MadSci Network: General Biology

Re: How does heat react with food to make it rot faster?

Date: Wed Feb 14 20:20:08 2001
Posted By: Dean Cliver, Faculty, Food Safety Unit, Uiversity of California, Davis
Area of science: General Biology
ID: 981579676.Gb

	Life at any level (in the cells of our bodies, or inside of 
bacteria) is an incredibly complex soup.  The things we eat, or the things 
that bacteria live on, get digested, absorbed into cells, and converted to 
whatever the cell needs.  The conversions (what gets turned into what) are 
governed by protein molecules called "enzymes."  There needs to be at least 
one enzyme  sometimes several  to control formation of every substance 
that makes up a cell; and there are many, many substances.  Most of the 
information in our chromosomes (and in bacterial chromosomes) is about 
which enzymes the cell can produce.  
	Most of the key enzymes in the human body work best at body 
temperature  98.6 F.  Bacterial enzymes have different temperature 
preferences: the bacteria that make us sick have enzymes that work best at 
body temperature and may even work OK when our body temperature goes up 
(fever).  Most bacteria that spoil food have enzymes that work best in the 
range from room temperature to body temperature.  These enzymes may also 
work in the refrigerator, but their action is slower.  These bacteria break 
down food for a living; they can usually still multiply in the fridge, but 
their enzymes don't break the food down as fast.  Most enzymes in our 
bodies' cells won't work at all at refrigerator temperatures.
	Many molds can also make enzymes that break down food at 
refrigeration temperature; molds also need air.  When you buy food in a 
vacuum or controlled-atmosphere package, the lack of oxygen keeps molds 
from growing on the food in the refrigerator.  When we put leftovers in the 
fridge, we usually try to seal the container, which can help slow down 
molds by excluding air. However, things still get moldy in the refrigerator 
unless they stay sealed in the original package.
 	All the same, everything spoils eventually at refrigeration 
temperatures because the enzymes, whether from bacteria or molds, slowly 
break the food down.  Life stops in the frozen state, so things in the 
freezer don't spoil.  Food in cans (the kind that don't say "keep 
refrigerated") has been heated to a high enough temperature to kill molds, 
bacteria, and all of their enzymes, so canned foods don't spoil, either.  

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