Due to technical improves inside heat controllers and running manage process, it has become you can easily to consist of drying heavens heat control steps (nonisothermal drying), where you can realize sinusoidal trend profiles (Shape 1a), square-wave or field means pages (Profile 1b), growing and you will p profiles, saw-tooth trend profiles, and you will trapezoidal wave profiles (Contour 1c), as well as others. Nonisothermal drying out made it you can locate facts out of highest quality and also shorter drying out minutes than those acquired with lingering convective drying ( Chua and others 2002 ). No matter if certain high quality properties was basically examined in the material published to nonisothermal drying, structural functions haven’t been stated, neither provides equations come suggested to describe its conclusion ( Chua although some 2000 ; Chua and others 2002 ). Up to now, zero equations have been proposed to associate changes in the fresh structural qualities from content confronted by changeable additional standards.
It has been observed that there’s zero significant difference ranging from the fresh decisions out-of true occurrence according to X of the information presented throughout the convective drying and you will once are rehydrated to different moisture contents; not, distinctions have been noticed anywhere between obvious occurrence according to the X of the procedure during lyophilization and you may then rehydration to various moisture content material ( Krokida and you may ).
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.
Occurrence Designs
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 ).
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Real occurrence (?p) patterns
Various authors keeps recommended correlations acquired compliment of nonlinear regression to own anticipating genuine occurrence and you will apparent occurrence due to the fact a function of wetness blogs. not, the outcomes not getting prevalent and generally are only legitimate toward thing, geometry, and you can drying conditions included in people really works (Dining table step 3).
It noticed linear conclusion regarding occurrence for different suspensions off natural compounds, such necessary protein, oils, carbohydrates, fibers, and you can ash. Such people opposed their designs with experimental occurrence viewpoints having whole milk, lime liquid, and you may bratwurst sausage, obtaining an optimum mistake of 1.45%, and you will wanting a great quadratic capability to have h2o.
