Biodisponibilidade de ferro de genótipos de milho: avaliação por métodos in vitro e in vivo
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2010-03-29
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Universidade Federal de Viçosa
Resumo
A fortificação dos alimentos é uma alternativa adotada no combate à anemia ferropriva. Entretanto, o acesso limitado aos alimentos industrializados e a baixa biodisponibilidade dos sais minerais utilizados podem reduzir sua eficácia. Nesses casos, a biofortificação com minerais de alta biodisponibilidade pode ser uma alternativa. A biodisponibilidade de ferro pode ser avaliada por técnicas in vitro como a diálise, e in vivo com animais e humanos. A técnica in vitro é um método mais barato e mais fácil de executar que as metodologias in vivo, e assim poderia ser utilizada para selecionar os genótipos mais promissores num programa de melhoramento genético. Portanto, o objetivo deste estudo foi avaliar a biodisponibilidade de ferro de diferentes genótipos de milho e a possível correlação entre os resultados obtidos por método in vitro e in vivo. Objetivou-se ainda verificar a influência do teor de fitato e a razão fitato:ferro na biodisponibilidade de ferro. Os teores de ferro total, solúvel e dialisável de 13 amostras de milho foram determinados por espectrometria de absorção atômica em forno de grafite e o de fitato foi quantificado por método colorimétrico. O teor de ferro dos genótipos teve valor médio de 17,93±2,93 mg/kg. O teor de fitato das amostras variou de 0,77% (3E4744 e DKB390) a 1,03% (2E4794), e a razão molar fitato:ferro de 30,64 (1F5924) a 55,41 (DKB390). O percentual de ferro solúvel variou de 13,17 a 39,63% para Caimbé e 3E5335, respectivamente. O maior valor de ferro dialisável também foi para 3E5335 (19,14%), entretanto o menor foi de 3,71% para 3E4824. O ferro total apenas se correlacionou significativamente (P<0,05) com o percentual de ferro solúvel (r= -0,597), sendo uma relação inversa. O teor de fitato e a razão molar fitato:ferro não se relacionaram com os valores de solubilidade e diálise. O ferro solúvel e dialisável tanto em μg/g como em valor percentual, correlacionaram-se significativamente (r = 0,944 e r = 0,951; respectivamente). O milho 3E5335 foi o que apresentou melhor potencial para a biofortificação devido ao seu maior teor de ferro disponível. No ensaio biológico, avaliou-se a biodisponibilidade de
ferro de cinco genótipos de milho, pelo método de depleção-repleção em ratos. Os animais receberam dieta AIN93-G sem ferro na fase de depleção por 21 dias. Na fase de repleção (n=8), receberam dietas com 12 mg/kg de ferro, por 14 dias, provenientes de: D1:Sulfato ferroso, D2:Caimbé, D3:1F5924, D4:2E5305, D5:3E4824, D6:2E4794. A hemoglobina (Hb) foi mensurada no início e no final da fase de repleção. Foi avaliado ganho de Hb, ganho de Hb por grama de ferro consumido, eficiência na regeneração de Hb (HRE) e valor biológico relativo de HRE (RBV de HRE). Não houve diferença no consumo alimentar, ganho de peso, Hb inicial, ganho de Hb e ganho de Hb por grama de Fe consumido. Todos os grupos apresentaram HRE maior que o controle, exceto D2; e não houve diferença entre os grupos teste, quando avaliados entre si. O RBV indicou que D5 e D6 foram os que apresentaram melhor valor de HRE em relação ao controle. O grupo D2 consumiu a maior quantidade de ferro, porém apresentou o menor valor de RBV. Não houve correlação entre consumo de ferro e ganho de Hb. Houve correlação positiva significativa entre ganho de Hb por gramade ferro consumido e HRE (r = 0,883), e ganho de Hb e HRE (r = 0,723). O ganho de hemoglobina por grama de ferro consumido e HRE não apresentaram correlação com os resultados obtidos no estudo in vitro. O ganho de hemoglobina não apresentou correlação significativa, ao nível de 5%, com nenhum valor obtido na diálise, porém foram observadas correlações positivas que variaram de 0,653 a 0,809. Os genótipos de milho analisados apresentaram ferro biodisponível, visto que essas amostras continham valores semelhantes ao grupo controle quanto ao ganho de hemoglobina, ganho de hemoglobina por grama de ferro consumido e eficiência na regeneração de hemoglobina. Entretanto, a quantidade de ferro desse alimento e os resultados do ensaio in vitro indicaram que ainda deve ser feita uma melhor seleção de genótipos quanto ao conteúdo de ferro e fitato. Também foi observado que o teor de fitato e a razão molar fitato:ferro não apresentaram correlação com os resultados obtidos nas análises de biodisponibilidade de ferro, tanto in vitro como in vivo. O método da diálise pode ser uma alternativa na seleção das genótipos para o melhoramento genético visto os resultados concordantes com o ensaio biológico.
