CHEMICAL COMPOSITIONS, ANTIDIABETIC AND BLOOD PRESSURE REDUCING PROPERTIES OF WONDERFUL KOLANUT SEED (Buccholzia coriacea) PROTEINS

Abstract

The ability of foods to prevent the risk of chronic diseases like diabetes and hypertension is based on the biological activities of its protein components. These bioactive proteins when incorporated into food aid in the treatment and management of several chronic diseases. Thus, the present study aimed at determining nutrient compositions, structural-functional properties, blood pressure and glucose reducing potentials of the wonderful kola proteins and its formulated food samples. Wonderful kola seeds were purchased from Ojee market in Ibadan, Oyo State, and were processed into flour (WCF) samples. The wonderful kola protein isolate (WCI) was produced from the flour sample, while the isoelectric precipitated wonderful kola protein isolate was subjected to pancreatin hydrolysis to obtain hydrolysate (WCH). The WCH supernatant was sequentially passed through ultrafiltration membranes of 1, 3, 5 and 10 kDa molecular weight cut-off (MWCO) to obtain different molecular protein fractions. The wonderful kola flour (WCF) and popcorn flour were combined up to 30% (w/w) levels to obtain three composite combinations, that is, raw popcorn-wonderful kola (RPW), blanched popcorn-wonderful kola (BPW) and fermented popcorn-wonderful kola (FPW). The WCF, WCI, WCH and blended samples were evaluated for their chemical compositions, functional properties, antioxidant activities, protein digestibility, biochemical properties, microbial loads, blood glucose lowering potentials. The wonderful kola proteins were orally administered to spontaneous hypertensive rats (SHRs) to evaluate their blood pressure lowering potentials. Sensory attributes of constituted wonderful kola composite flours were evaluated by employing untrained panelist using 9-point Hedonic scale. Triplicate data were analysed using statistical package. Means were subjected to ANOVA and separated using Duncan New Multiple Range (DNMR) test at p<0.05. The WCF had 18.9 mg/100g crude protein content, while WCI and WCH had 61.2 mg/100g and 52.6 mg/100g respectively, whereas the energy values of WCF, WCI and WCH were 360.8, 360.7 and 348.89 kCal/100g respectively. Potassium was the most abundant mineral element (8.3 - 63.9 mg/100g), while the lowest concentration was phosphorus (0.28 - 0.33 mg/100g), but lead, chromium and selenium were not detected in the samples. Amino acid profiles of wonderful kolanut samples showed that glutamic acid had the highest concentration (13.12 - 17.04 g/100g protein), while methionine was the lowest concentration (0.72 - 1.19 g/100g protein). Phytate, oxalate, tannin, saponin, alkaloid, flavonoid and trypsin in WC were lower than tolerable levels. The WC composed of < 2 kDa molecular weight (M.W) of proteins with few free amino acids. Surface hydrophobicity of WCI was significantly (p<0.05) higher than WCF. The WCF and WCI protein solubility had minimum and maximum isoelectric point of pH 4-5 and pH 8.0 respectively. The 1-3 kDa molecular weight (MW) protein fractions had the higher antioxidant activities in DPPH (67.3%), FRAP (0.26), metal chelation activities (92.8%) and superoxide scavenging activities (9.2%) than other protein fractions and WC samples. The crude protein content of the formulated food samples, that is, RPW, BPW and FPW were 13.84, 13.84 and 19.16 g/100g respectively, while their energy values were 427.2, 430.85 and 427.1 kCal respectively. Biological values (BV) of the RPW, BPW and FPW samples were 69.5, 70.7 and 78.4% respectively, but were significantly (p<0.05) lower than RTU (a control sample) (84.99%), while their protein rating (PR) ranged from 0.91 to 1.20. The pack cell volume (PCV) of the rats fed on FPW (47.2%) was higher than those fed on RPW (38%). The red blood cell (RBC), Heamoglobin concentrations (Hbc) and white blood cells of the rats fed on the blended samples varied between 9.78 - 14.59 x 106 mm3, 12.7 - 15.9 g/dL and 14.85 - 16.4 x103mm3 respectively. The in vitro antihypertensive activities of WC samples showed that <1kDa MW fractions had the highest ACE – inhibitory activity (78.9%), while FPW blend had the lowest ACE-inhibitory activity (31.7%). In contrary, 5-10kDa protein fractions had the highest renin – inhibitory activity (86.5%), while WCI had no renin-inhibitory activity. The in vivo antihypertensive potentials of WC protein samples showed that < 1kDa protein fraction had the highest systolic blood pressure (SBP) (-33 mmHg) and diastolic blood pressure (-26 mmHg) reduction in SHRs after 6 h oral gavage. Blood glucose reducing potentials of the blends fed on alloxanized diabetic rats showed that RPW sample (51.9%) had the highest blood glucose lowering properties than those rats fed on FPW (42.1%) and BPW (24.4%) respectively, but were lower than those rats administered with metformin (67.9%), a synthetic antidiabetic agent. In conclusion, the study established that wonderful kola seed proteins and their blended samples were rich in vital nutrients with very low antinutritional factors. The wonderful kolanut proteins and their blended samples exhibited antioxidant properties with blood pressure and glucose reducing potentials. Hence, wonderful kola seed protein fractions and their composite flour may suitable as potential ingredients in nutraceutical or functional food for the treatment or management of diabetes and hypertension.