Mycoflora, mycotoxins, bacteriological analysis and molecular assay of some bacterial species from coffee beans in Saudi Arabia

ABSTRACT

The mycoflora analysis of some coffee beans in Saudi Arabia showed a wide range of fungal contamination in 31 samples collected from different markets in El-Riyadh. Thirty four species belonging to 16 genera and 28 species belonging to 18 genera were isolated from coffee beans on glucose and cellulose Czapek's agar medium at 25°C from seed-plate method. Aspergillus niger and A. flavus were the most prevalent species, but Penicilliun oxalicum was isolated in moderate occurrence, while 12 genera comprised 16 species and 8 genera comprised 10 species were isolated on the same types of media at 25°C from seed suspension method. A. niger was the most common species, while A. flavus and P. funiculosum were isolated in moderate occurrence. A. niger, also was the most prevalent on 20% sucrose-Czapek's agar medium at 25°C, but the genus Eurotium [3 spp] appeared in moderate occurrence. Five fungal species belonging to four genera were isolated on starch yeast extract agar medium at 45°C. A. fumigatvs and A. niger were the most prevalent thermo tolerant species, while three species of thermophilic fungi were of low or rare incidence. Thin layer chromatographic analysis of chloroform extracts of 31 coffee beans samples revealed that 20 samples were free from mycotoxins, while 11 samples were contaminate with aflatoxins B[1], B[2], G[1] and G[2] of concentrations ranged from 110-600 micro g/kg, but 6 samples were contaminate with sterigmatocystin ranged from 60-600 micro g/kg. Screening of the characteristic mycotoxins of 25 fungal isolates revealed that 17 of them produced, aflatoxin B[1] at 450 micro g/kg, ochratoxin A at 600 micro g/kg, ochratoxin B at 400 micro g/kg, and sterigmatocystin 280 micro g/kg from Aspergillus species, while three isolates of Penicillium produced penicillic acid [ranged from 720-240 micro g/kg] and one isolate of Trichoderma produced Trichodermine at 360 micro g/kg. The bacteriological analysis of the coffee bean samples indicated that Bacillus cereus was detected in six samples at levels [2x10 cfu/g], E. coli in two samples [14x10 and 89x10 cfu/g], Feacal coliform was detected in one sample only, while Staphylococcus appeared in 29 samples [55x103 cfu/g]. All samples were free from Salmonella. PCR assay for detection of some bacterial species revealed that all samples were negative for Yersinia enterocolitica, Campylobacter and Listeria monocytogenes, while the results of B. cereus and Salmonella were similar to the results obtained using cultural method: