Hydrolytic Stability at Intermediate pHs of the Common Purine Nucleotides in Food, Inosine-5'-monophosphate, Guanosine-5'-monophosphate and Adenosine-5'-monophosphate

When the purine nucleotides, inosine-5′-monophosphate (IMP), guanosine-5′-monophosphate (GMP) and adenosine-5′-monophosphate (AMP) were subjected to canning temperatures (121°C) at pHs between 3 and 8, extensive phosphate bond hydrolysis to the corresponding nucleoside occurred. The half life for hydrolysis at pH 5 was 63, 41, and 51 min for IMP, GMP, and AMP, respectively. Rates of hydrolysis were even greater at pH 3 because both hydrolysis of the phosphate bond and the glycosidic bond occurred simultaneously. An Arrhenius plot of data collected at different temperatures illustrated that the nucleotides were very stable at room temperature. Half lives for IMP, GMP, and AMP were estimated to be 36, 19, and 40 yr, respectively, at 23°C and a pH of 5.     

Phytate Reduction in Brown Beans (Phaseolus vulgaris L.)

Brown beans (Phaseolus vulgaris L.) were subjected to treatments to evaluate effects of pH, temperature, CaCl₂, tannase and fermentation on degradation of phytate. Soaking was performed at 21°C, 37°C and 55°C at pH 4.0, 6.0, 6.4, 7.0, and 8.0. Optimal conditions for phytate degradation were pH 7.0 and 55°C. After soaking 4, 8 or 17 hr at these conditions 79%, 87% and 98% of phytate was degraded, respectively. Addition of tannase enhanced reduction of phytate. Fermentation of presoaked whole beans resulted in reduction of 88% of phytate after 48 hr.     

Influence of enzymatic hydrolysis,pH and storage temperature on the emulsifying properties of canola protein isolate and hydrolysates

The aim of this work was to enhance emulsification properties of canola proteins through enzymatic proteolysis and pH variaton. Canola protein isolate (CPI) and hydrolysates (CPHs) were used to form emulsions at pH 4.0, 7.0 and 9.0 followed by storage at 4 or 25 °C for 7 days. Controlled enzymatic hydrolysis led to increased peptide bond cleavage with time (0.23 g/100 g in CPI to 7.18 g/100 g after 24‐h Alcalase hydrolysis). Generally, oil droplet sizes were smaller for emulsions made at pH 9.0, which suggest better quality than those made at pH 4.0 and 7.0. Trypsin hydrolysate emulsions were the most physically stable at pH 7.0 and 9.0; in contrast, the pepsin hydrolysate emulsions were unstable at all conditions. The results suggest that selective enzymatic hydrolysis could play an important role in enhancing successful incorporation of canola proteins and peptides into food systems as protein emulsifiers.     

Sensory Changes in Umami Taste of Inosine 5'-Monophosphate Solution after Heating

Discrimination in umami taste of inosine 5′-monophosphate (IMP) solution caused by thermal degradation was investigated by sensory evaluation. The difference threshold of umami taste of 0.005% IMP solution in the presence of 0.05% monosodium glutamate (MSG) was 0.002%. The difference threshold of a 0.005% IMP solution decreased by about one half when heated at 95°C for 15 h. Inosine, one of the main products of the thermal degradation of IMP, had a bitter taste. The detection threshold of inosine varied widely among panelists. Heating a 0.005% IMP solution at 95°C for 15 h formed inosine at about one tenth of its lowest detection threshold.     

Effects of Heat-Stable Alakaline Protease Activity of Atlantic Menhaden (Brevootii tyrannus) on Surimi Gels

Heat stable protease isolated from the sarcoplasmic fraction of menhaden (Brevoorti tyrannus) muscle tissue was characterized as to optimum temperature and pH against casein substrate and its degradative action on actomyosin and surimi during heating. The optimum conditions for activity were 60°C at a pH of 7.5 to 8.0. Activity dropped off remarkably at temperatures below 45°C or above 70°C and when pH was below 7.0 or above 8.0. The enzyme(s) was capable of degrading actomyosin as observed by sodium dodecyl sulfate electrophoresis. This implicated a causative role for this protease system in the texture degradation observed during thermal processing of menhaden surimi at temperatures of 50-70°C.     

