| Primary sources of microorganisms | - soil and water
- plants and plant products
- food utensils
- intestinal tract of humans and animals
- food handlers
- animal feeds and hides
- air and dust
- food ingredients
- equipment |
| Cell Wall (structure) | - peptidoglycan
- encloses cells of most prokaryotes (except for mycoplasma) |
| Cell Wall (function) | - provides shape and protection from bursting
- determines cell shape
- protection from lysis and harmful chemicals |
| Gram Stain | - differential stain
- one of the first steps in ID of bacteria
1) crystal violet, 2) iodine, 3) alcohol, 4) safranin |
| Gram-negative bacteria | - thin peptidoglycan layer
- do NOT retain CV - iodine stain when washed with alcohol
- stains pink
- dual cytoplasmic membrane |
| Gram positive bacteria | - thick peptidoglycan layer
- retain CV - iodine stain, not easily removed by acetone/alcohol
- stain blue |
| Cytoplasmic membrane (structure) | - lipid bilayer
- mainly phospholipids, membrane proteins
- fluid structure
- hydrophobic barrier
- severe damage can cause cell death |
| Cytoplasmic membrane (function) | - enzymes present: ATPase, dehydrogenase
- impermeable to protons
- facilitates nutrient transport
- hydrophobic barrier |
| Ribosomes (structure) | - give granular appearance to cytoplasm
- made up of protein and RNA |
| Ribosomes (function) | - synthesize cell protein
- 10k per cell |
| Nucleoid | - diffuse nucleus (no nuclear membrane)
- single circular DNA molecule
- major genetic material of the cell |
| Flagella (structure) | - helical filaments
- protein (flagellin)
- polar flagellum to 10s, 100s
- 3 parts: filament, hooks, basal body |
| Flagella (function) | - rotate to propel the cell
- help cell respond to chemical attractants and repellants (chemotaxis) |
| Pilli (structure) | - aka fimbriae
- ptrotein (pilin)
- straight rods |
| Pili (function) | - no rotation
- used for cell attachment
- bind to specific receptors
- special pili used for conjugation |
| Fungi | yeasts and molds |
| Yeasts | - oval, spherical, or elongated cells
- cell wall contains polysaccharides (glycan), protein, and lipids; some chitin
- cell membrane
- organelles in cytoplasm
- well defined nucleus
- nuclear membrane
- far larger than molds |
| Molds | - filamentous fungi
- cell wall of chitin, cellulose, or both!
- hyphae: filaments
- mycelium: numerous branches of hyphae |
| Hyphae | - filaments of molds
- can be vegetative or reproductive
- reproductive hyphae: form exospores
- aerial hyphae: bear conidia or sporangia
- subsurface hyphae: produce enzymes to digest substrate |
| Classifying microorganisms | - species: basic taxonomic group for yeasts/molds/bacteria
- genus: several species with similar characteristics
- family: several genera with similar characteristics |
| Microbes in food: bioprocessing | - use of food grade microorganisms as a starter culture
- different types of fermented foods made
- microbial enzymes also used |
| Microbes in food: biopreservation | - using antimicrobial metabolites from desirable microorganisms to preserve food
- control pathogens and spoilage organisms
- antimicrobial metabolites: lactic acid, acetic acid, propionic acid |
| Probiotics | - viable bacteria that seem to produce health benefits when consumed in foods
- specific strains (of Lactobacillus, Bifidobacterium, Lactococcus, Enterococcus) are important |
| Food spoilage | - growth of microbes in foods and/or action of their enzymes
- lead to undesirable changes in food texture, taste, flavor, color
- discoloration, softening, increased exudate, off-odors, bad taste
- causes substantial economic loss |
| Foodborne disease | - pathogenic microorganisms (bacteria, mold, viruses, parasites)
- caused by under-processing, cross-contamination, and mishandling of foods
- large-scale production of food & increase in foreign importation of food: increase chances of disease outbreaks and new pathogens
- most caused by foods of animal origin
- common causes: under processing, cross contamination, and mishandling of food |
| Bacterial spores | - endospores: formed inside vegetative cells
- exospores: vegetative cells change to cysts |
| Endospores | - one endospore per vegetative cell
- produced by some Gram-positive bacteria
- highly stress-resistant, dormant structure
- resistant to heat, chemical disinfectants, radiation, and desiccation |
| Destruction of endospores | - destroyed by very harsh chemical or physical treatments
- 121 deg C at 15psi for 20 minutes in an autoclave
- irradiation at 30-40 kGy
- Not killed by high pressure practically attainable by current technology ex 600-8800 MPa |
| Vegetative cells vs. bacterial endospores | . |
| Sporulation | - formation of spores in vegetative cells
- endospores appear as clear areas in vegetative cells |
| Germination | - formation of vegetative cells from spores
- only one veg. cell produced from one spore |
| Gram positive spore formers | - Bacillus spp - Clostridium spp - Alicyclobacillus spp - Sporosarcinia spp (cocci) |
