Use of mild heat pre-treatment of whole pineapples for quality retention and improved shelf-life of its fresh-cut fruits

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Mild heat pre-treatment has been used by a number of researchers to improve on the shelf-life and sensory qualities of fruits. The effect on sensory and nutritional attributes of fresh-cut MD2 and Smooth Cayenne pineapples subjected to mild pre-heat treatment at 60 °C, 70 °C, and 80 °C for 10, 20 and 30 min was studied. The optimum treatment condition that maintained the highest sensory and nutritional quality and variety was determined. Further studies was conducted to determine the effect of mild heat pre-treatment and storage condition (ambient and refrigeration) on the chemical (vitamin C content, pH values, TSS content and moisture content of treated and untreated pineapples), microbial (yeast, mould and aerobic bacteria) and sensory attributes of MD2 pineapple variety. A preference test to asses taste (sweet, sour balance), texture (firm, soft), and appearance/colour; and chemical (vitamin C and sugar content) analyses were carried out on the samples after a 24 h storage period during the first phase. Results showed that vitamin C content reduced with increased temperature and time of treatment in both varieties of pineapples. Total Soluble Solids (TSS) content of samples from both varieties increased with increase temperature at 10 min treatment. Sensory attributes (Taste, texture and appearance/colour) improved at some treatment conditions used in this experiment (80 °C -10min, 70 °C -10 min, 70 °C - 20 min, 60 °C -10 min). The optimum treatment condition and variety were 73.49 °C – 10 min and MD2 pineapple variety respectively where pineapples maintained the golden brown colour typical of MD2 variety and had an improved firmer texture and a good balance of sweet and sour taste highly preferred by consumers. Moisture, pH and TSS loss was reduced in treated MD2 fruits in both storage conditions during the second phase of the work. Shelf-life of the treated fruits was improved about a double fold in terms of microbial count (ambient treated and untreated = 2.3, 1.3; refrigerated treated and untreated = 6.2, 3.0) and vitamin C content (ambient treated and untreated = 12.0, 7.5; refrigerated treated and untreated = 27.0, 17.9).Thus mild heat pre-treatment technology for extending shelf-life of fresh-cut pineapples and maintaining sensory attributes will provide an alternative to the use of chemical additives.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Science.