共查询到20条相似文献,搜索用时 31 毫秒
1.
Doucet D Gauthier SF Otter DE Foegeding EA 《Journal of agricultural and food chemistry》2003,51(20):6036-6042
Extensive hydrolysis of whey protein isolate by Alcalase 2.4L produces a gel. The objectives of this study were to compare enzyme-induced gelation with the plastein reaction by determining the types of interactions involved in gelation. The average chain length of the peptides did not increase during hydrolysis and reached a plateau after 30 min to be approximately 4 residues, suggesting that the gel was formed by small molecular weight peptides held together by non-covalent interactions. The enzyme-induced gel network was stable over a wide range of pH and ionic strength and, therefore, showed some similarities with the plastein reaction. Disulfide bonds were not involved in the gel network. The gelation seems to be caused by physical aggregation, mainly via hydrophobic interactions with hydrogen bonding and electrostatic interactions playing a minor role. 相似文献
2.
Otte J Lomholt SB Halkier T Qvist KB 《Journal of agricultural and food chemistry》2000,48(6):2443-2447
The purpose of the present study was to identify the peptides responsible for aggregate formation during hydrolysis of beta-lactoglobulin by BLP at neutral pH. Hydrolysates taken at various stages of aggregate formation were separated into a precipitate and a soluble phase and each was analyzed by CE and mass spectrometry. The aggregates consisted of six to seven major peptides of which four were tentatively identified. The peptides were positively charged at neutral pH and had a high charge-to-mass ratio at low pH. The fragment f135-158 seemed to be the initiator of aggregation, since it was present at high concentration in the aggregates at all stages, and the concentration of this peptide remained low in the supernatant. F135-158 contains several basic and acid amino acids alternating with hydrophobic amino acids, which is in accordance with formation of noncovalently linked aggregates, as previously shown. 相似文献
3.
Guyomarc'h F Renan M Chatriot M Gamerre V Famelart MH 《Journal of agricultural and food chemistry》2007,55(26):10986-10993
Changes in the acid gelation properties of skim milk as a result of variations in the micelle/serum distribution of the heat-induced whey protein/kappa-casein aggregates, induced by the combination of heat treatment and limited renneting, were investigated. No dramatic change in the zeta potential or the isoelectric point of the casein micelles was suggested, whether the aggregates were all attached to the casein micelle or not. Fluorescence intensity measurement using 8-anilino-1-naphthalenesulfonic acid (ANS) showed that the heat-induced aggregates were highly hydrophobic. Dynamic oscillation viscosimetry showed that acid gelation using glucono-delta-lactone (GDL) started at a higher pH value in prerenneted milk. However, no change in the gelation profile of skim milk could be related to the proportion of aggregates bound to the surface of the casein micelles. The results support the idea of an early interaction between the serum aggregates and the casein micelles on acidification. 相似文献
4.
Alting AC de Jongh HH Visschers RW Simons JW 《Journal of agricultural and food chemistry》2002,50(16):4682-4689
pH-Induced cold gelation of whey proteins is a two-step process. After protein aggregates have been prepared by heat treatment, gelation is established at ambient temperature by gradually lowering the pH. To demonstrate the importance of electrostatic interactions between aggregates during this latter process, beta-lactoglobulin aggregates with a decreased iso-electric point were prepared via succinylation of primary amino groups. The kinetics of pH-induced gelation was affected significantly, with the pH gelation curves shifting to lower pH after succinylation. With increasing modification, the pH of gelation decreased to about 2.5. In contrast, unmodified aggregates gel around pH 5. Increasing the iso-electric point of beta-lactoglobulin via methylation of carboxylic acid groups resulted in gelation at more alkaline pH values. Comparable results were obtained with whey protein isolate. At low pH disulfide cross-links between modified aggregates were not formed after gelation and the gels displayed both syneresis and spontaneous gel fracture, in this way resembling the morphology of previously characterized thiol-blocked whey protein isolate gels (Alting, et al., J. Agric. Food Chem. 2000, 48, 5001-5007). Our results clearly demonstrate the importance of the net electric charge of the aggregates during pH-induced gelation. In addition, the absence of disulfide bond formation between aggregates during low-pH gelation was demonstrated with the modified aggregates. 相似文献
5.
