Effect of pasteurization temperature on quality of aonla juice during storage

A study was carried out to detect the changes in colour and quality attributes of aonla juice during storage after pasteurization at different temperatures. After extracting juice from aonla cv. Chakaiya, it was pasteurized at five different temperatures and preserved with 500 ppm SO2 in PET bottles under ambient conditions. Juice was periodically analysed for colour and chemical characters up to 9 months of storage. Though the contents of ascorbic acid and polyphenols in juice decreased with increase in storage period, the effect of pasteurization temperature was not significant. High degree of browning was observed in juice heated at higher temperatures (90 and 95 °C) as compared to lower temperatures (75 and 80 °C) throughout the storage period as indicated by increase in NEB values. The degree of browning was further confirmed by higher negative numerical values of whiteness index in Hunter's scale for intensity of colour. HPLC data indicated that content of gallic acid in juice decreased initially but increased sharply as the storage period prolonged. Higher amount of gallic acid was detected after 9 months of storage in juice pasteurized at 95 °C than in juice heated at 75 °C. The contents of kaempferol and caffeic acid decreased throughout the storage period irrespective of pasteurization temperature. Though least browning was observed in juice pasteurized at 75 °C, but microbial growth was observed after 9 months of storage. Hence, pasteurization temperature of 80 °C was found optimum for preservation of aonla juice under ambient conditions.