Towards a better identification of naringin and narirutin dispersion state in grapefruit peel press liquor

The objective of this work was to describe the dispersion state of flavonoids (i.e. naringin and narirutin) in the press liquor obtained after filtration-compression of fresh citrus (grapefruit) peels. An original methodology for the quantification of the dispersion, based on a size fractionation, and its evolution over time was proposed. Three fractions were identified: (i) a particulate fraction, (ii) a large-colloidal fraction and (iii) a small-colloidal and soluble fraction. Narirutin and naringin were initially found on small-colloidal/soluble form. During time, an aggregation of the compounds present in the press liquor, revealed by turbidity measurements, was observed. This aggregation resulted in an increase of the particulate fraction, at the expense of the colloidal one. This aggregation seemed to trap naringin, that progressively appeared in the particulate fraction, although that no evolution of narirutin location was observed. The tendency to sediment of the formed aggregates was evaluated, by a Turbiscan optical analyser, in the objective of their future isolation. The stability study of the press liquor over time showed that this suspension was physically stable; the aggre-gates/flocs were not able to settle at room temperature, certainly because of interparticle repulsion or other reasons as low floc density, porous floc structure, etc. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.