高粱醇溶蛋白-卡拉胶复合纳米颗粒负载姜黄色素的特性研究

本研究以姜黄色素为芯材,高粱醇溶蛋白为壁材,卡拉胶自组装,采用反溶剂法制备负载姜黄色素的中空和实心复合纳米颗粒,并对其理化性质及体外消化特性进行研究。结果表明,制备中空(C-HNP)和实心纳米颗粒(C-SNP)的最佳芯壁比为1∶10,其粒径约为71 nm和135 nm,电位为-37.7 mV和-38.2 mV,包埋率为89.6%和84.1%,负载率为8.01%和7.49%。透射电镜显示两种纳米粒子呈规则的球形形态,C-HNP具有内部中空结构。红外光谱结果显示复合颗粒中酰胺峰Ⅰ和Ⅱ均发生蓝移,卡拉胶和姜黄色素一些吸收峰发生相应偏移,说明它们与蛋白质分子发生相互作用。体外消化模拟实验显示复合纳米颗粒显著地增加了姜黄色素的体外溶解释放率,C-HNP具有更高的控释能力。结果表明,高粱醇溶蛋白是一种适合疏水性分子包埋与控释的生物原材料。     

Effect of kafirin protein coating on sensory quality and shelf-life of 'Packham's Triumph' pears during ripening

BACKGROUND: Pears are exported in large quantities from South Africa, resulting in large revenues. Minimisation of quality losses once the fruit has reached the export destination is as important as following strict export and distribution protocols. Kafirin can form edible films. In this study an edible coating made from 20 g kg^?1 kafirin coating solution was applied as a postharvest treatment to retard quality deterioration of ‘Packham's Triumph’ pears during storage at the typical ripening temperature (20 °C). Changes in physicochemical and sensory quality were monitored over a period of 24 days. RESULTS: The kafirin coating was unable to retard the onset of ripening but decreased the respiration rate and retarded the progression of senescence. However, moisture loss was exacerbated in the kafirin‐coated fruit during ripening at 20 °C, especially towards the end of the shelf‐life. CONCLUSION: The kafirin coating extended the eat‐ripe quality of the pears by 1–2 weeks. However, the appearance of the fruit was unacceptable after 14 days of storage in terms of wrinkled skin. Further work is needed to improve the water barrier properties of the kafirin coating by incorporating a wax or triglyceride into the coating formulation or more simply by applying a kafirin coating to waxed fruit. Copyright © 2011 Society of Chemical Industry     

牛至精油-白藜芦醇乳液的制备及抑菌活性研究

基于牛至精油具有较强的刺激性气味、白藜芦醇溶解性低,以及二者稳定性差的应用缺陷,构建以酪蛋白酸钠为乳化剂,菊粉和阿拉伯胶为稳定剂,牛至精油为油相并包埋白藜芦醇的乳液;以鼠伤寒沙门氏菌为目标微生物,探讨牛至精油、白藜芦醇、牛至精油-白藜芦醇及其乳液的抑菌效果,以及4,25℃储藏期间抑菌效果的变化,并在鲜切卷心菜中初步应用。结果表明:牛至精油和白藜芦醇对鼠伤寒沙门氏菌有很好的协同抑菌作用;2.0%菊粉/阿拉伯胶可以提高牛至精油-白藜芦醇的抑菌效果;乳液可降低二者的氧化降解速率并保护其生物活性,乳液4℃贮藏20d,25℃贮藏12d后仍有较好的抑制作用。接种鼠伤寒沙门氏菌的鲜切卷心菜在牛至精油-白藜芦醇及其酪蛋白酸钠、酪蛋白酸钠-菊粉/阿拉伯胶乳液中处理1min,8℃储藏4d后菌落数分别降低了1.52,2.04,2.67,2.98lg CFU/g。     

Effect of beta-lactoglobulin A and B whey protein variants on the rennet-induced gelation of skim milk gels in a model reconstituted skim milk system

