Food Microbiology Lecture Notes PDF

Foods sample: DiluBon factor for each step = Vol of the sample added to the tube Final volume in the tube 13 Examination methods Microbiological test procedures: Total Vi...

Foods sample: DiluBon factor for each step = Vol of the sample added to the tube Final volume in the tube 13 Examination methods Microbiological test procedures: Total Viable Count (TVC) TVC is the one of the most common techniques carried out on food examina7on, which is known as Standard plate count (SPC) or aerobic plate count (APC) used to determine number of viable bacteria, and the count perform manually using colony counter. ideal plate counts range from 30 to 300 colonies 14 Examination methods Nutrient agar or plate count agar media used to enumera7on bacterial growth (aerobes and faculta7ve anaerobes), pH (7.0 to 7.4) Incuba7on temperature: 55 oC for thermopiles 35 - 37 oC for mesophiles 20 - 30 oC for spoilage bacteria and psychrophiles 15  Indicator organism Basic concept of indictor organism test 1- presence of indicator organism in foods suggests the possibility of pathogen being present. 2- indicator organism presence indicates to the general microbiological condi7on of the foods 3- include: colifrom, E. coli, Enterococci, Staphylococcus aureus, Listeria monocytogenes, salmonella, ….etc 16  Coliforms: The principal coliform bacteria are Escherichia coli and Enterobacter aerogenes. E. coli is normally found in gastrointes7nal tract. E. aerogenes associated with vegeta7on and is only occasionally found in the intes7ne. E. coli indicator organism in water for the possible presence of enteric pathogens (faecal). Why? In food, the presence of E. coli is of less signiIcance faecal indicator. Why? contamina7on actually grown in food poor cleaned equipment Personal contamina7on coliform bacteria can be enumera7on by: 1- Most probable number (most common) 2- Membrane Iltra7on technique 17 Indicator organism cont. Food poisoning bacteria Enterococci: Indicators of faecal pollu7on in water, but less conclusive evidence of faecal contamina7on due to found in non-faecal environment. comprise two species found in human and animal intes7ne, namely E. faecalis and E. faecium 18 Indicator organism cont. Food poisoning bacteria Staphylococus aureus: Staph.aureus produce thermostable deoxyribonuclease (TNase) which it used as rapid procedure to enumera7on in foods. growth ≥ 10 6 and possible produce toxin used as indicator of improper handling and heat processing, also used as indicator for ready-to-eat food which extensive human handling organism harbored in nasal cavity and skin and skin gland 19 Indicator organism cont. Food poisoning bacteria Salmonella :  used as indicator for cross contamina=on, environmental contamina=on and movement of dust to the food through the air Listeria monocytogenes  used as indicator for foods that store in low temperature containers (refrigerator ), drains and equipment sanita=on presence indicates that adequate sanita=on has not be complete 20 Indicator organism cont. Compylobacter used as indicator recover low number of the organism from Bacillus cereus: used as indicator organism for bacillus food poisoning in foods specially strachy foods (rice, cereal ,…etc) 21 Indicator organism cont. Echerichia coli:  used as indicator organism for many products to indicate the condi=on of low level of hygiene in raw and processed plant or animal foods.  organism harbored in gastrointes=nal tract of warm-blooded animals, presence in foods indicate poten=al contamina=on with animal faeces or poten=al pathogens 22 Indicator organism cont. Clostridium. (botulinum, perfringenes) clostridium used to evaluate the eFects of thermal heat in processing foods specially canned foods Yeast and moulds: Used as indicator for fruit and vegetables and other food spoilage 23