鲢鱼鱼糜在冻藏过程中理化特性的变化

研究了鲢鱼鱼糜在-10℃与-20℃冻藏过程中盐溶性蛋白含量、Ca2+-ATPase活性及保水性的变化。结果表明,三项指标在冻藏过程中都显著下降,且呈现二段下降规律;三项指标的变化之间呈现一定的相关性;SDS-PAGE电泳显示,鲢鱼鱼糜蛋白在冻藏过程中形成了二硫键。     

酸碱处理对鲢鱼肌原纤维蛋白热变性、聚集、胶凝性质的影响

酸碱法(pH-shifting)提取鱼蛋白是鱼糜加工新丁艺,能提高蛋白得率.酸碱法中极端pH(2.3和11.8)对肌原纤维热变性、热聚集、热致胶凝特性有很大影响.酸碱处理使肌原纤维部分变性,其中酸处理使肌原纤维肌球蛋白完全变性,肌动蛋白变性温度F降(从8l℃降低到77.6℃),碱处理使肌动和肌球变性温度都下降:酸碱处理使肌原纤维发牛聚集,酸处理肌原纤维发牛聚集最严重;酸碱处理使肌原纤维胶凝过程发生明显变化,凝胶强度明显降低,其中酸处理肌原纤维凝胶强度最低(最大储能模量分别为1150、25、135Pa).所以,鱼糜pH-shifting工艺用碱法更合适.     

选择不同提取剂制备斑点叉尾鲴鱼皮胶原蛋白的研究

选择不同提取剂对斑点叉尾鲴鱼皮胶原蛋白进行制备,并对胶原蛋白进行了部分定性研究。实验结果表明,4℃条件下,鲴鱼鱼皮先用0．1mol／LNaOH浸泡6h再用2．5％NaCl浸泡6h,比单独或同时使用NaOH、NaCl能更好的去除杂蛋白,用10％的异丙醇溶液去除脂肪,用0．1mol／L柠檬酸浸提3d能较好的提取胶原蛋白,无色无味,提取率可达34．67％。获得的胶原蛋白中甘氨酸含量丰富,质量分数为21．19％,其变性温度为50．2℃。SDS．PAGE实验结果表明,提取的鲴鱼皮酸溶胶原具有较高的纯度,含有两条α链,β链含量较高。鱼皮胶原蛋白溶液具有较高的黏度,且随着蛋白浓度的增大而增大。     

Physicochemical properties of lactoferrin stabilized oil-in-water emulsions: Effects of pH,salt and heating

Lactoferrin is a globular protein from bovine milk with an unusually high isoelectric point (pI > 8), which may lead to novel functional properties in foods and other products because it is cationic across a wide pH range. In this study, we investigated the influence of pH (2–9), NaCl addition (0–200 mM), CaCl₂ addition (0–200 mM), and thermal processing (30–90 °C, 20 min) on the stability of lactoferrin (LF) stabilized oil-in-water emulsions. At ambient temperature, the emulsions were stable to droplet aggregation at low pH (pH ≤ 6), but exhibited some aggregation at pH ≈ pI (pH 7–9). The thermal stability of the emulsions depended on pH, holding temperature, and thermal history. When LF-coated droplets were heated in distilled water, and then their pH was adjusted in the range 2–9, they were highly unstable to aggregation at pH 7 and 8. On the other hand, when the pH was altered in the range 2–9 first, and then they were heated, the LF-coated droplets were highly unstable to aggregation at pH ≥ 5 when heated above 50 °C. The stability of the emulsions to salt addition depended on pH and salt type, which was attributed to counter-ion binding and electrostatic screening effects. For NaCl, emulsions were stable from 0 to 200 mM at pH 3 and 9, but aggregated at ≥100 mM at pH 6. For CaCl₂, emulsions were stable from 0 to 200 mM at pH 3, but aggregated with ≥150 mM CaCl₂ at pH 6 and 9. These results have important implications for the formulation and production of emulsion-based products using lactoferrin as an emulsifier.     

SDS-PAGE法检测动物肌肉蛋白质加热终点温度的研究

为了探索检测动物组织蛋白质热变性程度的方法,分别对猪、牛、羊、鸡、鱼五种新鲜动物肌肉组织进行不同温度的热处理（新鲜未加热、50、60、70、80、90、100℃）,对处理后的样品提取蛋白质进行十二烷基磺酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）分析。结果显示,同种动物组织经不同温度热处理,所得电泳图谱具有较大差异,电泳条带的数量随温度的升高逐渐减少,猪、牛、羊三种动物肌肉组织加热到80℃后,电泳图谱不再变化,达到加热终点温度;鸡和鱼的肌肉组织加热到70℃后,电泳图谱不再变化,达到加热终点温度。不同种动物组织经相同温度热处理所得电泳图谱显示：猪、牛、羊三种动物组织蛋白质的电泳图谱相似,与鸡和鱼组织蛋白质的电泳图谱差异显著。     

Effect of pasteurization on membrane proteins and oxidative stability of oil bodies in various crops

