or Gluconobacter.(mostly fermentation) - aids in food preservation
Buttermilk, sour cream, yogurt, cottage cheeses, cheese. Fermentation by Lactobacillus, Streptococcus sp., Leuconostoc sp., Proprionibacterium, Brevibacterium, Penicillium sp. etc. Use starter culture, stop fermentation by cooling or by acid production. Rennin (a digestive enzyme from calf stomachs or recombinant bacteria) aids in curd formation
1. Sausage - salami, lebanon etc.
2. Ham - cured
3. Fish sauces - mainly Japanese Bacillus sp., Lactobacillus sp., Aspergillis sp.
Can use natural fermentation or treat by Pasteurization or Sulfur dioxide to kill native organisms and then add a defined culture. Grains must be crushed and mixed with water to form a mash before they can be fermented, and the supernatant wort then used for further treatment, unlike fruits which have readily available nutrients
1. Wines - Sacchromyces cerevisiae or Sacchromyces ellipsoides - ferment 3 - 5 days at
20 - 28oC ---> 10 - 18% EtOH. Microbes die and/or produce byproducts which are
removed (most wines by centrifugation and/or filtration - some by pasteurization,
champagnes by collecting the sediment in the bottle neck and then freezing the neck,
removing the sediment and recorking). Vinegar is made by treating the wine or fruit
juice with Acetobacter
or Gluconobacter.
2. Beer and ale - Germination of barley --> enzyme action --> malt, add Sacchromyces carlsbergensis var. (bottom yeast) --> 7 - 12 days --> beer (pH 4.1- 4.2). If use Sacchromyces cerevisiae var. (top yeast) --> ale (pH 3.8). Age (lager) and add CO2, pasteurize or filter.
3. Distilled products - take any product made as in 1. or 2. above, heat in a still, collect the distillate produced at a given temperature range. Can add flavoring
4. Bread - Kneading moist dough releases amylases which digest the complex carbohydrates to limit dextrans and maltose. Add yeast (Sacchromyces cerevisiae var.) which ferments the maltose and gives off CO2 and ethanol (the CO2 makes the bread rise - about 2 hr at room temperature - the ethanol evaporates) and produces enzymes - maltase, zymase, invertase - which change the state of the dough, then bake. Some specialty breads use a starter mix with both microorganisms and/or special ingredients (caraway seeds etc.) that is made in advance and then added to the dough
5. Sauerkraut - first Leuconostoc sp. ferments until lactic acid is about 0.7 to 1% ; then Lactobacillus sp. ferments until acid concentration is 1.6 to 1.8%. pH kills off the bacteria
6. Pickles - done more or less as above, but with the addition of brine and dill seeds. In addition to the above bacteria, Streptococcus faecalis, Pediococcus cerevisiae and especially Lactobacillus are the major fermenting organisms
Proteolysis (putrefaction --> smelly amines; pectinolysis degrades pectins; fermentations and hydrolysis act on carbohydrates and fatty acids are broken down with fermentations and fatty acid degradation)
These can change with time during the shelflife of the food
1. Temperature - high temperatures 30 - 42oC best for growth of most microorganisms
2. Relative humidity - if it is high, microorganisms may grow even at low temperatures. Moisture can be absorbed by the food and promote growth
3. Gas(es) present - some plastic films such as those used in shrink wraps allow gases to diffuse across them. Excess CO2 lowers the pH and kills most gram (-) organisms, Lactobacillus sp can still grow. Oxygen allows aerobic growth, which is usually faster than anaerobic
4. Microorganisms present - obvious: can they utilize the food under the storage conditions
1. pH - if low, fungi grow best, if neutral or alkaline, bacteria grow best.