Food fortification is an alternative adopted to reduce anemia prevalence. However, limited access to industrialized food and the utilization of low bioavailability mineral salts reduce its efficacy. In these cases, biofortification with high bioavailable minerals can be an alternative. The bioavailability can be evaluated, by in vitro techniques, as dialysis, and in vivo techniques, with animals and humans. The in vitro methodology is cheaper and easier to execute than in vivo methodology, so it could be adopted to select the genotypes with promising characteristics in plant breeding programs. Thus, the objective of this study was to evaluate iron bioavailability of maize genotypes, and analyze the correlation between in vitro and in vivo methodologies. It was also verified the influence of phytate and phytate:iron molar ratio on iron bioavailability. Total, soluble and dialyzable iron content of 13 samples of maize were determined by atomic absorption spectrometer equipped with a graphite furnace, and phytate was determined by a colorimetric method. The mean iron content of maize genotypes was 17.93±2.93 mg/kg. The phytate content varied from 0.77% (3E4744 e DKB390) to 1.03% (2E4794), and phytate:iron molar ratio from 30.64 (1F5924) to 55.41 (DKB390). Soluble iron varied from 13.17 to 39.63% for Caimbé and 3E5335, respectively. The major value for dialyzable iron was for 3E5335 (19.14%), otherwise the lower value was 3.71% for 3E4824. Total iron correlated (p<0.05) only with soluble iron in percent (r = -0.597). Phytate content and phytate:iron molar ration did not correlated with any value of solubility and dialyzability. Iron solubility and dialyzability in μg/g and in percent value had a significant correlation (r = 0.944 e r = 0.951; respectively). The maize 3E5335 presented the best potential for biofortification analyzing by in vitro method. In the biological assay, five genotypes were evaluated by the depletion-repletion methodology in rats. The animals received AIN93-G diet without iron during the depletion period, which lasted 21 days. In the repletion phase (n = 8), the animals received diets with 12 mg/kg of iron for 14 days, from D1:Ferrous sulfate, D2:Caimbé, D3:1F5924, D4:2E5305, D5:3E4824, D6:2E4794. Hemoglobin (Hb) was measured at the beginning and at the end of repletion phase. It was evaluated Hb gain, Hb gain per gram of iron consumed, Hb regeneration efficiency (HRE), and HRE relative biological value (HRE RVB). It was not observed difference in food intake, weight gain, initial Hb, Hb gain, and Hb gain per gram of iron consumed. All groups presented HRE higher than the control group, except for D2; and there was no difference between the test groups. HRE RBV indicated that D5 and D6 presented the higher values compared to the control group. The group D2 consumed the highest amount of iron, however presented the lower value of RBV. It was not observed correlation between iron intake and Hb gain. There was a positive and significative correlation between Hb gain per gram of iron consumed and HRE (r = 0.883), and Hb gain and HRE (r = 0.723). Hb gain per gram of iron consumed and HRE did not present correlation with the results obtained in the in vitro assay. Hb gain did not present significative correlation with the results obtained in the in vitro assay either, otherwise it was observed positive correlations that varied from 0.653 to 0.809. The maize genotypes presented bioavailable iron because these samples promoted same Hb gain, Hb gain per gram of iron consumed and Hb regeneration efficiency as the control group that received ferrous sulfate. However the iron content of these genotypes and the results obtained in the in vitro assay showed that a better selection has to be made to provide genotypes with higher iron and lower phytate contents. It was also observed that phytate content and phytate:iron molar ratio did not present correlation with the results obtained in the in vitro and in vivo assays. The dialysis methodology may be an alternative choice in the selection of best genotypes in the plant breeding programs because of the concordance results with the biological assay.
