Newtown Pippin and Winesap apples were taken from terminal storage, and prepared as slices to be processed in re-tortable pouches to determine an optimum process using the relatively new pouch technology. Preprocessing treatments included calcium chloride as a texture modifier, sodium bisulfite as a microbial inhibitor and colour stabiliser, and sodium acid pyrophosphate as a colour stabilizer. These reagents were added to the slices by vacuum infusion, hot blanching or cold dipping to determine their effects on the final product. The slices were packed in 300 gram pouches that were evacuated, then flushed with either nitrogen or carbon dioxide before sealing. The samples were stored at 22 and 35°C and were examined by physical, chemical and sensory methods, at intervals of two weeks, six weeks and five months after processing to determine the changes occurring within the samples. During storage, quality changes did occur, which affected the acceptance of the samPles/ particularly at the higher temperatures. Texture was vastly improved with the addition of calcium ions to old apples. Colour remained significantly lighter in samples with higher SO₂ levels. The addition of pyrophosphate was also shown to increase the lightness of the samples. The levels of reducing sugars and pH were shown to increase with the length and temperature of storage. Preparatory methods were also shown to have a great influence on the quality of the final product. Hot blanching of apple slices lead to a lower quality product than either vacuum infusion or cold dipping. Vacuum infusion was by far the most efficient preparatory method but resulted in a product with a translucent appearance and a bland flavour. Cold dipping produced the best final product. The use of carbon dioxide atmospheres within the pouch produces a lower pH and a softer texture in the samples. Nitrogen was found to be the better of the two gases for quality maintenance. In general, it was determined that apples from terminal storage were more difficult to process into a product of good quality than were apples stored for only a short time after harvest. / Land and Food Systems, Faculty of / Graduate

The application of pulsed electric fields (PEF) in food processing is a novel technique that requires careful study. In addition, improved understanding of the effect of PEF parameters on both physical and qualitative attributes of agrifood products is a requirement for the application and control of this emerging technology. PEF parameters investigated were pulse widths of 100, 200, and 300 mus, with electric field strengths of 0.75 and 1.5 kV/cm. The amount of pulses used for apples was up to 60, whereas up to 120 pulses were used for potatoes. Initially, apple and potato slices were exposed to various combinations of PEF parameters in order to evaluate the change in their electrical conductivities as an indicator of the disruption of the cell membrane. Subsequently, the impact of PEF on color and texture attributes was studied. In the final set of experiments, PEF was applied as a pre-treatment in order to accelerate the diffusion of moisture in a convective air-drying process at 70°C. / Results regarding the electrical conductivity and the changes in color revealed the similar effect of applying pulses with 100, 200 and 300 mus of duration. Increasing the number of pulses and/or the electric field strength resulted in increased electrical conductivity and discoloration rates of samples. PEF reduced the compressive strength of apple tissues between 21 to 47%. However, the compressive strength of potato tissues did not seem to be affected by the application of PEF. When PEF was applied as a pre-treatment, it caused an increase of up to 30% in the moisture diffusion coefficients of potatoes. In the case of apples, PEF pre-treated samples did not show any increase in drying rates.

No description available.