Bioatividade do grão de amaranto : avaliação in vitro da atividade ligante de acidos biliares e inibidora da enzima conversora de angiotensina. / Bioactivity of the amaranth grain : in vitro assessment of the binding bile acids and inihibitory activity of the angiotensin converting enzyme.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Amaranth has been highlighted as an excellent alternative or complementary source of food protein due to its balanced amino acid composition. The culture of amaranth has been introduced into Brazil on account of its optimum nutritional (high protein content and better biological quality than that of cereal protein) and functional quality, apart from its agricultural characteristics and adaptability. Although amaranth has been well characterised chemically and present components related to different biochemical activities with physiological potential, little is known about its functional potential. The objective of the present work was to evaluate the inhibitory activity of the angiotensin converting enzyme (ACE) and the capacity to bind with the bile acids (BA) of defatted amaranth flour and its products. Whole flour was obtained by grinding the Amaranthus cruentus grain (BR Alegria variety), and treating with hexane to obtain the defatted flour (ADF), used to produce the amaranth protein concentrate (APC). To obtain the protein hydrolysates, APC, with and without prior heat treatment (90ºC/ 30 minutes), was hydrolysed using the enzyme Alcalase to a 12% degree of hydrolysis (DH). The flours and their derived products were characterised with respect to the electrophoretic and chromatographic compositions and profiles of their proteins. The in vitro digestibility of the proteins was also evaluated and the digested material used to determine the ACE inhibitory activity. The whole amaranth flour and its derivatives presented a composition similar to that found in the literature, and the prior heat treatment of the APC did not alter the activity pattern of the enzymes used, since the electrophoretic and chromatographic profiles (reverse phase and molecular exclusion) were shown to be similar. All the protein hydrolysates, before and after digestion, showed in vitro ACE inhibitory capacity. However, the digested APC, with or without prior heat treatment (DAPCnt and DAPCht, respectively) presented less ACE inhibitory activity (IC50 of 0,439 mg protein/mL and 0,475 mg protein/mL, respectively) than the Alcalase hydrolysates both before (APHnt and APHtt) and after in vitro digestion (DAPHnt and DAPHtt), which presented IC50 values of from 0,118 to 0,176 mg protein/mL. These results suggest that, in vivo, the ingestion of intact amaranth protein could present less ACE inhibitory activity than when ingesting protein previously hydrolysed with Alcalase. In vitro digestion did not change the ACE inhibitory activity of the hydrolysates, suggesting that the ACE inhibitory peptides liberated by the action of Alcalase were resistant to gastro-intestinal hydrolysis. The bile acid binding capacity of the amaranth products (ADF, APC, APHnt and the alkaline residue - AR - obtained from the extraction of APC) and of cholestyramine (used as the positive control), varied as a function of the bile acid studied (cholic, taurocholic, glycocholic and deoxycholic acids). The cholestyramine showed greater binding activity with all the BAs tested, differing from all the samples (p<0,05). The fibre-rich (8,6%) AR presented the least binding activity with all the BAs tested, as compared to the other products, with the exception of with glycocholic acid. The ADF presented intermediate binding activity with all the BAs, which was nevertheless similar to that of APC with glycocholic acid and of APHnt with taurocholic acid, which presented the highest activities. The ADF and APC presented binding capacity with the secondary bile acids toxic to the intestinal mucous membrane. From the results obtained, it was not possible to affirm if it was the proteins, fibres or even some other non-evaluated component, that was responsible for this activity. Having proven the ACE inhibitory and bile acid binding activities in vitro, it is important to also carry out in vivo studies, since the in vivo experiment is a more reliable method to evaluate the biological activity of the amaranth proteins and their other components.

ASSUNTO(S)

amaranto digestão enzimatica amaranth bile acids enzima conversora de angiotensina protein hydrolysates enzymatic digestion acidos biliares hidrolisados proteicos angiotensin coverting enzyme

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