Band 1, Heft 2

Three-dimensional mathematical model of the heat transfer during the sterilization process of a conductive baby food packed into glass container was built using the finite element technique. The heat transfer model was experimentally validated through processes carried out in water at 121°C. Chi-square and regression lines were obtained for each set of temperatures generated by the model against experimental data. Thermal death parameters, D and z, of Bacillus stearothermophilus in baby food were determined. The results obtained for D 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 also estimated and experimental processes were carried out at 110 and 115°C in order to validate the microbiological destruction model. For 110°C processes the differences between experimental and predicted results were less than 12% and for 115°C processes these differences were less than 27%.

Thirty longissimus dorsi (LD) muscles from Omani male goats were dried by five methods (sun, air, vacuum, freeze and modified atmosphere drying). Dried strips from the longissimus dorsi samples were evaluated for microbial, chemical and fatty acid composition and physical quality (pH, expressed juice, rehydration ratio, and color L*, a* and b* values). The method of drying had a significant effect on the microbial counts, pH, volume of expressed juice, color, rehydration ratio, and fatty acids content of LD samples. Immediately after drying and 6 weeks of storage, sun dried sample showed significantly higher aerobic plate counts, and levels of Pseudomonas and Staphylococcus compared to other methods of drying. The drying method significantly affected the types of mold growth in the samples.

The effects of quasi-nanoscale silver on preservation of both tomato juice and mixed juice from tomato and carrot were studied in this paper. The effective dose of quasi-nanoscale silver on tomato juice was found to be 0.1ppm, but when the same dose was applied to the mixed juice, heating at 100 deg.C for 5min was necessary. Furthermore, the effects of quasi-nanoscale silver combined with nipagin A on preservation of both tomato juice and the mixed juice from tomato and carrot were also investigated. The optimum combination pattern of quasi-nanoscale silver and nipagin A on both tomato juice and the mixed juice was found to be 0.04ppm of quasi-nanoscale silver and 200ppm of nipagin A. When this combination pattern was used in preservation of the mixed juice, it was again needed to heat the mixed juice at 100 deg.C for 5 min to be effective.

A step-by-step procedure for scaling up of an osmotic distillation system from laboratory to pilot plant is discussed. The newly built pilot scale OD system featured a flexibility of using 1 or 2 hollow fibre modules at a time to suit the concentration demands. Three types of hollow fibres were tested on the new system. Pilot trials for OD concentration of apple, grape juices and freeze concentrated (FC) grape juice were successfully carried out to achieve a final concentration up to 65°Brix with fluxes ranging from 2.4 to 0.69kg.m-2.h-1 depending on the fibre types and the operating conditions. Cascade effect was also employed to deal with high viscosity to achieve high concentration. The obtained pilot OD fluxes were comparable to the ones obtained in the lab under similar conditions, and they fitted well with the developed models. Sensory evaluation indicated that OD well preserved the quality attributes of the fruit juices.

Surface tension of different homogenized milk and cream, available in New Zealand, has been measured using the ‘Capillary Rise’ method as well as the automated ‘Wilhelmy Plate’ method. The measured values are slightly higher than the values reported in the literature. Increasing the fat content is found to have an inverse effect on the surface tension. This effect diminishes progressively for fat concentrations beyond 30%. Milk proteins, reported in the literature as surface-active components, are observed to have no effect on the surface tension.