Towards by-product utilisation of pea hulls: Isolation and quantification of galacturonic acid

Abstract

In order to evaluate by-products from food processing as alternative raw materials for pectin extraction, their amount of galacturonic acid (GalA) has to be analysed as a marker for pectin content. In the present study, significant differences in GalA release using different digestion methods are shown for pea hulls, as an example of by-products with a high content of cellulose. Complete digestion of the fibre matrix was assumed for Saeman hydrolysis as a reference protocol. Significantly lower GalA release was achieved by a treatment with trifluoracetic acid (TFA). An alternative treatment with ethylenediaminetetraacetic acid (EDTA) at pH 11 followed by an enzymatic digestion at pH 4.5 using a combination of polygalacturonase (Vegazyme M) and cellulase (Celluclast 1.5L) resulted in a similar release of GalA compared to Seaman hydolysis. Pea hull samples, analysed by this alternative protocol, showed on average a GalA content of 11.2%. Therefore, pea hulls may serve as new raw material for pectin extraction.