液相色谱法测定核桃乳中糠氨酸含量

目的建立液相色谱法测定核桃乳中糠氨酸含量的检测方法。方法样品经酸水解、乙酸铵缓冲溶液定容后,经反相C18色谱柱分离,以甲醇/三氟乙酸溶液为流动相,流速为1.0mL/min,梯度洗脱,在紫外检测器波长为280 nm下检测。结果糠氨酸浓度在2～50μg/L的范围内线性关系良好,相关系数均大于0.999。糠氨酸在2.00、5.00和10.00mg/100g蛋白质添加水平的回收率为88.82%～91.95%,相对标准偏差(relative standard deviation, RSD)小于3.55%(n=6),方法检出限为1.0 mg/100 g蛋白质。结论该方法操作过程简单、方法准确、可靠、重现性好、回收率较高,适合于核桃乳中糠氨酸含量的分析检测。     

Tyramine content of some Cuban cheeses

The tyramine content of 8 types of cheeses made in Cuba were determined. Values obtained ranged from 0-425 micrograms/g. Highest results were found in Camembert-type cheese and lowest ones in Salami (processed type) cheese. It may be concluded that patients taking monoamine-oxidase inhibiting drugs should better not eat cheese, except processed or short-maturing types.     

High content of biogenic amines in Pecorino cheeses

Pecorino refers to Italian cheeses made exclusively from raw or pasteurized ewes' milk, characterized by a high content of fat matter and it is mainly produced in the Middle and South of Italy by traditional procedures. The autochthonous microbiota plays an important role in the organoleptic traits of Pecorino cheese and it can influence biogenic amines (BA) content.     

Effects of different heat treatments on the furosine content in fresh filled pasta

The effect of different heat treatments on the furosine content in fresh filled pasta was studied and the rate of furosine increase after treatment has been found to be influenced by the initial furosine content in the mixture and by the treatment design. A mathematical model to describe the experimental data has been developed. The reaction of furosine formation appears to follow a pseudo-zero kinetic order. The estimated value of activation the energy is roughly 111 KJ mole⁻¹ and the z value has been estimated around 22.9 °C. The “furosine increase” (If) parameter has been calculated from processing data in order to compare samples obtained with different time–temperature processing combinations. Calculated values were correlated with F₇₀¹⁰ values (pasteurising effect) and results indicate a good linear relationship between the furosine increase and F₇₀¹⁰ values (r²=0.963; P<0.01). The comparison of the pasteurisation curve with the furosine increase curve shows that an optimal process design for thermal processing of fresh filled pasta under our experimental conditions is obtained at temperatures between 95 and 99 °C for times from 6 to 2 min.     

Kinetics of hydroxymethylfurfural,lactulose and furosine formation in milk with different fat content

In the context of the general applicability of hydroxymethylfurfural (HMF), lactulose and furosine as time-temperature integrators (TTIs) for thermal processing of milk, the influence of milk fat content was studied. Formation kinetics were analysed for milk with fat content of 4.0 +/- <0.1%. In previous experiments, it was observed that, under isothermal and non-isothermal heating conditions, formation of the three chemical compounds could be described by pseudo-zero order kinetics. Since the kinetic model was known, the experimental design could be simplified. Data were analysed by a non-linear regression procedure and results were evaluated by construction of joint confidence regions and temperature time tolerance (TTT-) diagrams. Formation kinetics of HMF and lactulose was not affected by milk fat content. Regarding furosine, significant differences were observed between kinetic parameters in whole, semi-skimmed and skimmed milk. The observed differences however were negligible in the context of process impact evaluation.     

