Distribution and stability of aflatoxin M1 during processing, ripening and storage of Telemes cheese

Telemes cheeses were produced using milk that was artificially-contaminated with aflatoxin M1 at the levels of 0.050 and 0.100 microg/l. The cheeses produced in the two cheese-making trials were allowed to ripen for 2 months and stored for an additional 4 months to simulate commercial production of Telemes cheese. Concentrations of aflatoxin M1 in whey, curd, brine, and the produced cheeses were determined at intervals by liquid chromatography and fluorometric detection coupled with immunoaffinity column extraction. Concentrations of aflatoxin M1 in the produced curds were found to be 3.9 and 4.4 times higher than those in milk, whereas concentrations in whey were lower than those in curd and milk. Aflatoxin M1 was present in cheese at higher concentrations at the beginning than at the end of the ripening/storage period, and it declined to concentrations 2.7 and 3.4 times higher than those initially present in milk by the end of the sixth month of storage. Concentrations of aflatoxin M1 in brine started low and increased by the end of the ripening/storage period but only a portion of the amounts of aflatoxin M1 lost from cheese was found in the brine. Results showed that Telemes cheeses produced from milk containing aflatoxin M1 at a concentration close to either the maximum acceptable level of 0.05 microg/l set by the European union (EU) or at double this value, will contain the toxin at a level that is much lower or slightly higher, respectively, than the maximum acceptable level of 0.250 microg of aflatoxin M1/kg cheese set by some countries.     

Biogenic amines in Iranian white brine cheese: modelling and optimisation of processing factors

The simultaneous effects of processing factors such as ripening time (25–75 days), ripening temperature (4–14 °C) and brine concentration (10–13%) on biogenic amines content, proteolysis and sensory score of Iranian white brine cheese were studied, in 12 cheeses. Response surface methodology (RSM) was used to minimise biogenic amines content. At low level of ripening time, biogenic amines content decreased with increasing levels of brine concentration but at high level of ripening time, brine concentration had inverse effect. Ripening time showed quadratic effect on biogenic amines content. Based on biogenic amines content and sensory score, the optimum conditions were 13% brine and ripening at 9–14 °C for 43–65 days.     

Distribution and stability of Aflatoxin M1 during processing and ripening of traditional white pickled cheese

The distribution of aflatoxin M₁ (AFM₁) has been studied between curd, whey, cheese and pickle samples of Turkish white pickled cheese produced according to traditional techniques and its stability studied during the ripening period. Cheeses were produced in three cheese-making trials using raw milk that was artificially contaminated with AFM₁ at the levels of 50, 250 and 750 ng/l and allowed to ripen for three months. AFM₁ determinations were carried out at intervals by LC with fluorescence detection after immunoaffinity column clean-up. During the syneresis of the cheese a proportionately high concentration of AFM₁ remained in curd and for each trial the level was 3.6, 3.8 and 4.0 times higher than levels in milk. At the end of the ripening, the distribution of AFM₁ for cheese/whey + brine samples was 0.9, 1.0 and 1.3 for first, second and third spiking respectively indicating that nearly half of the AFM₁ remained in cheese. It has been found that only 2-4% of the initial spiking of AFM₁ transferred into the brine solution. During the ripening period AFM₁ levels remained constant suggesting that AFM₁ was quite stable during manufacturing and ripening.     

Fate of aflatoxin M1 in cheese whey processing

Aflatoxin M₁ (AFM₁) is an important mycotoxin frequently found in milk and in dairy products. It is a minor metabolic product of Aspergillus flavus and A parasiticus. However, it occurs in dairy products as a metabolite formed in cows from aflatoxin B₁ contained in animal feeds. In cheese production, AFM₁ distributes between curd and whey, being present in products derived from cheese whey processing. In this study, cheese whey from dairy processing was artificially contaminated with the mycotoxin at about 0.1 µg l⁻¹. Ultra‐filtration experiments of whey were carried out in order to determinate AFM₁ distribution between retentate (protein‐rich fraction) and permeate (lactose‐rich fraction). Recoveries of AFM₁ in retentate were 72.6–86.4% while, in permeate, recoveries were in the range 2.4–14.7%. Partition coefficients of AFM₁, lactose and protein were calculated to determine whether there was an interaction between AFM₁ and protein. In all experiments, AFM₁ partition coefficient was lower than 1, whilst for lactose coefficients close to 1 were determined, showing an affinity of aflatoxin M₁ to the protein‐rich fraction (retentate). Copyright © 2005 Society of Chemical Industry     

Survey of aflatoxin M1 in milk and dairy products consumed in Burdur,Turkey

The aim of this study was to investigate the occurrence of aflatoxin M₁ (AFM₁) in dairy product samples in Burdur city. A total of 315 samples of dairy products were collected during 2008. Of the 315 samples analysed, AFM₁ in 246 samples (78.1%) was found to range from 5.5 to 800 ng/kg. In addition, AFM₁ levels of 16 raw milk, two pasteurised milk, only one milk powder and three white cheese samples were above the Turkish Food Codex. It is concluded that the occurrence of AFM₁ in dairy products may be considered as a possible hazard for public health.     

