Thermal Destruction of 5-Methyltetrahydrofolic Acid in Buffer and Model Food Systems

Thermal kinetic data (rate constants, k, and activation energies, Ea) for 5-Methyltetrahydrofolic acid (5-CH₃-H₄PteGlu) were determined in citrate buffers (pH 3-6) and in model food systems between 100° and 140°C. As pH increased from 3.0 to 6.0, the rate constants decreased as the temperature increased from 100° to 130°C, the rate constants increased. Ea values were 19.0, 17.0, 19.7 and 19.8 kcal/mole at pH 3, 4, 5 and 6, respectively. In the model food systems, the Ea values (kcal/mole) were 7.85 in apple juice and 10.6 in tomato juice. When dissolved oxygen content was reduced to 5.3 ppm, the stability of the 5-CH₃H₄PteGlu was increased substantially.     

Cold dependence of fatty acid profile of different lipid structures of Listeria monocytogenes

Listeria monocytogenes membrane lipid fatty acids (FA) play a role in its cold adaptation. Our previous study indicated that in newly synthesized neutral lipids, from the early stage of the temperature response (3 days at 5 °C), only the anteiso-15:0 FA was selectively increased. In this study we focus on several NL class comparisons. Cells of L. monocytogenes were grown until stationary phase at 30 and 5 °C and the FA from 1.2 diglyceride (DG), 1.3 DG and free FA as well as NL (in bulk) from each culture were analysed by GC. At 30 °C, L. monocytogenes showed a FA profile from 1.2 DG, 1.3 DG, free FA and NL, dominated by anteiso-15:0 percentages 28.4%, 45.1%, 30.4%, 45.2%, respectively. Also from the three first classes the ratio anteiso-15:0/anteiso-17:0 FA averaged 2.0, but the ratio of branched chain FA to straight chain FA of each class was 1.2, 4.7 and 2.3, respectively. L. monocytogenes cold adaptation response was based singularly on the increase (×5.9, ×5.4, ×8.3 and ×7.3-fold) of the ratio anteiso-15:0/anteiso-17:0 FA for 1.2 DG, 1.3 DG, free FA and NL, respectively, in contrast to a negligible change of the ratio branched to straight chain FA. Using ¹H-NMR analysis it was revealed that the % reduction of ratio variation [-CH₂-]/[-CH₃] at cold (4.65%) for the NL class of Listeria’s fatty acyl chains reflected the increase of the ratio value branched-15:0/branched-17:0 FA that was determined by GC analysis (×6.1-fold).     

Effect of Iron Form, Temperature, and Inoculation with Clostridium botulinum Spores on Residual Nitrite in Meat and Model Systems

The effect of iron form (ferrous, ferric, heme), temperature and botulinal spores on nitrite level was determined in meat. In model systems, ferritin iron was also included, and ascorbate was used as a reducing agent. Reduced hemoglobin caused the most rapid nitrite depletion in both systems. Ferrous iron caused faster nitrite depletion in model systems than in meat. Ferrous iron reduced nitrite readily in model systems at 27°C, but not at 5°C. Ferritin iron did not affect nitrite level. In meat at 27°C, nitrite depletion was much faster in inoculated samples. Protein-bound nitrite levels were higher in meat with added ionic iron. In cured meat with added ionic iron, iron-NO-protein complexes may form, lowering the amount of nitric oxide (NO) available to inhibit botulinal spore outgrowth.     

Antioxidant Action of Tetrandrine: An Alkaloid from the Roots of Radix stephania tetrandra,S Moore

The antioxidant action of the alkaloid tetrandrine(TD), was investigated using systems generating biologically relevant reactive oxygen species. TD appeared to scavenge OH^• produced in a mixture of EDTA-Fe³⁺/ascorbate and H₂O₂ and suppressed the peroxidation of phospholipid liposomes in the presence of iron(III) and ascorbate. TD was a good scavenger toward trichloromethyl peroxyl with a rate constant of 6·5±0·3×10⁷ M ^-1 s^-1 generated by pulse radiolysis. TD did not promote DNA damage in the bleomycin-Fe³⁺ system and a concentration up to 500 μM produced a weak inhibition of DNA damage by bleomycin-Fe³⁺ in the presence of ascorbic acid. The present data suggest that TD possess antioxidant properties. © 1997 SCI.     