Oil bodies (OBs) are natural pre-emulsion systems and an ideal green food additive. However, their proclivity to oxidation limits the applications of OBs. In this study, the effect of pasteurization (85 and 125 °C; 1 min) on membrane proteins and the oxidative stability of various OBs (soybean, sunflower, peanut, sesame, and walnut) were investigated. The membrane proteins are extracted from the OBs. The ultrahigh-temperature pasteurization (125 °C, 1 min) eliminated lipoxygenase of soybean and peanut OBs. Furthermore, oleosin exhibited a higher denaturation temperature (approximately 100 °C) than extrinsic proteins (approximately 50 °C). Pasteurization induced the conversion of the α-helix structure to a disordered structure by rearranging the hydrogen bonds. The pasteurized soybean and peanut OBs exhibited a high oxidative stability owing to their stable membrane structures and decreased lipoxygenase activity, while sunflower, sesame, and walnut OBs did not exhibit good oxidative stability because of their vulnerable membranes, a large number of unsaturated fatty acids, and severe aggregation of droplets. Simulated milk based on pasteurized soybean and peanut OBs (125 °C, 1 min) maintained outstanding storage stability. These results confirmed that pasteurized soybean and peanut OBs have the potential as a skim milk additive for the benefit of the consumer.     

Mechanism of inhibition of rice bran lipase by polyphenols: a case study with chlorogenic acid and caffeic acid

ABSTRACT:  Rice bran is a byproduct obtained from the rice milling industry, and to arrest lipolysis caused by lipolytic enzyme, rice bran lipase (RBL) was inactivated by inhibitors such as polyphenols. This study describes the inhibition and interaction of enzyme with chlorogenic acid (CGA) and caffeic acid (CA). The inhibition of the enzyme was competitive in nature in both CGA and CA. The inhibition constant K _i of the reaction was found to be 1.8 and 1.5 μM for CGA and CA, respectively. Fluorescence emission measurements indicated a decrease in the fluorescence emission intensity and a red shift in the emission maximum as these ligands concentrations are increased, indicating the minor changes in the tryptophan environment and the effect of binding that is stronger in the case of CA compared to CGA with RBL. Far UV-circular dichroic data suggest that there are no significant changes in the conformation of the enzyme as a result of binding of CGA or CA. The instability of the enzyme in the presence of these polyphenols has been indicated by decrease in apparent thermal transition temperatures of the enzyme from a control value of 60 °C as revealed by thermal denaturation measurements. These results demonstrate that both CGA and CA are inhibitors of RBL and bind to the enzyme through both hydrogen and hydrophobic interaction in bringing about inhibition with minor structural alterations. These inactivation phenomena of polyphenols that act as inhibitors on RBL can be utilized to prevent oxidation of the rice bran oil.     

Soybean Protein Dispersions at Acid pH. Thermal and Rheological Properties

The influence of pH, protein concentration, and ionic strength, on rheological properties of thermally treated acidic soy protein dispersions, was studied. Structural changes due to pH effect and thermal treatment were analized. DSC-thermograms at pH 3.5 showed a shoulder at 74.11±0.16°C that could be attributed to both β-conglycinin and the hexameric form of glycinin; and a peak at 81.88±0.29°C corresponding to 11S dodecameric form. At pH 2.75 one endotherm corresponded to denaturation of β-conglycinin. The acidic dispersions presented pseudoplastic behavior with_app values higher than those at pH 8.0. At pH 3.50 the ±_app was higher than at pH 2.75.The maximum viscoelasticiy was obtained with addition of 0.1 and 0.25M NaCl in the dispersions of pH 3.50 and 2.75, respectively. The increase in viscoelasticity was enhanced by the formation of 11S native fraction dimers.     

Sarcoplasmic proteins influence water-holding capacity of pork myofibrils

Water-holding capacity (WHC) is one of the main pork quality characteristics. The objective of this study was to determine the influence of (denaturation of) sarcoplasmic proteins on WHC. Myofibrils extracted from red, firm, non-exudative (‘normal’) and PSE (pale, soft, exudative) pork longissimus muscle were combined with sarcoplasmic extracts (with or without proteins) from PSE and normal pork longissimus samples. Weight increase of myofibrils (mg increase mg⁻¹ myofibrillar protein) was used as a measure of WHC. When combined with protein-containing sarcoplasmic extract from normal pork, WHC of myofibrils from PSE (2.6 mg mg⁻¹) and normal (2.8 mg mg⁻¹) pork was higher (P < 0.05) than when combined with sarcoplasmic extract from PSE meat (1.3 mg mg⁻¹ for PSE and 1.9 mg mg⁻¹ for normal myofibrils). Protein-free sarcoplasmic extracts were prepared by heating the extracts for 30 min at 80 °C. WHC of myofibrils combined with protein-free sarcoplasmic extract from PSE and normal pork was not significantly different. WHC of myofibrils combined with protein-free extract was lower than WHC of myofibrils combined with protein-containing extract. Ionic strength or pH could not explain the observed differences. It was concluded that sarcoplasmic proteins do influence WHC. The mechanism of this influence still needs to be determined. © 1999 Society of Chemical Industry