超声辅助处理对乳清分离蛋白糖基化产物的理化特性影响

采用超声辅助技术对乳清分离蛋白(WPI)进行糖基化改性,并与水浴加热法进行比较,探究两种处理方式对糖基化反应产物理化性质的影响。结果表明,与水浴法相比,超声辅助法可以更快地促进糖基化反应的进行,且对糖基化产物的理化性质有较大改善;当超声温度为70℃,功率为300 W,超声时间为40min时,乳清分离蛋白和葡萄糖的接枝度达到48. 10%,且乳清分离蛋白—葡萄糖接枝物的乳化性、在等电点处溶解性均增大。乳化系数由23.67 m~2/g增大到40.84 m~2/g;等电点附近的溶解度由19.09%增大到47.95%。且以接枝物为基质的乳液的粒径更小,储藏稳定性更好。     

肌肉蛋白乳化特性改善方法研究进展

乳化特性是肌肉蛋白的重要功能特性之一,对加工肉制品的品质和价值有关键性影响。肌肉蛋白的溶解度、尺寸大小、巯基分布以及表面疏水性等自身特性共同决定其乳化能力,而不同物化修饰方法能够通过改变蛋白上述结构与聚集程度,从而提高蛋白质乳化特性。本文系统综述了改善肌肉蛋白乳化特性的几种方法,包括高压均质、高静压、超声波、微波和等离子体技术等物理手段以及糖基化修饰和酸碱处理等化学手段,同时论述了不同方法改善蛋白乳化特性的机制及适宜处理条件,以期为肌肉蛋白乳化特性的提升以及乳化类肉制品的开发应用提供技术支持。     

糖基化方法对于大豆7S球蛋白糖基化反应及产物的影响

针对传统的两种糖基化接枝方法和改进方法从糖基化反应程度进行系统比较,并对产物氨基酸组成进行分析,以期进一步揭示蛋白质糖基化方法对于糖基化反应过程及产物的影响机制。本文利用干热法、湿热法和加压辅助湿热三种糖基化方法,对大豆7S球蛋白和葡聚糖的糖基化产物从反应程度、氨基酸组成等方面进行研究发现,结果表明:三种制备方法的反应程度高低顺序依次为:湿热法>加压辅助湿热法>干热法,说明压力能够对Maillard反应的进行具有一定的抑制作用,可以控制反应向理想阶段进行。大豆7S球蛋白和葡聚糖的糖基化主要发生在蛋白质肽链上的赖氨酸和精氨酸侧链上的自由氨基,干热法与其它两种方法相比糖链更有易于和精氨酸侧链上的自由氨基发生共价交联,而湿热法和加压辅助湿热法相比糖链更易于和赖氨酸侧链上的自由氨基发生共价交联。     

Moisture-induced aggregation of alpha-lactalbumin: effects of temperature, cations, and pH

Abstract: Alpha‐lactalbumin is an important dairy protein ingredient, and has been widely used in high‐protein foods such as infant formula and nutritional bars for its nutritional and functional properties. The purpose of this study was to investigate the moisture‐induced aggregation of alpha‐lactalbumin in premixed protein dough model systems, and to illustrate the effects of temperature, cations, and pH on the progress of protein aggregation. Our results suggested that storage temperature was a critical factor for protein aggregation in model systems, and the formation of protein aggregates became faster with increases in storage temperature. Calcium significantly improved the thermal stability of alpha‐lactalbumin and slowed down the formation of protein aggregates. The increases in pH accelerated the aggregation of alpha‐lactalbumin. Our results also suggested that the formation of intermolecular disulfide bonds together with noncovalent interactions are the main mechanisms resulting in the moisture‐induced aggregation of alpha‐lactalbumin in model systems. Practical Application: Alpha‐lactalbumin is an important dairy protein ingredient, and has been widely used in high‐protein foods such as infant formula and nutritional bars for its nutritional and functional properties. Our results suggested low storage temperature, the presence of calcium and low pH condition can make high‐protein food products containing alpha‐lactalbumin more stable.     

