LAB Flashcards
Lactic acid is also known as:
milk acid
2-hydroxypropanoic acid
What organism makes lactic acid, and what substrate is used?
lactic acid bacteria
breaks down SIMPLE CARBS: glucose, sucrose, galactose
Where can lactic acid be found in the human body? (2)
produced by LAB in mouth (causes cavities)
L-lactate produced by muscles during exertion
True/false: lactic acid is the most common organic acid produced in fermentations
true
What sugars can be used for lactic acid fermentations?
almost any C5 or C6 sugar (sucrose, glucose, raw sugar, etc)
The 2 classes of LAB:
- homofermentative
2. heterofermentative
What is the main difference between the 2 classes of LAB?
homofermentative makes 2 MOLES of lactic acid per mole glucose
heterofermentative makes 1 MOLE lactic acid + CO2 + byproduct (ethanol, acetic acid, etc)
Describe the cell morphology and characteristic of LAB:
GRAM POSTIVE
Rods or cocci
non-spore forming
ferment simple sugars into lactic acid
name 5 common LAB types:
Enterococcus Leuconostoc Lactobacillus Lactococcus Streptococcus
Why are LAB so useful in the food industry? (3)
fermentation process
prevent pathogen/spoilage by outcompeting other microbes (and acidity)
Use as probiotic
True/False: LAB are very good at surviving in low nutrient environments.
FALSE: adapted to nutrient/sugar rich environments; limited biosynthetic activity (cannot make many compounds)
True/False: LAB are acid tolerant
True
What is the streptococcus species used in food, and for what purpose?
S. thermophilus
used in yogurt; or in co-culture for cheese
Is enterococcus useful for food production?
No; not commonly used, and some species PATHOGENIC
what species of lactococcus are used by the food industry?
L. lactis
used in dairy technology
What are the tetrad forming species of LAB? What is the significance of each in food products?
Aerococcus (greening/off color of meat): BAD
Pediococcus: (beer spoilage): BAD; (silage or sausage inoculant): GOOD
Tetragenococcus: (used in soy sauce): GOOD
What is a particular feature of Tetragenococcus?
very salt tolerant (up to 18%)
What are the coccoid LAB? What are their associated uses?
Leuconostoc: spontaneous veg. fermentations
Oenococcus
Weisella: used in silage; found in meat
What is the largest genus in LAB? What is their defining feature?
lactobacillus
most acid tolerant (final survivors of fermentation)
What are some LAB species that thrive in many habitats?
brevis, casei, plantarum
What are the 3 groups of lactobacillus?
Group 1: obligately homofermentative
Group 2: facultative heterofermentative
Group 3: obligately heterofermentative
What groups of Lactobacillus will produce CO2?
Groups 2 and 3
True/False: a ferment done with Group 1 lactobacillus will become acidic at a faster rate than using Group 3
True
What is the effect of changing the growing conditions for Lactobacillus?
different chemical environment (O2, diff. substrate) -> change metabolism to produce different products -> affect flavor and other qualities