Chun Cui

Purification and identification of antioxidant peptides from grass carp muscle hydrolysates by consecutive chromatography and electrospray ionization-mass spectrometry

Grass carp muscles were hydrolyzed with various proteases (papain, bovine pancreatin 6.0, bromelain, neutrase 1.5MG and alcalase 2.4L) to extract antioxidant peptides. The hydrolysates were assessed using methods of hydroxyl radical scavenging ability and lipid peroxidation inhibition activity. Hydrolysate prepared with alcalase 2.4L was found to have the highest antioxidant activity. It was purified using ultrafiltration and consecutive chromatographic methods including ion-exchange chromatography, multilayer coil high-speed counter-current chromatography, and gel filtration chromatography. The purified peptide, as a potent antioxidant, was identified as Pro-Ser-Lys-Tyr-Glu-Pro-Phe-Val (966.3Da) using RP-HPLC connected on-line to an electrospray ionization mass spectrometry. As well, it was found that basic peptides had greater capacity to scavenge hydroxyl radical than acidic or neutral peptides and that hydrophobic peptides contributed more to the antioxidant activities of hydrolysates than the hydrophilic peptides. In addition, the amino acid sequence of the peptide might play an important role on its antioxidant activity.

Identification of phenolics in the fruit of emblica (Phyllanthus emblica L.) and their antioxidant activities.

An activity-directed fractionation and purification process was used to identify the antioxidative components of emblica fruit. Dried fruit of emblica was extracted with methanol and then partitioned by ethyl ether, ethyl acetate, butanol and water. The ethyl acetate fraction showed the strongest 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity among four fractions. The ethyl acetate fraction was then subjected to separation and purification using Sephadex LH-20 chromatography and reverse-phase high-performance liquid chromatography (HPLC). Six compounds were identified to be geraniin (1), quercetin 3-β-d-glucopyranoside (2), kaempferol 3-β-d-glucopyranoside (3), isocorilagin (4), quercetin (5), and kaempferol (6), respectively, by spectral methods, (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy, ultraviolet-visible (UV-Vis) spectrophotometry and mass spectroscopy (MS), and comparison with literatures. Compounds 2-4 and 6 were identified from emblica fruit for the first time. Furthermore, the antioxidant activities of purified compounds were screened for their antioxidative potential using lipid peroxidation and DPPH systems. All the purified compounds showed strong antioxidant and radical scavenging activities. Amongst, geraniin showed the highest antioxidant activity (4.7 and 65.7μM of IC50 values for DPPH and lipid peroxidation assay, respectively) than other purified compounds.

Structural characterisation of polysaccharides from Tricholoma matsutake and their antioxidant and antitumour activities

In this study, polysaccharides from Tricholoma matsutake (TM-P) were purified using a DEAE-Sepharose fast flow column and three polysaccharide fractions (TM-P1, TM-P2 and TM-P3) were obtained. The chemical composition and structural characteristics of TM-P2 were quite different from those of TM-P1 and TM-P3. TM-P2 consisted of glucose, galactose and mannose with a molar ratio of 5.9:1.1:1.0. The glycosidic linkages were mainly composed of 1,6- and 1-linked glucose. Furthermore, TM-P2 showed the strongest in vitro antioxidant and antitumour activities. The oxygen radical absorbance capacity (ORAC) of TM-P2 was 2100.44 μmol Trolox/g. The antiproliferative activities of TM-P2 (4.0mg/ml) on the growth of HepG2 and A549 cells were 67.98% and 59.04%, respectively.

Effect of ultrasonic treatment on the graft reaction between soy protein isolate and gum acacia and on the physicochemical properties of conjugates.