Comparison of nixtamalization and extrusion processes for a reduction in aflatoxin content

Traditional nixtamalization and an extrusion method for making the dough ( masa ) for corn tortillas that requires using lime and hydrogen peroxide were evaluated for the detoxification of aflatoxins. The traditional nixtamalization process reduced levels of aflatoxin B 1 (AFB 1 ) by 94%, aflatoxin M 1 (AFM 1 ) by 90% and aflatoxin B 1 -8,9-dihydrodiol (AFB 1 -dihydrodiol) by 93%. The extrusion process reduced levels of AFB 1 by 46%, AFM 1 by 20% and AFB 1 -dihydrodiol by 53%. Extrusion treatments with 0, 0.3 and 0.5% lime reduced AFB 1 levels by 46, 74 and 85%, respectively. The inactivation of AFB 1 , AFM 1 and AFB 1 -dihydrodiol in the extrusion process using lime together with hydrogen peroxide showed higher elimination of AFB 1 than treatments with lime or hydrogen peroxide alone. The extrusion process with 0.3% lime and 1.5% hydrogen peroxide was the most effective process to detoxify aflatoxins in corn tortillas, but a high level of those reagents negatively affected the taste and aroma of the corn tortilla as compared with tortillas elaborated by the traditional nixtamalization process.     

定性测定羊奶中黄曲霉毒素M1残留高灵敏度检测卡的研制

研制定性测定羊奶中黄曲霉毒素M1残留的高灵敏度检测卡.在硝酸纤维素膜上预包被黄曲霉毒素M1全抗原作为检测线,以及预包被羊抗鼠二抗作为质控线.将抗黄曲霉毒素M1单克隆抗体用胶体金标记作为金标垫.将样品垫、金标垫、预包被黄曲霉毒素M1的硝酸纤维素膜以及吸水垫依次粘贴在PVC板上,切割成试纸条并组装成检测卡.结果表明:该检测卡的检测限为0.5μg/L,对黄曲霉毒素M1的交叉反应率为100％,而与同族的其他物质的交叉反应率小于5％.假阳性率小于5％,假阴性率为0％,检测卡常温储存,保质期18个月.本研究的检测卡,可快速准确地应用于羊奶中黄曲霉毒素M1残留的定性检测,为快速准确地测定羊奶中黄曲霉毒素M1残留提供了依据.     

Proteolysis in ultra-filtered and conventional Iranian white cheese during ripening

Conventional and ultra-filtered (UF) Iranian white cheeses were made with almost identical gross chemical composition and the extent and characteristics of proteolysis were studied during ripening. UF cheeses exhibited a lower rate of development of pH 4.6-soluble nitrogen than conventional cheeses. The rates of degradation of α_s1-casein and particularly β-casein were lower in UF cheeses than in conventional cheeses. Plasmin activity was lower in UF cheeses than that in conventional cheese, whereas coagulant activity was higher in the former. Noticeable qualitative and quantitative differences were observed in reverse-phase high performance liquid chromatography (RP-HPLC) peptide profiles between UF and conventional white cheeses and chemometric analysis of peak height data distributed the cheeses into two separate groups. The levels of free amino acids in UF cheeses were lower than in conventional cheeses. Lower peptide degradation and production of amino acids suggested slower ripening, which may have been associated with the weak aroma development characteristic of UF cheeses.     

Modeling of proteolysis and lipolysis in Iranian white brine cheese

The simultaneous effects of processing variables such as ripening time (20–60 days), ripening temperature (6–10 °C), level of rennet added (1–2 g/100 kg milk) and brine concentration (8–14%, w/v) on the proteolysis, lipolysis and sensory score of Iranian white brined cheese (Feta type) were explored by the means of response surface methodology. The most important effect in proteolytical terms was produced by ripening temperature and ripening time in linear form, but level of rennet added and brine concentration were also significant at the 5% level. In terms of lipolysis, ripening time was dominant factor in both linear and quadratic forms; quadratic effect of ripening temperature was greater than its linear effect.     

