Eur Food Res Technol (2003) 217:23–33 DOI 10.1007/s00217-003-0724-1 ORIGINAL PAPER C. I. Clarke · T. J. Schober · E. Angst · E. K. Arendt Use of response surface methodology to investigate the effects of processing conditions on sourdough wheat bread quality Received: 3 February 2003 / Published online: 10 May 2003  Springer-Verlag 2003 Abstract Response surface methodology was used to investigate the influence of three factors, sourdough fermentation time, proof time and amount of yeast addition on the quality of sourdough wheat bread. Each predictor variable was tested at five levels. Sourdough fermentation times were 5, 11, 20, 29 and 35 h, yeast addition rates were 0.05, 0.75, 1.77, 2.80 and 3.50% (flour weight basis) and proof times were 16, 40, 75, 110 and 134 min. The performance of two different starter culture types, a mixed strain starter culture called Böcker Reinzucht–Sauerteig Weizen and a single strain starter culture of Lactobacillus brevis, was compared by sepa- rately completing the experimental design for each. Independently non-acidified control bread was prepared. A range of loaf quality parameters was determined including pH, total titratable acidity, loaf height, specific volume, crumb mean cell area and crumb hardness. Overall breads with better specific volume values were achieved with the use of sourdough relative to the control. Results indicated that maximum loaf specific volume was achieved when L. brevis sourdough was used particularly when it was used in conjunction with a high rate of yeast. Given a lower rate of yeast addition however, the mixed strain starter culture yielded better bread. Key words Sourdough · Wheat bread · Response surface methodology Introduction and objectives Sourdough fermentation is one of the oldest biotechno- logical processes used in food production and indeed it was the only bread leavening method used before the discovery of yeast in beer production [1]. The acidifica- tion process effected by the use of sourdoughs remains a necessary prerequisite for the preparation of rye breads or rye–wheat combination breads [2]. For wheat breads, however, in spite of the wide use of baker’s yeast today, the application of sourdough to wheat breads has regained importance as a means to improve the quality and flavour of wheat breads [3, 4, 5, 6]. It has also been reported that the use of sourdough can have positive nutritional implications by increasing mineral bioavailability [7, 8] and by lowering the glycaemic response to baked goods [9, 10]. More recent studies have confirmed the positive impact of sourdough antifungal compounds on the mould- free shelf-life of baked goods [11, 12]. The incorporation of sourdough during wheat bread production can have a considerable effect on the charac- teristics of the dough. The effects are complex because of variation between sourdoughs with regards to the type of starter culture, dough yield and fermentation regime used [13]. The length of the fermentation period for example will impact on the properties of the resulting sourdough in view of the fact that growth of the bacteria used for inoculation proceeds in a number of stages including lag phase, exponential phase, stationery phase and lethal phase. Immediately subsequent to inoculation therefore there is little change in the nature of the sourdough and, after a period of time, the dough gradually becomes more acidic as the sourdough microflora becomes dominated by lactic acid bacteria [1]. Sourdoughs are considered ‘ripe’ or ‘mature’ when they have achieved the required degree of acidification, which has been reported to be within the range of pH values 3.6–4.0 [1]. The acidity of sourdough is measured as a function of both its pH and total titratable acidity values. This is in view of the fact that there is no direct correlation between the pH and total titratable acid value because of the presence of buffering substances in the dough system. In order to obtain leavened bread, gas formation by microorganisms is necessary. In the case of sourdough breads, carbon dioxide is produced by both lactic acid C. I. Clarke · T. J. Schober · E. Angst National Food Biotechnology Centre, National University of Ireland, Cork, Ireland C. I. Clarke · T. J. Schober · E. Angst · E. K. Arendt ( ) ) Department of Food and Nutritional Sciences, National University of Ireland, Cork, Ireland e-mail: e.arendt@ucc.ie Tel.: +353-21-4902064, Fax: +353-21-4270213