Miriam Dupas Hubinger

Prediction of water activity of osmotic solutions

Models to correlate and predict water activity in aqueous solutions of single and multiple solutes, including electrolytes, relevant for osmotic processing of foods are reviewed. During the last decade a significant number of theoretical thermodynamic models that are applicable to these systems have been developed and published. Though their use is still limited, their performance is in general very good, similar to the best traditional empirical equations. Their predictive character together with built-in capabilities to work at different temperatures and in some cases pressure suggests that an increased effort to their wide use should take place. It was found that predictions of water activity in aqueous solutions may easily be made with average relative deviations of less than 2%; this value is of the same order or in some cases less than the typical error of current instrumentation available to measure water activity.

RHEOLOGICAL PROPERTIES AND COLOUR EVALUATION OF PAPAYA DURING OSMOTIC DEHYDRATION PROCESSING

Abstract Osmotic dehydration of papaya pieces using sucrose solution with additives was studied. Four types of solutions with different concentrations of sucrose, citric or lactic acid and sodium lactate or calcium chloride were employed. Water loss and sugar gain were fitted to a Fick mathematical model and showed that mass transfer increases as temperature or soaking solution concentration increases. The presence of calcium chloride in the osmotic solution seemed to improve sugar impregnation during the osmotic process. The results showed that high temperatures with the combined use of lactic acid and sodium lactate promoted faster water activity decay. The effect of osmotic dehydration on the colour parameters (luminosity and chroma) and rheological properties (stress at rupture and relaxation time) were investigated. Chroma values increased, denoting colour intensification along the process. Luminosity showed a slight increase for samples treated with CaCl2, but for the other treatments lightness decreased in the first hour and returned for the initial values along the process. Calcium chloride showed to be effective in reinforcing tissue structure, presenting stress at fracture values for dehydrated papaya with calcium salt around three-fold higher than for other treatments. Processing at 50 °C with sodium lactate prevented over-softening of the tissue during the whole process, with greater water activity reduction.

Microencapsulation of Flaxseed Oil by Spray Drying: Effect of Oil Load and Type of Wall Material

The objective of this work was to evaluate the effect of the type of wall material and the oil load on the microencapsulation of flaxseed oil by spray drying. Gum arabic, whey protein concentrate, and a modified starch were used to produce the microcapsules, each with four oil concentrations (10, 20, 30, and 40% oil, w/w, with respect to total solids), for a total of 12 tests. Initially, the feed emulsions were characterized for stability, viscosity, and droplet size. Then they were dried in a laboratory-scale spray dryer and the resulting particles were analyzed for encapsulation efficiency, lipid oxidation, moisture content, and bulk density. The increase in oil concentration led to the production of emulsions with larger droplets and lower viscosity, which directly affected powder properties, resulting in lower encapsulation efficiency and higher lipid oxidation. Among the three wall materials evaluated, the modified starch showed the best performance, with the highest encapsulation efficiency and lowest peroxide values.

Effect of Cassava Starch Coating on Quality and Shelf Life of Fresh‐Cut Pineapple (Ananas Comosus L. Merril cv “Pérola”)

This research studied the influence of treatment with ascorbic acid, citric acid, and calcium lactate dipping and cassava starch edible coatings on quality parameters and shelf life of fresh-cut pineapple in slices during 12 d at 5 °C. After previous tests, the treatments selected for this study were samples dipped into antibrowning solution with 0.5% of ascorbic acid and 1% of citric acid, with and without 2% of calcium lactate and coated with 2% of cassava starch suspensions. Changes in weight loss, juice leakage, mechanical properties (stress at failure), color parameters (L* and H*), ascorbic acid content, sensory acceptance, and microbial growth of fruits were evaluated. Samples only treated with antibrowning agents were used as control. Edible coatings with and without calcium lactate were efficient in reducing weight loss, juice leakage, and maintaining firmness during storage. However, these samples showed more browning and the ascorbic acid content was reduced. All treatments presented good sensory acceptance (scores above 6). The determining factor of shelf life of pineapple slices was the microbial spoilage. A shelf life of 8 d was obtained for pineapple slices only treated with antibrowning agents. On the other hand, coated samples showed a reduced shelf life of 7 d and higher yeast and mold growth. Thus, although cassava starch coatings were efficient in reducing respiration rate, weight loss, and juice leakage and maintained mechanical properties, these treatments were not able to increase the shelf life of minimally processed pineapple. Practical Application: Pineapple fruit is highly appreciated for its aroma, flavor, and juiciness, but its immediate consumption is difficult. Therefore, pineapple is a potential fruit for minimal processing. However, shelf life of fresh-cut pineapple is very limited by changes in color, texture, appearance, off-flavors, and microbial growth. The use of edible coatings as gas and water vapor barrier and antibrowning agents can extend the storage time and maintain the quality of fresh-cut produce. Cassava starch and alginate coatings are alternative to preserve minimally processed pineapples without changing the quality parameters of fresh fruit. Thus, this study is useful for consumers and fresh-cut industry interested in knowing factors affecting shelf life and quality of fresh-cut pineapple.

