Furan formation from vitamin C in a starch-based model system: Influence of the reaction conditions

The generation of furan from vitamin C during thermal treatment of a starch-based model system, which simulated baby food, was studied. Results indicated that the amount of sample heated in the vial influenced the furan generation from ascorbic acid. Increasing the amount of heated sample from 5% to approximately 98% of the total vial volume, drastically reduced furan formation from 70 ppb to 16 ppb. Changes in ascorbic acid concentrations from 0.1 to 4.5 mg/g did not influence furan concentration nor did different ascorbic/dehydroascorbic acid molar ratios. Interestingly, waxy corn starch itself considerably enhanced furan generation from ascorbic acid. Under the same conditions, 13.2 ppb of furan was generated in starch-based samples, while in ascorbic acid buffered solutions only 0.4 ppb of furan was formed. Application of other matrices, in particular agar and hydrolysed starch, resulted in similar furan concentrations as for native starch, while in polyol solutions furan concentrations were comparable to those obtained for the buffered ascorbic acid solutions.     

Photostabilization of ascorbic acid with citric acid, tartaric acid and boric acid in cream formulations

This study involves the evaluation of the effect of certain stabilizers, that is, citric acid (CT), tartaric acid (TA) and boric acid (BA) on the degradation of ascorbic acid (AH(2) ) in oil-in-water cream formulations exposed to the UV light and stored in the dark. The apparent first-order rate constants (0.34-0.95 × 10(-3) min(-1) in light, 0.38-1.24 × 10(-2) day(-1) in dark) for the degradation reactions in the presence of the stabilizers have been determined. These rate constants have been used to derive the second-order rate constants (0.26-1.45 × 10(-2) M(-1) min(-1) in light, 3.75-8.50 × 10(-3) M(-1) day(-1) in dark) for the interaction of AH(2) and the individual stabilizers. These stabilizers are effective in causing the inhibition of the rate of degradation of AH(2) both in the light and in the dark. The inhibitory effect of the stabilizers is in the order of CT > TA > BA. The rate of degradation of AH(2) in the presence of these stabilizers in the light is about 120 times higher than that in the dark. This could be explained on the basis of the deactivation of AH(2) -excited triplet state by CT and TA and by the inhibition of AH(2) degradation through complex formation with BA. AH(2) leads to the formation of dehydroascorbic acid (A) by chemical and photooxidation in cream formulations.     

Dietary plant materials reduce acrylamide formation in cookie and starch-based model systems

BACKGROUND: Dietary plant materials have attracted much attention because of their health benefits to humans. Acrylamide is found in various heated carbohydrate‐rich foods. Our previous results showed that crude aqueous extracts from diverse dietary plants and some phenolic compounds could mitigate acrylamide formation in an asparagine–glucose model system. Based on our previous study, several plant materials were selected to further investigate their inhibitory effects on acrylamide formation in cookies and starch‐based model systems. RESULTS: Addition of raw powders from selected dietary plants and their crude aqueous extracts could considerably reduce acrylamide formation in both cookie and potato starch‐based models. Aqueous extracts of clove at 4% caused the largest reduction (50.9%) of acrylamide in cookies, whereas addition of 2% proanthocyanidins from grape seeds gave the greatest acrylamide reduction (62.2%) in a starch‐based model system. CONCLUSION: It may be feasible to use some of the tested dietary plant materials to reduce acrylamide formation in cookies and other starchy foods. Copyright © 2011 Society of Chemical Industry     

Photochemical interaction of ascorbic acid with riboflavin, nicotinamide and alpha-tocopherol in cream formulations

