SOP: Microbiological Safety Verification of Enzyme-Based Thermal Processes

GIFSQ — Global Institute for Food Safety & Quality

Principle

When a thermal process for canned fruits in syrups, fruit juices or pulps has been evolved on the basis of enzyme inactivation (rather than on the destruction of Cl. botulinum spores), tests must ensure the process also renders the product microbiologically safe. The procedure isolates the spoilage flora that survives underprocessing of the overripe fruit, determines its heat resistance in the product’s pH range, and checks that the process destroys it — including the reported acid spoilage organisms B. coagulans, Cl. butyricum and Cl. pasteurianum.

Apparatus required

• Cans for the underprocessing series
• Incubators (30 °C, 37 °C and 50 °C)
• TDT tubes or cans for heat resistance determination

Procedure — Isolation of the spoilage flora

Allow the fruits to overripen and can them without acidifying

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Process the cans for various time intervals; incubate at 30 °C and 37 °C for 4 weeks and at 50 °C for 2 weeks

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Select the can that received the maximum process but still underwent spoilage (mostly swelling, occasionally flat-sour); isolate the organism(s) and characterize them — Gram-positive or Gram-negative, aerobic or anaerobic, spore-formers or not

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For spore-formers, subculture and harvest the spores

Procedure — Growth range and heat resistance

Study whether the isolated organism grows in the pH range at which the product is canned (3.6 to 4.2): adjust the pulp or juice to the desired pH (pH 3.6, 3.8, 4.0 and 4.2), sterilize, and inoculate with the organism; note the lowest pH at which growth occurs

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Subculture and isolate the organism; determine its heat resistance (TDT) and use it for inoculated pack studies

Procedure — Check against reported acid spoilage organisms

Since B. coagulans, Cl. butyricum and Cl. pasteurianum have been reported to cause spoilage in canned acid products, ensure that the process developed on the basis of enzyme inactivation also renders the canned product safe with respect to these organisms

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Determine the TDT of the spores of these organisms in tomato juice to confirm that their heat resistance compares well with the reported values (the book’s Table 25-9)

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Determine whether the test material (fruit) supports the growth of these organisms, and determine the TDT in the test material at the pH range used for canning

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Finally, carry out the inoculated pack studies

Precautions

• In the book’s work, the organisms isolated from spoiled cans of overripe guava, mango, muskmelon and papaya canned at natural pH consisted of mixed flora that did not grow in sterile acidified material, and in the acidified canned product they did not survive process times even lower than the calculated time; none of the fruits tested supported the growth of B. coagulans; guava at pH 5.0 and above, and Totapuri mango at pH 3.8 and above, supported the growth of Cl. pasteurianum; the F value of this test organism was lower than the F values of pectinesterase, the most heat-resistant enzyme in these fruits; in the inoculated pack studies the organisms did not survive process times slightly lower than the calculated process times.

References

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