Songlin Zhao

Chemical composition changes of post-harvest coconut inflorescence sap during natural fermentation

Coconut inflorescence sap (CIS) is sweet, oyster-white and translucent and was reported to be highly nutritive and a good digestive agent. The chemical composition changes including total sugar, reducing sugar, ethanol, total acidity, volatile acid, amino acid, vitamin C and total phenolic contents of postharvest coconut inflorescence sap (PCIS) were investigated during a 12-day natural fermentation, and the variety and content of phenolic compounds of fresh coconut inflorescence sap (FCIS) and natural fermented coconut inflorescence sap (NCIS) were also studied by an high performance liquid chromatography (HPLC) system. Total acid, volatile acid and total phenolic contents increased during natural fermentation, while total sugar contents decreased during natural fermentation. The amino acid content declined steadily after harvesting until 3 days, but then remained almost constant. Vitamin C content decreased on day 1, slowly rose to 20.7 mg/L on day 3, and then decreased obviously. Five kinds of phenolic compounds were detected by HPLC. These compounds all increased in NCIS compared with FCIS; both NCIS and FCIS also contained other kinds of phenolic compounds.

Fractionation, physicochemical properties, nutritional value, antioxidant activity and ACE inhibition of palm kernel expeller protein

Five protein fractions (albumin, globulin, prolamines, glutelin-1 and glutelin-2) from palm kernel expeller were fractionated and characterized. Their nutritional value, physicochemical properties, antioxidant activity and angiotensin I-converting enzyme (ACE) inhibition were also investigated. Results showed that the globulin and glutelin-2 were the predominant fractions. The albumin and globulin were rich in arginine, and the glutelin-2 had a high content of sulfur amino acids and showed good nutritional quality. In both the native and reduced states, albumin and glutelin-1 consisted of three polypeptides (18.8, 22.1 and 51.5 kDa) and five peptides (20.7 to 51.5 kDa), respectively. The globulin and glutelin-2 were composed of polypeptides linked via one or more disulfide bonds. Albumin, prolamines and the total palm kernel expeller protein (TPKP) had endothermic peaks at 53.8, 126.5 and 102.3 °C respectively. All the fractions except globulin exhibited a good emulsifying capacity (137.87–269.54 m2 g−1) and emulsion stability (75.13–89.71%) but poor foaming capacity (≤47.56 g/100 g). Among the fractions, prolamines showed the highest inhibiting ability of lipid autoxidation, ACE inhibition (13.63 ± 2.18%) and free radical-scavenging activity on DPPH (79.45 ± 6.80%), hydroxyl (93.40 ± 1.46%) and ABTS (79.35 ± 1.99%). Overall, these palm kernel expeller protein fractions could be used in the food or other industries.

Purification, characterization and synthesis of antioxidant peptides from enzymatic hydrolysates of coconut (Cocos nucifera L.) cake protein isolates

Papain was optimized to hydrolyze coconut cake protein isolates (CCPI) to produce peptides with high antioxidant activity. From the response surface methodology generated model, the optimum conditions were using papain at a concentration of 0.97 g/100 g CCPI, a hydrolysis time of 6.45 h, a temperature of 49.09 °C and a pH of 6.68. The coconut cake protein isolates hydrolysates were separated by G-25 gel chromatography and five fractions were obtained. The amino acid composition and antioxidant activity of the fractions were investigated. Fraction E with the highest antioxidant activity was further purified using gel filtration chromatography, ion exchange chromatography and RP-HPLC (reversed-phase high performance liquid chromatography). Finally, two peptides Pro-Gln-Phe-Tyr-Trp (865.02 Da) and Arg-Pro-Glu-Ile-Val (612.36 Da) were identified. Their IC50 (the concentration of peptide that is required to scavenge 50% of radical activity) on hydroxyl radical scavenging activities were 4.28 and 7.65 μg mL−1. Furthermore, these two peptides were chemically synthesized and the synthetic peptides showed good stability against simulated gastrointestinal protease digestion.

