Influence of High-Pressure Homogenization on the Physicochemical Properties and Betalain Pigments of Red Beetroot (Beta vulgaris L.) Juice

Abstract

High-pressure homogenization (HPH) is considered an innovative and modern method of processing and preserving liquid and semi-liquid foods. The aim of this research was to examine the impact of HPH processing on the content of betalain pigments and physicochemical properties of beetroot juice. Combinations of the following HPH parameters were tested: the pressure used (50, 100, 140 MPa), the number of cycles (1 and 3) and the applied cooling or no cooling. The physicochemical analysis of the obtained beetroot juices was based on the determination of the extract, acidity, turbidity, viscosity and color values. Use of higher pressures and a greater number of cycles reduces the turbidity (NTU) of the juice. Moreover, in order to maintain the highest possible extract content and a slight color change of the beetroot juice, it was crucial to perform sample cooling after the HPH process. The quantitative and qualitative profiles of betalains have been also determined in the juices. In terms of the content of betacyanins and betaxanthins, the highest values were found in untreated juice at 75.3 mg and 24.8 mg per 100 mL, respectively. The high-pressure homogenization process resulted in a decrease in the content of betacyanins in the range of 8.5-20.2% and of betaxanthins in the range of 6.5-15.0%, depending on the parameters used. Studies have shown that that the number of cycles was irrelevant, but an increase in pressure from 50 MPa to 100 or 140 MPa had a negative effect on pigment content. Additionally, juice cooling significantly limits the degradation of betalains in beetroot juice.

Keywords: HPLC-DAD; PCA analysis; beetroot juice; betalains; betanin; color; high-pressure homogenization; juice turbidity.

Figure A1

HPLC chromatogram of betalains at a wavelength of 480 nm: 1—vulgaxanthins I and II, 2—betanin, 3—isobetanin.

Figure A2

HPLC chromatogram of betalains at a wavelength of 538 nm: 1—betanin, 2—isobetanin.

Figure 1

Influence of HPH processing on beetroot juice parameters: (a) Direct turbidity (NTU). (b) Serum cloudiness (absorbance at 660 nm). C—control; 50/1, 50/3, etc.,—pressure/number of cycles; H—samples without cooling. The values with different letters are significantly different (p < 0.05).

Figure 2

PCA results: (a) Score plot, PC1 versus PC2 of all samples. (b) Score plot, PC1 versus PC2 of data from determinations used as variables. C—control sample; HPH samples marked as blue squares are labeled as level of pressure/number of cycles; HPH samples marked as red squares with H are samples without cooling.

Figure 3

Schematic diagram of the high-pressure homogenizer used in the study. 1—feeding hopper, 2—piston pump, 3—first stage valve, 4—second stage valve, 5—intermediate container with cooling capability; T_in—inlet temperature measured at the feeding hopper, P—summary pressure of first and second stage valves measured by digital manometer, T_out—outlet temperature measured after leaving the head with the valves.