Estudo de carotenoide e pro-vitamina A em alimentos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1993

RESUMO

Many analytical methods have been developed with the purpose of establishing a simple, rapid and economic procedure for determining the provi tamins A in foods. In the present study, three methods were assessed: those of COST91, IVACG and RODRIGUEZ-AMAYA et alii simplied. Kale, carrot, papaya and tomato were chosen as food samples because of their distinct characteristics in terms of the provitamin A composition. Incomplete extraction and drastic saponification were the principal deficiencies of the COST91 method. In addition, α – and β-carotene eluted together and β- cryptoxanthin and γ -carotene were not considered. For the IVACG method, the extraction was insufficient only for kalei it was more versatile than that of COST91, since the different provitamins were separated. Of the different saponification procedures, cold saponification was confirmed to be the best technique. The RODRIGUEZ-AMAYA et alii simplified method proved to be the method of choice, principally for its simplicity and accuracy. Irrespective of the cromatographic proçess utilized, the absorption coefficients are used for the calculation of the concentrations carotenoids. Thus, coefficients hitherto unestablished, or are discrepant in current literature, were determined since the cis-isomers have lower biological potency than the corresponding trans-carotenoids, concern has been raised over the necessity of separating the isomers of provitamins A so as to determine the vitamin A value of foods more accurately. In this paper 12 frui ts, some of different cultivars, 11 fresh vegetables and 7 cooked vegetables, totalling 198 samples, were analyzed in duplicate, to get an idea of the natural ocurrence of cis~isomers of provitamins A. The presence of isomers was confirmed by open column chromatography and HPLC. The different fruits can be divided into two main groups: (1) those having β -carotene as the principal provitamin, and. (2) those with β -cryptoxanthin as the major provitamin. cis-isomers of provitamins A were not found in "cajá", papaya cultivars Solo and Tailândia, passionfruit, "pitanga". and West Indian cherry. Traces of 13-cis- β -carotene were observed in some samples of loquat and mango cultivars Tommy Atkins and Haden. 13-cis- and 9¬cis- β -carotene were found at low levels in mamey, "buriti", nectarine, peach cultivar Diamante and Chilean peach and "pequi". Nectarine, peach and "pequi" had neo- β -cryptoxanthin, probably 13-cis. utilizing the currentlyemployed calculation procedure, the vitamin A values of the fruits were calculated, with and without isomer separation. Overestimations of only 3-10% of the retinol equi valents occurred when the isomers were not individually quantified, indicating that isomer separation is not necessary in the provitamin A determination of fresh fruits. On the other hand, the fresh vegetables, except tomato and carrot, had cis-isomers. Overestimations of 10-22% were obtained when individual quantif ication of isomers was not accomplished. All cooked vegetables analyzed, including. carrot, had isomers of provitamins A, the overestimation being 5-20% when the isomers were not separated. Thus, isomer separation appears to be necessary for most vegetables, fresh or cooked. Considering the other physiological functions, the complete carotenoid composition of some Brazilian fruits was determined. Mamey (Mammea americana L.) showed quantitative variation greater than normally found in fruits. Violaxanthin, β ¬carotene and β -apo-8 -carotenol alternated as principal pigmento Moreover, for two reasons, the composition was atypical: the presence of B-apo-I0 I -carotenal, especially at high levels, and of a new carotenoid,β- apo-8 -carotenol,alsopresent in appreciable amounts. Mass spectro.metry unequi vocally proved the structure. The vitamin A value (483 RE/100g) was high because of substantial amounts of β -carotene and β -apo-10 I -carotenal, the pigments with the highest vitamin A activity (100%). with its structure, the B-apo-8 -carotenol was considered a vitamin A precursor with activity similar to β -apo-8 -carotenal (72%). In "buriti" (Mauritia vinifera Mart.) eight carotenes (13-cis- α -carotene, α -carotene, 13-cis- β -carotene, β -carotene, 9-cis- β -carotene, ζ -carotene, β-zeacarotene and γ -carotene) and only one xantophyll (zeaxanthin) were identified. (1- and B-carotene were the principal pigments, with 80.1 and 359.8 pg/g, respectivetly (16" and 70% of total carotenoid content). The vitamin A value, 6489 RE/100g, was high because of the high amounts of B-carotene, making "buriti" one of the richest sources of provitamin A. "Pequi" is usually cited as a rich source of provitamin A. The Caryocar villosium species, however, presented a low vitamin A value, 65 RE/100g. This is because the major pigment zeaxanthin (56% of the total carotenoid content) is inactive, and β -cryptoxanthin (31% of the total carotenoid) has only 50% activity. The other pigments identified, in small amounts, were: α -carotene, 13 -cis- β -carotene, carotene and neocryptoxanthin. 13 -cis- β -carotene, β -carotene, β -carotene, -carotene,neurosporene,β -cryptoxanthin, 5, 6-mono-epoxy- β -cryptoxanthin, violaxanthin, auroxanthin and neoxanthin were found in loquat. β -carotene and β –cryptoxanthin were the principal pigments, representing 45% and 27%, respectively, of a total carotenoid content of 17.7 pg/g. Both were the major contributors to the vitamin A value of 179 RE/100g. The carotenoids encountered in peach cultivar Diamante were: 13-cis- β -carotene, β -carotene, 9-cis- β -carotene, ζ -carotene, neocrypto~anthin, β -cryptoxanthin, violaxanthin, auroxanthin and luteoxanthin. The first seven carotenoids were also found in the Chilean variety, besides lutein and zeaxanthin. In both varieties, B-cryptoxanthin was the principal pigment, being responsible for 75% ofthe total carotenoid in Diamante and 43% in the Chilean peach. The mean vitamin A value was 55 RE/100g and 73 RE/100g for the Diamante and Chilean fruit, respectively. 13 -cis- β -carotene, β -carotene, 9 -cis- β -carotene, γ -carotene, neocryptoxanthin, β -cryptoxanthin,lutein, zeaxanthin, violaxanthin, mutatoxanthin and auroxanthin were identified in nectarine. β -cryptoxanthin was the major pigment, accounting for 41% of the total carotenoid content (9.6 }lg/g). Considering the low pigment leveI, the vitamin A value was low, 54 RE/100g.

ASSUNTO(S)

vitamina a carotenoides alimentos - conteudo vitaminico

ACESSO AO ARTIGO

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