Osmótica dehydration in ternary solutions, thermal drying and transistions of filé of tilápia (Oreochromis niloticus) / Desidratação osmotica em soluções ternarias, secagem e transições termicas de file de tilapia (Oreochromis niloticus)

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

In this work the osmotic dehydration in ternary solutions (NaCl-water-sucrose) and drying processes of Tilapia fillet (Oreochromis niloticus) were studied. Moreover the calorimetric study of impregnated fillet with sodium cWoride, sucrose or both solutes was developed and denaturation and glass transition temperatures were determined. The osmotic dehydration was carried out at 20°C, using well agitated solutions at different concentrations (0-35.14 g of NaCI and 0-100 g of sucrose, in 100 g water) and small relation volumes (solution/fillet, 4/1). Kinetics of water activity, moisture content reduction and solute gain were studied, and the apparent diffusion coefficients of solutes were determined. For binary solutions, the diffusive model for limited volumes was used with the analytical solution; for temary solutions, a multicomponent diffusive model for small volumes was used. The drying of osmotically dehydrated Tilapia fillets in aqueous binary solutions of sodium chloride and ternary (NaCl-water-sucrose) ones, processed up to 5 and 10 hours, was studied. This step was carried out at temperatures of 50 and 60°C with flowing air parallel to surface. The influence of process temperature and solutes gain during pretreatment in drying kinetics was evaluated. A diffusive model considering shrinkage was used and the model also considered constant and variable apparent water diffusivity. The effective water diffusivity, when constant, was obtained through fitting of diffusive model, which enabled an analytical solution, to the experimental data. In the other case, the model that considered apparent diffusivity as linear and as exponential function of moisture content was solved by finite difference explicit method. The effect of sodium chloride and sucrose gains, during the osmotic dehydration of Tilapia fillets, on proteins denaturation temperatures (Td) and glass transition temperatures (Tg) was studied, with the aim of determining the maximum drying temperatures and adequate storage conditions. The differential scanning calorimetry (DSC) and differential scanning calorimetry with modulated temperature (TMDSC) techniques were used to determine the denaturation and glass transition temperatures, respectively. Enthalpy and denaturation temperature of myofibrilar proteins decreased with increasing in NaCl contents on finet, but increased slightly with sucrose increase. A higher influence of NaCl on this property was observed when temary solutions were used (NaCl-water-sucrose). The glass transition temperature was mainly influenced by sodium ch1oride finet content. In comparison to fillet without treatment, the Tg presented a higher value at low water activity and smaller values at high water activity

ASSUNTO(S)

massa - transferencia calorimetria diffusion difusão glass transistion temperature

ACESSO AO ARTIGO

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