Lecture 23: Food Microbiology
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- Name five intrinsic factors that relates to food spoilage
-
1) Food composition
2) pH
3) water availability
4) physical structure
5) presence of natural antimicrobial substances - Name 3 types of food composition
-
1) High protein food spoilage
2) High fat food spoilage
3) High carbohydrate food spoilage - If a high protein food spoils, and proteins break down, the proceess is called _____
- proteolysis/putrefaction
- If a high protein food spoils, and proteins break down, the proceess is called proteolysis/putrefaction. Smelly _____ such as _____ are released
-
amines
cadaverine - High fat food spoilage undergoes ______
- lipid hydrolysis
- High fat food spoilage undergoes lipid hydrolysis. ______ fatty acids
- rancid
- High carbohydrate food spoilage is not _____
- smelly
- High carbohydrate food spoilage is not smelly. First signs of food spoilage is usually ______
- fungi
- High carbohydrate food spoilage is not smelly. First signs usually fungi. Fruits/veggies get soft rot because of _______ which produces hydrolytic enzymes
- Erwinia carotovora
- High carbohydrate food spoilage is not smelly. First signs usually fungi. Fruits/veggies get soft rot because of Erwinia carotovora which produces _____
- hydrolytic enzymes
- Low pH favors _____
- yeast or molds (fungi)
- Higher pH favors ______
- bacteria
- Meats tend to be ______ (favoring bacteria)
- alkaline
- Higher pH favors bacteria. Meats tend to be alkaline (favoring bacteria). Meats undergo _________, which gives off a smell
- putrefaction/proteolysis
- Drying of water ________ spoilage (no water=no life)
- controls/eliminates
- dehydration of microorganisms is achieved by _____
- hypertonic solutions (salt or sugar)
- Drying controls/eliminates spoilage (no water=no life). Dehydration of microorganisms achieved by hypertonic solutions (salt or sugar). Exceptions: _________ organisms (yeast) can tolerate high salt/sugar
- osmophilic
- ______ organisms (molds) prefer low water availability
- xerophilic
- osmophilic organisms
- yeast- can tolerate high salt/sugar
- xerophilic organisms
- molds- prefer low water availability
- name 3 prepared meats that spoil easily
- hamburger, sausage, cold cuts
- prepared meats have an increased surface area and altered ______, resulting in rapid spoilage. Contaminants distributed more evenly.
- cell structure
- Steak is safer than ___
-
hamburger
A raw steak is not likely to spoil quickly because microoranisms cannot penetrate the meat easily. However, an uncooked hamburger can deteriorate rapidly, since microogranisms exist within the loosely packed ground meat as well as on the surface. - Give examples of antimicrobial foods
-
1) Cinnamon, mustard, oregano
2) Garlic
3) egg whites
4) cloves
5) unfermented green teas - Cinnamon, mustard, oregano contain antimicrobial _____ and ____
- aldehydes and phenols
- Garlic contains ____
- allicin
- egg whites contain ______ and has a pH of ____
-
lysozyme
9.0 - While Egg whites contain lysozyme and is an antimicrobial food, egg yolks tend to get contaminated easily. ____ species cause black rot in eggs as hydrogen sulfide gas (H2S) accumulates
- Proteus
- Proteus species cause _____in eggs as hydrogen sulfide gas accumulates
- black rot
- Proteus species cause black rot in eggs as _________ gas accumulates
- hydrogen sulfide
- Green rot is caused by ____
- pseudomonas
- red rot is caused by ____
- serratia marcescens
- Cloves contain _____
- eugenol
- Unfermented green teas contain _____
- polyphenols
- Polyphenols contain both ____ and possibly ______ properties
-
antimicrobial
anticancer - Polyphenols get rid of _____
- oxygen free radicals
- Polyphenols get rid of oxygen free radicals and cause ____
- RNA damage
- There are 4 major classes of polyphenols called _____
- Catechins
- Green tea is unfermented. It has ______ properties that are preserved after heating
-
antioxidant
Oolong tea is semi-fermented
Black tea is fermented - What are 3 extrinsic factors related to food spoilage?
-
1) temperature
2) humidity
3) atmosphere - _____ temperatures reduce microbial growth/prolong storage
- lower
- Some microorganisms may survive storage and start growing at _____ temperature
- room
- _______ bacteria can tolerate low temperature. (S. aureus)
- psychrotrophic
- humidity. Lower ____ tends to prolong storage
- moisture
- Atmosphere. What allows for oxygen diffusion?
- shrink-wrap
- Oxygen allows for increased growth of microorganisms such as _____ on the surface
- Pseudomonas (obligate aerobe)
- _____ inhibits bacteria (mostly G-) and reduces spoilage
- Carbon dioxide
- Milk is a soln of proteins, fats, and carbohydrates that is an ideal environment for spoilage organisms. What is the first step to milk spoilage?
- Acid production by Lactococcus lactis
- Acid production by Lactococcus lactis. Growth of acid-tolerant ______ (more acid produced), causing milk curdles to form
- lactobacillus
- Acid production by lactococcus lactis. Growth of acid-tolerant Lactobacillus (more acid produced). Yeasts/molds dominate at lower pH, degrade ____ and ____
- lactic acid and raise pH
- Acid production by Lactococcus lactis. Growth of acid-tolerant Lactobacillus (more acid produced). Yeasts/molds dominate at lower pH, degrate lactic acid, raise pH. At higher pH, protein-digesting bacteria become active, resulting in a ______ flavor and
-
bitter
putrid - What are four types of foods that spoil quickly?
