BLBS102-c31 BLBS102-Simpson March 21, 2012 14:0 Trim: 276mm X 219mm Printer Name: Yet to Come
31 Bakery and Cereal Products 607Fermented cereals are therefore usually regarded as safer than
their unfermented counterparts (Nout and Motarjemi 1997). A
weaning food made from unmalted cereals may be a cause of
malnutrition because its thick viscosity limits the nutritional in-
take of a small child. Addition of malted flour decreases the vis-
cosity so that more food can be ingested. If the fermentation flora
includes yeasts in addition to LAB, a measurable reduction of
carbohydrate will occur due to the production of CO 2 and other
volatile compounds (Muyanja 2001). Analysis of fermented ce-
real products therefore shows that the protein:carbohydrate ratio
is improved during the fermentation, and this obviously has nu-
tritional benefits.
Milling of cereals into flour is usually done prior to fermen-
tation, but in some products, for example, borde (Ethiopia), wet
milling is used. This technique can be used when mechanical
grain mills are not available and if the product is required to
be smooth and without bits of suspended bran. The starch is
also liberated from the grain more thoroughly when slurried
with water and sieved than if it has been previously dry milled
(Abegaz 2002).
A heat treatment step is found at some point in the production
technology of most fermented cereal products and may involve
boiling, steaming, or roasting. The type of heating employed is
likely to have an effect on the flavor of the product, certainly if the
temperature attained is sufficient to promote Maillard reactions.
The heat also gelatinizes the starch, making it more suscepti-
ble to amylolytic enzymes, thus providing greater amounts of
fermentable carbohydrates. However, at the same time, most of
the natural contaminating (and potentially fermenting) flora and
cereal enzymes are destroyed. Such products are also prone to
contamination after the heat treatment step, and are thereby po-
tentially unsafe should pathogenic organisms grow during the
subsequent fermentation. The traditional solution to this is to
use “backslopping,” the addition of some of a previous batch of
the product, and/or the addition of malted flour. Regular back-
slopping results in a selection of acid-tolerant organisms and
functions as an empirical starter culture.
Fermentation usually takes place at ambient temperatures, and
this may cause seasonal variations in products due to selection of
different microorganisms at different temperatures. The duration
of fermentation is largely a matter of personal choice, based on
expected sensory attributes. Heat treatment after fermentation
makes for a safer product, but it has the disadvantage of change
of taste or loss of volatile flavor and aroma compounds.The Microflora of Spontaneously
Fermented CerealsSpontaneously acid-fermented cereal products may contain a
variety of microorganisms, but the flora in the final product
is generally dominated by acid-tolerant LAB. Yeasts are also
invariably present in large numbers when the fermentation is
prolonged. A typical fermented cereal product contains approx-
imately 10^9 and 10^7 cfu/g of product, of LAB and yeasts, re-
spectively. However, since yeast cells are considerably larger
than bacteria cells, their metabolic contribution to product char-
acteristics is likely to be just as important as that of the LAB.The buffer capacity of cereal slurries is low, and the pH there-
fore drops quickly as acid is produced. Pathogenic organisms
are inhibited by a fast acid production, so the addition of starter
cultures, either as a pure culture or by “backslopping” promotes
acid production and contributes to the safety of the fermented
product (Nout et al. 1989).
The potential and the need for upgrading traditional fermenta-
tion technologies have initiated considerable research (Holzapfel
2002). In some recent studies of spontaneously fermented ce-
reals, the LAB and yeasts have been isolated and identified
as a first stage towards developing starter cultures for small-
scale production of traditional fermented cereals. Muyanja et al.
(2003) recorded that bushera, a traditional Ugandan fermented
sorghum beverage that contains high numbers of LAB, was
usually consumed by children after one day of fermentation
as “sweet bushera.” After 2–4 days, the product became sour
and alcoholic and was consumed by adults. However, the sweet
bushera showed very high counts of coliforms and had a repu-
tation for causing diarrhea (Muyanja 2001). Clearly, the devel-
opment of defined starter cultures would improve the safety of
this and similar products.
Some recent examples of studies on the microbial flora of
spontaneously fermented cereals are shown in Table 31.3. For
each product, several different types of organisms have been
isolated. In other words, a specific product is not produced from
fermentation by a specific organism or organisms.Lb. plantarum
seems to be the most commonly isolatedLactobacillusspecies in
fermented cereals. In addition, heterofermentative LAB such as
leuconostocs,Lb. brevis, andLb. fermentumfrequently occur.
Yeasts are always present in spontaneously fermented prod-
ucts, but few studies have characterized the predominating
species. However, Jespersen (2003) reported thatS. cerevis-
ciaeis the predominant yeast in many African fermented foods
and beverages.
All spontaneously fermented products contain, or have con-
tained, many different types of microorganisms. These have
grown in the product and will have metabolized some of the
cereal components, thereby making a contribution (positive or
negative) with their metabolites to the overall sensory charac-
teristics of that product. However, studies on spontaneously fer-
mented products have focused on LAB and yeasts since these
organisms are often associated with other, better known, fer-
mented products and have a history of safe use in food. Stanton
(1998) proposed that the nature of the substrate (raw material)
and the technology used to produce fermented foods are the
predominating factors that determine the development of mi-
croorganisms and, thereby, the properties of a product.Desirable Properties of the
Fermenting MicrofloraThe most important property of a starter culture for a fermented
cereal is the ability to quickly produce copious amounts of lac-
tic acid in order to achieve a rapid decline in pH and retard
the growth of pathogens and other undesirable organisms. Some
workers (Sanni et al. 2002) have sought amylolytic LAB strains,
as this could remove the need for using the highly contaminated