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The impact of heating at 85°C during 8 h on overall color and betalain pattern of red beet (Beta vulgaris L. ssp. vulgaris) juice was investigated. Although the hue angle of 358° in fresh juice was indicative of the typical red-purple appearance, heating for 8 h induced an unexpected shift to 62° resulting in a yellow-orange solution. To monitor the underlying structural alterations of betalains, a new high-performance liquid chromatography separation compatible with mass spectrometry was developed. Applying this method, 2 novel yellow neobetanin structures and 2 orange-red betanin degradation products were preliminarily identified, and neobetanin formation resulting from heat exposure was proven for the 1st time. These 5 compounds were held responsible for the orange shift of red beet juice during thermal treatment. The relevance of these findings for industrial beet processing was demonstrated by comparison of pigment patterns of heated red beet juice samples and a commercial concentrate. On the basis of these results, a scheme for the thermal degradation of betanin is proposed.

Some chemical and physical factors were evaluated for their effects on stability of betanin in model systems and in beet juice. Results indicate that the stability of betanin color is pH sensitive and generally is less than that of artificial dyes. The color of betanin is most stable between pH 4.0 and 6.0. Thermostability of betanin was pH dependent and was greatest between pH 4.0 and 5.0. The half-life of betanin at pH 5.0 and 100°C was 14.5 min, and increased in an unprotected model system to 1150 min at 25°C. The rate at which betanin degraded in model systems was affected by air and/or light. The cumulative effect of these two conditions was a reduction in the half-life of betanin by 28.6%. The half-life of betanin in beet juice at pH 5.0 was greater than in model systems. Despite limited stability of betanin in model systems, there are many foods in which betanin could be used as a colorant. Foods to be colored with betanin should have a pH between 4.0 and 7.0, be exposed to low temperatures and be protected from air and/or light to achieve maximum color stability.

Spectral, colorant, and stability properties of colorants based on red cabbage, grape, cranberry, beet, and Red No. 40 were compared in buffer and in a simulated beverage. At pH 3, red cabbage imparted a red color similar to that of beet juice and less orange than that of the other colorants. Increasing the pH of red cabbage extracts to 4 produced a bathochromic shift and decreased color strength. Tristimulus parameters displayed maxima when L was varied. Red cabbage pigments were more stable during heating and storage than were the other colorants tested. pH had little effect on color stability; exposure to light greatly increased color loss during storage.

Recent limitations on the use of artificial red food colorants has prompted extensive research into finding suitable natural red pigments as color additives. Investigations have shown that water-based concentrates or powders of red beet root (Beta vulgaris) are applicable colorants in some food systems. However, presently available commercial beet preparations have relatively low pigment concentration; therefore, large quantities are required to obtain the desired color strength. Fermentation of ultrafiltered red beet juice by Candidu utilis under partial anaerobic conditions was shown to substantially reduce solids, resulting in a five- to sevenfold increase in betacyanine content on a dry basis. A 668% betacyanine content was achieved in the final dry product, The fermentable carbohydrate, nitrates and 80% of the Kjeldahl nitrogen were assimilated by Gmdida utilis after 6.5 hr of fermentation by maintaining the pH at 5.0 with NaOH and HCl solutions. After drying, the product lacked the characteristic beet flavor and aroma and was readily water soluble. This dry betacyanine concentrate may have application as a red food colorant.

Samples of 48 beet cultivars were screened for differences in pigment content and stability. Large differences were found between cultivars in betacyanine content and in the proportion of betacyanines and betaxanthines. Extensive variability in pigment content was seen within samples. The thermal stability of betacyanines in diluted beet juice at 100°C was not subject to varietal effects. Differences in betacyanine stability at 25°C between cultivars were significant at the 0.10 level, but not at 0.05. Betacyanines were less stable at pH 3 than at pH 5 and were highly light sensitive. Betaxanthines were similarly affected by pH and light; betaxanthines were much less stable than betacyanines at 25°C.

Samples of red beets were analyzed for betacyanin pigment losses during processing by high performance liquid chromatography. Total pigment loss was 41% after canning relative to the pigment content of fresh beets. Blanching to an internal temperature of 66°C caused a 23% loss while sterilization at 126°C for 10 min accounted for a loss of 22% of the pigment content of blanched beets. The betanin-isobetanin ratio changed with increasing heat treatment. The ratio for fresh, blanched and sterilized beets was 25:1, 9:1, and 2.5:1, respectively. Pigment regeneration after heating was observed in all samples, and was measured in beet juice and purified pigment solutions immediately and after appropriate intervals. Completion of pigment regeneration occurred within 10 hr in beet juice and 2 hr in purified pigment solutions.