The effect of fortifying reconstituted skim milk with increasing levels of the β-lactoglobulin (β-LG) genetic variants A, B, and an A-B mixture on rennet-induced gelation was studied by small deformation-sensitive rheology. Free-zone capillary electrophoresis and high-sensitivity oscillatory rheology were used to elucidate the role of potential heterotypic associative interactions between whey proteins and casein in a mixed colloidal system, subjected to moderate heating (65°C for 30 min) prior to renneting, on the gelling properties of the system. Increasing levels of added whey protein, in the concentration range of 0.225 to 1.35% of added protein, led to a concomitant progressive increase in the equilibrium shear storage modulus, G′ (recorded after ∼10,800 s), in the order β-LG B > β-LG A and β-LG A-B, as the general expected consequence of the setup of denser casein gel networks. The preferential effect of β-LG B over β-LG A on the mechanical strength of the gels may be due to the formation of cross-links and aggregates involving whey proteins and rennet hydrolysis products or an increase in the size of the casein micelle caused by the grafting of β-LG B to its surface, or both. The results of free-zone capillary electrophoresis were consistent with the notion that β-LG B (and not β-LG A) binds to the casein micelle under an optimal stoichiometry of 1:0.045 (mg/mg), even in the absence of heat treatment. The liquid-like character of the gel networks formed, tan δ, was a parameter sensitive to the level of addition of β-LG A in particular. At low concentrations (up to 0.45%) of β-LG A, tan δ increased by almost twice as much, which was interpreted as a result of the increase in the loss modulus, G″, of the sol fraction because of the presence of unbound β-LG A. At greater incremental concentrations of β-LG (>0.45%), the formation of smaller whey protein aggregates confined to the sol fraction may have led to a progressive decrease in tan δ. The critical gel time, t_gel, was also affected by the concentration of added whey protein and described 3 zones of behavior, irrespective of the type of whey protein variant. The critical gel time was slightly shorter for β-LG B than for β-LG A at 0.45% of added whey protein, but this difference became larger at 0.67%. Even when only β-LG B was found to associate with casein prior to renneting, both β-LG A and β-LG B, either alone or mixed, had a profound influence on the mechanical strength and coagulation kinetics of the rennet-induced casein gels. This knowledge is expected to be useful to exert better control and optimize processing conditions during the manufacturing of cheese and cheese analogs.     

High-pressure-induced interactions between milk fat globule membrane proteins and skim milk proteins in whole milk

The association of beta-lactoglobulin (beta-LG) and alpha-lactalbumin (alpha-LA) with milk fat globule membrane (MFGM), when whole milk was treated by high pressure in the range 100 to 800 MPa, was investigated using sodium dodecyl sulfate (SDS)-PAGE under reducing and nonreducing conditions. In SDS-PAGE under reducing conditions, beta-LG was observed in the MFGM material isolated from milk treated at 100 to 800 MPa for 30 min, and small amounts of alpha-LA and kappa-casein were also observed at pressures >600 MPa for 30 min. However, these proteins were not observed in SDS-PAGE under nonreducing conditions. These results indicate that beta-LG and alpha-LA associated with MFGM proteins via disulfide bonds during the high-pressure treatment of whole milk. The amount of beta-LG associated with the MFGM increased with an increase in pressure up to 800 MPa and with increasing time of pressure treatment. The maximum value for beta-LG association with the MFGM was approximately 0.75 mg/g of fat. Of the major original MFGM proteins, no change in butyrophilin was observed during the high-pressure treatment of whole milk, whereas xanthine oxidase was reduced to some extent beyond 400 MPa. In contrast to the behavior during heat treatment, PAS 6 and PAS 7 were stable during high-pressure treatment, and they remained associated with the MFGM.     

Beta-lactoglobulin is a thermal marker in processed milk as studied by electrophoresis and circular dichroic spectra

As much of the sterilization process involves heat treatment during the preparation of milk on an industrial scale, the unpredictable measures of the process are an essential issue in determining the quality of the milk. The purpose of the present study was to investigate the major protein change(s) of whey proteins in processed milk and extend the knowledge for future reference in the dairy industry. Using a native polyacrylamide gel electrophoresis, we showed almost a 90% loss and denaturation of beta-lactoglobulin (LG), but not alpha-lactalbumin (LA), in some brands of the processed and dry milks. Immunochemical analysis using Western blotting revealed that part of the loss was attributed to the formation of large multiple forms of LG in the processed product. Such denaturation was presumably associated with the heating procedure used in the process. Essentially, LG was the only major fraction converted to aggregates in milk heated at 95 degrees C for 30 min on 2-dimensional PAGE. The detailed thermal denaturation of purified LG and LA at various temperatures (50 to 95 degrees C) and time (5 to 960 s) were investigated using a circular dichroic analysis. The maximal changes of ellipticity at 205 nm (converting beta-structure to disordered structure) were correlated to heating temperature and time. There were no significant conformational changes of LG at temperatures below 70 degrees C for as long as 480 s. Pronounced and rapid changes occurred between 80 to 95 degrees C in a time-dependent manner. Fifty percent of the maximal changes could be reached within 15 s. In conclusion, the unique chemical and immunochemical loss and conformational changes made LG a superior marker for evaluating the thermal processing of milk. The detailed thermal denaturation curves of LG constructed with its time and temperature in this study provide a valuable reference for the dairy industry. We postulate that heat treatment over 80 degrees C in 15 s may induce a significant denaturation of milk LG.     

