Diketopiperazines in wines

This study describes the identification of cyclic dipeptides known as diketopiperazines in red, white and sparkling wines from Greek market. Diketopiperazines have been isolated from bottled wines after liquid–liquid extraction and identified using gas chromatography coupled with mass spectrometry. Cyclo (Leu–Leu), cyclo (Leu–Pro), cyclo (Phe–Pro), cyclo (Leu–Phe), cyclo (Val–Phe) and cyclo (Ala–Phe) were the six diketopiperazines that were identified in bottled wines made from local and international plant varieties. The varieties tested were agiorgitiko, malagouzia, xinomauro, roditis, muscat, athiri, mandilari, vidiano, cabernet sauvignon, syrah and merlot. The cyclo (Leu–Pro) was identified in eighteen bottled wines while the cyclo (Phe–Pro), cyclo (Leu–Phe), cyclo (Leu–Leu), cyclo (Ala–Phe) and cyclo (Val–Phe) were identified in a small number of samples. The analysis of some wine samples showed that the values of cyclo (Leu–Pro) ranged from 0.1 to 1?mg/L. These cyclic dipeptides have biological properties and may contribute to the beneficial health effects of wine.     

Novel diketopiperazine metabolism in a microorganism: two-step hydrolysis of cyclo(Gly-Leu) to amino acids and preliminary characterization of cyclo(Gly-Leu) hydrolase and dipeptidase

A bacterium, strain NM 5-3, isolated from soil exhibited the highest cyclo(Gly-Leu) (CGL)-hydrolyzing activity and was identified as Agrobacterium radiobacter. The reaction products from CGL were dipeptides (Leu-Gly and Gly-Leu) and amino acids (Leu and Gly). Inhibitors for the dipeptidase of this strain did not inhibit the hydrolysis of CGL to dipeptides, indicating that two distinct enzymes, CGLase and a dipeptidase, were involved in its hydrolysis. The activities of these two enzymes were separated by anion-exchange column chromatography. The results indicated that strain NM5-3 hydrolyzed CGL via the dipeptides to the corresponding amino acids. The CGLase fraction was found to catalyze the hydrolysis of cyclo(Gly-D-Leu), cyclo(Gly-Gly), cyclo(L-Ala-Gly), and cyclo(D-Ala-Gly). On the other hand, the dipeptidase fraction exhibited L-specific substrate specificity.     

玉米浆化学成分的分离纯化与结构鉴定

将玉米浆用4倍体积的甲醇进行醇沉，去除无机盐等强极性物质后，浓缩至小体积，用乙酸乙酯萃取，制得乙酸乙酯萃取物。利用硅胶柱色谱、HPLC等分离方法对玉米浆乙酸乙酯萃取物进行分离纯化，得到 23 个化合物。通过理化性质及波谱数据分析鉴定它们结构分别为对羟基苯丙酸（1）、3,4-二羟基-5-甲氧基苯丙酸甲酯（2）、R-2-羟基-3-苯基丙酸甲酯（3）、吲哚-3-乙酸甲酯（4）、2-羟基-3-甲基丁酸（5）、2-羟基-4-甲基戊酸（6）、3,4-二羟基苯丙酸甲酯（7）、二氢阿魏酸甲酯（8）、油酸（9）、对羟基苯乙酸（10）、三油酸甘油酯（11）、R-2-羟基-3-苯基丙酸（12）、环（缬-亮）二肽（13）、环（亮-亮）二肽（14）、环（苯丙-酪）二肽（15）、环（苯丙-缬）二肽（16）、环（亮-异亮）二肽（17）、环（苯丙-苯丙）二肽（18）、环（脯-亮）二肽（19）、尿嘧啶（20）、环（苯丙-甘）二肽（21）、环（苯丙-丙）二肽（22）、环（苯丙-丝）二肽（23）。这些化合物以环二肽、酚酸及其酯类为主，除化合物9以外，其余成分均为首次从玉米浆中分离得到。     

Enzymatic conversion of cyclic dipeptides to dehydro derivatives that inhibit cell division