The present work is based on a study of the effect of some vitamins such as riboflavin (RF), nicotinamide (NA) and alpha‐tocopherol (TP) on the photodegradation of ascorbic acid (vitamin C) (AH₂) in oil‐in‐water cream formulations using a UV irradiation source. A UV spectrophotometric and the official iodimetric methods have been used for the assay of AH₂ in cream formulations. These methods have been validated in the presence of RF, NA and TP before their application to the creams. The recoveries of AH₂ in the creams are in the range of 90–95% and the reproducibility of the method is within ±5%. The apparent first‐order rate constants (k_obs) for the photodegradation of AH₂ in the presence of RF, NA and TP, individually, in the creams have been obtained. The second‐order rate constants for the photochemical interaction of AH₂ and the vitamins RF, NA and TP have been determined from the plots of k_obs for AH₂ photolysis versus the individual vitamin concentration along with the values of k₀ from the intercept on the vertical axis. The values of k₀ in the presence of RF and NA are lower than those of the k_obs, indicating that these vitamins act as photosensitizers for the degradation of AH₂ in creams. On the contrary, the value of k₀ in the presence of TP is higher than that of the k_obs, suggesting a stabilizing effect of this vitamin on the degradation of AH₂ in creams. The mode of interaction of the individual vitamins with AH₂ on photolysis has been discussed.     

Antioxidant capacity of different fractions of vegetables and correlation with the contents of ascorbic acid, phenolics, and flavonoids

The antioxidant capacity of different fractions of 17 vegetables were analyzed using ferric reducing antioxidant power assay (FRAP assay) after water and acetone extractions. The contents of ascorbic acid, phenolics, and flavonoids were determined and their correlations with FRAP value were investigated. The results showed that the peel or leaf fractions of vegetables were stronger than the pulp or stem fractions in antioxidant capacity based on total FRAP value. Lotus root peel was the highest and cucumber pulp the lowest in total FRAP value among the vegetable fractions analyzed. All water extracts were higher in FRAP value than the acetone extracts. The FRAP value was significantly correlated with the contents of ascorbic acid, phenolics, or flavonoids in water extracts, in which the phenolics contributed most based on multivariate regression analysis. We conclude that different vegetable fractions were remarkably different in antioxidant capacity. The phenolics are responsible mostly for the antioxidant capacity of vegetables in vitro.     

The effect of supplementing red deer (Cervus elaphus) with different forms of ascorbic acid upon the concentration of ascorbic acid in rumen fluid and blood plasma

Two indoor experiments were conducted at the Massey University Deer Research Unit to study whether the blood plasma ascorbic acid (AA) concentration in farmed red deer (Cervus elaphus) could be raised, using a single large intraruminal administration of AA (2.7 g kg^?1 live weight) prior to a simulated slaughter situation. Deer fistulated in the rumen were individually fed chaffed lucerne hay ad libitum at 30 min intervals; feed was then withdrawn 8 h before AA was administered, and fasting continued during the period of rumen fluid and blood sampling (30 h of fasting in total). Blood (jugular vein) and rumen fluid samples were taken 15 min before and at various intervals after dosing with AA. Rumen fluid pH values were also recorded. In Experiment 1 the effects of administration of pure ascorbic acid (AA), ethyl cellulose‐coated ascorbic acid (EC) and silicone‐coated ascorbic acid (SC) were compared. All three types increased rumen fluid and blood plasma AA concentrations to a desirable level (500 µg ml^?1 blood plasma or greater), with the maximum concentrations in both sites occurring 1 h after administration. The area under the concentration versus time curve (AUC), the area under the curve corrected for baseline concentration (AUCB) and the maximum concentration (MAX) of AA in both rumen fluid and blood plasma were not significantly different among the three formulations of AA, indicating that all three were degraded at similar rates in the rumen and that their bioavailabilities were similar. Rumen pH decreased from approximately 7.0 to 5.0 within 1 h of administering each compound, increased to 6.0 after 4 h and then progressively increased to approximately 7.0 after 22 h. Experiment 2 was conducted to investigate the rumen‐buffering effect after dosing with AA with and without added sodium bicarbonate. Including NaHCO₃ increased rumen pH by approximately 1 unit during the first hour after dosing and by 0.7–0.4 units thereafter. AUC and AUCB for rumen fluid were significantly lower for the AA + NaHCO₃ group of deer than for the AA group (p < 0.05), indicating that increasing rumen pH increased the rate of ruminal destruction of AA. AUC, AUCB and MAX of AA in blood plasma were not statistically different between the two treatments (p > 0.05). It was concluded that the single large intraruminal AA dose technique could be used to consistently increase AUC, AUCB and MAX of AA in both rumen fluid and blood plasma. Methods for improving the efficiency of the technique are discussed. © 2002 Society of Chemical Industry     

