Effect of ultrasonication on the quality of amla pulp (Emblica officinalis): Optimization and comparison with the thermal processing

Abstract

Amla pulp was treated with ultrasonication technique under the different set of designed conditions in order to optimize the ultrasonic conditions. A two factor four level Taguchi design was adopted to study the effect of ultrasonic intensity (180 – 717 W/cm2) and treatment time (4 – 16 min) on the ascorbic acid, naringin, total phenolic content, titratable acidity, total soluble solids, browning index, polymethylesterase and polyphenol oxidase activity of amla pulp. The optimal conditions were determined as ultrasonic intensity, 359 W/cm2 and treatment time, 12 min on the basis of S/N ratio analysis. Optimized ultrasonicated pulp was compared with the thermally treated pulp (90 °C/ 5 s) to observe the effect on quality parameters. Enzymatic activity reduced to a lower level at optimal ultrasonic processing conditions. Total phenolic content increased after ultrasonication treatment. LCMS of the optimized sample depicted the presence of compounds like ascorbic acid, corilagin, gallic acid, kaempferol, chebulagic acid and many more. Thermal treatment showed lower retention of bioactives and there were notable losses in ascorbic acid and total phenolic content. Browning index was also higher than control and ultrasonicated pulp sample. Microstructure of ultrasonicated sample showed damage to cells but thermal treated sample exhibited major cell damage.