Because of scientific improves when you look at the heat controllers and processing control procedure, it has become you can easily so you’re able to add drying out sky temperatures manage steps (nonisothermal drying out), where you can realize sinusoidal wave users (Contour 1a), square-wave otherwise field form profiles (Figure 1b), increasing and you can p profiles, saw-enamel revolution users, and you will trapezoidal trend pages (Profile 1c), among others. Nonisothermal drying makes they possible to obtain products regarding large quality as well as quicker drying out times than others received having lingering convective drying out ( Chua while some 2002 ). Regardless of if various high quality qualities was in fact learned during the materials submitted to nonisothermal drying out, structural services have not been stated, neither possess equations started recommended to spell it out their behavior ( Chua while others 2000 ; Chua while others 2002 ). Up until now, no equations was in fact suggested in order to associate alterations in the fresh new structural properties regarding materials confronted by varying exterior criteria.
It’s been noticed that there is zero factor ranging from the new conclusion away from genuine occurrence depending on the X of the material while in the convective drying and you may just after becoming rehydrated to several moisture information; however, variations was noticed anywhere between noticeable density depending on the X of the procedure during the lyophilization and you will after that rehydration to various water information ( 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 ).
True occurrence (?p) activities
Some experts has actually proposed correlations gotten as a consequence of nonlinear regression having anticipating true occurrence and you can noticeable density as a function of dampness blogs. Yet not, the results not be prevalent and are just legitimate on the question, geometry, and you can drying requirements found in men and women performs (Dining table step 3).
They noticed linear choices from occurrence for various suspensions regarding sheer substances, for example protein, fats, carbs, fibers, and you will ash. These people compared their activities which have fresh occurrence values to have milk products, tangerine fruit juice, and bratwurst sausage, getting a maximum mistake of 1.45%, and you will interested in an excellent quadratic capability for h2o.