Physico-chemical properties of cell wall materials obtained from ten grape varieties and their byproducts: grape pomaces and stems

The availability and the potential of wine by-products, grape pomaces and stems, obtained from ten different grape (Vitis vinifera L.) varieties (six red and four white) as raw materials for the production of dietary fibre (DF) concentrates were evaluated. The overall chemical composition, carbohydrate analysis and functional properties of DF from fresh grapes, grape pomaces and stems from those grape varieties were analysed. Both winemaking by-products presented considerable quantities of DF, ranging from 60% to 90% of total dry matter. The cell wall polysaccharides (CWP) composition of grape pomaces and fresh grapes was rather similar, pectic substances being the main component of the cell walls (40–54% total CWP). In contrast, cellulose was the predominant cell wall polymer for the stems (40–49% total CWP). In addition, the pectin content of grape pomaces exhibited significant differences between red and white grape varieties. The degree of methyl-esterification of uronic acids from wine by-products ranged from 21 to 39%; thus, pectic polysaccharides from the different samples could be classified as low methyl-esterified pectins. Klason lignin accounted for around 20–25% of DF in both grape pomaces and stems. With regard to the potential incorporation of DF concentrates into the food chain, functional properties were also determined. Swelling, water and fat retention capacity results showed great variability depending on the grape variety analysed.