Microbiological quality of pork meat from local Hong Kong markets

Over a 3-week period, samples of fresh, chopped, pork meat were taken every morning and afternoon from 50 meat stalls. Microbiological examination revealed that the samples had (c.f.u./g): total microbes, 1×10³ to 2.14×10⁶; mean probable numbers of coliforms and Escherichia coli, 1.51×10³ to 1.15×10⁴; and yeasts and moulds, 0 to 1.28×10⁴. Salmonella, found in 32 samples from 21 stalls, were serotyped as B (three samples), C1 (four) or E (25). No Campylobacter were found. Because microbial growth and/or contamination of the meat occurred during the day, samples taken in the afternoon had greater total counts (P<0.05) and contained detectable numbers of Salmonella more frequently (42% versus 22%) than those taken in the morning.The author is with the Department of Biology and Chemistry, City Polytechnic of Hong Kong, 83 Tat Chee Ave, Kowloon, Hong Kong     

Microbial flora and some chemical properties of ersho,a starter for teff (Eragrostis tef) fermentation

Ersho is a clear, yellow liquid that accumulates on the surface of fermenting teff-flour batter and is collected to serve as an inoculum for the next fermentation. The pH of ersho samples was about 3.5 and titratable acidity ranged between 3.1% and 5.7%. The mean aerobic mesophilic counts from four households varied between 6.9×10⁶ and 1.3×10⁸ c.f.u./ml and the aerobic bacterial flora consisted of Bacillus spp. Mean yeast counts ranged between 5.2×10⁵ and 1.8×10⁶ c.f.u./ml and comprised, in order of abundance, Candida milleri, Rhodotorula mucilaginosa, Kluyveromyces marxianus, Pichia naganishii and Debaromyces hansenii. Candida milleri was the most dominant isolate in all samples. About 90% of the teff flour samples had aerobic mesophilic counts 10⁵ c.f.u./g and Gram-positive bacteria constituted about 71% of the total isolates. About 80% of samples had Enterobacteriaceae counts of 10⁴ c.f.u./g.M. Ashenafi is with the Department of Basic Sciences, Awassa College of Agriculture, Addis Ababa University, PO Box 5, Awassa, Sidamo, Ethiopia.     

Isolation and characterization of pathogens attacking Pomacea canaliculata

Seven microorganisms capable of killing Pomacea canaliculata were isolated from soil samples obtained from various agricultural areas of Thailand. The identification of these microorganisms was performed using microscopic examination and biochemical tests. Five strains were identified as Pseudomonas aeruginosa and were designated P. aeruginosa 19.1, 21.2.1, B1.1, P1 and P2. The other two strains were identified as Pseudomonas fluorescens and were designated P. fluorescens 13.1 and Ct1. Pathogenicity studies of these microorganisms to P. canaliculata (Lamarck) were performed and characterized by LC₅₀ levels. The LC₅₀ levels of non-autoclave-treated and autoclave-treated cell suspensions to P. canaliculata were found to be 3.56 × 10⁴–1.35 × 10⁶ c.f.u./ml and 3.09 × 10⁴ to 1.23 × 10⁶ c.f.u./ml, respectively.     

Diversity of lactic acid bacteria and yeasts in Airag and Tarag,traditional fermented milk products of Mongolia