Conservação do açaí pela tecnologia de obstáculos

The study of preservation process of the assai pulp through the application of hurdle technology was done by the application of the following preservation factors: reduction of pH at about 3.5 by the addition of 0.5% w/w of citric acid, thermal treatment (82.5°C for 1 min), reduction of the water activity by the addition of sucrose (10, 25 and 40% w/w) and addition of potassium sorbate (0.075 and 0.15% w/w). A full factorial experimental design was used in the elaboration of the formulations of the product, that were stored at 25°C in the absence of light for 5 months. The formulations 1, 2 and 8 were discarded sensorially before 3 months storage. Besides, the formulations 2 (40%w/w of sucrose), 4 (40%w/w of sucrose and 0.15%w/w of potassium sorbate) and 5 (25%w/w of sucrose and 0.075%w/w of potassium sorbate) showed a good overall acceptability shelf-life time of 5 months.

Kinetic Aspects, Texture, and Color Evaluation of Some Tropical Fruits during Osmotic Dehydration

ABSTRACT Osmotic dehydration of some tropical fruits like guava, melon, and papaya using sucrose and maltose solutions is presented in this article. The influence of sugar type and concentration, process temperature, and calcium salt addition on osmotic solution was investigated. Water loss and sugar gain up to 6 h of processing were evaluated and the effect of osmotic dehydration on fruit quality parameters like color and texture was analyzed. All studied variables affected the osmotic process kinetics, while for quality parameters the influence of sugar type or solution concentration and temperature was dependent on fruit and process conditions.

MASS TRANSFER AND DIFFUSION COEFFICIENT DETERMINATION IN THE WET AND DRY SALTING OF MEAT

ABSTRACT Dehydrated salted meat is widely used in Brazil as a very important source of animal protein. The main objective of this kind of processing is water removal. initially by osmotic pressure changes and then by drying, resulting in a product with intermediate moisture levels. In this work, mass transfer and salt diffusion in pieces of meat submitted to wet and dry salting were studied. Slabs of beef m. trapezius with an infinite plate geometry were salted in a NaCl saturated solution or in a dry salt bed, at two temperatures (10 and 20°C) and different time exposures (120 min and 96 hours). Equilibration studies were extended up to six days. It was observed that water loss increased with salt uptake, for increasing periods of times. At 20°C the moisture loss was higher than it was at 10°C in both salting processes. On the other hand, the kinetics of salt uptake and moisture loss were of greater importance in the process of dry salting than in that of wet salting. The salt diffusion coefficient for w...

Influence of spray drying conditions on physicochemical properties of chicken meat powder.

The influence of spray-drying conditions on the physicochemical properties of chicken meat hydrolysate powder was studied in this work. Enzymatic reaction, using Alcalase® (Novozymes, Bagsvaerd, Denmark), was carried out at 52.5°C, 4.2 g enzyme/100 g protein, and pH of 8.0 to obtain protein hydrolysate. The spray drying was carried out on a laboratory spray dryer and maltodextrin 10DE was used as carrier agent. A central composite rotatable design was used to evaluate the effect of the independent variables inlet air temperature, feed flow, and maltodextrin concentration on the responses powder moisture content, bulk density, mean particle diameter, and hygroscopicity. All variables had a significant effect on the properties and morphology of protein hydrolysate powder.

Influência da temperatura do ar de secagem e da concentração de agente carreador sobre as propriedades físico-químicas do suco de açaí em pó

The objective of this work was to study the influence of inlet air temperature and maltodextrin concentration on the physicochemical properties of acai juice powder produced by spray drying. The process was carried out in a mini spray dryer and the maltodextrin 10DE was used as carrier agent. Inlet air temperature varied from 138 to 202 °C and maltodextrin concentration varied from 10 to 30%. The characteristics analyzed were: moisture content, hygroscopicity, anthocyanin retention, color, particle size distribution, and morphology. The increase in the temperature resulted in particles with larger size, less moisture content, more hygroscopy and with lower anthocyanin retention, besides promoting a reduction in the color parameter L* and in the hue angle H*. The increase of maltodextrin concentration resulted in less hygroscopy, particles with larger size, , with higher luminosity (L*), lower C* values and higher H* values. With respect to morphology, the increase in the temperature led to the formation of a great number of particles with smooth surface, which is due to the higher heat transfer and, consequently, to the faster formation of a membrane around the atomized drop.

Influence of Process Conditions on the Mass Transfer Kinetics of Pulsed Vacuum Osmotically Dehydrated Mango Slices

The pulsed vacuum osmotic dehydration of mango slices was studied using a 25–1 fractional factorial design. The process responses were water loss, solids gain, water activity, and the effective diffusivities of the water or solids. Statistical analyses revealed that temperature and solution concentration were significant for all the responses studied. Vacuum time was significant for solids gain and the effective diffusivity of water. Diffusion coefficients were determined using an analytical solution of Ficks unidirectional diffusion equation for flat plates, showing a good fit to the experimental data. Osmotic recirculation and vacuum pressure had no effect on any of the responses studied.