pH对阴离子瓜尔胶溶液流变特性的影响研究

应用无重复双因素5水平方差分析法,在pH7.0～pH3.0之间研究了柠檬酸及乳酸不同pH对阴离子瓜尔胶溶液流变特性的影响。表明:在α=0.05水平上不同酸对零剪切黏度、黏度、黏度衰减、剪切稀化指数、弹性模量、黏性模量、复合黏度、频率扫描与温度扫描时G’=G’’的交点频率及凝胶点温度无明显差异,而对黏弹性比值tan(delta)及松驰时间具有显著性差异。另外,pH值影响上述各指标,特别是当pH3时瓜尔胶溶液流变特性发生显著变化。     

Effects of pre-rigor injection of sodium citrate or acetate, or post-rigor injection of phosphate plus salt on post-mortem glycolysis, pH, and pork quality attributes

Forty pork carcass sides were assigned to one of four treatments: pre-rigor citrate (CIT) or acetate injection (ACE); post-rigor phosphate and salt injection (PHOS); and non-injected control (CON). Loins in 20 sides were injected at 50 min post-mortem with 4% solutions of CIT or ACE to approximately 110% of projected loin weights, and 10 loins were injected at 24 h post-mortem to 106.6% with a solution of 4.4% PHOS and 2.2% salt. Although CIT increased pH (P < 0.05), neither CIT nor ACE altered (P > 0.05) glycolytic metabolite concentrations. The pH increase in muscles from the CIT treatment was most likely due to its buffering ability rather than to its glycolytic inhibition. Pre-rigor CIT injection improved tenderness without the detrimental effects on color or flavor found with PHOS, but neither CIT nor ACE altered glycolytic metabolites or improved firmness, wetness, or fresh visual color over CON. Poor flavor attributes of the ACE treatment will hinder its use as an ingredient for pork enhancement solutions.     

Effects of calcium and pH on spun fibres produced from plasma-alginate mixtures

When a solution of blood plasma and sodium alginate (protein: polysaccharide ratio 3:1) was extruded into coagulating baths of calcium chloride there was a rapid increase in shear strength of the fibre bundles with a rise in salt concentration up to 3% calcium chloride. Above this concentration no further increase in shear strength was observed. The ratio of plasma protein to alginate was between 0·84 and 1·1 in all tows produced from unbuffered calcium chloride baths.

Extruding the dope into 5% calcium chloride baths of pH values between 2 and 8 indicated that fibre strength was independent of pH in the range 4 to 8. Below pH 4 the tows rapidly decreased in shear strength to a minimum at pH 3·5. Decreasing the pH further led to an increase in fibre strength as acid denaturated protein coprecipitated with the polysaccharide. The ratio of plasma to alginate in the tows was around 1·0 for pH values above 3·5, rapidly increasing to 2·8 at pH 2·0.     

Minerals,polysaccharides and antioxidant properties of aqueous solutions obtained from macroalgal beach-casts in the Noto Peninsula,Ishikawa, Japan

To clarify the useful properties of the macroalgal beach-casts for food, we determined mineral, water-soluble polysaccharide and total phenolic compound contents and antioxidant properties of aqueous solutions obtained from frond of eight brown and four green algae. These algae were washed ashore from the East Sea (the Sea of Japan) to the northeast beaches of the Noto Peninsula in autumn. There were fresh and large amounts of Ecklonia stolonifera (Es), Ecklonia kurome (Ek), Sargassum ringgoldianum subsp. coreanum (Sr) and Sargassum macrocarpum on the beaches. Potassium, magnesium and calcium ions were high in Sr-solution. High molecular weight water-soluble polysaccharide, mainly alginates, and relative viscosity were also high in Sr-solution. Both Es and Ek solutions showed high contents of total phenolic compounds and high antioxidant activities, including DPPH radical- and hydroxyl radical-scavenging and ferrous reducing power. On the other hand, the highest superoxide anion radical-scavenging activity was in the Sr solution. In the case of Sr, the same antioxidant properties were also found in the aqueous solution obtained from stem. These results suggest that some macroalgal beach-casts, especially Sr, can be utilised as new natural resources for functional foods, cosmetics, medical applications and fertilizer instead of being processed to landfill or incineration.     

