Effect of various heat treatments on plasminogen activation in bovine milk during refrigerated storage

Plasmin and plasminogen‐derived plasmin activities were measured in heated milk with and without the addition of plasminogen activator, before and after storage at 4 °C for 96 h. The effect of a free sulfhydryl group donor, β‐lactoglobulin or cysteine, on plasminogen activation was investigated in a model system and milk. Heating milk to 75 °C enhanced plasminogen activation that was marked by a considerable increase in plasmin activity. Heating at 85 and 90 °C caused a significant decrease in plasmin and plasminogen‐derived plasmin activities. However, after storage, significant plasmin levels were restored because of the activation of remaining unfolded plasminogen. Both β‐lactoglobulin and cysteine significantly decreased plasmin and plasminogen‐derived plasmin activities in a model system. While endogenous β‐lactoglobulin was not sufficient to completely eliminate plasminogen activation in milk, cysteine addition prior to pasteurisation significantly decreased plasmin and plasminogen‐derived plasmin activities. Results highlighted the importance of the remaining plasminogen in heated milk systems.     

Effect of heat on the distribution of fluorescently labeled plasminogen and plasminogen activators in bovine skim milk

ABSTRACT:  Differentially fluorescently labeled bovine plasminogen (PG-594) and human tissue- and urokinase-type plasminogen activators (tPA-647 and uPA-546) were added to bovine skim milk to track the effect of heat on the location and concentration of these plasmin system components following acid precipitation or ultracentrifugation. In unheated milk, the majority (71.7% to 89.0%) of the added PG and PAs associated with casein micelles or acid curd, and PG-594 in the serum fraction was partially due to associations with nonsedimentable caseins. Heat treatment (85 °C for 16 s) significantly ( P < 0.05) affected distribution of PG-594, tPA-647, and uPA-546, resulting in reduced concentrations of PG and PAs in the serum fractions and reciprocal increases in their levels in the nonsedimentable casein fractions. Overall, almost all of the added PG and PAs (95.9% to 97.5%) became associated with caseins following heat treatment. This is the 1st study to successfully use fluorescent labeling to quantify effects of heat on the location of plasmin components in skim milk.     

Effect of thermal treatment on the proteins of amaranth isolates

The effect of thermal treatment of proteins from Amaranthus hypochondriacus was studied. Two protein isolates were obtained from the defatted flour by water extraction at a pH of 9 (A9 isolate) and 11 (A11 isolate), followed by isoelectric precipitation at a pH of 5. Effect of thermal treatment (70 and 90 °C, during 3, 5, 10, 15 and 30 min) on A9 and A11 dispersions were analyzed by differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis, UV spectrophotometry, superficial hydrophobicity and solubility in water. Thermal treatment induced the aggregate formation of high molecular mass stabilized by disulfide and non‐covalent bond. Thermal treatment at 70 °C produced a 30% denaturation in both, while at 90 °C A9 was more denatured than A11 (75% and 55% of denaturation, respectively). An increase in thermal stability was also detected by DSC in A9 treated at 90 °C. The denaturation process was accompanied at short heating times by an increase in UV absorbance and changes in superficial hydrophobicity. A decrease in water solubility (35–50%, depending on time–temperature conditions) was also observed for the A9 isolates. The results suggest that the A9 isolates, enriched in a globulin protein fraction, are more sensitive to thermal treatment than isolates A11 enriched in glutelin protein fraction. The changes shown by both isolates, indeed, could affect their functional properties and could definitely limit their use in food products. Copyright © 2007 Society of Chemical Industry     

Effect of salt addition on the thermal behavior of proteins of bovine meat from Argentina

Research was undertaken to investigate how the addition of sodium chloride (NaCl) and/or sodium tripolyphosphate (TPP) to sous vide cooked meat pieces produces an increase in water holding capacity (WHC). Semitendinosus muscles were injected to obtain tissue final concentrations of 0.70% NaCl, 0.25% TPP, 0.70% NaCl+0.25% TPP, and 1.20% NaCl+0.25% TPP. SDS-PAGE analysis showed increased protein solubilization in those treatments which included NaCl. Thermal analysis of whole muscles and isolated myofibrils showed the destabilizing effect of NaCl and a global stabilizing effect of TPP. Both salts together induced a destabilizing global effect, where TPP assisted NaCl in breaking the meat structure. It is suggested that the WHC increments are related to conformational changes in myofibrillar proteins and to the weakening of myofibrillar structure by the removal of myofibrillar proteins.     

