AQUEOUS EXTRACTION OF ANTHOCYANINS FROM HIBISCUS BY COUPLING INSTANTANEOUS PRESSURE DROP AND MICROWAVE ASSISTED PROCESS

Abstract

Colours are used in food to enhance the quality to clout the consumer and also for balancing the colour loss during processing. Since the consumers are becoming aware of the various hazards of using synthetic colours, natural colours are gaining importance. The commonly used conventional extraction methods possess disadvantages such as low extraction efficiency and high extraction time. A swelling operation using ‘Instantaneous Pressure Drop’ process prior to extraction could produce high quality anthocyanin by improving the hydration kinetics and capacity. Microwave energy could be used effectively to mediate extraction of anthocyanin in place of conventional aqueous methods. The anthocyanin from Hibiscus were extracted by a coupled process of instantaneous pressure drop pre- treatment and microwave assisted extraction. The developed extraction system consists of a steam generation system, processing vessel, vacuum system and supporting frame. The steam generator produces steam from water using LPG as heating medium. Steam outlet from steam generator was connected to the processing vessel which accommodates the raw material. The vacuum system consists of a vacuum tank, vacuum pump, controlled instant pressure drop valve and associated measuring systems. The whole IPD equipment is supported by frame structure. A microwave oven was used as the microwave reactor. A Box-Behnken design of response surface methodology was employed to characterize and optimize the process parameters of the coupled extraction process and investigate the effect of independent variables viz., process pressure (0.56, 0.84 and 1.14 kg/cm2), treatment time (1, 2 and 3 min), microwave power (480, 720 and 960 W) and solvent- sample ratio (15, 27.5 and 40 ml/g). Optimisation of process parameters of the coupled process of anthocyanin extraction from Hibiscus was carried out using design expert software version 7.0.0, based on desirability analysis. From the analysis, a process pressure of 0.905 kg/cm2; treatment time of 2.272 minutes; microwave power of 707.302 W and solvent- sample ratio of 30.415 ml/g were found to be optimum values. The results revealed that the coupled IPD and microwave assisted process of extraction resulted in enhanced anthocyanin yield and antioxidant activity with increased redness as desired by anthocyanin pigment when compared to conventional extraction process. Beside the coupled process takes reduced time for extraction, thereby reduces the energy requirement and cost for the extraction process.