Guowan Su

Isolation and characterization of an oxygen radical absorbance activity peptide from defatted peanut meal hydrolysate and its antioxidant properties.

Defatted peanut meal hydrolysate (DPMH) was purified using ultrafiltration, gel filtration chromatography, and high-performance liquid chromatography. A tripeptide with strong oxygen radical absorbance capacity (ORAC) was isolated and identified as Tyr-Gly-Ser by ESI-MS/MS. It was then synthesized to measure its antioxidant properties in different systems. The ORAC value of Tyr-Gly-Ser was 3-fold higher than that of glutathione (GSH), and it displayed a stronger protective effect on linoleic acid peroxidation and H(2)O(2)-induced oxidative injury in rat pheochromocytoma line PC12 cells than GSH (p < 0.05). However, Tyr-Gly-Ser showed negligible DPPH radical scavenging activity, reducing power, and no metal chelating ability. The results suggested that Tyr-Gly-Ser displayed antioxidant activity via the hydrogen atom transfer mechanism, and the Tyr at the N-terminal was the hydrogen donor. The ORAC assay was recommended as a reliable and effective method to measure the antioxidant activity in the course of antioxidant peptide isolation.

In Vitro and In Vivo Studies on Adlay-Derived Seed Extracts: Phenolic Profiles, Antioxidant Activities, Serum Uric Acid Suppression, and Xanthine Oxidase Inhibitory Effects

This study aimed to explore the potential of polished adlay, brown adlay, adlay bran, and adlay hull to prevent and treat hyperuricemia. Brown adlay extract effectively decreased the serum uric acid levels of oxonate-induced hyperuricemic rats. Free and bound phenolic extracts from these materials contained significant amounts of phenolics, with free phenolics dominated by chlorogenic acid and p-coumaric acid while bound phenolics dominated by p-coumaric acid and ferulic acid. Free and bound phenolics of adlay bran exhibited significant xanthine oxidase inhibition activities, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities, oxygen radical absorbance capacities, and superoxide radical scavenging activities. Adlay bran phenolics could be effective xanthine oxidase inhibitors and radical scavengers. p-Coumaric acid is a xanthine oxidase inhibitor with strong superoxide radical scavenging activity. However, ferulic acid is a xanthine oxidase inhibitor with weak superoxide radical scavenging activity. Chlorogenic acid is a superoxide radical scavenger with weak xanthine oxidase inhibitory activity.

Evaluation of aroma differences between high-salt liquid-state fermentation and low-salt solid-state fermentation soy sauces from China.

Two types of Chinese soy sauce, high-salt liquid-state fermentation soy sauce (HLFSS) and low-salt solid-state fermentation soy sauce (LSFSS), were used to investigate their differences in aroma profile by headspace solid-phase microextraction (HS-SPME) and gas chromatography-olfactometry/mass spectrometry (GC-O/MS). Results from descriptive sensory analysis showed that the alcoholic, cooked potato-like and caramel-like attributes were significantly higher in HLFSS, while LSFSS exhibited significantly higher sour and burnt attributes. In addition, aroma extract dilution analysis (AEDA) revealed 37 and 33 odour-active regions for HLFSS and LSFSS, respectively. Ethanol, 3-methyl-1-butanol, phenylacetaldehyde, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol and 3-(methylthio)propanal detected in HLFSS showed the highest flavour dilution (FD) factors, while 3-methylbutanal, phenylacetaldehyde and ethyl propanoate possessed the highest FD factors in LSFSS. Therefore, the traditional Chinese soy sauce HLFSS contained more complex volatiles and exhibited a richer aromatic profile compared with LSFSS.

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.

Practical problems when using ABTS assay to assess the radical-scavenging activity of peptides: Importance of controlling reaction pH and time.

Effects of reaction pH and time on the antioxidant behaviors of Tyr, Trp, Cys, and their related peptides (Tyr-Gly, Tyr-Glu, Tyr-Lys, Trp-Gly, Trp-Glu, Trp-Lys, Cys-Gly and Cys-Gly) in ABTS assay were investigated. Results showed that all these amino acids and peptides displayed a biphasic kinetic pattern with a fast initial step and a slow secondary step. The initial reaction rates of Tyr, Trp and their related peptides were strongly dependent on pH, while those of Cys and Cys-containing peptides were unaffected by pH. They failed to reach equilibrium over the short incubation period of 6-10 min typically used in this assay. Longer incubation time was needed for most of the peptides to approach equilibrium at lower pH. The observed biphasic kinetic pattern as well as the high TEAC values for these amino acids and peptides, could be a result of combined antioxidant behaviors of themselves plus the generated reaction products.