Thermal stability of plasminogen activators and plasminogen activation in heated milk

Thermal stabilities of bovine plasminogen (PG) activators, tissue and urokinase type (t-PA and u-PA), and their impact on activation of PG, were studied after application of various heating conditions (65, 75, 85, or 90 °C for 15, 20, or 30 s), in both milk and buffer systems. Both t-PA and u-PA were thermally stable in milk heated at ⩽75 °C. However, almost half of the t-PA activity and 30% of u-PA activity was lost after heating milk at 85 °C for 30 s. A lower heat stability of both t-PA and u-PA was observed in buffer than in milk. The decrease in level of PG was more pronounced than that of active plasmin in milk heated at ⩾85 °C for 30 s; however, the residual level of PG was considerably higher than the residual level of active PL. Overall, results indicated that u-PA plays a more significant role than t-PA in the activation of PG during storage of heated milk.     

Effect of thermal treatment on the characteristic properties of loach peptide

The effects of thermal treatment on the changes in the colour, the molecular weight distribution, amino acid profiles and the overall antioxidant activities of loach peptide were investigated. When the thermal temperature was rising, the browning was enhanced. The contents of free amino acids Gly, Arg, Thr and Tyr were increased, whereas those of Asp, Ser, Met, Cys, Trp and Lys were decreased. The scavenging activities (1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging activity, the oxygen radical absorbance capacity (ORAC) and the reducing power of loach peptides after different thermal treatments were lower than those of the control, whereas the Cu²⁺ chelating activity was higher (except from the sample treated at 100 °C, 20 min). The heat treatment at 121 °C, 15 min was shown to be the best thermal processing, as it caused the least loss in radical scavenging activity and showed relatively higher Cu²⁺ chelating activity.     

Effect of thermal treatment on the enzymatic hydrolysis of chicken proteins

The proteins of chicken breast meat were thermally treated in this work. Treatment temperature and time were chosen to evaluate the effect of thermal treatment. By determination of SH and S-S group levels, the results indicated that the SH and S-S group levels in the chicken proteins without thermal treatment were 65.06 and 12.29 μmol/g. With the increase of treatment temperature, the SH group level decreased, while S-S group level increased gradually. Enzymatic hydrolysis by Alcalase was done to evaluate the nitrogen levels of hydrolysates. A temperature-dependent effect was observed for soluble and formaldehyde nitrogen levels. A slight increase of peptide nitrogen level was found with the increase of temperature. Treatment time had a similar effect to treatment temperature. The molecular weight of chicken protein hydrolysates was analysed by gel permeation chromatography. The chicken protein hydrolysates without thermal treatment showed an apparent peak at 27.5 ml of elution volume and a weak peak at 4.0 ml, which represented fractions with molecular weight of > 10,000 Da and < 2640 Da, respectively. Thermal treatment led to decreases of the fractions with molecular weight of > 10,000 Da, 3500–2640 Da and < 2640 Da, compared with hydrolysate fractions without thermal treatment. Treatment with a temperature higher than 60 °C for 20 min would completely eliminate the > 10,000 Da fraction from chicken protein hydrolysates. The percentage of fraction with molecular weight of 4500–3500 Da increased with the extension of treatment time to 20 min, thereafter decreased.Industrial relevanceThe annual yield of chicken meat in China ranks the second of the world. However, the extensive development of this resource is still limited. In this work, chicken breast meat was thermally treated and then hydrolysed by Alcalase. Effects of treatment temperature and time on the hydrolysates were investigated. The results indicated that thermal treatment could change the levels of soluble nitrogen, formaldehyde nitrogen and peptide nitrogen. The area percentages of fractions with different molecular weight were also changed. This work was helpful to understand the characteristics of bioactive peptides produced from chicken proteins.     

高压处理对牛骨骼肌原肌球蛋白结构的影响

从牛骨骼肌中提取原肌球蛋白,施行0.1～400MPa的高压处理,解压后测定原肌球蛋白荧光光谱、光谱质量中心、芳香族表面疏水性、脂肪族表面疏水性、表面巯基含量的变化来探讨压力对原肌球蛋白结构的变化。荧光光谱强度及光谱质量中心与对照组(0.1MPa)相比,随着压力的增加有逐渐下降趋势,最大荧光波长发生蓝移。100MPa时芳香族、脂肪族表面疏水基团显示出最低荧光强度值,压力继续升高时又逐渐上升。表面巯基含量在100MPa时大幅增长,随着压力的增加有缓慢的增长趋势。从此结果可推测压力引起原肌球蛋白的结构变化,而这些变化可能是一定程度的可逆性变化。     