反应温度和时间对抗坏血酸/精氨酸Maillard反应体系中挥发性化合物形成的影响

采用顶空固相微萃取-气相色谱-质谱联用技术对抗坏血酸/精氨酸反应体系在不同反应温度和时间下的产物进行鉴定,共鉴定出包括吡嗪、醛、呋喃、醇和吲哚在内的24种化合物,其中14种吡嗪化合物为主要香味化合物。考察了反应温度和时间对产物特别是对吡嗪化合物的影响。结果表明,随着反应温度的升高和反应时间的延长,吡嗪类化合物的总量均增加;其中,随反应温度的升高,相对其他吡嗪化合物2-乙基-6-甲基吡嗪、3-乙基-2,5-二甲基吡嗪的量明显增加;随反应时间的延长,2-乙基-6-甲基吡嗪的量明显增加。     

Changes in carbohydrates, proteins and lipids of finger millet after hydrothermal processing

Finger millet was soaked, steamed and dried to prepare hydrothermally processed millet, followed by decortication to prepare decorticated millet. The physicochemical properties and carbohydrate, protein and lipid profiles of control and processed millet were determined. The carbohydrates were fractionated to amlypectin and amylose equivalent fractions using gel permeation chromatography. The non-starch polysaccharides were isolated and their alditol acetyl derivatives were characterized by gas chromatography (GC). The proteins were extracted using different solvents and the total proteins were fractionated using SDS-PAGE. The ether extractable lipids were esterified and fractionated through GC. Hydrothermal processing decreased the amylopectin fraction and increased the amylose equivalent portion of the starch. Decortication further lowered the first fraction and increased the second fraction. A decrease in cold, hot water soluble and hemicellulose-B fractions and an increase in pectic polysaccharides, hemicellulose-A and cellulosic fractions were observed as a result of hydrothermal processing. Decortication significantly reduced the total non-starch polysaccharides specifically the cellulose fraction. Hydrothermal processing decreased the overall extractability of proteins by 50% but decortication increased it to 80%. It was observed that hydrothermal treatment did not change the gross nutrients composition of finger millet but for their profile. Decortication of hydrothermally processed millet caused significant changes in the nutrient contents and also in their profiles.     

Impact of lipid oxidation-derived aldehydes and ascorbic acid on the antioxidant activity of model melanoidins

As the heat-induced formation of antioxidants throughout the Maillard reaction is known, this study was undertaken to evaluate the impact of lipid oxidation-derived aldehydes and ascorbic acid in Maillard model systems on the resulting antioxidant activity. For this purpose, various fractions of melanoidin-like polycondensation products were obtained from mixtures of amino acids (glycine, lysine, arginine) and lipid oxidation-derived aldehydes (hexanal, (E)-2-hexenal), in the presence or absence of glucose or ascorbic acid. All fractions showed a significant radical scavenging capacity (DPPH assay) and ferric reducing power (FRAP assay). The activity varied according to the composition of the model system tested, although some similar trends were discovered in both assays applied. The presence of lipid oxidation products in the browning products augmented the antioxidant activity in specific cases. For instance, the combined presence of arginine, hexanal and glucose in heated model systems resulted in a significantly higher antioxidant capacity. With an exception of ascorbic acid-containing model systems, melanoidin-like polycondensation products possessed significantly stronger antioxidant activities than the corresponding unheated initial reactant mixtures. Water-soluble high molecular weight (>12kDa) and nonsoluble fractions comprised the major part of the antioxidants derived from amino acid/lipid oxidation product model systems, with or without glucose or ascorbic acid.     

