SDS—PAGE法分析含乳饮料和乳清粉的蛋白组成和含量

利用SDS-PAGE电泳结合凝胶成像分析测定了乳清粉及含乳饮料中的酷蛋白、α-乳白蛋白（α-LA）和β-乳球蛋白（β-LG）的含量,探讨了两种乳蛋白提取方法对测定结果的影响。     

Analytical‐Sensory Determination of Potential Flavour Deficiencies of Light Beers

Although currently light beers have a high market share in the US, this beer style is still not accepted on the European continent because light beers are considered watery, mainly on account of lack of mouthfeel. In this paper, the flavour quality, including flavour stability, of five commercial light beers was evaluated in comparison with their corresponding pilsner beers derived from the same breweries. Through detailed physico‐chemical and sensory evaluation, followed by multivariate data analysis, the fresh beers could be differentiated according to their origin (US or European) and beer style (light or pilsner). Potential flavour deficiencies of fresh light beers were determined as too much sweetness, lack of bitterness, and especially reduced fullness. As a result, the fresh light beers were less preferred than their corresponding pilsner. Upon ageing, the light beers were generally less flavour stable than their pilsner counterparts. This is mainly ascribed to increased sensory perception of cardboard and ribes staling flavours in most aged light beers. Nevertheless, based on detailed analytical/sensory investigation, it was clearly demonstrated that one of the light beers involved in this study showed enhanced flavour stability with respect to all other beers, including the pilsner beers.     

β‐Glucans and Pentosans and their Degradation Products in Commercial Beers

Several commercial beers have been analyzed for their content of β‐glucans, pentosans and their degradation products using high performance liquid chromatography, thin layer chromatography and chemical and enzymic analysis procedures. The beers tested contained high levels of residual high molecular weight pentosan, but much less high molecular weight β‐glucan. The beers also contained sizeable levels of oligosaccharides, especially trisaccharides, reflecting the incomplete degradation of polymeric materials in malting and mashing and the inability of yeast to ferment them. There is substantially more β‐linked glucosyl material in beer than pentosyl substances, although the higher molecular weight of the latter probably makes it more likely to represent soluble fibre. In respect of fibre claims for the beers examined, even for the beer containing the least pentosan, it seems that less than a litre of the product would afford sufficient material.     

Analysis of Folate Form Distribution in Spanish Beers Using Combined Affinity and Ion‐Pair Chromatography

Folates and derivatives usually occur as polyglutamates, in different oxidized forms and substitutions in nature. The multiplicity of forms and the generally low content in food makes quantitative analysis of folate a difficult task. A method that uses affinity chromatography followed by ion‐pair high performance liquid chromatography was adapted to the analysis of folate distribution in Spanish beers, with simultaneous information on the pteridine ring structure and the glutamate residues. On average, total folate concentration (as sum of individual vitamers expressed in folic acid) in the analyzed beers was 2.0 μg/100 mL. For all the beers, folates were present as monoglutamates and the analysis showed a total absence of polyglutamyl folates. The distribution of the monoglutamyl folate derivatives analyzed in Spanish beers was: 10‐formyltetrahydrofolate (41.7% of total folate), tetrahydrofolate (26.5%), 5‐methyltetrahydrofolate (17.2%) and folic acid (14.6%). This study provides new information regarding the distribution of naturally occurring folates in beer and contributes to the assessment of folate bioavailability in this beverage.     

Inhibition of amylases present in ruminal particle‐associated micro‐organisms

The effect of different substances potentially inhibitory of ruminal amylase activity in sheep was assessed using biochemical and electrophoretic assays. Most amylase activity was detected in the particle‐associated fraction (70%) of the ruminal contents (which was selected for the assays) in comparison with the bacterial (21%) and extracellular (9%) fractions. Salts of divalent ions such as Sn²⁺, Hg²⁺, Cu²⁺ and Zn²⁺ produced 90, 82, 65 and 44% inhibition of amylase activity respectively when assayed at a relative concentration of 5 × 10^?3 mol l^?1. Organic acids such as tannic, formic, ascorbic and benzoic acid produced 79, 48, 43 and 37% inhibition respectively, whereas chelators such as EDTA, EGTA and 1,10‐phenanthroline produced an inhibition ranging from 32 to 37%. Substrate SDS‐PAGE zymograms allowed the identification of different amylase‐active bands in ruminal extracts, showing a wide range of relative molecular masses (from 36 to more than 100 kDa). Such zymograms also confirmed the effect of some inhibitors. The reversibility of the inhibitory effect of some of the assayed substances was assessed. ZnSO₄ was the most persistent inhibitory substance even at low concentrations and, owing to its low toxicity, appears to be an adequate substance to reduce the high in vitro ruminal degradation of starch. Implications for the process of enzymatic digestion of starch are discussed. © 2002 Society of Chemical Industry     

