Preparation and characteristics of yak casein hydrolysate–iron complex

The effect of mass ratio between yak casein hydrolysate and FeSO₄, reaction temperature, pH and holding time on ferrous‐binding capacity of yak casein hydrolysate was investigated. Iron‐releasing percentage and structural characteristics of the formed yak casein hydrolysate–iron complex were also examined. Results showed that casein hydrolysates with different hydrolysis degrees (DH) possessed different ferrous‐binding capacities with the highest of 7‐h hydrolysate. The optimal binding conditions between yak casein hydrolysate and iron are mass ratio of casein hydrolysate to FeSO₄ of 15:1 for 20 min at 40 °C and pH 6.0. The principal binding site for Fe²⁺ in yak casein hydrolysate consists of the carboxylate groups and amide groups. Compared with ferrous sulphate, yak casein hydrolysate–iron complex has higher iron‐releasing percentage at basic conditions, such as pH 7.0, 7.5 and 8.0. Ferrous‐iron enriched casein hydrolysate, i.e. yak casein hydrolysate–iron complex, may have great potential as an effective delivery vehicle of bioavailable iron.     

Inactivation of staphylococcal enterotoxins by heat and reactivation by high pH treatment

Inactivation of staphylococcal enterotoxins (SE) added to different media upon heat treatment (80 degrees C or 100 degrees C for 10 min) and reactivation of inactivated SE was studied. In gelatin (pH 4.0), lettuce extract, peas and beans extracts and ovalbumin (pH 5.0) the immunological activity of SE was lost almost completely upon heating. The loss of immunological activity of SEA was accompanied by a concomitant loss of biological activity of this toxin (monkey feeding test). A high pH treatment (pH 11) of the different preparations restored both the immunological and biological activity in most samples tested. Heating at 80 degrees C or 100 degrees C for 10 min of SE containing gelatin (pH 7.0), cauliflower extract (pH 4.0 or pH 7.0), milk (pH 4.0), casein (pH 6.0), rice extract (pH 7.0), noodles extract (pH 4.0) and oat-flakes extract (pH 7.0) had a much lower effect on the immunological activity of the SE (activity greater than or equal to 25%).     

pH对红色红曲菌（Monascus ruber）M7生长及产孢的影响

研究红色红曲菌（Monascus ruber）M7生长、繁殖两个不同阶段对环境pH需求的差异,在孢子培养过程中对pH进行分段控制,旨在减小产孢条件对菌丝生长的影响,提高孢子产量。结果表明,菌株M7孢子在pH 3.0～6.0条件下培养8 h均可100%萌发,其中,pH 4.0～5.0最佳,萌发最为迅速,在pH 7.0～8.0时孢子萌发受到严重抑制,萌发率很低;菌落生长在pH 4.0～6.0时较快,其中,pH 5.0最佳,菌落直径最大,但在pH 3.0和7.0时菌落生长明显减慢,在pH 8.0时受到严重抑制,形成的菌落很小;pH＞8.0的碱性条件为极端pH条件,孢子萌发和菌落生长完全被抑制。在菌株M7生长的pH范围内,产孢能力随着pH的升高而提高,适宜的产孢pH范围为7.0～8.0。根据菌株M7生长和繁殖对pH的需求差异,控制培养前期pH值为5.0、后期pH值为7.0～8.0,在PDB和CYB培养基中的产孢量分别提高了12～16倍和3～4倍。     

pH treatment as an effective tool to select the functional and structural properties of yak milk caseins

