Structural studies of the fruit exudate arabinogalactans and pectin in mango (Mangifera indica L.) peel and technological options for their recovery

Mango (Mangifera indica L.) is one of the major tropical fruits. Industrial processing yields huge amounts of unexploited peel having the potential to be a starting material for upcycling concepts, especially for pectin recovery. However, previously reported pectin yields and quality varied tremendously. Moreover, sufficient amounts of storable peel of constantly high quality must be made available efficiently for commercial coproduct recovery, irrespective of seasonality, degree of fruit ripeness, different cultivars, and diverse fruit processing paths.

The first third of this thesis covered two feasibility studies aiming at optimized conversion of industrial mango peel waste into a storable starting material for the recovery of bioactive or functional ingredients. The main focus of this thesis was on structural and macromolecular characterization of the pectins and arabinogalactans in dried mango peel.

The main constituent of dried mango fruit exudate was shown to be its major carbohydrate polymer. It was identified as a glucuronorhamnoarabinogalactan. Various structural key characteristics of the latter were profoundly described for the first time. The possible presence of this type-II arabinogalactan as coextracted impurity in pectin from mango peel was unambiguously proven. Here, the specially developed HPAEC-PAD-method for concurrent quantitation of the characteristic neutral and acidic carbohydrate components played an important role. Suitable ways to obtain pure pectins from mango peel, using selective precipitation were demonstrated and assessed. In combination with the technologies suggested for the tailored bulk production of dried mango peel, an integrated utilization concept, based on the year-round recovery of pure pectin plus coproducts, was elaborated.