Method of Analysis

Milk

• It is general market milk is sampled in the container which it is solid .
• The sterile plunger is used for sampling and 10ml sample is taken. The collecting sample is put in sterile screw cap and immediately send to the lab.
• Before performing the test , the sample is mixed by inverting up and down for more than 10 times.
• For milk, bottle tap is flamed and the cap is removed with flame forceps .
• For plastic packed , the top and corners of the packet are swapped with spirit . After allowing to air , dry the swapped area is cut with sterile scissors.
• The collected milk is tested by methylene blue test, resazurin test, and MPN test . Three routine test prescribed for milk are;

1. Steriledilutionis made and pour planting is done from tubes of 10¯to 10¯8 dilution
2. For raw milk , DMC is usually done .
3. COlifrom test is done by MPN.

Mesophilic aerobic test

• Raw milk should not exceed total plate contains2×10^5 CFU/ml .
• Pasteurized milk should not exceed total plate count 2×10^4 CFU/ml .
• At 37°c coliform= 0 best.
• At 42°c , faecalcoliform=o best

For dried mesophilic aerobic bacteria.n=5,c=2, m= 5×10^4 ,M= 5×10^5 . coliform, n=2 , c=2 . m=10 and M=100 , Steptocouus aures , n=5 ,c=1 ,m=10 and M=10^2 and salmonell, n=1o , c=o and m=0.

Cheese

One sample is taken with the help of border

• .The collected sample is allowed to made in the lab below 20°c.
• The collected sample is made into fine pieces with the sterile grater( grater is a device with a rough surface for a grating.
• 10gm of graded sample is mixed with 90ml of warm diluent and homogenize in a blender.
• Serial dilution is performed.
• Plate count is performed on yeast extract milk agar medium similarly , coliform can also be counted.
• For directly microscopic examination , thin film slices cheese are made . They are defatted with Zylon. Zylon is washed with smear is stained and examined.For cheese , S aureus , n=5 , c=1 m=10 , M=10^.

Ice cream

If the ice cream is placed in small size , it should be taken lab in frozen condition (dry ice can be used )

• Melting ice cream should not be taken from the field .
• The wrapper is removed aseptically and content is put in trial screw capTURS
• The collected sample is allowed to meet in the lab below 20°c.
• 10mi sample is weighed in a screw cap jar and serial dilution is performed in 1% peptone water.
• Plate count is carried out from each dilution
• Mesophilic aerobic bacteria , n= 5, c=2 ,m=2.5×10^4 and M=2.5×10^5.
• Coliform , n=5 , c= 2 , m= 100 and M=100.
• S.aureus, n=5 , c= 1 , m=10 and M =100.
• Salmonella , n=10 . c=0 and m=0

Butter

The sampling of butter is done by using a sterile knife.

• 10ml of butter is emulsified in 90ml of warm water (40-50°c) diluent and plate count is perform.

Yoghurt

• Yogurt is a sample from the container in which it is fermented using spoon and spatula.
• Double-dilution of yogurt is prepared in 0.1% peptone water.
• 5ml of dilution is mixed with 5ml of melted differentials media.
• It is poured in plates , cooled to solidified and incubated at 43°c .

The sample is a procedure for meat and meat products.

No.of field sample (N) =s

Methods of analysis

• Enumeration of mesophilic , aerobic bacteria.
• The detection of Salmonella

Carcass sampling (Raw meat)

• Sterile large swabs are taken and they are moistened in 0.1% peptone water.
• The carcass is wiped with the swab .
• The carcass is again cleaned with the dry pad.
• The pads are taken and 250ml of diluent is added in the pad to dispersed the microorganisms from the trap.
• Serial dilution is performed .
• Plate count is made at 20c.
• For detection of Salmonella , plating is done in selective media.

Comminuted meat

• It may be fresh minced or chopped meat.
• Several random samples are taken . so , as to detect universally distributed microorganism .
• The sample is mixed with diluent and mixed oil.
• The sample is serially diluted.
• Plate count is performed from dilution 10^4 to 10^8.

Poultry

• Swab with the lengthy rods is taken and it is sterilized.
• The swabs are rinsed in 100ml peptone water .
• For each chicken, two swabs are taken one for swabbing body cavity of the chicken.
• The sample is serially diluent.
• Plate count is performed for the total count and coliform count selective media.
• To test for Salmonella . The dilution should be enriched in selenite or tetrathionate broth and the sample is further processed.

Fresh fish

• The whole fish is either webbed or washed with sterile 0.1% peptone water 1% NaCl in the serial plastic bag.
• Appropriate dilution is prepared and the total count is performed in marine agar medium which incubates at 20c for 5 days.
• Culture can also be done in glucose tryptone media , Mac-Conkey agar or media containing 5-10% NaCl for halophilic bacteria.

Egg

• Out surface of the egg shell is swabbed with the sterile swab.
• Sterile swabbed must be moistened before swabbing.
• Then,appropriate dilution is made from the swab
• Immer part of the egg can be taken as sample and diluent.
• No.of field sample , Salmonella = 10 field sample , Coliform = 5 field sample , Mesophilic bacteria = 5 filed sample

Method of analysis

• Immigration of mesophilic aerobic bacteria
• Immigration of coliforms.
• Detection of Salmonella.For mesophilic aerobic bacteria (TPC) n=5 , c=2 , m=10^4 and M= 10^3 and for Salmonella , n=10 . c=0 and m= o.

Reference

Frazier, WC and Westhoff DC. Food Microbiology. 3rd. New Delhi: Tata McGraw-Hill Publishing Company Limited, 1986.

Jay, MJ. Modern Food Microbiology. Ed. India. 3rd. Delhi: CBS Publications and Distributions, 1987.