The cell-free extract of an albonoursin-producing strain, Streptomyces albulus KO-23, was found to catalyze the conversion of several cyclic dipeptides having Phe and aliphatic side chain-containing amino acid residues to the corresponding dehydro derivatives. 3Z-Benzylidene-6S-methyl-2,5-piperazinedione, 3Z-benzylidene-2,5-piperazinedione, and 3Z, 6Z-dibenzylidene-2,5-piperazinedione were prepared by this conversion system. Among the dehydro cyclic dipeptides prepared, tetradehydro derivatives exhibited inhibitory activity toward the first cleavage of sea urchin embryo, while didehydro derivatives did not. We previously found that cyclo(Leu-Phe) and its didehydro derivatives did not show any inhibitory activity, in contrast to high activity in the case of albonoursin. Taken together, these findings indicate that dehydrogenation at the alpha,beta-positions of both amino acid residues in this type of cyclic dipeptide is required for the inhibitory activity.     

Effect of Actinidin on the Protein Solubility, Water Holding Capacity, Texture, Electrophoretic Pattern of Beef, and on the Quality Attributes of a Sausage Product

ABSTRACT:  The objective of this study was to study the effect of actinidin, a sulfhydryl protease from kiwi fruit, on the protein solubility (nitrogen solubility index [NSI]), water holding capacity (WHC), texture, and SDS–PAGE pattern of beef and to evaluate the effect of pretreatment of beef with actinidin on the quality attributes of a sausage product. Actinidin was partially purified by precipitation with ammonium sulfate, followed by DEAE-Sephadex column chromatography. Actinidin significantly ( P < 0.05) increased NSI and WHC of beef; the highest NSI and WHC (approximately 20% and 8% increase, respectively) was observed when beef was incubated with 0.9 unit enzyme/g beef. Texture analysis indicated increased tenderization (10% decrease in shear force) when slices of cattle beef were treated with actinidin at 37 °C for 2 h. SDS–PAGE results indicated appearance of several low molecular weight bands (<10 kDa) after treating beef with different levels of actinidin for 30 or 60 min. Slight changes in protein band in the range of 100 to 120 kDa and 13 to 25 kDa were also observed. Use of actinidin-tenderized beef significantly improved emulsion stability, texture, and organoleptic properties of the sausage product.     

Identification of new diketopiperazines in roasted coffee

This paper reports on the identification of new diketopiperazines (DKPs) in roasted coffee. The roasted coffee was extracted with hot water and CHCl₃ to achieve both a cleanup and a concentration of the DKPs. To get rid of the huge caffeine peak in both HPLC and GC analysis, this extract was cleaned up again by ion-exchange chromatography on Dowex 50Ǽ followed by gel chromatography on Sephadex G10. The identification was accomplished by HPLC-ESI-MS, HPLC-ESI-MS/MS, GC-EI-MS and by comparison with synthesised reference compounds. In roasted coffee the following DKPs were identified: cyclo(pro-gly), cyclo(pro-ala), cyclo(phe-val), cyclo(phe-leu), and cyclo(phe-ile). Except for cyclo(pro-gly), where only one isomer can be formed, each DKP was present in both possible isomeric forms.     

Effects of low-dose, low-penetration electron beam irradiation of chilled beef carcass surface cuts on Escherichia coli O157:H7 and meat quality

Low-dose, low-penetration electron beam (E-beam) irradiation was evaluated for potential use as an antimicrobial intervention on beef carcasses during processing. The objectives of this study were (i) to assess the efficacy of E-beam irradiation to reduce concentrations of Escherichia coli O157:H7 on a large beef surface and (ii) to evaluate the effect of the treatment on the sensory properties of the product. A 1-kGy dose of E-beam radiation reduced E. coli O157:H7 inoculated onto sections of cutaneous trunci at least 4 log CFU/cm2. In assessing organoleptic impact, flank steak was used as the model muscle. Flank steaks with various levels of penetration by radiation (5, 10, 25, 50, and 75%) were evaluated. None of the flank steak sensory attributes were affected (P > 0.05) by any penetration treatment. Ground beef formulations consisting of 100, 50, 25, 10, 5, and 0% surface-irradiated beef were tested. A trained sensory panel did not detect any difference between the control (0%) and either the 5 or 10% treatments. These results suggest that if chilled carcasses were subjected to low-dose E-beam irradiation, aroma and flavor of ground beef would not be impacted. The data presented here indicate that low-dose, low-penetration E-beam irradiation has potential use as an antimicrobial intervention on beef carcasses during processing and minimally impacts the organoleptic qualities of the treated beef products.     

