Furan formation in starch-based model systems containing carbohydrates in combination with proteins,ascorbic acid and lipids

Formation of the “possibly carcinogenic” furan during thermal treatment of a starch-based model food system containing selected sugars alone and in the presence of proteins, ascorbic acid and lipids, respectively, was investigated. The results showed that in starch gels containing various sugars significantly more furan was formed at pH 6 than at pH 4. Moreover, addition of whey proteins enhanced the generation of furan considerably at both pH values tested. In acidic conditions, no significant difference was observed between the amounts of furan found in a starch–carbohydrate–ascorbic acid model system and those formed in a starch-based samples containing only ascorbic acid. Addition of fresh lipids did not affect furan formation. However, when oxidised soybean oil was applied, the generated amounts of furan were higher than expected from the sum of furan found in the separate starch–carbohydrate and starch–lipid samples. Interestingly, the most efficient carbohydrate in furan generation, among the sugars tested, at pH 6, was lactose, especially when heated in the presence of proteins. This is the first report on the generation of furan from lactose.     

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.     

Enzymatic production of linear long-chain dextrin from sago (Metroxylon sagu) starch

Pullulanase (EC.3.2.1.41) was used to generate more linear-chain dextrin from sago starch (24.9% amylose) such that the resulting product could act as a high amylose starch. A starch suspension of 5.0% (w/v) sago starch was heated at 100 °C for 45 min and, after cooling, the gelatinized sago starch was hydrolyzed with 2.0% (v/dry weight starch) pullulanase (Promozyme 400L, Novozymes A/S, Denmark) for 24 h. The linear long-chain dextrin (LLD) content of the hydrolysate after drying, was then compared with the initial LLD content. The surface morphology of the starch granules was observed with a scanning electron microscope (SEM). The effects of gelatinization, time of reaction, pretreatment with different strengths of hydrochloric acid prior to enzyme hydrolysis, and starch and enzyme concentrations were studied. Raw sago starch was resistant to the action of pullulanase, but caused an increase in the LLD of that sago starch from an initial concentration of 24.9–33.2% following gelatinization. The best conditions to maximize the amount of LLD were 5.0% (w/v) sago starch, 2.0% (v/w) enzyme and 12 h reaction time. Acid pretreatment of the sago starch did not cause greater improvement in the accessibility and susceptibility of pullulanase as the LLD content, following pullulanase action did not change significantly. Shrinkage on the surface of the starch granules was observed with the SEM.     

Effect of pasteurisation on ascorbic acid,dehydroascorbic acid,tocopherols and fatty acids in pooled mature human milk

Ascorbic and dehydroascorbic acids (vitamin C), tocopherols (vitamin E) and unsaturated fatty acids are heat-sensitive and therefore, their concentrations in human milk could be affected by pasteurisation. Here we determined the concentrations of ascorbic acid plus dehydroascorbic acid, ascorbic acid alone, and α- and γ-tocopherols, and the percentages of fatty acids in samples of human milk after pasteurisation by a slow (62.5 °C, 30 min) or fast heating (100 °C, 5 min) procedure. Both methods led to a significant decrease in the concentrations of ascorbic acid plus dehydroascorbic acid (12% and 29%), ascorbic acid (26% and 41%), α-tocopherol (17% and 34%) and γ-tocopherol (13% and 32%), respectively. However, milk fatty acids, including the polyunsaturated long-chain fatty acids, were unaffected by the two methods. On the basis of these observations, we recommend that human milk be treated using a slow pasteurisation. In addition, we propose ascorbic acid as a marker of the degree of heat treatment.     

Prediction of the degree of starch gelatinization in wheat flour dough during microwave heating

In order to produce quick-boiling noodles, we made partially pre-gelatinized wheat flour dough by the microwave heating method. A cylindrical-shaped piece of wheat flour dough containing 3% NaCl was heated by 117 W microwave oven operating at 2450 MHz. The sample dough was intermittently heated to allow sufficient gelatinization of the starch granules of the dough. The resultant changes in the internal temperature profiles of the sample dough were measured and compared with numerical prediction, which is the two-dimensional heat conductive equation with a term for internal heat generation based on Lambert’s law. In order to calculate the internal heat generation during microwave heating, we measured the dielectric properties of wheat flour dough at 2450 MHz from 10 to 70 °C by the open-ended coaxial probe method. The calculated temperature history could describe the feature of the experimental one during intermittently microwave heating. Furthermore, the progress of starch gelatinization according to the heat transfer in the sample dough was predicted by the Runge–Kutta gel method. A tendency that the total gelatinization degree increased slowly during the microwave intermittent heating was obtained in the calculated result.     