Interactions between alpha-lactalbumin (alpha-La) and ovalbumin (OVA) in mixed systems (1:1 ratios; 2, 4, and 8% w/w total protein, respectively) heated at pH 7 and 80 degrees C for 15 min were studied using sodium dodecyl sulfate--polyacrylamide gel electrophoresis (SDS-PAGE), gel filtration chromatography (GFC), and competitive enzyme-linked immunosorbent assay (ELISA). Although alpha-La alone did not form aggregates upon heating, it formed large aggregates when heated with OVA. The aggregated molecules eluted at the void volume had a molecular mass >300 kDa. The aggregation process was quantitatively affected by different avian OVAs from five species, possessing different numbers of free sulfhydryl groups. The amount of aggregates (M(w) > 300 kDa) increased in proportion to total protein concentration, and the amount of intermediate components (M(w) < 300 kDa) and monomeric OVA and alpha-La also changed, correlating with total protein concentration during heating. The results also indicated that the aggregates and intermediates, which contained dimeric and trimeric alpha-La, were mainly formed by the intermolecular disulfide bonds. The different interactions observed in several avian OVAs may explain heat-induced gelation of various avian OVAs as well as the enhancement of heat-induced gelation of OVA by alpha-La. 相似文献
6.
Guyomarc'h F Queguiner C Law AJ Horne DS Dalgleish DG 《Journal of agricultural and food chemistry》2003,51(26):7743-7750
Gel formation was monitored by low amplitude rheometry during acidification at 40 degrees C with 1.5% glucono-delta-lactone in combined milk systems containing soluble and/or micelle-bound heat-induced (95 degrees C/10 min) aggregates of denatured whey proteins and kappa-casein and in heated dairy mixes with varying micellar casein/whey protein ratio (CN/WP). Both soluble and micelle-bound aggregates increased gelation pH and gel strength. Micelle-bound aggregates seemed to modify the micelle surface so that micelles were destabilized at a pH of 5.1 (instead of 4.7), while soluble aggregates precipitated at their calculated pI of approximately 5.3, and initiated an early gelation by interacting with the micelles. Decreasing the CN/WP ratio produced larger aggregates with higher whey protein: kappa-casein ratio, which gave more elastic gels. The specific effects of the micellar and soluble aggregates on gel strength are discussed with respect to their relative proportions in the heated milk. 相似文献
7.
Alting AC Hamer RJ de Kruif CG Visschers RW 《Journal of agricultural and food chemistry》2000,48(10):5001-5007
Cold gelation of whey proteins is a two-step process. First, protein aggregates are prepared by a heat treatment of a solution of native proteins in the absence of salt. Second, after cooling of the solution, gelation is induced by lowering the pH at ambient temperature. To demonstrate the additional formation of disulfide bonds during this second step, gelation of whey protein aggregates with and without a thiol-blocking treatment was studied. Modification of reactive thiols on the surface of the aggregates was carried out after the heat-treatment step. To exclude specific effects of the agent itself, different thiol-blocking agents were used. Dynamic light scattering and SDS-agarose gel electrophoresis were used to show that the size of the aggregates was not changed by this modification. The kinetics of gelation as determined by the development of pH and turbidity within the first 8 h of acidification were not affected by blocking thiol groups. During gelation, formation of large, covalently linked, aggregates occurred only in the case of unblocked WPI aggregates, which demonstrates that additional disulfide bonds were formed. Results of permeability and confocal scanning laser microscope measurements did not reveal any differences in the microstructure of networks prepared from treated or untreated whey protein aggregates. However, gel hardness was decreased 10-fold in gels prepared from blocked aggregates. Mixing different amounts of blocked and unblocked aggregates allowed gel hardness to be controlled. It is proposed that the initial microstructure of the gels is primarily determined by the acid-induced noncovalent interactions. The additional covalent disulfide bonds formed during gelation are involved in stabilizing the network and increase gel strength. 相似文献
8.
