Effect of ascorbic acid on iron release from the emulsifier interface and on the oxidative flavor deterioration in fish oil enriched mayonnaise

This research examines the effect of ascorbic acid (0-800 ppm) on the sensory perception of mayonnaises containing 16% fish oil and on the levels of iron and copper in the aqueous phase. Ascorbic acid increased the formation of fishy off-flavors in fresh mayonnaise. Simultaneously, the iron concentration increased from below the detection limit (1.8 microM) to 34 microM in the aqueous phase of mayonnaises. Model mayonnaises with various concentrations of egg yolk (1-7% w/w) and ascorbic acid (0-8000 ppm) were prepared. Iron concentrations in the aqueous phase increased with increasing ascorbic acid levels, whereas iron concentrations in the assumed interfacial layer decreased. It is proposed that ascorbic acid is able to complex and reduce Fe(3+) to Fe(2+) from phosvitin in the egg yolk, whereby iron is released from the interface. The ascorbic acid-iron complex subsequently reacts with lipid hydroperoxides, resulting in increased lipid oxidation and in the immediate formation of rancid and fishy off-flavors.     

Oxidation in fish oil enriched mayonnaise: ascorbic acid and low pH increase oxidative deterioration

The effect of ascorbic acid (0-4000 ppm) and pH (3.8-6.2) on oxidation and levels of iron and copper in various fractions of mayonnaise enriched with 16% fish oil was investigated. Ascorbic acid induced release of iron from the assumed oil-water interface into the aqueous phase at all pH levels, but this effect of ascorbic acid was strongest at low pH (pH 3.8-4.2). Ascorbic acid generally promoted formation of volatile oxidation compounds and reduced the peroxide value in mayonnaises. Peroxide values and total volatiles generally increased with decreasing pH values, suggesting that low pH promoted oxidation. It is proposed that iron bridges between the egg yolk proteins low-density lipoproteins, lipovitellin, and phosvitin at the oil-water interface are broken at low pH values, whereby iron ions become accessible as oxidation initiators. In the presence of ascorbic acid, oxidation is further enhanced due to the reduction of Fe(3+) to Fe(2+) that rapidly catalyzes lipid oxidation via lipid hydroperoxide decomposition at the oil-water interface in mayonnaise.     

Development of oxidized odor and volatile aldehydes in fermented cucumber tissue exposed to oxygen

Changes in volatile compounds in fermented cucumber tissue during exposure to oxygen were investigated by purge and trap sampling, followed by GC-MS. Hexanal and a series of trans unsaturated aldehydes, (E)-2-pentenal, (E)-2-hexenal, (E)-2-heptenal, and (E)-2-octenal, increased in fermented cucumber slurries exposed to oxygen. Sensory evaluation of oxidized odor was correlated with the increase in aldehyde concentrations. Other identified volatile components present after fermentation did not show major changes during exposure to oxygen. There was no decrease in the formation of aldehydes in fermented cucumber samples that were heated to inactivate enzymes before exposure to oxygen. These results indicated that the formation of aldehydes in oxygen was due to nonenzymatic reactions.     

Quenching mechanisms and kinetics of Trolox and ascorbic acid on the riboflavin-photosensitized oxidation of tryptophan and tyrosine

The effects of 0, 0.3, 0.6, and 0.9 mM Trolox and ascorbic acid on the singlet oxygen oxidation of tryptophan and tyrosine containing 25 ppm of riboflavin were determined by measuring tryptophan and tyrosine concentration by high-performance liquid chromatography analysis. The samples were stored in the a 1000 lx light storage box for 4 h at 30 degrees C. As the concentration of Trolox and ascorbic acid increased, the degradation of tryptophan and tyrosine decreased significantly at p < 0.05. Trolox reduced tryptophan and tyrosine degradation by quenching both singlet oxygen and excited triplet riboflavin, whereas ascorbic acid quenched singlet oxygen only. The total singlet oxygen quenchings of Trolox in the presence of tryptophan and tyrosine were 1.55 x 10(7) and 1.32 x 10(7) M(-1) s(-1), respectively. The total singlet oxygen quenchings of ascorbic acid in the presence of tryptophan and tyrosine were 1.16 x 10(7) and 1.10 x 10(7) M(-1) s(-1), respectively. Trolox was more effective than ascorbic acid in preventing the degradation of tryptophan and tyrosine.     

