Reavaliação de metodos analiticos e determinação da composição de carotenoides e valor da vitamina A em mamão e caja

AUTOR(ES)
DATA DE PUBLICAÇÃO

1989

RESUMO

Due to conflicting results and lack of definitions still existing in terms of the adequate methodology for determination of carotenoids and vitamin A value of fruits and vegetables, the more controversial steps of the analytical procedure were studied-Utilizing kale as test material, the efficiency of common extracting solvents was assessed. Samples extracted with acetone were slightly higher than those extracted with mixtures of hexane-acetone and petroleum ether-acetone in terms of β-carotene and significantly higher in terms of lutein. Extraction with methanol made the posterior transfer of the pigments to petroleum ether more difficult, causing significant reduction especially of lutein. The effect of antioxidant (BHT and pyrogallol) and neutralizing (MgC03 ) agents was also investigated. No significant difference was observed in both β-carotene and lutein, although the latter was slightly higher, as a consequence of the addition of these agents. Six saponification procedures were assessed, utilizing as test materials two synthetic carotenoids (β-apo-8’-carotenal and β-carotene) and two food samples (kale and papaya). Hot saponification resulted in greater losses and formation of cis and epoxy carotenoids. The degradation was agravated by more direct contact between the carotenoids and the alkali. The AOAC procedure, which involves saponification in the presence of acetone, led to complete transformation of β-apo-8’-carotenal to citranaxanthin. Saponification was found unnecessary for kale but was indispensable for good separation of papaya carotenoids. Saponification of the carotenoids dissolved in petroleum ether with equal volume of 10% methanolic KOH overnight at room temperature completely a hydro!yzed the carotenol esters and presented better pigment retention. The AOAC method for the determination of the vitamin A value proved inadequate for various reasons: 1- the volume of the extracting solvent is fixed; 2- less active or inactive carotenoids are equally quantified as β-carotene, and 3-active carotenoids can to be disregarded. When compared with the method of Rodriguez et al. (1976a) simplified, the AOAC method presented slightly lower value for kale, apparently due to the insufficient amount of extracting solvent used, and an overestimation of 131% for papaya, due to the inclusion of ζ-carotene, 5,6-monoepoxy- β -cryptoxanthin and part of β-cryptoxanthin as β-carotene. The Rodriguez et al. method, aside from being versatile and considers only the active carotenoids with their respective activities, presented repeatability comparable with HPLC methods. The complete carotenoid composition and vitamin A value of papaya and "cajá" were determined utilizing the Rodriguez et al. (1976a) method. In papaya, cultivar differences and geographic effects were also investigated. Nine carotenoids were identified in papaya: β-carotene, ζ-carotene, β-zeacarotene, γ-carofcene, 5,6-monoepoxy- β-cryptoxanthin, β-cryptoxanthin, antheraxanthin, cryptoflavin and lycopene. β -Zeacarotene and cryptoflavin were detected only in the Common cultivar, while γ-caratene was encountered only in the Solo cultivar. Lycopene, the principall Pigment of the red-fleshed papayas (Solo, Formosa and Tailândia), was inexistent in the yellow-fleshed papaya (Common). Antheraxanthin was also only encounteredin the red-fleshed papayas. The Formosa papayas cultivated in Bahia presented, except for 5,6-monoepoxy- β-cryptoxanthin, higher levels of carotenoids, especially of β-carotene, resulting in a vitamin A value markedly superior than that of the Formosa papayas produced in São Paulo. The average vitamin A values obtained were 1.934, 1.377, 1.199, 1.118 and 988 UI/100g for the papaya cultivars For¬mosa (Bahia), Tailândia, Solo, Common and Formosa (São Paulo), respectively, the principal carotenoid precursors being β -carotene and β -cryptoxanthin. In "cajá", seven carotenoids were identified: α -carotene, β-carotene,ζ-carotene, zeinoxanthin, β-cryptoxanthin, cryptoflavin and lutein. β -Cryptoxanthin was the principal carotenoid and that which contributed most to the vitamin A value. The removal of the peel caused a reduction of 28% in the vitamin A value.

ASSUNTO(S)

carotenoides vitamina a na nutrição humana

ACESSO AO ARTIGO

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