Aggregation properties of whey protein hydrolysates generated with Bacillus licheniformis proteinase activities 总被引:1,自引:0,他引:1
Spellman D Kenny P O'Cuinn G FitzGerald RJ 《Journal of agricultural and food chemistry》2005,53(4):1258-1265
Hydrolysis of whey protein concentrate (WPC) with Alcalase 2.4 L, a Bacillus licheniformis proteinase preparation, induces gelation. The aggregation behavior of WPC hydrolysates generated with Alcalase and Prolyve 1000, a Bacillus licheniformis proteinase that did not induce gelation, were studied by turbidity and particle size analysis. With the use of synthetic peptide substrates, it was shown that Alcalase contains a glutamyl endopeptidase (GE) activity not present in Prolyve. Comparison of the aggregation behavior of WPC hydrolysates generated with Alcalase, Prolyve, and combinations of Prolyve with a GE activity isolated from Alcalase showed that GE was responsible for the observed enzyme-induced peptide aggregation in Alcalase hydrolysates. Hydrolysates generated with Prolyve, having a degree of hydrolysis (DH) of 11.8% and 10.4% of peptide material greater than 10 kDa, could be induced to aggregate by the addition of GE. These results emphasize the contribution of enzyme specificity to the physicochemical and functional characteristics of proteinase hydrolysates of WPC. 相似文献
9.
Treimo J Aspmo SI Eijsink VG Horn SJ 《Journal of agricultural and food chemistry》2008,56(13):5359-5365
Brewer's spent grain (BSG) is an abundant, protein-rich coproduct from the beer industry. There is a growing interest in increasing and diversifying the exploitation of BSG and related coproducts for economic and environmental reasons. In this paper, we report on a study of the solubilization of proteinaceous material from BSG using several commercial peptidase preparations. Our data show that Alcalase is the most effective peptidase for solubilization of BSG proteins, with an ability to release up to 77% of total protein. The peptides produced by Alcalase had lower average molecular weight than peptides produced by the less effective enzymes. Processes that combined peptidase treatment with carbohydrate-degrading enzyme preparations such as Depol740 increased the solubilization of dry matter (from 30 to 43% under optimal conditions). However, such additional treatment had little effect on the solubilization of protein. The choice of enzyme dosage depends on the desired hydrolysis time and was assessed through several experiments. Protein solubilization was consistently better at pH 8.0 as compared to pH 6.8. Maximum protein solubilization at pH 8.0 within 4 h required the use of 10-20 microL Alcalase per g of dry matter. However, a considerable degree of solubilization (64%) and hydrolysates with high protein content could be obtained using doses down to only 1.2 microL. Amino acid composition analyses showed that Alcalase treatment solubilizes proline and glutamine (constituents of barley hordein) slightly more efficiently than the other amino acids in BSG. 相似文献
10.
Renan M Guyomarc'h F Chatriot M Gamerre V Famelart MH 《Journal of agricultural and food chemistry》2007,55(16):6736-6745
The effects of heat treatment and limited kappa-casein hydrolysis on the micelle/serum distribution of the heat-induced whey protein/kappa-casein aggregates were investigated as a possible explanation for the gelation properties of combined rennet and acid gels. Reconstituted skim milk was submitted to combinations of 0-67% hydrolysis of the kappa-casein at 5 degrees C and heat treatment at 90 degrees C for 10 min. The protein composition of the ultracentrifugal fractions was obtained by reverse-phase high-performance liquid chromatography (RP-HPLC). The aggregates contained in each phase were isolated by size-exclusion chromatography and analyzed by RP-HPLC and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon heating only, 20-30% of the total kappa-casein dissociated, while 20-30% of the total whey protein attached to the micelles. When heated milk was renneted, little changes were observed in the distribution and composition of the aggregates. Conversely, the heat treatment of partially renneted milk induced the formation of essentially micelle-bound aggregates. The results were discussed in terms of the preferred interaction between hydrophobic para-kappa-casein and denatured whey proteins. 相似文献
11.
