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I have just reviewed the most common search terms resulting in visits to this blog.

By far the most common has been "Coliforms in food".  This has been a regular search since I started writing Safe Food in 2006, but has perhaps appeared more frequently since the Escherichia coli O104:H4 outbreak in Europe.

Coliforms are used as "indicator organisms" to show whether the food has been processed under hygienic conditions.  Presence of these bacteria mean that the food has potentially been contaminated with faecal material and hence faecal organisms, but to confirm this, we look for Escherichia coli presence in the food.

Surprisingly, the next most common search has been "Safety of Probiotics".  Probiotic bacteria are those that confer some benefit on the host.  Thus many foods, such as yoghurt, contain live bacteria that may colonise the gut of the consumer and confer some benefit.  These bacteria are often lactic acid bacteria.  Many claims have been made for the benefits of consumption, though there are some indications that administration to critically ill patients with acute pancreatitis may have deleterious effects.  There is also some evidence that administration to infants under 6 months of age may render them more prone to development of sensitivity to allergens.  For the majority of consumers, however, probiotics will not be hazardous and may be beneficial.

Do not confuse probiotics with "prebiotics".   These were so named by Marcel Roberfroid in 1995, who later wrote the definition: "A prebiotic is a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health."  A major class of prebiotic is soluble fibre.

Much lower down the list are "Listeria in vegetables" and "Safety of chicken".  There has been a small spike in Listeria searches, probably as a result of recent recalls and the cantaloupe outbreak in USA that has killed approximately 29 people.  The incidence of listeriosis is very low and victims are usually neonates, the elderly and those people with compromised immune systems, but this outbreak seems to have been particularly dangerous.  Chicken has made regular appearances in the news, either being a vehicle for Salmonella or Campylobacter.  The incidence of Campylobacter infections in New Zealand has dropped significantly since the introduction of more stringent controls and biosecurity systems.

One new search now appearing is a bit disturbing: "Will eating spoiled food make you sick?".  I have previously written on this after receiving a direct question from a reader.  Is the increased interest a result of hardship in the community, or merely a thirst for knowledge?  I hope it is the latter.

Will spoiled food make you sick?

I recently received a message from Jo, asking me to comment on this subject.  Jo actually raised a lot of questions and, of course, the answers are not simple.

First question:  If the food smells off, tastes bad, has a poor colour etc. is that a good indicator it will make you sick?

Humans have been on the Earth for a long time and one of the reasons they have survived for so long is that they have evolved self preservation mechanisms.  If the food smells off or doesn't look right, there is a chance that it is poisonous in some way and we tend to avoid it.  Sometimes I wonder what the first people to taste durian or blue cheese thought they were doing!  So, clearly, the answer has to be a qualified "Yes, it might make you sick, but some sort of tribal wisdom suggests that a few foods can look and smell awful but still be OK to eat".

Jo then went on to say that she thought that the food was unlikely to make you sick, as the changes were caused by spoilage bacteria and enzymatic reactions, which are not the same as pathogenic bacteria, which she thought do not alter the food in the same way.

This is where it gets complicated.  Spoilage bacteria do cause some changes, which, by definition, make the food unacceptable to most people.  Other bacteria, such as Salmonella, may grow alongside the spoilage bacteria.  When the food is eaten, the salmonellae  set up an infection in the gut and produce the familiar food poisoning symptoms.

Second question: Is it true that pathogenic bacteria don't alter the food?  Again, it depends on the bacteria.  Generally, clostridia alter the food a lot, producing many smelly compounds and gas.  This would put most people off eating the food, so they would be safe.  But some Clostridium botulinum strains are non-proteolytic.  That is, they don't break down proteins and they don't produce the foul smells that the proteolytic strains make.  So you could find improperly processed canned foods that appear quite normal, but could kill you.

Jo's third question was perhaps the most fascinating: she was most interested in how the food could potentially have both types of bacteria on it near to the time it was made and correctly identified contamination of the food as the cause, possibly by cross-contamination from some source.  A good example would be a careless food handler.

At this point, the food could cause food poisoning if consumed - Salmonella transferred from raw meat to a cream pastry would be a good example here.

Jo went on "However as time goes on and assuming the food gives them all the things they both need to grow, is it as simple as the pathogens might be around for a short time until the spoilage guys, who being better competitors for resources, take over; so by the time the food
is showing signs of being spoiled, the pathogens have been killed off?"

That's a really insightful comment.  Many fermented foods are actually safe because of this pattern.  Take raw cabbage and make sauerkraut:  we shred the cabbage and add about 2.5% salt to it and then press it into a container and seal it.  The salt draws out the tissue fluids from the shredded leaves and bacteria naturally on the leaves begin to produce lactic acid.  If we sample on the first day, we can find all sorts of bacteria, including Escherichia coli and possibly Salmonella.  However, as more acid is produced, the pH falls and the potential pathogens die off.  Finished sauerkraut has a pH around 3.1 to 3.7 and is perfectly safe to eat, though there has been a lot of bacterial growth in it.

So, to return to Jo's original question, "Is spoiled food potentially safe to eat, even though it looks and tastes awful?"    Sorry Jo, I can't answer that.   But if it tastes awful, why would you want to eat it?

One last point:  there is an anecdote that a lady opened a can of peas and thought that they looked a bit different.  She tasted one and cooked the rest.  She died of botulism.  Ironically, if she had cooked them and then tasted one, she would have lived, as the botulin toxin is heat labile.  I don't remember where I read this - it was somewhere around 1980, but it's a good example with which to finish this article.