Date of Award

2013

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Department

Biological and Pharmaceutical Sciences

First Advisor

Dr Mary Concannon

Second Advisor

Professor Tony Pembroke

Abstract

Spent dairy yeast Kluyveromyces marxianus (SDYK), a by-product of whey to ethanol fermentations, was investigated as a natural biomass source for the production of alternative flavoured yeast extracts. SDYK which was characterised by a high protein content (55.3% (w/w) ± 0.8) and comparable levels of flavor enhancing amino acids to that of S. cerevisiae was prepared for induced autolysis at different pH values in the presence of inductors sodium chloride and the proteolytic enzyme papain. An induced autolysis process was developed for the production of flavoured yeast extracts in which pH and autolytic treatment applied were found to have a significant effect on free amino nitrogen content. Autolysis at pH 6.5 yielded the highest free amino nitrogen content with the addition of papain shown to have a significant effect. Induced autolysis of SDYK at pH 5.5 and 6.5 also provided yeast extracts with increased concentrations of flavour enhancing free amino acids glutamic and aspartic acid and a % DH range of 65%-83%. Other flavour related components identified in the yeast extracts were the flavour enhancing ribonucleotide 5’IMP, reducing sugars, peptides and glycoproteins. Yeast cell wall material a by-product of this process proved to be a good source of functional polysaccharides, ß-glucan and mannan. Descriptive sensory analysis was used to quantitatively describe odour and flavour and resulted in ten attributes being significantly discriminated between SDYK yeast extracts. Further analysis by principal component analysis (PCA) and relative positions on the PCA sensory biplot indicated that pH in association with autolytic inductors, salt and papain, had a significant effect on resultant flavour attributes which could prevent unwanted tastes whilst improving salty and savoury attributes. This could form the basis of an innovative process for the provision of alternative yeast extracts with improved flavour and reduced sodium content for use in dairy based products.

Access Level

info:eu-repo/semantics/openAccess

Coverage

July 2024

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