Efficiency of Bifidobacterium bifidum and Saccharomyces cerevisiae for detoxification of aflatoxin M1 in skim milk

Aflatoxin M1 (AFM1) is a carcinogenic mycotoxin mostly found in dairy products. The aim of this study was to evaluate the anti-aflatoxin effect of Bifidobacterium bifidum and Saccharomyces cerevisiae with two different concentrations (10⁸ and 10¹⁰ cfu/mL), alone or mixed, in contaminated skim milk with three concentrations of AFM1 (0.1, 0.25 and 0.5 μg/mL) and incubated at 4, 25 and 37°C for different times (30, 60, 120 min and 24 h). We found that the storage time is a key factor that significantly affects AFM1 removal. Also, removal of AFM1 was dependent on other factors such as micro-organisms' concentration, incubation temperature and toxin concentration. The effective strategy for the highest removal of AFM1 (90%) in contaminated milk spiked with 0.5 μg/mL, which was treated with mixed strains at concentration10¹⁰ cfu/mL and incubated at 37°C after 24 h. The presented methodology can be considered as a potential method for reducing the aflatoxin content of polluted dairy products.     

酶联免疫法测定食品和饲料中的黄曲霉毒素

本实验应用酶联免疫方法对食品和饲料中的黄曲霉毒素进行测定,奶粉中黄曲霉毒素M1的多次重复测定的结果的变异系数小于12%,回收率接近90%。说明本试剂盒测定结果比较精确,重现性较好。食品辅料及饲料中的黄曲霉毒素B1的测定结果的变异系数小于15%,说明实验结果的重现性较好。     

酶联免疫法测定食品和饲料中的黄曲霉毒素

本实验应用酶联免疫方法对食品和饲料中的黄曲霉毒素进行测定，奶粉中黄曲霉毒素M1的多次重复测定的结果的变异系数小于12％，回收率接近90％。说明本试剂盒测定结果比较精确，重现性较好。食品辅料及饲料中的黄曲霉毒素B1的测定结果的变异系数小于15％。说明实验结果的重现性较好。     

Occurrence of aflatoxin M1 in raw and market milk commercialized in Greece

From December 1999 to May 2000, 114 samples of pasteurized, ultrahigh temperature-treated (UHT) and concentrated milk were collected in supermarkets, whereas 52 raw milk samples from cow, sheep and goat were obtained from different milk producers all over Greece. Sample collection was repeated from December 2000 to May 2001 and concerned 54 samples of pasteurized milk, 23 samples of bulk-tank raw milk and 55 raw milk samples from cow, sheep and goat. The total number of samples analysed for aflatoxin M₁ (AFM₁) contamination by immunoaffinity column extraction and liquid chromatography was 297. In the first sampling, the incidence rates of AFM 1 contamination in pasteurized, UHT, concentrated and cow, sheep and goat raw milk were 85.4, 82.3, 93.3, 73.3, 66.7 and 40%, respectively, with only one cow raw milk and two concentrated milk samples exceeding the EU limit of 50 ng l^-1. In the second sampling, the incidence rates of AFM 1 contamination in pasteurized, bulk-tank and cow, sheep and goat raw milk were 79.6, 78.3, 64.3, 73.3 and 66.7%, respectively, with only one cow and one sheep raw milk samples exceeding the limit of 50 ng l^-1. The results suggest that the current regulatory status in Greece is effective.     

Short communication: Occurrence of aflatoxin M1 in the Manchego cheese supply chain

The importance of ewe milk lies in the production of high quality cheeses, such as Manchego cheese with a Protected Designation of Origin, whose safety must be guaranteed. In a 2-yr study, 407 bulk tank milk samples from farms and 82 silo milk and curd samples from cheese factories were collected from southeast Spain and tested for aflatoxin M1 (AFM1) using 2 commercial ELISA tests. Of these, 99.3% of the bulk tank samples had AFM1 levels below the European Union (EU) legal limit for milk (50 ng/kg), and well below the limit adopted by the Codex Alimentarius (500 ng/kg). Moreover, 98.8% of the silo milk and curd samples from cheese factories had AFM1 levels below the EU limit for milk. When considering median AFM1 concentrations, an average 4-fold increase was found in the final curd in relation to the corresponding silo milk. Control of AFM1 in Manchega ewe milk would enhance dairy product safety by the possible detection of faults in the manufacture of Manchego cheese.     

