Modelamento matematico do processo de esterilização de alimentos condutivos em embalagem de vidro / Mathematical model of the process of conductive food sterilization in glass packing

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

The aim of this work was to build a mathematical model of the heat transfer during the sterilization process of a conductive baby food packed in glass container. The 3-dimensional model was built using the finite element technique. The model considered the thermal properties of food, glass, headspace and metal cap individually. The sample initial temperature and the retort real temperature profile were the boundary conditions applied. Thermal properties of food, thermal conductivity, specific heat, density and thermal diffusivity, were experimentally determined. The obtained values were: 0.59 W/mºC, 3776 J/kgºC, 1024 kg/m3 e 1.54 x 10-7 m2/s, respectively. The value of the heat transfer coefficient (h) was calculated from time-Temperature profiles obtained experimentally. The thermal process was divided into 4 parts: come up, heating, early cooling (10 first minutes) and final cooling and different values of h were calculated for each part. The heat transfer model of the sterilization process was experimentally validated through processes carried out in water at 121°C. The linear regression between temperature profiles generated by the model and the ones experimentally obtained showed that they were in good agreement (R2=0.9925 and slope=1.0053), showing that the model was able to predict satisfactorily temperature distribution into the sample during sterilization process. Thermal death parameters, O and z, of Bacillus stearpthermophilus in baby food were determined. The results obtained for O value were 32.67,9.31 and 1.57 minutes at 110, 115 and 121°C, respectively. The z value obtained was 8.32°C. The mass average value was estimated and experimental processes were carried out at 110 and 115°C in order to validate the microbiological destruction mode!. At these processes, inoculated samples of baby food were submitted to sub lethal processes and the experimental microbiological destruction was determined and compared with the values estimated by the mode!. The results showed that for processes at 110°C the differences between experimental and predicted results were less than 12% and for those processes at 115°C this differences were less than 27%. Finally, two types of simulations set to achieve a Fp value of 9.42 minutes were done. The first group considering different retort heating rates (5 to 20°C/min) at 115 and 121°C and the latter obtaining part of Fp value at 115°C and part at 121°C. The thiamine retention of each process was estimated and the results showed that the higher Fp percentage is obtained at 121°C, the better the process is. No significant differences were observed in thiamine retention in equivalent process considering different retort heating rates at the same temperature

ASSUNTO(S)

autoclaves esterilização modelos matematicos metodo dos elementos finitos mathematical model baby foods method of finite elements alimentos sterilization

ACESSO AO ARTIGO

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