Survey of Fusarium toxins in foodstuffs of plant origin marketed in Germany

A total of 219 samples of foodstuffs of plant origin, consisting of grain-based food, pseudocereals and gluten-free food as well as vegetables, fruits, oilseeds and nuts, were randomly collected during 2000 and 2001 in food and health food stores. A spectra of 13 trichothecene toxins including diacetoxyscirpenol (DAS), 15-monoacetoxyscirpenol (MAS), scirpentriol (SCIRP), T-2 and HT-2 toxins (T-2, HT-2), T-2 triol, T-2 tetraol, neosolaniol (NEO) of the A-type as well as deoxynivalenol (DON), 3- and 15-acetyl-DON (3-, 15-ADON), nivalenol (NIV), and fusarenon-X (FUS-X) of the B-type were determined by gas chromatography/mass spectrometry. Analysis of zearalenone (ZEA), alpha- and beta-zearalenol (alpha- and beta-ZOL) was made by high-performance liquid chromatography with fluorescence and UV-detection. Detection limits ranged between 1 and 19 microg/kg. Out of 84 samples of cereal-based including gluten-free foods, 60 samples were positive for at least one of the toxins DON, 15-ADON, 3-ADON, NIV, T-2, HT-2, T-2 tetraol and ZEA, with incidences at 57%, 13%, 1%, 10%, 12%, 37%, 4% and 38%, respectively, whereas SCIRP and its derivatives MAS and DAS, T-2 triol, Fus-X as well as alpha- and beta-ZOL were not detected in any sample of this subgroup. Contents of DON ranged between 8 and 389 microg/kg, for all other toxins determined concentrations were below 100 microg/kg. The pseudocereals amaranth, quinoa and buckwheat were free of the toxins investigated. Ten of 85 samples of vegetables and fruits were toxin positive. ZEA and the type A trichothecenes MAS, SCIRP, DAS, HT-2 were detected in 7, 3, 2, 1 and 1 samples, respectively. Out of 35 samples of oilseeds and nuts, 7 samples were toxin positive. HT-2, T-2 and ZEA were detected in 4, 3 and 4 samples, respectively. In vegetables and fruits as well as in oilseeds and nuts, toxin levels were below 50 microg/kg. None of the B-type trichothecenes analysed was found for both subgroups.     

Presence of furosine in honeys

Nineteen commercial samples (with a shelf‐life of 2 years) and two artisanal samples (freshly collected and stored for 1 year respectively) of Spanish honeys were analysed for pH, protein content and furosine content. Most of the samples had pH values and protein contents within the limits reported in the literature. The presence of furosine was confirmed by comparison of its retention time with that of a furosine standard and by HPLC–MS. The level of furosine in the samples studied ranged from 4.32 to 13.62 g kg^?1 protein. The lowest furosine value was observed in the freshly collected artisanal sample. Heat treatment under severe conditions (90 °C for up to 135 min) increased the furosine content from 4.43 to 14.38 g kg^?1 protein. The results show that furosine seems to be a promising indicator to detect overheating during honey manufacture. © 2001 Society of Chemical Industry     

Provitamin A carotenoids and ascorbic acid contents of the different types of orange juices marketed in Spain

The vitamin C and provitamin A carotenoids contents of 25 commercially available Spanish orange juices were studied. Large differences in the levels of these compounds were found. On average, ultrafrozen orange juices (UFOJ) and orange juices from the ecological agriculture (OJFEA) showed the highest ascorbic acid contents (518 and 412 mg/l respectively) among the different kinds of orange juices studied. Some disagreement between the declared and the actual amounts of vitamin C were found. Provitamin A carotenoids were determined by means of the corresponding standards. The monohydroxycarotenoid accompanying β-cyptoxanthin in orange juices was identified as the non-provitamin A carotenoid, zeinoxanthin, on the basis of the methylation test with acidified methanol. Unusually high contents of β-carotene (>0.5 mg/l) were found in two samples, which could indicate that substantial amounts of the pigment were added to those juices. The mandarin juice analyzed showed the highest provitamin A activity (359.3 retinol activity equivalents/l) Among the orange juices surveyed, UFO proved to be the best source of provitamin A (78.5 retinol activity equivalents/l, on average). The lowest contents were found in orange juices from concentrate (OJFC) (22.4 retinol activity equivalents/l, on average, without considering the orange juices with unusual β-carotene contents).     