Isolation and identification of two novel umami and umami-enhancing peptides from peanut hydrolysate by consecutive chromatography and MALDI-TOF/TOF MS

Peanut hydrolysate produced by crude protease extract from Aspergillus oryzae HN 3.042 was found to elicit intense umami and umami-enhancing effect. Taste profiles, amino acid and organic acid composition of peanut hydrolysate and its separation fractions by ultrafiltration were evaluated. The results revealed that peanut hydrolysate was mainly low molecular weight compounds. Fractions of 1-3 kDa and below 1 kDa prominently contributed to the umami taste and umami-enhancing effect of the peanut hydrolysate. The two fractions were further purified, using gel filtration chromatography and reverse-phase high-performance liquid chromatography (RP-HPLC), in combination with sensory evaluation, to obtain a umami peptide and umami-enhancing peptide. The active peptides were identified as Ser-Ser-Arg-Asn-Glu-Gln-Ser-Arg (SSRNEQSR, 963.9 Da) and Glu-Gly-Ser-Glu-Ala-Pro-Asp-Gly-Ser-Ser-Arg (EGSEAPDGSSR, 1091.1 Da), by MALDI-TOF/TOF MS, respectively.

Comparison of in vitro digestion characteristics and antioxidant activity of hot- and cold-pressed peanut meals

Due to the poor protein solubility, hot-pressed peanut meal (HPM) has less value than cold-pressed peanut meal (CPM) in the food industry. The objective of this study was to determine whether the denatured proteins in HPM were suitable for hydrolysis by digestive enzymes. The hydrolysis characteristics and antioxidant activity of HPM and CPM during in vitro digestion were compared. The results showed that HPM was hydrolysed more extensively than CPM. There were more free amino acids and small peptides with MW<5 kDa in HPM hydrolysates. In addition, HPM hydrolysates displayed stronger 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,20-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical-scavenging activities, ORAC value and reducing power than CPM hydrolysates, which could be due to the higher content of small peptides, antioxidative amino acids and melanoidins in HPM hydrolysates. The above results indicated that HPM was a potential source of protein supplement for human consumption.

Approaches of aroma extraction dilution analysis (AEDA) for headspace solid phase microextraction and gas chromatography–olfactometry (HS-SPME–GC–O): Altering sample amount, diluting the sample or adjusting split ratio?

Aroma extract dilution analysis (AEDA) is widely used for the screening of aroma-active compounds in gas chromatography-olfactometry (GC-O). In this study, three aroma dilution methods, (I) using different test sample volumes, (II) diluting samples, and (III) adjusting the GC injector split ratio, were compared for the analysis of volatiles by using HS-SPME-AEDA. Results showed that adjusting the GC injector split ratio (III) was the most desirable approach, based on the linearity relationships between Ln (normalised peak area) and Ln (normalised flavour dilution factors). Thereafter this dilution method was applied in the analysis of aroma-active compounds in Japanese soy sauce and 36 key odorants were found in this study. The most intense aroma-active components in Japanese soy sauce were: ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, ethyl 3-methylbutanoate, ethyl 4-methylpentanoate, 3-(methylthio)propanal, 1-octen-3-ol, 2-methoxyphenol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, 2-phenylethanol, and 4-hydroxy-5-ethyl-2-methyl-3(2H)-furanone.

Binding of Aroma Compounds with Myofibrillar Proteins Modified by a Hydroxyl-Radical-Induced Oxidative System

The objective of this study was to investigate the influence of oxidation-induced structural modifications of myofibrillar protein on its binding ability with aroma compounds such as 2-methyl-butanal, methional, 2-pentanone, 2-heptanone, and nonanal. A method using solid-phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MS) was used to determine the corresponding binding ability. The binding with aroma compounds was found to be strongly affected by the oxidation levels of proteins, probably due to the varying modifications in protein structure and surface. Incubation with oxidants around or below 1 mM mainly caused the refolding of protein structure and accelerated the protein aggregation, which reduced the affinity of the aroma compounds, thus decreasing the binding ability. Nevertheless, treatment with oxidants over 2.5 mM would cause protein reaggregation and partial degradation, and thus, the subsequent modification of protein surface properties. The aggregated protein with wrinkled surfaces favored the hydrophobic interactions with aroma compounds, forming the protein-aroma compound complex, thus enhancing the resultant binding ability as evidenced by fluorescence quenching and SPME-GC/MS analysis.

Identification of antioxidative peptides from defatted walnut meal hydrolysate with potential for improving learning and memory

Defatted walnut meal (DWM), a main byproduct of walnut oil production, is rich in proteins with a high essential amino acid content. Our research was focused on the functional activities of defatted walnut meal hydrolysate (DWMH). DWMH exhibited relatively strong hydroxyl scavenging and oxygen radical absorbance capacities, protective effect on H2O2-injured PC12 cells compared with GSH and cerebrolysin. Besides, DWMH could combat d-galactose induced learning and memory impairments in the Morris water maze test and in the Dark/light avoidance test of mice. Seventy-seven peptides were identified by UPLC-ESI-MS/MS in the most potent antioxidative fraction of DWMH. WSREEQEREE and ADIYTEEAGR were the peptides that most likely accounted for the suppression of H2O2-induced apoptosis in PC12 cells. The mixture of the commercially available amino acids did not offer any protection on H2O2-injured PC12 cells, suggesting that amino acid sequence rather than amino acid composition was the dominant influencing factor. DWMH could be recommended as natural antioxidants for the development of functional foods targeting memory impairments.