High pressure processing of beet extract complexed with anionic polysaccharides enhances red color thermal stability at low pH

Abstract

High pressure processing (HPP; 600 MPa; 3 min; 25 °C) of beet root powder slurries complexed (1:1) with locust bean gum (LBG), sodium alginate, or gum arabic was assessed for its’ ability to affect the thermal stability of the red color presented by betalain pigments therein. HPP treated beet extract solutions alone did not show improved color stability during thermal treatment (50 and 80 °C) at pH 3, while those complexed with the anionic polysaccharides, alginate and gum arabic had dramatically improved color stability following HPP treatment compared to controls. The HPP treated complexes, particularly those with gum arabic, additionally maintained their red color through six weeks of unbuffered cold storage. The HPP treated LBG (neutral mannan gum) complexes also showed improved color stability at low pH although not as robust as the anionic polysaccharide complexes at high elevated temperatures. The improved color stability appears to be independent of any impact HPP may have on the beet extract solution alone. Measurement of the pigment complex zeta-potentials showed a reduction in LBG-beet root complex (least improved stability) negativity and an increase in the gum arabic-beet complex (most improved stability) negativity following HPP. ATR-IR spectroscopy showed relative peak height increases near wavenumbers 990 and 920 cm−1 following HPP for the beet extract alone and the tested complexes. This observation could suggest an increased exposure of pigment aromatic rings occurs with high pressure treatment. Furthermore, DPPH scavenging activity associated with the beet extract solutions was not dramatically reduced by polysaccharide complexation nor HPP treatment. The data suggest combined polysaccharide complexation and HPP can add much needed low-pH red color thermal stability to betalain containing solutions without adversely affecting the beneficial antioxidant potential of the pigments.