Soluble Sugar Content and Metabolism as Related to the Heat-Induced Chilling Tolerance of Loquat Fruit During Cold Storage

The effects of high-temperature, short-time hot air treatment (45 °C for 3 h) on soluble sugar metabolism and chilling tolerance in loquat fruit stored at 5 °C for 5 weeks were investigated. Heat treatment significantly reduced chilling severity, as evidenced by lower firmness and internal browning and higher levels of extractable juice. Meanwhile, this treatment accelerated the activities of acid invertase, neutral invertase, sucrose phosphate synthase and sucrose synthase during storage. However, sucrose degradation was predominant, which caused lower levels of sucrose and higher levels of glucose and fructose in the heat-treated group. In addition, the ascorbate acid content and the activities of ascorbate peroxidase and glutathione reductase in the heat-treated fruit were much higher than those in control fruit, resulting in lower levels of hydrogen peroxide (H₂O₂) and malondialdehyde and decreased membrane permeability as well as a higher unsaturated/saturated fatty acid ratio at the end of storage. Our results suggest that the increased levels of reducing sugars, especially those of glucose, may induce the ascorbate–glutathione cycle activity to scavenge for H₂O₂, whose content relates to the heat-induced chilling tolerance of loquat fruit.     

Nutritional properties of oat‐based beverages as affected by processing and storage

Oat‐based beverages enriched with vitamins and minerals were produced with common hydrothermal treatments and stored at 22 °C for 64 weeks. The effects of decanting on the retention of native vitamins, minerals and fatty acids, and different UHT holding time (5 s or 20 s) at 140 °C on vitamins were investigated. Fatty acid profile, vitamin retention and dissolved oxygen concentration were monitored during storage. The decanting process caused a 47% increase of vitamin B₆ and a 45–74% loss of phosphorus, zinc, calcium and iron. The steam‐injection UHT treatment caused a 60% loss of vitamin D₃ for both holding times and a 30% loss of vitamin B₁₂ for 20 s. During 1 year of storage, oleic and linoleic acids were stable, whereas linolenic acid decreased only slightly, even in the iron‐enriched variety. The dissolved oxygen concentration increased to a low value of 0.71 mg L^?1 and reached a balance after 16 weeks. Most enriched vitamins except vitamins A, D₃ and B₁₂ were stable during ambient storage. Oat‐based beverages with highly retained vitamins can be manufactured by adding vitamins prior to direct UHT treatment with a shorter holding time. Additionally, iron enrichment of such beverages, without affecting the fatty acid profile, can be achieved by filter sterilisation. Copyright © 2007 Society of Chemical Industry     

Comparison of Six Methylation Methods for Fatty Acid Determination in Yak Bone Using Gas Chromatography

Yak bone is rich in nutrition but not used efficiently. Six methylation methods (M1: acetyl chloride-methanol method, M2: H₂SO₄-methanol method, M3: HCl-methanol method, M4: KOH-methanol method, M5: M2 in combination with M4, and M6: M3 in combination with M4) with (system 1 (S1)) or without (system 2 (S2)) prior acid hydrolysis for fatty acid (FA) determination using gas chromatography in yak bone were comprehensively compared. The contents of total FA determined by using M1 and M2 were significantly higher (p < 0.05) than those by using M3 for both S1 and S2 (119.83 versus 118.34 versus 38.31 mg/g in S1; 104.03 versus 93.73 versus 30.08 mg/g in S2 for M1 versus M2 versus M3, respectively). The result determined by M4, M5, and M6 was less than 5 mg/g. Validation results of M1 and M2 indicate that for most (>90%) of the FA, the intra-day and inter-day CVs were <9%. Recoveries for more than 90% of the FA were within a range of 85–117%. In addition, C18:1n9c, C16:0, C18:0, and conjugated linoleic acid were the major FAs in yak bone, approximately accounted for 50, 20, 10, and 10% of the total FA, respectively. And the ratio of saturated and unsaturated FA in yak bone was about 1:2. The acid hydrolysis/H₂SO₄-methanol esterification method would be more efficient for the accurate determination of FA in yak bone, whereas the direct acetyl chloride-methanol method would be used as an alternative for the fast analysis.     

