Thesis (doctoral)--University of Helsinki, 2005. / Includes bibliographical references. Also available on the World Wide Web.

Microbial contamination and survival during storage of bread are a cause of both health concerns and economic losses. Traditional fermentation systems were studied as sources of lactic acid bacteria (LAB) with antagonistic potential against foodborne pathogens and spoilage organisms, with the aim to improve the safety and shelf life of bakery products. The antagonistic activity of four types of buttermilk (BM) products fermented with Lactococcus lactis subsp. lactis was evaluated against a number of pathogenic bacteria to select the best fermented-BM for application as bio-preservatives in bread crumpets, showing up to 9 µg/ml of nisin equivalent antimicrobial activity. These food ingredients could be suitable to be used in crumpet formulations, BM fermented with Lc. lactis subsp. lactis and nisin influenced the quality and shelf life of crumpets; the pH value and firmness of products with fermented BM was lower and the acidity and springiness was higher than for unfermented BM treatment and control withouth additive. The nisin and fermented BM treatment had beneficial effects on the pore size and colour in comparison with the control, and improved microbial shelf life by 2 days. Commercial and traditional sourdough and bread samples (n=18) were collected to assess the diversity of LAB strains and potential properties when applied to dough and bread. DGGE followed by sequencing showed that Lactobacillus was the predominant genus in the studied sourdoughs. Lb. plantarum and Lb. brevis strains accounted for 69% of the 32 isolates, out of which 10 were amylolytic and 12 had proteolytic activity. Most were also good acid producers after 24 h at 30°C. Some LAB strains presented a strong in vitro inhibitory activity against five indicator strains, showing potential as starter cultures to ferment sourdough. In subsequent experiments, the properties of 24 sourdoughs were evaluated, and one of them, fermented with Lb. plantarum (SIN3) yielded low pH value, high lactic acid production, and suitable microbial growth, and was selected for further bread making performance trials. The bread with fast fermentation and high sourdough concentration (FFHSD) had a lower pH, higher acidity and increased the quality attributes with significantly better shelf life comparing to the other treatments during the storage period. Sensory evaluation demonstrated that fast-fermented breads were more acceptable than the slow-fermented counterparts. Bread prepared with high level (18%) of sourdough fast-fermented with the selected culture (SIN3) had a good eating quality and shelf life. The approach of this study is likely to yield feasible improvements of the current methods of preparation of baking goods.

Inledning: Surdeg är idag en trend som fångats av många och de flesta bagerier ochdagligvarubutiker säljer bröd som kallas för surdegsbröd. Ett traditionellt surdegsbröd är ettbröd där surdegen används som enda hävningsmedel i brödet. Syfte: Syftet var att undersöka skillnader i sensoriska egenskaper, utifrån ettkonsumentperspektiv, samt GI-värde mellan surdegsbröd, jästbröd och bröd bakat på bådesurdeg och jäst. Material och metod: Metoderna som användes var två olika konsumenttester för att bestämmaskillnader mellan de tre bröden, och en in vitro-metod för att bestämma GI-värde. Resultat: Resultatet visade att konsumenter känner skillnad mellan surdegsbröd och jästbrödoch mellan surdegsbröd och bröd bakat på både surdeg och jäst men däremot inte mellanjästbröd och bröd bakat på både surdeg och jäst. Den syrliga smaken i surdegsbröd minskar ombrödet bakas på både surdeg och jäst. GI-mätningen genom in vitro-metoden visade att brödetbakat på både surdeg och jäst hade lägst GI medan surdegsbrödet hade högst. Slutsats: Ett bröd bakat på både surdeg och jäst är mer likt ett jästbröd än ett surdegsbröd. In vitro-metoden är inte den mest tillförlitliga för att undersöka skillnader i GI för justsurdegsbröd samtidigt som surdegsbrödets pH-värde kan ha varit för högt för att kunna sänkabrödets GI-värde. Inga slutsatser kunde därför dras från GI-mätningen. / Introduction: Sourdough is today a trend that has been caught by many and most bakeries andgrocery stores sell bread called “Sourdough bread”. Traditional sourdough bread is bread wherethe sourdough is used as only leavening agent. Purpose: The purpose was to examine differences in sensory attributes, from a consumerperspective, and glycemic index between sourdough bread, yeast bread and bread baked withboth sourdough and yeast. Material and Method: The methods used were two different consumer tests to determinedifferences between the three breads, and an in vitro-method for determining the glycemicindex. Result: The results showed that consumers can sense the difference between sourdough breadand yeast bread and between sourdough bread and bread baked with both sourdough and yeastbut not between yeast bread and bread baked with both sourdough and yeast. The sourish tasteof sourdough bread decreases if the bread is baked with both sourdough and yeast. Theglycemic index measurements by the in vitro-method showed that the bread baked with bothsourdough and yeast had the lowest glycemic index value whilst the sourdough bread had thehighest. Conclusion: Bread baked with both sourdough and yeast more resembles yeast bread thansourdough bread. The in vitro-method is not the most reliable for examining differences inglycemic index value for sourdough bread meanwhile the pH-value of the sourdough breadmay have been too high to be able to lower the glycemic value of the bread. No conclusionscould therefore be made from the glycemic index measurements.