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Flashcards in microbes as food Deck (43):

when did we start eating bacteria

cheese in 5500 BCE
wine in 4100 BCE


we have been using microbes for food preservation since the ______



edible fungi

-mushrooms: fungal fruiting bodies are a sources of proteins and minerals:
-underground truffles
-agaricus bisporus:button and portobellos


edible algae

-red algae porphyra: nori (sushi wrap)
-brown algae macrocystis: (Alginate, a thickener)


edible bacteria

nucleic acid often too concentrated for food
exception currently used:the cyanobacterium spirulina is a used as a single celled protein source and nutritional supplement


why ferment foods

virtually all human cultures have developed varieties of fermented foods: food products modified biochemically by microbial growth
purposes are :
-to preserve food: by limiting growth of spoilage organisms and also many pathogens
-to improve digestibility: for example by breaking down lactose
-to add nutrients (such as vitamins) and flavour molecules (such as esters and sulfur compounds)


traditional fermented foods usually depend on _________________.

indigenous flora (found naturally in the food) or starter cultures (from a previous fermentation)


major classes of fermentation reactions include:

-homolactic acid fermentation (yogurt, cheese)
-propionic acid fermentation (swiss cheese)
-heterolactic acid fermentation (kefir)
-ethanolic fermentation (wine, beer)
-alkaline fermentation (brie cheese)


acidic fermentation of dairy products

cheese production
-milk fermentation begins by lactic acid fermentation with lactobacillus and streptococcus
-this is followed by rennet proteolysis (by chymosin and pepsin), rendering casein insoluble
-the cleaved peptides coagulate to form a semisolid curd
-separated from the liquid portion called whey


cheese production

involves a standard series of steps:
1. milk is filtered and subjected to pasteurization
2. fermenting microbes are added as a starter culture of different mixtures of bacteria for different cheeses
3.drop in pH and/or added rennet (stomach proteases) help denature the milk protein called casein, which coagulates and precipitates out of solution (curds)
4. the solid curd is then cut
5. curd is then lightly heat-treated
6.the pressed curd is shaped into a mold
7.the cheese is then ripened (or aged)


acidic fermentations: cabbage, cucumbers, olives, fermented meats

-pickling: fermentation in brine (high salt)
the high salt selects for specific bacteria (gram positive), starter cultures can be used or not. room temperature or cold fermentation also selects against some pathogens
-pediococcus, streptococcus, lactobacilus, leuconostoc depending on the food material and the process


fermented cabbage

include sauerkraut , kimchi


fermented meats

montreal smoked meat, mettwurst, genoa salami


ethanolic fermentation: bread

initially bread was allowed to rise using a natural mixture of wild yeasts and heterolactic lactic acid bacteria (sourdough)
-more recent develpment, the use of pure saccharomyces cerevisiae: baker's yeast
pyruvate->ethanol + CO2
-CO2 causes bread to rise


ethanolic fermentation: beer

saccharomyces cerevisiae: also brewers yeast
beer derived from alcoholic fermentation of grain
-barley grains are germinated, allowing enzymes to break down the starch to maltose for yeast fermentation. so maltose is the primary sugar fermented
-secondary products, such as long-chain alcohols and esters, generate some of the special flavours of beer


ethanolic fermentation

saccharomyces cerevisiae: brewers yeast
-wine derives from alcoholic fermentation of fruit, usually grapes
-1. the grapes are crushed to release juices
*for white whine skin is removed
2. the yeast ferment sucrose, fructose and glucose to ethanol
-red whines and some white undergo malolactic fermentation by oenococcus oeni bacteria
-converts malate to lactate plus CO2 reducing the acidity


making chocolate still starts with a complex series of natural fermentations

-this fermentation is done in piles on banana leaves. the fermentation is required prior to roasting of the beans for flavour development
-to standardize the process scientists are still trying to develop a defined starter culture in order to perform the fermentation in a controlled way.
-because the fermentation involves a succession of populations, it makes the development of a starter culture more difficult


food spoilage

-refers to microbial changes that render a product obviously unfit or unpalatable for consumption
*acids=sour tastes
*oxidation of fats =rancidity
*decomposition of proteins =putrefaction
*alkalinity=bitter taste


Food contamination or food poisoning

refers to the presence of pathogens


food spoilage of dairy products

can be soured by excessive fermentation or made bitter by bacterial proteolysis


meat and poultry food spoilage

are putrefied by decarboxylating bacteria, which produces amines with noxious odors


seafoods spoil rapidly because their...