Pacific Cod Muscle 5'-Nucleotidase

SUMMARY: A 5'-nucleotidase, widely distributed in teleost fish muscles, was purified about 20-fold from Pacific cod (Gadus macrocephalus) by chromatography of a dialyzed aqueous extract of the muscle on DEAE-cellulose. The enzyme was unstable and lost 85% of its activity in 1 hr at 37°C 53% in 10 min at 42°C and 40% in 1 hr at 30°C. It was stable for 6 days at 0°C, could be dialyzed for up to 3 days at 0°C against 1 mM tris buffer pH 7.5 and quickly frozen and thawed without loss of activity. However, it was inactivated rapidly when held at −30°C. Brief exposure to pH 4.0 or 5.0 effected marked destruction. Attempts at further purification by means of chromatography on hydroxylapatite, adsorption using alumina Cγ and starch gel electrophoresis failed due to instability.
The enzyme was strongly inhibited by EDTA, pyrophosphate, KF and ZnCl₂ (1-10 mM); less markedly inhibited by GSH, 2-mercaptoethanol, carbonate and CaCl₂ (10 to 100 mM). It was strongly activated by Mn⁺⁺ and weakly activated by Mg⁺⁺. The optimum pH was 7.6, and the Km was 5 × 10⁻⁴M with UMP and 8 ⁻⁴M with IMP. It hydrolyzed, in order of effectiveness, LJMP, IMP, CMP, d-AMP, GMP, d-IMP, d-GMP, d-UMP and AMP, but not p-nitro phenylphosphate, sugar phosphates or a number of other compounds including 2',3'-nucleotides.     

Production of Fungal α-Galactosidase and Its Application to the Hydrolysis of Galactooligosaccharides in Soybean Milk

Production of extracellular α-galactosidase of Aspergillus oryzae was induced remarkably well by the addition of soybean carbohydrate to culture medium. Addition of stachyose or raffinose induced slight production. Soybean carbohydrate, stachyose, and raffinose also served well for the synthesis of invertase. Maximum hydrolysis of p-nitrophenyl-α-D-galactopyranoside (PNPG) by the enzyme occurred at pH 4.0, and optimum temperature for hydrolysis of PNPG was 50° C. The enzyme seemed to be stable from 30-50° C. The mixture of α-galactosidase and invertase totally hydrolyzed raffinose and stachyose at 50° C, pH 4.0 in 2 hr. The mixed preparation of the enzyme substantially hydrolyzed galactooligosaccharides in soybean milk at 50° C, pH 6.3 in 2 hr.     

Degradation of inosine-5′-monophosphate (IMP) in aqueous and in layering chicken muscle fibre systems: Effect of pH and temperature

Studies were carried out to assess the effect of pH and temperature on the degradation of major meat flavour precursor inosine mono-phosphate (IMP) in model systems. Breast and leg muscles from Indian domesticated layer chicken (Gallus gallus) were washed repeatedly with 0.1 M phosphate buffer of pH 6 to obtain pigment-free muscle fibres. Degradation of IMP in water and in muscle fibre-IMP systems were studied at 80, 100, and 120 °C under three pH (2, 7 and 11) conditions. The pH of muscle fibres was 6.2-6.4. The IMP content (mg/100 g) of fresh breast muscle (188.5) and its fibre (7.9) were higher (P?0.05) than fresh leg muscle (135.2) and its fibre (1.9). Inosine and hypoxanthine contents were also higher in breast than in leg muscles and their fibres. Degradation of IMP in both model systems was significantly influenced by pH and thermal treatment. In water systems, the degradation of IMP increased with temperature. Acidic pH caused greater degree of degradation than neutral or alkaline pH.     

Characterisation and application of Halomonas shantousis SWA25, a halotolerant bacterium with multiple biogenic amine degradation activity

Biogenic amines are identified as toxicological substances in foods and may have detrimental effects on consumers’ health. In recent years, the application of microorganisms that can degrade biogenic amines has become an emerging method for their reduction. The degradation characteristics and application potential of a salt-tolerant bacterium Halomonas shantousis SWA25 were investigated in this study. H. shantousis SWA25 exhibited degradation activity against eight biogenic amines at 10–40°C (optimum, 30–40°C) and pH 3.0–9.0 (optimum, 6.0–7.0) in the presence of 0–20% (w/v) NaCl (optimum, 0%). Specifically, H. shantousis SWA25 degraded all tryptamine (TRY) and tyramine (TYR) in 6 h, all phenethylamine (PHE) in 9 h, 66.7% of histamine (HIM), 52.4% of cadaverine (CAD), 48.0% of spermidine (SPD), 42.9% of putrescine (PUT) and 42.0% of spermine (SPM) in 20 h at 30°C and pH 7.0 with shaking at 120 r min^?1. The enzymes from H. shantousis SWA25 responsible for degradation of biogenic amines were mainly amine oxidases located on the cell membrane. Further studies showed that H. shantousis SWA25 effectively degraded TRY, PHE, PUT, CAD, HIM and TYR in commercial fish sauce and soy sauce samples. Nevertheless, significant SPD and SPM degradation were not observed due to low initial concentrations. Therefore, H. shantousis SWA25 can be applied as a potential biogenic amines degradation bacterium in foods.     

