Viviana O. Salvadori

Weight loss during freezing and storage of unpackaged foods

Dehydration of unwrapped foods occurs during freezing and frozen storage. Coupled heat and mass balances were proposed incorporating solidification of water and sublimation of ice. The mathematical model was solved using an implicit finite-differences method, with a variable grid to follow the moving sublimation front. The model evaluates temperature and water concentration profiles and was used to predict the kinetics of weight loss for different products. Model predictions were favourably compared against experimental data on weight loss during storage of unwrapped meat, potato and tylose.

Analysis of impingement freezers performance

In recent years, several manufacturers have developed mechanical freezing tunnels incorporating impingement technology. This technology consists in directing high velocity air jets against the food surface to break the insulating boundary layer that surrounds the product. This operation helps to reduce processing times considerably, giving freezing times similar to those provided by cryogenic equipment. In addition, operating costs are similar to those of traditional mechanical equipment. The objective of the present work is to study heat and mass transfer that occur in impingement freezing equipment. An extensive bibliographic search was carried out to find correlations that adequately predict heat transfer coefficients. A previously developed numerical model was used to analyze the simultaneous heat and mass transfer during freezing in such equipments. The predicted values satisfactorily fitted experimental data from the literature.

Freezing of strawberry pulp in large containers: experimental determination and prediction of freezing times

Abstract Strawberry pulp packed in bulk in containers of various shapes and of large sizes (10–2001) was frozen in a tunnel at −35°C. Time-temperature curves and freezing times for heat transfer in one, two and three dimensions were obtained. Experimental freezing times were compared with predicted values given by approximate methods based on two different equations for the calculation of freezing times in slabs, which in turn used three different methods for the calculation of shape factors. The predicted results obtained in this work confirmed that both the simplified prediction methods of freezing times and the shape factors used were sufficiently accurate for the design of freezing equipments for these types of product and working conditions.

Baking of muffins: Kinetics of crust color development and optimal baking time

Baking is a decisive stage in the production of bakery products, in general—muffins, in particular—for most of the quality attributes of the final products depend on it. The aim of this work is to model the kinetics of muffin crust color development during baking and to evaluate the feasibility of this kinetic model to predict the baking times. Surface color is represented by the Browning Index, and the effect of baking temperature (from 140 to 220 °C) and process convective characteristics (natural convection, forced convection, and steam-assisted forced convection) are analyzed. Minimal baking times are calculated from experimental core temperature measurements. The modeling of browning kinetics, which incorporates the optimal crust color determined by sensory analysis, allows the estimation of optimal baking times. For all the tested conditions top > tmin, assuring a product whose inner structure was already totally baked. Finally, minimal, half, and optimal baking times present an exponential dependence with the oven temperature. Besides, there are no significant differences between both forced convection modes.

Optimization of thermal processing of canned mussels

The design and optimization of thermal processing of solid–liquid food mixtures, such as canned mussels, requires the knowledge of the thermal history at the slowest heating point. In general, this point does not coincide with the geometrical center of the can, and the results show that it is located along the axial axis at a height that depends on the brine content. In this study, a mathematical model for the prediction of the temperature at this point was developed using the discrete transfer function approach. Transfer function coefficients were experimentally obtained, and prediction equations fitted to consider other can dimensions and sampling interval. This model was coupled with an optimization routine in order to search for different retort temperature profiles to maximize a quality index. Both constant retort temperature (CRT) and variable retort temperature (VRT; discrete step-wise and exponential) were considered. In the CRT process, the optimal retort temperature was always between 134 °C and 137 °C, and high values of thiamine retention were achieved. A significant improvement in surface quality index was obtained for optimal VRT profiles compared to optimal CRT. The optimization procedure shown in this study produces results that justify its utilization in the industry.

Application of transfer functions to the thermal processing of particulate foods enclosed in liquid medium

Abstract The application of transfer functions in foods for heat and mass transfer problems with variable boundary conditions has been the subject of several studies over the last decade. In this work, the heat processing of products immersed in a low-viscosity medium (where convection is the main heat transfer mechanism), is analyzed. The thermal histories are related to kinetic parameters to evaluate the target value of different processing conditions to inactive quality-degrading enzymes.

Effect of Processing Conditions on Calcium Content, Firmness, and Color of Papaya in Syrup

Calcium impregnation is used as a pretreatment in the processing of papaya in syrup. The effect of process temperature (30 and 45°C), calcium source (calcium gluconate and calcium lactate), calcium concentration (0.5 and 1.5% w/w), and pH (4.2 and 6) were studied. The mineral source affected significantly the calcium uptake and the fruit firmness, and therefore, the product quality maximum content of calcium in the fruit was 240 and 72 mg/100 g fresh fruit in 8 h of treatment with calcium lactate and calcium gluconate, respectively. Greater firmness was observed in samples impregnated with calcium lactate. Impregnation treatments did not affect the surface color of fruit. Finally, the effect of cooking in sucrose syrup on product quality attributes (calcium retention, firmness, and color) was analyzed. Cooking in syrup had a positive effect on tissue firmness, despite the decrease of calcium content. During cooking in syrup, calcium content of treated fruit decreased between 9% and 37%. However, the calcium content of fruit in syrup was up to 6 times higher than in fresh fruit. Moreover, the cooking stage had a strong influence on color parameters, leading to a processed product darker than fresh fruit.

Influence of baking conditions on the quality attributes of sponge cake

Sponge cake is a sweet bakery product characterized by its aerated and soft crumb and by its thin-coloured crust. The aim of this work is to analyse the influence of baking conditions (natural or forced convection, steam injection, oven temperature from 140 ℃ to 180 ℃) on sponge cake quality. Both crust and crumb regions were characterized by means of colour development, water content, crust/crumb relation, crust thickness and crumb structure (in terms of porosity, crumb density and texture). Colour measurements allowed obtaining an accurate model for browning kinetics. Crumb water content remains almost constant, while considerable dehydration occurs in the crust. In general, no significant differences due to baking conditions were found in the instrumental quality analysis.

An Algorithm for the Prediction of Freezing Times and Heat Loads Adequate to Use for the Control of Food Freezing Equipment

Abstract An existing simplified algorithm for food freezing time calculations is adapted to also predict thermal centre temperature and heat load. The algorithm divides the freezing process in three stages: prefreezing (cooling), phase change and tempering. For each stage specific calculation procedures are developed. Predicted results of heat load and freezing time are favourably compared against an already proven numerical model for the same process.