Incidence and characterization of Staphylococcus aureus in fishery products marketed in Galicia (Northwest Spain)

A total of 298 fishery products purchased from retail outlets in Galicia (NW Spain) between January 2008 and May 2009 were analyzed for the presence of Staphylococcus aureus. S. aureus was detected in a significant proportion of products (~25%). Incidence was highest in fresh (43%) and frozen products (30%), but it was high in all other categories: salted fish (27%), smoked fish (26%), ready-to-cook products (25%), non-frozen surimis (20%), fish roes (17%) and other ready-to-eat products (10%). A significant proportion of smoked fish, surimis, fish roes and other ready-to-eat products did not comply with legal limits in force. RAPD-PCR of 125 S. aureus isolated from fishery products was carried out using three primers (AP-7, ERIC-2 and S). Isolates displayed 33 fingerprint patterns. Each pattern was attributed to a single bacterial clone. Cluster analysis based on similarity values between RAPD fingerprints did not find relationship between any RAPD pattern and any product category. Isolates were also tested for se genes and susceptibility to a range of antibiotics (cephalothin, clindamycin, chloramphenicol, erythromycin, gentamicin, oxacillin, penicillin G, tetracycline, vancomycin, methicillin, ciprofloxacin and trimethoprim-sulfamethoxazole). Most isolates (88%) were found to be sea positive. Putative enterotoxigenic strains counts reached high risk levels in 17 products. No relationship was found between the presence of se genes and RAPD patterns. All isolates were resistant to penicillin, chloramphenicol and ciprofloxacin, and most to tetracycline (82.4%), but none was methicillin-resistant. A revision of pre-requisite programs leading to improve hygienic practices in handling and processing operations from fishing or farming to retail is recommended to ensure fishery products safety.     

A tribological analysis of cream cheeses manufactured with different fat content

Fat globules interspersed in the protein network have a major role in cream cheese texture that greatly impacts on its consumer acceptability. This study investigated the effects of fat content on the lubrication, rheological, and structural characteristics of cream cheeses manufactured with 0.5, 5.5 or 11.6% (w/w) fat content. All three cheese samples showed viscoelastic, non-Newtonian and shear thinning behaviour. The fat contents were shown to affect tribological behaviour and their high-speed regimes correlated well with the bulk rheology (viscosity). The low-fat content was associated with higher friction, firmer texture and reduced spreadability of the cream cheese, due to fewer fat globules being interspersed in the protein matrix, which was confirmed from confocal images.     

Differentiation of milks and cheeses according to species based on the mineral content

Summary The mineral composition of 113 samples of ewes', cows', and goats' milk and 68 samples of different types of pure-milk cheeses made from the milks of these species was analysed. Stepwise discriminant analysis of the milk samples yielded the variables K/Mg, Na/Ca, Zn, Cu/Zn, and Cu/Na as the most useful in differentiating the samples, achieving correct classification in 98.2% of cases. The most useful variables for the cheese samples were Fe/K, Na/Ca, Zn/Cu, Na/Mg, and Zn, which yielded correct classification in 97.1% of cases. The three goat's milk cheeses were successfully distinguished using the variables K/Zn, Fe/Cu, and P.

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Unterscheidung zwischen verschiedenen Milch- und Käsesorten anhand ihrer Mineralstoff-Zusammensetzung

Zusammenfassung An 113 Milchproben und 68 mit Schafmilch, Kuhmilch und Ziegenmilch hergestellten Käseproben wurde die Mineralstoff-Zusammensetzung analysiert. Die Anwendung der schrittweisen Diskriminatoriusanalyse bei den Milchproben ergab die Auswahl der Veränderlichen K/Mg, Na/Ca, Zn, Cu/Zn und Cu/Na als beste Unterschiedlichkeitsparameter mit einer zu 98,2% einwandfreien Klassifizierung. Die bei Käse ausgewählten Veränderlichen waren Fe/K, Na/Ca, Zn/Cu, Na/Mg und Zn mit einer zu 97,1% einwandfreien Klassifizierung. Die Unterscheidung zwischen den 3 geprüften Ziegenmilch-Käsesorten wurde durch die Veränderlichen K/Zn, Fe/Cu und P ermöglicht.