We used culture- and molecular-biology-based methods to investigate microbial diversity in the traditional Mongolian fermented milks “Airag” (fermented mare’s milk) and “Tarag” (fermented milk of cows, yaks, goats, or camels). By rRNA or functional gene sequencing, we identified 367 lactic acid bacteria (LAB) strains and 152 yeast strains isolated from 22 Airag and 31 Tarag samples. The total concentration of LAB in Airag (10^{7.78 ± 0.50} c.f.u. ml^–1; mean ± SD) was significantly lower (P < 0.01) than in Tarag (10^{8.35 ± 0.62} c.f.u. ml⁻¹), whereas the total concentration of yeasts in Airag (10^{7.41 ± 0.61} c.f.u. ml^-1) was significantly higher (P < 0.01) than in Tarag (10^{5.86 ± 1.29} c.f.u. ml^-1). Lactobacillus helveticus and Lactobacillus kefiranofaciens were isolated from Airag as the predominant LAB strains at levels of about 10⁷ c.f.u. ml⁻¹, whereas Lactobacillus delbrueckii subsp. bulgaricus, L. helveticus, and Streptococcus thermophilus were the predominant isolates from Tarag at about 10⁷ c.f.u. ml⁻¹. The lactose-fermenting Kluyveromyces marxianus was isolated predominantly from Airag as its major alcoholic fermentation component. Non-lactose-fermenting yeasts such as Saccharomyces cerevisiae, Issatchenkia orientalis, and Kazachstania unispora were the predominant isolates from Tarag, at about 10⁵ c.f.u. ml⁻¹. The apparent geographic differences in the L. kefiranofaciens and S. thermophilus contents of Tarag strongly suggested that differences among the animal species from which the milk was sourced, rather than geographic distances, were the most important factors influencing the diversity of the microbial composition of traditional fermented milks in Mongolia.     

Microbiological changes in mawè during natural fermentation

Lactic acid bacteria increased from 3.2 × 10⁶ and 1.6 × 10⁷ c.f.u./g (wet wt) to 2 × 10⁹ and 1.6 × 10⁹ c.f.u./g after 12 to 24 h of fermentation of home-produced mawè (a dough produced from dehulled maize) and commercial mawè, respectively. In commercial mawè, the yeast count increased from 1.3 × 10⁵ to 2.5 × 10⁷ c.f.u./g after 48 h of fermentation before decreasing, whereas in the home-produced mawè it increased from 2.5 × 10⁴ to 3.2 × 10⁷ c.f.u./g after 72 h of fermentation; the dominant yeasts were mainly Candida krusei, although C. kefyr, C. glabrata and Saccharomyces cerevisiae were also present. Enterobacteriaceae counts increased slightly during the initial stage ofthe fermentation, but decreased below the detection level after 24 to 48 h. Enterobacter cloacae was mostly found in commercial mawè and Escherichia coli mostly in homeproduced mawè.D.J. Hounhouigan and C.M. Nago are with the Université Nationale du Bénin, Faculté des Sciences Agronomiques, Département de Nutrition et de Sciences Alimentaires, BP 526, Cotonou, Benin; M.J.R. Nout and F.M. Rombouts are with the Agricultural University, Department of Food Science, Bomenweg 2, 6703 HD Wageningen, The Netherlands. J.H. Houben is with Utrecht University, Department of the Science of Foods of Animal Origin, Yalelaan 2, 3508 TD Utrecht, The Netherlands.     

Measurement of particle diameter of <Emphasis Type="Italic">Lactobacillus acidophilus</Emphasis> microcapsule by spray drying and analysis on its microstructure

Lactobacillus acidophilus, as a probiotic, is widely used in many functional food products. Microencapsulation not only increases the survival rate of L. acidophilus during storage and extends the shelf-life of its products, but also optimal size microcapsule makes L. acidophilus have an excellent dispersability in final products. In this paper, L. acidophilus was microencapsulated using spray drying (inlet air temperature of 170°C; outlet air temperature of 85–90°C). The wall materials used in this study were β-cyclodextrin and acacia gum in the proportion of 9:1 (w/w), and microcapsules were prepared at four levels of wall materials (15, 20, 25 and 30% [w/v]) with a core material concentration of 6% (v/v). The microcapsule diameters were measured by Malvern’s Mastersizer-2000 particle size analyzer. The results showed that the particle diameters of microcapsule were mostly within 6.607 μm and 60.256 μm and varied with 2.884–120.226 μm (the standard smaller microcapsule designated as <350 μm). Through comparison of microcapsule size and uniformity with different concentration of wall materials, we concluded that the optimal concentration of wall material was 20% (w/v), which gave microcapsule with a relatively uniform size (averaging 22.153 μm), and the number of surviving encapsulated L. acidophilus was 1.50 × 10⁹ c.f.u./ml. After 8 weeks storage at 4°C, the live bacterial number was above 10⁷ c.f.u./ml, compared with unencapsulated L. acidophilus, 10⁴–10⁵ c.f.u./ml. Through the observation of scanning electron microscopy, we found that the shapes of microcapsule were round and oval, and L. acidophilus cells located in the centre of microcapsule.     

