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Red palm oil to combat vitamin A deficiency in developing countries

C. Rukmini

Abstract

Red palm oil (RPO), besides providing calorie density to the diet, is also the richest natural source of ß-carotene, a precursor of vitamin A and an antioxidant that destroys singlet oxygen and free radicals. Chemical analysis of the fatty acid composition of RPO indicates that it has 50% saturated, 40% mono-unsaturated, and 10% polyunsaturated fatty acids. RPO contains 550 mg/g of total carotenoids, of which 375 mg/g represent ß-carotene. It also contains 1,000 mg/g of tocopherols and tocotrienols.

Nutritional values in rats fed 10% RPO in a 10% casein diet were comparable to those fed 10% ground nut oil (GNO) or 10% RBDPO (refined, bleached, deodorized palm oil). Rats fed RPO or RBDPO had significantly lower plasma cholesterol concentrations than those fed GNO. Significant inhibition of micro-somal 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was observed in the RPO and RBDPO groups, indicating reduced synthesis of endogenous cholesterol. Toxicological studies also indicate that RPO is safe for human consumption. Indian school children fed supplementary snacks prepared with RPO for 60 days had significant increases in serum retinol levels as well as an increased liver retinol store, suggesting the ready bioavailability of ß-carotene.

Introduction

Red palm oil (RPO), derived from the mesocarp of the oil palm (Elaeis guineensis), although categorized as a saturated fat, can serve the dual role of providing a source of provitamin A and fulfilling the energy needs of developing nations. The edible grade of unrefined RPO is the richest and cheapest natural source of {-carotene. It has been consumed for many centuries in some African countries and has recently been produced in India by indigenous technology [1].

A systematic and comprehensive safety evaluation on RPO was carried out by the Indian Council of Medical Research at the National Institute of Nutrition with the purpose of recommending its use in supplementary feeding programmes. Vitamin A deficiency is one of the major public health problems in India, and the Nutrition Foundation is exploring the natural sources available in the country to combat the disorder through dietary improvement [2]. The present report on some aspects of the health and nutritional effects of RPO is a result of that study.

In all these studies, refined, bleached, and deodorized palm oil (RBDPO) imported from Malaysia for public distribution, which has no §-carotene, was used for comparison. Groundnut oil (GNO) was used as a control. The chemical analysis of these oils is shown in table 1 [3].

Nutritional and biochemical evaluation

In a study in which albino rats of Wistar/NIN strain were fed 10% (w/w) RPO, RBDPO, or GNO in a 10% (w/w) casein diet for periods of four weeks and 90 days [4], results were comparable in all three groups in relation to growth rate, feed efficiency, protein efficiency ratio, net protein utilization, digestibility, fat absorption, nitrogen balance, phosphorus and calcium retention, serum enzymes, and blood values.

In a separate study, carried out to establish the serum lipid profile on high-cholesterol and cholesterol-free diets in rats [5], total serum cholesterol, triglycerides, and low-density lipoprotein (LDL) cholesterol were significantly lower in the RPO and RBDPO groups than in the GNO group. However, high-density lipoprotein (HDL) cholesterol was not significantly different from the control (fig. 1). In animals fed either RPO or RBDPO, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase was significantly lower than in the control animals fed GNO, indicating reduced synthesis of cholesterol (fig. 2). Faecal excretion of bile acids and neutral sterols was greater with RPO and RBDPO than with GNO (fig. 3). Both RPO and RBDPO exhibited a hypocholesterol effect despite their low polyunsaturated:saturated (P:S) ratios (0.24). This effect was demonstrated to be due to the presence of minor components in palm oil [6].

TABLE 1. Chemical characteristics of red palm oil, refined, bleached, and deodorized palm oil, and groundnut oil

FIG. 1. Levels of cholesterol and triglycerides in the serum of rats fed 10% groundnut oil (GNO), refined, bleached, and deodorized palm oil (RBDPO), or red palm oil (RPO) in high-cholesterol and cholesterol-free diets. An asterisk (*) indicates a value significantly different from the corresponding values for RBDPO and RPO(p<.05)

FIG. 2. Liver microsomal HMG-CoA reductase in rats fed 10% GNO, RBDPO, or RPO. *Significantly different (p < .05)

FIG. 3. Faecal excretion of bile acids and neutral sterols in rats fed 10% GNO, RBDPO, or RPO. *Significantly different (p <.05)

TABLE 2. Serum retinol DR:R ratio of subjects before and after supplementation with red palm oil or vitamin A

Values are mean ± SEM.

Tocotrienols have been found to inhibit HMG-CoA reductase activity significantly, thereby resulting in hypocholesterolaemia [7]. Our studies on rice-bran oil [8] demonstrated a similar action in both animals and humans. The hypocholesterolaemic action of palm oil in humans has also been demonstrated [9]. Although rice-bran oil and groundnut oil have the same P:S ratio, rice-bran oil is more hypocholesterolaemic than GNO owing to its high tocotrienol content [10]. Similarly, palm oil and coconut oil have the same P:S ratio, but palm oil is more hypocholesterolaemic than coconut oil because of its tocotrienol content.

RPO is nutritionally superior to RBDPO since it is rich in ß-carotene. When it is cooked, 70%-88% of its ß-carotene has been found to be retained [11].