3-Hydroxy-4,5-dimethyl-2(5H)-furanone (Sotolon) causing an off-flavor: elucidation of its formation pathways during storage of citrus soft drinks.

Gas chromatography/olfactometry (GCO) and gas chromatography-mass spectrometry (HRGC-MS) revealed 3-hydroxy-4, 5-dimethyl-2(5H)-furanone (sotolon) to be responsible for the "burnt" and "spicy" off-flavor observed in citrus soft drinks during storage. Among the ingredients of citrus soft drinks, ethanol and ascorbic acid were identified as the essential precursors of sotolon. Two formation pathways were postulated by studies using (2)H (D)- and (13)C-labeled ethanol and ascorbic acid; i.e., sotolon is formed from two molecules of ethanol and carbons 2 and 3 of ascorbic acid (pathway 1), or it is generated from one molecule of ethanol and carbons 3-6 of ascorbic acid (pathway 2).     

Formation of N-nitroso-N-methylurea in various samples of smoked/dried fish, fish sauce, seafoods, and ethnic fermented/pickled vegetables following incubation with nitrite under acidic conditions

In continuation of our previous studies on N-nitroso-N-methylurea (NMU) formation in cured meats following incubation with nitrite at gastric pH, we extended the investigation to other foods mentioned in the title of this paper. The main objective was to determine whether these foods have the potential to form NMU at pH's that can be found in the human stomach. This was done by nitrosating an aliquot (5 g for fish sauce, 10 g for the others) of each with 7.25 microM to 1.59 mM levels of sodium nitrite for 2 h at room temperature at pH 0.8--1.5 and measuring the amounts of NMU formed. Of the samples tested, fish sauce formed 2--712 ng of NMU, followed in decreasing order by herring (<0.3--688 ng); dried anchovy, shrimp, and other fishes (<0.3--134 ng); crab and lobster paté (<0.3--342 ng); sardines (6--59 ng); oysters and mussels (11--31 ng); dried squid (3--47 ng); kimchi (7--107 ng); and Japanese pickled radish (<0.3--72 ng). Incorporation of 200-2000 ppm of ascorbic acid in the fish sauce and other foods, prior to nitrosation, appreciably inhibited such NMU formation. Although previous researchers in China reported NMU formation in nitrosated samples of fish sauce, this is the first reported formation of NMU upon nitrosation of the other foods mentioned above, and the first reported inhibition of such formation by added ascorbic acid.     

Factors affecting thermally induced furan formation

Furan, a potential carcinogen, can be induced by heat from sugars, ascorbic acid, and fatty acids. The objective of this research was to investigate the effect of pH, phosphate, temperature, and heating time on furan formation. Heat-induced furan formation from free sugars, ascorbic acid, and linoleic acid was profoundly affected by pH and the presence of phosphate. In general, the presence of phosphate increased furan formation in solutions of sugars and ascorbic acid. In a linoleic acid emulsion, phosphate increased the formation of furan at pH 6 but not at pH 3. When an ascorbic acid solution was heated, higher amounts of furan were produced at pH 3 than at pH 6 regardless of phosphate's presence. However, in linoleic acid emulsion, more furan was produced at pH 6 than at pH 3. The highest amount of furan was formed from the linoleic acid emulsion at pH 6. In fresh apple cider, a product with free sugars as the major components (besides water) and little fatty acids, ascorbic acid, or phosphate, small or very low amounts of furan was formed by heating at 90-120 degrees C for up to 10 min. The results indicated that free sugars may not lead to significant amounts of furan formation under conditions for pasteurization and sterilization. Importantly, this is the first report demonstrating that phosphate (in addition to pH) plays a significant role in thermally induced furan formation.     