The complement of enzyme activities of a selection of commercial protease preparations were determined using fluorogenic substrates. Alcalase was used in combination with other commercial enzyme preparations to produce cod muscle (Gadus morhua) hydrolysates. Each muscle hydrolysate was characterized with respect to the percentage degree of hydrolysis (DH %), peptide molecular weight range, and free amino acid content. The enzyme preparations containing predominantly protease or endopeptidase activities achieved high DH % and produced significant amounts of peptides below a molecular weight of 3000. Alcalase combined with exopeptidase-rich preparations produced hydrolysates rich in low-molecular-weight peptides. Selecting combinations of enzyme preparations with complementary activity profiles could be used to manipulate the peptide molecular weight profile of hydrolysates. 相似文献
12.
分步酶解制备花生短肽的研究 总被引:3,自引:1,他引:2
为了高效制备花生短肽,在花生蛋白Alcalase酶水解的研究基础上,进一步采用N120P酶水解花生蛋白并对各种影响因素进行了系统地研究;建立了短肽得率与各种影响因素的回归模型;确定出了N120P继续酶解花生蛋白Alcalase酶解物制备花生短肽的最佳工艺参数为pH值6.0,水解时间65 min,水解温度57℃,酶与底物比2061 U/g,。在此条件作用下,体系中短肽得率为89.01%,比Alcalase 单独酶解提高10.86个百分点;水解度为23.76%,平均肽链长度为4.21。经高效液相色谱测定,大部分水解产物的相对分子质量小于1000。 相似文献
13.
14.
The effects of several conditions on the amounts and compositions of aggregates formed in mixtures of whey protein hydrolysate, made with Bacillus licheniformis protease, and whey protein isolate were investigated using response surface methodology. Next, the peptides present in the aggregates were separated from the intact protein and identified with liquid chromatography-mass spectrometry. Increasing both temperature and ionic strength increased the amounts of both intact protein and peptides in the aggregates. There was an optimal amount of added intact WPI that could aggregate with peptides, yielding a maximal amount of aggregated material in which the peptide/protein molar ratio was around 6. Under all conditions applied, the same peptides were observed in the protein-peptide aggregates formed. The dominant peptides were beta-lg AB [f1-45], beta-lg AB [f90-108], and alpha-la [f50-113]. It was hypothesized that peptides could form a kind of glue network that can include beta-lactoglobulin via hydrophobic interactions at the hydrophobic binding sites at the surface of the protein. 相似文献
15.
Heat-induced gelation of a cold-water insoluble polysaccharide, Curdlan, was investigated using atomic force microscopy (AFM). Curdlan dissolved into NaOH aqueous solutions exhibited a spectral transition around 0.2 mol/L NaOH, which is an indicative of conformational transitions from a single helix at a lower alkali concentration to a disordered chain at a higher concentration. Nevertheless, AFM images of Curdlan solubilized in 0.01 mol/L NaOH revealed the presence of heterogeneous supramolecular assemblies of Curdlan: the majority of the molecules were in the form of microfibrils, the lengths of which were on the order of micrometers and the cross-sectional heights of which were approximately 2-3 nm, whereas single molecular chains, partially dissociated from these microfibrils, were also observed. Heating such a sol resulted in the formation of densely cross-linked microgel networks. Heat-induced gelation of Curdlan appears to be initiated by partial dissociation of single chains from supramolecular microfibrils and followed by cross-linking of microfibrils via hydrophobic interactions among these partially dissociated chains. 相似文献
16.