Effect of high-pressure treatment on denaturation of bovine lactoferrin and lactoperoxidase

Lactoferrin and lactoperoxidase are whey proteins with biological properties that may provide health benefits to consumers. These properties are vulnerable to potentially denaturing conditions during processing. High-pressure treatment is an appealing alternative to the traditional heat processing of foods because it exerts an antimicrobial effect without changing the sensory and nutritional quality of foods. In this work, the effect of high-pressure treatment on the denaturation of lactoferrin and lactoperoxidase present in skim milk and whey, and as isolated proteins in buffer, was studied over a pressure range of 450 to 700 MPa at 20°C. Denaturation of lactoferrin was measured by the loss of reactivity with their specific antibodies using a sandwich ELISA. Denaturation of lactoperoxidase was determined by measuring the loss of enzymatic activity using a spectrophotometric technique. No substantial inactivation of lactoperoxidase was observed in any treatment assayed. The concentration of the residual immunoreactive lactoferrin after each pressure treatment was determined, and the data were subjected to kinetic analysis to obtain D and Z values. Denaturation of lactoferrin increased with pressure and holding time, and D values were lower when lactoferrin was treated in whey than in milk, and lower in both whey and milk than in phosphate buffer. Thus, protein is denatured more slowly in buffer and in milk than in whey. Denaturation of lactoferrin in the 3 media was found to follow a reaction order of n=1.5. Volumes of activation of about -34.77, -24.35, and -24.09 mL/mol were obtained for lactoferrin treated in skim milk, whey, and buffer, respectively, indicating a decrease in protein volume under pressure.     

Effect of thermal treatment on some properties of lime wood

Thermal treatment of lime wood was performed in a drying oven at two temperature levels (180 and 200 °C) and for four durations (1, 2, 3 and 4 h). Mass loss, color change, swelling and hygroscopicity were investigated. The dimensional stabilization reached up to 66.4 % and the hygroscopicity reduction up to 33 %, both maximum values being attained at 200 °C/4 h, associated with a mass loss of 9.3 %. The results will be realized in the manufacturing of solid wood panels made of heat-treated lime wood lamellas for outdoor uses.     

Enzymatic assays for native plasmin, plasminogen and plasminogen activators in bovine milk.

Rapid and sensitive assays for plasmin, plasminogen and plasminogen activators (PA) were developed and applied to bovine milk. The reaction medium was clarified by addition of a dissolving agent after hydrolysis of a fluorescent substrate specific for plasmin. This final step enabled the use of larger sample amount with higher substrate concentration than other methods, and avoided previous sample preparation. The use of 4 g gelatin/l in buffers preserved plasmin activity, thus avoiding risks of overestimation of the assays results. Sensitivity, detection level, repeatability and analysis run time of plasmin and plasminogen assay were improved over previous enzymatic methods with synthetic substrates. The PA assay was assessed by measuring conversion of exogenous plasminogen into plasmin. A new kinetic approach was used to enable the direct determination of global PA activities on raw milk samples without interference from indigenous plasmin.     

热处理与微波处理对蓝莓汁品质的影响

采用一级反应动力学模型和Arrhenius经验方程,通过对蓝莓汁分别进行热处理和微波处理,研究了两种处理过程中蓝莓汁中花青素含量、色泽(色度)及抗氧化能力(清除DPPH自由基能力)的变化规律,并建立了相关动力学模型。实验结果表明:热处理和微波处理过程中蓝莓汁中花青素含量、色泽及抗氧化能力的变化均符合一级反应动力学模型(R2>0.9),并可用Arrhenius方程拟合(R2>0.99);热处理温度升高或微波处理功率增大,花青素和色泽的变化速率随之增大,而抗氧化能力随之减小;各模型预测值与实验值之间相对误差均不超过1%,所有模型的预测准确性均较高。     

高压结合热处理对猪肉滋味的影响

为研究高压结合热处理对猪肉滋味物质的影响,以猪背最长肌为原料,用不同压力(200~600 MPa)结合热(20~60℃)处理10 min,然后测定各样品氨基酸组成、核苷酸组成、还原糖含量、硫胺素含量、脂肪酸组成,并用电子舌对样品的整体滋味进行评价。高压结合热处理极显著(p<0.01)影响猪肉中游离氨基酸总含量和组成;核苷酸及降解产物总含量极显著(p<0.01)增加,特别是次黄嘌呤核苷酸(IMP);还原糖和硫胺素含量都显著降低(p<0.05);但高压结合热处理对猪肉总脂肪酸组成影响不明显(p>0.05)。偏最小二乘回归(APLSR)分析表明压力和温度对各样品滋味的影响程度相当;电子舌分析表明处理条件越剧烈样品的整体滋味和对照样的差异越大,在200和400 MPa下温度对整体滋味的影响较大,而在600 MPa下温度的作用很小。在实际应用中为了更好地保留新鲜肉的滋味应避免采用600 MPa或60℃的条件对猪肉进行处理。      

