Sourdough and Cereal Beverages - Sourdough Biotechnology - page 264

In addition to improved sensory and rheological properties, the use of controlled
starter cultures in boza fermentation aimed at incorporating bacteriocin-producing
strains in boza fermentations; Todorov and Dicks [ 8, 10, 11 ] isolated a number of
bacteriocin-producing strains from boza and also partially characterised many bac-
teriocins (Table 11.1 ). Bacteriocins are small proteinaceous metabolites that are
excreted by the host strain during its stationary growth phase, and they exhibit lethal
or static effects against bacteria closely related to the host, which may prolong shelf
life and improve the safety of the products.
Boza, as a semi-sterile base, lacks the enzyme activity of cereal raw materials,
which in sourdough fermentation, for instance, play a significant role. This sets
requirements for starter strains to grow as well as offers some possibilities for food
technologists to take advantage of specific catalytic activities of starter strains of
even added exogenous catalysts. Petrova et al. [ 9 ] identi fi ed two amylolytic lacto-
bacilli strains from Bulgarian boza. The strains, Lactobacillus plantarum Bom 816
and L. pentosus N3, used starch as a sole carbohydrate source, and the amylolytic
activity of the cell-wall associated enzymes was optimal at pH 5.5 and 45 °C. No
research on the synthesis of extracellular polysaccharides (EPS) exists though boza
could serve as a potential matrix for this as it can be fermented with selected starter
cultures (e.g. EPS-producing starter cultures) and its carbohydrate composition
could be adjusted to meet the desired EPS-synthesis profiles. For instance, the syn-
thesis of homopolysaccharides by glucansucrases or fructansucrases of LAB is
boosted by high matrix sucrose content. In addition, future works could focus on
investigations related to other bioactivities such as vitamin B profile and their
changes during boza fermentation.

11.3 Togwa

Togwa is a Tanzanian beverage prepared from cereal porridge by liquefying the
starch paste with malt followed by fermentation. The flour used to make the por-
ridge is usually from maize, sorghum or finger millet, though cassava is a common
ingredient as well. The addition of germinated sorghum or finger millet, with high
amylolytic activity, induces saccharification of gelatinised starch and results in a
sweetened slurry with reduced viscosity. Ripe togwa from a previous fermentation
batch usually serves as a starter for the fermentation of the liquefied and saccharified
slurry. Togwa is described as having an opaque, brownish appearance and a slightly
fl oury mouthfeel [ 13 ]. A more detailed illustration of the manufacturing process for
togwa is provided in Fig. 11.2 (Modi fi ed after [ 13, 14 ] ).
Lactic acid bacteria and yeasts are the dominant microorganisms in togwa.
Mugula et al. [ 14, 15 ] investigated some key fermentation parameters and identified
dominant microorganisms from Tanzanian togwa samples. The final pH-values for
togwa were between 3.1 and 3.5 and most of the LAB isolates were heterofermenta-
tive and roughly every third isolate produced dextran. Homofermentative L. plantarum ,
however, dominated fermentations and three of its isolates showed amylolytic activity