Mass Transport in Apple Tissue: Effects of Tissue Structure and Osmotic Processing Conditions

University dissertation from Nikolaos E. Mavroudis, Unilever Research at Colworth, Sharnbrook, Bedford, MK441LQ, UK

Abstract: Osmotic processing can be a very useful processing step in today’s food industry enabling the production of high quality natural food ingredients out of plant tissues. The maintenance of high product quality is quite product specific with regard to quality attributes. These attributes include fresh/like appearance, taste, texture and composition. Modern manufacturing trends and legislation regarding food labelling imposes great demand on methods to deliver the quality attributes imposed on the food industry by consumer preferences. This includes the accurate control of raw material characteristics and process parameters in each unit operation used for the manufacturing of an ingredient/product. This in turn calls for an improved understanding of product–process interactions. The present study attempts to enhance our understanding of product-process interactions in mass transport phenomena during osmotic processing. Recognising the biological nature of plant tissue and the significance of tissue structure in mass transport, the emphasis was placed on understanding the effects of initial tissue structure, raw material characteristics and structural alterations at the tissue and cellular level. Process conditions have been studied extensively in the past, therefore, the contribution to this area was focused on parameters useful for validating assumptions/suggestions arising from the interpretation of our results based on plant physiology concepts (i.e. temperature, medium composition). The medium agitation was the only process condition studied for clarifying its impact on the kinetics of water loss and solid gain, the two main process responses in osmotic processing. Acknowledging the biological nature of the raw materials led to the combination of food engineering and plant science concepts/methodologies. The best illustration of the synergy between these two different scientific areas has been the documentation of the existence of cell death instead of the previously held assumption that only cell plasmolysis proceeds immersion of plant tissue into the osmotic solution.

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