Soy protein isolate (SPI) was grafted with gum acacia (GA) in this work. In comparison with classical heating at high water activity, ultrasound could accelerate the graft reaction between SPI and GA. A degree of graft (DG) of 34 was obtained by ultrasonic treatment for 60 min, whereas 48 h was required with classical heating. Ultrasonic treatment improved the concentration of available free amino groups of SPI. The grafted SPI showed significantly (p < 0.05) higher levels of emulsifying activity index, emulsifying stability index, and surface hydrophobicity than native SPI. The droplet size (D[3,2] and D[4,3]) of SPI emulsion decreased from 8.3 to 2.3 microm and from 25.7 to 7.1 microm through ultrasound-assisted grafting, respectively. Moreover, SPI-GA conjugates gave emulsions exhibiting more stability against creaming than those prepared with only SPI during ambient temperature storage (20 days). Decreases of lysine and arginine contents during the graft reaction indicated that these two amino acid residues attended the covalent linkage between SPI and GA. The results of secondary structure suggested that grafted SPI had decreased alpha-helix and beta-sheet levels and increased unordered coils level.

Effect of maillard reaction products derived from the hydrolysate of mechanically deboned chicken residue on the antioxidant, textural and sensory properties of Cantonese sausages.

Protein hydrolysates as precursors of Maillard reaction were obtained via enzymatic hydrolysis of mechanically deboned chicken residue (MDCR). The Maillard reaction products (MRPs) were prepared at 90 (M1), 100 (M2), 110 (M3) and 120 degrees C (M4), respectively. MRPs possessed a strong reducing power and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity. According to the evolution of total free fatty acids and peroxide value of Cantonese sausage with MRPs during storage, M1 and M3 had a potent antioxidant activity (P<0.05) due to their antioxidant abilities and inhibitory action against lipolytic enzymes. Cantonese sausages treated with M1 and M2 showed good textural and sensory properties. However, M3 and M4 had a negative (P<0.05) effect on the flavour and texture of Cantonese sausages compared to control. The results suggested that M1 was very potential to be used to improve their antioxidant, textural and sensory quality.

Physicochemical changes of myofibrillar proteins during processing of Cantonese sausage in relation to their aggregation behaviour and in vitro digestibility

The physicochemical changes of myofibrillar proteins, especially oxidation behaviour, were measured to determine their mechanism of action on in vitro protein digestibility during Cantonese sausage processing. The results indicated that the carbonyl level significantly increased (p<0.05) during the process. The SH group level decreased, while S-S group level increased gradually. Protein aggregation was induced by oxidation and heat treatment. Result from Fourier transform infrared (FTIR) spectroscopy confirmed protein aggregation occurred. The analysis of in vitro digestibility showed a highly significant (p<0.05) correlation between pepsin activity and carbonyl group formation, S-S group level, protein surface hydrophobicity, D4,3. A negative and highly significant correlation between trypsin, α-chymotrypsin activity and carbonyl group formation was measured, while no significant correlation with S-S groups, protein surface hydrophobicity, D4,3 was observed. It indicated that not only protein oxidation and aggregation but also degradation by pepsin would influence proteolysis with trypsin and α-chymotrypsin.

Effect of acetic acid deamidation‐induced modification on functional and nutritional properties and conformation of wheat gluten

BACKGROUND Acids are often used for deamidating proteins, but the literature on acetic acid deamidation of proteins is sparse. Previous research on acetic acid-induced modification of proteins has focused on peptide proteolysis by relatively high concentrations of acetic acid (>1.5 mol L(-1)) rather than on the accompanying effect of deamidation. Therefore the objective of this study was to determine the deamidation effect of acetic acid with as little peptide proteolysis as possible by employing low-concentration acetic acid (<0.05 mol L(-1)) to deamidate wheat gluten. Changes in surface hydrophobicity, conformation, functional properties and nutritional characteristics of acetic acid-modified samples were determined and compared with those of hydrochloric acid (HCl)-modified samples. RESULTS At similar degree of deamidation and nitrogen solubility index, samples deamidated with acetic acid showed less destruction of peptides bandings, better foaming properties and a more decompacted form (lower S--S content in protein as determined by Raman spectroscopy) than those deamidated with HCl and also exhibited improved emulsification capacity and emulsion stability compared with native wheat gluten. Acetic acid deamidation led to fewer changes in peptide molecular size and secondary structure of wheat gluten compared with HCl deamidation according to the results of sodium dodecyl sulfate polyacrylamide gel electrophoresis and Fourier transform infrared spectroscopy respectively. Amino acid analysis revealed that the nutritional characteristics of wheat gluten were well maintained after deamidation with acetic acid. CONCLUSION The results show that low-concentration acetic acid can modify wheat gluten mainly by deamidation, resulting in deamidated wheat gluten with good functional and nutritional properties.