Toxicological evaluation of RPO by multi-generation breeding studies according to US Food and Drug Administration protocol have indicated it to be safe for human consumption [12]. Mutagenicity studies of repeatedly heated RPO as well as products prepared from RPO indicated its safety [1].

Sensory evaluation of Indian foods prepared with the oil have shown that RPO was well accepted and can be used in supplementary feeding programmes in preschool children [14].

Bioavailability of ß-carotene from RPO

Twenty-four schoolchildren 7-9 years old, belonging to a low socio-economic group, were selected for a study of the bioavailability of ß-carotene from RPO. The modified relative dose-response test (MRDR) was applied to measure vitamin A status. In this test, 3,4-didehydroretinol (DR) was used as a ligand to bind apo-RBP (retinol binding protein), which accumulates in the liver on vitamin A depletion and is released as holo-RBP into plasma [15]. Five hours after an oral dose of DR, serum retinol (R) and DR were measured. The DR:R ratio reflects liver vitamin A stores. Liver saturation of vitamin A is indicated at DR:R above 0.03 [16].

Twelve children (six boys, six girls) were given a recommended daily allowance of ß-carotene in a snack, sujihalwa, made with RPO. A similar group were given a daily dose of vitamin A for 60 days. The MRDR test was performed before and after the 60-day feeding.

FIG. 4. Increases in serum retinol levels in schoolchildren given a dose of vitamin A or a snack containing RPO daily for 60 days

FIG. 5. Decreases in DR:R ratios in schoolchildren given a dose of vitamin A or a snack containing RPO daily for 60 days

A significant increase in serum retinol levels, almost twofold, was observed after feeding the RPO snacks (table 2). A similar increase in retinol levels was observed in the group receiving vitamin A (fig. 4). The DR:R ratio decreased significantly after supplementation with RPO (0.073 + 0.025 to 0.023 + 0.014). In the vitamin A group, it decreased from 0.106 + 0.025 to 0.024 + 0.003 (fig. 5).

This study demonstrated that the ß-carotene from RPO is readily bioavailable and is a good source of provitamin A for combating vitamin A deficiency. In addition, since the {carotene is in an oil medium, it is readily absorbable.

Conclusion

Red palm oil is a rich source of provitamin A and antioxidant nutrients-ß-carotene, tocotrienols, and tocopherols, which have the capacity to retard peroxidation and scavenge free radicals-besides having antimutagenic and hypocholesterolaemic potential, and is nutritionally safe and wholesome. The combination of these characteristics makes it an excellent oil for human consumption. Developing countries should therefore have no hesitation in creating strategies to increase the use of RPO for combating vitamin A deficiency.

References

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2. Gopalan C, Narasinga Rao BS, Subhadra S. Combating vitamin A deficiency through dietary improvement. Hyderabad: Nutrition Foundation of India, 1992.

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6. Rukmini C. The minor components of palm oil in relation to hypocholesterolemia. Hyderabad, India: Malaysian Palm Oil Promotion Council, 1991.

7. Qureshi AA, Burger WC, Peterson DM, Elson CE. The structure of an inhibitor of cholesterol biosynthesis isolated from barley. J Biol Chem 1986;261: 10544-50.

8. Rukmini C, Raghuram TC. Nutritional and biochemical aspects of the hypolipidemic action of rice bran oil: a review. J Am Coll Nutr 1991;10(6):593-601.

9. Wood R. O'Brien B. Kubena K et al. Effect of palm oil and other dietary fats on serum lipids and lipoproteins. In: Loke KH, Basiron Y. eds. Progress, prospects and challenges toward 21st century. Proceedings of the PORIM International Conference, 9-14 Sept 1991. Kuala Lumpur, Malaysia: PORIM, 1991:41

10. Raghuram TC, Brahmaji Rao U. Rukmini C. Studies on hypolipidemic effect of rice bran oil in humans. Nutr Rep Intl 1989;39(5):889-95.

11. Manorama R. Rukmini C. Effect of processing on ß-carotene retention in crude palm oil and its products. Food Chem 1991;42:253-64.

12. Manorama R. Chinnasamy N. Rukmini C. Multi-generation studies on red palm oil and on hydrogenated vegetable oil containing mahua oil. Food Chem Toxicol 1993;31:369-75.

13. Manorama R. Harishankar N. Polasa K, Rukmini C. Mutagenicity on repeatedly heated crude and refined palm oil. J Oil Tech Assoc (India) 1989;21 :29-30.

14. Manorama R. Rukmini C. Sensory evaluation of foods prepared in crude palm oil. J Food Sci Tech (India) 1992;29(1):70-72.

15. Rukmini C. Carotenes from red palm oil: current status and future prospects. In: Gopalan C, Narasinga Rao CS, Subhadra S. eds. Combatting vitamin A deficiency through dietary improvement. Hyderabad, India: Nutrition Foundation of India, 1992:149-57.

16. Tanumihardijo SA, Furr HC, Olson JA, Erdman JW. Use of the modified relative dose response (MRDR) assay in rats and its application to humans for the measurement of vitamin A status. Eur J Clin Nutr 1990;44: 219-24.

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