Provitamin a activity of raw and cooked Brazilian leaves

Atividade pró-vitamínica a de folhas brasileiras, cruas e cozidas

Abstracts

The purpose of this study was to determine, through beta-carotene analysis, the provitamin A value of three vegetables leaves ("serralha", celery and mint), raw and submitted to two ways of cooking: boiling and microwave. Samples of "serralha" presented the better provitamin A value beyond the three leaves analyzed: 1, 373 RE/100g for raw samples. Except for mint, it was observed a significant lost of provitamin A due the two ways of cooking.

carotenoids; provitamin A; vegetable leaves; "serralha"; celery; mint

O objetivo do presente trabalho foi determinar, através da análise de beta-caroteno, o valor pró-vitamínico A de três folhas (serralha, salsão e hortelã), cruas e submetidas a dois tipos de cozimentos: fervura e microondas. As amostras de serralha apresentaram os mais altos valores pró-vitamínicos A dentre as três folhas analisadas: 1373 ER/100g para as amostras cruas. Exceto para a hortelã, foi observada uma perda significativa dos valores pró-vitamínicos A devido aos dois tipos de cozimentos.

carotenóides; pró-vitamina A; vegetais folhudos; serralha; salsão; hortelã

PROVITAMIN A ACTIVITY OF RAW AND COOKED BRAZILIAN LEAVES¹

Ligia Bicudo ALMEIDA MURADIAN²,^*, Daleth Walkiria VANDERLINDE², Renata SASAKI²

SUMMARY

The purpose of this study was to determine, through b-carotene analysis, the provitamin A value of three vegetables leaves ("serralha", celery and mint), raw and submitted to two ways of cooking: boiling and microwave. Samples of "serralha" presented the better provitamin A value beyond the three leaves analyzed: 1, 373 RE/100g for raw samples. Except for mint, it was observed a significant lost of provitamin A due the two ways of cooking.

Keywords: carotenoids; provitamin A; vegetable leaves; "serralha"; celery; mint.

RESUMO

ATIVIDADE PRÓ-VITAMÍNICA A DE FOLHAS BRASILEIRAS, CRUAS E COZIDAS. O objetivo do presente trabalho foi determinar, através da análise de b-caroteno, o valor pró-vitamínico A de três folhas (serralha, salsão e hortelã), cruas e submetidas a dois tipos de cozimentos: fervura e microondas. As amostras de serralha apresentaram os mais altos valores pró-vitamínicos A dentre as três folhas analisadas: 1373 ER/100g para as amostras cruas. Exceto para a hortelã, foi observada uma perda significativa dos valores pró-vitamínicos A devido aos dois tipos de cozimentos.

Palavras-chave: carotenóides; pró-vitamina A; vegetais folhudos; serralha; salsão; hortelã.

1 — INTRODUCTION

Beyond the many functions of carotenoids, an important group of natural pigments, is their provitamin A value. The lack of vitamin A on diet can cause xerophtalmy, ceratomalace, blindness and death [10].

Leafy vegetables are sources of carotenoids that could be used in prevention of vitamin A deficiency. The provitamin A from leaves are edible and may offer the consumers an option of an inexpensive an easily obtainable source of this provitamin. Considering the generally much higher cost of animal foods, the provitamin of plant leaves foods constitute a major portion of dietary vitamin A, with estimated going as high as an average of 82% for developing countries [12, 15]. Even in developed countries, the contribution of the provitamin can not be ignored (30-50%).

Other carotenoid function on diet is their prevention on some kinds of cancer. MORENO et al, in 1995 [8], studied the b-carotene and vitamin A effect in hepatic cancer through biologic assays and concluded that b-carotene can inhibit preneoplasic damage in the liver, and this property is not related with their provitamin A activity of b-carotene.

Actually it is necessary to review the data of Brazilian Food Composition Tables regarding the provitamin A values, which are generally overestimated in fruits and vegetables [13, 15]. In Brazil, there are no completed and updated Tables with the nutrient composition [6]. So, it is important to give updated data to a future updating of a Brazilian Food Composition Table.

The purpose of this study is to determine the provitamin A value through b-carotene analysis of three vegetable leaves ("serralha", celery and mint), raw and submitted to two ways of cooking (boiling and microwave). The proximate analysis is also presented for a better characterization of these vegetables.

2 — MATERIAL AND METHODS

2.1 – Material

Samples of "serralha" (Sonchus oleraceus L. ) were obtained from Campus of University of São Paulo; samples of celery (Apium graveolens L. ) and mint (Mentha piperita L. ) were obtained in the main markets of São Paulo.

From each lot of the leaves were cut in small pieces and mixed. Samples of 5g were used raw for analysis and from the same batch 5g were separated and submitted to 10 minutes boiling and the other 5g to microwave cooking (7 minutes at medium potency in a Panasonic Jr. Model microwave oven). A hundred milliliters of distilled water were used for both cooking methods.

