SOP: Examination of Rot in Canned Tomatoes

GIFSQ — Global Institute for Food Safety & Quality

Principle

Rotten portions in canned tomatoes are detected by individually inspecting the drained tomatoes, and by counting mould in the pulped tomato and in the drained juice using the Howard cell, since mould filaments are a reliable index of rotten raw material having gone into the can.

Apparatus required

• Suitable sieve (for draining the contents)
• Laboratory pulper having 0.27 in. diameter screen openings
• Howard mould counting cell with cover glass (see “Mould Counting in Tomato Products by the Howard Method” for the cell, its cleaning, and the counting procedure)

Reagents

None are required for this examination.

Sample preparation

Drain the contents of the can on a suitable sieve.

Procedure

Go through the drained tomatoes one by one and look each over

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Note down how many rotten portions are found and how large each one is

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Work the tomatoes through the laboratory pulper fitted with 0.27 in. diameter screen openings

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Using the Howard cell, count the mould in the pulped tomato and in the drained juice, following the Howard mould count procedure (field diameter 1.382 mm; at least 25 fields from each of two or more mounts; a field counts as positive only when the combined length of not more than three filaments exceeds about one-sixth of the field diameter)

Calculation

Report the result as the percentage of fields containing mould filaments, as in the Howard method:

• Percentage of positive fields = (Number of positive fields × 100) / Total number of fields examined

Precautions

• Examine every drained tomato individually; do not rely on the bulk appearance
• Record both the number and the size of rotten portions

References

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