BIOACTIVE PROPERTIES, CHEMICAL COMPOSITION AND IN-VITRO PROTEIN QUALITY EVALUATION OF AMARANTH SEED FLOURS AND COOKIES

Abstract

This study investigated the bioactive potentials of some amaranth grain proteins. The grains of Amaranthus cruentus PI538319 (CRUS 1) and PI538326 (CRUS 2) and Amaranthus caudatus PI515959 (CAU)) were processed into flour and protein isolate using isoelectric point precipitation. The protein isolates (PI) were sequentially hydrolysed using pepsin + pancreatin (2E) and pepsin + pancreatin + trypsin (3E). The flours were evaluated for proximate composition, protein solubility, antioxidant activity and amino acid composition. The protein isolates and protein hydrolysates (PH) were analysed for molecular weight by electrophoretic method, protein solubility, amino acid composition and nutritional quality, in-vitro antioxidative potentials, in-vitro anti-diabetic and antihypertensive properties. The functional groups of the flour, protein isolates and hydrolysates were determined using the Fourier transform infrared (FTIR) spectroscopy method. Proximate compositions of the grain flours (g/100g) revealed that the crude protein ranged from 15.2 to 16.1; moisture 6.8 to 8.3; crude fat 6.7 to 8.0; total ash 2.3 to 3.1; crude fibre 3.6 to 4.1 and carbohydrate 61.2 to 65.4. Glutamic acid and glutamine were the most abundant amino acid in the grain flour, protein isolate and hydrolysates. The predominant essential amino acid in the flour, protein isolate and hydrolysates was lysine. The isolate molecular weight ranged from 14 to 97 kDa and from 6 to 32 kDa for the hydrolysates under reducing conditions, respectively. The surface hydrophobicity of the protein isolates and hydrolysates revealed that protein isolate of CRUS 1 and hydrolysates of CAU had the highest surface hydrophobicity of 84.49 and 520.22. The minimum protein solubility (PS) was observed at pH 5.0, indicating isoelectric point (pI) of amaranth proteins isolate and hydrolysates. FTIR spectral analysis showed seed flour to contain major functional groups such as: amines, amides, amino acids, polysaccharides, carboxylic acids, esters and lipids. Furthermore, the FTIR spectra of 2E and 3E PH of CRUS 1, CRUS 2 and CAU revealed α-helix, β-sheets and random coil conformations in the secondary structure. The CRUS 1 had the best DPPH radical scavenging activity and ability to decolourize ABTS.+ assay. The samples also posses the ability to reduce the ferrous ion (Fe2+) to Ferric ion (Fe3+). The protein isolate and hydrolysates significantly inhibit the key digestive enzymes (α-amylase and α-glucosidase) in all the samples. The angiotensin-1-converting enzyme (ACE) inhibitory activity of the protein isolate and hydrolysates ranged between 15.34 and 75.68% while that of rennin ranged between 7.58 and 45.11%. 3E PH CRUS 1 was the most effective in inhibiting ACE while 3E PH CRUS 2 was very effective in inhibiting the rennin. As the amaranth grains flour, protein isolates and hydrolysates possess a rich nutraceutical value, it has high potential to be used as a basic raw material to develop new low cost nutritious functional foods. The formulated multi-grain cookies possessed low glycemic index and significantly high in-vitro protein digestibility index. All parameters evaluated indicated that all the multi-grain cookies could serve as a functional snack in the management of hyperglycemia (diabetes) and prevention of associated degenerative diseases.