Proteolytic specificity of cathepsin D on bovine F-actin

Proteolysis of bovine F-actin by cathepsin D (E.C. 3.4.23.5) in 50 mM Na acetate buffer, pH 5.5, at 37°C was investigated using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and reverse-phase high performance liquid chromatography (RP-HPLC). Actin was hydrolyzed by cathepsin D during incubation to peptides detectable by RP-HPLC, although no degradation products were detected by SDS-PAGE. Peptides (2% trichloroacetic acid-soluble) from the hydrolyzate were isolated by RP-HPLC on a C(18) column using an acetonitrile/water gradient and identified from their N-terminal sequence and mass. Cathepsin D cleavage sites were identified at Cys(12)-Asp(13), Gly(22)-Phe(23), Arg(30)-Ala(31), Thr(79)-Asn(80), Ile(87)-Trp(88), Thr(91)-Phe(92), Phe(92)-Tyr(93), Arg(97)-Val(98), His(103)-Pro(104), Leu(107)-Thr(108), Thr(108)-Glu(109), Lys(120)-Met(121), Leu(144)-Tyr(145), Ile(153)-Val(154), Leu(155)-Asp(156), Ile(167)-Tyr(168), Leu(180)-Asp(181), Met(192)-Lys(193), Leu(195)-Thr(196), Arg(208)-Glu(209), Arg(212)-Asp(213), Leu(223)-Asp(224), Lys(240)-Ser(241), Thr(262)-Leu(263), Trp(342)-Ile(343), Arg(349)-Ser(350), Trp(358)-Ile(359), and Lys(375)-Cys(376). In general, cathepsin D preferentially cleaved bonds containing at least one hydrophobic amino acid residue. The results of this study showed that actin was degraded extensively by cathepsin D with peptides released from numerous locations in the protein molecule.     

Chemical Modification and Functional Properties of Acylated Beef Heart Myofibrillar Proteins

Beef heart myofibrils were acylated with 0.1, 0.3, 0.6, 0.8, 1.0, 1.5, 2.0, 3.0, and 5.0 mmoles anhydride/g protein, at pH 8.0–8.5 and 2–3°C, with acetic anhydride (AA), succinic anhydride (SA), cis,cis,cis,cis-tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride (FA), and 1,2,4-benzenetricarboxylic anhydride (BA). The anhydride reacted with e-amino groups of lysine, sulfhydryl groups, and hydroxyl groups of tyrosine, serine, and threonine. Chemically modified beef heart myofibriliar proteins were superior to native heart myofibriliar proteins in solubility, emulsifying capacity, emulsion activity, and emulsion stability in a low salt solution of 0.1M NaCl, 0.05M potassium phosphate at pH 7.4 and 6.0. Protein modified with 0.5 mmole anhydride/g protein in 0.2M NaCl had a solubility greater than unmodified proteins in 0.6M NaCl at pH 7.4. Chemical modification also altered the pH-solubility profile. The chemically modified beef heart myofibrillar proteins exhibited an emulsifying capacity at pH 6.0 and 7.4 that was greater than that of the native proteins at pH 7.4. The recommended extent of acylation for modifying beef heart myofibrils on a gram protein basis is 0.6 mmole AA, 1.5 moles SA, 0.6 mmole FA, and 0.6 mmole BA.     

Prediction of the fatty acid composition of beef by near infrared transmittance spectroscopy

The intramuscular fat content and composition influence consumer selection of meat products. A study predicting the fatty acid (FA) profile of ground beef from the Longissimus thoracis of yearling bulls (n=100) using near infrared transmittance spectroscopy (NIT) was conducted. The samples were scanned using an Infratec 1265 Meat Analyzer which operates in transmittance mode from 850 to 1050nm. NIT technology was able to accurately predict (R(CV)(2) over 0.76) some prominent FAs such as C14:0, C16:0, C16:1cis9, C17:0, C18:1cis9 and C18:1cis11, and minor FAs like C13:0, C15:0, C17:1cis9 and C18:1cis13. When studying FA groups, NIT spectra were able to accurately predict saturated (R(CV)(2)=0.837), branched (R(CV)(2)=0.701) and monounsaturated (R(CV)(2)=0.852) FAs. In addition, NIT spectra provided useful information on the contents of conjugated linoleic acids (CLA) in beef. These results show the potential of NIT technique as a rapid and easy tool to predict the major FAs in beef, especially those located in triglycerides.     