Effect of calcium carbonate,calcium citrate,tricalcium phosphate,calcium gluconate and calcium lactate on some physicochemical properties of soymilk

Soymilk fortified with 25 mm Ca (Ca carbonate, Ca citrate, triCa phosphate, Ca gluconate or Ca lactate) was compared with the properties of unfortified soymilk (control). Calcium carbonate, Ca citrate and triCa phosphate did not significantly affect [Ca²⁺], absolute viscosity and particle size of soymilk, but Ca gluconate and Ca lactate significantly increased these properties. The pH of soymilk was significantly increased by adding Ca carbonate but significantly reduced by adding Ca gluconate and Ca lactate. Dry sediment of soymilk increased significantly with the addition of all Ca salts excluding triCa phosphate. Freezing point depression increased significantly only for Ca gluconate and Ca lactate, mainly owing to their higher solubility.     

pH和NaCl质量浓度对发酵鱼糜中腐败菌Aeromonas veronii bv. veronii群体感应的影响

细菌通过群体感应(Quorum sensing,QS)系统来调控自身一些代谢行为,如生物膜的形成、鞭毛运动等,可引起食品腐败和食源性疾病,分析环境因素对细菌QS的影响对控制水产品质量安全具有重要意义。该研究以从发酵鱼糜中分离的腐败菌Aeromonas veronii bv.veronii为研究对象,利用生物报告菌根癌农杆菌及激光共聚焦显微镜等技术分析了pH(6.0、7.0、8.0)和Na Cl(5、10、20 g/L)对细菌N-酰基高丝氨酸内酯(N-acyl homoserine lactone,AHL)类信号分子介导的QS及代谢行为的影响。研究发现,培养基初始pH 8.0或NaCl质量浓度为20g/L时能显著降低细菌产生的AHLs活性、生物膜形成能力及泳动能力(p0.05)。由此认为,通过控制环境中的pH和Na Cl质量浓度能影响细菌合成AHLs及其QS系统的表达,并调控细菌的代谢行为。     

Effects of pH, chloride, and bicarbonate on Cu(I) oxidation kinetics at circumneutral pH

The oxidation kinetics of nanomolar concentrations of Cu(I) in NaCl solutions have been investigated over the pH range 6.5-8.0. The overall apparent oxidation rate constant was strongly affected by chloride, moderately by bicarbonate, and to a lesser extent by pH. In the absence of bicarbonate, an equilibrium-based speciation model indicated that Cu(+) and CuClOH(-) were the most kinetically reactive species, while the contribution of other Cu(I) species to the overall oxidation rate was minor. A kinetic model based on recognized key redox reactions for these two species further indicated that oxidation of Cu(I) by oxygen and superoxide were important reactions at all pH values and chloride concentrations considered, but back reduction of Cu(II) by superoxide only became important at relatively low chloride concentrations. Bicarbonate concentrations from 2 to 5 mM substantially accelerated Cu(I) oxidation. Kinetic analysis over a range of bicarbonate concentrations revealed that this was due to formation of CuCO(3)(-), which reacts relatively rapidly with oxygen, and not due to inhibition of the back reduction of Cu(II) by formation of Cu(II)-carbonate complexes. We conclude that the simultaneous oxygenation of Cu(+), CuClOH(-), and CuCO(3)(-) is the rate-limiting step in the overall oxidation of Cu(I) under these conditions.     

