Thirsty vines Summer girdling Compost teas Organic marketing The ...

Gold kiwifruit jellies - the perfect setting
Ross Atkinson, HortResearch - Mt Albert, Auckland
Figure 1: Jellies set perfectly when they contain pieces of ZESPRI GOLD fruit (Gold) or contain no fruit (Control). Jellies fail to set when they contain ZESPRI
GREEN fruit pieces (Green). Photo credit: Tim Holmes
You can’t add fresh kiwifruit to a jelly and
have it set – at least that’s what your
grandmother used to say - and that’s
certainly true for jellies made with the
traditional ZESPRI GREEN kiwifruit. The
reason the jellies won’t set is the presence
of an enzyme in the fruit called actinidin.
The actinidin enzyme breaks down the
gelatine that holds the jelly together.
Recently scientists at HortResearch (funded
by the New Zealand Foundation for
Research Science and Technology) showed
that ZESPRI GOLD kiwifruit contain less
than one per cent of the actinidin enzyme
found in ZESPRI GREEN kiwifruit [1]. This
means jellies made with fresh ZESPRI
GOLD Kiwifruit set perfectly every time
(Figure 1).
WANT TO TENDERIZE THAT
STEAK?
The actinidin enzyme, abundant in ZESPRI
GREEN kiwifruit, affects fruit processing
characteristics and their healthful properties.
Actinidin is responsible for the meat
tenderizing properties of kiwifruit. The
enzyme breaks down the links between
proteins in muscle allowing the fi bres to
move apart. Actinidin is quite selective in
the type of muscle fi bre proteins it will
attack. Although other enzymes (e.g. papain
from papaya) can do the same job – they
tend to over-tenderize the surface,
producing a mushy texture [2].
LOVE IT OR HATE IT?
Actinidin has benefi cial effects on human
health. It is purifi ed from kiwifruit to make
digestive aids such as Zyactin. The actinidin
enzyme in these products helps to improve
the breakdown of food protein into peptides
and amino acids, promoting healthy
digestive function. However, actinidin has
also received some bad press, as it may
potentially cause an allergic reaction in
some sensitive people (http://www.
zesprikiwi.com/allergies.htm).
WHEN AND WHERE IS ACTINIDIN
FOUND IN FRUIT?
HortResearch scientists have found that
actinidin levels increase throughout fruit
development, peaking at harvest, then
decrease as fruit ripen [1]. They have also
looked to see where the actinidin enzyme
was found in the four distinct zones of the
fruit: core, fl esh, area around the seeds, and
peel. Actinidin was present in all four tissue
zones in ZESPRI GREEN kiwifruit, with the
highest levels in the fl esh (Figure 2). In
ZESPRI GOLD kiwifruit, actinidin was only
found at low levels around the seeds.
Interestingly, actinidin levels in many other
gold fruit from Actinidia chinensis breeding
populations are similar to those in ZESPRI
GREEN fruit [1, 2].
WHAT’S IN IT FOR THE PLANT?
Why kiwifruit plants make so much actinidin
is something of a mystery but high levels of
similar enzymes are also found in other fruit
e.g. papain in papaya and bromelain in
pineapple. One possibility is that actinidin
might act as a store of protein in the fruit.
Both sugar and protein attract animals (and
human consumers!) to the fruit, which
helps the plant to disperse its seeds.
Another possibility is that actinidin is
involved in defence against insects or fungi.
HortResearch scientists have recently
NZ KIWIFRUIT JOURNAL JANUARY / FEBRUARY 2008
49