Process-induced water-soluble biopolymers from broccoli and tomato purées: Their molecular structure in relation to their emulsion stabilizing capacity.

The emulsification capacity of process-induced tomato and broccoli sera, containing proteins and pectin with distinct molecular structures, was investigated. Targeted pectin molecular modifications were induced by applying combinations of treatments to prepare the purées, and subsequently, the serum pectin-protein mixtures were isolated and assessed in terms of their capacity to stabilize oil-in-water (o/w) emulsions at different pH conditions (pH 3.5 or 6.0). Regardless of the processing applied, broccoli sera presented a better emulsion stabilizing capacity than tomato sera due to the higher protein content and probably the presence of more acetylated and branched pectin. In tomato sera, where a low amount of protein was detected, differences in emulsification capacity were identified depending on pectin molecular structure. Tomato sera, obtained from purées treated at low temperature for the stimulation of pectin-related enzymes which led to pectin with a high molecular weight, low degree of methyl-esterification and relatively high degree of acetylation, formed stable o/w emulsions. The vegetable sera exhibited higher capacity to form stable emulsions at pH 3.5 compared to pH 6.0, which can be attributed to a lower dissociation of the pectin carboxylic groups at low pH leading to less intramolecular repulsions resulting in a more compact conformation of the adsorbed species at the oil-water interface and better electrostatic interactions with positively-charged proteins. Thus, selective processing of vegetable purées is a promising strategy to induce molecular changes in water-soluble biopolymers with potential use as natural emulsifiers in acid/acidified foods. [ABSTRACT FROM AUTHOR]