SOP: Sampling of Can Contents for Microbiological Examination

GIFSQ — Global Institute for Food Safety & Quality

Principle

The sample must come from the part of the can where the spoilage organisms live: the centre of the can in underprocessing, the exterior ends in leakage. Liquid, solid and mixed products are opened by different tools, each sterilized, so the sample is taken without contamination.

Apparatus required

• Sterile tapered can opener (tapered punch)
• Length of sterile glass tubing (7–8 mm outside diameter)
• Wide-mouthed pipettes (20 ml capacity)
• Sterile cork borer
• Sterile rod (for expelling the sample from the borer)
• Sterile spatula (alternative to the cork borer)
• Wide-mouthed sterile bottle with screw cap or conical flask (containing 50 ml of water and a few glass beads)
• Bunsen burner

Sample preparation

Open the can by the aseptic opening procedure. Sterilize the punch, borer or opener before use by flaming.

Procedure — Liquid products

Cut a hole of about 0.5 in. diameter with the tapered punch, sterilized before use by flaming

↓

While opening, hold a Bunsen flame near the opening

↓

Remove the sample with a length of sterile glass tubing of 7–8 mm outside diameter or with wide-mouthed pipettes of 20 ml capacity — the tubes are more suitable for semi-solid or viscous products

↓

Inoculate directly into the media or transfer into a sterile cotton-plugged test tube for subsequent subculturing

Procedure — Solid or semi-solid products

Sterilize the opener and cut out a circular disc around the central puncture

↓

With solid packs, remove a cylinder with a sterilized cork borer and expel it from the borer with a rod if necessary — a spatula may be used instead of a cork borer. Use a fresh sterile borer for each can.

↓

Choose the sampling point by the suspected cause: in underprocessing the organisms are most likely confined to the centre of the can — take the sample from the geometric centre; in leakage the organisms are at the exterior ends — push the borer obliquely in several directions and collect the sample

↓

Remove 10–20 g of sample

↓

Expel the samples from the borer or spatula into a wide-mouthed sterile bottle with a screw cap or a conical flask containing 50 ml of water and a few glass beads

↓

Plug the bottle or flask tightly with cotton

↓

Shake to distribute the sample — use this for subsampling

Procedure — Products containing liquid and solid constituents, as in canned fruits and vegetables

Sample as in the case of liquid or semi-solid products

↓

During the examination, to prevent contamination from air, cover the can with a sterile Petri dish, a sterile new can lid or a disinfectant-moistened towel

Precautions

• Sterilize every opener, punch, borer and spatula before use, and use a fresh sterile borer for each can.
• Keep the Bunsen flame near the opening while sampling liquids.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.