World Journal of Microbiology and Biotechnology 6, 159-162
Effect of curd-cooking temperatures on the microbiological quality of ayib, a traditional Ethiopian cottage cheese
Mogessie Ashenafi
Aylb was made following traditional methods of curd cooking at 40 ~ 50 ~ 60 ~ and ?0~ requiring 10 h, 7 h, 145 min and 55 mln, respectively. During the natural fermentatlon 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~ counts of enterococci and members of Entarobacterlaceae decreased by e 100-fold and lactic acid bacteria and staphylococci by a 1000-fold. At 50~ the count of enterococci, members of Enterobacterieceae and staphylococci was lower than could be detected (107 c.f.u./g). At 60~ yeasts and moulds decreased by 1000-fold and at 70~ they decreased below detectable levels (107 c.f.u./g.). A la temp6rature de euisson du lair caill(~ de 60~ les levures et les moisissures ont d6cru de 1000 fols, et ~ 70~ on d(~cru au dessous du seuil de d(~tection ( < 1 0 = c.f.u./g). Cette derni6re temp6ralure est donc recommandable car elle r6suIte en un ayib molns contamin0 et plus sain.
LS Differential (LSD) medium for lactic acid bacteria and Mannitol/Salts (MS) agar for staphylococci (all from Oxoid). For the enumeration of yeasts and moulds, appropriate dilutions were plated in duplicates on to Chloramphenicol/Bromphenol Blue (CB) agar plates (yeast extract, 1 g; glucose 20 g; chloramphenicol, 0.1 g; bromphenol blue, 0.01 g; agar, 15 g; distilled water, 1000 ml; pH, 6.0 to 6.4). For the enumeration of aerobic spore formers, portions of 4 ml and 0.4 ml from the 1:10 homogenate of milk, sour milk or ayib were added to two different bottles containing 40 ml of molten PC agar and heat-shocked by holding in a water bath at 80~ for 10 min. The contents of each bottle were then distributed between two petri dishes. All PC, KAA, VRBG and MS plates were incubated at 30 to 32~ for 48 h. LSD agar plates were incubated at 43~ for 48 h in an anaerobic jar (Oxoid). CB agar plates were incubated at 25 to 27~ for 3 to 5 days. Ayib making in the laboratory Ayib was made in the laboratory following traditional methods practised in this country. Raw milk was pooled from three different small farms and from the college dairy farm. The milk was divided into 750 ml amounts in four Erlenmeyer flasks and incubated at room temperature ( ~ 25~ for 24 h to sour naturally. The butter was then removed by churning. The casein and some of the unrecovered fat in the sour skimmed milk was heat-precipitated at 40~ 50~ 60~ or 70~ in a water bath. Heating continued until a distinct curd formed that floated on the surface of the whey; the whey was allowed to cool gradually and the curd was recovered by filtering through layers of sterile cheesecloth.
Resul~ Counts of the various microorganisms in raw milk, sour milk and ayib cooked at different temperatures are presented in Table 1. During the natural fermentation of raw milk into sour milk (i.e. curd), the total aerobic count and the count of lactic acid bacteria increased by 1000-fold and the other groups of microorganisms increased by about a 100-fold. Staphylococci and aerobic spore formers did not show any marked increase. Subsequent cooking of the curd at different temperatures resulted in different bacterial load of ayib. At 40~ staphylococci were not detected in the samples, and lactic acid bacteria and members of Enterobacteriaceae decreased by about a 1000-fold. At 50~ enterococci, members of Enterobactericeae and staphylococci were not detected in the samples. However, a substantial number of yeast and moulds and lactic acid bacteria survived cooking temperatures of 50~ and 60~ The count of most of the bacterial groups, yeasts and moulds was below detectable levels ( < 102 c.f.u./g) at 70~ heat treatment. Aerobic spore formers remained at about 103 c.f.u./g in all stages of ayib making.