Food fortification is an alternative adopted to reduce anemia prevalence. However, limited access to industrialized food and the utilization of low bioavailability mineral salts reduce its efficacy. In these cases, biofortification with high bioavailable minerals can be an alternative. The bioavailability can be evaluated, by in vitro techniques, as dialysis, and in vivo techniques, with animals and humans. The in vitro methodology is cheaper and easier to execute than in vivo methodology, so it could be adopted to select the genotypes with promising characteristics in plant breeding programs. Thus, the objective of this study was to evaluate iron bioavailability of maize genotypes, and analyze the correlation between in vitro and in vivo methodologies. It was also verified the influence of phytate and phytate:iron molar ratio on iron bioavailability. Total, soluble and dialyzable iron content of 13 samples of maize were determined by atomic absorption spectrometer equipped with a graphite furnace, and phytate was determined by a colorimetric method. The mean iron content of maize genotypes was 17.93±2.93 mg/kg. The phytate content varied from 0.77% (3E4744 e DKB390) to 1.03% (2E4794), and phytate:iron molar ratio from 30.64 (1F5924) to 55.41 (DKB390). Soluble iron varied from 13.17 to 39.63% for Caimbé and 3E5335, respectively. The major value for dialyzable iron was for 3E5335 (19.14%), otherwise the lower value was 3.71% for 3E4824. Total iron correlated (p<0.05) only with soluble iron in percent (r = -0.597). Phytate content and phytate:iron molar ration did not correlated with any value of solubility and dialyzability. Iron solubility and dialyzability in μg/g and in percent value had a significant correlation (r = 0.944 e r = 0.951; respectively). The maize 3E5335 presented the best potential for biofortification analyzing by in vitro method. In the biological assay, five genotypes were evaluated by the depletion-repletion methodology in rats. The animals received AIN93-G diet without iron during the depletion period, which lasted 21 days. In the repletion phase (n = 8), the animals received diets with 12 mg/kg of iron for 14 days, from D1:Ferrous sulfate, D2:Caimbé, D3:1F5924, D4:2E5305, D5:3E4824, D6:2E4794. Hemoglobin (Hb) was measured at the beginning and at the end of repletion phase. It was evaluated Hb gain, Hb gain per gram of iron consumed, Hb regeneration efficiency (HRE), and HRE relative biological value (HRE RVB). It was not observed difference in food intake, weight gain, initial Hb, Hb gain, and Hb gain per gram of iron consumed. All groups presented HRE higher than the control group, except for D2; and there was no difference between the test groups. HRE RBV indicated that D5 and D6 presented the higher values compared to the control group. The group D2 consumed the highest amount of iron, however presented the lower value of RBV. It was not observed correlation between iron intake and Hb gain. There was a positive and significative correlation between Hb gain per gram of iron consumed and HRE (r = 0.883), and Hb gain and HRE (r = 0.723). Hb gain per gram of iron consumed and HRE did not present correlation with the results obtained in the in vitro assay. Hb gain did not present significative correlation with the results obtained in the in vitro assay either, otherwise it was observed positive correlations that varied from 0.653 to 0.809. The maize genotypes presented bioavailable iron because these samples promoted same Hb gain, Hb gain per gram of iron consumed and Hb regeneration efficiency as the control group that received ferrous sulfate. However the iron content of these genotypes and the results obtained in the in vitro assay showed that a better selection has to be made to provide genotypes with higher iron and lower phytate contents. It was also observed that phytate content and phytate:iron molar ratio did not present correlation with the results obtained in the in vitro and in vivo assays. The dialysis methodology may be an alternative choice in the selection of best genotypes in the plant breeding programs because of the concordance results with the biological assay.
Descrição
Palavras-chave
Biodisponibilidade de ferro, Milho, Biofortificação, Iron bioavailability, Maize, Biofortification
Citação
NAKAJIMA, Vânia Mayumi. Iron bioavailability of maize: in vitro and in vivo evaluation. 2010. 83 f. Dissertação (Mestrado em Valor nutricional de alimentos e de dietas; Nutrição nas enfermidades agudas e crônicas não transmis) - Universidade Federal de Viçosa, Viçosa, 2010.