Qula is made from yak milk after defatting, acidifying, and drying. Yak milk caseins are purified from Qula by dissolving in alkali solution. The effects of different pH treatments on the functional and structural properties of yak milk caseins were investigated. Over a broad range of pH (from 6.0 to 12.0), functional properties of yak milk caseins, including solubility, emulsifying activities, and thermal characteristics, and the structural properties, including 1-anilino-8-naphthalene-sulfonate fluorescence, turbidity and particle diameter, were evaluated. The results showed that the yak milk casein yield increased as the pH increased from 6.0 to 12.0. The solubility dramatically increased as the pH increased from 6.0 to 8.0, and decreased as the pH increased from 9.0 to 12.0. The changes in emulsifying activity were not significant. Caseins were remarkably heat stable at pH 9.0. The turbidity of the casein solution decreased rapidly as the pH increased from 6.0 to 12.0, and the results suggested that reassembled casein micelles were more compact at low pH than high pH. At pH values higher than 8.0, the yield of yak milk caseins reached more than 80%. The highest solubility was at pH 8.0, the best emulsification was at pH 10.0 and the greatest thermal stability was at pH 9.0. According to the functional characteristics of yak milk caseins, alkali conditions (pH 8.0–10.0) should be selected for optimum production. These results suggested that pH-dependent treatment could be used to modify the properties of yak milk caseins by appropriate selection of the pH level.     

Gelling properties of whey protein isolate: influence of calcium removal by dialysis or diafiltration at acid or neutral pH

Dialysis of whey protein isolates (WPI) removed much more calcium when carried out at an acid pH (close to 4.0) than at neutral pH. Diafiltration at acid pH was also effective. The characteristics of thermally-induced gels prepared from WPI dialysed at acid or neutral pH were studied at pH 3.75 or pH 7.0, respectively, and at calcium concentrations ranging from 0 to about 60mM (with addition of calcium chloride). The water-holding capacity (WHC) and elasticity of gels increased with decreasing calcium concentration, at both pHs. Gel firmness was maximum at 10–20 mM calcium. The solubility of the protein constituents of WPI gels in a pH 8.0 buffer was high in the case of acid gels (especially at calcium concentrations lower or equal to 20 mM) and low for neutral gels at all calcium concentrations. Protein solubility values in the presence or absence of denaturing and reducing agents reflect the existence of intermolecular disulphide bonds in neutral gels and their absence in acid gels.     

加工工艺对荞麦蛋白功能特性的影响

探讨了加工工艺对荞麦蛋白(BWP)功能特性的影响。pH＜5．0和 pH＞6．0时,喷雾干燥制备的荞麦蛋白(SBWP)的溶解度高于商品大豆分离蛋白(SPI)(P＜0．05)。pH＜7．0时,超声协助提取荞麦蛋白(U- BWP)的溶解度较搅拌提取荞麦蛋白(M-BWP)和脱脂、超声协助提取荞麦蛋白(DU-BWP)好；pH＞7．0时,结果相反。总体来说,BWP 持油能力较 SPI 强,且冷冻干燥制备的荞麦蛋白(F-BWP)的持水、持油能力强于 S-BWP (P＜0．05)。BWP 的乳化活性与其溶解度呈正相关。pH 4．0～5．0时,BWP 的乳化活性指数(EAI)最小而乳化稳定性(ES)最高。脱脂处理明显提高了 BWP 的 EAI 和 ES。     

PURIFICATION AND CHARACTERIZATION OF THREE POLYPHENOL OXIDASE ISOZYMES FROM LOBSTER (HOMARUS AMERICANUS)

ABSTRACT Three isozymes of polyphenol oxidase (PPO I, PPO II and PPO III) were purified from lobster (Homarus americanus) by ion-exchange chromatography and preparative isoelectric focusing using a Rotofor cell. The purified isozymes migrated as single protein bands in polyacrylamide gels with R_f values corresponding to molecular weights of 32,180, 35,480 and 39,300, respectively. The pI values of the PPO isozymes were 3.89, 4.26 and 4.54, respectively. PPO I was most active at pH 6.5 and most stable from pH 6.0 to 7.0; PPO II was most active within the pH range 6.0 to 7.0, and most stable within the pH range 4.0 to 9.0; while PPO III was most active at pH 7.0 and most stable in the pH range 6.0 to 8.0. The temperature optimum for the PPO-dihydroxyphenylalanine oxidation reaction was 35C with PPO I and 45C with PPO II or III. Lobster PPO I lost about 30% of its initial activity after 30 min incubation at 45C, while PPO II and II retained virtually all their activity after the same heat treatment. The catalytic specificities of the PPO isozymes were relatively higher with dihydroxyphenylalanine as substrate than with chlorogenic acid.     

