Browsing by Author "Calton, Alex"

There is increasing demand for functional ‘clean label’ bakery ingredients for extending shelf life of baked products. The literature review introduces physical (staling) and microbiological spoilage of wheat bread and current methods of their control. In addition, wheat sourdough fermentation with an emphasis on antifungal (AF) and dextran-producing lactic acid bacteria (LAB) starters as a ‘clean label’ alternative to chemical preservatives and hydrocolloid additives is reviewed. The aims of this study were to 1) Isolate and select promising antifungal or dextran-producing LAB strains, 2) Optimise dextran production in a cereal ingredient medium (CIM), produce prototype bakery ingredients under optimised conditions and to study their effects on wheat bread quality, 3) Investigate in vitro AF activity of strains cultivated in a CIM. The effects of fermentation time (16 – 32 h), CIM (8-14% w/v) and sucrose content (4 – 14% w/v) on viscosity and dextran production by the best Weissella strain were modelled using response-surface methodology. Moreover, cell growth, acidification, and oligosaccharide (OS) production during fermentations were determined. Further, the effects of enzyme treatment and longer fermentation time (40 – 72 h) were studied. Crumb firming during storage (0 – 4 days), the specific volume and acidity of wheat bread supplemented with fermented CIMs (5 – 10% flour weight) were measured. The AF activities of Lactobacillus-fermented CIM against a Penicillium spp. indicator mould was measured by agar diffusion assay. Under the optimal conditions (32 h at 25°C; 10% w/v CIM; 14% w/v sucrose) the best Weissella strain increased viscosity of the CIM significantly and produced technologically significant amounts of dextran (3.5% w/v) with simultaneous OS formation. At 5% of flour weight, dextran-enriched CIM increased loaf specific volume by 5% and gave 14% softer bread loaves of mild acidity after 4 days of storage compared to control wheat bread (P < 0.05). At 10% of flour weight, dextran-enriched CIM reduced loaf volume and increased crumb hardness. AF activity by Lactobacillus strains was detected only when cultivated in deMan-Rogosa-Sharpe (MRS) media but not in the CIM. AF activity could be enhanced by supplementing CIM with the MRS media component sodium acetate. Hence, sodium acetate at low pH appeared to be the main contributor to the AF activity of Lactobacillus strains. The dextran-enriched CIM is a promising baking ingredient for increasing the physical shelf life of wheat bread.