Determination of nitrite in cured meats by ion-exclusion chromatography with electrochemical detection

A rapid liquid chromatographic (LC) method was developed for a sensitive determination of nitrite in cured meats, using ion-exclusion chromatographic separation and electrochemical detection (IEC-EC). The current AOAC colorimetric method requires 2 h shaking in a steam bath to eliminate interference from reducing compounds such as ascorbic acid. In the present method, nitrite was analyzed in the presence of ascorbic acid without interference, and the extraction time was reduced to 1 min. The extracted nitrite was determined by ion chromatography using anion-exclusion/HS column and amperometric detector equipped with platinum or glassy carbon electrode operating at +1.0 V vs Ag/AgCl reference electrode. The detection limit was 1 ppb as NO2-. The recoveries of 50 ppm nitrite added to frankfurter and meat stick were 103 and 99.6%, respectively, with relative standard deviations less than 4%. The high speed, sensitivity, and selectivity make the new method a useful alternative to the AOAC colorimetric method.     

Inhibition of citral degradation by oil-in-water nanoemulsions combined with antioxidants

The aim of the present study was to investigate the effects of oil-in-water (O/W) nanoemulsions combined with six different natural antioxidants on the stability of citral. Acidic emulsions (lecithin-stabilized palm kernel lipid in pH 3 buffer) containing 1000 ppm citral and 1000 ppm antioxidants (black tea extract, ascorbic acid, naringenin, tangeretin, β-carotene, and tanshinone) were stored at 25 and 50 °C, respectively. The emulsions with and without antioxidants were analyzed by solid phase microextraction gas chromatography (SPME-GC) to monitor the degradation process of citral and the formation of different off-flavor compounds, such as α,p-dimethylstyrene and p-methylacetophenone. The results suggested that encapsulation of citral in emulsions and the addition of the appropriate antioxidants (β-carotene, tanshinone, and black tea extract) could greatly enhance citral's chemical stability during storage.     

Fresh cucumber flavor in refrigerated pickles: comparison of sensory and instrumental analysis

The ability of nonacidified, refrigerated pickled cucumbers to produce the fresh cucumber flavor impact compounds (E,Z)-2,6-nonadienal and (E)-2-nonenal declined during storage. Production of these compounds decreased as the pH of refrigerated cucumbers was reduced. Despite the fact that the concentrations of (E,Z)-2,6-nonadienal and (E)-2-nonenal generated were over 10(5)-fold greater than the threshold levels, it was possible for a sensory panel to consistently detect differences in the intensity of fresh cucumber flavor, provided the pH difference between samples was 1 unit or greater. The presence of spices did not interfere with the ability of panelists to detect differences in fresh flavor intensity. There was a linear correlation between sensory scores and the amount of (E,Z)-2,6-nonadienal produced by cucumbers equilibrated at different pH levels.     

Formation of furan from carbohydrates and ascorbic acid following exposure to ionizing radiation and thermal processing

This study was conducted to investigate the formation of furan from sugars, ascorbic acid, and organic acids as affected by ionizing radiation and thermal treatments. Results showed that both thermal treatments and irradiation induced formation of furan from ascorbic acid, fructose, sucrose, or glucose. Little furan was produced from malic acid or citric acid. The pH and concentration of sugars and ascorbic acid solutions had profound influences on furan formation due to either irradiation or thermal treatment. The rate of irradiation-induced furan formation increased with decreasing pH from 8 to 3. Approximately 1600 times less furan was formed at pH 8 as apposed to pH 3. At the same pHs, the amounts of furan formed from irradiation of ascorbic acid, fructose, and sucrose were always higher than from glucose. As pH decreased from 7 to 3, an increase in thermally induced furan was observed for sucrose and ascorbic acid solutions, but for glucose solution, less furan was formed at pH 3 than at pH 7. The levels of sugars commonly found in fruits and fruit juices, upon irradiation, would be high enough to potentially produce low parts per billion (ppb) levels of furan. The concentration of ascorbic acid at which a maximum of furan was produced upon irradiation was about 0.5 mg/mL, a level commonly found in some foods. Five furan derivatives were tentatively identified in thermally treated ascorbic acid solution, while one furan derivative was tentatively found in both irradiated and thermally treated samples.     

