Isolation and characterisation of bioactive peptides derived from milk and cheese

Abstract

This research investigated the presence of antimicrobial, antihypertensive and antioxidant peptides derived from fermented milk protein, hydrolysed milk protein as well as various Cheddar cheese peptide extracts. In Chapter one, the introduction and literature review, background information on known bioactive peptides are given. Bioactive peptides are specific fragments of protein that have a positive impact on health. They can be derived from fermentation and/or hydrolysis of protein and have been shown to have various properties including antimicrobial, antihypertensive, antioxidant, immunomodulatory, mineral-binding and opioid. Currently, the reported literature has identified bioactive peptides obtained from fermented milk protein predominantly by Lactobacillus helveticus and this research studied the use of other probiotic bacteria to derive bioactive peptides. Similarly, the previous literature has investigated the presence of bioactive peptides after hydrolysis using digestive enzymes such as trypsin, chymotrypsin (rennin) and pepsin. This study used enzymes derived from various plant and animal sources to hydrolyse milk protein and then investigated if any bioactive peptides have been obtained. Also, the literature on bioactive peptides derived from cheese is minimal therefore the presence of bioactive peptides in five Australian Cheddar cheeses was investigated. The literature pertaining to bioactive peptides derived from milk via hydrolysis using digestive enzymes is vast and shows the variety of peptides that can be derived when milk is used as the substrate. This food has been shown to contain the most active and potent bioactive peptides to date particularly antihypertensive peptides. The discovery of novel bioactive peptides could potentially lead to the production of functional foods containing bioactive peptides or as use as food ingredients in various food substrates. The general screening process included screening of the whole extracts, then the most bioactive extracts were separated by centrifugation using molecular-weight cut-off (MWCO) membranes (5 kDa and 10 kDa) and subsequently the most bioactive samples were fractionated by RP-HPLC, if deemed appropriate. The extracts were screened for antioxidant activity against the free radical DPPH, antimicrobial activity against three bacteria: E. coli, B. cereus and S. aureus and ACE-inhibitory activity against the angiotensin-I-converting enzyme (ACE).

Date of Award	2012
Original language	English