On the free fatty acids of wheat flour. With reference to their contribution to chemical changes which occur during the mixing of doughs

Morrison, William R (1963) On the free fatty acids of wheat flour. With reference to their contribution to chemical changes which occur during the mixing of doughs. PhD thesis, University of Glasgow.

Abstract

It is known that, during the storage of wheat flour, lipase activity leads to an increase in the amounts of free fatty acids present in the flour. It has been shown by indirect means that the free fatty acids are associated with the development and character of the rheological properties of flour-water doughs. The strengthening (improvement) of doughs is an oxidative process and can occur naturally or due to the addition of oxidising agents (flour improvers). Improvement is generally thought to involve oxidation of sulphydryl groups of the structural proteins of dough (gluten) to intermoleculur disulphide groups. Improvement during the mixing of flour-water doughs is accompanied by the absorption of atmospheric oxygen. Free fatty acids, and in particular linoleic and linolenic acids, are involved in the absorption of oxygen, which is largely, if not entirely, an ensymio process. It has been suggested that the mechanism of these processes is lipoxidase-catalysed oxidation of free linoleic and linolenic acids of the flour, with coupled oxidation of gluten sulphydryl groups. The thesis describes a direct study of the fatty acids of flour and flour-water mixtures. Methods were developed for this study, and, after elimination of all phospholipids and galactolipids, the lipids were separated into free and esterified fatty acids, and their compositions determined by gas chromatography. A reappraisal of data published by other authors showed that there was reason to believe that lipoxidase activity was not the complete explanation of the absorption of oxygen by flour. Examination of three flours confirmed this, since it was found that there were not enough linoleic and linolenic acids present to account for the known oxygen absorptions. Analysis of the free and esterified fatty acids recovered from flour-water mixtures showed that losses had occurred only in the free fatty acids, and these were due to enzymic oxidations. The losses were shown to be due to oxidation of linoleic and linolenic acids by lipoxidase, or a similar enzyme, and to general oxidation of all free fatty acids by enzymes of the type involved in beta-oxidation. The latter is a novel finding in flour-water mixtures. The theoretical oxygen absorption of the flour was calculated on the basis of these two types of fatty acid oxidation, and was found to agree with published values. Lipoxidase activity was calculated to account for 1 volume in 17.6 volumes of the oxygen absorbed, and this was shown to agree with the known levels of lipoxidase-catalysed coupled oxidations in flour. Experiments in which oxidising, reducing and antioxidant conditions were present during the mixing process were described, and the results discussed in relation to the two types of fatty acid oxidation. The thesis has a supplementary section containing a description of rheological dough testing experiments, and reprints of three published papers relevant to the thesis.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: John Hawthorn
• Keywords: Food science
• Date of Award: 1963
• Depositing User: Enlighten Team
• Unique ID: glathesis:1963-73098
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73098