In‐situ pectin de‐esterification of alkali‐treated fruit waste materials

Abstract

AbstractWaste peel and pulp materials from orange, lime and mango fruits were treated with sodium carbonate which increased the pH and resulted in the de‐esterification of pectin in situ. Chemical and enzymic (pectinesterase) de‐esterification occurred in each of the treated fruit waste materials. A specific carbonate enhancement of pectinesterase activity which was clearly demonstrated in orange peel was found to a lesser extent in lime pulp but not at all in mango peel. During treatment of the dispersions with Na2CO3, each of the three fruit waste materials gelled. The pectin degree of esterification of the orange and lime dispersions was below 50% (low methoxyl pectin) on gelling but the mango peel dispersions gelled at pectin degree of esterification levels above 50% although the gelation mechanism was that of a low DE pectin. The degree of esterification of the soluble pectin in the mango dispersion was, however, found to be very much lower than the overall pectin degree of esterification determined. It is suggested that in‐situ pectinesterase activity is restricted to the soluble pectin in mango peel whereas in the citrus residues both soluble and bound pectin are de‐esterified.