Dr Carlene Starck, Postdoctoral Research Fellow at Riddet Institute, New Zealand: http://www.kiwifruitsymposium.org/presentations/kiwifruit-and-digestive-comfort-in-vitro-and-in-vivo-supporting-evidence/ Presentation at the 1st International Symposium on Kiwifruit and Health. Kiwifruit (Actinidia deliciosa) hosts a number of beneficial properties for gut health. In addition to its high fibre content, water holding capacity and levels of the vitamins C and E, its consumption has been reported to provide relief of symptoms of gastrointestinal discomfort.

1. Kiwifruit and digestive comfort:
In vitro and in vivo supporting evidence
Dr Carlene Starck
Riddet Institute, New Zealand

2. Kiwifruit and
digestive comfort:
In vitro and in vivo supporting evidence
Carlene Starck, PhD
Riddet Institute
Massey University
Palmerston North

3. Dr Carlos Montoya
Riddet Institute
Dr Sharon Henare
Riddet Institute
Dr Lovedeep Kaur
Riddet Institute
Distinguished Prof Paul Moughan
Riddet Institute, Co-director
Dr Mike Boland
Riddet Institute Assoc Prof Shane Rutherfurd
Riddet Institute

4. 1. stomach
2. small
intestine
3. large
intestine
Digestive comfort = digestive health
4. rectum
4-8 hours
18-64 hours
Laxation
Functional gut
‘motor’ for optimal
transit time
Stool characteristics
Guttransittime
Digestion
Enzyme function
Microbiota
Gut physiology

5. 1. stomach
2. small
intestine
3. large
intestine
Optimal laxationEfficient digestion
What does digestive health ‘look like’?
4. rectum
Guttransittime
*Optimal transit
time - absence of both
constipation and diarrhea
*Microbiota
- healthy composition of
gut bacteria and their
metabolites (SCFAs)
* Healthy
mucous layer
(gut lining)
*Comfort
- absence of bloating,
pain and excessive
flatulence
*Soft, bulky stool
*Frequent bowel
movements
How does
kiwifruit promote
these outcomes?

6. Kiwifruit are well-known to promote laxation
Three clinical trials:
As well as the
preliminary results
you just heard aboutRush et al 2002
Chan et al 2007
Chang et al 2010
What are the mechanisms?
And what about digestion?

7. Model systems to investigate the effects of kiwifruit components on digestive health:
Mimics the chemistry of human
digestion (37°C):
Phase 1. Stomach
- Simulated juice with
pepsin, pH = 2, 30 mins
Phase 2. Small intestine (ileal)
- Simulated juice with
pancreatin, pH = 8, 120
mins
In vitro
The growing pig
(25-60 kg)
Best model of human upper
tract digestion
Meal-eating omnivore
In vivo
Rat
Easy and inexpensive to
raise although digestive
system has some
differences to human

8. Laxation effects are generally attributed to fibre
High proportion of fibre:
= 2-3 % of fresh weight
green > gold
Both insoluble (eg. cellulose)
and soluble (eg. pectin) fibre:
- ratio is 3:1
Reduced diffusion and
mixing
- Metabolic health benefits (Session
3 tomorrow)
Hydration properties:
- Swelling
- High water holding capacity
Bacterial fermentation and production
of short-chain fatty acids (SCFAs)
Undigested fibre
increases bulk of
stool

9. Water holding capacity
(amount of water bound tightly to the fibre)
Swelling
(volume occupied by fibre)
* Undigested fibre adds bulk to the stool
Sims and Munro (2013) Adv Food Nutr Res. 68:81-99
Improve laxation

10. Kiwifruit fibre is a prebiotic and is fermented to short-chain fatty acids:
Prebiotics selectively promote the growth of ‘good’ bacteria in the colon,
such as Lactobacilli and Bifidobacteria.
The gut microflora have a key role in digestive health through the
development and promotion of gastrointestinal motor function.
The intestinal microflora ferment dietary fibre to produce a number of important
compounds, such as short-chain fatty acids (SCFAs) and polyphenol metabolites.
 SCFAs may stimulate the gut ‘motor’
+ Important fuel for colon cells and other ‘good’ bacteria.
 Polyphenols may inhibit the growth of unwanted bacteria
A number of studies have demonstrated an association between gastrointestinal
disorders such as IBS and a microbial imbalance in the intestine

11. Kiwifruit fibre is a prebiotic and is fermented to SCFAs:
Parkar et al (2012) Plant Foods Hum Nutr. 67: 200-207
Kiwifruit fibre:
- Increases the growth of ‘good’ bacteria (vs negative
control)
- Fermented for production of SCFAs butyrate, acetate
and propionate
Butyrate suggested to promote motor
function via stimulation of the gut’s nervous
system
* *
*

12. Polyphenols in kiwifruit may inhibit pathogenic bacterial growth:
Kiwifruit contain a number of
polyphenols that have been
shown to inhibit the growth of
pathogenic bacteria in isolation.
Salmonella typhimurium
A healthy digestive system requires both growth of ‘good’ bacteria
as well as the prevention of growth of ‘bad’ bacteria

