3‐Hydroxypyridinone‐l‐phenylalanine conjugates with antimicrobial and tyrosinase inhibitory activities as potential shrimp preservatives

To explore the potential of novel tyrosinase inhibitors, 3‐hydroxypyridinone‐l ‐phenylalanine conjugates, as shrimp preservatives, compounds 1 and 2 were evaluated for the antimicrobial activity, and compound 2 was investigated for the shrimp preservative efficacy. It was found that they both possess a stronger antibacterial effect than kojic acid against two Gram‐positive bacteria and three Gram‐negative bacteria. The minimum inhibitory concentrations (MICs) of compound 2 against Escherichia coli, Staphylococcous aureus, Salmonella gallinarum, Vibrio parahaemolyticus and Bacillus subtilis were determined as 18.5, 37, 148, 37 and 295 μg mL^?1, respectively, whereas MICs of kojic acid against the same 5 bacterial strains were determined to be 355, 178, 1420, 1420 and 355 μg mL^?1, respectively. It has also been demonstrated that treatment with compound 2 improves the sensory properties, retards the growth of spoilage bacteria, decreases the total volatile basic nitrogen (TVB‐N) and increases the pH of Penaeus vannamei Boone, thereby extending the shelf life to 10 days. In contrast, the shelf life of shrimp treated with kojic acid and the control group was 7 and 6 days, respectively. Clearly, 3‐hydroxypyridinone‐l ‐phenylalanine conjugates could find application as shrimp preservatives by inhibiting melanosis and by preventing the growth of bacteria during the storage.     

铆钉菇D447黑色素高产菌株诱变育种及遗传稳定性研究

为提高铆钉菇（Gomphidius sp.）D447的诱变育种的效率,首先对该菌的孢子最佳活化时间及定向筛选剂曲酸的最优添加量进行了研究,结果表明孢子最佳活化时间为6.0 h,曲酸的最优添加量为0.4%。在此基础上,以紫外线、硫酸二乙酯、氯化锂、5-溴尿嘧啶等诱变剂对D447的活化孢子进行了单一及复合诱变,通过曲酸平板初筛,摇瓶复筛方法,最终获得一株黑色素产量为（2.45±0.16） g/L的诱变株DB-3,较出发菌株D447提高了1.57倍。对突变株进行传代稳定性试验,结果表明诱变株DB-3经斜面传代9代以后,黑色素产量仍较稳定,无明显的回复突变。     

Screening of Toxic Inorganic Arsenic Species in Garlic (Allium sativum L.)

It has been evidenced that arsenic in garlic is present in the most toxic inorganic species As(III) and As(V). A non-chromatographic speciation method has been developed for the screening of inorganic toxic species of As in garlic samples by hydride generation atomic fluorescence spectrometry. The determination of As(III) and As(V) was based on the different efficiencies of hydride generation with NaBH₄ with and without a previous reduction with ascorbic acid and KI using a system of two proportional equations corresponding to these two different measurement conditions. The extraction efficiency of total arsenic and the stability of As(III) and As(V) in different extraction media (sulphuric acid, perchloric acid, and methanol/water) were evaluated. Based on the extraction yield and the stability of extracted species, 1.0 mol L⁻¹ H₂SO₄ was selected as the best extracting solution for speciation analysis. The methodology developed allows us a limit of detection of 0.8 and 0.6 ng g⁻¹ for As(III) and As(V), respectively. The relative standard deviation values were 4% for As(III) and 7% for As(V). This method was applied to determine As(III), As(V), and total As in different Spanish garlic samples. The arsenic (III) content varied from 17.1 to 22.1 ng g⁻¹ and As(V) from 54.7 to 67.6 ng g⁻¹. The accuracy of the method was confirmed by the analysis of a certified reference material of tomato leaves treated in the same way as the garlic samples.     

Colour and flavour of potato protein preparations,depending on the antioxidants and coagulants used

The colour and profile of the aromatic compounds of potato juice (PJ) protein preparations were investigated following various process modifications. Several antioxidants (sodium bisulphate, tartaric acid, ascorbic acid), acidulants (tartaric, ascorbic and hydrochloric acids) and chelating agents (chloride, lactate and calcium hydrogen phosphate salts) used for pectin removal during the coagulation of the PJ proteins were evaluated. The combination of sodium bisulphate or ascorbic acid as antioxidants, with calcium chloride or lactate, and ascorbic acid as the protein coagulant, increased the brightness of the protein preparations. Forty-one aromatic compounds, including aldehydes, alcohols and alkanes, were identified. The total concentration of volatiles ranged 59–105 μg g⁻¹. The ascorbate variant contained the lowest n-hexanal concentration. Different treatments did not impact significantly on the 2-methyl-propanal and 2-methyl-butanal concentrations. Interestingly, 2-pentylfuran production was dramatically reduced (16.48 μg g⁻¹) in the lactic variant in comparison to 40.52 μg g⁻¹ with CaHPO₄ addition.     