Analytical grade solvents and reagents were used. Sigma's b-carotene was used as standard.

2.2 – Methods

2.2.1 – Open Column Chromatography of Carotenoids

The method used was similar to the one by ALMEIDA & PENTEADO [1] which was based on the procedure of RODRIGUEZ et al [11]. The method consisted of:

A) Extraction and Isolation of Carotenes

- Extraction with cooled acetone in a Waring Blender followed by extract filtration under suction through fritted glass plate filter;

- Transfer of the extract to light petroleum in a separation funnel and washing repeated additions of distilled water. The extract was dried over sodium sulfate and concentrated in a rotary evaporator;

- Column chromatography in a 2 X 20 cm glass column using MgO : Hyflosupercel (1 : 2) to a height of about 35 cm, packed by pressing down with a rubber stopper, containing approximately 0, 3cm of anhydrous Na₂SO₄ on the top. The mobile phase was light petroleum with increasing acetone concentrations. The bands were cut and eluted with acetone and then transferred to light petroleum.

B) Quantification

- Absorption spectra were recorded in a Beckman DU-70 spectrophotometer with an Epson printer;

- Quantification of each carotene was done as recommended by DAVIES [3] using the maximum absorbances and applying the Beer's law.

C) Confirmation of Identity

- Thin-layer chromatography was developed using 20 X 20 cm plates with 0, 25mm thickness of silicagel 60G, using a solution of 3% methanol in benzene as mobile phase.

- Chemical reactions [3]:

1. Epoxide tests:

- The presence of 5, 6-epoxide group is detected by the decrease of 20nm in the absorption spectrum, after adding drops of 0,1N HCl to an alcoholic solution of the pigment.

- The chromatography TLC plate, with the pigments adsorbed, was exposed to HCl vapor. The reaction is positive when the yellow spots become blue or green.

2. Cis-trans isomers were detected by adding iodine solution in light petroleum to the cuvette immediately after recording the spectrum. After 5 min of exposure to light, the spectrum was taken again. In the case of all-trans isomers, there is an hypsochromic shift (to shorter wavelengths) as well as an increased in the peak. In the case of cis isomers, there is normally a bathochromic shift (to higher wavelengths) or no shift.

2.2.2 – Vitamin A Evaluation

The quantification of vitamin A value was done based on the provitamin A activity of each carotenoid. As recommended by NATIONAL ACADEMY OF SCIENCES AND NATIONAL RESEARCH COUNCIL [9], it was assumed that 6 mg of b-carotene, which has 100% of provitamin A activity, corresponded to 10 International Units (IU) of vitamin A or 1 Retinol Equivalent (RE).

2.2.3 – Statistical Analysis

The statistical analysis of data was done using t Student's test and STATGRAPHICS'S software (Statistical Graphics Corporation USA, STSC Inc., 1987).

3 — RESULTS AND DISCUSSION

The two carotenes, b-carotene and lutein, were identified in all extracts of leaves, prepared as outlined in this paper. Their characteristics are listed in Table 1.

The first fraction was identified as b-carotene and the second one as lutein. As lutein doesn't have provitamin A activity, it hadn't been quantitated. b-carotene has provitamin A activity of 100% [2].

The main carotene was b-carotene for all leaves analyzed. The quantitative results of carotene analysis obtained by Open Column Chromatography are presented in Table 2 for "serralha", celery and mint leaves.

To perform the statistical analysis, we used the t Student's test to detect the difference between the effect of thermal treatment.

For "serralha", there was a significant lost of 21% with boiling and 20% for microwave cooking (level of 5% of significance).

For celery, there was a significant lost of 11% with boiling and 26% for microwave cooking (level of 5% of significance).

For mint, there was no significant lost for microwave cooking (level of 5% of significance) and an increase of 12.53% with boiling.

The work of MERCADANTE & RODRIGUEZ -AMAYA [7] showed the value of 63 ± 14mg/g of b-carotene for ra "serralha" leaves which is lower than our results.

Provitamin A value of three kinds of leaves was calculated using the data of Table 2, as recommended by NAS/NRC [9] and the results are shown in Table 3.

Based on the statistical analysis, "serralha" is the richest leaf in provitamin A content of the three leaves analyzed. Except for mint, it's observed a significant lost of provitamin A due the two ways of cooking.

The Brazilian Food Composition Tables: ENDEF [5] shows the value of 480 RE/100g for raw "serralha", and the Table of FRANCO [4] shows the same 480 RE/100g for raw "serralha", 105 RE/100g for celery and 360 RE/100g for mint leaves. The work of RODRIGUEZ -AMAYA [14] mentioned the value of 1050±230 RE/100g for raw "serralha" leaves. All these values above are lower than ours.

