5. Soils and Biofilms Flashcards
Definition of soil
Unwanted matters in food contact surfaces; can be visible or invisible
Primary source of soil
- From food being handled (carbs, fat, protein, minerals)
- From water and cleaning residues (e.g. cleaning compounds)
- Microbiological biofilms
Complex soil films contain
- Combination of food components
- Surface oil or dust
- Insoluble cleaner components
- Insoluble hard water salts
Soil film solubility varies depending on:
- Heat
- Age
- Dryness
- Time
Why is understanding soils important?
- Improper use of detergents can set soils, making it more diff. to remove (e.g. acid cleaners precipitate protein)
- Many films and biofilms require more sophisticated cleaners amended with oxidizing agents (e.g. chlorine detergent)
Rule of thumb of soils
Acid cleaners dissolve alkaline soils (minerals)
Alkaline cleaners dissolve acid soils (protein)
Classification of visible soils
- Soluble in water (sugars, some starches, most salts)
- Soluble in acid (limestone, most mineral deposits)
- Soluble in alkali (protein, fat emulsions)
- Soluble in water, alkali, or acid
Characteristics of carb based soils
- simple sugars readily soluble in warm water
- starch residues are easily removed with mild detergent
- starch assc w proteins/fats are easily removed w highly alkaline detergents
Characteristics of fat based soils
- present as emulsion, generally can be rinsed away w hot water above melting point
- more diff oil/fat residues can be removed w alkaline detergents w good emulsifying/saponifying ingredients
Characteristics of protein based soils
- most diff to remove
- more complex protein, more diff to remove
- heat denatured protein can be extremely diff to remove
- req highly alkaline detergent w peptizing/dissolving properties
- wetting agents to increase wettability and suspend ability of proteins
- protein films require alkaline cleaners w hypochlorite and wetting agents
Characteristics of mineral salt based soils
- Ca, Mg most difficult (when heated under alkaline conditions can combine w bicarbonate to form highly insol complex)
- Fe, Mn also difficult
- Salt films can cause sorrosion of surfaces, require [organic] acid cleaners
- Sequestering agents (eg phosphates) or chelating agents are often used
What are invisible soils
-Resulted from microscopic organisms in food processing facilities
- Consists of bacterial spores and (lesser) vegetative bacteria; fingal spores; yeast
- In cracks and pits on surfaces of equipments, walls, etc
- Microbes that attach to solid surfaces may form biofilms
Definition of biofilm
A collection of microorganisms, mainly bacteria, growing together in a matrix of polymers (EPS secreted by microbes) on solid surfaces
Diff between planktonic and sessile cells
Sessile: attached to surface
Planktonic: living in liquid phase
Benefits of biofilms
- in the bottom of water bodies known to reduce pollutants
- play important role in wastewater treatment
- used to extract minerals or metal in mining
- simulated in fermentation techniques (immobilized bacteria/microbes)
