Contribution of Milk Enzymes, Starter and Rennet to Proteolysis During Storage of Quarg

The relative contributions of rennet, starter and plasmin to proteolysis during storage of the acid-coagulated cheese quarg were investigated. In the experimental design used, each agent was, in separate treatments, either omitted (rennet), replaced by a nonproteolytic substitute (glucono-δ-lactone instead of starter) or alternatively either increased by the addition of exogenous enzyme or decreased by addition of a specific inhibitor (plasmin). A final experimental variable involved heating milk to 90°C for 10 min prior to acidification. All quarg samples were thermised after acidification, to reduce levels of adventitious microflora and to extend shelf life. The experimental treatments used had little effect on composition or yield of quarg, with the exception of high heat treatment, which increased yield and moisture content due to whey protein denaturation. Omission of rennet during manufacture significantly reduced proteolysis during ripening of quarg, and altered both urea-polyacrylamide gel electrophoresis and reversed-phase HPLC patterns of proteolysis. Omission of starter had a considerably lesser effect. The role of plasmin was also minor, resulting in production of the large water-insoluble γ-caseins. The principal ripening agent in thermised quarg appeared to be rennet, while starter enzymes and plasmin played a lesser role.     

The Use of Different MS Techniques to Determine Glutathione Levels in Marine Tissues

Several techniques were used, mainly mass spectrometry connected with gas chromatography, matrix-assisted laser desorption with ionization time-of-flight and mass spectrometry connected with liquid chromatography. A major problem was encountered in determining glutathione, which can be conditioned by the pH and selected reducing agents. The GSH form can be oxidized through derivatization, and a small glutathione amount in the biological samples may hinder the determination process. Another problem is the existence of a metal ion in the tested organism; therefore, often a reagent with a chelating function is added to the sample and the mobile phase in liquid chromatography is applied with appropriate polarity for GSH and GSSG. We determined the concentrations of total, reduced, and oxidized glutathione in the liver, hepatopancreas, muscle, and gonad tissues of brown shrimp (Crangon crangon) and fish (Psetta maxima and Clupea harengus membras). The highest concentrations of tGSH were recorded in the shrimp hepatopancreas (7.21?±?0.011 μmol g^?1 wet weight), in herring liver (2.85?±?0.025 μmol g^?1), and in turbot liver (1.86?±?0.063 μmol g^?1). In turn, the highest concentrations were reported for GSSG in the muscle of shrimp (0.140?±?0.000204 μmol g^?1), and in the testis of turbot (0.063?±?0.000170 μmol g^?1) and herring (0.009?±?0.000015 μmol g^?1). We also investigated seasonal changes in the concentrations of glutathione in the muscle of C. crangon shrimp in the annual cycle. The lowest values of total glutathione were recorded during spring and autumn, which could be correlated with the increase in lipid peroxidation and oxidative stress.     

不同质量浓度低聚果糖和低聚半乳糖对发酵乳品质的影响

研究不同质量浓度低聚果糖和低聚半乳糖对发酵乳在发酵期和贮藏期内乳中菌落活菌数、滴定酸度和黏度的影响。结果表明：在发酵期低聚果糖（QHT-90 FOS）对发酵乳中乳酸菌活菌数的增殖作用要显著高于低聚半乳糖（QHT-60 GOS）,在QHT-90 FOS质量浓度为1.5 g/100 mL的样品中,12 h时瑞士乳杆菌（Lactobacillushelveticus）MB2-1活菌数可达到4.44×109 CFU/g,而不同质量浓度和结构的低聚果糖和低聚半乳糖对样品滴定酸度和黏度的影响差异不显著;此外在4 ℃发酵乳贮藏期间,QHT-90 FOS对L. helveticus MB2-1有一定保护作用,在QHT-90 FOS质量浓度为1.5 g/100 mL的样品中,贮藏14 d后,活菌数仅减少11.90%,而滴定酸度基本不变,产品黏度保持在9 000 mPa·s。     