Viability of Lactobacillus plantarum in Orange Juice under Low pH and Temperature Conditions

A strain of Lactobacillus plantarum, isolated from fermenting orange juice (OJ), was inoculated into unpasteurized or reconstituted OJ and held under low pH/low temperature conditions. Viability decreased more rapidly at subfreezing temperatures near – 5°C than at lower or higher temperatures. Viability decreased 0.37 log CFU/mL/hr at - 6.6°C and 0.05 log CFU/mL/hr at - 18°C. Rates of population decrease in frozen samples at - 5°C were about three times greater than in unfrozen samples at the same temperature. An inverse linear relationship existed between rate of population decrease (log CFU/mL/day) at - 7°C and OJ pH, with the rate of decrease at pH 4.1, about 1 log cycle lower than at pH 3.5 (0.024 and 0.60, respectively).     

Influence of pH,water activity and temperature on the inactivation of Escherichia coli and Saccharomyces cerevisiae by pulsed electric fields

The aim of this study was to examine the influence of pH, water activity (a_w) and temperature on the killing effect of pulsed electric fields (PEF). Escherichia coli and Saccharomyces cerevisiae suspended in a model media were subjected to 20 pulses with 4 μs duration in a continuous PEF system, during which the effects of pH (4.0–7.0), a_w (1.00–0.94) and inlet temperature (10°C and 30°C) could easily be studied. Electrical field strengths were set to 25 kV/cm for S. cerevisiae and 30 kV/cm for E. coli and the highest outlet temperature was monitored to 44°C. A synergy of low pH values, high temperatures and PEF processing was observed. A drop in pH value from 7.0 to 4.0 resulted in the reduction of E. coli by four additional log units, whereas for S. cerevisiae, the pH effect was less pronounced. Lowering a_w seems to protect both E. coli and S. cerevisiae from PEF processing.     

Thermal Properties of Yak α-Lactalbumin and β-Lactoglobulin: a DSC Study

A differential scanning calorimetry (DSC) method was used to investigate the denaturation temperature of yak α-lactalbumin (α-La), β-lactoglobulin (β-Lg), and a mixture of two proteins and the thermal properties of α-La and β-Lg in the presence of glucose, lactose, sucrose, NaCl, CaCl₂, and at various pH (4.0–10.0). The denaturation temperature (T _d) of α-La increased from 52.1 °C in the absence of β-Lg to 53.9 °C in the presence of β-Lg, while the T _d of β-Lg decreased from 81.4 °C in the absence of α-La to 79.9 °C in the presence of α-La. α-La was thermal stable in the range of pH 4.0–10.0, while β-Lg was more thermal stable in acidic pH than in alkaline pH. Sugars, Na⁺, and Ca²⁺ influenced the stabilization of the two proteins against thermal denaturation with greatly influenced for β-Lg. α-La kept reversibility in the presence of sugars, NaCl, CaCl₂, and over a wide pH range (4.0–10.0), with most of the reversibility values being greater than 90%. In contrast, β-Lg was completely irreversible whether in its native state or in the presence of the additives.     

Effect of vanillin concentration,pH and incubation temperature onAspergillus flavus,Aspergillus niger,Aspergillus ochraceusandAspergillus parasiticusgrowth

The effects of incubation temperature (10–30°C), pH (3.0–4.0) and vanillin concentration (350–1200ppm) on the growth ofAspergillus flavus, Aspergillus niger, Aspergillus ochraceusandAspergillus parasiticuswere evaluated using potato–dextrose agar adjusted to water activity (a_w) 0.98. The radial growth rates after a lag period followed zero-order kinetics with constants that varied from 0 (no growth) to 0.63mmh⁻¹. The lag period depended on vanillin concentration, pH and incubation temperature. The germination time and the radial growth rates were significantly affected by the three studied variables (P<0.001). The inhibitory conditions (no growth after 30 days) depend on the type of mold. A niger, the most resistant species, was inhibited at 15°C, pH 3.0 and 1000ppm. ForA. ochraceus, the most sensitive, the inhibitory conditions in presence of 500ppm vanillin were pH 3.0 and temperature ≤25°C or pH 4.0 with temperature ≤15°C.     

Decomposition of the Flavor Enhancers, Monosodium Glutamate, lnosine-5'-Monophosphate and Guanosine-5'-Monophosphate during Canning

Monosodium glutamate (MSG) was found to be very stable to canning conditions. Both flavor nucleotides inosine-5'-monophosphate (IMP) and guanosine-5'-monophosphate (GMP) were lost through hydrolysis, up to 50% or more, depending on the canning conditions. IMP was more stable than GMP with increased hydrolysis for both compounds occurring at lower pH and longer canning time. The loss of IMP and GMP was shown to go via phosphate hydrolysis to the corresponding nucleosides, inosine and guanosine, followed by base hydrolysis of the nucleosides to hypoxanthine and guanine.     

