Sourdough bread enriched with soluble fibres: development, characterisation and nutritional aspects of a functional food product

The application of sourdough in breadmaking has multiple technological and nutritional benefits. However, the use of soluble fibres in sourdough technology is a currently understudied area. Given that the UK fibre intakes (at average of 14g/d for adults) fall short of government recommendations, the aim of this PhD was to develop soluble fibre-enriched sourdough bread with a low glycaemic index (GI). The PhD comprised three key phases: 1) product development, 2) physico-chemical and sensory characterisation, and 3) GI analysis of the fibre-enriched sourdough breads. After undertaking a product development trial, the physico-chemical properties of five sourdoughs and the resultant breads were assessed using pH measurements, Chen-Hoseney dough stickiness rig and rapid viscosity analysis (RVA). Bread volume, texture analysis, C-Cell image analysis, fibre and resistant starch determination were also conducted. Consumer acceptability of the developed breads was assessed using an untrained sensory panel (n = 100). The content of lactic acid and ethanol was studied using high-performance liquid chromatography (HPLC) analysis. The glycaemic and satietogenic properties of sourdough bread enriched with soluble fibre (XG/GA/Pec), control sourdough bread and white wheat bread (WWB) were tested in a cross-over study using 11 healthy participants (mean age 35 ± 10 years, BMI 23.7 ± 2.86 kg/m2), a standard seven-point protocol and Satiety Labelled Intensity Magnitude (SLIM) scale. The results of this study showed a negative correlation between the value of pH and the dough stickiness for control sourdough bread (R2 = 0.618) and for control sourdough bread with added wheat bran (R2 = 0.532). The RVA results showed that the addition of 10% of soluble significantly influenced the gelatinisation and properties of starch in flour pastes. The research showed that the addition of 10% soluble and insoluble fibre (wheat bran) to sourdough bread significantly (p 0.05). The values of GI obtained in the intervention study were 66 for control sourdough bread (p = 0.03) and 59 for XG/GA/Pec (p = 0.006) when compared to glucose reference food. The subjects reported greater satiety after consumption of bread with iii XG/GA/Pec than after consuming white wheat bread (p = 0.036). These results show that sourdough bread enriched with soluble fibres played a role in reducing glycaemia and in increasing the perception of satiety following ingestion. This PhD makes contribution to knowledge by applying high amounts of soluble fibres, which are routinely used in much lower concentrations in food industry. The research described within this thesis provides a formula and processing conditions for the production of a functional food product. This study adds to the existing knowledge of food science and human nutrition. Within this thesis it is demonstrated that sourdough and soluble fibre may act simultaneously on the gastrointestinal tract and jointly exert effects on postprandial blood glucose concentration and satiety. By demonstrating prolonged satiety of bread characterised by lower GI, this PhD makes a contribution to the debate on the satietogenic properties of dietary carbohydrates. Further research is now needed to explore the hormonal and metabolic effects after ingestion of soluble fibre-enriched sourdough bread. Future studies of the fermentability of these breads by colonic microflora could also provide insight into their prebiotic properties.