Packaging Affects Formation of Botulism Toxin
In August of 2004, new Virginia Tech Food Science Ph.D. recipient Fletcher Arritt presented his findings at the conclusion of his doctoral research. Dr. Arritt’s work was focused on the prevention of toxin production by Clostridium botulinum in fishery products. In his research, Arritt investigated the effects of different types of packaging for breaded and battered Alaskan Pollock fillets and raw flounder fillets.
Different packaging techniques can have a pronounced effect on the spoilage attributes of food. For example, packaging under vacuum (VAC) and/or modified atmosphere packaged (MAP) conditions can significantly extend the shelf life of fish products. But how does this ‘airless’ packaging, which greatly hinders the action of aerobic bacteria affect the growth of an obligate anaerobe like Clostridium botulinum? Most epidemiologists would agree that botulism has a much greater propensity to be lethal when compared with most other foodborne illnesses. Could VAC and MAP packaging actually encourage the accumulation of botulinum toxin in foods? Could the levels of toxin rise to dangerous levels while the food still smelled and tasted ‘okay’? The answers to these questions are essential for processors of VAC and MAP refrigerated fishery products.
The study compared aerobically packed, vacuum packed, and MAP packed (100% CO2 atmosphere) aquacultured summer flounder (Paralichthys dentatus) fillets and fully cooked breaded and battered Alaskan Pollock (Theragra chalcogramma) stored at different temperatures over 35 days. The aerobically packed samples used a plastic film with an oxygen transmission rate (OTR) of 3000 and 6000 cc/m2/24h@70°F for the flounder and pollock, respectively. FDA requires for aerobic packaging to have an OTR of at least 10000, so technically the packaging used was not regulation aerobic packaging, but it still was sufficient for the purposes of the study. The MAP and vacuum packaging had an OTR of just 7.3 for both types of fish. The flounder fillets were stored at either 4 or 10°C while pollock portions were stored at 8 or 12°C. Based on the time to spoilage, additional samples were inoculated with five strains of nonproteolytic C. botulinum and analyzed qualitatively for the presence of botulinum toxin using a mouse bioassay.
Conclusions
Refrigerated Raw Flounder Fillets
- Absolute sensory spoilage and microbial spoilage occurred prior to toxin formation in refrigerated raw flounder fillets packaged using a film with an OTR of 3,000 cc/m2/24h@70°F and stored at 39°F (4°C) or 50°F (10°C).
- Toxin formed in VAC fillets (OTR 7.3 cc/m2/24h@70°F) on day 20 and microbial spoilage occurred >22 days at 39°F (4°C).
- Toxin formed in VAC fillets (OTR 7.3 cc/m2/24h@70°F) on day 9 and microbial spoilage occurred on day 9 at 50°F (10°C).
- Toxin did not form in MAP fillets (100% CO2 and OTR 7.3 cc/m2/24h@70°F) when held at a constant temperature of 39°F (4°C).
- Toxin formed in MAP fillets (100% CO2 and OTR 7.3 cc/m2/24h@70°F) on day 9 and microbial spoilage occurred on day 9 at 50°F (10°C).
Fully Cooked Refrigerated Battered and Breaded Pollock Portions
- There was no correlation between APC and toxin formation for fully cooked refrigerated battered and breaded Pollock portions.
- Mold did not form and toxin was not present in the aerobically packaged product (OTR 6,000 cc/m2/24h@70°F) stored at 47°F (8°C) for 35 days.
- Mold formed (absolute sensory rejection for appearance) on day 20 and toxin was present on day 25 in the aerobically packaged Pollock portions (OTR 6,000 cc/m2/24h@70°F) at 53°F (12°C).
- Toxin formed in the VAC Pollock portions (OTR 7.3 cc/m2/24h@70°F) on day 25 when stored at 47°F (8°C) and 53°F (12°C). Mold formation did not occur in the VAC Pollock portions (OTR 7.3 cc/m2/24h@70°F) even after 35 days at 47°F (8°C) and 53°F (12°C).
- Toxin never formed in MAP (100% CO2) Pollock portions (OTR 7.3 cc/m2/24h@70°F) when stored for more than 35 days at 47°F (8°C) and 53°F (12°C).
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