Ascorbic acid,nitrate, and nitrite concentration relationship to the 24 hour light/dark cycle for spinach grown in different conditions

Nitrate, nitrite and ascorbic acid (vitamin C) concentrations were determined for spinach (Spinacia oleracea L.) over a 24 h period to determine if light intensity (including dark periods) at time of harvest impacts concentrations in raw vegetables. Nitrate, nitrate and ascorbic acid concentrations varied significantly over the 24 h period and appeared to be related to changes in light intensity. Light intensity at the time an experimental sample is collected may affect the concentration of some constituents that a researcher is studying. Also, nitrate and nitrite concentrations in raw spinach can be reduced by harvesting at the best time of day. The highest nitrate concentrations in spinach occurred in the dark just prior to an increase in light intensity. Ascorbic acid was near its highest level for the 24 h period when the light intensity initially increased, then decreased to its lowest level around 3–6 h later.     

Investigation and kinetic evaluation of furan formation in tomato paste and pulp during heating

Due to its high ascorbic acid content and acidic environment, tomato is susceptible for furan formation during heat treatment. In this study, kinetics of furan formation was analyzed in order to have an understanding of the reactions taking place in tomato pulp during heating. Also several tomato paste samples were investigated in terms of their furan and hydroxymethylfurfural (HMF) concentrations, and the possible furan precursors. Paste samples were found to contain 3.3–13 ng/g furan and 0.9–39.4 μg/g HMF (dry weight basis). Freshly prepared tomato pulps were heated at 70, 80, and 90 °C for different times, and analyzed for ascorbic acid, dehydroascorbic acid, and furan concentrations. The formation rates of furan in the very first 5 min of heating at 70, 80, and 90 °C were 0.0071, 0.0130, and 0.0168 nmol/g·min, respectively. Rate constants related to reactions taking place during furan formation were estimated by multi-response kinetic modeling. The results revealed that ascorbic acid oxidation is the critical step in furan formation reaction mechanism during heating of tomato pulp, and prevention of oxidation during processing might help to limit furan formation.     

Synthesis,characterisation and in vitro digestibility of carboxymethyl potato starch rapidly prepared with microwave-assistance

Carboxymethyl potato starch was synthesised with the aid of microwave. Optimal degree of substitution (DS) of 0.32 was obtained at 45 °C in 25 min using aqueous ethanol media with water/solvent of 0.15 at 200 W. The molar ratio of sodium hydroxide and monochloroacetic acid to anhydroglucose unit for optimal DS were 2.5 and 1.0, respectively. FT-IR spectrometry revealed the carboxymethyl starch to show new bands at ν = 1614 cm⁻¹ and ν = 1429 cm⁻¹. Wide angle X-ray diffractometry and DSC revealed a remarkable reduction in starch crystallinity after carboxymethylation, which was consistent with destroyed surface observed in SEM. The digestibility of carboxymethyl starch (CMS) was lower than that of native starch. With similar DS, there was no difference in digestibility of carboxymethyl starch prepared with and without microwave. As DS increased from 0.05 to 0.32, the amount of resistant starch in microwave-assisted carboxymethyl starch was elevated from 14.6% to 20.0%, which was much higher than that of native starch (10.8%).     

