Decomposer microorganisms break down dead matter and wastes, returning nutrients to the non-living environment. Photosynthetic phytoplankton contribute to primary production and oxygen release. Some digestive microorganisms help process food. Humans also use microbes in bread, yoghurt and other fermented foods. Genetically modified microorganisms can produce proteins such as human insulin when given appropriate genetic instructions.
Spoilage occurs when microbial activity changes food quality. Refrigeration commonly slows growth; heating can destroy susceptible microbes; drying reduces available water. Salt or concentrated sugar lowers water availability and can draw water from microbial cells. Acids inhibit organisms outside their suitable pH range. Preventing recontamination also matters: slowing growth is different from making a product sterile.
Example 1
Why does drying fruit slow many spoilage microorganisms?
Drying reduces water availability, limiting the cellular processes and growth of many microbes.
Example 2
A treatment reduces a population from 10000 to 10 viable cells. What percentage reduction is this?
1010000−10000×100=99.9%. Ten viable cells remain; this is not sterilisation.
Watch out:It generally slows microbial growth and does not necessarily kill all microorganisms.
Microbial roles and food preservation practice | Year 11 Biology | Ascent Arcade