Atlantic Cod Gastric Protease. Characterization with Casein and Milk Substrate and Influence of Sepharose Immobilization on Salt Activation, Temperature Characteristics and Milk Clotting Reaction

The temperature coefficient for the enzymic phase of milk clotting was lower for cod gastric protease than for calf rennet and various other rennet substitutes. Immobilization of cod pepsin on Sepharose resulted in an increase in Arrhenius activation energy for hemoglobin hydrolysis from 8.5 Kcal/mole to 12.8 Kcal/mole. Sepharose-cod protease did not catalyze the enzymic phase of milk clotting. Cold renneting of milk substrate with cod gastric protease at 0°C resulted in continued formation of nonprotein nitrogen (NPN) after the enzymic phase of milk clotting was complete. Initiation of milk clotting by raising the temperature to 39°C prevented the subsequent formation of NPN.     

The Use of Multiplex PCR to Determine the Prevalence of Enterotoxigenic Staphylococcus aureus Isolated from Raw Milk,Feta Cheese,and Hand Swabs

Staphylococcus aureus (S. aureus) can cause mastitis in cattle and, therefore, can be present in milk. This study was undertaken to determine the prevalence of coagulase positive S. aureus and its enterotoxin genes sea, seb, and sec in isolates recovered from raw milk, feta cheese, and human hand swabs of milk and cheese handlers in Beni‐Suef province, Egypt. A total of 100 samples of raw milk and 50 samples of pasteurized‐milk feta cheese were collected. In addition, 50 hand swabs from milk handlers and 25 hand swabs from cheese handlers were examined for the presence of coagulase positive S. aureus. The isolates were characterized by multiplex PCR for detection of sea, seb, and sec genes, and for resistance to 5 classes of commonly used antibiotics. Twelve (12/100), 12 (6/50), and 17% (13/75) of milk, cheese, and hand swab samples, respectively, were positive for coagulase positive S. aureus. One isolate was obtained from each positive sample (31 isolates), and none contained genes for SEA or SEC production. Twenty‐five percent, 33%, and 31%, respectively, of the isolates contained the genes for SEB, resulting in 3%, 4%, and 5% of samples being positive for toxin producing coagulase positive S. aureus, respectively. At least one isolate was resistant to each of the antibiotics tested. Despite the low potential for SEB production shown, preventative measures, such as maintenance of the cold‐chain and good hygienic practices should be implemented to further reduce the potential risk to public health from SEB, and to reduce the spread of antimicrobial resistance.     

果蔬抗氧化活性测定方法的比较

采用DPPH法、硫氰酸铁(FTC)法、β-胡萝卜素-亚油酸乳化液法3种常用果蔬抗氧化活性测定方法,对杭州市场常见的20种果蔬进行了抗氧化活性测定,比较3种果蔬抗氧化活性测定方法的差异,寻求合适的果蔬抗氧化活性测定方法。结果表明:DPPH法测定果蔬抗氧化活性简便,重现性好;FTC法测定结果与DPPH法较为接近,但操作相对复杂;而β-胡萝卜素-亚油酸乳化液法虽筒捷方便,但测定结果与前2种相比差异较大。     

Yield and Quality of Cheddar Cheese from High Somatic Cell Milk Supplemented with Retentate to Varying Concentrations or Directly Ultrafiltered

High somatic cell milk with a mean cell count of 2,235,000/ml was supplemented to 1.25:1 to 1.88:1 total protein with approximately 5.5:1 low somatic cell whole milk retentate of UF. Curd formation time of cheese milk decreased with increasing concentration of SCC. Supplemented milk concentrated to 1.65: 1 and 1.88:1 total protein displayed normal curd formation times: 34 and 31 min, respectively. Also, cheese made from these mixtures had normal moisture, whereas the remaining cheeses had higher than normal moisture. Supplementation to 1.65:1 and 1.88:1 total protein increased cheese yield by 9.67% and 11.38%, respectively, and produced excellent quality cheese after 2 mo at 10°C.Direct UF of high SCC milk to 1.84:1 total protein improved cheese quality and increased yield over control milk cheeses but not to the same high level attained with retentate supplementation.     