     

Survey of benzoic acid in cheeses: contribution to the estimation of an admissible maximum limit

Benzoic acid and its salts are commonly used additives in the food industry. Their use is not allowed in dairy products even though they can be found naturally. In this work, 100 cheese samples were tested to establish the maximum concentration that can be considered as “natural” and, therefore, permitted in cheeses. Analyses were carried out by a validated ion chromatography method and “positive” samples were confirmed by two other HPLC methods. Benzoic acid concentrations higher than the method LOQ (8.8?mg?kg^?1) were found in 18 samples, ranging from 11.3 to 28.7?mg?kg^?1, with a mean value of 20.5?mg?kg^?1. Taking into account the distribution of benzoic acid concentrations observed in “positive” samples, it is plausible to estimate a maximum admissible limit of 40.0?mg?kg^?1 for benzoic acid in cheese. Below this value, samples can be considered “compliant”.     

HPLC法测定乳品中的糠氨酸

本文采用高效液相色谱法测定乳品中的糠氨酸,应用耐酸的C18色谱柱和紫外检测器.本方法的最低检测限为1.48×10-9g,变异系数CV(%)为1.23,回收率为98.2%～100.8%.     

Survey of glycoalkaloids content in the various potatoes

The content of potato glycoalkaloid (PGA) was investigated in 27 cultivars of raw potatoes and 31 potatoes in commercial foods with peel. The investigation of the 27 cultivars of potatoes showed different contents of glycoalkaloids. "May queen" and "Sherry" showed high contents of PGA (180 mg/kg and 320 mg/kg, respectively) among the raw potatoes of middle size (ca. 100 g). On the other hand, "Inca red" showed the lowest content of 21 mg/kg. Higher contents of PGA were found in smaller potatoes in this study. The content of PGA varied in the range of 48-350 mg/kg in the potatoes in commercial foods with peel.     

Resveratrol content in wines and musts from the south of Spain

Trans- and cis-resveratrol and their glycosides have been determined in eighty-one samples including musts, substrate wines and commercial wines (red, white and Sherry-type wines) from the south of Spain. Sample analysis was performed using a direct injection technique by HPLC with photodiode array detector. Prior to the injection, the sample was filtered using a filter selected through a complete filtration study. Climatological data can affect total resveratrol levels. Values obtained for total resveratrol content in red wines ranged from 0.038 mg/l in a dry year to 1.164 mg/l for a normal year. The pressure applied to the berries to obtain must, has been object of study in order to ascertain its influence in final resveratrol content. For the same vintage, the total resveratrol content ranged from 0.032 mg/l in a wine, obtained from the lighest pressure musts, to 0.873 mg/l for those obtained from the highest pressure musts. No resveratrol has been found in Sherry wines, being present in the substrate wines in all cases.     

Sodium content in retail Cheddar, Mozzarella, and process cheeses varies considerably in the United States

Reducing the sodium content in cheese is expected to contribute to reducing the overall intake of sodium by US consumers. The purpose of this study was to measure the sodium levels in cheeses that are most commonly purchased by US consumers in the retail market, including brand and private label. A secondary purpose of the study was to generate data that can enable the dairy industry to adopt best practices regarding sodium levels in cheeses. The sodium content of a total of 1,665 samples of Cheddar (650 samples), low moisture part skim (LMPS) Mozzarella (746 samples), and process cheese singles (269 samples) from 4 geographical regions were collected over a period of 3 wk, and were analyzed over a 1-mo period. Process cheese contained the highest mean level of sodium (1,242 mg/100 g), followed by string cheese (724 mg/100 g). Across Cheddar cheese forms and brands, the mean analytical sodium was 615 mg/100 g, with 95% between 474 and 731 mg/100 g; label sodium ranged from 600 to 800 mg/100 g (mean 648 mg). Across all LMPS Mozzarella forms and brands, the mean analytical sodium was 666 mg/100 g, with 95% between 452 and 876 mg/100g; label sodium ranged from 526 to 893 mg/100 g (mean 685 mg). Across all process cheese forms and brands, the mean analytical sodium was 1,242 mg/100 g, with 95% between 936 and 1,590 mg/100 g; label sodium ranged from 1,185 to 1,740 mg/100 g (mean 1,313 mg/100 g). These findings demonstrate that manufacturers tended to be conservative with their reporting of sodium on labels. Manufacturers need to reduce variability to better target desired sodium levels, which is an opportunity for better process control, and will enable them to label sodium more accurately.     

