Influence of Pre-treatment on Secondary Metabolites and Hypo-Glycemic Activity of Custard Apple (Annona squamosa) Peel

ABSTRACT

Plant secondary metabolites, present in the outer layers of fruits and vegetables in higher amounts, are structurally diverse and comprise different classes of phyto-constituents that have a number of health-promoting properties. Blanching is an important pre-treatment that is used to inactivate the enzymatic oxidation. Methods: This study was designed to investigate the effects of steam blanching (3, 5 and 7 min) and drying (50ºC) of custard apple (Annona squamosa) peel on the quantification of secondary metabolites and hypo-glycemic activity. Unblanched sample dried at 50ºC served as control. Quantitative tests for alkaloids, tannins, saponins and flavonoids were carried out for all samples and in vitro alpha amylase inhibition test was done to confirm the hypo-glycemic properties. All analyses were done in triplicates. Results: Quantitative results for alkaloids, tannins, saponins showed a significant reduction (p0.05). The exception was observed in the flavonoid content which showed a significant increase for 3 min and 5 min blanched samples, while the 7 min blanched sample showed a reduction in flavonoid content over the unblanched and fresh samples. Alpha amylase inhibition test similarly showed a decreasing trend for blanched samples ranging from IC50 value of 3.31 to 5.53 μg/mL compared to the unblanched with IC50 value of 4.92 μg/mL and fresh sample with IC50 value of 6.37μg/mL. Conclusion: From the study, it is inferred that steam blanching and drying have a significant impact on the quantification of secondary metabolites and subsequently on its hypo-glycemic activity. A steam blanching time of 5 min is the optimum for processing of custard apple peel.