Development and Performance of Crystallization with Additives Applied on Different Milk Samples

Crystallization with additives is developed on milk samples from different processing treatments. Performance tests are carried out based on structure analysis of the crystallization patterns. Crystallization with milk as additive is applied following changes in milk after different processing treatments. When an aqueous cupric chloride dihydrate solution crystallizes in the presence of milk as additive, specific patterns emerge, which can be evaluated by image analysis. Milk samples were heated and homogenized in a pilot plant and characterized by various parameters. Furthermore, milk samples from the market were tested. Patterns from milk after heat treatment and homogenization are significantly different from those derived from untreated milk. The experiments could be reproduced for other milk samples, on different days and in another laboratory.     

不同储藏年限稻谷的品质及蒸谷米加工适应性分析

为了解不同储藏年限的稻谷加工蒸谷米的品质变化,为蒸谷米加工原料的选择提供依据.以不同储藏年限的籼稻、粳稻各40份样品为研究对象,将其加工成蒸谷米,并对蒸谷米的蒸煮特性、外观及其制备米饭的食用品质与质构特性等指标进行测定,采用描述统计分析、方差分析、主成分分析等方法对蒸谷米的品质指标进行分析,采用聚类分析探讨稻谷的蒸谷米...     

Simultaneous Curdling of Soy/Cow's Milk Blends with Rennet and Calcium or Magnesium Sulfate, Utilizing Soymilk Prepared from Soybeans or Full-Fat Soy Flour

Mixed soy/cow's milk curds were prepared by simultaneous curdling of soy/cow's milk blends, utilizing rennet as cow's milk coagulant and calcium or magnesium sulfate as soymilk coagulant. The method produced curds of similar characteristics (compactness and yield), whether soymilk prepared from soybeans or full-fat soy flour was used. The effect of a number of process variables on curd characteristics was studied, utilizing a fractional factorial design. Generally, large changes in process variables (23 – 230%) produced relatively small charges in curd characteristics (1 – 16%). Protein contents of raw materials and proximate chemical analyses of pure and mixed milk curds, prepared under conditions yielding maximum curd compactness were determined. Protein recoveries in curd preparation were calculated.     

牛乳饮品中乳化剂的作用机理及其选用原则

本文阐述了乳化剂在牛乳饮品中的作用机理，并对影响牛乳饮品乳状液稳定性的因素进行了分析。在此基础上，提出了牛乳饮品中选择和使用乳化剂的依据和原则。     

Use of Electrodialysis to Improve the Protein Stability of Frozen Skim Milks and Milk Concentrates

Removal of calcium from skim milk by electrodialysis was logarithmically related to the extent of demineralization (log% calcium removed = 0.18% ash removed + 0.53). This removal of calcium caused a logarithmic dissociation of micellar to serum (sub-micellar) casein (log% total casein in serum = 0.020% calcium removed + 0.70). Increases in protein stability for skim milk and concentrated skim milk were related to this dissociation of micellar casein, and the initial degree of dissociation persisted throughout frozen storage. Protein stability was > 53 wk at –8°C when 80% of the casein in unconcentrated skim milk was dissociated. Concentrated skim milk was stable for > 30 wk at –8°C when 45% of the casein was dissociated. Control samples (7–9% casein dissociated) were stable for only 4–8 wk at –8°C.     

