Influence of drying conditions on the gelling properties of the 7S and 11S soy protein fractions

Soy protein fractions rich in β-conglycinin (7S) or glycinin (11S) were freeze dried or spray dried at temperatures of 120, 150 or 180 °C. The fractions were characterized for their particle size distribution, sorption isotherms and by scanning differential calorimetry. The gelling capacity of the protein fractions was studied at pH values of 3 and 7 using oscillatory measurements, mechanical properties and water holding capacity. The rheological measurements showed that viscous modulus (G″) predominated at low temperatures and the elastic modulus (G′) at high temperatures. At pH 3, the G′–G″ crossover occurred at lower temperatures when compared to pH 7. This behaviour was more accentuated for the 11S fractions due to its capacity to form stronger gels. An increase of drying temperature led to a displacement of the gel point to higher temperatures and decreased the elasticity modulus or gelling capacity of protein fractions. These results were confirmed by the mechanical properties, since at higher temperatures the gels were more fragile and brittle, especially when formed at pH 7.     

Evaluation of the mechanical properties and diffusion coefficients of osmodehydrated melon cubes

The objective of this work was to evaluate the influence of osmotic agents, their concentration and temperature, on the mass transfer kinetics and mechanical properties of osmodehydrated melon cubes. Samples were immersed in a hypertonic solution of sucrose or maltose up to 8 h under controlled temperature and agitation. Water loss, sugar gain and mechanical properties were analysed throughout the process. Mass transfer kinetics was modelled according to Peleg and Fick equations. Higher water loss, lower sugar uptake and stress at rupture values more similar to fresh fruit were observed in samples treated with maltose solutions. Peleg’s model showed the best adjustment to all the experimental data, however the k₁ and k₂ parameters did not show a clear trend with the solution concentration or temperature increase. The effective diffusivity obtained using Fick’s equation varied from 3.93 × 10^?9 to 6.45 × 10^?9m² s^?1 for water loss and from 7.57 × 10^?10 to 3.14 × 10^?9m² s^?1 for sugar gain.     

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

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 wet salting was 0.26 × 10^-10m²/s at20°C and 0.25 × 10^-10 m²/s at 10°C and for the dry salting the values were 19.37 × 10^-10 m²/s at 20°C and 17.21 × 10^-10 m²/s at 10°C.     

Development of Active Films From Pectin and Fruit Extracts: Light Protection,Antioxidant Capacity,and Compounds Stability

Pectin films containing fruit extracts were developed and tested in relation to ultraviolet light transmission, phytochemical contents, and antioxidant capacity during 90 d shelf life storage. Aqueous and alcoholic extracts from 5 different fruits (acerola, cashew apple, papaya, pequi, and strawberry) were obtained. Because the alcoholic extracts from acerola, cashew apple, and strawberry presented the highest phytochemical content and antioxidant capacity, they were incorporated into pectin films individually or as a mixture. Incorporation of these extracts into pectin films provided antioxidant capacity while retaining the physical properties. The pectin films containing fruit extract acted as adequate light barrier and prevented photooxidation. Among the prepared films, the pectin film containing acerola extract afforded the highest antioxidant capacity, with a half‐life of 99 d. Overall, the results revealed that incorporation of fruit extracts into pectin films potentially produces antioxidant films and coatings for different food applications.     

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 wet salting was 0.26 × 10^?10m²/s at20°C and 0.25 × 10^?10 m²/s at 10°C and for the dry salting the values were 19.37 × 10^?10 m²/s at 20°C and 17.21 × 10^?10 m²/s at 10°C.     

DRYING OF ONION: EFFECTS OF PRETREATMENT ON MOISTURE TRANSPORT

ABSTRACT

This study investigated the drying of osmosed and fresh onions. Onion slices (0.8 × 0.8 × 0.15 cm) soaked in sodium chloride solutions (10 and 15% w/w) for 60 min at 22°C were submitted to air drying. The experimental kinetics data obtained were employed to determine effective diffusivity, using a mass transfer model based on Fick's law of diffusion applied to thin slabs. The results show those samples soaked in the 10% NaCl solution had faster drying rates and larger moisture diffusion coefficients. The drying time of onions can be reduced to less than half by introducing an hour of osmotic dehydration in a salt solution. The dried previously osmosed samples presented a more natural coloration than the untreated ones did.     

Mass transfer kinetics and mathematical modelling of the osmotic dehydration of orange‐fleshed honeydew melon in corn syrup and sucrose solutions

A simple mathematical model to predict dehydration and impregnation process during osmotic dehydration of orange‐fleshed honeydew in sucrose and corn syrup solutions was proposed. Results showed low dispersion and a good fitting capability for WL and SG kinetics. Diffusivity values for WL ranged from 0.96 × 10^?10 to 2.22 × 10^?10 and 1.04 × 10^?10 to 3.10 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. For SG, the obtained range was 0.72 × 10^?10 to 2.35 × 10^?10 and 0.71 × 10^?10 to 2.46 × 10^?10 m² s^?1 in corn syrup and sucrose solutions, respectively. The half‐life of dehydration rates (t_1/2) was from 30.9 to 71.2 min and from 19.4 to 57.5 min in corn syrup and sucrose solutions, respectively. Diffusivities values obtained according to the proposed model were close to the ones observed from diffusive model; t_1/2 was a promising criterion for the process time definition.     

Modelling of mass transfer and texture evaluation during osmotic dehydration of melon under vacuum

The influence of vacuum time and solution concentration on mass transfer and mechanical properties of osmodehydrated melon cubes has been studied. Pulsed vacuum osmotic dehydration (PVOD) was carried out at 30 °C for 4 h, using sucrose solutions (40, 50 or 60°Brix) and applying a vacuum pulse (100 mbar for 5, 10 or 15 min). Kinetics of water loss, solid gain and stress at rupture were analysed, as well as effective diffusivities using the hydrodynamic model. The increase in solution concentration favoured water removal, but no significant effect of vacuum time was observed. The use of less concentrated solutions coupled to the action of vacuum pulse resulted in greater solid uptake. Samples subjected to PVOD using 60°Brix sucrose solution presented greater water loss, lower sugar uptake and better maintenance of fresh fruit texture throughout the process. Diffusion coefficients estimated by the hydrodynamic model showed a good fit to the experimental data.     

Calcium lactate effect on the shelf life of osmotically dehydrated guavas

The effect of calcium lactate on osmodehydrated guavas in sucrose and maltose solutions was monitored during storage under passive modified atmosphere for 24 d at 5 °C. Sample texture and color characteristics, microbial spoilage, sensory acceptance, structural changes, and gas composition inside the packages were periodically evaluated. Calcium lactate inhibited microbial growth on guavas, with yeast and mold counts in the order of 10(2) CFU/g throughout storage. The calcium salt reduced respiration rate of guava products, showing O(2) and CO(2) concentrations around 18% and 3% inside the packages. A firming effect on fruit texture, with up to 5 and 2 times higher stress and strain at failure values and tissue structure preservation could also be attributed to calcium lactate use. However, fruits treated with calcium lactate, osmodehydrated in maltose and sucrose solutions, showed sensory acceptance scores below the acceptability limit (4.5) after 13 and 17 d of storage, respectively.