Compositional characteristics and antioxidant properties of fresh and processed sea cucumber (Cucumaria frondosa)

The antioxidant activity of fresh and rehydrated sea cucumber (Cucumaria frondosa) samples with/without internal organs was evaluated for the first time. In addition, their proximate, amino acid, and fatty acid compositions were examined. Rehydrated sea cucumber samples in distilled water were prepared from oven-dried products. All samples contained 83-90% moisture, but showed a significant difference among groups in their protein and lipid contents. Glutamic acid was the predominant amino acid in sea cucumber, followed by glycine and aspartic acid. Essential amino acids such as leucine and lysine were also present at high levels. The trend for free amino acid was different from that of total amino acids and varied among groups. Lipids in sea cucumber were dominated by eicosapentaenoic acid (EPA, C20:5n-3), ranging from 43.2 to 56.7% of the total fatty acids. Docosahexaenoic acid (DHA, C22:6n-3) was present at a much lower concentration of 2.0-5.8%. All sea cucumber samples exhibited radical scavenging property against 2,2'-azobis(2-aminopropane) dihydrochloride (AAPH) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, with rehydrated samples, especially those with internal organs, possessing higher antioxidant activity than their fresh counterparts. No correlation existed between radical scavenging capacity and total phenolics content, suggesting that other components, in addition to phenolic compounds, contribute to the antioxidant activity of sea cucumber.     

Biologically active secondary metabolites from Ginkgo biloba

Three new compounds, (7E)-2beta,3alpha-dihydroxy-megastigm-7-en-9-one (1), 3-[5,7-dihydroxy-2-(4-methoxyphenyl)-4-oxo-4H-chromen-8-yl]-4-methoxybenzoic acid (2), and 4'-O-methyl myricetin 3-O-(6-O-alpha-L-rhamnopyranosyl)-beta-D-glucopyranoside (3), were isolated from Ginkgo biloba, together with 27 known compounds. The structures of the new compounds were determined primarily from 1D- and 2D-NMR analysis. The 4-O-methylbenzoic acid structural feature at C-8 in 2 is encountered for the first time. The antioxidant activities of 29 compounds isolated from Ginkgo biloba were evaluated on intracellular reactive oxygen species in HL-60 cells. It was found that quercetin, kampferol, and tamarixetin had antioxidant activity that was approximately 3-fold greater than that of their respective glycosides and also approximately 3-fold greater than that of a standard ascorbic acid with an IC(50) at maximum effectiveness.     

Levels of active oxygen species are controlled by ascorbic acid and anthocyanin in Arabidopsis

Stabilization of the levels of active oxygen species (AOS) is important to the survival of organisms. To clarify the system controlling levels of AOS in plants, this study used an electron spin resonance (ESR) method to directly measure superoxide radical (O(2)(.-)) scavenging activities in the wild-type Arabidopsis thaliana (Col and Ler ecotypes), two anthocyanin mutants (tt3 and ttg1), and an ascorbic acid mutant (vtc1). Under ordinary growth conditions, Arabidopsis contained superoxide-scavenging activity (SOSA) of approximately 300-500 SOD units/g of fresh weight. The ESR pattern indicated that most (40-50%) of this activity was due to ascorbic acid. For the analysis of SOSA under conditions of oxidative stress, synthesis of AOS was induced by gamma-irradiation. The radical scavenging activity in irradiated plants increased approximately 10-fold following an associated increase in the accumulation of ascorbic acid and anthocyanin. The accumulation of ascorbic acid and anthocyanin was suppressed by treatment with an antioxidant before irradiation and was induced by treatment with a radical-generating reagent. The contributions of ascorbic acid and anthocyanin to the total superoxide radical scavenging activity differed among ecotypes. In the Ler ecotype, ascorbic acid accumulated at twice the level of that in the Col ecotype, and induction of anthocyanin was half that in Col. To confirm the activity of ascorbic acid and anthocyanin against AOS stress, the viability of the wild type and mutants (tt2, tt3,tt5, ttg1, and vtc1) was examined after gamma-irradiation. Only the plants in which ascorbic acid and anthocyanin were induced had the ability to grow and flower.     