Effects of different pre-salting methods on protein aggregation during heavy salting of cod fillets

The use of injection and brining as the first step in heavy salting of cod increases weight yields of the products through both salting and rehydration, compared to other pre-salting methods, like brining only and pickling. This is interesting since salt content of the muscle exceeds 20% NaCl, in all procedures. Therefore, the dissimilarities in yield were presumed to depend on the degree of protein denaturation and aggregation as influenced by the different salting procedures. This hypothesis was studied and confirmed with the aid of SDS–PAGE and DSC-analysis. Higher water retention of injected products was explained by stronger salting-in effects on proteins during pre-salting, reducing aggregation of muscle proteins during the dry salting step. The degree of protein aggregation during salting increased in the following order with regard to the different pre-salting methods: injection and brining < brining < pickling. These effects were still observed after rehydration. Furthermore, differences in denaturation/aggregation were assigned to both myosin and collagen.     

Antioxidant activity of Maillard reaction products from a Yak casein-glucose model system

Maillard reaction products (MRPs) were prepared by reacting both Yak and Holstein casein with different ratios of glucose to casein from 0:1 to 2.5:1. The results showed that the content of intermediate products and browning intensity of the Yak casein-glucose system increased with increasing concentrations of glucose, but were lower than for the Holstein system at the same ratio. With glycosylation, the reducing power and the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity of both Yak and Holstein caseins were enhanced. With increased glucose content, the reducing power of Yak MRPs increased at the same concentration. The metal chelating activity of Holstein MRPs decreased or was eliminated in the ratio range of 0.5:1 to 2.0:1 g glucose g⁻¹ casein, while that of Yak MRPs were reduced in general. Improvement of the inhibitory activity for Yak casein was lower than that of Holstein casein after glycosylation by glucose.     

Maillard Reaction Products as Encapsulants for Fish Oil Powders

The use of Maillard reaction products for encapsulation of fish oil was investigated. Fish oil was emulsified with heated aqueous mixtures comprising a protein source (Na caseinate, whey protein isolate, soy protein isolate, or skim milk powder) and carbohydrates (glucose, dried glucose syrup, oligosaccharide) and spray‐dried for the production of 50% oil powders. The extent of the Maillard reaction was monitored using L*, a*, b* values and absorbance at 465 nm. Encapsulation efficiency was gauged by measurement of solvent‐extractable fat and the oxidative stability of the fish oil powder, which was determined by assessment of headspace propanal after storage of powders at 35 °C for 4 wk. Increasing the heat treatment (60 °C to 100 °C for 30 to 90 min) of sodium caseinate‐glucose‐glucose syrup mixtures increased Maillard browning but did not change their encapsulation efficiency. The encapsulation efficiency of all heated sodium caseinate‐glucose‐glucose syrup mixtures was high, as indicated by the low solvent‐extractable fat in powder (<2% powder, w/w). However, increasing the severity of the heat treatment of the sodium caseinate‐glucose‐glucose syrup mixtures reduced the susceptibility of the fish oil powder to oxidation. The increased protection afforded to fish oil in powders by increasing the temperature‐time treatment of protein‐carbohydrate mixtures before emulsification and drying was observed irrespective of the protein (sodium caseinate, whey protein isolate, soy protein isolate, or skim milk powder) and carbohydrate (glucose, glucose/dried glucose syrup, or oligosaccharide/dried glucose syrup) sources used in the formulation. Maillard reaction products produced by heat treatment of aqueous protein‐carbohydrate mixtures were effective for protecting microencapsulated fish oil and other oils (evening primrose oil, milk fat) from oxidation.     

EFFECT OF pH ON ANTIOXIDATIVE ACTIVITY AND OTHER CHARACTERISTICS OF CARAMELIZATION PRODUCTS

Antioxidative activity and other characteristics of caramelization products (CPs) from fructose or glucose solutions prepared at pHs ranging from 7.0 to 12.0 with heating at 100C for various times (0–180 min) were investigated. The degradation of both sugars increased with increasing pH levels and heating time (P < 0.05). The intermediate degradation products and browning intensity also increased when pH and heating time increased (P < 0.05) as evidenced by the increase in A₂₇₀, A₂₈₅ and A₄₂₀, respectively. The reducing power and 2–2‐diphenyl‐1‐picrylhydrazyl radical scavenging activity of CPs were coincidental with the browning development and the intermediate formation. Generally, CPs from fructose showed greater antioxidative activity as shown by the higher reducing power and scavenging effect than CPs from glucose. Therefore, CPs from both sugars with pronounced antioxidative activity can be prepared by heating fructose or glucose solutions at very alkaline pH for an extended time.     

