Sugar reduction in sweet bakery products: sourdough technology as a novel technological approach to overcome quality loss
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Date
2019
Authors
Sahin, Aylin W.
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University College Cork
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Abstract
Sugar reduction in food and beverages represents one of the major trends followed by consumers. Sugar is one factor, which promotes non-communicable diseases, such as type-2- diabetes, obesity and cardiovascular health issues. This doctoral dissertation, firstly, highlights the need for sugar reduction in bakery products in form of a literature review. Commonly known strategies, such as the replacement of sugar by bulking agents and artificial sweeteners, are discussed and the potential of sourdough technology to overcome techno-functional limitations is introduced. Several lactic acid bacteria and yeast strains are natural polyol producers and, furthermore, are able to produce exopolysaccharides, which makes sourdough a functional ingredient. The essential role of sugar is shown by the simple reduction of sugar by wheat starch, a non-sweet bulking agent, in a burger bun system. Sugar reduction increased specific volume (+0.99 ml/g) and changed the texture and structure of the burger buns significantly. Furthermore, sweetness intensity decreased, and microbial shelf life was shortened (-6 days). The replacement of sugar by commercially available polyols, such as xylitol, maltitol or mannitol, instead of wheat starch, revealed a significantly lower specific volume (-30 to -48%) and a harder crumb texture (+135% to +678%) compared to the full-sugar control. Moreover, polyols did not contribute to Maillard browning resulting in lighter crust colour. Among all polyols tested, mannitol showed the most promising results as a partial sugar replacer. An alternative approach to overcome quality loss during sugar reduction is the application of mannitol-rich sourdough. The heterofermentative lactic acid bacteria (LAB) strain Leuconostoc citreum TR116 was isolated from a yellow pea sourdough and characterised as a high mannitol producing strain. Wheat sourdough fermented with this LAB strain was performed with fructose addition, which was converted to mannitol (yield: 87%). The optimal fermentation time for high mannitol production was 30 h and mannitol-rich sourdough showed a production of metabolites in the ratio 1:0.34:0.15 (mannitol:lactate:actate). The incorporation of sourdough into a 50%-sugar-reduced burger bun system caused the same effect on gluten network development and viscoelastic properties, as the full-sugar control. Furthermore, no differences in specific volume and crumb hardness occurred, and mannitol-rich sourdough also contributed to sweetness and flavour. Additionally, a prolonged microbial shelf life was achieved. The addition of 10% mannitol-rich sourdough in a burger bun system is recommended. Since mannitol-rich sourdough could compensate quality loss in sugar-reduced burger buns, its effect on a 50% -sugar-reduced cake was investigated. Mannitol-rich sourdough increased the specific volume and softened the crumb texture (-8.6 N) of a 50%- sugar-reduced cake. Furthermore, it increased the sweetness intensity by 93% and contributed to aroma (+30%) and flavour (+25.5%). In sugar-reduced cakes a sourdough addition level of less than 10% is recommended. The positive impact of sourdough technology on buns and cakes led to the investigation of the effect of mannitol-rich sourdough in low-sugar biscuits. Since Leuconostoc citreum TR116 is a multifunctional strain, which is also able to produce exopolysaccharides, a mannitol-rich sourdough and a mannitol-rich sourdough with exopolysaccharides was fermented and incorporated in the biscuits. Sourdough addition caused an improvement in biscuit spreading and hardening. Furthermore, it contributed to colour and increased sweetness and flavour intensity (+140%, +139% respectively). It has to be noted that sourdough incorporation did not negatively influence the predicted glycemic index of low-sugar biscuits. The outcome of this research thesis provides a starting point for the development of sugar-reduced, low-sugar, or even no-sugar, highly consumer accepted bakery products using natural functional ingredients.
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Keywords
Lactic acid bacteria , Fermentation , Cakes , Biscuits , Low sugar , Sugar reduction
Citation
Sahin, A. 2019. Sugar reduction in sweet bakery products: sourdough technology as a novel technological approach to overcome quality loss. PhD Thesis, University College Cork.