Abstract
The rheological performance of pectin-enriched products extracted from red beet ( Beta vulgaris L. var. conditiva) root by-products was evaluated in the present work. They were extracted through an alkaline pre-treatment with or without a subsequent enzymatic (hemicellulase or cellulase) hydrolysis at pH 5.2. Flow assays performed with 2.00% w/v-pectin aqueous systems showed pseudoplastic (flow index, n ≈ 0.4 or 0.8) or Newtonian ( n = 1.0) behaviour after fitting of experimental data to Ostwald’s law, also showing poor thickening effect. When Ca 2+ was added to water with the same pectin concentration, true gels developed as confirmed by the mechanical spectra obtained through dynamic assays. Junction zones of homogalacturonan (HG) side chains mediated by Ca 2+ were able to build up rigid networks in water. Isolated pectins (2.00% w/v) were also used to constitute milk model systems. Whole and skimmed milk were used at two different concentrations. Milk systems showed more transient and weaker gel networks when compared to Ca 2+-aqueous systems, and were associated to the formation of a [κ-casein⋯calcium cross linked low methoxyl pectin] complex dampened by the included milk fat globules. Relaxation spectra of pectin–milk systems were in general extended to large relaxation times (10 4 s) for all isolated fractions studied, which is typical of structured systems. Since all pectin fractions showed very similar chemical composition and molecular weight (average value and distribution), it was suggested that some differences in the rheological performance of each pectin product came from the different length of arabinans and distribution of rhamnose kinks (RG-I, random coil) as well as from the length of demethylated HG chains (semi-flexible coils). The results of this research show that the pectin-enriched fractions isolated from red beet root wastes are useful as additives in food formulation.
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