Sourdough: a tool for the improved flavour, texture and shelf-life of wheat bread

摘要

The aim of this thesis was to develop means to optimize the biochemical activity of sourdough to achieve improved bread flavour, texture and shelf-life, and to determine how the structure of fresh and aged bread is altered by the use of sourdough. The influence of process conditions of prefermentation on subsequent bread quality is clarified through this thesis. The importance of an optimised sourdough process in improving the flavour and texture of subsequent bread was demonstrated. The sourdough process had to be optimised in a strain-specific manner to obtain improved flavour and texture. Lactic acid bacteria fermented sourdoughs were more effective in tuning bread quality compared to yeasted preferments if the appropriate conditions were utilised. The ash content of flour and fermentation time were the main factors regulating bread flavour and texture in all of the sourdough types studied. The possibility to improve bread flavour by utilising sourdough with moderate acidity and an enhanced level of amino acids was demonstrated in this study. Bread volume and shelf-life were also improved by sourdough, which was fermented with low ash content flour and with optimised fermentation time. A new type of sourdough was presented: bran sourdough, which could effectively compensate the negative effect of added wheat bran on bread volume and shelf-life in high-fibre baking. An altered microstructure (improved protein network, enhanced swelling of starch and modified degradation of cell wall components) of bran sourdough breads, especially if made with enzymes, was related to improved volume. A reduced staling rate of bran sourdough breads was further explained due to reduced starch retrogradation and a slower loss of molecular mobility.