4 — CONCLUSIONS

We can conclude that "serralha" is the leaf that presents the highest provitamin A value between the three leaves analyzed. Regarding both cooking effect, except for mint, it was observed a significant lost (P<0.05) of provitamin A activity.

5 —

6 — ACKNOWLEDGMENTS

Thanks are due to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for scholarship granted to the first and the second authors. We also thank Fundação de Amparo à Pesquisa de São Paulo (FAPESP) for scholarship granted to the third author. The authors are also grateful to Liandra M. Magri and Juliana Nitta.

² Profa. Dra. do Departamento de Alimentos e Nutrição Experimental, Faculdade de Ciências Farmacêuticas da Universidade de São Paulo, Av. Prof. Lineu Prestes 580, CEP 05508-900, São Paulo, SP, Brasil, E-mail: [e-mail]

* A quem a correspondência deve ser enviada.

References

• [1] ALMEIDA, L.B. & PENTEADO, M.V.C. Carotenoids and provitamin A value of white fleshed Brazilian sweet potatoes (Ipomoea batatas Lam. ). J. Food Comp. Anal, Blacksburg, v. 1, p. 341-52, 1988.
• [2] BAUERNFEIND, J.C. ed. Carotenoids as colorants and vitamin A precursors New York, Academic Press, 1981. 938p.
• [3] DAVIES, B.H. Carotenoids. In: GODWIN, T.W. Chemistry and Biochemistry of plant pigments. 2 ed. London, Academic Press, 1976, v. 2, p. 38-165.
• [4] FRANCO, G. Nutrição: texto básico e tabela de composição química de alimentos. 6. ed. Rio de Janeiro/São Paulo, Edições Ateneu, 1982, 230p.
• [5] FUNDAÇÃO INSTITUTO BRASILEIRO DE GEOGRAFIA E ESTATÍSTICA. Tabelas de Composição de Alimentos. Rio de Janeiro, 1985. 2216p. (Estudo Nacional da Despesa Familiar, v. 3; publicações especiais, t.1).
• [6] LAJOLO, F.M. & VANUCCHI, H. Tabelas de composição de nutrientes em alimenos: situação no Brasil e necessidades. Arch. Latinoam. Nutr, Caracas, v. 37, n. 4, p. 702-13, 1987.
• [7] MERCADANTE, A.Z. & RODRIGUEZ - AMAYA. Carotenoid composition and vitamin A value of some native brazilian green leafy vegetables International Journal of Food Science and Technology v. 25, p. 213-219, 1990.
• [8] MORENO, F.S.; WU, T.S.; PENTEADO, M.V.C.; RIZZI, M.B.S.L. JORDÃO, Jr., A.A.; ALMEIDA-MURADIAN, L.B.;DAGLI, M.L.Z. A comparison of beta-carotene and vitamin A effects on a hepatocarcinogenesis model. Internat. J. Vit. Nutr. Res. v. 65, p. 87-94, 1995.
• [9] NATIONAL ACADEMY OF SCIENCES/ NATIONAL RESEARCH COUNCIL. Recomended dietary allowance 9. ed. Washington, 1980. p. 55-60.
• [10] OLSON, J.A. Biological actions of carotenoids - introduction. J. Nutr, Philadelphia, v. 119, p. 94-5, 1989.
• [11] RODRIGUEZ, D.B.; RAYMUNDO, L.C.; LEE, T.C.; SIMPSON, K.L.; CHICHESTER, C.O. Carotenoid pigments changes in ripenning Momordica charantia fruits. Ann. Bot, London, v. 40, p. 615-24, 1976.
• [12] RODRIGUEZ-AMAYA, D. Critical review of provitamin A determination in plant foods. J. Micronutr. Anal., Barking, v. 5, p. 191-225, 1989.
• [13] RODRIGUEZ-AMAYA, D.B. Os carotenóides como precursores de vitamina A. Bol. Soc. Bras. Ciênc. Tecnol. Aliment, Campinas, v. 3, n. 2, p. 109-16, 1983.
• [14] RODRIGUEZ-AMAYA, D.B. Assessment of the provitamin A contents of foods: The Brazilian experience. J. Food Comp. Anal., v. 9, p. 196-230, 1996.
• [15] SIMPSON, K.L. & TSOU, S.C.S. Vitamin A and provitamin A composition of foods. In: BAUERNFEIND, J. C. ed. Vitamin A deficiency and it's control, New York, Academic Press., 1986. p. 461-78.

1

Recebido para publicação em 10/07/98. Aceito para publicação em 22/09/00.

Publication Dates

• Publication in this collection
  20 Apr 2001
• Date of issue
  Aug 2000

History

• Accepted
  22 Sept 2000
• Received
  10 July 1998