Effects of the fermentation process on gas-cell size two-dimensional distribution and rheological characteristics of durum-wheat-based doughs Simonetta Fois a, 1 , Costantino Fadda b, 1 , Roberto Tonelli a , Manuela Sanna a , Pietro Paolo Urgeghe b , Tonina Roggio a , Pasquale Catzeddu a, ⁎ a Porto Conte Ricerche Srl, Località Tramariglio, Alghero (SS), Italy b Dipartimento di Agraria, Università degli Studi di Sassari, viale Italia 39, Sassari, Italy abstract article info Article history: Received 20 April 2012 Accepted 26 July 2012 Keywords: Durum wheat Gas-cell size Sourdough Leavening In this study, the effects of baker's yeast and sourdough fermentation on gas-cell size distribution and height of leavened doughs were evaluated in eight durum-wheat-based doughs of different strengths. Furthermore, the chemical and rheological properties of the doughs were analyzed to determine their effects on the leav- ening process. The gas-cell size distribution was modeled by a log-normal distribution across the full range of gas-cell sizes (10 -4 to 10 2 mm 2 ), and by a power-law distribution for the large gas cells. The power law α exponent analysis of variance showed that α distinguished between the two empirical distributions, which indicated that there were more larger cells in the sourdough samples than in the baker's yeast samples. The distribution of the small-to-medium gas cells was the same for the two processes, as indicated by the log-normal parameters. The leavened dough height was generally higher for the baker's yeast dough samples, compared to the sourdough samples, except in the case of samples with very strong and elastic gluten. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction In Mediterranean regions durum wheat is traditionally used to make specialty breads, either flat and hearth breads. Nowadays meals from durum wheat (semolina, low grade semolina and flour) are largely used as ingredient for all types of breads, and there is increasing interest in durum wheat exploitation for its bread making potential. The chem- ical and rheological properties of the meals strongly affect the bread-making process. They have significant roles in the handling prop- erties of the dough, its gas-retention capacity, and the quality attributes of the finished baked goods. Indeed, meal with a high gluten index, which indicates a strong gluten network, has increased gas retention, which leads to bread with a higher specific volume and a softer crumb (Armero & Collar, 1998). Poor quality meal forms a discontinuous glu- ten network that interacts strongly with starch granules. This interac- tion results in reduced viscous flow behavior and consequently less gas retention. The dough, therefore, does not expand. A further negative aspect of low quality meals is an air-cell size that is not homogenously distributed, thus resulting in a coarse dough structure (Oates, 2001). This phenomenon was explained by Van Vliet, Janssen, Bloksma, and Walstra (1992), whose theory asserts that for good breadmaking per- formance, the dough film between two expanding gas cells has to be stable against rupture, to prevent coalescence of the cells. Thus, a good breadmaking meal will produce a gluten dough with more strain hardening than for a meal of poor breadmaking quality. Microbial fermentation is a fundamental aspect of bread making, and it can be performed using baker's yeast or sourdough. The dough leavening is an easily visible consequence of microbial fermentation, which results in an increase in the specific volume of the dough due to the production of the CO 2 that becomes trapped in the gas cells that originate in the dough during its mixing. This CO 2 is produced mainly by the yeast, and to a lesser extent by the heterofermentative lactic acid bacteria (LAB) in sourdough. The main function of commer- cial baker's yeast in bread making is the leavening of the dough through this generation of CO 2 . The higher the level of yeast, the faster the rate of CO 2 production. This fermentation process is vigorous, predictable and reproducible, and for this reason it is particularly appreciated by bakers (Kulp, 2003). Sourdough fermentation is a more complex process, and this proceeds more slowly. It is characterized by an undefined number of LAB and yeast strains that drive the process (Catzeddu, 2011). The sourdough affects the mechanical properties of the dough, leading to a less elastic and firm dough (Angioloni, Romani, Pinnavaia, & Dalla Rosa, 2006), thus reducing matrix rigidity and increasing cohesiveness (Fadda, Santos, Piga, & Collar, 2010). There are contradictory results Food Research International 49 (2012) 193–200 Abbreviations: AACC, American Association of Cereal Chemists; BYD, baker's yeast dough; CCDF, complementary cumulative distribution function; CDF, cumulative distri- bution function; LAB, lactic acid bacteria; PCA, principal component analysis; PDF, probability distribution function; PMMA, polymethylmethacrylate; TTA, total titratable acidity; TPA, texture profile analysis. ⁎ Corresponding author at: Porto Conte Ricerche Srl, Località Tramariglio, 07041 Alghero, Italy. Tel.: +39 079 998400; fax: +39 079 998567. E-mail address: catzeddu@portocontericerche.it (P. Catzeddu). 1 These authors contributed equally to this study. 0963-9969/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodres.2012.07.058 Contents lists available at SciVerse ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres