Actinidin : the predominant protease in kiwifruit : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Food technology at Massey University, Manawatū, New Zealand
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Date
2016
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Massey University
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Abstract
Kiwifruit protein (actinidin) has been widely known as a protease. Kiwifruit
protein has the potential of utilization in food industry as an enzyme that aids food
digestion.
In this project, the soluble kiwifruit proteins were extracted from fresh Hayward
and SunGold kiwifruit. Soluble kiwifruit proteins were analysed by the
Hartree-Lowry method, SDS-PAGE, enzyme activity determination,
ion-exchange chromatography and mass spectrometry. Anti-actinidin antibodies
were raised by the injection of purified actinidin into rabbits. The main soluble
kiwifruit protein was recognized by anti-actinidin antibodies using Western blot.
Moreover, the effects of post-harvest storage on protein content, total enzyme
activity and specific enzyme activity were investigated. Comparable studies on
both Hayward and SunGold kiwifruit were also carried out in this project.
The results showed that Hayward and SunGold kiwifruit had a similar protein
content. However, the total enzyme activity of Hayward kiwifruit was about 8
times higher than that of SunGold kiwifruit. The protein with enzyme activity
(active actinidin) had a molecular weight of about 27 kDa according to
SDS-PAGE and was one of main soluble proteins in Hayward and SunGold
kiwifruit. This protease was purified from fresh kiwifruit by anion-exchange
chromatography. A polyclonal antibody against actinidin was successfully
generated in a rabbit using purified actinidin. Protein with a molecular weight of
27 kDa was recognized by the anti-actinidin antibodies. Post-harvest storage at 1
°C for up to 12 weeks significantly increased the total and specific enzyme
activities of SunGold kiwifruit (P<0.05). By contrast, the total and specific
enzyme activities of Hayward kiwifruit had a significant decrease after 16 weeks’
storage (P<0.05). Hayward kiwifruit had no significant changes in protein content
after storage (P<0.05) while the protein content of SunGold kiwifruit fluctuated in
a range from 5.04 to 5.84 mg/mL during post-harvest storage.
This study may help to understand the nature of kiwifruit proteins with enzyme
activity, which contributes to a full understanding of the health benefits of
kiwifruit.