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Food Biotechnology Dr. Kamal E. M. Elkahlout Applications of Biotechnology to Food Products 3. Production of Fermented Foods (Bread making). INTRODUCTION
Production of Fermented Foods
In contrast, yeasts form a small proportion by weight on bread, but are responsible for the flavor of bread; hence bread is a fermented food.
(c) Fermentation sometimes removes unwanted or harmful properties in the raw material; thus fermentation removes flatulence factors in soybeans, and reduces the poisonous cyanide content of cassava during garri preparation.
Fermented foods are influenced mainly by the nature of the substrate and the organisms involved in the fermentation, the length of the fermentation and the treatment of the food during the processing.
These components depend on the type of bread and on the practice and regulations operating in a country.
After allowing the dough to stand for an hour the starch can be washed off under a running tap water leaving a tough, elastic, sticky and viscous material which is the gluten.
‘Hard’ wheat with a high content of protein (over 12%) are best for making bread because the high content of glutenins enables a firm skeleton for holding the gases released curing fermentation.
(d) Good keeping quality i.e., ability to resist autolysis when stored at 20°C;
The amount of yeasts used during baking depends on the flour type, the ingredients used in the baking, and the system of baking used.
Yeast ‘food’ The name yeast ‘food’ is something of a misnomer, because these ingredients serve purposes outside merely nourishing the yeasts.
Oxidizing agents which have been used include iodates, bromates and peroxide.
Ordinarily however, proteases have the effect of reducing the mixing time of the dough.
(d) First (intermediate) proofing: The dough is allowed to rest for about 15 minutes usually at the same temperature as it has been previous to this time i.e., at about 27°C.
During this period the sponges rises five to six times because of the volatile products released by this yeast and usually collapses spontaneously.
The enzymes alpha and B amylases are active for a while as the temperature passes through their optimum temperatures, which are 55-65°C and 65-70°C respectively.
(ii) The liquid ferment system. In this system water, yeast, food, malt, sugar, salt and, sometimes, milk are mixed during the pre-fermentation at about 30°C and left for about 6 hours.
During this period .the risen dough is occasionally knocked down to cause it to collapse.
CO2 is evolved on contact of the components with water: part of the CO2 is evolved during dough making, but the bulk is evolved during baking.
In practice however yeasts are used; even when it is desirable to produce bread quickly such as for the military or for sportsmen and for other emergency conditions the use of yeasts recommends itself over the use of baking powder.
The CO2 dissolves continuously in the dough, until the latter becomes saturated.
Fermentation of the fructose moeity of sucrose is initiated after an induction period of about 1 hour.
The level of salt addition is maintained as a compromise on account of its role in gluten formation.
(iv) Effect on fungal inhibitors (anti-mycotic agents): Anti-mycotics added to bread are all inhibitory to yeast.
Provided that enough sugar is available the higher the yeast concentration the more rapid is the leavening.
During baking the lower boiling point materials escape with the oven gases; furthermore, new compounds result from the chemical reactions taking place at the high temperature.
In oven vapor condensates ethanol constitutes 11-12 % while other alcohols collectively make up only about 0.04%.