Enzymatic hydrolysis as a means of expanding the cold gelation conditions of soy proteins 总被引:1,自引:0,他引:1
Kuipers BJ van Koningsveld GA Alting AC Driehuis F Gruppen H Voragen AG 《Journal of agricultural and food chemistry》2005,53(4):1031-1038
Acid-induced cold gelation of soy protein hydrolysates was studied. Hydrolysates with degrees of hydrolysis (DH) of up to 10% were prepared by using subtilisin Carlsberg. The enzyme was inhibited to uncouple the hydrolysis from the subsequent gelation; the latter was induced by the addition of glucono-delta-lactone. Visual observations, confocal scanning laser microscopy images, and the elasticity modulus showed that hydrolysates gelled at higher pH values with increasing DH. The nonhydrolyzed soy protein isolate gelled at pH approximately 6.0, whereas a DH = 5% hydrolysate gelled at pH approximately 7.6. Gels made from hydrolysates had a softer texture when manually disrupted and showed syneresis below a pH of 5-5.5. Monitoring of gelation by measuring the development of the storage modulus could be replaced by measuring the pH onset of aggregate formation (pH(Aggr-onset)) using turbidity measurements. The rate of acidification was observed to also influence this pH(Aggr-onset). Changes in ionic strength (0.03, 0.2, and 0.5 M) had only a minor influence on the pH(Aggr-onset), indicating that the aggregation is not simply a balance between repulsive electrostatic and attractive hydrophobic interactions, but is much more complex. 相似文献
17.
Capuano E Fedele F Mennella C Visciano M Napolitano A Lanzuise S Ruocco M Lorito M del Castillo MD Fogliano V 《Journal of agricultural and food chemistry》2007,55(10):4189-4195
Amadoriase I is a fructosyl amine oxidase from Aspergillus fumigatus that catalyzes the oxidation of Amadori products (APs) producing glucosone, H2O2, and the corresponding free amine. All the enzymes of this family discovered so far only deglycate small molecular weight products and are inactive toward large molecular weight substrates, such as glycated BSA or ribonuclease A. Therefore, they cannot be used to reverse protein glycation occurring in diabetes or in foods. In this paper, the effect of Amadoriase I added during the in vitro reaction between glucose and peptides having different polarities or proteins with molecular weights ranging from to 5 to 66 kDa was tested. The formation of APs was monitored by ESI-MS of intact glycated protein or peptides and by measuring the Nepsilon-(1-deoxy-d-fructos-1-yl)-L-lysine and furosine concentrations. Results showed that the formation of APs is reduced up to 80% when peptides and glucose are incubated in the presence of Amadoriase. The effect is more evident for hydrophobic peptides. In protein-glucose systems, the effect was dependent on the molecular weight and steric hindrance being negligible for BSA and at a maximum for insulin, where the formation of APs was reduced up to 60%. These findings indicate new potential applications of Amadoriase I as an efficient tool for inhibiting protein glycation in real food systems. 相似文献
18.
碱性蛋白酶Alcalase凝固大豆分离蛋白的分子间作用力 总被引:1,自引:0,他引:1
为了进一步揭示蛋白酶凝固豆乳的机理,该文通过添加不同化学试剂研究碱性蛋白酶Alcalase凝固大豆分离蛋白(SPI)过程中的分子间作用力。结果发现凝固过程中的分子间作用力主要是氢键和疏水作用,而离子键和二硫键对凝固过程影响不大。大豆蛋白质分子间的交联主要由次级键起作用,同时需要克服由负电荷引起的静电斥力,这就解释了为什么与无机盐和酸相比,Alcalase得到的SPI凝固物强度低。根据以上结论,该文还对豆乳凝固酶当前的筛选策略进行了评价。 相似文献
19.