Effects of Trolox and ascorbic acid on the riboflavin photosensitised oxidation of aromatic amino acids

The effects of 0, 100, 250, 500, 750 or 1000 ppm Trolox and ascorbic acid on the singlet oxygen oxidation of aromatic amino acids viz. phenylalanine, tryptophan, tyrosine in the presence of 25 ppm riboflavin were determined by measuring depleted headspace oxygen by gas chromatography and aromatic amino acid content by high performance liquid chromatography. The coefficients of variations (CVs) for headspace oxygen analysis and HPLC analysis of aromatic amino acids were 1.4% and 4.7%, respectively. Samples were stored under light (1000 lux) at 30 °C for 10 h. Both Trolox and ascorbic acid acted as antioxidants. As the concentration of Trolox and ascorbic increased from 0 to 1000 ppm, the head space oxygen depletion increased. This was due to the oxidation of Trolox and ascorbic acid along with amino acids in the presence of riboflavin. High performance liquid chromatography analysis of the samples clearly indicated that both Trolox and ascorbic acid minimised the degradation of phenylalanine, tryptophan, tyrosine significantly (p < 0.05), but did not prevent their oxidation completely. Trolox acted as a better antioxidant than ascorbic acid in protecting phenylalanine, tryptophan and tyrosine. Type-I mechanism was mainly responsible for riboflavin photosensitised degradation of aromatic amino acids.     

Effects of mechanical handling,storage on ice and ascorbic acid treatment on lipid oxidation in cultured Newfoundland blue mussel (Mytilus edulis)

Lipid oxidation of cultured blue mussels (Mytilus edulis) during mechanical handling and storage on ice was investigated. Furthermore, the exposure of blue mussels to ascorbic acid (Asc) as an antioxidant and its effects on lipid oxidation of sample was monitored. Thiobarbituric acid reactive substances (TBARS) of stored mussels were significantly (p < 0.05) higher than those of the fresh mussels. Mechanical handling of mussels, which includes washing, sorting and packaging, for up to 1 h did not affect their oxidative status significantly (p < 0.05). Furthermore, exposing live mussels to specific concentrations of Asc retarded lipid oxidation significantly (p < 0.05) during storage on ice for only 5 days, after which the Asc became a pro-oxidant.     

Treatments to inhibit the browning reactions in model solutions of olive fruit extracts

Crude enzymatic and polyphenol extracts from olives were subjected to reaction at diverse buffered pH values. At pH values similar to those found in olive flesh (pH 5.0), the colour of the solution increased with reaction time and, simultaneously, a consumption of phenols and oxygen in the reaction medium was observed, especially under aerated conditions. In alkaline solutions (pH 12.4), a strong initial solution browning was noticed while the phenols from the extract reacted with the oxygen present in the solution and caused a significant decrease in the total phenols and oxygen concentrations. This darkening was due to the appearance of non-enzymatic browning reactions since, at this pH, the polyphenoloxidase is not active. Under acidic conditions (pH 3.0), and in solutions with ascorbic acid added (100 mM), the consumption of oxygen and total phenols was negligible, under both aerated and non-aerated conditions; as a result, no significant changes in the colour of the solutions were observed. So, low pH or ascorbic acid solutions may be useful to prevent browning in the bruised areas of hand- or mechanically-harvested table olives.     

Amperometric detection of ascorbic acid in honey using ascorbate oxidase immobilised on amberlite IRA-743

A differential amperometric method for the specific determination of ascorbic acid in honey was developed by association of a flow injection analysis (FIA) system and a tubular reactor containing the ascorbate oxidase enzyme immobilised. A gold electrode modified by electrochemical deposition of palladium was employed as working electrode. Ascorbic acid was quantified in seven samples of commercial honeys using a potential of +0.60 V vs. Ag/AgCl_(sat). The linear dynamic range in ascorbic acid extends from 1 to 50 μmol L⁻¹, at pH 7.0. At flow rate of 1.5 mL min⁻¹ and injecting 250 μL sample volumes, a sampling frequency of 180 determinations per hour is afforded. The detection and quantification limit of this method are 0.14 and 0.49 μmol L⁻¹, respectively. The samples analyses were compared with the volumetric method, and showed an excellent correlation between the methods.     

DPPH antioxidant assay revisited

Scavenging of DPPH free radical is the basis of a common antioxidant assay. A number of protocols have been followed for this assay resulting in variation in the results of different laboratories. We present a perspective of the protocols followed by different workers with incongruity in their results and recommend a standard procedure within the sensitivity range of spectrophotometry. Three common standard antioxidants viz. ascorbic acid, BHT and propyl gallate have been used in this study. The IC₅₀ values for ascorbic acid and propyl gallate were 11.8 μM and 4.4 μM in methanol and 11.5 μM and 4.7 μM in buffered methanol as reaction medium, respectively. The free radical scavenging by BHT was markedly influenced by the reaction medium. The IC₅₀ values were 60.0 μM and 9.7 μM when the reaction was done in methanol and buffered methanol, respectively.     

