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Title: Chemical and sensorial properties of cereals fermented with human derived lactic acid bacteria
Author: Ochoa, Ivan Salmeron
ISNI:       0000 0004 2687 6035
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2010
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Foods targeting gut health (probiotics and/or prebiotics) constitute one of the largest and fastest growing sectors within functional foods. The majority of probiotic products in the market are dairy-based. The increasing demands for this health enhancing products have created opportunities for the development of non-dairy probiotic formulations. Previous work has demonstrated that cereals and cereal fractions are good substrates for the proliferation of lactobacilli and bifidobacteria strains (main probiotic microorganisms). Cereals could be used to design novel cereal-based fermented beverages with probiotic characteristics if these have acceptable physicochemical and organoleptic characteristics. The purpose of this work is to study the flavour development of cereal substrates fermented with human derived lactic acid bacteria. The production of volatile and non-volatile flavour compounds, physicochemical and sensory properties will be evaluated in wheat, barley, malt and oat media individually inoculated with Lactobacillus acidophilus NCIMB8821, Lactobacillus plantarum NCIMB8826, and Lactobacillus reuteri NCIMB 11951. A considerable amount of development work was done to optimize the analytical techniques for the determination of volatiles, and a broad range of those were detected in fermented and unfermented cereal substrates. Volatile compounds that had been reported to exhibit flavour attributes in fermented products were selected. The evaluation of acetaldehyde, diacetyl, ethyl acetate, acetone and ethanol was carried out through the application of a headspace gas chromatography method (HSGC). It was observed that the values of these volatiles were specific to each substrate tested and their concentrations varied during the fermentation process. Acetaldehyde, which had been reported as an impact flavour compound in other fermented products, was detected in concentrations above its threshold in some of the cereal beverages. Diacetyl was only detected in products formulated with malt substrate. Lactic acid concentrations where always greater than the values of acetic acid which could be a positive outcome since acetic acid has flavour attributes associated with "vinegar" while lactic acid has been described to exhibit a more "mild acidic" taste. During the sensory evaluation it was found that those products formulated with L. plantarum had a greater acceptance. After correlating the chemical, physicochemical and sensory properties it was observed that malt fermented beverages had higher values of most of the chemical components and physicochemical properties evaluated. Our results showed that the acceptance of those products formulated with L. plantarum was characterized by having greater concentrations of the volatile acetaldehyde and pH values above 3.5. Of the formulations tested L. plantarum is the most preferred lactobacilli strain in the malt and barley media. The use of mixed cultures could also be considered in future work and shelf life studies should also be performed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available