Hemoglobin-mediated lipid oxidation of protein isolates obtained from cod and haddock white muscle as affected by citric acid,calcium chloride and pH

Acid or alkali solubilization followed by isoelectric precipitation can be used to isolate proteins with good functional properties from muscle tissue. Both acid (pH 3.0) and alkali (pH 10.5) treatment of the muscle decreased lipid oxidation catalyzed by hemoglobin. Citric acid and calcium chloride improved the oxidative stability of both acid- and alkali-solubilized muscle protein isolates when added to the homogenized muscle before separating the membrane or directly to the isolated membranes in the assay. Citric acid may have functioned in part by lowering the pH and destroying preformed peroxides. Exposing the muscle and the hemoglobin together at pH 3 promoted lipid oxidation, while addition of citric acid/calcium chloride or press juice to washed cod prior to solubilization inhibited lipid oxidation even when the tissue and hemoglobin were acidified together.     

Effects of pH, calcium chloride, and chymosin concentration on coagulation properties of abnormal and normal milk

Individual Holstein cow milk samples were selected for good and poor chymosin-coagulation characteristics. The effect of pH adjustment, addition of .02% calcium chloride, and variation in chymosin concentration on coagulation properties of good and poor coagulating samples was evaluated. Pooling 50% good and 50% poor coagulating samples did not improve the average coagulation properties of the poor samples. Reducing milk pH to 6.3 caused a significant decrease in coagulation time but a less marked increase in curd firmness. The greatest increase in curd firmness was obtained by a combination of reducing milk pH, addition of .02% calcium chloride, and reducing chymosin concentration. High-chymosin concentration at reduced pH decreased coagulation time without substantially increasing curd firmness. Curd disintegration was more apparent at high-chymosin concentration in the poor coagulating samples.     

High pressure effect on the color of minced cured restructured ham at different levels of drying, pH, and NaCl

Color changes of minced cured restructured ham was studied considering the effects of high pressure (HP) treatment (600 MPa, 13 °C, 5 min), raw meat pH₂₄ (low, normal, high), salt content (15, 30 g/kg), and drying (20%, 50% weight loss). Raw hams were selected based on pH₂₄ in Semimembranosus, mixed with additives, frozen, sliced, and dried using the Quick-Dry-Slice® process. Meat color (CIE 1976 L*a*b*) and reflectance spectra were measured before and after HP treatment. HP significantly increased L*, decreased a*, and decreased b* for restructured ham dried to 20% weight loss, regardless of salt content and pH₂₄. L* and a* were best preserved in high pH/high salt restructured ham. HP had no effect on the color of restructured ham dried to 50% weight loss. HP had no effect on the shape of reflectance curves, indicating that the pigment responsible for minced cured restructured ham color did not change due to HP.     

Effect of solvent treatment on morphology,crystallinity and tensile properties of cellulose acetate nanofiber mats

Aligned nanofiber mats were prepared from cellulose acetate using an electrospinning technique. The nanofiber mats were then immersed in an ethanol/acetone mixture. The solvent treatment led to denser, more compact fibrous structure and slight decrease in fiber alignment. It increased fiber diameter and polymer crystallinity within fibers. These effects resulted in increase in the tensile strength of fibrous mats. Solvent treatment may offer a simple, efficient approach to improve the mechanical strength of nanofibrous mats.     

Thermal stability of moniliformin at varying temperature, pH, and time in an aqueous environment

Moniliformin (MON) is a widely occurring mycotoxin, produced mainly by Fusarium proliferatum and Fusarium subglutinans in corn, that has been shown to be acutely toxic for various animal species and is a suspected cause of Keshan disease in China. The effects of temperature (100, 125, and 150 degrees C) and pH (4, 7, and 9) on the stability of MON were determined in aqueous buffer solutions at processing times ranging from 10 to 60 min. The percentage of MON reduction was positively related to increasing temperature and pH. MON was most stable at pH 4. After 60 min at pH 4 and 150 degrees C, MON was reduced by only 5%. Heating at pH 10 caused major reduction of MON. After 60 min at pH 10 and 100, 125, and 150 degrees C, MON was reduced by 56, 72, and 83%, respectively. One trial done at 175 degrees C and pH 10 showed that less than 1% MON remained after 60 min of processing.     