The Contribution of 4‐Hydroxyfuranone Derivatives to the Aroma of Commercial Beers and Malts

Analysis of hot water extracts from a range of commercial malts showed that 2,5‐dimethyl‐4‐hydroxy‐3(2H)furanone (DMHF) varied from undetectable (lager malt) to 4.2 mg/litre (crystal malt), a concentration twenty‐six times the flavour threshold in water. 5‐Methyl‐4‐hydroxy‐3 (2H)furanone (MHF) was detected in all samples except one but was always well under its flavour threshold value. 2(or 5)‐Ethyl‐5(or 2)‐methyl‐4‐hydroxy‐3(2H)furanone (EMHF) was not detected in any of the samples. Fermentation of lager, ale and crystal malt extracts with an ale strain of yeast led to the appearance of EMHF in all cases as well as additional DMHF. The greatest increases in both compounds was with the ale malt. Both increases and decreases occurred in MHF concentration as a result of fermentation but final levels were always well below the flavour threshold value. Analysis of ten commercial beers found DMHF in all the samples and in five cases levels exceeded twice the flavour threshold value in beer with flavour units from 2.4 to 9.1. A flavour panel noted that in four of these cases the beer had a distinctly sweet/caramel aroma which is typical of DMHF. EMHF was undetectable in six samples, detectable, but unquantifiable, in three cases but at about 80% of the flavour threshold value in the remaining sample. MHF was found in all samples but at insignificant levels. The results show that DMHF is an important flavour compound in British ales and EMHF may make a contribution in a limited number of situations. The contribution of malt type, brewery processing and yeast strain in determining the concentration of the two 4‐hydroxyfuranones in beer remains uncertain.     

Formation of 4‐Hydroxyfuranones and their Precursors during Production of Worts and Beers

Laboratory beers and samples taken at each stage of production, were analysed for the flavour active 4‐hydroxyfuranones; 5‐methyl‐4‐hydroxy‐3(2H)‐furanone (MHF), 2,5‐dimethyl‐4‐hydroxy‐3(2H)‐furanone (DMHF) and 5‐(or 2)‐ethyl‐2(or 5)‐methyl‐4‐hydroxy‐3(2H)‐furanone (EMHF). The length and temperature of mashing, the length of boiling, the rate of cooling the worts and the effects of grist composition were investigated to identify the 4‐hydroxyfuranone content of worts and subsequent beers. Fermentation temperature and the use of the stabilising agents, PVPP and Lucilite PC5, on the 4‐hydroxyfuranone content of the beer was also investigated. The results demonstrated that several aspects of beer production procedures affect the furanone content of the beer, but in practice the important factors are grist composition, the rate at which the boiled wort is cooled and fermentation temperature. Fermentation has a major effect on final furanone content as yeast produces both DMHF and EMHF. The results suggest that malt levels of precursor compounds, which can be converted to 4‐hydroxyfuranones by the Maillard reaction or by yeast, may prove to be more important than the quantities of the furanones found in malt in determining the final furanone content of beer. A clearer understanding of the nature of the precursors should allow manipulation of their production and beer furanone content.     