Preparation,antioxidant activity and protective effect of coconut testa oil extraction on oxidative damage to human serum albumin

Extraction, physicochemical properties and fatty acid composition analysis of coconut testa oil (CTO), antioxidant activity and the protective effect on oxidative damage to human serum albumin (HSA) of coconut testa oil extract (CTOE) were investigated. Results showed that the optimal extract condition of CTO was B₃A₂C₂ (temperature of 60 °C, material‐to‐solvent of 1:4 g mL^?1 and extraction time of 3 h) with the maximum oil yield (76.83 ± 0.53%). The obtained CTO was nondrying oil with iodine value of 14.69 g per 100 g, and lauric acid was the main component of 42.28%. Hydrogen peroxide scavenging activity of CTOE can reach to 49.81% at 2.5 mg mL^?1, while antioxidant activity (AA) on the oxidation of linoleic acid dropped from 56.82% to 31.70% during the first 80 min. CTOE could prevent HSA from oxidative damage induced by hydrogen peroxide via inhibiting the formation of protein carbonyl and increase of hydroperoxides content effectively. Total phenolic content was 68 mg g^?1, and the epicatechin and catechin were 2.74 and 2.26 mg g^?1 in its phenolic compositions, respectively. These all suggested CTO and CTOE might be new worthy exploiting functional sources.     

Effect of storage on the bioactive compounds and antioxidant activity of quince nectar

The changes of bioactive components and antioxidant activity of quince nectar were determined during 9 months of storage at 5, 20, 30 and 40 °C. The amount of total phenolics, flavonoids and antioxidant activity was significantly declined during storage at all temperatures. Loss of L‐ascorbic acid at 5, 20, 30 and 40 °C was 32.08%, 43.69%, 65.21% and 88.82%, respectively. L‐ascorbic acid degradation was in accordance with the first‐order reaction kinetics, and activation energy was found as 43.65 kJ mol^?1. After 9 months of storage, Hydroxymethylfurfural (HMF) contents of quince nectars were 15.01, 16.64, 21.69 and 57.89 mg kg^?1 at 5, 20, 30 and 40 °C, respectively. HMF accumulation fitted a zero‐order kinetic model, and activation energy was found as 88.30 kJ mol^?1. A significant correlation was found among L‐ascorbic acid, total phenolics, flavonoids and antioxidant activity.     

Isolation and characterization of melanin from Osmanthus fragrans’ seeds

Melanin derived from Osmanthus fragrans’ seeds was isolated from O. fragrans’ seeds by alkaline extraction, acid hydrolysis, and repeated precipitation with a yield of 0.34 g/100 g (wet weight basis). Physical and chemical properties of the melanin revealed that the melanin derived directly from O. fragrans’ seeds were similar to typical melanin. The melanin was stable under ultraviolet light or room-light, stable in the range of 25-100 °C, relatively stable in alkaline solution, reducer and salt, but was bleached by strong oxidants (KMnO₄, K₂Cr₂O₇ and NaOCl). The metal-ion of Ca²⁺, Cu²⁺, Fe³⁺ and Zn²⁺ had the function of color increase or color preservation to the melanin. Although Mg²⁺, Al³⁺ and Na⁺ reduce pigment color, it was not obvious. Amino acid and organic acid did not affect the melanin, while sugar, starch, and glucose affected it slightly.     

Effects of light exposure on chlorophyll,sugars and vitamin C content of fresh‐cut celery (Apium graveolens var. dulce) petioles

Effects of light exposure (24 μmol m^?2 s^?1) on fresh‐cut celery nutritional quality were evaluated during 8‐day storage at 7 °C using darkness as control. Light exposure preserved 47% chlorophyll a and 48% chlorophyll b contents more than darkness at the end of storage. Sucrose, reducing sugar and glucose contents in light‐stored petioles were 17%, 25% and 67% higher than those in dark‐stored petioles after 8‐day storage, respectively, thus resulting in higher total soluble solids content in light condition. Moreover, l ‐ascorbic acid content increased at 2‐day storage in light condition and was 46% more than in darkness at the end of storage. The fresh weight loss significantly increased in all petioles, and this increase was markedly accelerated by light exposure with a maximum of 1.43% at the end of storage. Dry matter content was induced more by light exposure than by darkness at 2‐day storage.     

