Improvement in the nutritive value of tomatoes : vitamin A potent tomatoes and some aspects of carotenoid and vitamin A

Abstract

Chapter 1 Different tomato varieties that are commonly cultivated in our country differ in their yield, size and shape of the fruit, disease resistance etc. However, all of them contain very little amount of carotene, the bulk of the pigment that is chiefly responsible for their red colour being lycopene, which is not a precursor of vitamin A.

Some of the “High carotene” strains obtained from U.K., U.S.A. and Poland, and cultivated under our conditions, contained significantly high amounts of carotene in their fruits. But these fruits ranged from yellow to pale orange red in colour. This poor pigmentation is due to the low levels of lycopene as well as total carotene content. The amount of carotene produced by these strains at Bangalore was also far below what has been attributed to them at their place of origin, which could be due to their poor adaptability to the local conditions. In spite of these facts, the carotene content of these fruits was several fold higher than that found in the local varieties.

Crossing such “High carotene” strains with the local variety Pusa Ruby yields fruits with significant improvement in colour as well as in the carotene content of the local variety, Pusa Ruby. Thus, these hybrids yield fruits, the daily intake of 50–100 g of which would be adequate to meet the requirements of vitamin A.

Since reciprocal matings yielded fruits of similar carotene composition, it is concluded that probably no maternal inheritance or any cytoplasmic factor influences the carotene biosynthesis in tomatoes.

Even though the “High carotene” selections chosen for the cross breeding programme bred true, the behaviour of a small number of progenies of some crosses suggested that at least a few of the seeds of the original stock might be heterozygous with respect to the B gene. Hence, in the cultivation of progeny, unless the “High carotene” seed stock is checked for generations with regard to the breeding qualities, any one of the following types could be observed at the F level: (1) All the F s are of the “intermediate ” types with respect to the carotene composition of their parents; or (2) Only 50% of the population are of the “intermediate ” types, the rest 50% being Pusa Ruby types.

The carotene composition of the F segregates of some of the select (Pusa × High ) hybrids shows that the B gene is dominant. However, a “spread” in the carotene content among the F segregates indicates that several factors may be involved in the carotene biosynthesis.

Since the type “deep Red Orange” fruits with 30–40 g of carotene and 50–60 g of lycopene (per g fresh weight) occur in a distinct frequency among the F segregates, it may be possible by further cross breeding programmes to stabilise this character. Such hybrids will be more suitable for market acceptability.

As no remarkable difference either in the frequency of individual classes of segregates or in the carotene composition of individual classes of the F population is observed in both the crosses, viz., (Pusa × OF) and (Pusa × Pol ), it is surmised that these two hybrids must have the same genetic pattern with respect to carotene composition. This strongly suggests that the modifier locus segregates independently of the B gene. In this respect, it would be of interest to study (Pusa × ORP) and (Pusa × U.K. Int. ) F hybrids for their segregates and compare them with the population of (Pusa × OF) F hybrid.

Since extensive vitamin A deficiency is prevalent in our country, the cultivation of such “High carotene” mutants may, in the long run, serve as one of the most effective measures to tackle this problem. IN VIEW OF THE MAGNITUDE OF ENDEMIC BLINDNESS DUE TO VITAMIN A DEFICIENCY IN OUR COUNTRY (IT IS ESTIMATED THAT NEARLY 15–20,000 PEOPLE GO PERMANENTLY BLIND EVERY YEAR), THE AUTHOR STRONGLY SUGGESTS THAT IT IS IMPERATIVE THAT THE ENTIRE COMMERCIAL RED TOMATOES MUST BE REPLACED BY SUCH "HIGH CAROTENE" STRAINS. Such a measure may initially invoke problems like “colour consciousness” that play a vital role in marketability. This could be partly overcome by educating people through mass media programmes about the nutritive value of such tomatoes. Cultivation of hybrid tomatoes, as suggested in Chapter I, can improve acceptability in the market. Ultimately, the goal is to develop a true breeding “Red Orange type” with about 40 g of carotene for nutrition and about 60 g of lycopene (both per g fresh weight) for colour appeal.

Chapter 2

The bioassay experiments carried out on vitamin A deficient rats conclusively demonstrate that the pigment identified in these “High carotene” mutants as carotene is really all trans carotene. (Since any structural alteration that gives the same absorption characteristics would make the molecule biologically inactive.)

Besides, the carotene in these mutants is as equally available as the synthetic all trans carotene administered in oil to vitamin A deficient rats.

The cultivated hybrids are much superior in potentiating liver stores of vitamin A in vitamin A deficient rats than the local variety Pusa Ruby fed on comparable amounts.

Absorption of carotene from tomatoes seems to be superior to absorption from carrots (reported in human volunteers by earlier workers). This may be due to the more pulpy nature of tomato fruits compared to the harder nature of carrots.

Another point to note is that the presence of lycopene does not affect the utilisation of carotene, but it might actually act as an antioxidant protecting carotene against intestinal oxidase activity - mimicking vitamin E usually added when synthetic carotene is given. Thus, a “Red Orange” phenotype has its own superior claims both for market acceptability and for optimal lycopene levels that promote better utilisation of carotene.

One surprising aspect is the peculiar nature of specific sites present on the dioxygenase enzyme system. Even though this enzyme is not inhibited by very close structural analogues, it seems to cleave quite a number of substrates like monoepoxy carotene, cryptoxanthin, 5 apocarotenal etc., to vitamin A. These aspects must await a homogeneous enzyme preparation.

Prolonged periods of vitamin A deficiency may affect intestinal conversion of carotene to vitamin A. Hence “High carotene” tomatoes may not cure acute deficiency, but they are proposed as a preventive measure.

Chapter 3

The B gene appears to be highly specific in its site of expression; it promotes excess carotene synthesis only in the fruits. Neither the chloroplast carotenoids of leaves nor the chromoplast pigments of flowers are altered by its presence. Since several fruit biochemicals share the same precursor (acetyl CoA), it would be interesting to study whether introduction of B gene affects other metabolites.

Increased amounts of zeacarotene and carotene accompany increased carotene synthesis. Direct precursor studies are required using labelled intermediates (neurosporene, zeacarotene, carotene).

The new TLC method described serves as a simpler way of separating and estimating provitamin A content of foodstuffs. It is particularly useful in genetic work on carrots and tomatoes.

Chapter 5

Tecoma stans constitutes one of the most common hedge plants in this region. The chief pigments in its flower petals are the xanthophylls violaxanthin and antheraxanthin.

Minor carotenoids detected include carotene, mutatochrome, 5,6 monoepoxy cryptoxanthin, 5,6;5 ,6 diepoxy cryptoxanthin. Pathways of violaxanthin formation and epoxide cycles would be interesting to study.

Chapter 4

Next to retinol, retinoic acid has stimulated considerable interest. Although many analogues are known, retinoic acid anhydride has not been described earlier.

Treatment of retinoic acid in benzene/pyridine with thionyl chloride results in retinoic acid anhydride. It differs in chromatographic behaviour, melting point, UV and IR spectra, and X ray characteristics, but resembles retinoic acid in NMR and biological activity.

Alcohols in the reaction medium convert the anhydride to the respective esters - making it a useful intermediate. Apocarotenoic acids can also be esterified similarly.

In light of the interest in retinoic acid in wound healing and cancer therapy, retinoic acid anhydride might be valuable due to its controlled release.