Analysis of vicilin (7S)‐class globulin in cocoa cotyledons from various genetic origins

Cocoa cotyledons contain vicilin (7S)‐class globulin (VCG), a major storage protein. It is the native source of oligopeptides and free amino acids which have been identified as precursors of cocoa‐specific aroma and are formed through proteolysis during fermentation. High‐resolution electrophoresis of native proteins isolated from ripe, unfermented cocoa cotyledons harvested from different cultivars was used to determine genetic differences of the genotypes. Flavour differences have been reported to exist after standard fermentation in cocoa beans harvested from various genotypes. In this paper, SDS‐PAGE and 2D IEF/SDS‐PAGE polypeptide separation patterns are shown which were separately isolated from cotyledons of various genetic origins. Cotyledons from three cultivars belonging to genetically distant varieties and a hybrid, Criollo, Forastero and Trinitario, did not reveal any analytical identity differences of VCG subunit polypeptide bands. Additionally, proteins of cotyledons harvested from three of those clones which were reported to produce genotype‐specific flavour differences in raw cocoa after standard fermentation, SCA 12, UIT1 and PBC 140, when analysed in the same way, did not indicate differences. Thus the cotyledon storage proteins from various genetically different cocoa trees are, within methodological limits, the same. We conclude that aroma differences in raw cocoa harvested from various genotypes are the result of other genetic, physiological or curing‐related factors, but are not due to genetic differences of aroma precursors derived from storage proteins. © 2002 Society of Chemical Industry     

Autolysis detection and evaluation of some lactic acid bacteria by renaturing sodium dodecyl sulphate‐polyacrylamide gel electrophoresis and polymerase chain reaction assays

Eleven lactic acid bacterial strains were tested for autolysis ability and the presence of autolytic enzymes by renaturing sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE). Polymerase chain reaction (PCR) assays for the detection of lysogenic strains were performed. Autolysis in a buffer system was observed in Lactobacillus delbrueckii subsp. bulgaricus DSM 20080, L. delbrueckii subsp. bulgaricus DSM 20081, Bifidobacterium longum subsp. infantis DSM 20088, B. angulatum DSM 20098 and Streptococcus thermophillus DSM 20617. Mitomycin C induction of prophage was demonstrated in B. longum subsp. infantis DSM 20088, B. angulatum DSM 20098, Lactobacillus acidophilus DSM 20242 and S. thermophillus DSM 20617. The presence of genes encoding known bacteriophage lysins was demonstrated by a PCR assay and correlated well with the autolytic phenotypes of the strains, indicating that PCR screening is useful in the rapid identification of autolytic strains.     

ELISA法检测牛奶中链霉素残留量

从抗原的制备、抗体的获得、酶结合物的合成等基础入手,建立了牛奶中链霉素残留量快速筛选检测方法,检测历时60min,方法的临界值为110μg/L。经试验证明该方法检测限可达20μg/L或以下,奶样用水稀释后可直接测定,批内变异系数小于20%,板间变异系数小于30%,200μg/L质量浓度处空白奶样添加回收率在60%-110%,符合快速筛选方法的要求。     

Proteolysis of reconstituted goat whey fermented by Streptococcus thermophilus in co‐culture with commercial probiotic Lactobacillus strains

Reconstituted goat whey was fermented with the starter Streptococcus thermophilus TA‐40 in co‐culture with four probiotic adjuncts (independent treatments): Lactobacillus casei BGP93 (T1), Lactobacillus paracasei BGP1 (T2), Lb. paracasei LPC37 (T3) and Lactobacillus rhamnosus LR32 (T4). Lactobacillus populations were higher than 7 log cfu/mL after fermentation and storage. Proteolysis increased significantly (P < 0.05) during fermentation in all trials. Relative amount of low‐molecular‐weight protein fractions (<6.5 kDa) increased in goat whey trials with T1, T3 and T4 during fermentation and storage. The goat whey powder was considered a potential substrate for starter and probiotic cultures, which raised the opportunities to upgrade this by‐product into a functional food.     

