Because of technological advances from inside the temperatures controllers and processing handle procedure, it has become you can easily so you’re able to incorporate drying air heat handle actions (nonisothermal drying out), where you could go after sinusoidal trend pages (Profile 1a), square-wave otherwise box form pages (Shape 1b), broadening and you may p pages, saw-enamel revolution users, and you can trapezoidal trend profiles (Contour 1c), yet others. Nonisothermal drying out has made it you are able to to find circumstances regarding highest quality as well as quicker drying moments than others obtained that have ongoing convective drying ( Chua while others 2002 ). In the event various top quality functions had been studied when you look at the content published to nonisothermal drying, architectural properties haven’t been reported, neither possess equations started advised to describe their conclusion ( Chua while some 2000 ; Chua although some 2002 ). Up to now, zero equations was recommended in order to connect changes in the fresh new architectural qualities from material exposed to variable additional criteria.
It’s been noticed that there surely is no factor ranging from the fresh conclusion away from true occurrence with regards to the X of the materials through the convective drying and you will shortly after being rehydrated to different dampness information; although not, differences was observed farmers dating site ranging from visible occurrence according to the X of your question throughout lyophilization and you will further rehydration to various dampness content ( 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 ).
Correct density (?p) models
Individuals article authors has actually recommended correlations gotten compliment of nonlinear regression having predicting true thickness and you will noticeable occurrence just like the a purpose of dampness stuff. Although not, the outcome perhaps not be extensive as they are just legitimate towards the material, geometry, and you will drying out criteria found in men and women functions (Dining table step 3).
They noticed linear conclusion out-of occurrence a variety of suspensions out-of absolute compounds, such as proteins, oils, carbohydrates, materials, and you will ash. Such authors compared their models with experimental occurrence opinions for milk, lime liquid, and bratwurst sausage, obtaining a max error of 1.45%, and searching for good quadratic abilities to possess liquids.