Whole-genome association study for milk protein composition in dairy cattle

Our objective was to perform a genome-wide association study for content in bovine milk of α_S1-casein (α_S1-CN), α_S2-casein (α_S2-CN), β-casein (β-CN), κ-casein (κ-CN), α-lactalbumin (α-LA), β-lactoglobulin (β-LG), casein index, protein percentage, and protein yield using a 50K single nucleotide polymorphism (SNP) chip. In total, 1,713 Dutch Holstein-Friesian cows were genotyped for 50,228 SNP and a 2-step association study was performed. The first step involved a general linear model and the second step used a mixed model accounting for all family relationships. Associations with milk protein content and composition were detected on 20 bovine autosomes. The main genomic regions associated with milk protein composition or protein percentage were found on chromosomes 5, 6, 11, and 14. The number of chromosomal regions showing significant (false discovery rate <0.01) effects ranged from 3 for β-CN and 3 for β-LG to 12 for α_S2-CN. A genomic region on Bos taurus autosome (BTA) 6 was significantly associated with all 6 major milk proteins, and a genomic region on BTA 11 was significantly associated with the 4 caseins and β-LG. In addition, regions were detected that only showed a significant effect on one of the milk protein fractions: regions on BTA 13 and 22 with effects on α_S1-CN; regions on BTA 1, 9, 10, 17, 19, and 28 with effects on α_S2-CN; a region on BTA 6 with an effect on β-CN; regions on BTA 13 and 21 with effects on κ-CN; regions on BTA 1, 5, 9, 16, 17, and 26 with effects on α-LA; and a region on BTA 24 with an effect on β-LG. The proportion of genetic variance explained by the SNP showing the strongest association in each of these genomic regions ranged from <1% for α_S1-CN on BTA 22 to almost 100% for casein index on BTA 11. Variation associated with regions on BTA 6, 11, and 14 could in large part but not completely be explained by known protein variants of β-CN (BTA 6), κ-CN (BTA 6), and β-LG (BTA 11) or DGAT1 variants (BTA 14). Our results indicate 3 regions with major effects on milk protein composition, in addition to several regions with smaller effects involved in the regulation of milk protein composition.     

Formation of electrostatic complexes using sodium caseinate with high‐methoxyl pectin and carboxymethyl cellulose and their application in stabilisation of curcumin

Despite many reported bioactivities of curcumin, its application is limited due to its low bioavailability, solubility and stability. Proteins have been reported to stabilise curcumin in aqueous media, and stabilisation of curcumin could be enhanced when proteins form an electrostatic complex with polysaccharides. In this study, electrostatic complexes of sodium caseinate (NaCas) were prepared using high‐methoxyl pectin (HMP and NaCas‐HMP) and carboxymethyl cellulose (CMC and NaCas‐CMC). NaCas to polysaccharide ratio of 1:2 resulted in the lowest turbidity and sedimentation. The electrostatic complexes were more stable than native NaCas against pH change and ionic strength. Binding of curcumin to NaCas and the electrostatic complexes were confirmed by UV‐vis and fluorescence spectra and Fourier transform infrared spectroscopy (FT‐IR). The electrostatic complexes showed a higher binding constant and protected curcumin better than the native NaCas. This study suggests that the electrostatic complexes may be a superior carrier to NaCas at an acidic environment.     