降解黄曲霉毒素M1菌株筛选方法的建立与菌株鉴定

为实现对黄曲霉毒素M1(Aflatoxin M1,AFM1)的生物降解,建立从环境中筛选AFM1降解菌株的方法并得到降解菌株。结果表明:对采自农田、粮库、牛场的300个土壤或粪便样品,初筛选出能在以香豆素为唯一碳源的培养基上生长的菌株37株;用液相色谱法测定降解率进行复筛,得到3株降解率在50%以上的菌株;进而对复筛菌株进行生长条件和耐受性实验,筛选出降解率为78.6%,生长速度快、长势好、稳定期长,且降解过程中热稳定性好的菌株102807。经过菌落细胞形态学、生理生化特征及16S r DNA序列系统发育分析,鉴定为纤维纤维微菌(Cellulosimicrobium cellulans)。首次发现了纤维纤维微菌对AFM1的生物降解功能。      

Reduction in aflatoxin M1 concentration during production and storage of selected fermented milks

This study focused on monitoring changes in aflatoxin M1 (AFM1) concentrations during production and storage of different fermented milks using selected probiotic and nonprobiotic combined cultures. Milk samples intended for fermentation were intentionally contaminated by adding a standard of AFM1. All of the tested cultures caused remarkable reductions in AFM1 concentrations during the fermentation process. Probiotic cultures were more effective than nonprobiotic cultures, with Lactobacillus caseiLC‐01 strain being the most efficient, achieving a reduction level of approximately 58%. Among the nonprobiotic cultures, yoghurt culture YC‐380 was the most efficient, with a reduction level of approximately 41%.     

Occurrence of aflatoxin M1 in randomly selected North African milk and cheese samples

Forty-nine samples of raw cow's milk and 20 samples of fresh white soft cheese were collected directly from 20 local dairy factories in the north-west of Libya and analysed for the presence of aflatoxin M₁ (AFM₁). The samples were analysed using a high-performance liquid chromatography technique for toxin detection and quantification. Thirty-five of the 49 milk samples (71.4%) showed AFM₁ levels between 0.03 and 3.13 ng ml^-1 milk. Multiple analyses of five milk samples free of AFM₁ artificially contaminated with concentrations of AFM₁ at 0.01, 0.05, 0.1, 1.0 and 3.0 ng ml^-1 showed average recoveries of 66.85, 72.41, 83.29, 97.94 and 98.25%, with coefficients of variations of 3.77, 4.11, 1.57, 1.29 and 0.54%, respectively. Fifteen of 20 white soft cheese samples (75.0%) showed the presence of AFM₁ in concentrations between 0.11 and 0.52 ng g^-1 of cheese. Multiple assays of five cheese samples free of AFM₁ spiked with different concentration of AFM₁ (0.1, 0.5, 1.0 and 3.0 ng g^-1) showed average recoveries of 63.23, 78.14, 83.29 and 88.68%, with coefficients of variation of 1.53, 9.90, 4.87 and 3.79%, respectively. The concentrations of AFM₁ were lower in the cheese products than in the raw milk samples.     

ELISA and HPLC determination of the occurrence of aflatoxin M 1 in raw cow's milk

Raw cow's milk collected from dairy farms in the province of Leon, Spain, was examined for aflatoxin M 1 (AFM 1 ). The samples were analysed with a commercial competitive enzyme-linked immunosorbent assay (ELISA) kit and high-performance liquid chromatography (HPLC). The concentrations of AFM 1 in the milk extracts were initially estimated by ELISA, with recovery rates of 74.6-109% for artificially contaminated milk at levels of 10-80 ng l 1 . Samples found to contain more than 10 ng l 1 were further quantified with HPLC. The mean recovery for this method was 89.3%. The quantification limit was 10 ng l 1 for both ELISA and HPLC. Although AFM 1 was confirmed in only 3.3% of the samples, the concentrations in all these cases were lower than the maximum limit applicable to these products pursuant to European Union legislation. Both methods were validated with reference material certified by the Community Bureau of Reference.     

Influence of storage,brine concentration and in‐container heat treatment on the stability of white brined Nabulsi cheese

Microbial levels were significantly (P < 0.05) affected by the temperature‐time treatments used during in‐container heat treatment of the curd, brine concentration and storage duration. A heat treatment of 115 °C × 2 min, in the absence of NaCl, was sufficient to eliminate Mesophilic micro‐organisms, Coliforms, Staphylococcus aureus and Yeast and Moulds for the duration of 1 year of storage. Sensory scores for colour, appearance and texture increased significantly (P < 0.05) with the increase in the NaCl in brine concentration regardless of the temperature‐time treatment.