Robert MC Razaname A Mutter M Juillerat MA 《Journal of agricultural and food chemistry》2004,52(23):6923-6931
Angiotensin-I-converting enzyme (ACE) inhibitory activity was identified in milk proteins fermented with Lactobacillus (Lb.) helveticus NCC 2765 (Nestle Culture Collection, Vers-chez-les-Blanc, Switzerland). Hydrolyzing sodium caseinate for 1 and 2 h inhibited ACE activity, as measured by an in vitro ACE inhibition test. The hydrolysates with the highest ACE inhibitory potential were fractionated by gel permeation chromatography and their low molecular weight fractions collected. These fractions were subsequently subfractionated by reverse-phase high-pressure liquid chromatography. Several hydrophobic subfractions showed high ACE inhibitory potential, and their peptide composition was determined using an ion trap mass spectrometer equipped with an elctrospray ionization source. Analysis of the low molecular weight fraction identified 14 peptides with known antihypertensive activity and 1 with previously described opioid activity. On the basis of the peptide composition of active subfractions, two potentially active novel sequences were defined, and the following synthetic peptides were synthesized: FVAPFPEVFG (alphaS1 39-48), ENLLRFFVAPFPEVFG (alphaS1 33-48), NENLLRFFVAPFPEVFG (alphaS1 32-48), LNENLLRFFVAPFPEVFG (alphaS1 31-48), NLHLPLPLL (beta 147-155), ENLHLPLPLL (beta 146-155), and VENLHLPLPLL (beta 145-155). The ACE inhibitory potential of these synthetic peptides was assessed, and IC50 values were determined. NLHLPLPLL (beta 147-155), which was the only synthetic peptide also present in the sodium caseinate hydrolysates, and NENLLRFFVAPFPEVFG (alphaS1 32-48) showed the highest inhibition of ACE activity, with IC50 values of 15 and 55 microM, respectively. Furthermore, the stability of all synthetic peptides was assessed using an in vitro model simulating gastric digestion. The beta-casein-derived peptides remained intact following the successive hydrolysis by pepsin and pancreatin, whereas alphaS1-casein-derived peptides were degraded by pepsin. 相似文献
20.
不同人工恢复林对退化红壤团聚体组成及其有机碳的影响 总被引:1,自引:0,他引:1
研究土壤团聚体的组成及其有机碳的分布,有助于从微观角度理解土壤结构与功能的相互作用.采用于筛法和湿筛法,研究南方红壤退化地实施人工恢复30年后,马尾松与阔叶复层林(PB)、木荷+马尾松混交林(SP)和阔叶林(BF)3种典型林分在0~60 cm土层的团聚体组成及其有机碳分布特征,分析土壤团聚体有机碳与总有机碳相关关系.结果表明:各恢复林分土壤机械稳定性团聚体质量分数,以>2 mm粒径所占比例最大(均在60%以上),而在水稳性团聚体中,以<0.05 mm粒径占优势.不同林分土壤团聚体结构破坏率顺序依次为BF(53.38%~84.27%) >SP(52.22% ~70.86%) >PB(22.70% ~47.83%).机械稳定性和水稳性团聚体有机碳质量分数均以PB最高,随着土层深度的增加,各林分土壤团聚体有机碳质量分数呈下降趋势.水稳性大团聚体(>0.25 mm粒径)有机碳质量分数总体高于相应土层的总有机碳质量分数,而微团聚体的(<0.25 mm粒径)则低于后者,说明有机碳对于大团聚体的形成和水稳性具有积极作用.土壤团聚体有机碳与总有机碳的相关关系分析表明,土壤团聚体有机碳的增加,对总有机碳的积累具有正面影响.保留密度大、灌木(草)层盖度高的马尾松与阔叶复层林土壤团聚体的数量和质量更高;因此,在红壤侵蚀退化地森林恢复初期,可通过适当密植、增加林下灌草覆盖等措施,增加有机碳的输入,促进团聚体的形成和稳定,从而加速了退化土地的土壤结构改善和功能恢复.该研究可为南方严重红壤退化地生态恢复中的林分类型选择和优化配置提供科学依据. 相似文献