Antioxidant Fraction from Bark of Dillenia Indica

Barks of various plants have been reported to possess both in vitro and in vivo antioxidant activity. In this study, antioxidant activity of the extract from the barks of Dillenia indica was evaluated by various in vitro methods. The bark of D. indica was extracted with 70% aqueous acetone. The total phenolic content was determined by Folin-Ciocalteu method and the antioxidant activity was assayed through various in vitro methods such as antioxidant capacity by phosphomolybdenum method, radical scavenging activity using α, α-diphenyl-β-picrylhydrazyl method, hydroxyl radical (^?OH) scavenging activity by deoxyribose method, and superoxide anion (O₂ ^??) scavenging activity by phenazine methosulphate/NADH-nitroblue tetrazolium system. The total phenolic content of the extract as tannic acid equivalents was 54%. The total antioxidant capacity of the extract was found to be 3.12 mmoles/g as equivalent to ascorbic acid at 50 ppm concentration. At 25 ppm concentration, the radical scavenging activity of butylated hydroxyanisole and extract showed 90.9% and 91.0%, respectively. The ^?OH scavenging activity of the extract was shown to be 53.9% at 100 ppm concentration. At a concentration of 50 μg, the O₂ ^?? scavenging activity of the extract was 31.7% as compared to 47.7% by gallic acid. These results indicated that Dillenia indica barks contained large amount of phenolics and possessed potent antioxidant property.     

Chilling prior to low intensity pulsed electric field processing improved vitamin C stability of carrot purée (Daucus carota cv. Nantes)

Effects of chilling (5 °C) prior to low intensity pulsed electric fields (PEF) (0.1–1.1 kV cm^?1) on vitamin C and activity of peroxidase (POD) and ascorbic acid oxidase (AAO) in carrot purée were studied. The effect of PEF on carotenoids extractability was evaluated and compared to that of purée pre‐conditioned at 20 °C (control). PEF enhanced carotenoids extractability for purée with and without pre‐chilling, up to 25% and 66%, respectively. Vitamin C content decreased after PEF but combined pre‐chilling and PEF maintained vitamin C stability and reduced AAO and POD activities. AAO and the heat‐stable POD fraction were found to be more thermolabile (i.e. higher k_ref value) after PEF, particularly at 0.6 kV cm^?1, which implies elimination of their enzymatic action towards oxidation of bioactive compounds. It was suggested that chilling prior to low intensity PEF modified enzyme properties and secured the stability of vitamin C and carotenoids.     

Inhibitory effects of various antibrowning agents on apple slices

A comprehensive study to evaluate the relative antibrowning activity of 36 known compounds was conducted. Five chemical groups, including carboxylic acids, ascorbic acid derivatives, sulfur containing amino acids, phenolic acids and other miscellaneous compounds, were tested on apple slices under the same conditions. Among the compounds tested, oxalic acid, oxalacetic acid, ascorbic acid-2-phosphate, cysteine, glutathione, N-acetylcysteine, kojic acid and 4-hexyl resorcinol belonged to a group that showed the highest inhibitory activity on apple browning. The minimal concentrations of oxalacetic acid, oxalic acid, cysteine and kojic acid, for an effective antibrowning activity, were 0.25, 0.05, 0.05 and 0.05%, respectively. Oxalic acid showed a synergistic effect when 0.02% oxalic acid was used with 1% ascorbic acid or its derivatives.     

Composition and biological activities of the essential oil from Schisandra chinensis obtained by solvent-free microwave extraction

Applicability of solvent-free microwave extraction (SFME) for extraction of the fruits of Schisandra chinensis essential oil was examined; the composition and antioxidant activities and antibacterial activities of the essential oil were assessed in vitro. An orthogonal experiment (L₉ (3)⁴) was applied to optimize the extraction process. The optimum conditions were: extraction time, 45 min; microwave power, 800 W; diameter of powder particles, 0.25 mm; and proportion of water pretreatment, 30%. Under these conditions, the extraction yield was 1.75%. Thirty-five compounds, representing 91.12% of the oil, were identified, of which the major ones, ylangene (50.11%), β-himachalene (10.76%)，α-bergamotene (9.52%) and β-Chamigrene (5.41%), accounted for of 75.80% the oil.Antioxidant activity, IC₅₀ value of the essential oil was determined as 3.87 mg/mL by DPPH assay, and the inhibition values of the essential oil at 1.8 mg/mL was 41.88% by β-Carotene–linoleic acid bleaching assay. The essential oil was screened for antibacterial activity against both Gram positive (Staphylococcus epidermidis, Staphylococcus aureus, Bacillus subtilis) and Gram negative (Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris) bacteria. The essential oil showed antibacterial effect against all the gram (+) bacteria and gram (−) bacteria tested. These results show that S. chinensis essential oil could be considered as a natural alternative to food antioxidants and preservatives.     

