Date of Award
Doctor of Philosophy
Dr Rosemary Rea
Dr Helena Stack
Enterococci are lactic acid bacteria (LAB) that have the paradoxical position of possessing biochemical properties of technological importance, but are also considered as opportunistic pathogens capable of causing infection in immunocompromised patients. However, they have a long history of safe use in foods and have been evaluated in several studies for their role as starter, adjunct, probiotic and protective cultures. They show higher proteolytic activities than other LAB and have demonstrated the ability to produce bioactive peptides during the fermentation of milk. The aim of this project was to identify proteolytic Enterococcus faecalis isolates capable of generating health-promoting bioactive peptides during the fermentation of bovine skim milk. Twenty-five E. faecalis strains were isolated using Kanamycin Skim Milk Aesculin Azide (KSMEA) agar, a selective and differential growth medium developed in this work for the isolation of proteolytic enterococci. The isolates were assessed for proteolytic activity and putative pathogenic traits to assess their suitability for use in milk fermentations. E. faecalis DPC5154 proved the most promising strain, demonstrating the highest level of proteolytic activity, sensitivity to all eleven antibiotics used and harboured few virulence determinants. The DPC5154 milk fermentate displayed the highest antioxidant, angiotensin converting enzyme inhibitory (ACEI) and α-glucosidase inhibitory (α-GI) activity. Further analysis of the DPC5154 fermentate by RP-HPLC and mass spectrometry resulted in the identification of three β-casein-derived peptides: IPPLTQTPVVVPP, VLPVPQK and AVPYPQR. These peptides were chemically synthesised for assessment of the aforementioned bioactivities in vitro. All three peptides displayed ACEI (IC50 = 523.8, 776.9 and 387.60 μM, respectively), antioxidant and α-GI activity (IC50 = 62.32, 61.78 and 60.77 mM, respectively). This work is the first to report on the multifunctional bioactive properties of these three peptides which could be further developed as food ingredients for the production of functional foods and nutraceuticals to improve human nutrition and health.
Graham, Kenneth Patrick, "Isolation, identification and characterisation of Enterococcus faecalis isolates for the generation of multifuctional bioactive peptides from milk" (2019). Theses [online].
Available at: https://sword.cit.ie/allthe/38
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