Paste viscosity of rice starches of different amylose content and carboxymethylcellulose formed by dry heating and the physical properties of their films

Starch modified by combination with sodium carboxymethylcellulose (CMC) has been reported to have improved film properties. In this study, rice starches with different amylose content were heat-treated in a dry state after being impregnated with low or medium-viscosity CMC. Noticeable change was found in pasting properties of the starches after dry heat treatment with CMC. It indicated that crosslinkage occurred between the starch and CMC. The waxy starch showed significant change in viscosity throughout pasting after dry heating with CMC, suggesting that the ester bonds were mostly formed between the hydroxyl groups in amylopectin branches of rice starch and carboxylate acid groups of CMC. Particle size also increased after heat treatment with CMC. The modified starch-based films showed improvement in the tensile strength. Both water vapor and oxygen permeability reduced for the modified starch-based films. Dynamic mechanical analysis (DMA) study showed that the values of G′ of modified starch-based film were higher than those of native starch-based film over the temperature range −40 to 60 °C. The heating process with CMC could be used as a modification method for starch and provide desirable properties of starch-based films.     

Antioxidant mechanisms of Trolox and ascorbic acid on the oxidation of riboflavin in milk under light

Antioxidant activities and the mechanism of water-soluble Trolox and ascorbic acid on the oxidation of riboflavin in milk were studied. Trolox or ascorbic acid at 0, 100, 250, 500, or 1000 ppm was added to milk with or without added 50 ppm riboflavin and stored under light at 27 °C. Headspace oxygen was analysed by GC and Trolox, ascorbic acid, and riboflavin were determined by HPLC. The headspace oxygen of milk with added 50 ppm riboflavin depleted faster than that of milk without added riboflavin (p < 0.05). Trolox and ascorbic acid decreased during storage under light and riboflavin was completely destroyed within 24 h. As the concentration of Trolox or ascorbic acid increased, the riboflavin loss decreased. Riboflavin, Trolox, and ascorbic acid competed to react with singlet oxygen which was formed in the presence of riboflavin under light. Trolox and ascorbic acid protected riboflavin in milk under light by reacting with singlet oxygen.     

Determination of vitamin C in tropical fruits: A comparative evaluation of methods

Two analytical methods for extracting vitamin C (l-ascorbic and l-dehydroascorbic acids) in tropical fruits [banana, papaya, mango (at three maturity stages) and pineapple] were evaluated. These methods used ion-pair liquid chromatography (LC) for detecting ascorbic acid, but differed in the preparation of the sample (extraction with 3% metaphosphoric acid −8% acetic acid or 0.1% oxalic acid). Results were validated by comparison with ascorbic acid content obtained by the AOAC’s official titrimetric method, by performing a recovery study and by the determination of within-day repeatability and inter-day reproducibility. There were differences in the efficiency of vitamin C extraction related to the fruit matrix and especially to the maturity stage in climacteric fruits. The LC-extraction method using 3% metaphosphoric acid −8% acetic acid shows high mean recoveries (99 ± 6%) for all matrices assayed, while the LC-extraction method with 0.1% oxalic acid proved to be unacceptable in some cases (unripe, half ripe and ripe banana and ripe mango) obtaining mean recoveries of 39.9 ± 9.1% and 72 ± 13% for banana and mango, respectively. The detection limit achieved with the metaphosphoric acid-acetic acid LC-extraction method for ascorbic acid (0.1 mg/l) allowed the determination of this vitamin in fruits analysed with good precision (5.94–12.8%), making its use as a routine analysis method perfectly valid. Recommendations about storage temperature, methods of thawing l-ascorbic acid extracts and the addition of antioxidants to extracts were made.     