Table 1. Counts of microorganisms in raw milk, sour milk and ayib cooked at different temperatures. Sample
pH
Total count
Enterococcl
Enterobacteriaceae
Lactic acid bacteria
Staphylococci
Yeasts/ moulds
Aerobic spore formers
R a w milk Sour milk
6.7 4.0
5.4 x 106 1.8 x 10Q
1.6 x 10 4 2.2 x 10 6
3.5 x 104 1.8 x 106
4.3 x 10 5 5.8 x 10 8
2.0 x 104 2.3 x 104
5.0 x 103
6.6 x 10~
3.4 x 103 2.0 x 103
3.8 4.0 4.0 4.0
4.2 6.2 1.4 4.0
x 108
7.0 x 104
8.8 x 103
X 10 7
Effect of curd-cooking temperatures on the microbiological quality of ayib, a traditional Ethiopian cottage cheese
Mogessie Ashenafi
Aylb was made following traditional methods of curd cooking at 40 ~ 50 ~ 60 ~ and ?0~ requiring 10 h, 7 h, 145 min and 55 mln, respectively. During the natural fermentatlon 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~ counts of enterococci and members of Entarobacterlaceae decreased by e 100-fold and lactic acid bacteria and staphylococci by a 1000-fold. At 50~ the count of enterococci, members of Enterobacterieceae and staphylococci was lower than could be detected (107 c.f.u./g). At 60~ yeasts and moulds decreased by 1000-fold and at 70~ they decreased below detectable levels (107 c.f.u./g.). A la temp6rature de euisson du lair caill(~ de 60~ les levures et les moisissures ont d6cru de 1000 fols, et ~ 70~ on d(~cru au dessous du seuil de d(~tection ( < 1 0 = c.f.u./g). Cette derni6re temp6ralure est donc recommandable car elle r6suIte en un ayib molns contamin0 et plus sain.
LS Differential (LSD) medium for lactic acid bacteria and Mannitol/Salts (MS) agar for staphylococci (all from Oxoid). For the enumeration of yeasts and moulds, appropriate dilutions were plated in duplicates on to Chloramphenicol/Bromphenol Blue (CB) agar plates (yeast extract, 1 g; glucose 20 g; chloramphenicol, 0.1 g; bromphenol blue, 0.01 g; agar, 15 g; distilled water, 1000 ml; pH, 6.0 to 6.4). For the enumeration of aerobic spore formers, portions of 4 ml and 0.4 ml from the 1:10 homogenate of milk, sour milk or ayib were added to two different bottles containing 40 ml of molten PC agar and heat-shocked by holding in a water bath at 80~ for 10 min. The contents of each bottle were then distributed between two petri dishes. All PC, KAA, VRBG and MS plates were incubated at 30 to 32~ for 48 h. LSD agar plates were incubated at 43~ for 48 h in an anaerobic jar (Oxoid). CB agar plates were incubated at 25 to 27~ for 3 to 5 days. Ayib making in the laboratory Ayib was made in the laboratory following traditional methods practised in this country. Raw milk was pooled from three different small farms and from the college dairy farm. The milk was divided into 750 ml amounts in four Erlenmeyer flasks and incubated at room temperature ( ~ 25~ for 24 h to sour naturally. The butter was then removed by churning. The casein and some of the unrecovered fat in the sour skimmed milk was heat-precipitated at 40~ 50~ 60~ or 70~ in a water bath. Heating continued until a distinct curd formed that floated on the surface of the whey; the whey was allowed to cool gradually and the curd was recovered by filtering through layers of sterile cheesecloth.
Resul~ Counts of the various microorganisms in raw milk, sour milk and ayib cooked at different temperatures are presented in Table 1. During the natural fermentation of raw milk into sour milk (i.e. curd), the total aerobic count and the count of lactic acid bacteria increased by 1000-fold and the other groups of microorganisms increased by about a 100-fold. Staphylococci and aerobic spore formers did not show any marked increase. Subsequent cooking of the curd at different temperatures resulted in different bacterial load of ayib. At 40~ staphylococci were not detected in the samples, and lactic acid bacteria and members of Enterobacteriaceae decreased by about a 1000-fold. At 50~ enterococci, members of Enterobactericeae and staphylococci were not detected in the samples. However, a substantial number of yeast and moulds and lactic acid bacteria survived cooking temperatures of 50~ and 60~ The count of most of the bacterial groups, yeasts and moulds was below detectable levels ( < 102 c.f.u./g) at 70~ heat treatment. Aerobic spore formers remained at about 103 c.f.u./g in all stages of ayib making.
Table 1. Counts of microorganisms in raw milk, sour milk and ayib cooked at different temperatures. Sample
pH
Total count
Enterococcl
Enterobacteriaceae
Lactic acid bacteria
Staphylococci
Yeasts/ moulds
Aerobic spore formers
R a w milk Sour milk
6.7 4.0
5.4 x 106 1.8 x 10Q
1.6 x 10 4 2.2 x 10 6
3.5 x 104 1.8 x 106
4.3 x 10 5 5.8 x 10 8
2.0 x 104 2.3 x 104
5.0 x 103
6.6 x 10~
3.4 x 103 2.0 x 103
3.8 4.0 4.0 4.0
4.2 6.2 1.4 4.0
x 108
7.0 x 104
8.8 x 103
X 10 7
