3.4.1. Carboxylic acids
As the consequence of butyric acid fermentation, spoiled
cheeses contaminated with C. tyrobutyricum CECT 4011 and INIA
68 reached the maximum levels of butyric acid (Table 4), consistent
with the premature and noticeable symptoms of LBD. Unexpectedly,
levels of acetic acid in these spoiled cheeses were lower
than in control cheese, most probably consequence that acetic acid
is formed as an intermediate of butyric fermentation, and is
required in high concentrations to drive the butyryl coA-acetylcoA
transfer reaction involved in butyric acid synthesis (Yang &
Zhu, 2003). The high levels of propionic and, especially, pentanoic
acids were noteworthy in cheeses made with both
C. tyrobutyricum strains. A metabolic pathway of propionic acid
formation from lactic acid by C. tyrobutyricum was found by Thylin
(2000). The capability of some butyric-acid clostridia to produce 5,
6 and 8 carbon carboxylic acids is not widely known, as Tracy,
Jones, Fast, Indurthi, and Papoutsakis (2012) have recently
reviewed, and no data are available about C. tyrobutyricum. Some
Clostridium may produce pentanoic acid when grown on amino
acids, and Clostridium kluyveri also produces it when grown on
propanol and acetic acid, but its biosynthetic pathway has not
been reported (Tracy et al., 2012). Cheese made with C. beijerinckii
INIA 63 also showed higher concentrations of propionic, butyric