Food Biochemistry and Food Processing

648 Part VI: Fermented Foods

Thus, starters such as Lactobacillus plantarumor
Pediococcus acidilactici,which grow well at those
temperatures, are typically used. In Europe, differ-
ent technologies may be found, depending on the
location and climate. There is a historical trend to-
wards short-processed, smoked sausages in cold and
humid countries, as in northern Europe, and long-
processed, dried sausages in warmer and drier coun-
tries, as in the Mediterranean area. In the case of
northern European (NES) countries, sausages are
fermented for about 3 days at intermediate tempera-
tures (25–30°C), followed by short ripening periods
(up to 3 weeks). These sausages are subjected to a
rapid pH drop and are usually smoked for a specific
flavor (Demeyer and Stanhke 2002). On the other
hand, Mediterranean sausages require longer pro-
cessing times. Fermentation takes place at milder
temperatures (18–24°C) for about 4 days, followed
by mild drying conditions for a longer time, usually
several weeks or months. L. sakeior L. curvatusare
the LAB most often used as starter cultures (Toldrá
et al. 2001). The time required for the fermentation
stage is a function of the temperature and the type of
microorganisms used as starters.
The technology is quite different in China and
other Asian countries. Sausages are first dried over
charcoal at 48°C and 65% relative humidity for 36
hours and then at 20°C and 75% relative humidity

for 3 days. Water activity rapidly drops below 0.80,

although pH remains about 5.9, which is a relatively

high value. Fermentation is relatively poor, and the

sour taste, which is considered undesirable, is re-

duced. Chinese raw sausage is consumed after heat-

ing (Leistner 1992).

MICROBIALMETABOLISM OF

CARBOHYDRATES

The added carbohydrate is converted, during the fer-

mentation, into lactic acid of either the D(-) or L()

configuration, or a mixture of both, depending on

the species of lactic acid bacteria used as starter. The

ratio between the L and D enantiomers depends on

the action of L and D lactate dehydrogenase, respec-

tively, and the presence of lactate racemase. The rate

of generation and the final amount of lactic acid

depend on the type of LAB species used as starter,

the type and content of carbohydrates, the fermenta-

tion temperature, and other processing parameters.

The accumulation of lactic acid produces a pH drop

more or less intense depending on its generation

rate. Some secondary products such as acetic acid,

acetoin, and others may be formed through hetero-

fermentative pathways (Demeyer and Stahnke 2002).

Acid pH favors protein coagulation, as pH ap-

proaches its isoelectric point, and thus also favors

water release. Acid pH also contributes to safety by

contributing to the inhibition of undesirable patho-

genic or spoilage bacteria. The pH drop favors initial

proteolysis and lipolysis by stimulating the activity

of muscle cathepsin D and lysosomal acid lipase,

both active at acid pH, but an excessive pH drop

does not favor later enzymatic reactions involved in

the generation of flavor compounds (Toldrá and

Verplaetse 1995).

PROCESSING STAGE 4: RIPENING

AND DRYING

Temperature, relative humidity, and air flow have to

be carefully controlled during fermentation and ripen-

ing to allow correct microbial growth and enzyme

action while maintaining adequate drying progress.

The air velocity is kept at around 0.1 m/s, which is

enough for a good homogenization of the environ-

ment. Ripening and drying are important for enzy-

matic reactions related to flavor development and

obtaining the required water loss and thus reduction

Figure 28.5.Example of a fermentation/drying cham-

ber with computer control of temperature, relative

humidity, and air flow rate. (By courtesy of Embutidos y

Conservas Tabanera, Segovia, Spain.)