Curcuma longa L.- and Piper nigrum-based hydrolysate, with high dextrose content, shows antioxidant and antimicrobial properties

A turmeric-and-black-pepper-based hydrolysate (HTBP) was developed. The polyphenolic compounds content, antioxidant activity [1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and ferric reducing antioxidant power (FRAP)] and antimicrobial activity [minimal inhibitory concentration (macro-dilution method) and minimum bactericidal concentration (inoculating the surfaces of agar plates)] were evaluated. Furthermore, the best solvent for extraction of the polyphenolic compounds and curcumin, the main bioactive in turmeric flour (TF), was established. In addition, the tautomeric conformation of curcumin (present in TF and HTBP) was determined by using Fourier-transform infrared spectroscopy (FT-IR). The HTBP was obtained by complete hydrolysis of the starch to dextrose and showed the same curcumin content as TF, suggesting that the starch hydrolysis allowed the release of curcumin from the starch matrix. The antioxidant results indicated that curcumin was responsible for reducing the ferric ion, in the FRAP assay. The presence of piperine in HTBP was confirmed by FT-IR. The ethanol extracts of TF and HTBP showed antibacterial activity against Staphylococcus aureus, Bacillus cereus, Escherichia coli, Klebsiella pneumoniae, Salmonella Enteritidis, Salmonella Typhi and Pseudomonas aeruginosa.