Effect of Oxygen-Absorbing Packaging on the Shelf Life of a Liquid-Based Component of Military Operational Rations

ABSTRACT: Oxygen within the sealed package can reduce the quality of liquid‐based food products with high oil content such as hot‐filled meal‐ready‐to‐eat (MRE) cheese spread, a component of military operational rations. The aim of this study was to test a novel oxygen absorber‐containing laminate material and its ability to maintain and/or extend shelf life of a cheese‐spread MRE item. An iron‐based oxygen absorber (ABSO₂RB®) activated by moisture was incorporated into the laminate and used to pack hot‐filled cheese spread MREs. The kinetics of oxygen absorption due to humidity and temperature were characterized and peel tests performed to ensure pouch seal integrity. Accelerated shelf‐life tests of ABSO₂RB and regular MRE pouches without the O₂‐absorber were conducted for 3 mo at 51.7 °C (125 °F), and 6 mo at 37.8 °C (100 °F) by measuring oxygen concentration (Mocon O₂‐analyzer), microbiological, and physicochemical quality characteristics, including color, texture, moisture, free fatty acid (FFA), pH, water activity, and vitamins and A. Pouches stored at 26.7 °C (80 °F) for 12 mo served as calibrated controls. Consumer tests were conducted in‐house and a confirmatory sensory test was conducted at Natick by a trained panel using a 9‐point hedonic scale. ABSO₂RB‐laminates maintain the same seal integrity and strength as those of the control samples. The headspace oxygen concentrations in these pouches reached (P < 0.05) < 0.5% in 11 d of storage at 26.7 °C (80 °F) and remained below this level throughout the storage period (1 y). No microbial growth (aerobic, coliforms, yeast, and molds) was detected (P < 0.05) for both packages. Overall, the ABSO₂RB‐pouches indicate an improved reduction in oxygen and vitamin C retention compared with MRE controls and maintained product quality (physicochemical and organoleptic). ABSO₂RB‐laminates met the accelerated shelf‐life requirement of 1 mo at 51.7 °C (125 °F), and 6 mo at 37.8 °C (100 °F). This study clearly shows the benefits of using active packaging technology on retaining nutrition and prolonging shelf life of high‐fat, liquid content MRE items.     

Lipid Stability of Beef Model Systems with Heating and Iron Fractions

Catalytic effects of different temperatures (55, 70, 85, and 100°C) on lipid oxidation were studied in aqueous- and chloroform/methanol-extracted beef model lipid systems containing iron forms inherent in beef (water-extractable, diffusate, nondiffusate, ferritin, myoglobin, hemoglobin), hematin, FeCl₂, or FeCl₃. Heating increased thiobarbituric acid and peroxide values in both systems. All forms of iron catalyzed lipid oxidation in aqueous systems, with greatest oxidation by heme and low molecular weight iron fractions. Oxidation in lipid extracts was not increased by ferritin, FeCl₂, or FeCl₃, but heme iron was the major oxidation catalyst. Lipid stability decreased with addition of any iron forms inherent in beef or with increased heating, which helps understanding of rapid oxidation of meat during refrigerated storage or after cooking.     

Metal-Catalyzed Oxidation of Ascorbate, Deoxyribose and Linoleic Acid as Affected by Phytic Acid in a Model System

Antioxidant activity of phytate was investigated in metal-catalyzed model systems. In a dose-dependent manner, phytate facilitated oxidation of Fe (II) to Fe (III) and inhibited formation of thiobarbituric acid-reactive substances (TBARS) from Fe (II)- or hemeprotein-catalyzed deoxyribose degradation. In the presence of 100 μM Fe (III), phytate inhibited reduction of Fe (III) to Fe (II) by 100 μM ascorbic acid and it consequently inhibited ascorbate oxidation. Phytate inhibited hemeprotein- and H₂O₂-catalyzed TBARS formation from linoleic acid micelles. Inhibition by phytate of iron + ascorbate-dependent lipid peroxidation depended on the concentration of ascorbate. These results indicate that phytate may be a useful antioxidant in the protection against oxidative deterioration of foods.     

Effect of trimethylamine-<Emphasis Type="Italic">N</Emphasis>-oxide demethylase from lizardfish kidney on biochemical changes of haddock natural actomyosin stored at 4 and −10 °C

The addition of partially purified trimethylamine-N-oxide demethylase (TMAOase) from lizardfish kidney to haddock natural actomyosin (NAM) in the presence of cofactors (FeCl₂, ascorbate, and cysteine) accelerated formaldehyde (FA) formation throughout the storage either at 4 or −10 °C (p < 0.05). ¹H NMR spectroscopic study revealed that the formation of dimethylamine was enhanced with a concomitant decrease in trimethylamine oxide (TMAO) content when TMAOase was added, particularly at higher concentration. The loss of protein solubility increased as the result of FA formation, which was associated with the increased denaturation/aggregation of proteins. Lipid oxidation determined as hexanal content occurred during extended storage at different degrees. Generally, simulated systems without TMAOase and TMAO contained the highest hexanal content. Differential scanning calorimetry of NAM after storage at 4 and −10 °C for 15 days and for 8 weeks, respectively, showed the lower T _m and enthalpy of endothermic peaks corresponding to myosin and actin, suggesting the conformational changes induced by FA formed. Therefore, TMAOase exhibited the detrimental impact on haddock NAM, mainly caused by FA formation.     