unsaturated fatty acids rapidly oxidize (become rancid)
-psychotrophic bacteria reduce TMAO (Trimethylamineoxide) to the fishy smelling trimethylamine


plant foods spoil by...

excess growth of bacteria and molds, which can cause them to wilt, brown and loose texture


pathogens contaminate food

-food borne pathogens typically arise from a range of sorces
*listeria monocytogenes, a psychotrophic bacterium that invades the cells of the intestinal epithelium
-causes listeriosis, enhanced b/c it can grow under refrigerated conditions


physical means of preservation

-dehydration and lyophilization (freeze-drying)
-controlled or modified atmosphere
-ionizing radiation
-refrigeration and freezing


chemical means of food preservation

-organic acids
*benzoic acid, sorbic acid, and propionic acid
*fatty acid esters and benzoic acid esters
-other organic compounds
*cinnamon contains the benzene derivative eugenol (a potent antimicrobial agent)
-mustard contains sinalbin which can release isothiocyanate, which is toxic to bacteria
-inorganic compounds
*salts such as phosphates, nitrates, and sulfites


industrial microbiology

-the commercial exploitation of microbes
-includes food production and preservation
-also the production of :
* vaccines, pharmaceuticals, and therapeutics
*industrial solvents, biodegradable plastics
*genetically modified plant and animal cells



-2.4 million canadians have type 1 or type 2 diabetes
-6.8% of population (1/11 Canadians over 20)



protein hormone produces by the beta-islet cells (pancreas)
-metabolism of carbohydrates into glucose


type 1

5-10% of cases
-beta islet cells are destroyed by immune system


type 2

insulin receptors on cells desensitized to insulin


insulin was harvested from ...

dog pancreas first
-later lilly began large scale commercial production
*ground up bovine and swine pancreas


animal insulin ahs limitations

although similar to human insulin, bovine and porcine insulin are not the same
-many patients from antibodies against the foreign protein
-causes inflammation and allergic responses
-fear of long-term affects of using foreign protein stimulated for new ways of making HUMAN insulin in large volumes
solution: insert human insulin gene into E.coli
produce human insulin -recombinant DNA technology


structure of insulin

insulin-protein hormone
51 amino acids
two chains
-A chain- 21 a.a
-B chain-30 a.a
held together by disulfide bridges


manufacturaing human insulin

synthesis of DNA containing the nucleotide sequences of the A and B polypeptide chains of insulin
-DNA containing the A chain gene and B chain gene individually cloned into a plasmid vector
-the recombinant plasmids DNA are then introduced into E. coli
-bacteria containing the plasmid grown as large scale cultures in fermenters
-become insulin factories that produce large amounts of a chain and b chain polypeptide
-extraction and purification of A and b chains
-A and B chains connected by disulfide bridges results in pure synthetic human insulin


radioactive bacteria reduce the spread of pancreatic cancer

-pancreatic cancer
*highly aggressive
*poor survival-


listeria monocytogenes

a promising alternative
-weakened lab form (=attenuated) of L.m can infect cancer cells without healthy cells
-normal tissues -immune system clears bacteria
-immune suppression in tumor region-bacteria enter tissue and kill cells
-used L.m to deliver anticancer radionnuclides (beta-particle radiation) targets and kills cancer cells
-anti-listeria antibody linked to 188Re used to tag bacteria with deadly radioactivity called RL for treatment


listeria multiplies in

metastases, less abundantly in primary tumors but not in normal tissues


largest number of bacteria

metastasis tissues less in tumor tissue and very little in healthy spleen
L.m is multiplying in cancerous cells


treatments with 188Re-listeria RL markedly reduced metastases in mice

4 treatment groups
-panel A: group receiving RL showed best results. 90% less tumors and 64% reduction in primary tumor weight
-panel B: very little cancerous tissue remaining in liver (metastatic)



-attenuated lm infected pancreatic metastatic cancer cells
-when injected into tumor bearing mice, bacteria selectively delivered to metastases where it spread cell to cell without being eliminated by the immune system
-poorly delivered to healthy tissue
-neither L.m nor radioactivity detected in normal or tumor tissue 1 week after treatment


why does it affect metastatic tissue most?`

-radiation-induces irreparable DNA damage in fast growing cells (=metastatic)
-tumor cell division is much less than metastases
-normal tissue is generally not dividing


summary of findings

live attenuated bacteria can deliver radioactivity to pancreatic cancer metastases without severe side effects