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Submited by: K. Dhanasekaran



Colours play an important role in enhancing the aesthetic appeal of food products. Owing to some food processing procedures such as heat treatment, pH changes, light exposure and storage condition, many food products suffered colour loss. Previously, synthetic food colourants are incorporated to recover colour loss and to enhance the appearance of food products. Unfortunately, some synthetic colourants such as tartrazine and sudan red which has prolong history in food industry has been reported to be heath hazardous lately. Although, the side effects of some synthetic colourants remained controversial, this further alarmed the consumers about the safety of synthetic colourant. In addition, the tightening government restrictions are some reasons persuade the food industries to search for alternative colours. As a replacement colouring agent, it must at least fulfilled two major concerns in which it should be free of side effects and harmless to public health. Natural pigments from biological sources came into consideration especially pigment extracted from plant, fungi, bacteria, algae and insect.
Natural products with high medicinal values are gaining much importance in light of serious side effects posed by the medicinal derivatives from chemical origin. Natural pigments are another class of natural products that have attracted considerable attention as antioxidants that induce beneficial effects on human health and disease prevention.
Some major categories of plant pigments include betalain, anthocyanins and other flavonoids, carotenoids and chlorophylls. Among these categories of pigment, anthocyanin earned the most attention due to its colour and antioxidant properties. Betalains, carotenoids, anthocyanins are such natural pigments that have proven to possess health benefits. Although betalain is the five most widely used colourants in the food industries, research involved in betalain has not been as thorough as compare to its counter parts. Betalain is a class of natural pigments comprising yellow betaxanthins and betacyanins. The distribution of betalain in nature is limited to confined plant species of Caryophylalles such as cacti, red beet, (Chenopodaceae) and certain fungi such as fly-agaric mushroom (Amanita muscaria). Several edible sources of betalain are red and yellow beetroot (Beta vulgaris L. sp. vulgaris, Chenopodiaceae), coloured Swiss chard (Beta vulgaris L. sp. cicla, Chenopodiaceae), grain or leafy amaranth (Amaranthus sp., Amaranthaceae) and cactus fruits (Cactaceae).
Betalains are water-soluble nitrogen-containing pigments, which are synthesised from the amino acid tyrosine into two structural groups: the red-violet betacyanins and the yellow-orange betaxanthins. Betalamic acid, whose structure is presented in (Fig. 1.1, respectively) is the chromophore common to all betalain pigments. The nature of the betalamic acid addition residue determines the pigment classification as betacyanin or betaxanthin.


Fig1.1 General structure of Betacyanins

The structural differences reflect in varying appearance of the betalain subgroups. Betacyanins contain a cyclo-3, 4-dihydroxyphenylalanine (cyclo-Dopa) residue. The condensation with the closed structure of cyclo-Dopa extends the electronic resonance to the diphenolic aromatic ring. This extra conjugation shifts the absorption maximum from 480 nm (yellow, betaxanthins) to about 540 nm (violet, betacyanins).
Betanidin is the aglycone of most betacyanins; different substitution (glycosylation and acylation) patterns of one or both hydroxyl groups located at position 5 or 6 of betanidin result in the formation of the various betacyanins. Most of these are 5-O-glucosides, but 6-O-glucosides have also been detected.
Red beetroot is the major commercially exploited betalain crop. It is approved to be used in food industries as food additive in United States (Title 21 of Code of Federal Regulations, 21 CFR 73.40) and in European Union (E162). Betalain obtained from red beetroot is exempted from batch certification. Till date, it is widely used as natural pigment in food industries especially ice creams and yoghurt. However, beetroot pigments have some major drawbacks in which its earthy odour caused by geosmin which is not favourable among some consumers.
Since the betalain spectrum of red beets is restricted mainly to betanin, colour variability is poor. Moreover, an adverse earthy-like flavour because of geosmin and some pyrazines is undesirable when applying beet extracts to, for instance, dairy products. Therefore, attempts have been made to explore alternative sources of betalains. The most promising family among betalain-bearing plants is the Cactaceae. Among those, cactus pears (genus Opuntia) and pitayas (genera Cereus, Hylocereus and Selenicereus) are most commonly cultivated as fruit crops and best suited to be studied as betalain sources for colouring food.
Indian Fig Opuntia (Opuntia ficus-indica) in culinary term called as prickly pear is a purple to red fruit in semi-arid parts of the world. Cactus fruits, in contrast to red beetroot, may be used in food without negative flavour impacts as those derived from beetroot extracts. On the contrary, the faint flavour tends to impair the market potential for plain cactus fruits, making their utilisation for colouring applications. The betalains in cactus fruits also cover a broader colour spectrum from yellow–orange (Opuntia sp.) to red–violet (Hylocereus sp.) compared to red beet and thus may open new windows of colour diversification.

Most of the natural pigments are highly instable and this has limited their application especially in foods undergoing thermal treatment. Betalain has been reported as sensitive to heat, pH, light, moisture and oxygen. Therefore, the pigment is only suitable to be added in food with short shelf lives. Alternatives natural food colourant with higher stability towards the above mentioned factors are indeed necessary to facilitate the food industries. Moreover, the low levels of colourless phenolic compounds in cactus fruits make them very promising, since potential interactions of betalains with these phenolics are avoided. An additional advantage of cactus fruits are their minimal soil and water requirements and semi-arid regions.
Several reports on cactus fruits and Amaranthaceae plants as the potential source of natural food colourant provide a gate way to the alternative source of red beet betalain. A study conducted by demonstrated promising results with applying the spray dried. Opuntia stricta fruit juice to yoghurt and soft drink. The observation showed that the colour in the product maintained a vivid red-purple tonality even after one month of refrigeration storage. Therefore, betalain extracted from prickly pear (dark magenta) as an alternative source to beetroot betalain is optimistic. In the present study, locally cultivated prickly pear was chosen as the source of betalain. Storage stability of prickly pear betalain in different treatments and storage conditions was observed. And the stabilized pigment was incorporated into acidic and alkaline foods and biochemical changes in food were studied.
Objective of the study

 Extraction of Betalain pigment from Opuntia ficus indica.
 Stabilizing the Betalain pigment.
 Incorporation into food material.
 Analysing the colour retention time.

Fig1.2 Fruits of Opuntia ficus indica

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