Antioxidant capacity of anthocyanins from Rhodomyrtus tomentosa (Ait.) and identification of the major anthocyanins

The anthocyanins in the fruits of Rhodomyrtus tomentosa (ACN) were extracted by 1% TFA in methanol, and then purified by X-5 resin column and C18 (SPE) cartridges. The purified anthocyanin extract (ART) from the fruits of R. tomentosa showed strong antioxidant activities, including DPPH radical-scavenging capacity, ABTS radical scavenging capacity, reducing power and oxygen radical absorbance capacity (ORAC). The purified anthocyanin extract was analyzed by high performance liquid chromatography (HPLC). The major anthocyanins were purified by semi-preparative HPLC and Sephadex LH-20 column chromatography, and were identified as cyanidin-3-O-glucoside, peonidin-3-O-glucoside, malvidin-3-O-glucoside, petunidin-3-O-glucoside, delphinidin-3-O-glucoside and pelargonidin-3-glucoside by HPLC-ESI/MS and nuclear magnetic resonance spectroscopy (NMR). Cyanidin-3-O-glucoside was considered as the most abundant anthocyanin, which was 29.4 mg/100 g dry weight of R. tomentosa fruits. Additionally, all the major anthocyanins were identified from R. tomentosa fruit for the first time.

Characterisation of aroma profiles of commercial soy sauce by odour activity value and omission test

Twenty-seven commercial soy sauces produced through three different fermentation processes (high-salt liquid-state fermentation soy sauce, HLFSS; low-salt solid-state fermentation soy sauce, LSFSS; Koikuchi soy sauce, KSS) were examined to identify the aroma compounds and the effect of fermentation process on the flavour of the soy sauce was investigated. Results showed that 129 volatiles were identified, of which 41 aroma-active components were quantified. The types of odorants occurring in the three soy sauce groups were similar, although their intensities significantly differed. Many esters and phenols were found at relatively high intensities in KSS, whereas some volatile acids only occurred in LSFSS. Furthermore, 23 aroma compounds had average OAVs>1, among which 3-methylbutanal, ethyl acetate, 4-hydroxy-2-ethyl-5-methyl-3(2H)-furanone, 2-methylbutanal and 3-(methylthio)propanal exhibited the highest average OAVs (>100). In addition, omission tests verified the important contribution of the products resulting from amino acid catabolism to the characteristic aroma of soy sauce.

Oxidation of sarcoplasmic proteins during processing of Cantonese sausage in relation to their aggregation behaviour and in vitro digestibility.

The physicochemical changes of sarcoplasmic proteins, especially oxidation behaviour, were measured to determine their mechanism of action on in vitro protein digestibility during Cantonese sausage processing. The results indicated that carbonyl level increased (p<0.05) during the process. The fluorescence loss of tryptophan residues was a direct consequence of the oxidative degradation. All the parameters of protein aggregation were highly (p<0.05) correlated with carbonyl level and protein surface hydrophobicity (H(0)), indicating that protein oxidation and thermal denaturation could induce protein aggregation, leading to secondary structural changes. The analysis of in vitro digestibility showed no correlation between pepsin activity and protein oxidation, due to the biphasic response of sarcoplasmic proteins toward proteolysis. However, a highly significant (p<0.05) correlation was observed with trypsin and α-chymotrypsin activity, indicating that protein oxidation induced the changes in H(0), protein aggregation and secondary structure, which further influenced in vitro digestibility.