The effect of different folate forms on denaturation of bovine folate binding protein

Denaturation temperatures (T_max) of folate binding protein (FBP) complexed with various folate derivatives were studied using differential scanning calorimetry. Surface plasmon resonance technique was used to elucidate the effect of heat treatment, i.e., pasteurization and UHT treatment, of FBP on FBP content and its binding capacity to folate. The folate derivatives studied were (6S)5-HCO-H₄folate, (6S)5-CH₃-H₄folate and pteroyl-l-glutamic acid (PteGlu). The results showed that different folate forms affected the heat denaturation temperature of FBP differently. Apo-FBP underwent an endothermic transition with a maximum at 60.5 ± 0 °C. After ligand binding, the maximum of the denaturation shifted with a transition maximum at 72.4 ± 0.3 °C for (6S)5-HCO-H₄folate and 78.7 ± 0.5 °C for (6S)5-CH₃-H₄folate. The highest temperature shift was observed for PteGlu with maximum transition temperature at 83.7 ± 0.2 °C. Pasteurization temperatures did not eliminate the binding capacity of FBP regardless of folate form bound, whereas the UHT-treatment did.     

Role of Alpha-Tocopherol, Ascorbic Acid, Citric Acidand EDTA as Oxidants in Model Systems

The effects of four widely employed “antioxidants” on iron-mediated hydroxyl radical formation and lipid peroxidation were studied in aqueous model systems. Iron and copper served as catalysts for the reactions which oxidized ascorbic acid and alpha-tocopherol and reduced oxygen. Ferrous ion spontaneously reduced oxygen to O^?₂ (su-peroxide anion radical) which led to OH (hydroxyl radical) and H₂O₂ generation and lipid peroxidation. Precipitation or sequestration of iron greatly depressed these oxidative events. Complexation by EDTA and citric acid, however, formed catalytically active iron chelates. The concomitant increase in iron solubility explained the substantial enhancement of iron-driven redox reactions by EDTA and citric acid.     

Methionine Sulfoxide Determination After Alkaline Hydrolysis of Amino Acid Mixtures, Model Protein Systems, Soy Products and Infant Formulas

Two previously reported methods (2M NaOH, 18 hr, 100°C; 3M NaOH, 16 hr, 110°C) for alkaline hydrolysis of proteins containing methionine sulfoxide (MetSO) were compared in free amino acid and model protein systems. Recoveries of MetSO from amino acid mixtures after 2M NaOH hydrolysis and ion-exchange chromatography were higher than after 3M NaOH hydrolysis. Recoveries of methionine (Met), MetSO and methionine sulfone (MetSO₂) from model proteins after 2M NaOH hydrolysis suggested destruction of Met, no production of MetSO₂ and, in the presence of glucose, possible production of small amounts of MetSO. Except for one soy isolate, measured MetSO was ≦ 7% of total methionine (oxidized plus unoxidized) in soy products. In milk- and soy-based infant formulas, measured MetSO ranged from 7 - 32% of totalmethionine.     

Ferulic Acid Dehydrodimers in the Cell Walls of Beta vulgaris and their Possible Role in Texture

