Date of Award

4-2013

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Department

Biological and Pharmaceutical Science

First Advisor

Mr. Brendan Mc Carra

Second Advisor

Dr. Daniel J. Walsh

Abstract

Biochemical analysis of spent Kluyveromyces marxianus yeast confirmed the following composition on a dry matter basis: 43.16 % crude protein, 34.56 % total carbohydrate, 7.02 % RNA, and 13.12 % ash content. Carbohydrate components were shown to consist of 20.97 % β-glucan, 9.76 % mannan and 1.21 % chitin while protein characterisation confirmed this yeast’s protein to be a good source of essential amino acids. Total nitrogen, α-amino nitrogen, and descriptive sensory analysis was carried out on yeast extracts derived from yeast autolysis processes carried out at different pH and temperature values. Yeast extract obtained at 50ºC, pH 7.0 was the most sensory acceptable with significantly higher savoury attributes than other extracts.

Phosphorylation of yeast protein led to a reduction in nucleic acid content (55%) of yeast protein concentrates with an appreciable increase in protein extraction (10%) from yeast extract. The phosphorylated yeast protein produced was rich in essential amino acids except for sulfur containing amino acids.

Enzymatic digests of phosphorylated yeast protein using pepsin, pancreatin, and papain resulted in angiotensin-I-converting enzyme inhibitory indices within the range of 54 - 62 %. Of all the hydrolysates tested, the 26 % DH pepsin generated hydrolysate demonstrated greatest ACE inhibitory potency with a measured IC50 value of 1.38 mg/mL. Further purification of pepsin digested yeast protein resulted in a peptide mixture with IC50 value of 19.31μg/mL. This inhibitory activity was comparable to values reported for a variety of ACE inhibitory food protein hydrolysates. The peptide content of this potent fraction was characterized by electrospray LC-MS-MS and resulted in large numbers of peptides with peptide sequence shown to have amino acid residues and active amino acid motifs that are previously reported in ACE inhibitory peptide.

Yeast cell wall extracts that retained their native structure were enzymatically processed to produce different soluble β-glucan preparations. The cell wall preparations obtained were assessed for their immunomodulatory activity using both in vitro murine J774.A1 cell line and ex vivo human whole blood assays models. This study showed that cell wall preparations (particulate and soluble glucan) from spent Kluyveromyces marxianus enhanced the production of T helper cell type 1 cytokines under both in vitro and ex vivo conditions. This indicated that cell wall preparations from Kluyveromyces marxianus may enhance the protective Th1 mediated innate immune responses in both in vitro mammalian cell line and ex vivo human whole blood assay model. Simple chemo-enzymatic treatments of yeast cell wall also resulted in protein enriched secondary yeast extracts from cell wall waste.

This study has shown that recovery of functional and bioactive extracts from spent yeast waste presents opportunities to innovate, add value and provide a more sustainable approach to better utilisation of Irish food industry waste streams. Such an approach is one step closer towards an amelioration of the economic and environmental problems facing the Irish food industry today.

Access Level

info:eu-repo/semantics/openAccess

Project Identifier

info:eu-repo/grantAgreement/HEA/TSR Strand 1//IE//

Coverage

August 2024

Download

Share

COinS