Decreased dosage of acidified sodium chlorite reduces microbial contamination and maintains organoleptic qualities of ground beef products

Acidified sodium chlorite (ASC) spray was evaluated at decreased dosages and application rates to determine its efficacy for reducing bacterial contamination on boneless beef trimmings used for production of raw ground beef products while maintaining desirable consumer qualities in the finished ground beef products. Two different applications of ASC (600 ppm applied at a rate of 1.3 oz/lb and 300 ppm applied at a rate of 1 oz/lb) were used to treat boneless beef trimmings before grinding. The effect of ASC treatment on 50/50 lean beef trimmings was greater than on 90/10 trimmings. ASC at 600 ppm reduced both the aerobic plate counts (APC) and Enterobacteriaceae counts (EBC) by 2.3 log CFU/g on 50/50 trimmings, whereas treatment with 300 ppm ASC reduced APC and EBC of 50/50 trimmings by 1.1 and 0.7 log CFU/g, respectively. Ground beef formulations of 90/10 and 73/27 were produced from the treated boneless beef trim and packaged in chubs and in modified atmosphere packaging. The efficacy of ASC spray treatment to inhibit APC and EBC over the shelf life of each ground beef product was monitored. The APC and EBC in ground beef chubs were reduced by 1.0 to 1.5 log CFU/g until day 20. The APC and EBC for products in modified atmosphere packaging were reduced 1.5 to 3.0 log CFU/g throughout their shelf life. Both decreased dosages of ASC were equally effective on 90/10 lean ground beef, but the 300 ppm ASC treatment was slightly better at reducing the EBC of 73/27 ground beef. The organoleptic qualities (color, odor, and taste) of the ground beef products treated with 300 ppm ASC were found to be superior to those treated with 600 ppm ASC. Our results indicated that decreased dosages of ASC reduce contamination and lengthen the shelf life of ground beef. Furthermore, the 300 ppm ASC treatment reduced bacterial counts while maintaining desirable organoleptic ground beef qualities.     

Application of biospeckle laser technique for determining biological phenomena related to beef aging

Among the features of beef quality, color is a major factor that influences marketing since it is the only characteristic consumers can see at the time of purchase, although tenderness is the organoleptic trait that most affects consumer acceptance of beef. Thus, an effective technology to predict meat quality is highly desirable for the meat industry. Among many emerging technologies, optical methods have the greatest potential since they are fast, nondestructive, and generally low cost. This study evaluated the potential application of laser biospeckle technique and its methods of image processing in order to assess and quantify biological phenomena related to beef aging. Samples of muscle Longissimus thoracis were aged for 21 days and underwent biospeckle analysis, objective color and Warner–Bratzler Shear Force (WBSF). According to the results, biospeckle laser parameters may, possibly, assess biological activity resulting from action of endogenous enzymes (calpains and cathepsins) responsible for the aging process through its correlation (R = 0.6146) with analysis of WBSF and of the correlation (−0.7973) with aging time. High correlation of biospeckle analysis, related to traditional out puts and to new proposals, were obtained to color parameters, especially hue angle (h^*) whose R value was 0.7953, redness intensity (R = 0.8120) and percentage of metmyoglobin (MMb) showed that R value of 0.9119, demonstrates the potential of this technique for evaluating quality of meat color.     

