Microbial Indicators Of Food Safety PDF

# Microbial As An Indicator Of Food Safety ## Learning Outcomes 1. Understand microorganism as indicator for product safety 2. Understand coliform as microbial indicator 3. Know the standard techniques of testing used ## Function of Microbial as an indicator of food safety 1. To assess food safety...

# Microbial As An Indicator Of Food Safety ## Learning Outcomes 1. Understand microorganism as indicator for product safety 2. Understand coliform as microbial indicator 3. Know the standard techniques of testing used ## Function of Microbial as an indicator of food safety 1. To assess food safety 2. To assess food quality 3. To predict product shelf life ## Criteria of Microbial Indicators 1. Should be present & detectable 2. Enumerable in a short period of time 3. Numbers & growth should have negative correlation with product quality 4. Easily detected & enumerated & clearly distinguishable 5. Growth not affected by other components ## Some organisms that are negatively correlated with product quality | Organisms | Products | | ----------------- | ------------------ | | Bacillus spp | Bread Dough | | Clostridium spp | Hard Cheeses | | Zygosaccharomyces bailii | Mayonnaise, salad dressing | ## Some Microbial Metabolic Products That Negatively Correlate With Product Quality | Metabolites | Applicable Food Product | | ------------- | ------------------------ | | Histamine | Canned Tuna | | Lactic Acid | Canned Vegetables | | Ethanol | Apple Juice, Fishery products | ## Organism used as an indicator - Coliforms: - Normally use as an index of faecal pollution - Especially *E.coli* - Function: To assess water quality ## Distribution - Primary habitat of *E.coli* -> intestinal tract of most warm-blooded animals ## Coliform Standard - Not over 10/ml in milk products, frozen foods - Not over 100/ml in crabmeats ## The Criteria of Coliform Strains - Gram-ve - Produce gas - Produce dark colonies with ametallic sheen on Endo-type agar - Ferment Lactose within 48 hours - Represented by 4 genera (*Citrobacter*, *Enterobacter*, *Escherichia*, *Klebsiella*) - Asporogenous (not produce spores) ## Growth of Coliform - Grow slow at 5°C - Grow well on large number of media & in many foods - Able to grow in the presence of bile salts, which inhibits the growth of gram +ve bacteria - Grow well on nutrient agar & produce visible colonies within 12-16 hours - pH range 4.4-9.0 - Grown in minimal medium contain carbon & nitrogen source # Related Food Regulation ## Regulation 39: Microorganism and their toxins. 1. In these Regulations, "microorganisms and their toxins" includes bacteria, fungi and their toxins. 2. No person shall import, prepare or advertise for sale or sell any food ready for consumption that is contaminated with pathogenic microorganisms. 3. No person shall import, prepare or advertise for sale or sell any food, excluding water, specified in column (1) fo Table I to the Fifteenth Schedule which contains bacteria in numbers greater than the numbers specified opposite that food in columns (2), (3) and (4) of the said Table for the total plate, coliform and *Escherichia coli* count respectively. 4. No person shall import, prepare or advertise for sale or sell any food which contains the mycological contaminant specified in column (2) of Table II to the Fifteenth Schedule in proportion greater than the proportion ermitted opposite thereto in column (3) of the said Table. ## Fifteenth Schedule (Regulation 39) Microorganisms and their toxins: ### Table 1: Microbiological Standard | Food | Total Plate Count at 37°C for 48 hr. | Coliform Count at 37°C for 48 hr. | *Escherichia coli* Count | | ------------------------------------------------------------------------ | --------------------------------------- | --------------------------------------- | -------------------------- | | Pasteurized milk, pasteurized cream and milk powder | 10⁵ per g or per ml | 10⁶ per g or per ml | Absent in 1 g | | (including full cream and skim milk powder) | | | | | Ice cream | 5 x 10⁴ per g | 100 per g | | | Meat and meat product ready for consumption, excluding meat and meat product in hermetically | 5 x 10⁴ per g | 100 per g | 50 | | sealed containers | | | | | Fish and fish product ready for consumption, excluding fish and fish product in hermetically sealed containers | 10⁶ per g | 5 x 10⁴ per g | | | Infant formula | 10⁴ per g | 10 per g | | | Liquid egg, liquid egg yolk, and liquid egg white | 5 x 10⁴ per ml | 5 x 10⁴ per ml | | | Dried liquid egg, dried liquid egg yolk, dried liquid egg white | 5 x 10⁴ per g | 5 x 10⁴ per g | | **Note:** In places where the *Escherichia coli* count is not specified, it shall comply with good manufacturing practice. ## Standard Test Method - **Standard Plate Count (SPC):** Method for determining the numbers of viable cells or colony forming units (CFU) in a food product - **Swab Test:** Method for surface assessment in food operations & to maintain hygienic state of food contact surfaces - **MPN Method:** Method for determining number of coliform ## Standard Plate Count (SPC) - **Spread Plate Method:** 1. Pipette bacterial sample onto surface of agar plate 2. Spread sample evenly over surface 3. Incubate - Colonies grow on surface - **Pour Plate Method:** 1. Pipette bacterial sample onto petri dish 2. Pour liquid nutrient agar 3. Swirl to mix 4. Incubate - Colonies grow on agar surface and subsurface ## Standard Plate Count Methods - Pour Plate - Spread Plate - Drop Plate - Membrane Filter ## Swab Test - **Swab-rinse method** 1. Cotton or calcium alginate 2. Rub the surface with moistened swab 3. Put into test tube containing suitable diluent 4. Enumerate (suitable method: SPC) ## Most Probable Number (MPN Method) - **Presumptive test:** 1. Food Sample 2. Dilution 3. Mc Conkey Broth 4. Incubate at 37°C, 24-48 hours ## Confirmation test - Positive (gas, turbidity, yellow) Negative 1. Selective media for *E.coli* (EMB) 2. Incubate (37ºC, 24 hours) 3. *E. coli* colony - **Completion test:** 1. Nutrient agar Slant - Incubate 37°C, 24 hrs - Colony (gram staining) 2. Lactose Broth single strength - Incubate 37°C, 24 hrs - Gas formation (positive)