Abstract:
The objective of the present study is to investigate the effect of pineapple variety and size on the yield and optimization on the physicochemical properties of the juice pasteurised by microwave and conventional method employing Response Surface Method (RSM). The pineapple variety significantly (p<0.001) influenced the total soluble solids, titratable acidity and ascorbic acid. Large size smooth cayenne variety had the highest (559.256 ml/kg) juice content. The sugarloaf variety recorded the highest brix content while the MD2 variety had the highest titrable acidity(TA) and acsobic acid(AA). Data obtained were compared with conventional pasteurisation (80-90oC for 60-180 secs). It was shown that microwave pasteurised pineapple juice had a significant positive influence on total soluble solids, pH, total antioxidant content, ascorbic acid and total phenol compared to conventional pasteurisation treatment. The optimised microwave and conventional pasteurised juice were obtained at 900W/180secs and 90oC/60 secs, respectively. Optimised microwave pasteurised pineapple juice was prepared and stored under room temperature, supermarket and refrigeration conditions and quality changes studied every (7) day for 21 days. The shelf life of refrigerated microwave pasteurised pineapple juice was 21 days compared to only 14 days for supermarket and room temperature conventional pasteurised pineapple juice. No significant changes were detected in total antioxidant values after storage of both pasteurised pineapple juice. However, the differences in pH, total soluble solids (TSS), titratable acidity (TA) total phenolic (TP) content, ascorbic acid content, and total phenols (TP) throughout the 21days storage period was observed to decrease in a fluctuating order under room and supermarket condition. The degradation of these nutrients was rapid in the conventional pasteurised juice during storage, as compared to refrigerated microwave pasteurised pineapple juice. Therefore, it can be concluded that microwave treatment is a potential alternative for fruit juice pasteurisation, especially for small scale industrial application.
