656 Part VI: Fermented Foods
2- and 3-methylbutanoic and 2-methylpropanoic
acids, and esters such as ethyl 2- and 3-methylbu-
tanoate (Stahnke 2002). Some of these branched-
chain aldehydes may also be formed through the
Strecker degradation, consisting in the reaction of
amino acids with diketones. However, conditions
found in sausages are far from those optimal for this
kind of reaction, which needs high temperature and
low water activity (Talon et al. 2002).
Methyl ketones may be formed either by -
oxidation of free fatty acids or decarboxylation of free
-keto acids. Other nonbranched aliphatic compounds
generated by lipid oxidation are alkanes, alkenes,
aldehydes, alcohols, and several furanic cycles.
A large number of volatile compounds are gener-
ated by chemical oxidation of the unsaturated fatty
acids. These volatile compounds are mainly generated
during ripening and further storage. Other low mo-
lecular weight volatile compounds are generated by
microorganisms from carbohydrate catabolism. The
most usual compounds are diacetyl, acetoin, butane-
diol, acetaldehyde, ethanol, and acetic propionic and
butyric acids. However, some of these compounds
may be derived from pyruvate originated through
other metabolic pathways than carbohydrate glycol-
ysis (Demeyer and Stahnke 2002, Demeyer and
Toldrá 2004). The flavor profile may have important
variations dependant on the type of microorganisms
used as starters (Berdagué et al. 1993).
GLOSSARY
ATP—Adenosine triphosphate.
Aminopeptidases—Exopeptidases that catalyze the
release of an amino acid from the amino terminus of
a peptide.
Backslopping—Traditional practice consisting in the
addition of previously fermented sausage with suc-
cessful sensory properties.
Bacteriocin—Peptides of low molecular mass pro-
duced by lactic acid bacteria with inhibitory action
against certain spoilage bacteria and foodborne
pathogens.
Catalase—Enzyme able to catalyze the decomposition
of hydrogen peroxide into molecular oxygen and
water.
Cathepsins—Enzymes located in lysosomes and able
to hydrolyze myofibrillar proteins to polypeptides.
Decarboxylases—Enzymes able to transform an amino
acid into an amine.
DFD—Pork meat with dark, firm, and dry characteris-
tics due to a lack of carbohydrate in muscle and thus
poor glycolysis and reduced latic acid generation.
These meats have pH values above 6.0 after 24 hours
postmortem and are typical of exhausted, stressed
pigs before slaughtering.
Glycolysis—Enzymatic breakdown of carbohydrates
with the formation of pyruvic acid and lactic acid
and the release of energy in the form of ATP.
Homofermentative—Bacteria generating a single end
product (lactic acid) from fermentation of carbohy-
drates.
Heterofermentative—Bacteria generating several end
products (lactic acid, acetoin, ethanol, CO 2 , etc.)
from fermentation of carbohydrates.
Lactate dehydrogenase—Enzyme that catalyzes the oxi-
dation of pyruvic acid to lactic acid.
Lactate racemase—Enzyme that catalyzes lactic acid
racemization reactions.
Lipolysis—Enzymatic breakdown of lipids with the
formation of free fatty acids.
Lysosomal acid lipase—Enzyme that catalyzes the re-
lease of fatty acids by hydrolysis of triacylglycerols
at positions 1 and 3.
Peroxide value—Term used to measure rancidity and
expressed as millimoles of peroxide taken up by
1000 g of fat.
Proteolysis—Enzymatic breakdown of proteins with
the formation of peptides and free amino acids.
PSE—Pork meat with pale, soft, and exudative charac-
teristics resulting from an accelerated glycolysis and
thus rapid lactic acid generation. The pH drop is very
fast, reaching values as low as 5.6 in just 1 hour
postmortem.
Water activity(aw)—It indicates the availability of
water in a food and is defined as the ratio of the equi-
librium water vapor pressure over the system to the
vapor pressure of pure water at the same temperature.REFERENCES
Baldini P, Cantoni E, Colla F, Diaferia C, Gabba L, Spotti
E, Marchelli R, Dossena A, Virgili R, Sforza S, Tenca P,
Mangia A, Jordano R, Lopez MC, Medina L,
Coudurier S, Oddou S, Solignat G. 2000. Dry sausages
ripening: Influence of thermohygrometric conditions on
microbiological, chemical and physico-chemical char-
acteristics. Food Research Int 33:161–170.
Berdagué JL, Monteil, P, Montel, MC, Talon R. 1993.
Effects of starter cultures on the formation of
flavour compounds in dry sausages. Meat Sci
35:275–287.