2. Aw - if too low, no growth, fungi grow until to 60%, bacteria only at 90 - 95%.
3. Redox potential - cooking lowers redox potential (reduces) of most foods so that anaerobes such as Clostridium can grow on them
4. Nutrients - need the proper nutrients for the bacteria present in the environment
5. Structure - larger surface areas - faster growth, whipping or grinding of food (ground meat, whipped cream) distribute microorganisms throughout food, let air in --> rapid spoilage
6. Antimicrobial agents - natural compounds in some foods - aldehydes, phenolics found in some spices, coumarins in fruit, lysozyme in eggs etc. can retard bacterial growth. Cooking can affect some of them.
most caused by poor hygiene, fecal - oral route
Eat contaminated food, microorganisms grow and infect and/or produce toxins,
cause "gastroenteritis"
1. Campilobacter jejuni - Campilobacteriosis appears 16 - 48 hr after ingestion, need 1 -
10 organisms to infect, produces toxins; sources - milk, pork, and especially poultry.
Prevention - cooking, good hygiene, washing utensils etc.
2. E. coli - E. coli enteritis appears in 6 - 36 hr, with or without toxins; sources - cheese,
raw vegetables.
Prevention - washing, good hygiene, cooking
3. Listeria monocytogenes - Listeriosis - meningitis, abortion; source - dairy products.
Prevention -proper processing, good hygiene.
4. Salmonella typhimurium, enteridis - Salmonellosis - appears in 12 - 24 hrs,
enterotoxins and cytotoxins; sources - meats, poultry, fish, eggs, dairy products.
Prevention - cleaning, cooking, good hygiene
5. Shigella sonnei, flexneri - Shigellosis - appears in 1 - 7 days, shigella toxins; sources -
egg products, poultry.
Prevention - good hygiene, cooking
6. Vibrio parahemolyticus - gastroenteritis - appears in 16 - 48 hrs; sources - seafood,
shellfish.
Prevention - cooking, good hygiene
7. Yersinia enterocolitica - Yersiniosis - toxins; sources - milk, meat products.
Prevention - proper treatment, cooking, good hygiene.
Don't need live organisms, toxins left behind cause disease.
1. Bacillus cereus - Bacillus cereus food poisoning - appears in 1 - 6 hr; severe nausea and
vomiting, 6 -17 hr; diarrhea; sources - meats, rice products and cereals, potatoes,
puddings.
Prevention - proper treatment of food.
2. Clostridium botulinum - Botulism - appears in 12 - 36 hr, botulinum toxin (deadly)
released after cell death; sources - fish, meats, canned foods that are low in acid.
Prevention - proper treatment of food, proper canning procedures.
3. Clostridium perfringins - Perfringins food poisoning - appears in 8 - 24 hr, heat labile
enterotoxin produced during sporulation either in food or in intestine of ingester. Need
106 organisms/gm food. Heat food --> low O2, --> slow cooling, bacterium grows -->
spore formation --> toxin production.
Prevention - quick cooling of food after cooking,
proper procedures.
4. Staphylococcus aureus - Staphylococcal food poisoning - appears in 2 - 6 hr,
enterotoxins; sources - meat, dairy products, poultry, custards, starchy foods. S. aureus
in human nose, --> hands --> food --> grows at room temperature.
Prevention - good hygiene.
Filtration (wine, beer, juices, soda, etc.), centrifugation (wine)
Lowers growth rate (fungi and other psychrophillic and psychrotrophic organisms will still grow)
Pasteurization (can affect flavor), sterilization (canning approximates this), dehydration (heating or freeze-drying - lyophilization-)
As in C. above - removes water and increases solute (mainly ionic) concentration, both reduce or stop growth of most microorganisms, but xerophillic or osmophilic organisms can still grow. Lower availability of water by adding sugar or salt, reduces growth of most organisms except for those mentioned above.
Sulfite (stops generation of Clostridium spores), but is allergenic to some
people
ethylene oxide (can be highly toxic)
sodium nitrite (heat --> nitrosamines --> carcinogens)
ethyl formate
nisin (antibacterial compound made by S.lactis) is used, but not in the USA, to inhibit the growth of Clostridium sp.
Uv light kills on surface only, won't penetrate, Cobalt 60 gamma radiation penetrates, kills by ionization of water inside microorganisms to peroxides, good for the preservation of seafoods, fruits, vegetables