Purification, characterization, synthesis, in vivo and in vitro antihypertensive activity of bioactive peptides derived from coconut (Cocos nucifera L.) cake globulin hydrolysates

Coconut cake globulin hydrolysates (CCGH) with high ACE inhibitory activity (52.16%) were obtained by the sequential digestion of alcalase, flavourzyme, pepsin and trypsin assisted by high pressure pretreatment. It was found that systolic blood pressure of spontaneously hypertensive rats was reduced markedly (P < 0.05) after single and chronic oral administration of CCGH. CCGH were separated by ultrafiltration, Sephadex G-15 gel chromatography and RP-HPLC. Finally, two peptides Pro–Gln–Phe–Tyr–Trp (739.84 Da) and Val–Val–Leu–Tyr–Arg (648.81 Da) were identified. Their IC50 (the concentration of peptide that is required to inhibit 50% of ACE activity) were 0.104 ± 0.012 and 0.244 ± 0.026 mg mL−1. The two peptides exhibited potent non-competitive ACE inhibition and relatively good stability against gastrointestinal enzyme digestion. Furthermore, the two peptides could significantly lower the endothelin-1 content, and protect vascular endothelial cells from reactive oxygen species mediated damage. The results showed that coconut cake globulin could be effectively bioconverted to produce bioactive peptides, which could be used as a functional food ingredient to control ACE activity.

The inhibiting activity of areca inflorescence extracts on human low density lipoprotein oxidation induced by cupric ion

The oxidative modification of human low density lipoprotein (LDL) plays a significant role in atherosclerosis. In this study, the inhibiting activity of areca inflorescence extracts (AIEs) on LDL oxidation was investigated by an in vitro study with Trolox as the standard antioxidant. The kinetics of LDL oxidation, thiobarbituric acid reactive substances assay, ferric-reducing antioxidant power assay and copper chelation assay were also evaluated to assess the antioxidant activities of AIEs, and the results revealed that AIEs could delay the lag time and inhibit the formation of malondialdehyde in the process of LDL peroxidation induced by Cu2+. The boiled water extract displayed the highest antioxidant activity compared with the ambient water extract and ethanol extract. The total phenolic contents and phenolic components of AIEs were also measured by high performance liquid chromatography method. Epicatechin, gallic acid and coumalic acid were the primary phenolic acids in AIEs.

Chemical composition of Chinese palm fruit and chemical properties of the oil extracts

The proximate composition, mineral concentration of fleshy mesocarp, palm meat (PM) and palm kernel (PK) of oil palm fruit ( Elaeis guineensis S.L.Dura ) produced in Hainan, China were investigated. The fatty acid composition, chemical properties and minor constituents of palm oil (PO) and palm kernel oil (PKO) were also studied. The crude fat of PM and PK were 68.09±3.57% and 49.36±2.61%, respectively. The PM and PK were found to be good sources of minerals. The acid value (AV) and free fatty acid (FFA) of PO extracted from fresh PM were much higher. If the fresh PM were heated at 100oC for 30 min, the AV and % FFA could be reduced to 4.62±0.04 mgKOH/g and 2.72±0.002%, respectively. The major fatty acid of PO was palmitic acid 39.93±1.66% and that of PKO was lauric acid 48.01±0.69%. Tocopherol isomer (α-, (β+γ)- and δ-) contents in PO were 68.8±1.84, 22.8±0.54 and 11.8±0.12 mg/kg, respectively. The β-carotene content in PO was 901.5±11.95 mg/kg. The content of sterols in PO and PKO were 880.0±5.23 and 858.0±4.37 mg/kg, respectively. PO and PKO exhibited good chemical properties and could be used as edible oils and for industrial applications. There are almost no data about Chinese palm fruit now and this study systematically researched on it, which can provide useful information for Chinese oil palm industry. Key words: Chemical composition, palm fruit, palm oil, palm kernel oil, chemical properties.