Physicochemical and organoleptic characteristics of seasoned beef patties with added glutinous rice flour

This study was conducted to determine if glutinous rice flour (GRF) could be a functional food additive to potentially replace corn starch (CS), soy protein isolate (SPI) and/or sodium tripolyphosphate (STPP) to improve the physicochemical and organoleptic characteristics of seasoned beef patties. GRF had a lower cook loss among the treatment groups due to an increase in fat and moisture retentions (p<0.05). GRF lowered texture profile values for hardness, gumminess, springiness, and chewiness (p<0.05) of the patties, which are generally beneficial for this product. The beef patties with GRF were juicier and more tender than the control and other treatments (p<0.05). Hedonic scores for juiciness, tenderness and overall acceptability were the highest for the beef patties with 1 and 3% GRFs, suggesting that GRF may be an effective functional ingredient to improve the textural quality of seasoned beef patties.     

Outbreak of Escherichia coli 0157:H7 infections associated with consumption of beef donair

The Calgary Health Region identified an outbreak of Escherichia coli 0157:H7 infection in September 2004 following a fourfold increase in laboratory reports. Clinical isolates were indistinguishable by pulsed-field gel electrophoresis (PFGE), and the PFGE pattern was unique in North America. Most affected individuals reported beef donair consumption in 10-day food histories. We conducted a matched case-control study, inspected the implicated food premises, and conducted a traceback investigation of suspect ground beef to determine the source of the outbreak and implement prevention and control measures. A total of 43 laboratory-confirmed cases were identified, with symptom onsets between 8 September and 1 October 2004. Among 26 matched case-control pairs, consumption of beef donair from one of two locations of a local restaurant chain was the only statistically significant risk factor for infection (matched odds ratio undefined; P < 0.01). No samples of the implicated ground beef were available for microbiological testing. We identified several opportunities for time-temperature abuse and other factors that may have contributed to the serving of unsafe donair meat at the implicated restaurants. This outbreak highlighted gaps in food safety policy related to beef donair and similar products in Canada. Immediately following the outbreak, the Region implemented new safe food handling requirements and a Federal/Provincial/Territorial Working Group was established to make recommendations for national food safety policies specific to these products.     

Factors influencing proportion and composition of CLA in beef

Bovine meat is criticised for the bad nutritional image of its lipids and fatty acids. However, with dairy products, beef is the major source of conjugated linoleic acid (CLA) which could have several human health benefits. The present study compared, from data of five nutritional experiments on bovine animals performed by the laboratory, the impact of factors linked to the animals (breed, age, sex, type of muscle) and to feeding conditions (basal diet, lipid supplements) on the CLA proportion and composition in muscles. Among these factors, linseed supplementation was an efficient way to increase CLA proportion in beef (+22% to +36%) but was highly modulated by the nature of the basal diet, and by intrinsic factors (breed, age/sex, type of muscle) since these ones could modulate CLA proportion in beef from 24% to 47%. Moreover, these factors modified also the proportion of cis,trans-CLA, related to cis,cis- and trans,trans-isomers. Specific biological properties of these latter isomers should be determine to understand the consequences of intramuscular CLA isomer variations for the health of consumers.     

Comparative mutagenicity studies on fried minced beef,grilled sausage and grilled hamburgers

The mutagenicity of the basic fractions of fried beef patties, grilled hamburgers and grilled sausages was determined in the Ames test using activation systems (S9-mix) derived from untreated and Aroclor-pretreated rats and hamsters, and from rats pretreated with 3-methylcholanthrene or phenobarbitone. In order to indicate whether the mutagenic activity was due to the presence of thermally generated amino imidazo aza-arenes of the type previously identified in heated meat products (i.e. 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethylimidazo-[4,5-f]quinoline (MeIQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quin-oxaline), these compounds were assayed under the same conditions. The mutagenicity of the basic fractions of the cooked foods and of the three aza-arenes varied with the activation system used. The activation patterns of the basic fractions from fried beef and grilled sausages resembled that of IQ, whereas that of grilled hamburgers was more similar to that of MeIQ. Interestingly the total mutagenic activity of fried beef patties was greater than that of grilled hamburgers.     

