Exposure of Baby food and the degree of contamination
The hypothesis that baby food will become more contaminated when it is left out of the refridgerator for a longer period of time, is proven to be true.
It's interesting to note tthat meat products become contaminated much faster than vegetable or fruit products.
Babies have weak immunity systems and are more susceptible to food poisoning due to bacterial growth in their food. In addition, they do not have the ability to vocalize if they are experiencing stomach pains or nausea. Hence, extra care must be taken to prevent baby food from getting infected. Once a bottle of baby food is opened, it is best to consume the food as soon as possible. That's not just a ploy by food manufacturers to get you to buy more baby food - as you have observed from our experiment, bacterial growth in baby food is a very real threat.
The experiment can be repeated by using different brands of baby food.
Try to repeat the experiment using milk, porridge and soup. Also modify the experiment by dipping a used spoon (containing baby saliva) into the bottles of food, and observe if there is any difference in your results.
Food poisoning - http://kidshealth.org/PageManager.jsp?dndsHealth&lic
Food contaminants - http://en.wikipedia.org/wiki/Food_contaminants
The bacteria should be destroyed before it is disposed of. Pour some bleach into the petri dish to kill all the bacteria before disposing in the trash.