Aspectos nutricionais de fitatos e taninos

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Abstract

Os grãos de leguminosas contêm uma variedade de fatores antinutricionais que podem provocar efeitos fisiológicos adversos ou diminuir a biodisponibilidade de certos nutrientes. Danos crônicos leves devidos à prolongada ingestão de antinutrientes são muito difíceis de se avaliar. Como conseqüência, existem muitas controvérsias em estudos de biodisponibilidade in vivo a respeito da extrapolação de resultados de sistemas experimentais, para seres humanos que se alimentam com dietas complexas. O papel dos fatores antinutricionais tem sido rediscutido, em função de descobertas recentes que evidenciam o potencial de algumas dessas substâncias em exercer funções benéficas ao organismo humano. A habilidade do ácido fítico em atuar como anticarcinogênico, antioxidante e prestar contribuição nutricional no tratamento de diabetes, através da ação inibidora de a-amilases, são exemplos da diversidade de atuação dessas substâncias. Os taninos são antioxidantes, inibidores de determinadas enzimas e influenciam negativamente a digestibilidade de proteínas, no entanto, os seus efeitos em seres humanos ainda são desconhecidos.

Translated abstract

Legumes contain a variety of antinutritional factors which can provoke adverse physiological effects or reduce the bioavailability of certain nutrients. Slight chronic damage caused by ingestion of these antinutrients is difficult to evaluate. As a consequence, many controversies are found in in vivo studies on bioavailability, regarding the extrapolation of the results of experimental systems to humans on complex diets. The role of antinutritional factors is being rediscussed as a result of recent discoveries which show the potential of some of these substances in exerting beneficial effects on human organism. The capacity of phytic acid to act as an anticarcinogen and antioxidant and to contribute nutritionally in the treatment of diabetes, due to its a-amylase inhibiting activity, is an example of the diversity of action of these substances. The Tannins are antioxidants, inhibitors of certain enzymes and show a negative influence on protein digestibility. However, their effects on human beings are still unknown.

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Phytic acid interactions in food systems.

M Cheryan (1979)

Phytic acid is present in many plant systems, constituting about 1 to 5% by weight of many cereals and legumes. Concern about its presence in food arises from evidence that it decreases the bioavailability of many essential minerals by interacting with multivalent cations and/or proteins to form complexes that may be insoluble or otherwise unavailable under physiologic conditions. The precise structure of phytic acid and its salts is still a matter of controversy and lack of a good method of analysis is also a problem. It forms fairly stable chelates with almost all multivalent cations which are insoluble about pH 6 to 7, although pH, type, and concentration of cation have a tremendous influence on their solubility characteristics. In addition, at low pH and low cation concentration, phytate-protein complexes are formed due to direct electrostatic interaction, while at pH > 6 to 7, a ternary phytic acid-mineral-protein complex is formed which dissociates at high Na+ concentrations. These complexes appear to be responsible for the decreased bioavailability of the complexed minerals and are also more resistant to proteolytic digestion at low pH. Development of methods for producing low-phytate food products must take into account the nature and extent of the interactions between phytic acid and other food components. Simple mechanical treatment, such as milling, is useful for those seeds in which phytic acid tends to be localized in specific regions. Enzyme treatment, either directly with phytase or indirectly through the action of microorganisms, such as yeast during breadmaking, is quite effective, provided pH and other environmental conditions are favorable. It is also possible to produce low-phytate products by taking advantage of some specific interactions. For example, adjustment of pH and/or ionic strength so as to dissociate phytate-protein complexes and then using centrifugation or ultrafiltration (UF) has been shown to be useful. Phytic acid can also influence certain functional properties such as pH-solubility profiles of the proteins and the cookability of the seeds.