Functional fibre

These physicochemical properties have led to proposals that plant cell wall residues could be used as water (super)absorbants and natural ion exchangers. Indeed, ion exchange resins are widely used for water depollution. The

Table 16.2 Physicochemical characteristics of dietary fibre from fruit and vegetable wastes


Swelling (ml/g)


CEC (meq./g)


Apple pomace



Renard and Thibault (1991)

Apple pomace after



Renard and Thibault (l99l)

pectin extraction

Beet pulp




Thibault et al. (1994)





Thibault et al. (l992)




Thibault et al. (l992)

WBC; water-binding capacity; CEC, cation exchange capacity.

WBC; water-binding capacity; CEC, cation exchange capacity.

available commercial resins provide a wide selection of ion selectivities and performances; because of their high cost and thanks to their high chemical stability, synthetic resins can be regenerated. Regeneration needs, however, large amounts of water while in other cases fouling or poisoning of the resins may occur. Sugar beet pulp (Dronnet et al., 1997) and soybean hulls (Laszlo and Dintzis, 1994), for example, have been proposed as low-cost and single-use ion exchange resins. Furthermore, such preparations have been proposed for food or non-food uses. For instance, because of their low degree of methylation and great stability, alkali-treated citrus wastes have been suggested as thickening and gelling agents in place of the extracted and purified pectins (Speirs et al., 1980). Extrusion cooking was also proposed to increase the water-soluble (pectin) fraction: the extruded citrus or apples residues may have gelling properties and could find applications in the replacement of purified pectins (Ralet et al., 1994a). Wastes containing primary cell walls rich in cellulose or enriched in cellulose by different treatments have also been suggested for applications in paper-making (see Section 16.4.2).

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