Handbook of Meat Processing

190 Chapter 9

studied in detail and has been attributed
partly to the presence of genes involved in
the energetic catabolism of nucleosides, such
as adenosine and inosine that are abundant in
meat (Chaillou et al. 2005 ), and partly to its
mode of arginine catabolism (Champomier -
Verges et al. 1999 ; Zuriga et al. 2002 ;
Chaillou et al. 2005 ). Other species, such as
the ones mentioned in Table 9.1 , are also
likely to be sporadically present.

Biochemical Changes

during Ripening

The main biochemical changes that occur
during ripening, affecting appearance, organ-
oleptic quality, and safety of fermented
sausages, are shown in Figure 9.1. These
biochemical reactions lead to the formation
of a variety of metabolic end products, which
are summarized in Table 9.2.
Carbohydrates serve as carbon and energy
sources for the native microbiota or the added
starter culture. Microbial fermentation results
in the production of lactic acid, the confi gura-
tion of which depends upon the dominant
species. The lactic acid results in a decrease
of the pH value that has a manifold effect on
the quality of the product. This pH drop,

apart from contributing to the inhibition of

spoilage and pathogenic microorganisms,

favors water release through protein coagula-

tion, as well as the hydrolytic action of both

cathepsin D and lysosomal acid lipase.

Addition of heterofermentative lactic acid

bacteria results in the production of addi-

tional compounds, such as acetoin and diace-

tyl. On the other hand, addition of sugars,

apart from being the decisive parameter on

the fi nal pH, means that their residual amount

will inevitably contribute to taste develop-

ment, given that they are present in levels

above their sensory threshold.

As a general rule, proteolysis, at least at

its early stages, is primarily a function of the

muscle proteinases (Luecke 2000 ), especially

cathepsin D. Complete hydrolysis into free

amino acids takes place by bacterial pepti-

dases, along with endogenous ones (Sanz

et al. 1999a ). The proteolytic capacity of

several lactic acid bacteria and staphylococci

strains isolated from fermented meat prod-

ucts has been investigated (Fadda et al. 1998,

1999a, b ; Sanz et al. 1999a, b ; Mauriello et

al. 2002 ; Drosinos et al. 2007 ), and a rather

rare proteolytic capacity of lactic acid bacte-

ria has been stated, as well as a compara-

tively common one of staphylococci. In both

microbial metabolism

glycogen

glucose

glycogenolysis

organic acids

ATP

hydrolysis

ribose

proteins

Muscle proteases

peptides amino acids

Flavor volatiles

biogenic amines

triglycerides

phospholipids

long chain free

fatty acids

Tissue lipases

oxidation

Figure 9.1. Main biochemical changes occurring during sausage fermentation.