不同脂肪来源婴儿配方乳粉与母乳脂质组成的差异分析

研究4 种不同脂肪来源的婴儿配方乳粉与母乳在总脂肪酸、sn-2位脂肪酸及甘油三酯上的脂质组成差异。结果表明,从样品中共检测出27 种脂肪酸及87 种甘油三酯,与母乳相比,4 种婴儿配方乳粉含有更多的饱和脂肪酸,较少的多不饱和脂肪酸,且母乳中超过70%的饱和脂肪酸酯化在甘油三酯的sn-2位,而4 种婴儿配方乳粉甘油三酯sn-2位更多的被不饱和脂肪酸占据,尤其是植物油基IF1和IF2,sn-2位不饱和脂肪酸高达80%。在甘油三酯组成方面,母乳中1-油酸-2-棕榈酸-3-亚油酸甘油三酯、1,3-二油酸-2-棕榈酸甘油三酯及一些中长链甘油三酯显著高于4 种婴儿配方乳粉（P＜0.05）,而婴儿配方乳粉含有更多的三油酸甘油三酯、1-油酸-2,3-二亚油酸甘油三酯及一些中链甘油三酯（P＜0.05）,并且脂肪来源的不同会显著影响婴儿配方乳粉的脂质组成,同为植物油基的IF1和IF2具有更相似的甘油三酯、脂肪酸组成及分布,并与添加了乳脂成分的IF3和IF4形成明显区分,且牛乳/植物油混合基婴儿配方乳粉在整体脂质组成上更加接近母乳。最后,基于多变量分析,发现共有16 种甘油三酯可用于区分人乳和婴儿配方奶粉。本研究结果有助于研发更接近人乳的婴儿配方乳粉。     

不同嫩度羊肉肌浆蛋白质磷酸化水平随宰后成熟时间变化的研究

本文研究了不同嫩度羊肉肌浆蛋白磷酸化水平随宰后成熟时间的变化。取40只羊宰后0.5 h、1 h、4 h、12 h、24 h背最长肌样品,根据24 h剪切力和肌原纤维小片化指数分为高嫩度组和低嫩度组。采用SDS-PAGE电泳、荧光染色等方法,分析肌浆蛋白的磷酸化水平。研究结果表明在宰后24 h内肌浆蛋白磷酸化水平在不同嫩度和宰后成熟时间处理组之间差异显著(P0.05),低嫩度组的整体蛋白质磷酸化水平在宰后4 h达到最大,高嫩度组的整体蛋白质磷酸化水平在宰后12 h达到最大。宰后0.5 h、1 h、4 h低嫩度组的肌浆蛋白整体磷酸化水平显著高于高嫩度组(P0.05)。因此,肌浆蛋白磷酸化水平受不同嫩度和宰后成熟时间处理影响显著(P0.05),磷酸化可能通过对宰后肌肉糖酵解的作用影响宰后肌肉僵直进程,进而影响肌肉嫩度。     

不同冷藏时间牦牛乳中细菌群落结构和理化性质比较

低温贮藏有利于确保原料乳质量,然而也面临原料乳中嗜冷菌增多的风险,因此,了解不同冷藏时间原料乳中细菌群落结构变化对乳品工业持续发展具有重要意义。为此,该试验利用高通量测序技术和乳成分分析仪,分析和比较了4 ℃下贮藏24、72 h牦牛乳的细菌群落特征和理化特性。结果表明：冷藏24、72 h牦牛乳中第一、二优势菌属为乳球菌属、金黄杆菌属,该两类菌属的细菌分别占到冷藏24、72 h牦牛乳中细菌相对丰度的59.48%和67.51%。冷藏72 h牦牛乳中乳球菌属、金黄杆菌属相对丰度比冷藏24 h牦牛乳高出22.74%、3.56%,但是冷藏72 h牦牛乳中链球菌、不动杆菌属呈现降低趋势。冷藏24、72 h牦牛乳中假单胞菌属相对丰度较低,分别为1.69%和1.78%。冷藏72 h牦牛乳中酪蛋白、脂肪含量低于冷藏24 h牦牛乳,酸度增加到14.66 ºΤ。72 h的低温冷藏有助于控制牦牛乳细菌繁殖,维持乳品质。该研究为牦牛乳贮藏,干酪等乳制品加工,确保其品质和质量安全提供了理论依据。     

Concentration of Umami Compounds in Pork Meat and Cooking Juice with Different Cooking Times and Temperatures