Improvement in the yield of lipophilized lysozyme by the combination with Maillard‐type glycosylation

Hen egg white lysozyme was modified using the Maillard‐type glycosylation method prior to the lipophilization with palmitic acid. The yield of lipophilized lysozyme significantly increased by the pre‐glycosylation of the protein. The lipophilized lysozyme derivative was separated into two main fractions with different level of glycosylation. All fractions showed a strong antimicrobial activity against Gram‐negative bacteria,Escherichia coli. The lipophilization of the lysozyme combined with glycosylation is a promising method for potential industrial applications of the lysozyme due to the enhanced antimicrobial activity and the improved yield.     

ANTIMICROBIAL ACTIVITY AND PROTEIN PROFILES OF PEDIOCOCCUS SPP. ISOLATED FROM TURKISH "SUCUK"

In this study, a total of 206 lactic acid bacteria were isolated on De Man–Rogosa–Sharpe agar from 20 fermented Turkish “sucuk” samples. Twenty‐five isolates were identified as Pediococcus spp. and were tested for their antibacterial activity against Staphylococcus aureus, Micrococcus luteus, Listeria monocytogenes, Bacillus cereus, Salmonella Typhimurium and two strains of Escherichia coli. Only eight strains (32%) of pediococci showed a significant degree of antibacterial activity against L. monocytogenes and S. aureus. According to sodium dodecyl sulfate‐polyacrylamide gel electrophoresis results, among eight isolates, two showed different protein profiles. The size of proteins that made the difference was calculated from 60 to 80 kDa. After partial purification, the highest degree of inhibition against L. monocytogenes was caused by the protein fractions collected after 40% ammonium sulfate precipitation. Therefore, these isolates, which produce antimicrobial substances, have a potential especially to control L. monocytogenes in fermented meat products.     

脱脂牛乳体系中乳蛋白葡萄糖美拉德反应程度及产物功能性质研究

以脱脂牛乳为研究对象,以葡萄糖为还原糖,对乳蛋白进行美拉德反应修饰,研究葡萄糖添加量为0~9 g/100 mL脱脂乳时反应体系的糖基化程度、pH、中间产物含量、褐变程度、粒径,以及产物乳化性、发泡性和吸油性。结果显示,脱脂乳体系糖基化程度在葡萄糖添加量为3 g/100 mL时达到最大值,之后迅速降低;中间产物和褐变程度均在该添加量下达到最低值,之后迅速上升。反应体系pH并未随葡萄糖添加量的增加而显著变化。糖基化反应后,酪蛋白胶束粒径增加。糖基化修饰改善了脱脂乳体系的乳化性,当葡萄糖添加量为3 g/100 mL时,乳化活性和乳化稳定性均达到最大值。糖基化修饰后,脱脂乳体系的发泡性并未显著提高,但该体系10和30 min泡沫稳定显著增加(p<0.05)。糖基化修饰后乳蛋白的吸油性降低。研究结论可为脱脂乳体系中乳蛋白美拉德反应产物的应用提供基础数据。     

KINETICS OF BIOETHANOL PRODUCTION FROM WHEAT MILLING BY-PRODUCTS

An overview of the potential application of wheat milling by‐products as substrate for bioethanol production is presented. In order to select a suitable microorganism, model fermentations were conducted using glucose and dry baker's yeast. The overall ethanol yield was nearly stable (ca. 0.35 g/g), independent of mash glucose concentration; mashes with 100 g glucose/L resulted in an overall ethanol productivity of 3.48 g/L·h. Slurries containing low‐grade wheat flour (LG) (100, 200 or 300 g/L) were used for simultaneous saccharification and fermentation (SSF) with Zymomonas mobilis. Fermentation performance was evaluated based on ethanol concentration (P), productivity (Q_v), yield (Y_P/S), production rate (Q_p) and glucose consumption rate (Q_s). Mashes containing 200 g LG/L produced about 52 g ethanol/L, with Q_vof 2.17 g/L·h. Based on the relatively high fermentation rate of LG, reaching peak ethanol productivity within ca. 9 h of SSF, considerable savings on fermentation time was achieved. Using Z. mobilis for LG fermentation, P was about 30% higher than that obtained with Saccharomyces cerevisiae.     