Urease production by Streptococcus thermophilus

In order to identify potential alternative sources of urease for the removal of urea from alcoholic beverages, 205 strains of lactic acid bacteria belonging to 27 different species were screened for urease production. Only Streptococcus thermophilus produced urease. Cell permeabilization with toluene allowed to increase activity significantly. Optimal pH for urease activity in whole and permeabilized cells and of cell free extracts differed slightly, but was in the range 6.0-7.0. Significant activity was retained at pH 3.0 and 8.0, and, for cell free extracts, at pH 4.0 in the presence of ethanol. Urease production was evaluated in fermentations with pH control (5.25-6.5) and without pH control. Very little urease was produced in absence of urea, which at 5g/l slowed growth significantly in fermentations without pH control, but prevented a decrease in pH below 5.1 and resulted in higher final biomass. Optimal pH for growth was between 6.0 and 6.5 but specific urease activity was higher for fermentations at low pH at the beginning of the exponential phase. However, a higher total urease activity was obtained at pH 6.0 and 6.5 because of higher biomass. Potential technological applications of urease production by S. thermophilus are discussed.     

Effects of water-soluble carbohydrate content on silage fermentation of wheat straw

To determine a suitable initial water-soluble carbohydrate (WSC) content to make wheat straw natural fermentation successful and to study fermentation characteristics, glucose was used to adjust the initial WSC content to 1.4%, 4.0%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, and 10.0% dry matter (DM) in the wheat straw. At 30 d of fermentation, there were three pHs: when the initial WSC content was 1.4%, the pH was 5.5; when the initial WSC contents were 4.0%, 5.0% and 6.0%, the pHs were near 5.1; and when the initial WSC contents were 7.0%, 8.0%, 9.0% and 10.0%, the pHs were near 4.0. The pattern of changes in WSC content during the fermentation was similar to that in pH. At 30 d of fermentation, there existed a dividing line in WSC remnants between the initial 6.0% WSC treatment and the initial 7.0% WSC treatment. When the initial WSC content was more than 7.0%, the remaining WSC content was more than 23.7 g/kg DM. When the initial WSC content was less than 6.0%, the remaining WSC content was less than 13.6 g/kg DM. Particularly for the 1.4% WSC treatment, the remaining WSC content was 2.1 g/kg DM. The results of the microbiological enumeration showed that with the increase in initial WSC content, the numbers of lactic acid bacteria (LAB) and other bacteria generally decreased. Denaturing gradient gel electrophoresis (DGGE) results showed that when the initial WSC content was beyond 7.0%, the LAB of the fermentation system were detected.     

Stability of patulin at ph 6.0-8.0 and 25 degrees c.

Patulin was tested for stability at pH values of 6.0, 6.5, 7.0, 7.5, and 8.0, using S?rensen's phosphate buffer at 25 degrees C. Patulin was determined by high-performance liquid chromatography. When the percentage of patulin remaining was plotted versus reaction time, apparent first-order reaction plots were obtained. Reaction rate constants for disappearance of patulin ranged from 1.1 x 10(-2) h at pH 8.0-5.3 x 10(-4) h at pH 6.0. Values for half-life were calculated and ranged from 64 h at pH 8.0 to 1310 h at pH 6.0.     

Effects of pH and Sodium Chloride on the Gelling Properties of a Protein Concentrate Obtained from Jumbo Squid Mantle (Dosidicus Gigas)

Jumbo squid (Dosidicus gigas) is an underutilized fishery resource in the Gulf of California. Jumbo squid muscle could potentially be utilized to manufacture protein concentrates to be used as a base for surimi or as a food ingredient. However, the main problem is the low gelling ability of these protein concentrates compared those of with fish species. Consequently, the present study evaluated the effects of pH and the NaCl concentration on the gelling properties of protein concentrates from squid mantle. According to texture profile analysis, improved gelling properties were obtained at pH 6.0 and 1% of NaCl. During the sol-gel transition, decreased surface hydrophobicity that corresponded to an increased intensity of α-helix structures was detected. Moreover, the total sulfhydryl content decreased during gel formation. Viscoelasticity and water holding capacity analyses showed the formation of a more structured gel at pH 7.0. The higher enthalpy and denaturation temperature detected by differential scanning calorimetry at pH 7.0 and 1% NaCl showed that both variables (pH and NaCl concentration) affected the protein structure and conformation. The results demonstrated that varying pHs and NaCl concentrations improved the gelling properties of protein concentrates from squid.     