Survey of raw milk cheeses for microbiological quality and prevalence of foodborne pathogens

Cheese may be manufactured in the United States using raw milk, provided the cheese is aged for at least 60 days at temperatures not less than 35 °F (1.7 °C). There is now increased concern among regulators regarding the safety of raw milk cheese due to the potential ability of foodborne pathogens to survive the manufacturing and aging processes. In this study, 41 raw milk cheeses were obtained from retail specialty shops, farmers’ markets, and on-line sources. The cheeses were then analyzed for the presence of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, Staphylococcus aureus, and Campylobacter. Aerobic plate counts (APC), coliform and yeast/mold counts were also performed. The results revealed that none of the enteric pathogens were detected in any of the samples tested. Five samples contained coliforms; two of those contained E. coli at less than 10² cfu/g. Three other cheese samples contained S. aureus. The APC and yeast-mold counts were within expected ranges. Based on the results obtained from these 41 raw milk cheeses, the 60-day aging rule for unpasteurized milk cheeses appears adequate for producing microbiologically safe products.     

Fast and sensitive determination of furosine

Sensitive determination of furosine in acid hydrolysates of foods was achieved by isocratic ion-pair reversed-phase HPLC and direct UV-detection within a run time of 5 minutes and levels lower than 1.5 mg per kg of protein. The formation of furosine during hydrolysis of food samples with hydrochloric acid of varying concentration was studied. Furosine formation increased linearly with acid concentration (4 to 8 mol/L).

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Methode zur schnellen und empfindlichen Bestimmung von Furosin

Zusammenfassung Mittels isokratischer Ionenpaar-RP-HPLC gelang die empfindliche Bestimmung von Furosin in Säurehydrolysaten von Lebensmitteln innerhalb von 5 Minuten Laufzeit und mit einer Nachweisgrenze von unter 1,5 mg pro kg Protein. Die Bildung von Furosin während der Hydrolyse von Lebensmittelproben erwies sich zwischen Konzentrationen von 4 und 8 mol/L als linear von der Salzsäurekonzentration abhängig.

     

Survey of histamine content in seafood on the market

Food poisoning involving histamine has occurred almost every year for 20 years in Tokyo, and is usually due to ingestion of fish with lean meat, such as sardine, mackerel, horse mackerel and so on. Therefore, we were investigated the levels of histamine and 4 non-volatile amines (tyramine, putrescine, cadaverine, spermidine) in 637 samples on the market. The water activity of samples in which histamine was detected at 5 mg/100 g and over was examined. Histamine, tyramine, putrescine, cadaverine and spermidine were detected in 66, 43, 26, 64 and 5 samples, and the detection ranges were 5-340, 5-51, 5-42, 5-180 and 5-8 mg/100 g, respectively. Most of the samples in which histamine was detected were semi-dried round and split sardine. Water activity of 24 samples of semi-dried round and split sardine in which histamine was detected was in the range of 0.68-0.96.     

Survey of the occurrence of aflatoxin M1 in dairy products marketed in Italy: second year of observation.

During 1996, 161 samples of milk, 92 samples of dry milk for infant formula and 120 samples of yoghurt, were randomly collected in supermarkets and drug stores in four big Italian cities, and checked for aflatoxin M1 (AFM1) by immunoaffinity column extraction and HPLC. AFM1 was detected in 125 (78%) of milk samples (ranging from < 1 ng/l to 23.5 ng/l; mean level: 6.28 ng/l), in 49 (53%) of dry milk samples (ranging from <1 ng/l to 79.6 ng/kg; mean level: 32.2 ng/kg) and in 73 (61%) of yoghurt samples (ranging from <1 ng/kg to 32.1 ng/kg; mean level: 9.06 ng/kg). Altogether, only four samples of dry milk were over the legal limits established by the EC in 1999. It is concluded that during 1996, despite the widespread occurrence of AFM1, mean contamination levels in dairy products sold in Italy were not a serious human health hazard.