lecture 2 fermentation

I: Microbial enzymes* acting on substrate 

Proteolysis: digestibility, flavour and taste 
 Lipolysis: flavour 
 Amylolysis: digestibility, acid formation 
 Pectinolysis: digestibility 
 Cellulolysis: digestibility

2. Formation of metabolites  

2. Formation of metabolites  

Flavour compounds 
• acids, alcohol, esters, acetoin 
 Colouring substances 
• carotenoids 
 Vitamins 
• B-vitamins 
• yeast extract 
 Antimicrobial compounds 
• acids, alcohols, carbon dioxide 
• hydrogen peroxide 
• reuterin, bacteriocins, killer-toxins 

what are the main types of fermentation

Describe Lactic fermentation

1. Lactic ( Yoghurt, Cheese, Vegetables, Sausages) 

Efficient conversion of carbohydrates into lactic acid. Microbes have transporters, simple sugars are converted into lactic acid and other organic acids. It is FAST and energetically inefficient

what are types of lactic acid bacteria

1. Homofermentative: mainly 1 product  
-Homolactic fermentation: only lactate made 
- Mixed acid fermentation: many organic acids  
2. Heterofermentative: several main products

Heterofermentative

2.Heterofermentative : several main products made, co2 made  

- ethanol ( no 02) 

- acetate (02 present) 

- 1 atp (no 02) 

- 2 atp (02) 

Homofermentative

1. Homofermentative: mainly 1 product  
-Homolactic fermentation: only lactate made 
- Mixed acid fermentation: many organic acids  

 

 

Can switch from homolactic to mixed acid fermentation 
When?  conditions with limited substrate and during slow growth

why? more energy efficient

describe em pathway alcoholic fermentation

Embden-Meyerhof pathway is the main metabolic route to provide 
pyruvate for ethanol production 

whats the difference between EM pathway and Ehrlich pathway

explian the Ethanol tolerance importance for activity in ripening phase

As ethanol concentration rises during fermentation (especially in wine), many microorganisms stop growing — but the yeast must remain active to finish converting sugars to alcohol and to survive the final stages. 
So, yeast strain’s ethanol tolerance is crucial for successful wine fermentation and aging. 

Many yeast species have high ethanol tolerance

what are yeast cells efficient producers of

Yeast cells are efficient producers of ethanol and CO

what does amino acid degradation lead to

Amino acid degradation leads to production of higher alcohols (fusel 
alcohols) and thus aroma!