Effect of plant polyphenols and ascorbic acid on lipid oxidation,residual nitrite and N‐nitrosamines formation in dry‐cured sausage

The effects of green tea,grape seed polyphenols and ascorbic acid on pH, water activity (a_w), microbiological counts, TBARS, residual nitrite and N‐nitrosamines were determined in dry‐cured sausages during the ripening period. Results showed that TBARS increased gradually during ripening (P < 0.05), but were significantly reduced with plant polyphenols and ascorbic acid (P < 0.05). Green tea polyphenol (GTP) was most effective (P < 0.05) in reducing TBARS. Plant polyphenols and ascorbic acid significantly decreased residual nitrite, ascorbic acid being most effective (P < 0.05). The amount of N‐nitrosamines increased during ripening, but was significantly reduced with plant polyphenols and ascorbic acid (P < 0.05). Plant polyphenols had no significant effects on moisture content, a_w, pH or microbiological counts in dry‐cured sausage during ripening (P > 0.05). It was concluded that plant polyphenols and ascorbic acid were effective in maintaining the quality and safety of dry‐cured sausages.     

The antioxidant capacity of polysaccharide from Laminaria japonica by citric acid extraction

An optimal citric acid extraction condition (pH 2.0; extraction temperature: 120 °C; extraction time: 3 h) was developed to obtain polysaccharide from Laminaria japonica. The yield of polysaccharide was 13.31 ± 0.08%, with IC₅₀ value of DPPH radical scavenging activity of 0.98 ± 0.01 mg mL^?1. The viscosity of polysaccharide extracted by citric acid (LJPA) was eight times lower than that of polysaccharide extracted by hot water (LJPW), which may be attributed to the low average molecular weight of LJPA (17.12 kDa). Gas chromatography analysis indicated that LJPA was composed of rhamnose, fucose, xylose, manose, glucose and galactose with relative molar percentages of 4.51%, 20.27%, 12.43%, 12.81%, 10.29% and 39.69% respectively. Furthermore, LJPA exhibited significantly higher antioxidant capacities including oxygen radical absorbance capacity (ORAC), ABTS radical scavenging activity and reducing power than LJPW. Citric acid extraction showed a positive influence on the polysaccharide degradation and antioxidant capacities of L. japonica.     

Evaluation of hot and cold extraction of bioactive compounds in teas

This study evaluated the bioactive compounds of different types of tea by comparing hot and cold infusions. A multivariate data analysis was carried out, where the principal components analysis (PCA) and hierarchical cluster analysis (HCA) were used. Phenolic compounds varied between 267.27–2896.00 mg GAE L^?1 and 215.10–7351.33 mg GAE L^?1 for hot (80 °C) and cold extraction (20–25 °C), respectively. In the case of their antioxidant activity, results with DPPH were 43.10‐73.67% for hot extraction and 46.80‐77.13% for cold extraction. The average values for the ABTS˙⁺ method ranged between 2535.43 and 33 300.17 μmol TE L^?1 and between 1110.34 and 38 300.67 μmol TE L^?1, respectively, for hot and cold extraction. Different compounds were identified by liquid chromatography in the samples evaluated, where caffeine presented the higher concentrations in the teas. Samples of green and black tea (hot extraction) and white tea (cold extraction) showed bacteriostatic activity for S. aureus and E. coli. No extract had any bactericide activity. The current study revealed that cold infusion was more efficient in the extraction of bioactive compounds.     

Growth and viability of Lactobacillus acidophilus NRRL B-4495, Lactobacillus casei NRRL B-1922 and Lactobacillus plantarum NRRL B-4496 in milk supplemented with cysteine,ascorbic acid and tocopherols

The effect of three reducing agents (RAs), l-cysteine, ascorbic acid, and tocopherols, on the growth of Lactobacillus acidophilus, Lactobacillus casei, or Lactobacillus plantarum during milk fermentation was evaluated. pH, redox potential, and Lactobacillus counts were determined until pH ≈ 4.6. Further, the study aimed to optimise the concentration of the RAs by formulating the fermented milks with the same RA at different concentrations (0–250 mg L⁻¹ for l-cysteine or ascorbic acid and 0–15 mg L⁻¹ for tocopherols) using a Box–Behnken experimental design. After 45 days of refrigerated storage, the viability of each Lactobacillus species was maximised. We observed that the effect of RA on Lactobacillus is species dependent; ascorbic acid and tocopherols reduced the fermentation time (29%–43%), whereas l-cysteine enhanced the Lactobacillus counts (≥1 log₁₀ cfu mL⁻¹). Lactobacillus species differ in terms of oxygen sensitivity.     

