Mechanistic insight into common bean pectic polysaccharide changes during storage, soaking and thermal treatment in relation to the hard-to-cook defect

Different mechanisms responsible for the development of the hard-to-cook defect in common beans during storage, their soaking behavior and softening during thermal treatment have been previously suggested. However, these mechanisms have not been sufficiently confirmed by direct molecular evidence. This research aimed at gaining a detailed mechanistic insight into changes occurring in Canadian wonder bean pectic polysaccharides during storage, soaking and/or thermal treatment in different brine solutions in relation to the development and manifestation of the hard-to-cook (HTC) defect. Both fresh or easy-to-cook (ETC) and stored (HTC) bean samples were either soaked or soaked and thermally treated in demineralized water, solutions of Na2CO3 and CaCl2 salts followed by extraction of cell wall materials. Pectic polysaccharide properties examined included sugar composition, degree of methylesterification (DM), extractability and molar mass (MM). The DM of pectin from ETC and HTC beans was similar but low (<50%). Upon (pre)treatment in a Na2CO3 solution, solubilization of pectic polysaccharides, especially the strongly bound chelator- (CEP) and Na2CO3- (NEP) extractable pectins was enhanced leading to increased amounts of water extractable pectin (WEP). Also, there was a decrease in high MM polymers paralleled by an increase in -elimination degradation products. These observations are in line with the fast cooking behavior of beans (pre)treated in a Na2CO3 solution. In contrast, (pre)treatment in a CaCl2 solution hindered softening leading to the failure of the beans to cook. The beans (pre)treated in a CaCl2 solution showed increased high MM polymers and lack of cell wall separation. Therefore, it can be inferred that development of the hard-to-cook defect in Canadian wonder beans during storage and its manifestation during soaking and subsequent thermal treatment is largely reflected by the pectic polysaccharide properties in line with the pectin hypothesis. Our data suggest the release of Ca++ leading to pectin cross-linking and the increase or decrease of -elimination depolymerization. However, the relatively high amounts of neutral sugars and strongly bound NEP in HTC seeds do not allow to rule out the possible existence of non-Ca++ based pectin cross-linking.

Jaar van publicatie:2015

BOF-keylabel:ja

IOF-keylabel:ja

BOF-publication weight:6

CSS-citation score:3

Auteurs:International

Authors from:Higher Education

Toegankelijkheid:Closed