BLBS102-c31 BLBS102-Simpson March 21, 2012 14:0 Trim: 276mm X 219mm Printer Name: Yet to Come
31 Bakery and Cereal Products 605lactobacillus populations in sourdoughs may add to the reper-
toire of enzymes that will release amino acids from flour pro-
teins, including those from proline-rich gluten in wheat. Some
of the enzymes have been purified for further characterization
(Gobbetti et al. 1996), and they express interesting activity levels
at sourdough pH and temperatures.
The addition of exogenous microbial glucose oxidase, li-
pase, endoxylanase,α-amylase, or protease in the production
of sourdough with 11 different LAB cultures showed positive
effects on acidification rate and level for only three cultures, one
Leuconostoc citreum, oneLactococcus lactissubsp.lactisand
oneLb. hilgardii. Lactobacillus hilgardiiwith lipase, endoxy-
lanase orα-amylase showed increased production of acetic acid.
Lactobacillus hilgardiiinteracted with the different enzymes for
higher stability and softening of doughs (Di Cagno et al. 2003).
Recent work withLb. sanfranciscensis, Lb. brevis,andLb. al-
imentariusin model sourdough fermentations showed, by using
two-dimensional electrophoresis, that 37–42 polypeptides had
been hydrolyzed. The polypeptides varied over wide ranges of
pIs and molecular masses, and they originated from albumin,
globulin, and gliadin, but not from glutenin. Free amino acid
concentrations increased, in particular those of proline and glu-
tamic and aspartic acid. Proteolysis by the lactobacilli had a
positive effect on the softening of the dough. A toxic peptide
for celiac patients, A-gliadin fragment 31–43, was degraded by
enzymes from lactobacilli. The agglutination of human myel-
ogenous leukemia–derived cells (K562) by toxic peptic-tryptic
digest of gliadins was abolished by enzymes from lactobacilli
(Di Cagno et al. 2002).Volatile Compounds and Carbon DioxideBoth yeasts and LAB contribute to CO 2 production in sour-
dough products, but the importance of the two varies. In bread
production with only the (natural) sourdough microflora, the
input from LAB may even be decisive for leavening because
the counts and kinds of yeast may not be optimal for gas pro-
duction. Relatively low temperature (e.g., 25◦C) and low dough
yield (e.g., 135) would select for LAB activities and less yeast
metabolism. More complete volatile profiles were obtained at
higher temperatures (e.g., 30◦C) and with a more fluid dough.
Of course, increasing the leavening time may give substantially
richer volatile profiles (Gobbetti et al. 1995). If baker’s yeast,
S. cerevisiae, is added to optimize and speed up the production
process, the contribution from yeasts will dominate (Gobbetti
1998, Hammes and Ganzle 1998). ̈
Bread made with chemical acidification without fermentation
starter failed in sensory analysis. This indicates that fermentation
with yeasts and LAB is important for good flavor, although high
quality raw materials and proofing and baking are also decisive
factors. Flavor compounds distinguishing the different metabolic
contributions in sourdough are as follows (Gobbetti 1998):
Yeast fermentation (alcoholic): 2-methyl-1-propanol, 2,3-
methyl-1-butanol.
LAB homofermentative: diacetyl, other carbonyls.
LAB heterofermentative: ethyl acetate, other alcohols and
carbonyls.Antimicrobial Compounds from Sourdough LABThe primary antimicrobial compounds produced by sourdough
LAB are lactic and acetic acid, diacetyl, hydrogen peroxide, car-
bon dioxide, and ethanol, and among these, the two organic acids
continue to be the most important contributions for beneficial
effects in fermentations.
Researchers in the field, of course, also consider and test
possibilities that LAB may produce bacteriocins and other an-
timicrobials. Thus antifungal compounds fromLb. plantarum
21B have been identified, for example, phenyl lactic acid and
4-hydroxyphenyl lactic acid (Lavermicocca et al. 2000). Caproic
acid fromLb. sanfranciscensisalso has some antifungal activity
(Corsetti et al. 1998).
A real broad-spectrum antimicrobial fromLb. reuteriis
reuterin (β-hydroxypropionic aldehyde), which comes as a
monomer and a cyclic dimer (El-Ziney et al. 2000). Reuteri-
cyclin, which was isolated fromLb. reuteriLTH2584 after the
screening of 65 lactobacilli, is a tetramic acid derivative. Reuteri-
cyclin inhibited Gram-positive bacteria (e.g.,Lactobacillusspp.,
Bacillus subtilis, B. cereus, Enterococcus faecalis, Staphylococ-
cus aureus, andListeria innocua), and it was bactericidal towards
B. subtilis, S. aureus, andLb. sanfranciscensis. The ability to pro-
duce reutericyclin was stable in sourdough fermentations over
a period of several years. Reutericyclin produced in sourdough
was also active in the dough (G ̈anzle et al. 2000; Holtzel et al. ̈
2000; Ganzle and Vogel 2003). ̈
A few bacteriocins or bacteriocin-like compounds have also
been identified, isolated, and characterized (Messens and De
Vuyst 2002). Bavaricin A fromLb. sakeiMI401 was selected by
screening 335 LAB strains, including 58 positive strains (Larsen
et al. 1993). Bavaricin A (and Bavaricin MN fromLb. sakeiMN)
have theN-terminal consensus motif of bacteriocin class IIA in
common, comprise 41 and 42 amino acids, respectively, and have
interesting sequence homologies and similar hydrophobic re-
gions. Bavaricin A inhibitsListeriastrains and some other Gram-
positive bacteria but notBacillusorStaphylococcus(Larsen et al.
1993, Kaiser and Montville 1996). Plantaricin ST31 is produced
byLb. plantarumST; it contains 20 amino acids, and the activity
spectrum includes several Gram-positive bacteria but notListe-
ria(Todorov et al. 1999). A bacteriocin-like compound, BLIS
C57 from Lb.sanfranciscensisC57, was detected after screen-
ing 232Lactobacillusisolates, including 52 strains expressing
antimicrobial activity. BLIS C57 inhibits Gram-positive bacteria
including bacilli andListeriastrains (Corsetti et al. 1996).TRADITIONAL FERMENTED
CEREAL PRODUCTSOnly two cereals, wheat and rye, contain gluten and are thereby
suitable for the production of leavened bread, but many other
food cereals are grown in the world. On a global basis, a great
proportion of cereals are consumed as spontaneously fermented
products, in particular in Africa, Asia, and Latin America.
Most fermented cereals are dominated by lactic acid bacteria
(LAB), and the microflora associated with the grains, flour, or
any other ingredient, together with contamination from water,