Specific detection of an oil-degrading bacterium, Corynebacterium sp. IC10, in sand microcosms by PCR using species-specific primers based on 16S rRNA gene sequences

A species-specific PCR technique to detect an oil-degrading bacterium, Corynebacterium sp. IC10, released into sand microcosms is described. PCR primers, specific to strain IC10, were designed based on 16S rRNA gene sequences and tested against both closely and distantly related bacterial strains using four primer combinations involving two forward and two reverse primers. Two sets of them were specific to the strain IC10 and Corynebacterium variabilis and one set was selected for further analysis. The PCR amplification was able to detect 1 pg template DNA of strain IC10 and 1.2×10⁴ c.f.u. of IC10 ml wet sand^–1 in the presence of 3×10⁸ Escherichia coli cells. In non-sterile sand microcosms seeded with the strain IC10, the sensitivity of detection decreased to 9.6×10⁵ c.f.u. ml wet sand^–1. The detection sensitivity thus depends on the complexity of background heterogeneous DNA of environmental samples. The assay is suitable for detection of Corynebacterium sp. IC10 in laboratory microcosms, however, cross reaction with non-oil degrading coryneforms may prohibit its use in uncharacterized systems.     

Effect of yeast inoculation rate on the metabolism of contaminating lactobacilli during fermentation of corn mash

Two separate 4 (bacterial concentrations)×6 (yeast concentrations) full factorial experiments were conducted in an attempt to identify a novel approach to minimize the effects caused by bacterial contamination during industrial production of ethanol from corn. Lactobacillus plantarum and Lactobacillus paracasei, commonly occurring bacterial contaminants in ethanol plants, were used in separate fermentation experiments conducted in duplicate using an industrial strain of Saccharomyces cerevisiae, Allyeast Superstart. Bacterial concentrations were 0, 1×10⁶, 1×10⁷ and 1×10⁸ cells/ml mash. Yeast concentrations were 0, 1×10⁶, 1×10⁷, 2×10⁷, 3×10⁷, and 4×10⁷ cells/ml mash. An increased yeast inoculation rate of 3×10⁷ cells/ml resulted in a greater than 80% decrease (P<0.001) and a greater than 55% decrease (P<0.001) in lactic acid production by L. plantarum and L. paracasei, respectively, when mash was infected with 1×10⁸ lactobacilli/ml. No differences (P>0.25) were observed in the final ethanol concentration produced by yeast at any of the inoculation rates studied, in the absence of lactobacilli. However, when the mash was infected with 1×10⁷ or 1×10⁸ lactobacilli/ml, a reduction of 0.7–0.9% v/v (P<0.005) and a reduction of 0.4–0.6% v/v (P<0.005) in the final ethanol produced was observed in mashes inoculated with 1×10⁶ and 1×10⁷ yeast cells/ml, respectively. At higher yeast inoculation rates of 3×10⁷ or 4×10⁷ cells/ml, no differences (P>0.35) were observed in the final ethanol produced even when the mash was infected with 1×10⁸ lactobacilli/ml. The increase in ethanol corresponded to the reduction in lactic acid production by lactobacilli. This suggests that using an inoculation rate of 3×10⁷ yeast cells/ml reduces the growth and metabolism of contaminating lactic bacteria significantly, which results in reduced lactic acid production and a concomitant increase in ethanol production by yeast.     

Industrial wastewaters and dewatered sludge: rich nutrient source for production and formulation of biocontrol agent, <Emphasis Type="Italic">Trichoderma viride</Emphasis>