Effects of pH, temperature and NaCl concentration on the growth kinetics, proteolytic activity and biogenic amine production of Enterococcus faecalis

In this work, the combined effects of temperature, pH and NaCl concentration on the growth dynamics of Enterococcus faecalis EF37, its proteolytic activity and its production of biogenic amines have been studied. The effects of the selected variables have been analysed using a Central Composite Design. The production of biogenic amines, under the adopted conditions, was found to be mainly dependent on the extent of growth of E. faecalis. Its proteolytic activity was not a limiting factor for the final amine production, because in the system studied (skim milk) an excess of precursors was guaranteed. Quantitatively, the most important biogenic amine produced was 2-phenylethylamine but substantial amounts of tyramine were detected in all the samples. This work confirms that the main biological feature influencing the biogenic amine formation is the extent of growth of microorganisms, like E. faecalis, characterised by decarboxylase activity. In the traditional and artisanal cheeses produced using raw milk, enterococci usually reach levels of 10(7) cells/g. With this perspective, it is important that the presence of biogenic amines due to the activities of these microorganisms is maintained within safe levels, without affecting the positive effects of enterococci on the final organoleptic characteristics of the cheese.     

Effect of pH, NaCl content, and temperature on growth and survival of Arcobacter spp

Growth and survival of six human isolates of the pathogenic Arcobacter spp. in the presence of selected environmental factors were studied. Four strains of Arcobacter butzleri and two strains of Arcobacter cryaerophilus were exposed to pH levels of 3.5 to 8.0. Most strains grew between pH 5.5 and 8.0, with optimal growth of most A. butzleri and A. cryaerophilus strains at pH 6.0 to 7.0 and 7.0 to 7.5, respectively. The 24-h optimal growth range in the presence of NaCl was 0.5 to 1.0% for A. cryaerophilus. However, after 96 h, the optimum was between 0.5 and 2.0% NaCl. The optimum range for growth of A. butzleri strains was 0.09 to 0.5% NaCl after 96 h. The upper growth limits were 3.5 and 3.0% NaCl for A. butzleri and A. cryaerophilus, respectively. Survival at 25 degrees C in up to 5% NaCl was noted for A. butzleri 3556 and 3539 and A. cryaerophilus 3256. Decimal reduction times (D-values) at pH 7.3 in phosphate-buffered saline for three A. butzleri strains were 0.07 to 0.12 min at 60 degrees C, 0.38 to 0.76 min at 55 degrees C, and 5.12 to 5.81 min at 50 degrees C. At pH 5.5, decreased thermotolerance was observed, with D-values of 0.03 to 0.11 min at 60 degrees C, 0.30 to 0.42 min at 55 degrees C, and 1.97 to 4.42 min at 50 degrees C. Calculated z-values ranged from 5.20 to 6.28 degrees C. D-values of a three-strain mixture of A. butzleri in raw ground pork were 18.51 min at 50 degrees C and 2.18 min at 55 degrees C. Mild heat (50 degress C) followed by cold shock (4 or 8 degrees C exposure) had a synergistic lethal effect, reducing more cells than with an individual 50 degrees C treatment or with cold shock temperatures of 12 or 16 degrees C.     

Effects of atmospheric conditions, NaCl and pH on growth and interactions between moulds and yeasts related to blue cheese production

