Biomedical Engineering Reference
In-Depth Information
Thiamine content has been reported to increase especially in elongated yeast
fermentation [
8,
66
], but also to decrease in the actual baking process [
67
] . Prolonged
yeast or sourdough fermentation maintained the original content of vitamin B
1
in
whole wheat baking in contradiction to a short process, which reduced its amount.
Whole wheat breadmaking with yeast (from kneading to final bread), with long fer-
mentations time resulted in a 30% enrichment in riboflavin. The fermentation step
can thus improve the retention of vitamins in the baking process. The use of both
yeast and sourdough did not have a synergistic effect on B-vitamin levels [
8
] .
Production of the B
2
vitamin with strain selection for enrichment of pasta and bread
has also been recently demonstrated by Capozzi et al. [
68
] . The applied approaches
resulted in a considerable increase of vitamin B
2
content (about two- and threefold
increases in pasta and bread, respectively), thus representing a convenient and
efficient food-grade biotechnological application for the production of vitamin B
2
-
enriched bread and pasta. This methodology may be extended to a wide range of
cereal-based foods, feed, and beverages. However, sourdough or yeast fermentation
do not automatically increase the levels of all vitamins; decreased levels have been
observed for vitamin E during sourdough preparation and dough making [
69
] , and
for levels of tocopherol and tocotrienol in rye sourdough baking [
60
] .
9.3.2
Minerals
Whole grains are a good source of minerals, including calcium, potassium, magne-
sium, iron, zinc and phosphorus. As the bran fraction of the grain also contains
phytate (myo-inositol hexaphosphate), the bioavailability of minerals may be lim-
ited. This has a large impact especially in developing countries, where iron deficiency
is a common nutritional disorder, especially among children and women. Grains
contain 3-22-mg phytic acid per gram [
70
], concentrated in the aleurone layers.
Phytate has strong chelating capacity and forms insoluble complexes with dietary
cations, thus impairing mineral absorption. Phytases are able to dephosphorylate
phytate, forming free inorganic phosphate and inositol phosphate esters, which have
less capacity to influence mineral solubility and bioavailability. It has been shown
that iron was more bioavailable in mice when fed in sourdough bread vs. straight
dough bread [
71
], and absorption of zinc, magnesium, and iron was higher in rats
when bread was baked using sourdough [
72
] .
Grain endogenous phytase activity is accelerated in the acidic environment pro-
duced in sourdough fermentation. Lactic acid bacteria and yeasts may also possess
some phytase activity. The pH optimum of wheat phytase is pH 5.0, and that of
yeast is somewhat lower, i.e. pH 3.5 [
73
]. A moderate decrease of pH to 5.5 in fer-
mentation reduces phytate content of whole wheat flour by 70% due to enhanced
action of endogenous phytase present in the flour [
74
]. It was suggested that the
endogenous flour phytase activity was much more influential than the microbial
phytase of the sourdough. No major phytase activity was found in screening of 50
lactic acid bacteria strains isolated from sourdoughs [
75
], even though in studies
