The plant cell membrane permeabilizing action of high pressure may be utilised in juice processing to improve juice yield and the amount of phenolic compounds released into the juice (1, 2). The reactions of the cell wall degrading enzymes used to improve yields in conventional juice processing, may be inhibited or enhanced by high pressure treatment (3). In the first part of this work the effect of high pressure treatment of bilberry pulp on juice yield and phenolic content was studied. The juice yield or the content of phenolic compounds in the juice was not improved by high pressure treatment. The juice yield tended to decrease with increasing pressure, even though mechanical damage is expected to increase with increasing pressure. The work was continued by evaluating the possibilities of utilising the high pressure technology as part of the enzyme-aided juice production process. Three different types of processes were investigated. In the first process the bilberry pulp was high pressure treated together with added cell wall degrading enzymes. In the second process the pulp was high pressure treated without added enzymes before conventional enzyme treatment (2 h at 45°C). In the third investigated process the bilberry pulp was first conventionally enzyme treated and thereafter high pressure treated. The use of high pressure (50-600 MPa) was not beneficial in any of the studied cases, as the yield or total phenolic content of the obtained juices was not significantly improved. One reason for the reduced juice yields after high pressure treatment may be the gelatination of the soluble pectins that are released from the berry matrix during pulping and pressurization. The pectin depolymerising enzyme polygalacturonase is according to literature easily inactivated at moderate pressures. Pectinmethylesterase, which produces demethylated pectin that forms gels with calcium, is known to be much more pressure resistant and can even be stabilized in the pressure range studied in this work. With increasing viscosity of the berry pulp the extraction of phenolic compounds becomes more difficult. Our future work will concentrate on finding a way to utilise the high pressure technology for mechanical disruption of the berry matrix without increasing the viscosity of the pulp too much. REFERENCES 1. Dornenburg, H. & Knorr, D.: Food Biotechnology 7, 1 (1993). 2. Knorr, D.: Journal of Food Engineering 56, 2-3 (2003). 3. Hendrickx, M., Ludikhuyze, L., Van den Broeck, I. & Weemaes, C.: Trends in Food Science 9, 5 (1998).
|Publication status||Published - 2004|
|Event||2nd International Conference on Biocatalysis of Food and Drinks - Stuttgart, Germany|
Duration: 19 Sep 2004 → 22 Sep 2004
|Conference||2nd International Conference on Biocatalysis of Food and Drinks|
|Period||19/09/04 → 22/09/04|
- high pressure