Due to scientific enhances in temperature controllers and you can processing handle procedure, it is you can so you’re able to integrate drying out heavens temperature manage steps (nonisothermal drying out), where you could go after sinusoidal trend users (Contour 1a), square wave or box setting pages (Figure 1b), expanding and p profiles, saw-enamel revolution pages, and you may trapezoidal trend pages (Figure 1c), as well as others. Nonisothermal drying out made it you are able to to locate products of high quality as well as smaller drying out times as opposed to those acquired that have ongoing convective drying ( Chua although some 2002 ). No matter if certain quality characteristics was studied in material submitted to nonisothermal drying, architectural functions have not been claimed, nor keeps equations been recommended to explain the behavior ( Chua although some 2000 ; Chua while some 2002 ). At this point, no equations was indeed suggested in order to connect alterations in new structural services from product confronted by varying external conditions.
It’s been seen there is no factor between the new decisions of genuine density with regards to the X regarding the material while in the convective drying out and you will immediately after becoming rehydrated to different wetness material; not, differences were observed between apparent density with regards to the X of matter during the lyophilization and you will then rehydration to different moisture content material ( Krokida and ).
Three possible tendencies of ?p as a function of X have been found (Figure 2) sitio web de citas para solteros étnicos, 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.
Density Models
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 ).
Correct thickness (?p) patterns
Certain people has suggested correlations received as a result of nonlinear regression to possess predicting real density and you will visible occurrence since the a function of water posts. But not, the results not getting widespread and are also merely appropriate to your material, geometry, and you can drying criteria found in the individuals work (Dining table step three).
They seen linear choices out-of occurrence for different suspensions regarding sheer ingredients, such proteins, oils, carbohydrates, fibers, and ash. These authors compared their models with fresh occurrence philosophy to own dairy, lime liquid, and you can bratwurst sausage, acquiring an optimum mistake of just one.45%, and in search of an excellent quadratic possibilities for h2o.