This study examined the concentrations of umami compounds in pork loins cooked at 3 different temperatures and 3 different lengths of cooking times. The pork loins were cooked with the sous vide technique. The free amino acids (FAAs), glutamic acid and aspartic acid; the 5′‐nucleotides, inosine‐5′‐monophosphate (IMP) and adenosine‐5′‐monophosphate (AMP); and corresponding nucleoside inosine of the cooked meat and its released juice were determined by high‐performance liquid chromatography. Under the experimental conditions used, the cooking temperature played a more important role than the cooking time in the concentration of the analyzed compounds. The amino acid concentrations in the meat did not remain constant under these experimental conditions. The most notable effect observed was that of the cooking temperature and the higher amino acid concentrations in the released juice of meat cooked at 80 °C compared with 60 and 70 °C. This is most likely due to the heat induced hydrolysis of proteins and peptides releasing water soluble FAAs from the meat into the cooking juice. In this experiment, the cooking time and temperature had no influence on the IMP concentrations observed. However, the AMP concentrations increased with the increasing temperature and time. This suggests that the choice of time and temperature in sous vide cooking affects the nucleotide concentration of pork meat. The Sous vide technique proved to be a good technique to preserve the cooking juice and the results presented here show that cooking juice is rich in umami compounds, which can be used to provide a savory or brothy taste.     

不同质量浓度鲢鱼肌球蛋白低温自组装动力学及理化性质

以鲢鱼肌球蛋白为研究对象,通过粒径分布、激光共聚焦图像和浊度等指标比较不同质量浓度的肌球蛋白在低温下自组装动力学及理化性质,为提高其凝胶性能提供参考。结果表明：肌球蛋白在低温放置过程中会发生自组装,使浊度和粒径随放置时间延长及蛋白质量浓度增加而整体呈增大趋势;其自组装过程可分为成核、组装、平衡3 个阶段;质量浓度较低时（0.1～0.3 mg/mL）,自组装12 h即趋于平衡,当蛋白质量浓度大于等于0.5 mg/mL时,则需较长时间才能达到组装平衡。模型lgZ/270.0=（0.0182ρ+0.00679）t/2.303（ρ表示蛋白质量浓度/（mg/mL）;t表示组装时间/h;Z表示t时刻平均粒径/nm）可以很好地描述不同质量浓度肌球蛋白在低温自组装过程中粒径随放置时间的变化,提高质量浓度可促进分子间的相互作用,组装速率和尺寸也随之增大,当蛋白质量浓度高于0.5 mg/mL时,形成了激光共聚焦显微镜可观察到的组装体,肌球蛋白快速自组装的临界质量浓度是0.5 mg/mL。     

不同脂肪来源婴儿配方奶粉与母乳的甘油酯组成差异

对5 种脂质来源婴儿配方奶粉（infant formula powder,IFP）与母乳（human milk,HM）在甘油酯组成上进行比较研究。结果表明：不同脂肪来源的IFP与HM在脂肪组成、组分比例上有显著差异,HM中甘油二酯（diglyceride,DG）相对含量高达（7.84±0.57）%,显著高于IFP的最高对应值（1.26±0.22）%（P＜0.05）,其中DG(18∶2/18∶2)和DG(18∶1/18∶1)是HM中含量最高的DG种类,二者共占HM总DG的80%以上;在甘油三酯（triglyceride,TG）组成上,虽目前IFP已添加1,3-二油酸-2-棕榈酸甘油三酯成分,但TG(16∶0/18∶1/18∶1)相对含量（最高（6.70±0.19）%）仍显著低于HM对应值（（7.92±0.58）%）（P＜0.05）,同时,IFP中TG(16∶1/17∶2/22∶6)相对含量最低为（3.68±0.67）%,显著高于HM（0.02±0.01）%（P＜0.05）,这说明IFP中C22∶6的主要存在形式与HM不同。虽然目前IFP在主要脂肪酸组成上接近HM,但其在脂肪酸的存在形式上仍与HM存在明显不同。