A selected panel was used to determine the odor threshold of geosmin [trans-1, 10-dimethyl-trans-(9)decalol], an important aroma constituent of table beets, in juice made from cooked and peeled beets. The estimated threshold of 5.8 parts geosmin in 109 parts beet juice was 35 times higher than the odor threshold of geosmin in water determined by the same panel. Four samples of cooked beet juice containing different levels of geosmin were subsequently ranked according to their characteristic beet-like aroma. An increase in geosmin content was perceived as an increase in beet-like aroma up to a 5.8 ng/g concentration of geosmin. Juice made from cooked and peeled beets showed a 56–60% reduction in geosmin content in comparison with juice prepared from raw beets (with geosmin concentration below 5.8 ng/g). Therefore processing may reduce the characteristic aroma of beets.

A continuous counter-current diffusion apparatus was used for the extraction of betalaines from red beets. The apparatus was used with an incline of 4.0° and 4.5° and was operated at temperatures from 70-74°C. The efficiency of water and of citric acid solutions (0.050-0.125%) to extract betalaines was investigated. The solvent to sliced beet ratios were approximately 1.5/1. Best recoveries of about 71% betanine were found in the more acid systems at 4.5° incline angle. The betacyanine/betaxanthine ratio could be varied and was influenced by temperature and pH of the various processing operations used to produce beet juice powders i.e. diffusion-extraction, concentration and spray drying.

A fractionation procedure, based on extraction with acidified ethanol, was developed for the separation of betalaine pigments in beet juice powder. Extraction of lyophilized fresh beet juice with boiling 95% ethanol and subsequent chilling of the extract to −25°C yielded two fractions: an orange precipitate containing betaxanthines and a yellow pigment obtained from the filtrate. Three additional extractions of the beet juice powder residue were carried out at room temperature with 95% ethanol containing 1.0, 0.6 and 0.4% HCl, respectively, and the resulting fractions were combined. This extract contained mainly the betacyanines. This procedure achieved rapid and satisfactory separation of the principal constituents of betalaine, comparable to other more complex methods. Fractions were analyzed by thin-layer chromatography (TLC) on cellulose-coated plates developed sequentially with solvent mixtures consisting of ethanol, isopropanol, water and HCl.

The thermostability of red beet pigments (betanine and vulgaxanthin–I) was investigated in beet juice under atmospheric conditions at 61.5, 75.5 and 85.5°C and at pH range 4.8–6.2. The degradation of both pigments followed first-order reaction kinetics. The energies of activation were 19.2 ± 0.5 and 16.3 ± 0.6 Kcal/mole for betanine and vulgaxanthin–I respectively, and were independent of pH. Maximum thermostability was observed at pH 5.8 for both pigments. In beet juice under atmospheric conditions vulgaxanthin–I was more sensitive than betanine.

The activity of a betacyanine decolorizing enzyme present in raw beet tissue has been confirmed. The enzyme is postulated to be bound to the inner membrane of the cell wall. Comparison between the rate of betacyanine degradation for solutions containing the crude enzyme extract and solutions of identical pH and temperature void of enzyme indicated optimum enzyme activity at pH 3.4 and 40°C. Sample evaluations were made from 22–55°C over a pH range 2.0–4.8. Minimal enzyme activity was noted at pH and temperature extremes. The activity of this enzyme must be considered as an important factor in the extraction of raw beets and during storage and food product utilization of beet juices in that residual enzyme activity may decolorize substantial amounts of the betacyanine pigments. The enzyme has been found present in diffusion-type beet juice.

Isoascorbic acid was investigated as a stabilizer for red beet pigments. Sterilized samples of red beet juice containing 0.05–1.0% isoascorbic acid, with the pH adjusted to 3, 5, or 7, were stored under artificial light or in darkness at 25°C or at 5°C. The best pigment preservation was obtained with 0.1% added isoascorbic acid. After 30 days storage at 25°C, samples at pH 5 containing 0.1% isoascorbit acid retained 52% (under light) and 65% (in darkness) of the red beet pigments, whereas the controls faded to yellow within 6 days under the same conditions.

Betalaine pigments extracted from red table beets (Beta vulgaris L.) have been employed as color additives frequently since the Federal Food and Drug Administration prohibited the use of FD&C Red No. 2 and No. 4. The contribution of betanine and beet juice concentrate to the flavor of buffered solutions and gelatin dessert was assessed by sensory tests. Results of triangle tests indicated betanine to be flavorless while concentrated beet juice had a flavor which can be successfully masked when added to flavored gelatin dessert powders.