Antioxidant nature of bovine milk beta-lactoglobulin

Heating is necessary for processing milk in the dairy industry, which evidently produces a conformational change in β-lactoglobulin (β-LG). β-Lactoglobulin, a major protein that accounts for approximately 10 to 15% of total milk proteins, is a globular protein consisting of 162 AA with a relative molecular mass of 18.4 kDa. The purpose of the present study was to determine the antioxidant role of β-LG in milk and the possible mechanism involved. We showed that β-LG is a mild antioxidant whose potency is less than that of vitamin E and probucol (the latter being an antioxidant used for clinical therapy). The conversion of the β-LG monomer to dimer was responsible, in part, for the mode of action in protecting low-density lipoproteins against copper-induced oxidation. Cross-linking the free thiol groups of β-LG by heating (100°C for 2 min), or chemically modifying the β-LG by carboxymethylation to block the thiol groups resulted in a substantial loss of antioxidant activity. The data suggest that Cys-121 plays an essential role in the antioxidant nature of β-LG. By using an anti-LG antibody affinity column to deplete the β-LG from milk, we observed from the lost antioxidant activity that β-LG contributes approximately 50% of the total activity. Because β-LG is extremely sensitive to thermal denaturation, to maintain its antioxidant nature, dairy products consumed daily should not be overheated in order to maintain its antioxidant nature.     

Distinction between dry and raw milk using monoclonal antibodies prepared against dry milk proteins

It is well established that the heating process during the preparation of dry milk (DMLK) causes structural changes in some milk proteins. However, because such changes are subtle, whether they can be detected by an immunochemical approach remains questionable. The present study attempted to develop a sensitive mAb that might distinguish the DMLK from freshly prepared raw milk. To test this possibility, we immunized mice with commercially prepared DMLK and produced a panel of mAb. From 900 hybridomas screened using an ELISA, 4 clones were found to be specific to DMLK; the other 68 clones recognized both DMLK and raw milk. In contrast to polyclonal antibodies, only the specific mAb could detect the DMLK spiked into the raw milk at as low as 5% in concentration (vol/vol). Western blot analysis shows that these specific mAb were all directed against beta-lactoglobulin (LG) and LG-milk protein conjugates. These mAb reacted with raw milk heated at 95 degrees for 15 min; the reaction with LG-conjugates, however, was abolished when treated with reducing reagent. Thus, results suggests that a new antigenic epitope was exposed in a heating process, and the thio group of LG cross linked with other protein moiety played a provocative role in mAb recognition. A hypothetical model with respect to the interaction between the mAb and DMLK is proposed and discussed.     

Fluorescent labeling study of plasminogen concentration and location in simulated bovine milk systems

A fluorescent labeling method was developed to study plasminogen (PG) concentration and location in simulated bovine milk. Activity and stability of PG labeled with Alexa Fluor 594 (PG-594) were comparable to those of native PG. The fluorescent signal of PG-594 exhibited pH, temperature, and storage stability, and remained stable throughout typical sample treatments (stirring, heating, and ultracentrifugation). These characteristics indicate broad applicability of the fluorescent labeling technique for milk protease characterization. In an example application, PG-594 was added to simulated milk samples to study effects of heat and β-lactoglobulin (β-LG) on the distribution of PG. Before heating, about one-third of the PG-594 remained soluble in the whey fraction (supernatant) whereas the rest became associated with the casein micelle. Addition of β-LG to the system slightly shifted PG-594 distribution toward the whey fraction. Heat-induced PG-594 binding to micelles in whey-protein-free systems was evidenced by a decrease of PG-594 from 31 to 15% in the whey fraction accompanied by an increase of PG-594 from 69 to 85% in casein micelle fractions. When β-LG was present during heating, more than 95% of PG-594 became associated with the micelle. A comparison with the distribution pattern of PG-derived activities revealed that heat-induced PG binding to micelles accompanies heat-induced PG inactivation in the micelle fraction. Incubation of the casein micelles with the reducing agent β-mercaptoethanol revealed that disulfide bonds formed between PG and casein or between PG and casein-bound β-LG are the mechanisms for heat-induced PG binding to casein micelles. Western blotting and zymography results correlated well with fluorescent labeling studies and activity studies, respectively. Theoretically important findings are: 1) when heated, serum PG is capable of covalently binding to micellar casein or complexing with β-LG in whey and then coadhering to micelles, and 2) PG that associated with micellar casein through lysine binding sites before heating is capable of developing heat-induced disulfide bonds with casein. The overall results are PG covalently binding to micelles and inactivation thereafter. Our results suggest that, instead of thermal denaturation through irreversible unfolding, covalent bond formation between PG and other milk proteins is the mechanism of PG inhibition during thermal processing.     

