Effect of Pretreatments on Enzyme Inactivation Kinetics, Quality Attributes, and Microbial Stability of Amla (Emblica officinalis) Juice

Amla, highly valued for its exceptional nutritional and medicinal properties, has limited shelf-life and its astringent flavor limits its fresh consumption, thereby, necessitating processing into value-added products such as juice. This study evaluated the influence of different pretreatments - hot water (HB), steam (SB), and microwave blanching (MB) - on enzyme inactivation juice recovery, physicochemical and phytochemical quality, and microbial stability during ambient storage. The Polyphenol oxidase (PPO) and Peroxidase (POD) inactivation during each blanching was fitted to First order, Biphasic and Weibull model. In both the cases of enzyme inactivation, Weibull model was found to best fit the data. The blanching criterion was 90% reduction of enzyme activity; and it was achieved upon treatment for 180s, 120s, and 150s in case of HB, SB, and MB, respectively. Moreover, SB significantly improved juice yield but caused marked browning and substantial degradation of phytochemicals. In contrast, MB and HB produced juice yields comparable to the untreated control, although the latter resulted in greater losses. During seven days of ambient storage, all juice samples exhibited a decline in ascorbic acid and phenolic content, accompanied by increased browning and microbial growth, whereas pH and total soluble solids remained relatively stable. Also, SB juice exhibited the highest degradation rate constant, while MB exhibited lowest for ascorbic acid and HB juice exhibited higher degradation of phenolic compounds during storage in comparison to SB and MB. Spoilage occurred within six days for all treatments, with the control deteriorating fastest (within four days), followed by microwave- and hot water-blanched juices, which spoiled within five days. Overall, the findings demonstrate that the selection of appropriate pretreatment strategies can enhance processing efficiency, improve product quality, and reduce post-processing losses, thereby contributing to more sustainable amla juice production.