Electrostatic separation combined with ultra-fine grinding to produce beta-glucan enriched ingredients from oat bran
Résumé
Electrostatic separation was studied in a city fractionation diagram to obtain beta-glucan-enriched fractions from oat bran preparations. Ultra-fine grinding at ambient or cryogenic temperature was needed to achieve good dissociation between the macronutrients of oat bran particles. Particles rich in beta-glucan and starch were by electrostatic separation separated from particles rich in arabinoxylan. beta-Glucan was only little enriched in the non-defatted bran fractions from 19.6 to 25.0%. In contrast preliminary defatting by super critical carbon dioxide significantly improved the dissociation of particles during grinding and allowed enrichment of beta-glucan to 42.2 or 48.4% after one or two successive electrostatic separation steps. The twice separated positive fraction, containing 48.4% beta-glucan, was further fractionated by a combination of jet-milling and air classification, yielding up to 56.2% beta-glucan concentration. The results point out the good potential of using electrostatic separation as a bran-fractionation method to produce nutritionally interesting food ingredients. Industrial relevance: Oat beta-glucan has a widely accepted health claim related to cholesterol lowering, and has a great industrial applicability in functional foods and nutraceuticals. The high concentrations of beta-glucan obtained with defatted material are of major interest from an industrial point of view, since this kind of ingredients can be used in applications where normal oat bran preparations cannot provide beta-glucan at high enough concentration. In addition, the obtained beta-glucan fractions retained their original molecular weight The high beta-glucan fractions had an appealing white colour and were well solubilised in hot water and in 0.1 M NaOH compared to their low beta-glucan counter-fractions. Supercritical carbon dioxide extraction is a relatively costly method due to the long processing time (several hours per batch), but there are existing factories offering contract manufacturing. Lipid extraction and fractionation process can be economically feasible, especially when the fractions obtained are used in high-value applications. Ultra-fine grinding and electrostatic separation are energy intensive methods, but they enable enrichment of components without any liquids or solvents. These methods can be used to produce unique fractions which are not possible to obtain with conventional fractionation methods such as sieving and air classification.