Efficient Extraction of Olive Pulp and Stone Proteins by using an Enzyme‐Assisted Method

An efficient protein extraction protocol for proteins from olive pulp and stone by using enzymes was developed. For this purpose, different parameters that affect the extraction process, such as enzyme type and content, pH, and extraction temperature and time, were tested. The influence of these factors on protein recovery was examined using the standard Bradford assay, while the extracted proteins were characterized by sodium dodecyl sulfate?polyacrylamide gel electrophoresis (SDS‐PAGE). The best extraction conditions were achieved at pH 7.0 and 5% (v/v) Palatase® 20000 L (lipase) for pulp and Lecitase® Ultra (phospholipase) for stone proteins. The optimal extraction temperature and time were 30 and 40 °C for 15 min for pulp and stone tissues, respectively. Under these conditions, several protein extracts coming from olive fruits of different genetic variety were analyzed, their profiles being compared by SDS‐PAGE. The developed enzyme‐assisted extraction method showed faster extraction, higher recovery, and reduced solvent usage than the nonenzymatic methods previously described in the literature. In the case of stone proteins, different electrophoretic profiles and band intensities were obtained that could be helpful to distinguish samples according to their genetic variety.     

Purification of Polyphenoloxidase from the Purple‐fleshed Potato (Solanum tuberosum Jasim) and its Secondary Structure

ABSTRACT: Polyphenoloxidase (PPO) was purified from purple‐fleshed potatoes (Solanum tuberosum Jasim) using membrane concentration, ammonium sulfate fractionation, Resource Q ion exchange chromatography, and Sephacryl S‐200 HR gel permeation chromatography. PPO was purified 78‐fold from a crude extract. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis results showed that the purified enzyme has a major subunit molecular weight of 40 kDa. To elucidate the secondary structure of the purified PPO, circular dichroism (CD) was performed. The CD spectrum of the purified enzyme showed that PPO contains 35% α‐helix, 30% β‐turn, and 35% random coil structure.     

鳗鱼中恩诺沙星残留量的酶联免疫检测方法

运用酶联免疫分析方法测定鳗鱼中恩诺沙星残留。测试曲线线性范围为0.3～10μg/kg,最低检测限为3μg/kg。向样品中分别添加25、50、100μg/kg 3个浓度水平的恩诺沙星, 平均回收率分别为74.5%、76.6%和66.5%,批内变异系数为7.62%～14.31%,批间变异系数为6.03%～7.00%,灵敏度达到0.3μg/kg。特异性试验结果表明与喹诺酮类中的其它药物以及其它类抗生素均无交叉反应。     

The effect of ageing on changes in myofibrillar protein in selected muscles in relation to the tenderness of meat obtained from cross‐breed heifers

The aim of this study was to evaluate the impact of the ageing on changes in selected myofibrillar proteins and Warner–Bratzler shear force values in muscles from cross‐breed Charolaise × Holstein Friesian heifers. Triceps brachii (TB), infraspinatus (IS), vastus lateralis (VL), semimembranosus (SM), biceps femoris (BF) and semitendinous (ST) muscles after ageing were examined. A significant muscle effect was found in the case of basic chemical composition, Warner–Bratzler shear force values and cooking loss. The vastus lateralis characterised by the lowest intramuscular fat percentage (P ≤ 0.05). The highest connective tissue content was shown for infraspinatus. This muscle had the lowest Warner–Bratzler shear force values in every ageing time, regardless of the cooking method. Throughout the ageing process, selected myofibrillar proteins were altered in all examined muscles, but at varying rates. The SDS‐PAGE electrophoresis and Western blotting analysis showed that desmin and troponin‐T degradation affected both muscles and ageing effects (P ≤ 0.001).     

水产品中氯霉素含量的快速检测与分析

运用酶联免疫法检测了市场上水产品中氯霉素含量,结果表明:水产品中氯霉素的含量均低于1礸/kg,符合残留低限,氯霉素含量在0.05～2.00礸/kg范围内、线性关系很好,r2=0.9839,平均回收率为76.2%,本方法的检测低限为0.05礸/kg。     

A Review: The Role of Barley Seed Pathogenesis‐Related Proteins (PRs) in Beer Production

Pathogenesis‐related proteins (PRs) are involved in the protection of dormant and germinating cereal seeds against pathogenic microorganisms and pests. Moreover, barley grain PRs have considerable technological importance in the brewing of beer. The compact structure of PRs allows them to survive the hostile conditions of the extracellular compartments, where they are usually localized, and enables the endurance of certain classes of PRs during the harsh conditions of the technological steps of beer production. Beer proteome maps reveal a dominant presence of PRs and facilitate association between particular proteins and specific beer quality traits. Current knowledge on the influence of PRs on the various aspects of beer quality has been summarized in this review.