Molecular weight distribution and viscosity of water-soluble dietary fibre isolated from green beans, Brussels sprouts and green peas following different types of processing

The molecular weight distribution and the viscosity of water‐soluble dietary fibre polysaccharides isolated from green beans, Brussels sprouts and green peas were investigated following boiling, microwave treatment and canning. Blanching was used as a reference process. In green beans and Brussels sprouts microwave treatment had minor effects, while there generally was a small decrease of neutral sugars with boiling. The influence of canning was more pronounced and a decrease of uronic acid‐containing polymers in the high‐molecular‐weight fraction was obtained, simultaneously as the amount in the middle toed fraction increased. Further, in green beans there also seemed to be a loss of polymers containing galactose and uronic acids into the process water with boiling and canning, respectively. In peas, there was an increase of the fraction containing middle‐sized polymers (uronic acids and arabinose) with all processes. With microwave treatment there was a simultaneous loss in the high‐molecular‐weight fraction, whereas no such decrease could be obtained with boiling or canning. The lowest viscosity was obtained in extracts from canned materials and the highest with blanching, while boiling and microwave treatment had various effects in different vegetables. The soluble fibre fraction of blanched green beans had a higher viscosity than that of Brussels sprouts and green peas. Thus, both amount and properties—molecular weight distribution and viscosity—of soluble fibre in vegetables were affected by processing, but differently in various vegetables.