Sugarbeet, a form of Beta vulgaris var vulgaris, fails to soften completely after heating at 100°C for several hours. This is due to thermal stability of the cell–wall polymers involved in cell–cell adhesion. In contrast, beetroot softens within 25–30 min due to a relatively rapid increase in the ability of the cells to separate. Information concerning the cell–wall polymers responsible for cell–cell adhesion was obtained by subjecting sugarbeet and beetroot tissues to a range of chemical and biochemical treatments designed to cleave cell–wall chemical bonds selectively. Treatment of sugarbeet tissues with chelating agents, weak base (Na₂CO₃, 0·05 M ) or a purified, specific endoxylanase did not facilitate vortex-induced cell separation. However, this could be induced after extraction in dilute, cold alkali (0·05–0·1 M KOH) or dilute, hot acid (0·1 M TFA, 100°C). Tissues from beetroot behaved similarly. Furthermore, the cell walls of sugarbeet and beetroot were similar in yield and neutral carbohydrate composition; the cell–wall-galacturonic acid content of beetroot was 50% higher as compared with sugarbeet. They were also rich in ferulic acid (FA) and its derivatives (6–7 mg g^-1 CWM), and exhibited pH-dependent autofluorescence which disappeared during alkali-induced cell separation. In sugarbeet, over 20% of the FA was in dimer form. In beetroot, however, the value was only 10%. The main FA dimers were 8-O-4′DiFA and 8,5′DiFA (benzofuran form). The results indicate that the degree of thermal stability of cell–cell adhesion and, therefore, texture in Beta vulgaris tissues is related to the degree of FA-cross linking between pectic polysaccharides. © 1997 SCI.     

Selective Concentration of Bovine Immunoglobulins and α-Lactalbumin from Acid Whey using FeCl3

Immunoglobulins and α-lactalbumin of acid whey were concentrated in supernatant and precipitate when FeCl₃ was added at pH 4.2 and 2.8, respectively. Optimized conditions of pH 4.2 were preferable because of higher retention of immunochemical activity of immunoglobulins. In acid whey treated with 7.5 mM FeCl₃ at pH 4.2 and 4°C, 90% of β-lactoglobulin coprecipitated with serum albumin while 70% of immunoglobulins (92% immunochemically active IgG) and 95% of α-lactalbumin were retained in the supernatant. More than 98% of added iron was subsequently eliminated as precipitate by holding the treated whey at pH 8-9 and 4°C, without losing immunochemical activity of immunoglobulin G, in addition to retained activity of immunoglobulins A and M.     

Influence of System Composition on Ascorbic Acid Destruction at Processing Temperatures

The anaerobic L -ascorbic acid (AAs) destruction in glucose aqueous model systems (water activity, a_w, 0·94) of pH 3·5, 4·1 and 5·0 was studied. The AAs degraded as a function of time and temperature (70, 80 and 90°C) with a behaviour that, in general, could be described by first order kinetics except for AAs in the system containing L -lysine, in which the results adjusted to zero order. The increment of pH from 3·5 to 5·0 accelerated AAs destruction and browning reactions. The addition of tin(II) or lysine to the glucose medium, increased AAs loss and browning. No difference was observed in AAs degradation and colour intensity when sorbic or propionic acid were used as antimycotics, at pH 3·5. Packaging the glucose system of acid pH with an air chamber, produced a faster destruction of AAs and browning of the solution than the one observed for the same system in anaerobic condition. In aerobic condition, the presence of glucose produced a lesser degradation of AAs than the one observed in the system without humectants. © 1997 SCI     

A Device for Measuring Oxygen Solubility in Fluids and Oxygen Permeation through Polymers having Fluid Contact

An apparatus was developed which measured oxygen permeation from a gaseous environment into a liquid medium. Oxygen permeating the package material was detected in the liquid phase by an oxygen electrode. The oxygen permeation of 1 mil oriented polypropylene was 1417 cc/m² day at 25°C. Slopes of permeation lines were related to the oxygen solubility of various aqueous media. The oxygen solubility of an air-saturated 1.5% NaCl solution was 7.15 ppm O₂. Permeability and solubility values were both within 3% of known standards. The solubility method was used to determine the oxygen concentration of air-saturated single-strength tomato juice. At 25°C, the sample contained 7.3 ppm O₂.     

Microencapsulated Iron for Food Fortification

Lipid microcapsules of FeSO₄, alone or with ascorbic acid, and FeCl₃, were developed to fortify cheese and other high moisture foods with iron. Varying lipid coat composition and amount of core iron solution optimized their stability. A high melting fraction of milk fat (m.p. 43.5°C) was oxidized by iron and was thus unsuitable as coat material. Microcapsules made with cottonseed stearine (m.p. 62.8°C) had good oxidative stability and retained more iron under rapid stirring at 39°C than those made with hydrogenated milk fat (m.p. 49.0°C). Microcapsules having good oxidative stability and low leakage of iron were coated with stearine and had a ratio of 0.10g Fe solution/g lipid coat. Microencapsulation may allow fortification of cheese and other iron sensitive foods.