High pressure induced hydrolysis at C-terminus of peptide derivatives yielding bioactive peptides

If the cyclization of a peptide is associated with a volume reduction, pressure should displace the reaction equilibrium in the direction of a lower volume. Here, results in model solutions are considered, showing a pressure-accelerated transformation of linear dipeptides with reactive C-terminals. The theorised cyclization of dipeptides after hydrolysis of the C-terminal amide H–Leu–Gly–NH₂ or methyl ester groups H–Leu–Gly–OMe and H–Leu–Gly–OtBu was found to be significantly accelerated during application of combined pressure/temperature treatments up to 600–800 MPa and 60–80 °C. Yields were dependent on the nature of the reactive site. Products of those reactions were identified as H–Leu–Gly–OH and cyclo(Leu–Gly), which is a bioactive dipeptide. The dipeptide amide yielded only trace concentrations of the amino acid H–Leu–OH and the linear dipeptide. Steric hindrance prevented a pressure induced cyclisation of a dipeptide with tert-butyl ester at the C-terminus, and only the linear peptide H–Leu–Gly–OH was formed.     

酱油中鲜味二肽的分离鉴定及其呈味特性研究

为了明确酱油中鲜味肽的结构序列,本文对酱油中鲜味肽进行分离鉴定,并系统地研究了其呈味特性。酱油经超滤膜(膜通量:5 ku、3 ku和1 ku)分离获得4个组分(F1,F2,F3和F4),通过感官评定筛选出鲜味最强的组分F4(1 ku)。该组分通过Sephadex G-15凝胶层析色谱继续分离得到8个组分(P1、P2、P3、P4、P5、P6、P7和P8),经感官评定筛选出鲜味最强的组分P2。采用超高压液相色谱串联质谱技术对P2组分进行多肽结构鉴定,通过手动De novo测序得到4条新的鲜味肽,其序列分别是Asn-Pro(230.1135 u)、Ala-His(227.1026 u)、Gly-Pro(173.0929 u)和Gly-Leu(189.1230 u)。然后采用固相合成技术合成四条肽并通过感官评定和电子舌分析,结果表明四条肽均具有明显的鲜味或鲜味增强作用。进一步研究发现,酱油的鲜味不仅来自于谷氨酸和天冬氨酸等鲜味氨基酸,小分子肽类也是构成酱油鲜味的重要成分之一。     

2010—2012年新疆乌鲁木齐地区零售生肉中沙门菌污染情况调查

通过对2010—2012年新疆乌鲁木齐地区零售生肉中沙门菌的检测分析,了解沙门菌污染情况,掌握乌鲁木齐地区零售肉品中沙门菌污染动态变化。方法 按照沙门菌检验国家标准GB/T 4789.1—2010对乌鲁木齐地区的零售肉(鸡肉、羊肉、牛肉、猪肉)检测分离沙门菌并进行血清型分型。结果 2010—2012年共检测1406份零售生肉样品,生鸡肉的感染率达到9.14%,生猪肉为9.06%,生羊肉为8.05%,生牛肉为6.44%,检测共分离得到123株沙门菌,经血清型鉴定可以分为4个血清群,7种血清型,分别为肠炎沙门菌(n=17)、萨奥沙门菌(n=9)、塔西沙门菌(n=8)、乌干达沙门菌(n=6)、康科德沙门菌(n=3)、汤姆逊沙门菌(n=3)和德尔卑沙门菌(n=2),未定型沙门菌75株。结论 新疆乌鲁木齐地区零售肉类中存在沙门菌污染,沙门菌菌株为不同的表型,地区内生肉品中沙门菌污染不容忽视,需要加强对零售肉市场的卫生检疫,防控沙门菌病。     

GC-O与GC-MS结合分析竹荪牛肉香精中的挥发性成分

采用同时蒸馏萃取结合气相色谱-质谱联机,通过双柱定性对竹荪牛肉香精中的挥发性成分进行分析,并通过谱库检索和保留指数比对,共计从竹荪牛肉香精中鉴定出化合物169 种,其中醇类26 种、醛类21 种、酮类9 种、酸类18 种、酚类4 种、酯类4 种、醚类6 种、烃类49 种、杂环及其他类32 种,其中十六醛、丁香酚、β-倍半水芹烯、茴香脑、β-红没药烯、α-姜烯、油醇等相对含量较大;通过气相色谱-嗅觉测定法,采用芳香萃取物稀释分析法对其特征风味成分进行了分析,共鉴定出33 种特征成分,其中2-甲基-3-呋喃硫醇、α-荜橙茄烯、反-佛手甘油烯、反式石竹烯,红没药醇对牛肉香精风味贡献相对较大。