牛血浆蛋白凝胶特性研究

研究不同加工条件如蛋白浓度、加热温度、离子强度和pH对牛血浆蛋白凝胶特性的影响。结果表明:蛋白浓度的提高有利于凝胶的形成,且形成凝胶的最低血浆蛋白浓度是4.0%;4.8%的血浆蛋白,线性升温到85℃保温20 min,能够很好形成凝胶,呈果冻状,光滑有弹性;NaCl浓度在1.0 mol/L以下时,血浆蛋白凝胶强度随离子强度的变化是先增加后减小,0.3 mol/L时取得最佳效果;在pH6.0~9.0范围内,pH为9.0时牛血浆蛋白凝胶的凝胶强度较好,保水性高,蒸煮损失低。NaCl和pH对于牛血浆蛋白的凝胶特性有极显著的互作效应。     

莲藕可溶性膳食纤维与多酚复合物的稳定性及脂肪吸附活性研究

为研究莲藕可溶性膳食纤维与多酚复合物的降脂活性,采用离体试验模拟不同温度、pH值环境,探讨可溶性膳食纤维-多酚复合物的稳定性及对油脂、胆固醇、胆酸盐的吸附能力和阳离子交换能力.结果表明:复合物的稳定性随温度、pH值的升高而降低;可溶性膳食纤维-多酚复合物对油脂的吸附能力比可溶性膳食纤维及物理混合物好,效果极显著(P<0...     

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.     

Nitrogen extractability and buffer capacity of defatted linseed (Linum usitatissimum L.) flour

Defatted linseed flour was prepared from cold-pressed seed meal via hexane extraction of the residual oil, followed by removal of the major portion of the hulls through grinding and sieving (sieve size 0.25 mm). The resulting flour had 50% protein on a dry basis compared with 40% contained by the whole seed on an oil-free dry basis. Nitrogen extractability of the defatted flour in water was not influenced by the length of the extraction period but an increased extraction was observed at higher solid:liquid ratios up to the studied limit of 1:40. The smallest amount of nitrogen (20%) was extracted in the pH range 4.0–4.6 and the greatest (80%) at pH 12.0. Addition of NaCl (0.1–1.0 M) broadened the pH range of minimum nitrogen extractability and shifted it towards lower pH region. At higher concentrations (0.6 and 1.0 M) NaCl markedly increased nitrogen extractability in the pH range of 4.0 to 8.0. Precipitation of protein from an extract at pH 10.0 was maximum (77%) at pH 4.1. A higher buffer capacity of the flour was observed in the acidic medium (0.204 mmol HCl g^?1 flour) than in the alkaline medium (0.096 mmol NaOH g^?1 flour).     

Nitrogen extractability and functional properties of defatted Erythrina variegata flour

Defatted Erythrina variegata flour was prepared from dehusked seed meal by hexane extraction of residual oil. The resulting flour had 403 g kg⁻¹ of protein as compared to 282 g kg⁻¹ in the whole seed-defatted meal. Nitrogen extractability of the defatted flour in water was not much influenced by the length of extraction period above 40 min, but an increased extraction was observed at a higher liquid to solid ratio up to a studied limit of 1:60; the optimal ratio was found to be 1:30. The minimum of 26.9% nitrogen was extracted in the pH range 3.0–4.0 and maximum of 94.8% at pH 12. Addition of sodium chloride (0.1 or 0.5 M) broadened the pH range of minimum nitrogen extractability and shifted it toward a lower pH region. At both concentrations of sodium chloride, a marked increase in nitrogen extractability, in the pH range 3.0–7.0, was observed. Precipitation of protein from an extract of pH 10.0 was maximum (85.3%) at pH 4.75. A higher buffer capacity of the flour was observed in the acidic medium (0.195 mmol HCl g⁻¹ flour) than in alkaline medium (0.093 mmol NaOH g⁻¹). Water absorption and oil absorption values for the whole E. variegata seed flour and the dehusked, defatted flour were 1.81, 1.43 and 1.02, 1.52 kg kg⁻¹, respectively.     

