Biochemical and Mycological Studies on Stored Foods

Snow, Douglas (1944) Biochemical and Mycological Studies on Stored Foods. PhD thesis, University of Glasgow.

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Part I. The storage of feeding-stuffs with incorporated non-protein ntrogenous compounds The feasibility of including ammonium bicarbonate, ammonium sulphate and urea in cereal feeding-stuff mixtures is considered. Losses amounting to between one third and one half of the ammonium bicarbonate originally incorporated in such mixtures occurred during manufacture, but the corresponding losses from the ammonium sulphate and urea mixtures were very small. The mixtures were manufactured In cubes of different sizes and were stored in various types of containers under farm conditions for 30 weeks. Analyses were made on samples taken at Intervals during the storage period to determine the losses of nitrogen from these mixtures. The losses of ammonia sustained during the manufacture of the ammonium bicarbonate cubes continued during storage irrespective of the type of cube. There was some indication that cubes stored in paper bags lost less ammonia than cubes stored in jute sacks. Losses of ammonia from the cubes containing ammonium sulphate were small. The cubes containing urea suffered no significant loss of ammonia until deterioration of the cubes occurred with the development of moulding and heating. Laboratory experiments showed that the loss of urea from small samples stored at fixed temperatures and humidity was related to the development of these two forms of deterioration. Apparent increases of up to 6% in the total nitrogen values (calculated on a 100% dry matter basis) for some of these mixtures were recorded throughout the storage period. These were considered to be due to a loss of dry matter from these feeding-stuffs. Part II. The storage of bran. The apparent increases in total nitrogen found throughout the storage period of feeding-stuffs containing urea etc. (see Part I) were shown to be undoubtedly due to losses of dry matter. This was proved by analyses and weighings made on bran stored (a) In closed containers, (b) in sacks under farm storage conditions, and (c) as small 1 g. samples at controlled temperatures and humidity. Further analyses were made to estimate the chemical changes occurring with the development of moulding and heating in samples of bran. These showed that, with the onset of moulding, changes in the acidity fractions of the bran took place, the fat acidity value showing marked reduction. Where fermentation of the bran samples occurred in the closed tins, acids were produced which caused a rise in these acidity values. The development of moulding or heating also resulted in a loss of over half the ether-soluble fraction. Experiments have been made on the respiration of bran at different moisture levels using a continuous absorption apparatus in which the humidity of the air stream was adjusted to be at equilibrium with the respiring bran. The respiratory rate was accelerated with increased moisture content and was clearly attributable to two causes: (1) the respiration of the bran material itself and (2) the respiration of developing micro-organisms. Bran of 13% moisture content and below was shown to have a very low respiratory rate. It will, therefore, not be liable to heating during storage. Part III. Experiments on acidity values in stored feeding-stuffs. A critical survey is made of the methods that have been used by various authors to assess the different acid fractions of feeding-stuffs. The degree of fineness of grinding and the time and temperature of extraction with various solvents are shown to influence the results obtained by the generally recognised methods of estimation. The fat acidity value is shown to be the fraction most susceptible to changes in the condition of stored feeding-stuffs. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Psychobiology
Date of Award: 1944
Depositing User: Enlighten Team
Unique ID: glathesis:1944-79611
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 04 Mar 2020 16:38
Last Modified: 04 Mar 2020 16:38

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