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Refrigerated low-acid juices and the risk of botulism

A new guideline for commercial manufacturers of refrigerated low-acid juices was published by the United States Food and Drug Administration (USFDA) in June 2007, in response to a 2006 outbreak of foodborne botulism (http://www.foodsafety.gov/~dms/juicgu15.html). The outbreak affected six people in the US and Canada and the implicated product was carrot juice. The bottles of carrot juice were labelled 'Keep refrigerated' but the implicated juices were believed to have been temperature abused for an extended period of time, either during distribution or after purchase by the consumers.

Foodborne botulism is caused by consumption of food in which the spore-forming microorganism Clostridium botulinum has grown and produced neurotoxin. Botulism can severely affect the nervous system and even after treatment has commenced, prolonged recovery periods in hospital may be required. Incidents of foodborne botulism have been extremely rare in Australia.

There are two main control measures for proteolytic C. botulinum (the most heat resistant type): heat treatments severe enough to inactivate spores and ensuring products are below pH 4.6, to prevent germination and outgrowth of spores. Unless they meet at least one of these criteria, products must be kept adequately chilled to control C. botulinum spores, if present.

The carrot juice linked to the 2006 US and Canadian botulism cases was pasteurised. As this type of heat treatment is insufficient to inactivate proteolytic C. botulinum spores and the pH of carrots is typically above pH 4.6, refrigeration below 5°C should have been maintained.

In Australia, the growing number of outlets selling freshly squeezed juices illustrates their popularity. Some outlets sell juices in unlabelled screw-cap bottles which may be taken home for later consumption. Freshly prepared juices (291 samples) from Victorian retail outlets were analysed as part of a 2004 survey (http://www.health.vic.gov.au/foodsafety/downloads/fruit_juice_survey_report_aug05.pdf). Average pH values were above pH 4.6 for five of the eight categories of fruit or vegetable juices tested, with carrot juice samples giving the highest average, pH 5.5 (range pH 3.6 – 6.7). If these low-acid juices are not consumed straight after purchase, there is a risk of foodborne botulism occurring if C. botulinum spores are present and temperature abuse occurs.

USFDA industry guidelines recommend that manufacturers of low-acid juices for the commercial market apply validated control measures to ensure that C. botulinum growth and toxin production will not occur should the juice be kept unrefrigerated during distribution or by consumers. These control measures include acidification of the juice to pH = 4.6 or thermal treatment to inactivate spores. The USFDA also recommends that these products are labelled 'Keep refrigerated' (or similar). US retail businesses that sell low-acid juices directly to consumers are required to label products with a warning statement, specifying that the product has not been pasteurised. No similar guidelines or legislation currently exist in Australia for low-acid juices prepared at retail outlets.