超声波处理对牛血清白蛋白结构和乳化性的影响

采用圆二色谱（CD）、聚丙烯酰胺凝胶电泳（SDS-PAGE）、8-苯胺-1-萘磺酸（ANS）荧光探针及紫外（UV）光谱研究了不同超声强度和处理时间对牛血清白蛋白（BSA）结构和乳化性的影响。结果表明:超声波处理对BSA的一级结构无明显影响,但对其二级结构、三级结构有显著影响（p<0.05）。经过超声处理后,BSA中的α-螺旋明显降低、β-折叠含量明显增加、无规则卷曲总体上无显著变化（p>0.05）,β-转角含量随功率的增加而增大、随超声时间的延长先增加后减小,内源性荧光强度、表面疏水性及乳化性均随超声处理强度和时间的延长呈先增加后降低的趋势,当超声功率为240 W/cm²、超声时间为10 min时,乳化活性（EAI）和乳化稳定性（ESI）达到最大。这表明,超声波处理是一种潜在改变BSA结构与乳化性的方法,同时也为超声处理在乳化蛋白时对蛋白的改性机理提供理论依据。      

Effect of heat treatment on antirotaviral activity of bovine and ovine whey

Rotavirus is the major cause of infectious diarrhoea in infants and children throughout the world. Several studies have indicated that some milk fractions may protect against rotavirus infection. The present study evaluates the effect of some heat treatments on the antirotaviral activity of bovine and ovine whey by an immunofluorescence assay validated in this work. Neutralising activity of diverse proteins present in whey has also been verified individually. Bovine and ovine whey, at 1 mg mL⁻¹ protein, inhibit MA104 cells infection with bovine rotavirus strain WC3, with values of 89.2 and 76.6% inhibition, respectively. Furthermore, the inhibitory activity was influenced by temperature and duration of heat treatment. The ability of bovine and ovine whey to inhibit rotavirus infection was not affected by treatment at 75 °C for 20 s; after 85 °C for 10 min bovine and ovine whey still maintained 16.1 and 32.5%, respectively, of neutralisation activity.     

Effect of heat treatment of milk on activation of Bacillus spores

The quality and shelf life of fluid milk products are dependent on the amount and type of microorganisms present following pasteurization. This study evaluated the effects of different pasteurization processes on the microbial populations in fluid milk. The objective was to determine whether certain pasteurization processes lead to an increase in the amount of bacteria present in pasteurized milk by activating Bacillus spores. Samples of raw milk were collected on the day of arrival at the dairy plant. The samples were pasteurized at 63 degrees C for 30 min (low temperature, long time), 72 degrees C for 15 s (high temperature, short time), 76 degrees C for 15 s, and 82 degrees C for 30 min. The pasteurized samples were then stored at 6 and 10 degrees C for 14 days. The samples were analyzed for standard plate count and Bacillus count immediately after pasteurization and after 14 days of storage. Pasteurization of milk at 72 and 76 degrees C significantly (P < 0.05) increased the amount of Bacillus spore activation over that of 63 degrees C. There was no detection of Bacillus in initial samples pasteurized at 82 degrees C for 30 min, but Bacillus was present in samples after storage for 14 days, indicating that injury and recovery time preceded growth. The majority of isolates were characterized as Bacillus mycoides and not Bacillus cereus, suggesting that this organism might be more a cause of sweet curdling of fluid milk than previously reported.     

聚丙烯SMS非织造手术衣材料热处理温度研究

研究了聚丙烯纺粘-熔喷-纺粘复合(SMS)非织造手术衣材料在热处理过程中,材料结晶结构与结晶度的变化规律,以及热处理温度对力学性能的影响,结果表明:热处理温度的变化不会改变非织造布的内部晶型结构,非织造布的结晶度随热处理温度的升高而增大,晶粒尺寸随热处理温度升高先增大后减小.随热处理温度的升高,纵横向断裂强力和断裂伸长均呈现出先减小后增大的趋势,为获得更完善的晶型以及稳定的力学性能,合适的后整理温度为110～130℃.