Beef hydrolysis by Zyactinase™ enzymes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Auckland, New Zealand.
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Date
2016
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Massey University
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Abstract
Protein hydrolysis is the term that applies to all possible ways of splitting proteins to
produce products with lower molecular weight. There is a continuous search for novel
products derived from waste materials. In the developed nations considerable amount
of meat off-cuts are discarded each year. Utilizing these leftovers by developing new
technology for protein recovery and modification and production of a broad spectrum of
food ingredients greatly enhances its final value.
The aim of this research was to partially hydrolyse beef meat protein with a commercial
kiwifruit product called ZyactinaseTM, which is essentially freeze-dried kiwifruit to
determine the effect of various processing conditions that influence the extent of beef
meat hydrolysis. Secondly to determine the peptide and amino acid profile of the beef
meat sample after hydrolysis. Thirdly to determine the relative reaction of ZyactinaseTM
on various beef meat protein fractions. This study also aimed to evaluate the rate and
the extent of partial enzymic hydrolysis of lean beef using ZyactinaseTM enzymes in
order to obtain a better understanding of protein hydrolysis reaction.
Lean beef minced was partially hydrolysed using the Zyactinase enzymes for different
processing times (up to 360 minutes), temperatures (27°C to 70°C) and varying
enzyme concentrations. No pH adjustment on the raw material was carried out except
for pH studies. The hydrolysates were collected and analysed for total nitrogen content
and degree of hydrolysis. The method used to characterize the extent of protein
hydrolysis was SN-TCA index (fraction of nitrogen soluble in trichloroacetic acid) also
called non-protein nitrogen NPN. Peptide and amino acid in protein hydrolysates were
analysed by HPLC and different protein fractions in the hydrolysates were
characterised by SDS-PAGE.
The relationship between the reaction temperature, enzyme concentration and
processing time to the total nitrogen and NPN were determined. The total nitrogen
content remained relatively constant throughout the hydrolysis process. In addition, the
NPN content increased as the temperature, processing time and enzyme concentration
increased. The optimum pH range for the enzyme’s activity was 4 – 5.6 and optimum
temperature was 60°C. Furthermore, most of the higher molecular weight protein
bands on SDS- PAGE disappeared after hydrolysis and lower molecular weight protein
bands increased in intensity. Zyactinase was also found to digest protein in the
myobrilla and sarcoplasmic meat fractions at similar rates as whole beef meat.
The results provide basic understanding of the kiwifruit enzymes action toward protein
that may lead to improved methods for recovering meat protein or developing new food
materials.
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Keywords
Beef, Protein hydrolysates, Hydrolysis, Hydrolases, Research Subject Categories::TECHNOLOGY::Chemical engineering::Food technology