Abstract: The present study was conducted to identify the soil mycoflora which could utilize the milk as a sole source of nitrogen and carbon. Soil samples collected from dairy farms were screened for fungi which could utilize milk powder as a sole source of carbon and nitrogen for their growth. Aspergillus was the predominant genus with 23 species followed by Penicillium with 21 species. Other dominant genera were Chaetomium (11 species), Eupenicillium (8 species), Cladosporium (5 species) and Chrysosporium (5 species). Altogether 131 fungal species belonging to 50 genera were isolated .
Introduction
Milk and other dairy products are nutritious food. These are also a good medium for microbial growth. Studies on microbiology of milk and milk product have mainly concentrated on bacteria (Parry and Pawsey, 1984; Weiser et al., 1971). Various molds like, Aspergillus, Penicillium, Alternaria, chaetomium, Neurospora, Monilia, Mucor, etc. have been reported to cause deterioration of foods including milk products (Parry and Pawsey, 1984). Fungi such as Aspergillus, Penicillium, Rhizopus and various yeast and actinomycetes are used commercially for the production of milk products, bakery products, chemical and medicines (Casida, 1991; Weiser et al., 1971).
No work has been reported, so far, from Saudi Arabia about the mycoflora of milk and milk products. The aim of this study was to identify the soil mycoflora which could utilize the milk as a sole source of nitrogen and carbon.
Materials and Methods
Soil samples were collected from 3 dairy farms (Sanabil farms, Al Salehia farm, Newesir farm) located at on the outskirts of Riyadh City. Fifty replicate soil samples were collected from each dairy farm. All soil samples collected from one farm were mixed together and five gram of this mixed soil was taken at random and poured into 45 ml of pre-sterilized distilled water. Five replicates were prepared in the same way for each type of soil samples.
Fungi were isolated from soil by the dilution plate method (Bokhary and Parvez, 1992 b,c). One ml of this dilution (10-2) was poured in sterile disposable petridishes of 9 cm diameter (25 plates for each samples). Molten fox medium cooled at 45°C (KCI 0.5 g, MgSO4 0.19 g, KH2PO4 1 g, Agar 15 g, FeSO4 0.01 g), containing one gram of commercially available skinimed milk powder in plebe of sodium nitrate and sucrose was poured into each plate (20 ml per plate). Streptomycin sulphate (0.03 gL–1) was aseptically added in to the sterilized medium just before pouring the agar medium into plates, to inhibit the growth of bacteria and rose bengal (0.033 gL–1) was added before sterilization of medium to restrict colony diameter of growing fungi.
identification of isolated fungi was carried out with the of morphological characteristics described in the follow literature: Ellis (1971, 1976), Gilman (1971), Pitt (1979) Ramirez (1982), Raper and Fennell (1965), Schipper (1978) and Zycha et al. (1969).
Results
Total number of colonies isolated per gram of some different temperature (5-45°C) on milk agar medium is given in Table 1. The highest number of fungal colonies per gram of soil was isolated at 35°C . The least number of colony was isolated at 45°C. A total number of 141 fungal spore belonging to 50 genera were isolated on milk medium (Table 2). Aspergillus was the predominant represented by 23 species followed by Penicillium was represented by 21 species. Chaetomium was and dominant genus represented by 11 species following Eupenicillium (8 species), Cladosporium (5 species) Chrysosporium (5 species). The highest number of five species were isolated at 35°C (123 species belonging to genera) followed by at 25°C (93 species/31 genera), at 15°C (26 species/14 genera 0 and at 45°C (10 species genera), the least number of species was isolated artificially (8 species/6 genera).
Aspergilus fumigatus and Penicillium chrysogenum were only species which were isolated at all the temperature incubation. Aspergillus and Penicillium species genera exhibited the highest number of colonies per gram Aspergillus fumigatus and A. favus exhibited the high number of colonies per gram as compared to Aspergillus species. Penicillium chrysogenum exhibited (higher number of colonies per gram for Penicillium species Most of the fungal species could grow between 15-30. There were several fungal species which were isolated one particular temperature of incubation only. For exact Aspergillus aculeatus lizuka was isolated at only 25°C, A. penicilloides Speg at 35°C only. There was no fully isolated which could grow at 5°C or at 45°C only i.e it was no true psychrophilic fungi isolated.
| Table 1: | Total number of fungal colonies per gram of soil isolated on milk agar medium. |
| Each value is a mean of 5 replicates. Values parenthesis are standard deviation | |
| Table 2: | Mycoflora per gram of soil isolated on milk agar medium |
| Each value is a mean of 5 replicates. Values parenthesis arestandard deviation. | |
Discussion
Result of present study showed that a much wider range of potential food spoilage fungal flora was present in the soil samples analyzed, with 55 mycoflora genera represented and a total of 141 different species isolated. Previously only some common molds like Alternaria, Aspergillus (mainly A. niger and A. flavus), Mucor, Fusarium, Mondia, Thamnidium, Trichothecium, Sporotrichum, Cladosporium and Geotrichum etc. were reported as common food spoilage mycoflora including spoilage of milk (Weiser et al., 1971; Parry and Pawsey, 1984; Casida, 1991), while present study adds several other genera of fungal in the list of food spoilage mycoflora. Alternaria was surpassingly not isolated here although this fungus is a saprophytic fungus frequently reported in Saudi Arabia to be able to grow on various substrates studied (Bokhary and Parvez, 1988, 1992a; Bokhary et al., 1990) and also a commonly isolated soil soil fungus (Abdel-Hafez, 1982; Abdulla and El-Gindy 1987; Bokhary and Parvez, 1992 b,c). Aspergillus, Fusarium, Penicilliurn and other genera have been reported to produce various toxic chemicals such as mycotoxins during their growth (Bokhary and Naguib, 1983) which could be a health risk to consumers. Also worthy of note that more than 70 percent of fungal species isolated here are medical importance and have been reported earlier as causing various diseases such as aspergillosis, bronchial asthma, eczema, tinea, onychomycosis, ring worn etc. in humans and animals (Frey et al., 1981).