Plant Pectin Methylesterase Treatments Dramatically Reduce Water-binding in Sugar Beet Pulp via Calcium Crosslinking

We are investigating a novel application of a thermally-tolerant plant pectin methylesterase (TTPME) to improve energy efficiency in sugar beet processing. Sucrose diffusion from cossettes occurs in water heated to about 70°C, the optimal temperature for TT-PME activity. Drying pulp is necessary to stabilize it for storage and commercialization as animal feed, but this consumes up to 30% of total energy in a processing plant. Beet pulp’s high water binding is associated to its high content of pectin and associated polysaccharides. We hypothesize TT-PME action on pectin in the presence of calcium, can reduce water-binding in beet pulp by promoting calcium-mediated pectin crosslinking, resulting in a denser more compressible tissue. This may lower the energy cost of drying pulp through more efficient mechanical pressing. To test this hypothesis, we treated beet pulp with TT-PME and its identically acting homolog PME2, in the presence of calcium, under optimal enzymatic conditions. Calcium addition without enzyme treatment could improve water separation by 10%, while PME treatments without calcium addition showed no significant difference over untreated controls. PME treatments of beet pulp in combination with calcium showed dramatically reduced water binding, which was greater than 20% than by calcium alone. This establishes the potential utility for developing biotech beets that express TT-PME to provide an improved processing trait.