Axenic cultivation of biocontrol fungus Trichoderma viride was conducted on a synthetic medium and different wastewaters and wastewater sludges in shake flasks to search for a suitable raw material resulting in higher biocontrol activity. Soluble starch based synthetic medium, dewatered municipal sludge, cheese industry wastewater sludge, pre-treated and untreated pulp and paper industry wastewater and slaughter house wastewater (SHW) were tested for T. viride conidia and protease enzyme production. The maximum conidia production followed the order, soluble starch medium (>10⁹ c.f.u./mL), untreated pulp and paper industry wastewater (4.9 × 10⁷ c.f.u./mL) > cheese industry wastewater (1.88 × 10⁷ c.f.u./mL) ≈ SHW (1.63 × 10⁷ c.f.u./mL) > dewatered municipal sludge (3.5 × 10⁶ c.f.u./mL) > pre-treated pulp and paper industry wastewater (1.55 × 10⁶ c.f.u./mL). The protease activity of T. viride was particularly higher in slaughterhouse wastewater (2.14 IU/mL) and dewatered municipal sludge (1.94 IU/mL). The entomotoxicity of soluble starch based synthetic medium was lower (≈6090 SBU/μL) in contrast to other raw materials. The entomotoxicity inversely decreased with carbon to nitrogen ratio in the growth medium and the conidia concentration and protease activity also contributed to the entomotoxicity. The residual c.f.u./g formulation of T. viride conidia were up to approximately, 90% after 1 month at 4 ± 1 °C and about 70% after 6 months at 25 ± 1 °C. Thus, production of T. viride conidia would help in marketability of low cost biopesticide from the sludge and safe reduction of pollution load.     

Survival of Escherichia coli O157:H7 applied to cantaloupes and the effectiveness of chlorinated water and lactic acid as disinfectants

Initial survey of four packinghouses indicated that bacterial and fungal populations on the surface of cantaloupes were significantly reduced by sanitizing procedures particularly on faecal coliforms. In this study, several combinations of disinfectants were tested in an attempt to obtain a more effective antimicrobial activity on aerobic bacteria, fungi and total coliforms. The efficacy of aqueous chlorine (200 mg l^–1) and lactic acid (1.5%) on inactivation of inoculated Escherichia coli O157:H7 on cantaloupe surfaces was investigated using different temperatures (25 and 35 °C) and immersion times (1 and 10 min). Maximal log reductions were achieved with both sanitizing agents when the initial bacterial population of E. coli was 7.42 log c.f.u. cm^–2. A highly significant 7.2 log reduction (P < 0.01) was obtained with a solution of lactic acid with and without Tergitol (0.3%) surfactant when cantaloupes were immersed for 10 min regardless of the temperature of the solution. Although the sanitizers caused substantial mortality, some bacterial cells remained attached at relatively low numbers on the fruit surface. The development of sanitizers more efficacious than chlorine for total elimination of this pathogen from the surface of cantaloupes is needed.     

Production of improved infant porridges from pearl millet using a lactic acid fermentation step and addition of sorghum malt to reduce viscosity of porridges with high protein,energy and solids (30%) content

With the aim of improving the safety and nutritional quality of traditional African weaning porridge, the reduction of the viscosity of a high solids fermented pearl millet porridge by addition of sorghum malt (amylase rich flour, ARF) was investigated. The effect of fermentation, cooking, malt addition and recooking on the microflora of, and the survival of an inoculated pathogen were determined. Addition of 5% (w/v) sorghum ARF to the gelatinized millet porridge gave an acceptable viscosity of 2500–3000 cP at a high solid content of 30%. Fermentation inhibited the growth of microorganisms in the porridge and recooking the fermented porridge after sorghum ARF addition further eliminated (<10² c.f.u./g) the moulds and coliforms that were introduced with the sorghum ARF. The recooked, fermented millet plus sorghum ARF porridge prevented the proliferation of the inoculated Escherichia coli and reduced it to <10² c.f.u./g within 18 h. The porridge could supply children under 3 years with the daily required protein using 1.4 feedings per day and required energy with 4 feedings a day.     