The starter culture Penicillium roqueforti, undesired cultures Penicillium caseifulvum and Geotrichum candidum and the potential starter culture Debaryomyces hansenii were examined for their growth and interactions at environmental conditions similar to the Danish blue cheese Danablu. The combined effect of low oxygen (0.3%) and high level of carbon dioxide (25%) at 4% NaCl w/v (a(w) 0.97) and pH 4.5 and 6.5 on radial growth was examined on a cheese medium at 10 degrees C. P. roqueforti and G. candidum were well adapted to growth at low levels of oxygen and high levels of carbon dioxide but G. candidum was not able to grow in the presence of 4% NaCl (w/v). Growth of P. caseifulvum was strongly inhibited at atmospheric conditions comprising 25% carbon dioxide, especially in combination with 0.3% oxygen. Generally D. hansenii showed strong growth at all environmental conditions examined, except at 0.3% oxygen combined with 25% carbon dioxide and 4% NaCl (w/v). Growth and sporulation of P. roqueforti was highly affected in the presence of G. candidum at 25% carbon dioxide irrespective of levels of oxygen and NaCl in the cheese media. P. caseifulvum caused a pronounced inhibitory effect towards growth of P. roqueforti and D. hansenii at 21% oxygen. D. hansenii caused weak inhibition of P. roqueforti at 21% oxygen, while positive interactions between the two species were indicated at 25% carbon dioxide and 0.3% oxygen.     

Crude lipoxygenase from pig muscle: partial characterization and interactions of temperature, NaCl and pH on its activity

Crude lipoxygenase (LOX) was extracted from fresh pig bacon belly and studied of partial characteristics. The interactions of temperature, sodium chloride (NaCl) and pH on LOX activity were investigated by response surface methodology (RSM). Kinetic studies indicated that the Michaelis constant (K(m)) and maximum velocity (V(max)) for LOX activity using linoleic acid as substrate were 68 μM and 0.26 U/min at 20°C, respectively. The optimal conditions for this reaction were: substrate concentration 3.47 mM, reaction temperature 39°C and pH ≧9.0. The NaCl critical value for LOX activity was 3.0% (w/w) at 20°C, above which the LOX activity began to decrease. Temperature had significant interactions (p<0.05) with NaCl and pH. The temperature critical value decreased with NaCl content increasing, while increased with pH increasing. These indicated that LOX activity and enzyme-catalyzed lipid oxidation in dry-cured meat products could be regulated by controlling process factors during the processing.     

Effects of temperature,pH, organic acids,and sulfites on tagatose browning in solutions during processing and storage

Tagatose browning in solutions might be unacceptable to certain products containing tagatose during processing and storage. The objective of this study was to evaluate the effects of temperature, pH, organic acids, and sulfites on tagatose browning in solutions. Tagatose showed the fastest browning reaction, followed by fructose, xylose, glucose, and sucrose. Tagatose browning was temperature and pH dependent. As temperature and pH increased, tagatose browning was increased. Tagatose browning was slow at temperatures lower than 80°C and pH of 5. Organic acids, such as ascorbic acid, citric acid, and lactic acid, activated tagatose browning. Sodium bisulfite and potassium metabisulfite inhibited tagatose browning, whereas sodium sulfite had no effect on the inhibition of tagatose browning. During storage at 25°C, tagatose browning did not occur regardless of the pH, tagatose concentration, and storage time. It was suggested that tagatose browning in solutions might be prevented by controlling the temperature and pH.     

Measurement of ionic calcium, pH, and soluble divalent cations in milk at high temperature

Dialysis and ultrafiltration were investigated as methods for measuring pH and ionic calcium and partitioning of divalent cations of milk at high temperatures. It was found that ionic calcium, pH, and total soluble divalent cations decreased as temperature increased between 20 and 80°C in both dialysates and ultrafiltration permeates. Between 90 and 110°C, ionic calcium and pH in dialysates continued to decrease as temperature increased, and the relationship between ionic calcium and temperature was linear. The permeabilities of hydrogen and calcium ions through the dialysis tubing were not changed after the tubing was sterilized for 1 h at 120°C. There were no significant differences in pH and ionic calcium between dialysates from raw milk and those from a range of heat-treated milks. The effects of calcium chloride addition on pH and ionic calcium were measured in milk at 20°C and in dialysates collected at 110°C. Heat coagulation at 110°C occurred with addition of calcium chloride at 5.4 mM, where pH and ionic calcium of the dialysate were 6.00 and 0.43 mM, respectively. Corresponding values at 20°C were pH 6.66 and 2.10 mM.