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AuthorsRoss, Zara M.
MetadataShow full item record
AbstractTwo commercial garlic products; a steam distillate of garlic (G. 0) containing essential garlic oils AND a freeze-dried garlic powder (G. P) have been studied with respect to their antimicrobial modes of action with reference to gut environments. Results obtained in this thesis indicate: - 1) A method of preparing G. P for use was developed and the allicin content (from alliin) determined by both pyruvate and ammonia assays to be approximately I 1.00mg/ g was shown to be comparable to published data. 2) Quantitative and qualitative methods for determining the sulphide and thiosulphinate content of G. 0 and GY respectively, by gas chromatography (GC) analyses were performed. It was observed that G. P analysis (by conversion of allicin to vinyldithiins) provided an underestimate of the allicin content as compared to published data. For G. 0 seven sulphides were resolved, of these DADS, MATS and DATS contribute approximately 60% of the identified sulphide composition (70-80%). 3) G. 0 (and G. P) components were separated by high performance liquid chromatography (HPLC) and for G. 0 ten sulphides were resolved, of which eight were identified. Four of these sulphides (MATTS, DATTS, MAPS and DAPS) were not detected by GC analysis and in contrast MAD detected by GC was not identified by HPLC. 4) In addition HPLC analysis was used in conjunction with viability studies to monitor relative changes in GO sulphide composition with respect to time in the presence of microbial cells. 5) Both G. 0 and G. P exhibited antimicrobial properties against all the bacteria screened. The antimicrobial effectiveness was shown to be dependent upon garlic product concentration and time of exposure but independent of whether the bacteria were growing or not. 6) MIC determinations indicated differences in bacterial sensitivity towards both garlic products with respect to both species and even strain. For G. P, MIC values ranged from 25-3.125mg/ml, suggesting a limited variation in bacterial sensitivity whereas a much larger MIC ranges of 5.5-0.01mg/ml were obtained for G. O. Certain pathogenic bacteria (L. monocytogenes and Y enteroco§ticd) were shown to exhibit much greater sensitivity (MIC values of 0.02 and 0.17mg/ml respectively) towards G. 0 than other bacteria studied including normal microbial flora. 7) A decrease in G. 0 antimicrobial effectiveness with respect to time was observed during viability studies (not observed with G. P) and was partly attributed to the loss of antimicrobial components by volatilisation, interaction/association between the G. 0 sulphides and bacterial cells, and changes in chemical composition of the medium. 8) G. 0 was shown to be antimicrobially effective in a variety of media ranging from simple salt solutions, microbiological growth media (TSB and MRS), simulated intestinal fluids (simple and complex) to highly complex 'real' gut fluids (ileostomy effluents). In addition it was observed that the different chemical compositions of the various media can influence the antimicrobial effectiveness of G. O. 9) The presence of G. 0 (at specific concentrations) was shown to selectively reduce or eliminate the number of viable L monocytogenes cells from a range of media including ileostomy fluid whilst allowing natural intestinal bacteria to proliferate. This was in addition to an antagonistic (biocidal) effect on L nwnocytogenes ofnatural intestinal microflora and to some extent of non-cellular components of ileostomy fluid. 10) Individual dialkylsulphides (DMD, DMT, DAS and DADS), were shown to possess bacteriostatic and bacteriocidal activity. Comparison of the effectiveness with that of G. 0 indicated that alone these sulphides do not fully account for the high antimicrobial activity of G. O. 11) The effect of G. 0 on two enzymes (ADH and LDH) was tested. It was shown that lower G. 0 concentrations were required to inhibit ADH and LDH activity (0.00 13 and 0.0027mg/ml respectively) as compared to the inhibition of cellular growth (0.0 1- 5.5mg/ml), suggesting that cellular target sites are less sensitive to G. 0 than these two enzymes. 12) Progress in elucidation of the mode of antimicrobial action of GO was provided by the following areas: A) G. 0 sulphides are antimicrobial components; B) action on enzymes AND Q SH-groups as target sites for garlic sulphides. Point Q comes from evidence of a variety of sources including; antimicrobial activity of sulphides, effect of cysteine and tryptone on G. 0 activity and effect of G. 0 and sulphides on SH-enzymes and glutathione studies. 13) Results obtained in this thesis indicated that achievement of microbiostatic and perhaps microbiocidal concentrations of garlic products intestinally may appear realistic. The future potential of the oral consumption of garlic to prevent or overcome foodborne infection is discussed and evaluated.
PublisherUniversity of Wolverhampton
TypeThesis or dissertation
DescriptionA thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy
Except where otherwise noted, this item's license is described as https://creativecommons.org/licenses/by-nc-nd/4.0/