Nafila P.P. and Kunhi A.A.M. 2016. Tamarind (Tamarindus Indica L.) Seed Protein-Derived Peptides as Angiotensin I–Converting Enzyme (ACE) Inhibitors. Abstract Book. National symposium on ‘Biosciences and Technology –Recent Developments and Future Prospects’, SIAS-Centre for Scientific Research, Safi Institute of Advanced Study, Vazhayoor, Malappuram, Kerala, pp. 26-27.



Hypertension is a major risk factor for the development of cardiovascular diseases. Several synthetic drugs have been developed to combat this problem and most of these drugs have been shown to have drastic side effects. Some of these drugs function by inhibiting Angiotensin I-converting enzyme (ACE-I), which is the key enzyme involved in the biochemical pathway, renin-angiotensin-aldosterone system (RAAS). Several natural materials have been successfully tried to replace these synthetic drugs, which include peptides derived from foods as well as some plant seed proteins. However, ACE-inhibitory activity of tamarind seed protein derived peptides has not been reported so far. Hence, this study was taken up to isolate ACE-inhibitory peptides from the endosperm protein of tamarind (Tamarindus indica) seed. The in silico method has indicated the presence of ACE-inhibitory peptides in tamarind seed proteins. Hence, we tried to study the ACE-inhibitory in vitro. For this protein was extracted from tamarind kernel powder (TKP) by different solvents under different physical conditions like varying temperature, pH, etc. Better protein yield was obtained with 0.1 M NaOH at pH 10 and at 8°C. However, total recovery of protein was rather poor due to the presence of a highly jellifying polysaccharide, xyloglucan in the seed powder. To find out the interference of polysaccharide in the yield of protein, the Swelling Index (SI) of TKP with different solvents was determined. An inverse correlation was observed between protein yield and SI values with different solvents; better yield of protein was possible with 0.1 M NaOH (pH 10 at 8°C) which showed the lowest SI. Protein thus isolated was subjected to partial hydrolysis with gastrointestinal enzymes such as pepsin, trypsin and pancreatin, separately. Analysis of the isolated protein and hydrolysates by SDS-PAGE failed to show proper protein/peptide bands. Hence, the protein/peptide nature of the material had to be confirmed by Lowry’s and Biuret methods. The ACE-inhibitory activity of protein hydrolysates is generally concentration-dependent and also is influenced by the type of enzyme used for hydrolysis. Therefore, protein digests were prepared by pepsin, trypsin and pancreatin at 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0% levels (w/w) each, separately and ACE-inhibitory activity was assayed. All the digests showed the inhibitory activity; themaximum being 77.4, 57.9, and 45.7% for pepsin, trypsin and pancreatin digests, respectively. The activity increased steadily from 51% to 77.4% with 0.5 through 4.0% pepsin digests which then decreased with higher concentrations of the enzyme. Trypsin digests also followed the same pattern, whereas in the case of pancreatin digests the activity gradually increased even up to 10% enzyme without dropping, although the maximum activity was low. The presence of ACE-inhibitory activity obtained in the in vitro analysis very much correlated with the in silico analysis results. These findings strongly suggest that the hydrolysates of tamarind seed proteins have high potential for use in drug formulations for treatment of hypertension. However, more substantial research data have to be generated before getting into any solid conclusions. Due to its easy availability tamarind seeds as a by-product of tamarind, an important food ingredient, increases its chances to be suitable candidate for use as a natural source of ACE-I inhibitory peptides for drug manufacturing. 

Keywords: T. indica, Renin-angiotensin-aldosterone system, ACE-inhibitory peptides.