Different response to acetic acid stress in Saccharomyces cerevisiae wild‐type and l‐ascorbic acid‐producing strains

Biotechnological processes are of increasing significance for industrial production of fine and bulk chemicals, including biofuels. Unfortunately, under operative conditions microorganisms meet multiple stresses, such as non‐optimal pH, temperature, oxygenation and osmotic stress. Moreover, they have to face inhibitory compounds released during the pretreatment of lignocellulosic biomasses, which constitute the preferential substrate for second‐generation processes. Inhibitors include furan derivatives, phenolic compounds and weak organic acids, among which acetic acid is one of the most abundant and detrimental for cells. They impair cellular metabolism and growth, reducing the productivity of the process: therefore, the development of robust cell factories with improved production rates and resistance is of crucial importance. Here we show that a yeast strain engineered to endogenously produce vitamin C exhibits an increased tolerance compared to the parental strain when exposed to acetic acid at moderately toxic concentrations, measured as viability on plates. Starting from this evidence, we investigated more deeply: (a) the nature and levels of reactive oxygen species (ROS); (b) the activation of enzymes that act directly as detoxifiers of reactive oxygen species, such as superoxide dismutase (SOD) and catalase, in parental and engineered strains during acetic acid stress. The data indicate that the engineered strain can better recover from stress by limiting ROS accumulation, independently from SOD activation. The engineered yeast can be proposed as a model for further investigating direct and indirect mechanism(s) by which an antioxidant can rescue cells from organic acid damage; moreover, these studies will possibly provide additional targets for further strain improvements. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensorially important aldehyde production from amino acids in model wine systems: Impact of ascorbic acid,erythorbic acid,glutathione and sulphur dioxide

The efficiency of different white wine antioxidant systems in preventing aldehyde production from amino acids by oxidative processes is not well understood. The aim of this study was to assess the efficiency of sulphur dioxide alone and in combination with either glutathione, ascorbic acid or its stereoisomer erythorbic acid, in preventing formation of the sensorially important compounds methional and phenylacetaldehyde from methionine and phenylalanine in model white wine. UHPLC, GC–MS/MS, LC–MS/MS, flow injection analysis and luminescence sensors determined both compositional changes during storage, and sulphur dioxide–aldehyde apparent equilibrium constants. Depending on temperature (25 or 45 °C) or extent of oxygen supply, sulphur dioxide was equally or more efficient in impeding the production of methional compared to the other antioxidant systems. For phenylacetaldehyde, erythorbic acid or glutathione with sulphur dioxide provided improved inhibition compared to sulphur dioxide alone, in conditions of limited oxygen consumption. The results also demonstrate the extent to which sulphur dioxide addition can lower the free aldehyde concentrations to below their aroma thresholds.     

Activities of hydrocolloids as inhibitors of acrylamide formation in model systems and fried potato strips

Effects of eight hydrocolloids on acrylamide (AA) formation were compared. At 2% (w/w), pectin, alginic acid (>50% reduction) and xanthan gum (∼20%) significantly (P < 0.05) reduced acrylamide formation in chemical models. In the fried snack model, effective inhibition of acrylamide formation (∼30%) by most of the hydrocolloids was observed only when the concentration was increased to 5%. Immersing potato strips for 1 h in a 1% alginic acid solution before frying produced inhibition of acrylamide formation similar to that in a 5% solution, and immersing for 5 h led to a significantly lower AA content (∼60% versus ∼30% reduction) compared with immersing for 1 h in a 1% or 5% immersion solution. Similar phenomena were also observed for pectin. The findings suggest alginic acid and pectin are promising inhibitors of acrylamide formation, and immersion time is an important determinant for their effects against acrylamide formation in fried potato products.     

