Gluten-free bread. II. Compressed yeast versus gluten-free sourdough

The use of the sourdough as a form of leavening is one of the oldest biotechnological processes in baked goods production. When used in optimised amounts, in fact, sourdough can improve the volume, texture, flavor, and nutritional value of bread and can increase its shelf-life by retarding the staling process and by protecting bread from mould and bacterial spoilage (Moroni et al., 2009). However, few attempts have been made for producing and characterising GF sourdoughs and the functional properties of the resulting breads. In this contest, the aim of this study was to compare the properties and quality of GF breads obtained using an in-lab developed GF-sourdough (SD) (see: Gluten-free bread. I. Development of a gluten-free sourdough), compressed yeast (CY; Saccharomyces cerevisiae) or their mixture (SD+CY) as leavening agents. The different starters were added in proper amounts to a GF mixture containing corn starch, rice flour, pea isolate, hydrocolloids and fiber as main ingredients (the optimized recipe comes from previous studies; Mariotti et al., 2009). The resulting doughs were characterized in terms of number and type of microorganisms, dough consistency, dough titratable acidity, pH and capability to produce and retain CO2. Breadmaking was performed as reported by Mariotti et al. (2013), with some adjustments due to the different raw materials used in the current GF recipe. After baking, the loaves were removed from the moulds and cooled at room temperature before being characterized (t0) for weight, height, specific volume, crust and crumb color, moisture, aw, crumb hardness. Crumb surface aspect was also evaluated, by means of Image Analysis techniques. Breads were characterized also during storage (up to 69h) at controlled conditions (25°C, 60%RH). The main results will be presented. Significant (P<0.05) differences were evidenced among the 3 different types of GF breads, in particular in terms of maximum height (SD: 4.51±0.15cm; SD+CY: 4.83±0.24cm; CY: 5.34±0.09cm), specific volume (SD: 1.69±0.11mL/g; SD+CY: 2.54±0.13mL/g; CY: 2.65±012mL/g), and crumb hardness (SD: 8.73±0.81N; SD+CY: 2.74±0.11N; CY: 1.61±0.19N; to). The higher values of crumb hardness for SD are probably due to its lower development during breadmaking. However, CY crumb exhibited a crumbly behavior during storage, that was absent in SD. From a general point of view, when SD was used in combination with CY a synergic effect was highlighted and an improvement of the overall GF bread quality and shelf-life was achieved. Further studies are in progress to optimise the amount of the developed GF sourdough to be used in the breadmaking process, in order to exploit at the most all its positive functionalities.