-
1) moist foods
2) neutral foods (fish, bananna)
3) unrefrigerated
4) ground or sliced meat - What are 4 types of foods that resist spoilage?
-
1) Dry foods
2) acidic foods
3) refrigerated
4) whole meat - THe FDA acronym, GRAS, stands for ____
- generally recognized as safe
- CHemical Agents of Food Preservation. Sodium nitrite is good for what two reasons?
-
1) inhibits growth of Clostridium botulinum and increases meat safety
2) Nitrite decomposes to nitric acid. Nitric acid reacts with heme pigments to keep meat red to make meat more appealing to consumers - What is bad about sodium nitrite?
- Nitrites react with amines to form carcinogenic nitrosamines (can cause cancer)
- Give an example of a naturally produced antibiotic
- nisin
- Nisin is a naturally produced antibiotic made by ________, and it is nontoxic
- Lactococcus lactis
- Nisin inhbits _____ and targets _______ bacteria
-
peptidoglycan synthesis
gram-positive bacteria - Nisin inhibits peptidoglycan synthesis and targets gram-positive bacteria such as: ___ and ___
- enterococcus faecalis and Clostridium botulinum
- Vinegar is produced when yeast ferments _____to ____ until the concentration is about 10 to 20%
-
fruit juice
alcohol - Vinegar is produced when yeast ferments fruit juice to alcohol until the concentration is about 10 to 20%. ______ converts alcohol to _______ to ______
-
Acetobacter aceti
acetylaldehyde
acetic acid - Cheese production. Starter culture of _______ or ____, _______ or _____
- Lactococcus lactis or cremoris, lactobacillus or Streptococcus
- Cheese production. Starter culture of Lactococcus lactis or cremoris, lactobacillus or Streptococcus. Bacteria ferment lactose, make acid, causing ____ to form
- coagulating milk proteins (curds)
- Starter culture of Lactococcus lactis or cremoris, lactobacillus or Streptococcus. Bacteria ferment lactose, make acid- coagulating milk proteins. ____ is also added to help with curdling
- rennin
- Starter culture of Lactococcus lactis or cremoris, lactobacillus or Streptococcus. Bacteria ferment lactose, make acid- coagulating milk proteins. Rennin is also added to help with curdling. _____ is separated from curd (coagulated protein), curds are th
-
whey (liquid)
pressed and salted - Starter culture of Lactococcus lactis or cremoris, lactobacillus or Streptococcus. Bacteria ferment lactose, make acid- coagulating milk proteins. Rennin is also added to help with curdling. Whey (liquid) separated from curd (Coagulated protein), curds p
- ripened
- Cheese has over 2000 varieties from lactic acid fermentation of milk, coagulation of milk proteins, formation of curd. Swiss cheese is made by what type of bacteria?
-
Propionibacterium.
Propionibacterium produce organic compounds and carbon dioxide, which makes holes - Gorgonzola, Stilton, and Roquefort cheese is made by what?
- Penicillium roqueforti
- Soy Sauce is produced from roasted soybeans and wheat inoculated with what fungus for 3 days?
- Aspergillus oryzae
- Soy sauce is produced from roasted soybeans/wheat innoculated with Aspergillus oryzae for 3 days. The fungus-covered product, called ______, then is added to a solution of salt and microorganisms, and aged for about a year.
- Koji
- Soy sauce is produced from roasted soybeans/wheat innoculated with Aspergillus oryzae for 3 days. The fungus-covered product, called koji, then is added to a solution of salt and microorganisms, and aged for about a year. During this time, lactobacilli p
- pressed
- Name four types of beer
-
1) ales
2) stouts
3) lagers
4) pilseners - To make ales and stouts, use ____
- Saccharomyces cerevisiae
- To make ales and stouts, use saccharomyces cerevisiae, sometimes called ____
- top yeast
- Lagers and pilseners use ____
- Saccharomyces carlsbergensis
- Lagers and pilseners use Saccharomyces carlsbergensis, sometimes called ____
- bottom yeast
- Industrial Fermentation. _____ is held in malting tanks
- barley
- industrial fermentation. Barley is held in ______
- malting tanks
- industrial fermentation. Barley is held in malting tanks. Naturally occurring enzymes digest ______ to ______
- starch to malt sugar (maltose)
- industrial fermentation. Barley is held in malting tanks. Naturally occurring enzymes digest starch to malt sugar (maltose). Malt is mashed in ____
- mashing tank
- industrial fermentation. Barley is held in malting tanks. Naturally occurring enzymes digest starch to malt sugar (maltose). Malt is mashed in mashing tank. ____ or ____ is removed
- liquid or wort
- industrial fermentation. Barley is held in malting tanks. Naturally occurring enzymes digest starch to malt sugar (maltose). Malt is mashed in mashing tank. Liquid, or wort, is removed. ____ are added to wort. Hops gives flavor, color and stability.
- Hops
- industrial fermentation. Barley is held in malting tanks. Naturally occurring enzymes digest starch to malt sugar (maltose). Malt is mashed in mashing tank. Liquid, or wort, is removed. Hops are added to wort. Hops gives flavor, color and stability. Then
- yeast
- What is the purpose of the root beer lab?
- to produce root beer by fermentation of sugar
- What are the ingredients in root beer?
-
sugar (white and brown)
root beer extract
water
champagne yeast - A protozoan is also called the "first animal." It is ____ and ____
- unicellular and eukaryotic
- Protozoans are found in ____
- moist habitats
- Most protozoans are _____ and do not have ____
-
heterotrophic
chlorophyll