Biomedical Engineering Reference
In-Depth Information
Gliadins ( ),
Glutenins disulfide bonds:
, glutenins LMW (Low Molecular Weight),
, glutenins y-HMW (High Molecular Weight),
, glutenins x-HMW (High Molecular Weight),
, hydrolysis products,
, peptides
Primary proteolysis by cereal proteinases
Microbial reduction of disulfide bonds
Secondary proteolysis by
microbial enzymes, amino acids
catabolism
Addition of enzymes
(fungal or malt-derived)
- Peptides hydrolised to free amino acids
- Production of volatile compounds
responsable for the aroma
- Comple degradation of proteins to small
peptides and free amino acids
Fig. 7.7
Proteolytic scheme that occurs during sourdough fermentation. Figure shows substrates,
enzymes and the activities of primary and secondary proteolysis (Adapted from [
50
] )
elevated specificity towards dipeptides containing hydrophobic amino acids; a
75-kDa general aminopeptidase (PepN); and an X-prolyl-dipeptidyl aminopepti-
dase (PepX), which exclusively hydrolyzes substrates with the N-terminal
sequence X-Pro [
51,
54
]. The capacity to hydrolyze oligopeptides adjacent to
proline residues was shown in selected sourdough lactobacilli. However, the pro-
teolytic system of lactic acid bacteria does not cleave peptides with the sequence
motif XPP [
55
]. Overall, sourdough fermentation increases amino acid concentra-
tions compared to doughs that are chemically acidified [
48,
52
] . Proteolysis dur-
ing sourdough fermentation proceeds in two stages (Fig.
7.7
): (1) primary
proteolysis that releases oligopeptides, and is mainly operated by cereal endoge-
nous proteinases that are activated at low pH and by accumulation of thiols; and
(2) secondary proteolysis that releases free amino acids and small-sized peptides,
and is exclusively operated through peptidase activity of lactic acid bacteria.