Effect of Maillard‐based conjugation with dextran on the functional properties of lysozyme and casein

The purpose of this research was to find the best experimental conditions for glycosylation of lysozyme and casein with dextran, and to investigate the effect of glycosylation on the functional properties of these proteins. Glycosylation was performed by allowing proteins to react with dextran under Maillard reaction conditions. The extent of glycosylation was determined by sugar analysis, SDS‐PAGE, gel filtration and cation‐exchange chromatography. Glycosylation of lysozyme with a 1:5 weight ratio of protein to dextran, held at 60 °C for one week under a relative humidity of 79% resulted in coupling of 3.0 mole dextran to one mole lysozyme. In the case of casein, at 60 °C, 48 h and 79% relative humidity, 0.1 and 0.13 mole dextran was attached to one mole of casein when a weight ratio of protein to dextran of 1:5 and 1:7.5 was used, respectively. A decrease in the degree of glycosylation occurred when samples were incubated for 72 h. Enzymatic activity of glycosylated lysozyme was reduced by 20% compared with unmodified lysozyme (P < 0.05). Both proteins exhibited improved solubility at different pH values (3, 7 and 9), different temperatures (25, 40 and 60 °C) and increased heat stability, with a better emulsion activity and emulsion stability than with un‐modified proteins (P < 0.05). These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems. Copyright © 2005 Society of Chemical Industry     

Ultra-HPLC method for quality and adulterant assessment of steviol glycosides sweeteners – Stevia rebaudiana and stevia products

Stevia products are advertised as a zero-calorie sweetener. Glucose should not be an intrinsic component of this product, but it has been identified from some of stevia products in a preliminary study. An UHPLC-UV method was developed for the quantitative determination of glucose from stevia products. After stevia products reacted with 1-phenyl-3-methyl-5-pyrazolone (PMP), PMP derivatives were analysed and glucose was found in seven out of 35 products in the range 0.3–91.5% (w/w). Two products, SPR-12 and SPR-27, showed remarkable amounts of glucose at 61.6% and 91.5%, respectively. In addition, an UHPLC-UV-evaporative light-scattering detector (ELSD) method was developed for the quantitative determination of rebaudioside A, stevioside, rebaudioside D, dulcoside A and steviolbioside from Stevia rebaudiana and related products. In a 12 min run, five steviol glycosides were baseline-separated. ELSD and ultraviolet (UV) detections showed comparable results. The LC methods were validated for linearity, repeatability, accuracy, limits of detection (LOD) and limits of quantification (LOQ). For steviol glycosides, the LODs and LOQs were found to be less than 10 and 30 μg ml^–1, respectively. The RSD for intra- and inter-day analyses was less than 2.5%, and the recovery was 90–94%. For PMP derivative of glucose, the LOD and LOQ were 0.01 and 0.05 μg ml^–1, respectively. Repeatability (RSD) was less than 2.6%; recovery was 98.6–101.7%. The methods are useful for the identification, quality assurance, and adulterant assessment of S. rebaudiana and steviol glycosides sweeteners (stevia products).     

葡萄糖对大豆分离蛋白储藏中性质变化的影响

主要研究了葡萄糖对大豆分离蛋白产品在贮藏中溶解性及相关结构性质变化的影响。实验将添加不同葡萄糖含量的大豆分离蛋白在37℃,密封避光条件下储藏70d,在不同储藏时间下测定大豆分离蛋白的溶解性、表面疏水性、自由氨基含量和分子量分布。结果显示,大豆分离蛋白在储藏中溶解度持续下降;表面疏水性在前10d增大,之后保持稳定;自由氨基含量在前40d呈现下降趋势,之后基本稳定;分子量在贮藏期中的变动比较复杂,随着葡萄糖含量增加,产品本身的聚集程度下降,但是高含量葡萄糖会导致贮存过程中出现更严重的聚集和降解的倾向。由于溶解度变动与自由氨基变动、分子量变动不成正比,暗示着大豆分离蛋白贮藏过程中溶解性下降可能不仅仅由于葡萄糖导致的美拉德反应,还可能有其他因素如氧化、其他共价交联或者非共价结合的效应。     

Influence of inulin/oligofructose on the acid‐induced cold aggregation and gelation of preheated soy proteins