Functional improvement of milk whey proteins induced by high hydrostatic pressure

High pressure is emerging as a new processing technology that produces particular changes in the molecular structure of proteins and thus gives rise to new properties inaccessible via conventional methods of protein modification. This review deals with the main effects of high hydrostatic pressure on the physicochemical characteristics of milk whey proteins and how modifications in their structural properties contribute to functionality. In this paper the mechanism underlying pressure-induced changes in ss-lactoglobulin, a-lactabumin, and bovine serum albumin is explained, and related to functional properties such as gel-forming ability, emulsifying activity, or foaming capacity. The possibility of using high pressures to favor chemical reactions of proteins with other food components, such as carbohydrates, to produce novel molecules with new food uses is also considered.     

反相高效液相色谱法测定不同品种花生白藜芦醇含量

以珍珠红1号、花育20、花育22、花育31号为原料,采用反相高效液相色谱法(RP-HPLC)测定花生各部位中白藜芦醇含量。测定结果表明,不同品种花生其白藜芦醇含量不同,且花生各部位含量也有所不同;其中珍珠红1号花生根白藜芦醇含量最高,为90.37μg/g。该法回收率98.08%,RSD 2.01%,操作简便、结果准确可靠。     

不同溶剂提取葡萄酒中白藜芦醇及其糖苷异构体

利用白藜芦醇及其糖苷异构体几乎不溶于水,易溶于有机溶剂的性质,比较了乙酸乙酯、氯仿、乙醚,乙酸乙酯与正己烷、二氯甲烷混合溶液及双水相体系对葡萄酒中白藜芦醇及其糖苷异构体的提取效果,得到了最佳的提取溶剂。结果表明:乙酸乙酯对目标化合物的提取效果优于其他有机溶剂,对白藜芦醇苷的提取率可达90%以上,对白藜芦醇的提取率低于80%。乙酸乙酯萃取操作简单、提取率较高,切实可行。      

激素诱导和非生物胁迫对虎杖根中白藜芦醇含量影响及虎杖根中白藜芦醇闪提工艺优化

用紫外辐射和水杨酸、乙烯利、H2O2溶液对新鲜虎杖根进行处理,探究其对新鲜虎杖根中白藜芦醇含量的影响。采用闪式提取法从虎杖根中提取白藜芦醇,在单因素实验的基础上进行正交实验探究最佳提取工艺条件,用HPLC对白藜芦醇进行定性定量分析。结果表明:紫外辐射15 min,暗处理24 h后虎杖根中白藜芦醇的含量达到最大值,较辐射前提高了72%。10 mmol/L水杨酸溶液浸泡24 h后虎杖根中的白藜芦醇含量提升到原来的4倍多。5%H2O2溶液浸泡24 h后虎杖根中白藜芦醇含量上升了34%。而乙烯利溶液浸泡则会降低白藜芦醇的含量。闪式提取法提取虎杖根中白藜芦醇的最佳工艺条件是:提取温度50℃,提取时间60 s,乙醇浓度80%,料液比例1∶30 g/m L,在此条件下,白藜芦醇得率为0.1877%。      

Effect of sesame protein isolate in partial replacement of milk protein on the rheological,textural and microstructural characteristics of fresh cheese

Soft cheeses were manufactured from bovine milk with the addition of 0–12% sesame protein isolate (SPI) were utilised to investigate rheology, texture and microstructure at different stages of cheese making. SPI addition reduced the speed of milk fermentation, kappa‐casein proteolysis of rennet and elongated the time of cheese curd formation. Renneted milk storage modulus G′_60min was decreased and coagulation time increased with increasing SPI content. Low SPI supplements (4% and 8%) enhanced the hardness, cohesiveness, adhesiveness and gumminess of the soft cheese, while high SPI addition (12%) deteriorated the texture. In the cheese curd gel matrix, SPI distributed as specific SPI‐gel clusters on the surface of curd fractures, stacked or fused with ball‐shaped casein micelles and wrapped up to casein gel strands. In summary, SPI actively interacted with casein colloid throughout the cheese making process.