Procyanidin Content of Grape Seed and Pomace, and Total Anthocyanin Content of Grape Pomace as Affected by Extrusion Processing
Version of Record online: 15 JUN 2009
© 2009 Institute of Food Technologists®
Journal of Food Science
Volume 74, Issue 6, pages H174–H182, August 2009
How to Cite
Khanal, R.C., Howard, L.R. and Prior, R.L. (2009), Procyanidin Content of Grape Seed and Pomace, and Total Anthocyanin Content of Grape Pomace as Affected by Extrusion Processing. Journal of Food Science, 74: H174–H182. doi: 10.1111/j.1750-3841.2009.01221.x
- Issue online: 31 JUL 2009
- Version of Record online: 15 JUN 2009
- MS 20090188 Submitted 3/3/2009, Accepted 4/27/2009
- grape pomace;
- grape seed;
ABSTRACT: Grape juice processing by-products, grape seed and pomace are a rich source of procyanidins, compounds that may afford protection against chronic disease. This study was undertaken to identify optimal extrusion conditions to enhance the contents of monomers and dimers at the expense of large molecular weight procyanidin oligomers and polymers in grape seed and pomace. Extrusion variables, temperature (160, 170, and 180 °C in grape seed, and 160, 170, 180, and 190 °C in pomace) and screw speed (100, 150, and 200 rpm in both) were tested using mixtures of grape seed as well as pomace with decorticated white sorghum flour at a ratio of 30 : 70 and moisture content of 45%. Samples of grape seed and pomace were analyzed for procyanidin composition before and after extrusion, and total anthocyanins were determined in pomace. Additionally, chromatograms from diol and normal phase high-performance liquid chromatography were compared for the separation of procyanidins. Extrusion of both grape by-products increased the biologically important monomer and dimers considerably across all temperature and screw speeds. Highest monomer content resulted when extruded at a temperature of 170 °C and screw speed of 200 rpm, which were 120% and 80% higher than the unextruded grape seed and pomace, respectively. Increases in monomer and dimer contents were apparently the result of reduced polymer contents, which declined by 27% to 54%, or enhanced extraction facilitated by disruption of the food matrix during extrusion. Extrusion processing reduced total anthocyanins in pomace by 18% to 53%.
Practical Applications: Extrusion processing can be used to increase procyanidin monomer and dimer contents in grape seed and pomace. Procyanidins in grape by-products have many health benefits, but most are present as large molecular weight compounds, which are poorly absorbed. Extrusion processing appears to be a promising technology to increase levels of the bioactive low molecular weight procyanidins.