Effects of water extracts of a composted manure-straw mixture on the plant pathogen Botrytis cinerea

Manure-straw mixtures were composted and water extracts, made by incubating compost in water for 3 to 18 days, were assessed for antagonistic activity against Botrytis cinerea, using a range of tests. Extracts of all ages inhibited conidial germination on glass slides and reduced mycelial growth on agar. Mixing extracts of all ages with droplets of suspensions of B. cinerea conidia on detached Phaseolus bean leaves suppressed lesion development, but only 3- to 8-day-old extracts had an effect when sprayed onto leaves 2 days before inoculation. Extracts contained a large and varied microbial population of actinomycetes (0.3 to 2.4×10⁵ c.f.u.ml^–1), bacteria (1.5 to 5.6×10¹⁰ c.f.u.ml^–1), filamentous fungi (25.0 to 45.5 c.f.u. ml^–1) and yeasts (26.1 to 62.6 c.f.u.ml^–1). Eight- and 18-day-old extracts lost activity completely on filter sterilization or autoclaving. Weekly sprays of 8-day-old extracts onto lettuce in the glasshouse had no effect on the incidence of grey mould, but significantly reduced its severity and increased marketable yield. The use of compost extracts in biocontrol of plant diseases and their possible mode of action is discussed.M.P. McQuilken and J.M. Whipps are and J.M. Lynch was with the Microbiology and Crop Protection Department, Horticulture Research International, Littlehampton BN17 6LP, UK; J.M. Lynch is now with the School of Biological Sciences, University of Surrey, Guildford GU2 5XH, UK.     

Expression of the mosquitocidal cryIVB gene under the control of different promoters in Bacillus sphaericus 2362 and acrystalliferous Bacillus thuringiensis subsp. israelensis c4Q2-72

The 3.7 kb XbaI fragment harbouring the cryIVB gene which encoded a 130 kDa mosquitocidal toxin protein from Bacillus thuringiensis subsp. israelensis (B.t.i.) was placed downstream to the cat-86 gene promoter (P _cat-86, spore stage specific expression) or bgaB gene promoter (P _bgaB , vegetative stage specific expression). The constructs were subcloned into pBC16 to obtain pBTC3 and pBTC6, respectively. Both plasmids and the other construct, pBTC1 were successfully transferred into B. thuringiensis subsp. israelensis c4Q2-72 and B. sphaericus 2362. Western blot analysis showed that P _bgaB in front of P _cryIVB could enable cells to produce a 130 kDa protein from the vegetative stage (4 h) whereas those with P _cat-86 could not. The positive detection of 130 kDa crystal protein during the vegetative stage (4 h) by Western blot analysis indicated the vegetative-stage-specific expression of P _bgaB , while the 130 kDa crystal protein produced from cryIVB gene under control of P _cat-86 was detected only at 48 h. The strong activity of P _bgaB , together with P _cryIVB within pBTC6 in both bacterial hosts was also shown by the toxicity assay against Aedes aegypti larvae (B.t.i. c4Q2-72, 5.6 ± 3.6 × 10² c.f.u./ml; B. sphaericus 2362, 5.4 ± 2.5 × 10² c.f.u./ml) which were 100-fold and 10-fold more toxic to such larvae when compared with pBTC3 (P _cat-86 together with P _cryIVB ) and pBTC1 (contained only its self promoter) in the same bacterial host strains, respectively. The plasmid pBTC6 is not stable in either Bacillus host.     

Antibacterial effect of honey on the in vitro and in vivo growth of Escherichia coli

The study investigated the antibacterial effect of honey against pathogenic Escherichia coli. Honey showed inhibitory activity against the growth of E. coli (ATCC 25922) in agar plate assay. In liquid culture (48 h, 37 °C) the growth rate of bacterial cells decreased in the presence of honey (9.6 × 10⁵ c.f.u./ml) compared with sucrose (2.87 × 10⁸ c.f.u./ml). Rats fed with honey and orally inoculated with E. coli excreted significantly (P < 0.05) less bacterial cells in faeces compared to controls. Animals acclimatized to feeding of honey prior to E. coli inoculation showed a significant decrease in excreted bacterial load compared with the group provided with honey after bacterial inoculation. Consumption of honey also enhanced the concentration of short chain fatty acids in the intestine of rats (83 mM) compared with the control group (44.5 mM). The results show that honey possessed significant antibacterial activity against E. coli under in vitro and in vivo conditions, and indicate the potential benefit of consumption of honey regularly on the microbiological constitution of animals feeding on it.     