氨基酸对葡萄糖、半乳糖模型产生呋喃的影响

为研究氨基酸对葡萄糖和半乳糖模型产生呋喃的影响,通过向葡萄糖模型和半乳糖模型中加入不同含量的甘氨酸、丝氨酸、苏氨酸、谷氨酸,模拟密封罐装食品的灭菌条件（121 ℃条件下油浴30 min）,采用顶空气相色谱-质谱（headspace-gas chromatography-mass spectrometry,HS-GC-MS）法检测呋喃的含量。结果表明：低含量（≤5 mg）的甘氨酸、极低含量（1 mg）的丝氨酸、高含量（50 mg）的苏氨酸和谷氨酸的添加能够明显促进葡萄糖模型产生呋喃,而对于半乳糖模型,所有高含量（50 mg）氨基酸的添加都能够导致呋喃的大量产生。苏氨酸对葡萄糖模型产生呋喃的促进作用明显强于其余3 种氨基酸（P＜0.05）;对于半乳糖模型,甘氨酸、苏氨酸对其产生呋喃的促进作用最强,且它们之间无明显差异。     

Ascorbic acid contribution to ORAC values in berry extracts: An evaluation by the ORAC-pyrogallol red methodology

An oxygen radical absorbance capacity (ORAC) method based on pyrogallol red bleaching (ORAC-PGR) was used to evaluate the scavenging activity of berry extracts (blackberry, blueberry, and raspberry). Among berry extracts, only raspberry protected pyrogallol red through a clear induction time, related exclusively to ascorbic acid. The lag time allowed an estimation of the ascorbic acid concentration and its contribution to the total ORAC value, estimating that 66% of the ORAC-PGR value of raspberry is related to ascorbic acid. Also, from the induction time, an ascorbic acid concentration of 36 mg per 100 g of fresh weight was estimated for raspberry samples. The ORAC-PGR procedure could be considered as a fast and specific methodology for an estimation of ascorbic acid concentrations in complex samples.     

Antioxidant from maize and maize fermented by Marasmiellus sp. as stabiliser of lipid-rich foods

Mycelia of Marasmiellus sp. (KUM 50061) were grown on maize for antioxidant production. This formed the mycelial biomass which was then extracted with methanol. Antioxidant activity of methanolic extract was analysed by the TBARS assay, using egg yolk or palm cooking oil as a source of lipid, rather than the conventional rat liver microsomes or linoleic acid. Results showed that at low concentrations of extracts, inhibition of lipid peroxidation in buffered egg yolk was marginal, but significant inhibitory response was evident as the concentrations was increased. The concentration of extract of fermented maize that caused 50% inhibition of lipid peroxidation of buffered egg yolk was 6 mg/ml. Results also indicated a decrease in peroxidation in heated cooking oil supplemented with dried extract compared to unsupplemented cooking oil. The concentration range of dried extract supplementation was 0.2–5 mg/ml. Increasing the extract concentration did not significantly alter the inhibition of peroxidation. The inhibition effect was still evident even at the lowest concentration tested, and was found to be better than catechin and BHA. This pattern of observation was consistent over the 12-day period of observation. Therefore, the possibility of substituting synthetic antioxidants such as BHA and BHT, which are known to be carcinogenic, with antioxidants of natural origin is suggested.     

Effect of γ-radiation on green onion DNA integrity: Role of ascorbic acid and polyphenols against nucleic acid damage

The effect of γ-radiation on green onion DNA integrity, phenol content, oxygen radical absorbance capacity, employing pyrogallol red and fluorescein as probes, as well as ascorbic acid content has been evaluated. Measurements using thiazole orange-DNA fluorescence and agarose gel electrophoresis show that γ-radiation does not lead to an apparent DNA change in green onion. However, it was readily cleaved upon irradiation from the previously isolated nucleic acid. Furthermore, green onion exposure to γ-radiation produces slight increases in the polyphenol concentrations (163–188 μM Trolox eq.) and a decrease in the oxygen radical absorbance using fluorescein (from 245 to 200 Trolox eq.) Interestingly, a high ascorbic acid content (364 μM), which decreases by 40% after γ-ray exposure was measured by using pyrogallol-red-based oxygen radical absorbance capacity induction times from green onion aqueous extracts. Thus, our results suggest that ascorbic acid present in green onion plays a fundamental role in the plant antioxidant response toward γ-radiation exposure, while polyphenols remain largely unchanged, as revealed from oxygen radical absorbance capacity, employing pyrogallol red.