T1 Lactic Acid Bacteria in Wine Flashcards
What is the definition of lactic acid bacteria?
gram positive bacteria, non-sporing, microaerophilic.
end product of carbohydrate metabolism is at least 50% lactate.
What are the main Genera of LAB found in wine?
Pediococcus, Oenococcus, Lactobacillus.
What is a Homolactic fermentation aka homofermentative?
what LAB fall into this category?
Glucose yields only lactic acid and 2 ATP.
Pediococcus species (and some lactobacillus that are not present in wine). Generally, homofermentative spp. are not found in wine.
What is a heterolactic fermentation?
What LAB have this type of metabolism?
Glucose is broken down into equimolar amounts of lactic acid, ethanol and CO2 with a gain of 1 ATP.
Oenococcus oeni and Lactobacillus spp. possess this mechanism.
what are the sources for the different LAB types found in wine?
- Grape berry 10E2 cells/g. Mainly lactobacillus
- Winery equipment
- starter cultures added. Usually Oenococcus oeni.
Describe the growth pattern of LAB during fermentation
- decline immediately during alcoholic fermentation as a result of competition from yeast.
- A large increase in cell density during MLF from 1E1 to 1E8.
- Decline after MLF in conservation, especially if SO2 is added.
What effect does pH have on the genus of bacteria conducting MLF?
-Below pH 3.5 O. oeni spp are predominate. above this other species such as lactobacillus may contribute.
What is the effect of wine composition on LAB growth?
- pH- decrease favours O. oeni.
- SO2- both bound and free affect growth as LAB metabolise acetaldehyde bound SO2. linked to pH.
- Sugars- as pH increases more sugar is utilised, leading to higher VA.
- Malate- MLF increases with lower pH.
- Diacetyl- more produces at lower pH
- Ethanol- effect varies with sp.
In O. oeni, hexose utilisation occurs more rapidly when there are higher levels of malic acid, accelerating the growth of these spp. The utilisation of pentose sugars such as fructose is unaffected by malic concentration.
What is the arginine deiminase pathway and how might it be linked to ethyl carbamate production?
- The pathway where some LAB can utilize amino As directly for energy. products are ATP +NH3 +CO2.
- carbamyl phosphate is an intermediate in this pathway and there is the possibility of it reacting with ethanol to form ethyl carbamate.
What are the micronutrient requirements of O. oeni in wine?
Vitamins- nicotinic acid, thiamine, biotin. pantothenic acid. For coenzyme complexes.
Metal Ions- Na+, K+, Mg2+, Mn2+. enzyme cofactors, reactions with oxygen free radicals.
Nucleic acid bases - Components of nucleic acid molecules. adenine guanine, xanthine, uracil.
Growth is stimulated under anaerobic conditions but CO2 being stimulatory or not is unclear.
Can fungicides affect LAB growth?
YES. esp dichlorofluanid, which can decrease malate conversion proportionally to its concentration.
What are the negative influences of yeast on LAB growth?
- Compete for nutrients during alcoholic fermentation
- Produce inhibitory substances. ethanol, SO2, fatty acids, antibacterials.
- cause co-sedimentation of LAB as yeast settles out.
What are the positive influences of yeast on LAB growth?
Autolysis of yeast releases nutrients such as vitamins and minerals, as endogenous hydrolytic enzymes breakdown yeast cellular components.
Has a stimulatory effect on LAB growth.
Is bacteriophage a concern for LAB growth? how could this possibly be minimised?
Occurrence is RARE
low pH, bentonite use and SO2 can reduce phage activity.
What are the winemaker’s impacts on LAB growth?
- Temperature- ferm temp, thermovinification (may deactivate essential nutrients and increase SO2 retention).
- Clarification- can remove indigenous LAB, suspended solids (that contain nutrients). explains why MLF occurs more readily in red wine.
- Additions- SO2, acid,
