215: Nonthermal Membrane Concentration of Red Beetroot Juice: Product and Pigment Preservation

Introduction

Compared to thermal concentration, reverse osmosis (RO) and forward osmosis (FO) offer a nonthermal alternative that can preserve the color, taste, and nutritional compounds in fruit juices. An RO-FO process, which combines the rapid initial concentration of RO with the lower fouling propensity of FO, was explored to concentrate beetroot juice to levels comparable to those achieved by thermal concentration.

Methods

Red beetroot juice, reconstituted to 10°Brix from thermally concentrated juice, was RO concentrated using a pilot-scale RO unit at a transmembrane pressure of 22 bar at 25°C. Water flux was continuously monitored, and the process was stopped once the concentration plateaued at 17.1°Brix. Similarly, FO concentration of the beetroot juice was conducted starting at 10°Brix, until 51.9°Brix. Betalain content was determined spectrophotometrically, and Lab color was evaluated using a colorimeter. Both essays were evaluated on the membrane concentrated juice diluted to 10°Brix and compared to the initial product. All experiments were conducted in triplicate, and data evaluated statistically.

Results

RO and FO achieved a maximum concentration of 17.1 ± 0.1 and 51.9°Brix respectively. There were no significant differences in L* and b* color parameters between samples concentrated and diluted to single strength between the two processes. Betanin, the main color pigment responsible for the red and violet coloring characteristics of red beetroot, showed only minor differences in concentration in juice before and after processing, with less than 1% loss for RO and 3% for FO. This suggests that both concentration methods are suitable for color preservation, with FO holding the advantage of a high concentration factor.

Significance

This work is useful for the food industry interested in adopting RO and FO to concentrate fruit and vegetable juices, while maintaining their quality. Nonthermal concentration can also facilitate the use of red beetroot concentrate as a natural colorant for food products.

Authors: Eugenia Avellaneda, Carmen I. Moraru