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The moisture adsorption isotherms of pineapple processing waste – shell and central cylinder – were determined at 40, 50, 60 and 70C using a gravimetric method. The sorption data were fitted to six well-known sorption isotherm models. The Guggenheim–Anderson–de Boer model was found to be the most satisfactory to represent the equilibrium moisture content data for the pineapple shells and central cylinders. The thermodynamic properties – differential enthalpy and entropy – were estimated by the Clausius–Clapeyron method. The differential enthalpy of the pineapple shells and central cylinders ranged between 11.486 to 1.671 kJ/mol and 23.655 to −0.945 kJ/mol, respectively. The differential entropy had minimum values at 0.04 and 0.005 kgwater/kgdry solids for the pineapple shells and central cylinders, respectively. The pineapple shells presented two lines of compensation, one controlled by entropy and the other controlled by enthalpy and the pineapple central cylinders showed only one zone controlled by enthalpy mechanisms. Practical Applications This work presents information about the moisture sorption characteristics of pineapple processing waste. This kind of information is important for designing the unit operations necessary in the waste process use. In addition, knowledge of the moisture sorption characteristics is useful with respect to selection of packaging materials and storage stability. In general, this work gives relationship between water activity, entropy, enthalpy and moisture content of pineapple processing waste.

Summary In this study, physical characteristics of goat milk powder produced with the addition of soy lecithin at levels of 0 (control), 0.4, 0.8 and 1.0 g lecithin/100 g of total solids in concentrated milk before the spray drying process were investigated. Goat milk was pasteurised, concentrated at 40% of total solids, spray dried and packed in plastic bags under vaccum conditions. Lecithin addition decreased the wetting time of milk powders, although no influence was observed on dispersibility, water sorption, water activity and particle size distribution of the powders. Powders with higher levels of lecithin showed significantly lower brightness, with a greater intensity of yellow colour. It was concluded that lecithin addition before spray drying process at the minimal proportion in concentrated milk of 0.4 g lecithin/100 g of total solids in concentrated milk is useful for achieving more rapid wetting time of goat milk powder.

Data on pressure drop were obtained in stainless steel, sanitary fittings and valves during laminar and turbulent flow of aqueous suspensions of sucrose and bentonite. The rheological properties of these suspensions were determined and the Bingham model provided the best fitting with the experimental data. Friction losses were measured in fully- and partially-open butterfly and plug valves, bends and union. Values of loss coefficients (kf) were calculated and correlated as functions of the classical Reynolds number and the Reynolds number proposed by Govier and Aziz (1972) for viscoplastic fluids. The two-k method and a new proposed model presented the best adjustments for the Govier and Aziz Reynolds number, and Hedstrom and classical Reynolds numbers, respectively. On a obtenu des donnees sur la perte de charge dans des ajustages et des vannes sanitaires en acier inoxydable pour l'ecoulement laminaire et turbulent de suspensions aqueuses de sucrose et bentonite. Les proprietes rheologiques de ces suspensions ont ete determinees, et le modele de Bingham fournit le meilleur calage des donnees experimentales. Les pertes de friction ont ete mesurees dans des vannes a papillon et a opercule pleinement et partiellement ouvertes, les coudes et les raccords. Les valeurs des coefficients de pertes (kf) ont ete calculees et correlees en fonction du nombre de Reynolds classique et du nombre de Reynolds propose par Govier et Aziz (1972) pour des fluides viscoelastiques. La methode des deux k et un nouveau modele propose presentent les meilleurs ajustements pour le nombre de Reynolds de Govier et Aziz, et les nombres de Reynolds d'Hedstrom et classique, respectivement.

This article presents empirical correlations to predict the density, specific heat, thermal conductivity and rheological power-law parameters of liquid egg yolk over a temperature range compatible with its industrial thermal processing (0-61C). Moreover, a mathematical model for a pasteurizer that takes into account the spatial variation of the overall heat transfer coefficient throughout the plate heat exchanger is presented, as are two of its simplified forms. The obtained correlations of thermophysical properties are applied for the simulation of the egg yolk pasteurization, and the obtained temperature profiles are used for evaluating the extent of thermal inactivation. A detailed simulation example shows that there is a considerable deviation between the designed level of heat treatment and that this is predicted through process simulation. It is shown that a reliable mathematical model, combined with specialized thermophysical property correlations, provide a more accurate design of the pasteurization equipment that ensures effective inactivation, while preserving nutritional and sensorial characteristics.

Univ Estadual Paulista, Dept Engn & Tecnol Alimentos, BR-15054000 Sao Jose do Rio Preto, SP, Brazil

The net isosteric heat and entropy of water sorption were calculated for plum, based on sorption iso- therms obtained by the static gravimetric method at different temperatures (20 to 70 °C). The Guggenheim-Anderson- deBoer model was applied to the experimental data giving a good agreement between experimental and calculated values. The net isosteric heat of water sorption, estimated by applying Claussius-Clapeyron equation to sorption isotherms, was found to be different for plum skin and pulp, mainly at low moisture contents, and could be well adjusted by an empirical exponential relationship. Plots of enthalpy in contrast to entropy provided the isokinetic temperatures for skin and pulp, indicating an enthalpy-controlled sorption process. Thermodynamic data on water sorption for plums are not found in literature, as opposed to prunes for which the data are abundant.