Stability of lutein under various storage conditions

The stability of lutein, a major xanthophyll, was investigated under various storage conditions. Continuous exposure of lutein-containing samples to cold white fluorescent light (4600 lux) at 25 °C resulted in the degradation of lutein at 0.8%-10.7% per day in the samples containing ascorbic acid, ascorbic acid + KOH and H₂O (as control) over a period of 75 days. It was found that ascorbic acid could retard lutein degradation (0.04% - 2.5% per day) at temperatures from ?30 °C to 50 °C under the alkaline condition in darkness. High temperature promoted the degradation of lutein in all the samples. Under the alkaline condition and at low temperature (-12 °C), the stability of pure lutein was similar to that of the lutein extracted from the alga Chlorella protothecoides cultivated heterotrophically.     

ABILITY OF VARIOUS CHEMICALS TO REDUCE COPPER AND TO INACTIVATE MUSHROOM TYROSINASE1

Treatment of mushroom tyrosinase with reducing agents such as hydrogen peroxide, ascorbic acid, phenylhydrazine, gallic acid, ferrocyanide and NH₂OH resulted in inactivation of the enzyme. Under the conditions tested, 50% inactivation of the enzyme was obtained with 4 μM H₂O₂, 20 μM ascorbic acid, 40μM phenylhydrazine, 6 mM gallic acid, 12 mM ferrocyanide and 22 mM NH₂OH. The ability of the reducing agents to reduce Cu²⁺ in a chemical model system was determined and it was found that gallic acid, phenylhydrazine, ascorbic acid and NH₂OH are relatively good reductants of Cu²⁺ while H₂O₂ and ferrocyanide are relatively poor ones. The copper content of mushroom tyrosinase before and after inactivation by each of the reducing agents was determined. The copper content of the enzyme inactivated by H₂O₂, NH₂OH, phenylhydrazine, ferrocyanide, gallic acid and ascorbic acid was 100%, 90%, 90%, 85%, 85% and 76% compared to that of the control (enzyme not treated). It was concluded that the degree of inactivation of mushroom tyrosinase by the reducing agents was not correlated with the decrease in the copper content of the enzyme nor with their ability to reduce Cu²⁺ in a chemical model system.     

Effects of kojic acid on changes in the microstructure and myofibrillar protein of duck meat during superchilled storage

This study investigated the effect of 0.8% (m/v) kojic acid treatment on changes in the microstructure and myofibrillar protein of duck meat covered with oxygen-permeable polyvinylchloride (PVC) film (9 ± 0.5 µM) during superchilled storage (−1.65 ± 0.5°C). The superchilled samples exhibited wider gaps between muscle fibers at 5 weeks storage compared with kojic acid–treated groups. Based on the variation of water status, the water-holding capacity decreased significantly (p < 0.05), and bound water and immobilized water were gradually converted into free water during superchilled storage. For kojic acid–treated samples, however, no major changes were observed with respect to muscle structure, water status, and protein degradation at 6 weeks. The 0.8% (m/v) kojic acid treatment increased the water-holding capacity, reduced carbonyl content and protein degradation, and decreased the α-helix contents loss of myofibrillar proteins. Kojic acid treatment effectively protected myofibrillar protein structure from being destroyed during superchilled storage, suggesting that this method was a good way to reduce protein oxidation and prolonged its shelf life.     

Subcritical fluid extraction of Lycium ruthenicum seeds oil and its antioxidant activity

The effective, energy-saving and green subcritical fluid extraction (SFE) technology was applied to obtain the oil from Lycium ruthenicum seeds (LRSO). The optimal conditions of extraction parameters were found using response surface methodology with Box-Behnken experimental design. The maximum extraction yield of 21.20% was achieved at raw material particle size of 0.60 mm, extraction pressure of 0.63 MPa, temperature of 50 °C and time of 48 min. Other traditional extraction technologies were comparatively used. The physicochemical property of LRSO was analysed and the chemical compositions indicated that they were rich in unsaturated fatty acid, β-carotene, tocopherols and total phenolics. Furthermore, the antioxidant activity of LRSO was evaluated by scavenging activity of three kinds of radicals (DPPH·, ·OH and O₂^-·) and lipid peroxidation in vitro. And its results showed the oil had the potential to be a novel antioxidant agent for using in the field of food, pharmaceuticals and cosmetics.