Interaction between ascorbic acid and chlorogenic acid during the formation of nitric oxide in acidified saliva

When saliva and gastric juice are mixed, salivary nitrite is transformed to nitrous acid to produce nitric oxide (NO). The NO formation in acidified saliva was enhanced by ascorbic acid and chlorogenic acid. Thiocyanate ion (SCN(-)) also enhanced the transformation of nitrous acid to NO. During the NO formation in the presence of both ascorbic acid and chlorogenic acid, ascorbic acid was preferentially oxidized. Chlorogenic acid was oxidized after ascorbic acid had been oxidized. Ascorbyl radical was detected during the oxidation of ascorbic acid, and the radical intensity was decreased by chlorogenic acid. The decrease is discussed to be due to the reduction of the oxidation intermediate or product of chlorogenic acid by ascorbyl radical. The result obtained in this study suggests that ascorbic acid was preferentially oxidized and that not only ascorbic acid but also ascorbyl radical could interact with the oxidation intermediate or product of chlorogenic acid when chlorogenic acid was added to the mixture of saliva and gastric juice that contained ascorbic acid.     

Lipoperoxidation and cyclooxygenases 1 and 2 inhibitory compounds from Iryanthera juruensis

Plants from Iryanthera genus have been traditionally used as food supplements by South American Indians. The MeOH extract of leaves of Iryanthera juruensis, one of the plants endemic to the Amazon region and consumed in Brazil, and the hexane extract from its seeds inhibited lipid peroxidation (LPO) and cyclooxygenase (COX-1 and -2)) enzymes in in vitro assays. Further analyses of these extracts yielded 5-deoxyflavones (1-5) from the leaf extract and sargachromenol (6), sargaquinoic acid (7), a novel juruenolic acid (8), omega-arylalkanoic acids (9a-c), and the lignan guaiacin (10) from the seed extract. Compounds 3-5 inhibited LPO by 86%, 77%, and 88% at 10 ppm, respectively, and compounds 6 and 9a-c showed inhibition at 76% and 78% at 100 ppm, respectively. However, compounds 7 and 8 were inactive and lignan 10 exhibited LPO inhibitory activity by 99% at 100 ppm compared to commercial antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and vitamin E. The flavones 1-5 also inhibited COX-1 and -2 enzymes by 50-65% at 100 ppm. Compound 6 showed high but nonselective inhibition of COX-1 and COX-2 enzymes, when compared to aspirin and Celebrex, a nonsteroidal anti-inflammatory drug (NSAID). Compounds 7 and 10 inhibited COX-1 by 60% and 65% and COX-2 by 37% and 18%, respectively, whereas compounds 8 and 9a-c showed little or no activity against these enzymes.     

Factors influencing benzene formation from the decarboxylation of benzoate in liquid model systems

Benzene may occur in foods due to the oxidative decarboxylation of benzoate in the presence of hydroxyl radicals. This study investigated factors influencing benzene formation in liquid model systems. The type of buffer, other sources of hydroxyl radical formation in food (photo oxidation of riboflavin and lipid oxidation), transition metal ion concentrations, and the inhibitory effect of antioxidants were tested in benzoate containing model systems. Regarding the hydroxyl radical sources tested, the highest benzene formation was observed in light exposed model systems containing ascorbic acid, Cu(2+), and riboflavin in Na-citrate buffer (1250 ± 131 μg kg(-1)). In practice, it seems that the combination ascorbic acid/transition metal ion remains the biggest contributor to benzene formation in food. However, the concentration of Cu(2+) influences significantly benzene formation in such a system with highest benzene yields observed for Cu(2+) 50 μM (1400 μg kg(-1)). The presence of antioxidants with metal chelation or reduction properties could prevent completely benzene formation.     

