Technology of Baked Goods - Sourdough Biotechnology - page 56

crust during baking and ensures a soft crumb during storage. Fats such as olive oil,
lard or butter are also used. If the concentration of fat is lower than 5%, the main
technological role is as a lubricant: the gluten increases the extensibility before
rupture, favouring a higher dough volume [ 37 ]. If the formulation is very rich in fat,
the dough becomes short and loses its extensibility. This effect justifies the definition
of shortening for these components. Polar lipids such as mono- and di-glycerides
stabilize the air bubbles formed during mixing and provide a crumb with a finer and
more regular alveolar structure [ 38 ]. During storage, lipids prevent the interaction
among starch macromolecules, slowing down their reorganization into ordered and
crystalline structures (retrogradation), as well as the migration of water between
starch and proteins, slowing down the phenomena of staling and aging [ 39 ] .

3.3.3 Leavening Agents

Essentially three types of leavening agents are used for making baked goods: bak-
er's yeast, chemical agents and sourdough. Since sourdough will be covered in
detail in all the other chapters, this paragraph only aims at shortly describing the
main features of the other leavening agents.

3.3.3.1 Baker's Yeast

Baker's yeast refers to Saccharomyces cerevisiae strains. After a brief initial respi-
ratory activity due to the oxygen dispersed in the dough, baker's yeast ferments
glucose, fructose, maltose and sucrose from the flour to CO 2 and ethanol. Nowadays,
the types of baker's yeast available on the market have different shelf life (yeast
cream, compressed yeast, dried yeast), osmotolerance features (suitable for baked
goods with elevated levels of sugars) and activity at low temperatures (frozen dough)
(see Chap. 6 ). The use of baker's yeast as a leavening agent is very often an alterna-
tive to the use of sourdough, especially for industrial bakeries. During processing,
baker's yeast mainly determines the leavening of the dough due to the production of
CO 2 ; it also synthesizes some volatile compounds that positively affect the flavour
and taste of baked goods.

3.3.3.2 Chemical Agents

The production of CO 2 within the dough can also be obtained by a reaction between
sodium bicarbonate and an acid (e.g. tartaric acid). Chemical agents are not used for
bread making but for sweet baked goods, both dry and light (such as biscuits, sponge-
cakes, etc.). The use of chemical agents for leavening is recommended when CO 2 has
to be produced rapidly in doughs rich in sugars and fats, ingredients that slow down
and/or inhibit the metabolism of the biological agents. Sodium bicarbonate lacks