Preparation of a flowable liquid bacterial insecticide based on Bacillus sphaericus

Fermenter-produced Bacillus sphaericus 2362 was formulated into a thick, dark flowable liquid concentrate containing 4.8×10⁹ c.f.u./ml and charcoal as protector against ultraviolet light. The potencies of the formulation against L₄ Culex pipiens quinquefasciatus before and after storage for 2 years were 5714 and 5862 International Toxic Units (ITU), respectively, when compared with a standardized B. sphaericus from the WHO at 1000 ITU. In field trials, treatment at 1.01/ha gave 96 to 100% control of mosquito larvae. B. sphaericus could be re-isolated in 5% of the samples 9 months after application.The authors are at the Department of Applied Microbiology & Brewing, Anambra State University of Technology, P.M.B. 5025, Awka, Nigeria.     

Survey of petroleum-degrading bacteria in coastal waters of Sunderban Biosphere Reserve

A survey of petroleum-degrading bacteria was carried out in the Indian part of deltaic Sunderbans to evaluate the distribution of the naturally occurring petroleum-degrading aerobic bacteria. Bacteriological analysis of surface water samples collected from five different locations in the Hooghly–Matla river mouth showed that, depending on the location, 0.08–2.0% of the heterotrophic bacteria culturable in marine agar medium could degrade crude petroleum hydrocarbons as the sole source of carbon. In the entire study area, the number of heterotrophic bacteria ranged from 1 × 10³ to 3.8 × 10⁵ c.f.u/ml, amongst which 2.7 × 10¹ to 6 × 10³ c.f.u/ml were petroleum degraders. There was a maximum number of petroleum-degrading bacteria in the waters of Haldia Port and its surrounding areas, where the water is highly polluted by hydrocarbon discharges from a nearby oil refinery and from the ships docking at the port. Among the isolates, identified on the basis of their Gram reaction, morphological and biochemical tests including the use of API20E strips, Pseudomonas, Mycobacterium, Klebsiella, Acinetobacter, Micrococcus, and Nocardia were the most common petroleum degraders. Other heterotrophic bacteria included several species of Escherichia, Klebsiella, non-oil-degrading Pseudomonas, Vibrio, Streptococcus, Staphylococcus and Bacillus. Following preliminary selection, five strains, showing best growth in medium with oil fraction as sole carbon source, were chosen for estimation of the efficiency of crude oil biodegradation. The selected strains belonged to Pseudomonas (two strains), Mycobacterium (two strains), and Nocardia (one strain). These strains degraded 47–78% of Arab-Mix crude oil over a period of 20 days. The best oil-degrading isolate, a strain of Pseudomonas aeruginosa, (BBW1), was found to degrade and multiply more rapidly in crude oil than the rest. BBW1 showed profuse growth in Bushnell Haas medium containing crude oil (as sole source of carbon) at high concentrations ranging from 0.2 to 20% (v/v), with optimum at 10%. As much as 75% of the oil was degraded within 72 h of incubation with the bacteria. Physicochemical analysis showed considerable decrease in initial boiling point and carbon residue of the degraded oil. The ability to degrade crude oil was found to be associated with a single 70-kb plasmid, pBN70. Resistance to the metals Mn²⁺ (50 mM), Mg²⁺ (200 mM), Zn²⁺ (6 mM), Ni²⁺ (10 mM) and antibiotics like ampicillin (10 g/ml), cephalexin (30 g/ml), nitrofurantoin (300 g/ml) and penicillin (10 U/ml) were plasmid-mediated.     

Growth of Rhizobium leguminosarum in a periodic pressure oscillating, solid-state fermentation of wheat straw

Wheat straw impregnated with a nutrient solution was used to culture Rhizobium leguminosarum. The fermentation was carried out in a periodic pressure, oscillating, solid-state fermenter. At 30 °C and 3 atm, Rhizobium leguminosarum grew to 5.3×10¹⁰ c.f.u. g^–1 substrate dry matter in about 36 h, while only 1.8×10¹⁰ c.f.u. g^–1 substrate dry matter was obtained in a conventional static tray fermenter.     

