Food Biochemistry and Food Processing (2 edition)

BLBS102-c31 BLBS102-Simpson March 21, 2012 14:0 Trim: 276mm X 219mm Printer Name: Yet to Come

602 Part 5: Fruits, Vegetables, and Cereals

As wheat flour is able to form gluten, some of the consider-

ations about amylases and starch are not equally relevant when

baking wheat bread. Nevertheless, wheat flour is often used in

sourdough bread.

However, preferred qualities like improved keeping and safety

potential as well as the increased variety of flavors appeal to

many consumers. These desirable qualities are also praised be-

cause they represent an alternative natural preservation method

(Gobbetti 1998, Hammes and G ̈anzle 1998, Wood 2000).

Microbiology of Sourdough

An established, “natural” sourdough is dominated by a few rep-

resentatives of some bacteria and yeast species. This results

from the selective ecological pressures exerted in the (rye) flour-

water environment. Rye flour is an appropriate choice for this

mixture because leavening of the dough is dependent on sour-

dough development. At the start of fermentation, a 50:50 (w/w)

rye flour–water mixture at 25–30◦C will harbor approximately

the following:

Mesophilic micro- 103 –10^7 cfu/g

organisms, aerobes

Lactic acid bacteria <10 to 5× 102 cfu/g

Yeast 10–10^3 cfu/g

Molds 102 to 5× 104 cfu/g

Among the mesophiles at the start, members of the Enterobac-

teriaceae dominate. Microorganisms dominating in the sour-

dough after 1–2 days at 25–30◦C are as follows:

Lactic acid bacteria 109 cfu/g

Yeast 106 to 5× 107 cfu/g

Some important properties of the rye flour–water environment

determine that certain LAB and yeasts will compete most favor-

ably. Lactobacilli have a superior ability to ferment maltose, they

thrive despite limited iron due to the presence of phytic acid, and

they are able to grow at about pH 5.0 and lower.

Reports show that different LAB may be isolated from sour-

doughs; however,Lactobacillus sanfrancis censis has been

found most often. Table 31.2 presents some of the other

Lactobacillusspecies that have been isolated from sourdough.

The selection of yeasts may be even narrower, withCandida

millerioften cited (Table 31.2). Several other species are iso-

lated occasionally (Spicher 1983, Gobbetti and Corsetti 1997,

Hammes and Ganzle 1998, Martinez-Anaya 2003, Stolz 2003). ̈

Starters

It is traditional bakers’ practice to maintain a good sourdough

over time by regular transfer, for example, every 8 hours. This

is called “rebuilding.” Such established cultures are referred

to as Type I sourdoughs (Type I process), and a three-stage

fermentation procedure is considered necessary to obtain an

optimal sourdough. Each step is defined by specific dough yield,

temperature, and incubation time.

Dough yield is defined as:

(Flour+Water) by weight

Flour by weight

=×100 Dough yield

A high dough yield implies that a relatively large amount of

water is used to make the dough; such a dough would conform

with certain requirements in industrial production when there is

a need to pump the dough.

The lactobacilli and yeasts in Table 31.2 are all common in

sourdoughs; however, the composition of starter cultures for

Type I processes have been continuously stably maintained for

many years, and may be compared to certain mixed cultures

in dairy technology. The LAB and yeasts in such cultures will

be particularly well adjusted and adapted for the conditions in

sourdoughs. In Germany, established natural sourdough starter

cultures with a stable composition ofLb. sanfranciscensisand

Candida millerihave been propagated for decades; they are

marketed as “Reinzuchtsauerteig.” When the sourdough process

has been started through a one-stage or a three-stage proce-

dure, a part of the optimized dough is withdrawn to start up

the sourdough production for the next day. These sourdoughs

are mentioned in different languages as Anstellgut (German),

mother sponge (English), chef (French), masa madre (Spanish),

madre (Italian).

Sourdoughs in Type II processes are used mainly for enhanc-

ing the flavor and taste of the regular bread. Addition of baker’s

yeast is required for efficient leavening. Type I sourdoughs are

good alternatives as starters for the production of Type II sour-

doughs. At the start of a production period, industrially large

quantities of Type II sourdoughs may be stocked for portion-

wise use over time.

Sourdoughs for Type III processes are dried sourdough prepa-

rations.

Table 31.2.Common Representatives of Lactic Acid Bacteria and Yeasts Isolated from Mature Sourdoughs

Heterofermentative Homofermentative

Lactic acid bacteria Lactobacillus sanfranciscencis(formerlyLb.sanfrancisco, Lb. brevis

subsp.lindneri)Lb. brevis, Lb. fructivorans, Lb. fermentum, Lb. pontis,

Lb. sakei(formerlyLb. bavaricus, Lb. reuteri)

Lb. plantarum

Lb. delbrueckii

Yeasts Candida milleri, C. krusei, Saccharomyces cerevisiae, S. exiguus

Torulopsis holmii, T. candida