pH Induced Aggregation and Weak Gel Formation of Whey Protein Polymers

Whey protein polymers were formed by heating (80 °C) a 4% (w/v) whey protein (WP) isolate dispersion at pH 8.0 for 15, 25, 35, 45, or 53 min. Dispersions were adjusted to pH 6.0, 6.5, 7.0, 7.5, or 8.0 after heating and the rheological properties were determined. Viscosity increased with increased heating time and decreased pH. At pH 7.0 and 7.5, high-viscosity dispersions with pseudoplastic and thixotropic flow behavior were formed, while weak gels were formed at pH 6.0 and 6.5. The storage (elastic) and loss (viscous) moduli of pH-induced gels increased when temperature was increased from 7 °C to 25 °C, suggesting that hydrophobic forces are responsible for gelation. Key Words: weak-gels, whey proteins, polymers, gelation, functionality     

Effect of Diacetyl on Foodborne Microorganisms

A set of 70 organisms consisting of 9 lactic acid bacteria, 14 non-lactic gram positives, 16 yeasts, 6 molds, 12 pseudomonads, and 13 nonpseudomonad gram negative bacteria was tested on plate count agar (PCA) at pH 5.0 to 8.0 and in the presence of varying concentrations of diacetyl. All organisms were more sensitive to diacetyl at a pH of 7.0 and below than at pH 8.0 with the greatest sensitivity at pH 5.0. The lactic acid bacteria were the most resistant while the pseudomonads were the most sensitive. Excluding the lactic acid bacteria, 300 ppm completely inhibited 95, 90, 85, and 43% respectively at pH 5.0, 6.0, 7.0, and 8.0. Using PCA at pH 6.0, three Gram negative bacteria were inhibited by 86 ppm in pour plates while 6 of 7 nonlactic cultures were inhibited by 172 ppm. The compound was shown to be effective in fresh ground beef.     

Caseinophosphopeptide enrichment and identification

Caseinophosphopeptides (CPPs) were generated via tryptic hydrolysis of sodium caseinate followed by heat treatment (75 °C) at pH 6.0, 7.0 and 8.0. Calcium aggregation, ethanol precipitation and gallium immobilised metal affinity chromatography (IMAC) were applied to enrich the CPPs. Nano‐liquid chromatography electrospray ionisation‐quadrupole time‐of‐flight tandem mass spectrometry was used for phosphopeptide separation and identification. The combination of gallium IMAC isolation with calcium and ethanol precipitation appears to be a useful tool in characterising the fate of CPPs in CN hydrolysates during thermal processing. CPPs appeared to be less susceptible to thermal modification when heat‐treated at pH 7.0 than at pH 6.0 and 8.0. Different extents of methionine oxidation occurred in the CPPs depending on heat‐treatment pH. The results herein may have important implications for the manufacture of CPPs and for the quality control of CPP products.     

Effect of temperature and pH on survival of Listeria monocytogenes in coleslaw

The survival and growth of Listeria monocytogenes in fresh coleslaw, pH 3.9, and in coleslaw adjusted to pH 4.0, 5.0, 6.0 or 7.0 before inoculation was studied at three temperatures (4, 15 and 25 degrees C). L. monocytogenes was not detectable after 5 days incubation in fresh coleslaw nor in coleslaw adjusted to pH 4.0. Coleslaw at pH 5.0 was also inhibitory to L. monocytogenes at all three temperatures studied. A decline in viable numbers of L. monocytogenes in coleslaw at pH 6.0 occurred at 4 degrees C and at 15 degrees C, whereas at 25 degrees C the viable count of L. monocytogenes increased initially and remained high after incubation for 25 days. L. monocytogenes grew rapidly in coleslaw at pH 7.0 at all three temperatures studied, followed by an equally rapid decline in viable count.