.net/fr/rencontres-de-musique-fr/ those obtained which have constant convective drying out ( Chua while some 2002 ). Although certain quality functions had been learnt when you look at the information published to nonisothermal drying out, structural qualities have not been stated, neither provides equations started proposed to explain the choices ( Chua and others 2000 ; Chua while some 2002 ). Yet, zero equations have been proposed to connect changes in the newest architectural characteristics from product exposed to varying additional standards.
This has been noticed there is no significant difference ranging from new decisions of true density with respect to the X off the materials while in the convective drying and you may after are rehydrated to various dampness content; yet not, variations was seen between obvious density according to X of your situation during lyophilization and you can then rehydration to several water contents ( Krokida and you can ).
Three possible tendencies of ?p as a function of X have been found (Figure 2), both linear and nonlinear (concave-down and concave-up). p and X, which considers reduction in volume to be equal to the volume of the water eliminated from the material ( Madamba and others 1994 ). In tendency of Figure 2b, it can be observed how ?p increases slowly up to a critical point, followed by an exponential decay. This change has been explained by water loss in the material during drying ( Lozano and others 1983 ; Zogzas and others 1994 ). In tendency in Figure 2c, it is assumed that the increase in ?p to a critical point is due to the fact that the reduction in volume is greater than the reduction in mass; after this critical point, the pores in the material are considered to be closed, and measured volume is greater than true volume ( Lozano and others 1983 ). In the above-described tendencies, it is merely assumed that volume and solid dry mass are constant. However, when materials are heated, they may expand or contract; in such cases, volume is not constant.
Several efforts have been made to predict different tendencies of ? as a function of X. Generally in these models, the foodstuff is considered to be a binary compound (water–solid). Table 3 shows models for true and apparent density proposed for foodstuffs. The models for predicting ?b and ?p are based on the development of pores during the lyophilization process, as the formation of pores is considered to be a function of ideal conditions, since there is no reduction in the volume of the solid as a result of water sublimation ( Karathanos and others 1996 ).
Real thickness (?p) patterns
Certain writers enjoys advised correlations received as a result of nonlinear regression for anticipating genuine thickness and you can apparent thickness because the a purpose of water articles. Yet not, the outcome perhaps not be common and are also simply good with the matter, geometry, and you may drying requirements utilized in those functions (Desk 3).
It observed linear decisions away from density for several suspensions from sheer substances, eg proteins, fats, carbohydrates, fibers, and you will ash. Such experts compared the patterns that have fresh density philosophy for milk, lime juices, and you will bratwurst sausage, getting an optimum error of 1.45%, and you will seeking a beneficial quadratic abilities to have liquids.