Antioxidant activities of extracts from Barkleyanthus salicifolius (Asteraceae) and Penstemon gentianoides (Scrophulariaceae)

Various extracts of the aerial parts of Barkleyanthus salicifolius (Asteraceae) and Penstemon gentianoides (Scrophulariaceae) have been used in folk medicine to treat many ailments, particularly inflammation and migraine. Neither the bioactive components responsible nor the mechanisms involved have been evaluated. Here are reported antioxidant activities of their methanol, dichloromethane, and ethyl acetate extracts. Samples were evaluated for oxygen radical absorption capacity (ORAC), ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical scavenging, and inhibition of the formation of thiobarbituric acid reactive species (TBARS), a measure of lipid peroxidation. Antioxidant activities were strongly correlated with total polyphenol content. The most active extracts from P. gentianoides in scavenging DPPH radicals and inhibiting TBARS formation were the methanol extract (A) and a further ethyl acetate extract of this (E). Partition E was further divided into eight fractions, and both E and the fractions were compared for activity against butylated hydroxytoluene, quercetin, and tocopherol. Partition E and the most active fractions, 5 and 6, were found to have I(50) values of 14.1, 38.6, and 41.8 ppm, respectively, against DPPH and 18.5, 26.0, and 12.7 ppm, respectively, against TBARS formation. Consistent with this finding, partition E and fractions 4-6 had the greatest ORAC and FRAP values. These results show that these plants could be useful antioxidant sources.     

不同氮肥水平对日光温室黄瓜品质和产量的影响

为合理施肥，实现设施栽培蔬菜的优质高产，该文就5种氮肥水平（不施肥、只施基肥膨化于鸡粪22．5t／hm^2、基肥＋追肥N540、1080、2160kg／hm^2）对日光温室黄瓜品质和产量的影响进行了研究。结果表明：随施肥量的增加黄瓜果实的维生素C、可溶性蛋白、游离氨基酸、可溶性糖和有机酸含量均有增加的趋势，风味也有改善，味甜、香气浓，但黄瓜硝酸盐含量呈直线上升。施肥过量还会导致黄瓜脆度下降，商品瓜率和总产量显著降低。综合考虑产量和品质两个因素，在中等使用年限，中等土壤肥力的日光温室黄瓜冬春茬栽培中，每公顷施用于鸡粪22．5t作为基肥，配施化学肥料N540kg做为追肥，能获得较高的产量和较好的品质；过少或过量的施肥均不利于黄瓜产量和品质的形成。     

外源精胺对NO_3~-胁迫下黄瓜幼苗抗氧化酶活性及光合作用的影响

采用营养液培养方法,研究了添加不同浓度的精胺(Spm)对NO3-胁迫下黄瓜幼苗生长、叶片抗氧化酶活性及光合作用的影响。结果表明,140 mmol/L NO3-胁迫下,外加1 mmol/L Spm,10 d后,黄瓜幼苗叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)活性显著增加,电解质渗漏率和丙二醛(MDA)含量显著降低;气孔导度(Gs)、胞间CO2浓度(Ci)和净光合速率(Pn)显著升高,气孔限制值(Ls)显著降低。说明1 mmol/L Spm处理能增强黄瓜幼苗对活性氧的清除能力,降低膜脂过氧化程度;降低气孔关闭,改善叶片的气体交换,幼苗生长势增加,对高浓度NO3-胁迫的抗性增强。当Spm浓度高达1.5~2 mmol/L时,与1mmol/L Spm相比,SOD、POD、APX、CAT活性均开始降低,电解质渗漏率和MDA含量增加,Gs、Ci和Pn显著降低,黄瓜幼苗生长受到抑制。可见,外加一定浓度的Spm可通过提高抗氧化酶活性、降低膜脂过氧化程度及改善光合作用来缓解NO3-胁迫对黄瓜幼苗的影响。