茶多酚和维生素C对腌制猪肉亚硝酸盐残留量和脂肪氧化的影响

以腌制猪肉模型为材料,研究不同含量的茶多酚和维生素C对色泽、残留亚硝酸盐含量以及脂肪氧化TBARS值的影响。结果表明,茶多酚和维生素C都在一定程度上降低了腌制模型中亚硝酸钠的残留量,维生素C的作用效果要显著强于茶多酚(p<0.05)。腌制过程中TBARS值呈逐渐增加的趋势,茶多酚和维生素C有降低TBARS值的作用,茶多酚的作用效果要强于维生素C。在腌制过程中,维生素C组的色泽显著高于茶多酚组(p<0.05),而蒸煮后各组之间色泽差异不显著(p>0.05)。      

Effects of buffer and temperature on formation of furan, acetic acid and formic acid from carbohydrate model systems

Effects of temperature, pH and phosphate buffer on volatiles formed by heating model solutions of fructose, glucose, sucrose, lactose or starch were investigated by selected ion flow tube-mass spectrometry (SIFT-MS). Among the carbohydrates studied, the monosaccharide reducing sugars fructose and glucose were more reactive than macro molecular starch, lactose and sucrose, which are not reducing sugars. Furan was formed from fructose heated at 120, 100 and 80 °C at pH 5-7 in phosphate buffer and at 100 °C in unbuffered solution. Glucose did not yield furan in unbuffered solution at 100 °C but glucose did yield furan in phosphate buffer solution at a similar pH. Furan formation increased as temperature and pH increased. As temperature, pH value, and buffer components changed, furan formation may occur by different reactive pathways. Both of the buffer components, NaH₂PO₄ and citric acid, enhanced the formation of thermal degradation products from fructose. The enhancing effect of NaH₂PO₄ was stronger than citric acid. Formic and acetic acids were concomitantly formed with furan. More formic acid was produced from fructose than glucose, and more acetic acid was produced from glucose than fructose.     

Milk production, conjugated linoleic acid content, and in vitro ruminal fermentation in response to high levels of soybean oil in dairy ewe diet

Feeding vegetable oils rich in linoleic acid has been demonstrated to be an effective strategy to enrich milk with conjugated linoleic acid (CLA). However, high amounts of vegetable oil in the diet in free form could adversely affect animal performance, mainly in sheep. The aim of this work was to improve the ewe milk fatty acid profile by increasing potentially healthy acids such as CLA without any detrimental effects on milk production and ruminal fermentation with soybean oil (SBO) diet supplementation. Twenty-four ewes were assigned to 2 treatments and fed 2 diets (control or supplemented with 6% of SBO; 2 lots of 6 animals per treatment) and fed ad libitum for 4 wk. The forage:concentrate ratio was 20:80. Batch cultures of rumen microorganisms were used to study in vitro rumen fermentation. Changes in fatty acid profile were characterized as a reduction in C6:0 to C16:0 at the expense of an increase in C18:0, C18:1 isomers, and CLA concentrations. Proportions of milk CLA and trans-11 C18:1 (vaccenic acid) went from 1.04 to 3.44 and 2.08 to 6.20 g/100 g of total fatty acids, respectively. However, the SBO diet also increased trans-10 C18:1 and other trans C18:1 content. No significant decreases were found in the treatments for dry matter intake and milk production. The notable increases in trans-10, cis-12 and trans-9, cis-11 were not accompanied by fat level decreases in ewe milk. Concerning in vitro ruminal fermentation, no significant differences were found in the extent and rate of gas production, effective degradability, in vitro true digestibility, and volatile fatty acid production. The results demonstrate that dairy sheep milk CLA content can be substantially increased (more than 3-fold) by adding high levels of SBO in the diet as free oil, without any negative effects on animal performance.