Combining power ultrasound with enzymes in berry juice processing

Enzymes are currently used in juice processing. The main purpose is to disrupt the cell wall network and enhance the juice yield. Disruption of the network releases also bound components, such as phenolics into juice. Power ultrasound (US) is known to accelerate extraction processes of plant materials (Mason 1998, Vinatoru 2001). The mechanical effects of ultrasound provide greater penetration of solvent into the plant tissue and improve mass transfer. Ultrasonic waves generating cavitation can disrupt cell walls to facilitate the release of bound contents. Therefore, US may be utilised in juice processing. The effect US treatment on juice yield and extractability of phenolic compounds from bilberries and black currants was studied. For bilberries US treatment alone did not much improve the juice yield compared to traditionally used enzyme treatment, and with black currants no improvement occurred. This was probably due to gelling of pectin, which was observed visually during the US treatment especially with black currants. US treatment was then combined with enzyme treatment and performed after pectin hydrolysis. Commercial enzyme preparations, Pectinex BE 3-L for bilberries and Biopectinase CCM for black currants, were used. The enzymes were dosed as endopolygalacturonidase activity measured at pH 3.5, and two enzyme dosages, 100 nkat/g and 1000 nkat/g of berries, were used. With bilberries, US treatment did not improve the juice yield. At the lower enzyme level, US treatment increased the concentration of phenolic compounds of juice by more than 15 % and at the higher enzyme level it slightly decreased the concentration. Influence of US was more significant with black currants which are more challenging berries in juice pressing than bilberries due to their high content of pectin and different skin structure. Although the influence on juice yield was not remarkable, max. 6%, the concentration of phenolic compounds in the juice increased by 15-25% by using US treatment after enzyme incubation. The results indicate the potential of power ultrasound in juice processing. US might have potential in intensifying the effects of enzyme treatment, and hence reduce the amount of enzyme needed or increasing the yield of extractable health-relevant compounds.