BACKGROUND: In recent years inulin‐type prebiotics have attracted much attention due to consumers' awareness of the health benefits of functional foods. Currently no information is available about the possible texture‐modifying effect of these non‐ionizable polar carbohydrates in different soy‐based food systems. In this study, the effect of inulin/oligofructose on the cold aggregation and gelation of preheated soy protein isolate (SPI) and its fractions (7S, 11S, and their mixture), induced by glucono‐δ‐lactone (GDL), were evaluated by turbidity (A₆₀₀) and dynamic rheological measurements. RESULTS: Oligofructose significantly delayed the aggregation of all protein samples and decreased the end‐point optical density of 11S fraction and SPI. Inulin, a long‐chain fructan, only delayed the aggregation of 7S globulin and reduced the capacity of aggregation (A₆₀₀) of SPI. While oligofructose showed no significant effect, the addition of 5% (w/v) inulin enhanced the gelation of SPI and the 7S/11S mixture, which was demonstrated by the increase in gel storage modulus up to 13.6% and 10.1% (P < 0.05), respectively. CONCLUSION: Inulin was found to enhance the viscoelastic properties of GDL‐induced cold‐set soy protein gels. It is expected that ‘functional’ cold‐set gel products with improved texture can be prepared from preheated soy proteins and inulin. Copyright © 2009 Society of Chemical Industry     

The immunodetected yeast purine—cytosine permease is not N-linked glycosylated,nor are glycosylation sequences required to have a functional permease

The purine-cytosine permease (PCP) of the yeast Saccharomyces cerevisiae was detected by immunological methods. Using antibodies directed against synthetic peptides, whose sequences were derived from the primary structure of the PCP, immunoprecipitation of [³⁵S]methionine-labelled PCP was achieved either from cellular extracts or from in vitro translation mixtures. Non-labelled PCP was also detected on Western blots of membrane proteins. Similar migration rates were observed for PCP originating both from immunoprecipitated cellular extracts and from in vitro translation mixtures. Hence, post-translational processing, if any, only slightly affects the size of the protein. Also no evidence was found for N-linked core-glycosylation: identical migration rates were observed when immunoprecipitated PCP molecules were extracted from cells labelled for 10 min with [³⁵S]methionine, pretreated or not with tunicamycin. On the other hand, the suppresion of the two potential N-linked glycosylation sequences in the DNA did not lead to inactivation of the transport activity, confirming that N-linked glycosylation is not required for the permease activity.     

Availability of essential amino acids from proteins. I. Beef serum albumin

Available essential amino acids from beef serum albumin were determined microbiologically, after total enzymic hydrolysis of the protein by papain, leucine aminopeptidase and prolidase. Samples of pure beef serum albumin of different moisture content were heat-treated with glucose at 90° or without it at 121°. In the enzymic digest of the protein, available essential amino acids were determined using Streptococcus faecalis, S. zymogenes and Lactobacillus arabinosus. The content of essential available amino acids was correlated with the degree of in vitro digestibility of heat-treated albumin. The amount of lysine determined by Carpenter's method with fluordinitrobenzene did not correspond to the values found for lysine by microbiological analysis with S. faecalis. Lysine reactive with fluordinitrobenzene was found in the non-digestible residue of the protein, so that the values obtained by the chemical method are probably higher than the actual amount of available lysine. The results for the trypsin digest of the albumin were similar by both methods. The availability of lysine as well as that of amino acids in general depended on the enzymic digestibility.     

THE INFLUENCE OF MEDIA CONDITIONS ON THE UTILISATION OF MONOSACCHARIDES BY A STRAIN OF SACCHAROMYCES UVARUM (CARLSBERGENSIS)

The utilisation of glucose and fructose by the brewing yeast species Saccharomyces uvarum (carlsbergensis) was investigated. When sucrose was used as the substrate, one of the hydrolysis products, glucose was taken up preferentially over the other hydrolysis product fructose. However, when glucose and fructose were added separately to the media, the uptake profile for each sugar was very similar. Growth promoting media enhanced the differential uptake, whereas non-growth promoting media reduced it. Increase in osmotic pressure of the medium eliminated the preferential uptake of glucose over fructose. The results suggest the presence of a complex uptake system and could be explained by a combination of (1) molecular configuration of the sugars in aqueous solutions, (2) differential phosphorylation effect of glucose and fructose and (3) intracellular accumulation of ethanol in yeast.     

THE EFFECT OF CASEINOMACROPEPTIDE AND WHEY PROTEIN CONCENTRATE ON STREPTOCOCCUS MUTANS ADHESION TO POLYSTYRENE SURFACES AND CELL AGGREGATION

Caseinomacropeptide (CMP) from bovine, ovine and caprine milk and whey protein concentrate (WPC) were both evaluated for adhesion inhibition of Streptococcus mutans to polystyrene surface and cell aggregation. Adhesion inhibition by the CMPs and WPC at 1 mg/mL was higher than 84%. The CMPs and WPC caused aggregation of S. mutans cells at low concentrations. These findings suggest the application of these milk derived proteins as potential dental caries inhibitors and for possible food application uses.