J Sci Food Agric 1992, 58, 595-596

Stability of Red Beet Pigment Concentrate in Maize Starch Roland0 C Altamirano," Milan Drdak," Peter Simon,b Andrej Smelik" and Peter Simko" a Department of Chemistry and Technology of Foods, Department of Physical Chemistry, Slovak Technical University, Radlinskeho 9, 8 1237 Bratislava, Czechoslovakia (Received 24 September 1991 ; revised version received 25 November 1991 ; accepted 12 January 1992)

Two pigment concentrates, differentiated as dark (D) and rose (R), were prepared from fermented red beet (Beta uulgaris L var rubra) and applied to two types of maize starch, industrial (IS) and modified (MS). The samples were stored for 191 days at room temperature. The decay of the two red pigments in the two maize starches was DIS 12.70 %, DMS 9.43 YO, RIS 14.15 %, RMS 8.54 % and followed a first order reaction. The modified maize starch was found to be the most suitable carrier of the pigment. Water activity played a determining role in this result.

Key words : Beta uulgaris, maize starch, betacyanins, stability.

The group of red beet pigments known as betacyanins, isolated from bulbs of red beet (Beta vulgaris L), is characterised by poor stability. The use of betanin (the major pigment of this group) as a food colourant in meat (von Elbe and Maing 1973) and in sherbet (Pasch et a1 1975) has been studied. In this work, red beet concentrate obtained by fermentation was applied to maize starch and the decay of the pigment during storage was followed.

The concentrate was prepared according to the method patented by Drdak and NasEakova (1 985).

Two types of maize starch were used: an industrial maize starch (IS) and a modified maize starch (MS) prepared according to the method patented by Smelik et a1 (1 989).

To similar weights of IS and MS, similar volumes of fermented red beet concentrate corresponding to 0.7 g pigment kg-' starch for DIS and DMS were added. The samples were homogenised, milled in a mill mixer, vacuum dried (39 & 1 "C, 0.01 MPa) for 8 h, milled again and packed in laminated foil bags (Svital PE) for storage.

For the set of samples DIS and DMS, 1~000f0001 g was weighed, dissolved in 100 ml redistilled water and filtered through a frit disk funnel (No S4). For the set of samples RIS and RMS, 5 g was weighed, dissolved in 50 ml redistilled water and filtered in the same way as the previous set. Absorbance of the filtrates was measured at

537 nm (Spekol 11, Carl Zeiss, Jena, Germany). The relative error in seven measurements was 3 Yo.

The stored samples were monitored to follow the decay of pigment. In Fig I is shown the progress of the changes in red pigment during 191 days of storage expressed as log R =At), where R is the percentage retention of the initial absorbance and t is the time of storage. The measured values indicate that the de- composition of the red pigments followed a first order reaction. The straight line of the dependence log R = flt) confirmed the order of reaction in agreement with the published results. The reliability interval of two independent variables was tested and the calculated correlation coefficients were high even for a critical value of a = 0.001. From the measured values the rate constants for a first order reaction (supposing no change of order during the reaction) and the half-life were calculated; the results are shown in Table 1. The measured values of water activity for the samples (DMS U, = 0.11, RMS a, = 0.12, DIS a, = 0.28, RIS a, = 0.30) were determinant in the rate of reaction and in the better stability shown by the modified starch under the given storage conditions. For the practical application of red beet pigment carried on starch, it is necessary to emphasise the importance of starch purity and to take into account the possible changes of the pigment in the system.

595 J Sci Food Agric 0022-5142/92/$05.00 0 1992 SCI. Printed in Great Britain

596 R C Altamirano et a1

TABLE 1 Rate constants, half-life and correlation coefficient ( r ) for the

decay of red beet pigment in two types of maize starch

Sample k x la3 SD (days-') t; (days) r

DMS 0.508 0.014 1364 -0.997 DIS 0.703 0.0 16 985 -0.998 RIS 0.791 0.013 876 -0.999 RMS 0.466 0.008 1487 -0.999

Concentration of pigment in the samples RIS and RMS is 0.068 g kg-' starch.

A t the end of storage, deterioration in the industrial starch was characterised by a typical odour. The samples prepared with the modified starch and samples stored in cold conditions (- 18°C) did not have this odour. At the beginning and a t the end of the experiment, a gel (1 g starch + 5 g H,O) from the samples RIS and RMS was prepared (3 min cooking) and the colour intensity was compared visually ; significant change in colour intensity was not seen. The pigment concentration in the samples RIS and RMS was chosen so that the colour intensity was a s close as possible to that of the common pudding mixes after culinary finishing.

20 80 140 200 Time [days]

(b)

Fig 1. (a) Changes in red beet pigment content during storage. DIS, Industrially produced starch (dark hue); DMS, dark modified starch (dark hue). (b) Changes in red beet pigment content during storage. RIS, Industrially produced starch (rose

hue); RMS, modified starch (rose hue).

REFERENCES

Drdak M, NasEakova M 1985 SpBsob pripravy farbiaceho preparatu z Eervenej repy. Czechoslovakia Patent 225529.

Pasch J H, von Elbe J H, Seil R J 1975 Betalains as colorants in dairy products. J Milk Food Techno1 38 1 25-28.

Smelik A, Zajac P, Polivka L 1989 SpBsob ziskavania kavernovaneho kukurif neho Skrobu-Amyllum cavernatum. Czechoslovakia Patent A 0 2391 79/85.

von Elbe J H, Maing I 1973 Betalaines as possible food colorants of meat substitutes. Cereal Sci Today 18 263-254 3 16-31 7.