Ethanol tolerance in free and sol-gel immobilised Saccharomyces cerevisiae

The tolerance of sol-gel immobilised and free Saccharomyces cerevisiae to ethanol was studied. The effects of ethanol preincubation time showed that the specific death velocity decreased from 2×10⁵ c.f.u. min^–1 for free cells to 2×10⁴ c.f.u. min^–1 for immobilised cells thus indicating that immobilised yeast was far less sensitive to the ethanol damage. The specific glucose consumption of immobilised and free cells on a per cell basis was 3×10^–12 g cell^–1 h^–1 and 9×10^–12 g cell^–1 h^–1, respectively.     

Sources of microorganisms in pozol,a traditional Mexican fermented maize dough

Freshly prepared pozol, a traditional Mexican fermented maize dough, contained (c.f.u./g wet wt): lactic acid bacteria, 10⁴ to 10⁶; aerobic mesophiles, 10⁴ to 10⁵; Enterobacteriaceae, 10² to 10³; yeasts, 10² to 10⁴; and mould propagules, <10³. After 30 h at 28°C the numbers were, respectively: 10⁹, 7×10⁶, 5×10⁵, 10⁶ and 10⁴. Soaking alkali-treated grains overnight allowed lactic acid bacteria, aerobic mesophiles and Enterobacteriaceae to grow and these then constituted the primary microbial flora of the pozol dough. Grinding in a commercial mill inoculated the dough with lactic acid bacteria, aerobic mesophiles, Enterobacteriaceae and yeasts. Other processing stages, including the nature of the surface upon which the balls were made, handling of the dough, and air, contributed only minor numbers of microbes compared with the two major sources, soaking and grinding. The pH of pozol fell from an initial value of 7.3 to 4.6 after 30 h incubation at 28°C. The numbers of Enterobacteriaceae and other aerobic mesophilic bacteria remained constant between 11 and 30 h incubation and there was no evidence of the acidic conditions having any lethal effects on these organisms.     

Effect of curd-cooking temperatures on the microbiological quality ofayib,a traditional Ethiopian cottage cheese

Ayib was made following traditional methods of curd cooking at 40°, 50°, 60° and 70°C requiring 10 h, 7 h, 145 min and 55 min, respectively. During the natural fermentation of raw milk into sour milk (curd), the count of all groups of microorganisms increased by at least a 100-fold. When the curd was subsequently cooked at 40°C, counts of enterococci and members of Enterobacteriaceae decreased by a 100-fold and lactic acid bacteria and staphylococci by a 100-fold. At 50°C, the count of enterococci, members of Enterobacterlaceae and staphylococci was lower than could be detected (<10² c.f.u./g). Yeasts, moulds and lactic acid bacteria still had counts of about 10⁵ c.f.u./g. The total aerobic count decreased by a 100-fold but was still high (>10⁷ c.f.u./g). At 60°C, yeasts and moulds decreased by 1000-fold and at 70°C they decreased below detectable levels (<10² c.f.u./g). This latter temperature is thus recommended as it results in a less contaminated and saferayib.

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Résumé On a préparél'Ayib selon les méthodes traditionnelies de cuission du lait caillé à 40, 50, 60 et 70°C, ce qui a requis respectivement 10 h, 7 h, 145 et 55 min. Durant la fermentation naturelle du lait frais en lait caillé, le décompte de tous les groupes de microorganismes a crû d'au moins 100 fois. Quand le lait caillé était par la suite cuit à 40°C, le décompte des entérocoques et des membres des Enterobacteriaceae a décru de 100 fois et celui des bactéries lactiques et des staphylocoques de 100 fois. A 50°C, le décompte des entérocoques, membres des Enterobacteriaceae et des staphylocoques était inférieur au seuil de détection (<10² c.f.u./g). Les levures, moisissures et bactéries lactiques avalent toujours un décompte d'environ 10⁵ c.f.u./g. le décompte total aérobie décroissait de 100 fois mais restait néanmoins élevé (>10⁷ c.f.u./g.). A la température de cuisson du lait caillé de 60°C, les levures et les moisissures ont décru de 1000 fois, et à 70°C on décru au dessous du seuil de détection (<10² c.f.u./g). Cette dernière température est donc recommandable car elle résulte en unayib moins contaminé et plus sain.