Oxidation of Tryptophan by H2O2 in Model Systems

Degradation reactions of tryptophan (trp) and the dipeptides alanyltryptophan (ala-trp) and phenylalanyltryptophan (phe-trp), induced by H₂O₂, were investigated under different conditions in aqueous systems. Decreases in the content of trp as well as the formation of soluble degradation products were determined. Highest losses of trp were obtained after H₂O₂ treatment at 100°C for 2 hr at pH 8.5. Lowest losses occurred at pH 4.0, 25°C, for 30 min. The destruction of trp in ala-trp was similar, while losses of trp in phe-trp under the same reaction conditions were lower. This was indicative of a negative induction effect of the phenyl ring. The quantity of degradation products showed extensive variations, dependent upon the radical mechanism of the oxidation reaction.     

Effect of Temperature, Solute and pH on the Tolerance of Clostridium perfringens to Reduced Water Activities

Two strains of C. perfringens type A (FDI and S45) were grown in Thioglycolate medium adjusted to a_ws of 0.995, 0.975, or 0.965 by the addition of NaCl, KCL or LiCl. Combinations of controlled and uncontrolled pHs (7.0, 6.5 and 6.0) and incubation temperatures of 45°C, 37°C, or 30°C were observed at each a_w. Maximal numbers of cells and shortest lag times occurred at a_w of 0.995, 45°C and pH 7.0. No growth occurred at a_w of 0.965. At 0.985, growth did not occur when KCl was used as the solute and the temperature and pH were 30°C and 6.0, respectively. NaCl was less inhibiting than KCl. LiCl inhibited growth completely.     

Thermal Gelation of Pork, Beef, Fish, Chicken and Turkey Muscles as Affected by Heating Rate and pH

Effects of heating rate (3°C or 0.7°C/min) and pH (5.5, 6.0, 6.5, or 7.0) on thermal gelation properties of different muscle systems were evaluated (10% protein, 2% NaCl) using pork, beef, fish, and chicken and turkey (breast and thigh) muscles. Results indicated that, at pH 6.5 and 7.0, force required to rupture the gel (Pf), force required to move plunger through the gel (Fp), and viscosity index (Ni), using a slow heating rate, were higher than with rapid heating. All muscles (except breast muscles with the slow heating rate) yielded higher (P<0.05) gel strength (Fp, Pf) at pH 6.0 than at the other pHs.     

Thermal Destruction of Immunoglobulin A, Lactoferrin, Thiamin and Folic Acid in Human Milk

Kinetic parameters for thermal destruction of immunoglobulin A (IgA), lactoferrin, thiamin and folic acid in human milk were determined. Degradation proceeded following first order reaction kinetics. The times for 90% degradation (D value) at 60°C were, in seconds, 4.9 × 10⁴ (68°C C 78°C) for IgA; 2.4 × 10³ (58°C 70°C) for lactoferrin; 7.7 × 10⁵ (95°C C 110°C) for thiamin and 1.9 × 10⁴ (62°C C 78°C) for folic acid based on inactivation data at four constant temperatures between the range indicated. Z values (temperature change to alter degradation rate by a factor of 10) were 5.5°C, 4.7°C, 28.4°C, and 6.4°C for IgA, lactoferrin, thiamin and folic acid, respectively.     

Determination of Inosine-5-Monophosphate in Fish Tissue with an Enzyme Sensor

An enzyme sensor for IMP consisted of immobilized enzymes and an oxygen electrode. A nucleotidase (E.C. 3.1.3.5.), nucleoside phosphorylase (E.C. 2.4.2.1.) and xanthine oxidase (E.C. 1.2.3.2.) were immobilized on a membrane prepared from cellulose triacetate, 1,8-diamino-4-aminomethyloctane and glutaraldehyde. Optimum conditions for IMP determination were pH 7.8, 30°C, a flow rate of 1 ml min⁻¹ and sample volume of 20 μl. A calibration curve for IMP was linear up to 15 mM. This sensor could be applied to the determination of IMP in meats of sea bass, mackerel, yellowfish and saurel. Good correlative results were observed between the values obtained by the sensor and the conventional method. The sensor was stable for more than 15 days at 5°C and 100 assays.     

pH and Heat Treatment Effects on Foaming of Whey Protein isolate

The overrun obtained by whipping whey protein isolate (WPI) was significantly (p<0.05) affected by changing pH. Heating WPI at pH 4.0 reduced rate and amount of overrun. The highest overrun values for unheated WPI were observed at pH 5.0 and 7.0 after heating at 55°C for 10 min. The maximum foam stability for unheated WPI was obtained at pH 5.0. Heat treatment had little effect on stability at pH 4.0 or 7.0 but at pH 5.0, 80°C for 10 min improved stability by 65%. Based on surface pressure data, the rate of adsorption of β-lactoglobulin interfacial films and the work of compression correlated with overrun, maximum overrun, overrun development and foam stability.