1. Flavor-forming processes - enzymatic
OBJECTIVES
1. Formation of aroma compounds via enzymatic mechanism;
2. Transformation of carbohydrates, lipids and amino acids;
3. Transformation of other compounds.

2. Flavor-forming processes - enzymatic2
1. Carbohydrates
Lactic acid fermentation
Homofermentative LAB – used in dairy starter culture applications
(Lactobacillus delbruckii subspecies bulgaricus, Lb. acidophilus; Streptococcus
salivarius subsp. thermophilus, Lb. helveticus).
Heterofermentative LAB – ferment glucose with lactic acid, ethanol/acetic acid
and carbon dioxide as by products; used for some fermented milk products
(Lactobacillus brevis, Lb. fermentum, Lb. plantarum, Lb. casei).

3. Flavor-forming processes - enzymatic3
1. Carbohydrates – pyruvic acid and pyruvayes

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1. Carbohydrates – pyruvic acid

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diacetyl
Pyruvic acid – important
intermediate in carbo-
hydrate degradation
acetoin

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malty
flavor

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2. Amino acids and proteins
Formation of lactones – from glutamic acid

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2. Amino acids and proteins
Oxidative deamination - leucine
Found in banana oil
(could be obtained synthetically)
other use – obtaining of esters

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Skatole degradation - formation of o-amino acetophenone (aroma defect in tortillas, taco)
2. Amino acids and proteins
Skatole (o-cresol) formation
(Emmental cheese, tortillas, taco)

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3. Lipids
Formation of influential volatile flavor compounds from milk fat
Obtained through enzymatic cleavage of acylglycerols

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3. Lipids
Esters biochemical synthesis from fatty acids

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3. Lipids – occurrence and smell of lactones

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4. Other aroma substances – sulfur-containing
I – methional
II – methionol
III – 3-(methylthio)
propyl acetate
found in wines

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4. Other aroma substances –
sulfur-containing
Some thiazoles in
foods

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4. Other aroma substances – tertiary thiols

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4. Other aroma substances
allicin
alliin
alliinase
allyl-methyl sulfide
Propanethial S-oxide

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4. Other aroma substances - pyrazines
Formation of pyrazines – by Pseudomonas perolans and Pseudomonas taetrolens
As byproducts (off flavor in eggs, milk, fishes)

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4. Other aroma substances
dimethyl disulfide (in beers) – precursor is methionine
Amines formation (precursors – amino acids)