13. Kiwifruit fibre may also stimulate mucin production in the stomach and duodenum:
The mucous layer (complex mixture of mucins, bacteria + other material) sits on
the gut wall between the inside of the gut and the host
= is the front line of defence from environmental pathogens.
Influence on Muc5AC mRNA:
P = 0.067
Increase in Muc1 mRNA:
P < 0.05
 Growing pigs fed increasing
amounts of green kiwifruit
(control = 0%)
 Measured mucin production
and gene expression in:
- Stomach
- Small Intestine
- Colon
 Function depends on thickness and the rate it can be replenished (mucin production).
 A damaged mucous layer is associated with a number of colonic diseases, such as IBD.
Moughan, PJ et al (2013). Adv Food
Nutr Res. 68:169-851
Possible mechanisms:
Directly: abrasive effect (mucin turnover)
Indirectly: gut bacteria play a role in maintaining the mucous layer
Further research is currently underway

14. Other components of kiwifruit may also affect mucin production:
actinidin, polyphenols and raphides
Actinidin
- Protease (enzyme
that digests protein)
- may enhance the
natural proteolytic
degradation of the
mucous layer
→ greater production
of mucin
Like fibre,
polyphenols
modulate the
gut microbiota
Raphides
– small insoluble needle-
shaped calcium oxalate
raphide crystals
– may have a stimulatory
effect on mucin production

15. Fibre cannot take all the credit for laxation nor the
additional digestive health benefits of kiwifruit
Actinidin
protease
Other bioactives
‘KISSPER’
Polyphenols
Green kiwifruit (Hayward)
contains the protease
actinidin (285 units/gDM).
Sungold = about 26%
of the level in green.
Original gold (Hort 16A)
= no actinidin.
Raphides
Preliminary in vitro
research suggests a
role in contractions
of the gut through
ion channeling
activity.
Ciardiello et al. (2008). J
Peptide Sci. 14:742-754.
Negative control: comparable composition
to green kiwifruit minus actinidin

16. Actinidin: History
The presence and activity of a protease in kiwifruit had been known
anecdotally for many years.
 Jelly (gelatin) would not set if kiwifruit was added.
 Kiwifruit placed on meat has a marked tenderising effect.
Then:
1959 – Arcus (Otago Medical School)
 Presence of a proteolytic enzyme in “Chinese gooseberries” & named it “actinidin” -
hydrolyses several proteins (incl. haemoglobin, gelatin and whole milk)
1970s – McDowall (Australia)
 Purified the enzyme and showed details of hydrolysis of insulin (as a model protein)
1970s - Massey University
 Details of the specificity, mechanism of action and structure of actinidin

17. Efficient protein digestion → health and digestive comfort
17
 Meals high in protein can contribute to
gastrointestinal discomfort.
 Dietary proteases may assist with efficient protein
digestion and therefore may enhance digestive
comfort.
Does kiwifruit have a role in protein digestion in the
stomach and small intestine?
Comprehensive series of in vitro and in vivo experiments designed
and carried out

18. The digestion of food proteins was measured with and without a green kiwifruit extract:
Dietary protein Gastric phase
(stomach)
+ actinidin
Gastric and
small intestine
+ actinidin
Casein
(main protein in milk)
 
Meat protein  
Soy Protein  
Whey protein  
Zein (corn)  
Gelatin  
Gluten and gliadin
(main proteins in wheat)
 
1. In vitro: Actinidin enhances gastric and small intestine protein digestion
Casein
Casein +Pepsin
Casein +Pepsin +Act
‘SDS-PAGE’
Kaur et al. (2010) J. Agric. Food Chem. 58(8): 5068–5073
Kaur et al. (2010) J. Agric. Food Chem. 58(8): 5074–5080 Digestion enhanced compared to no kiwifruit control
 No enhancement of digestion compared to no kiwifruit control

19. Rats were fed diets containing specific proteins, together with either green (Hayward) or Gold (HORT
16A) kiwifruit.
19
↑
+35%
↑
+60%
↑
+27%
↑
+29%
No effect
2. In vivo (rat model):
Actinidin-containing kiwifruit enhances gastric protein digestion
Rutherfurd et al. (2011) 129(4):1681–1689

20. The 27Al peak in the stomach chyme of a
selected rat fed a beef muscle-based diet
supplemented with Hayward kiwifruit.
We use ‘Wide-bore Nuclear Magnetic Resonance’ (NMR) for real-time measurement of
stomach-emptying. 27Aluminium (natural Al isotope) is fed with the meal and detected at
low pH only.
3. In vivo (rat model):
Actinidin-containing kiwifruit enhances stomach emptying
Photos courtesy Drs C Montoya &
J Hindmarsh, Riddet Institute

21. Dietary
Protein
T ½ (mins) P-value
- Act + Act
Beef muscle 260 144 P < 0.05
Gluten 157 151
P > 0.05
Soy PI 189 159
Whey PI 182 185
40
60
80
100
0 25 50 75 100 125 150
Relative27Alconcentration,%
Time after feeding (min)
Beef muscle (with actinidin)
Beef muscle (no actinidin)
T1/2 = time required for half the stomach contents to be emptied
Smaller T1/2 = faster stomach emptying rate
An increase in stomach emptying rate by
actinidin may be related to the effects of
kiwifruit on gut transit time. Montoya et al. (2014) J Nutr. 144(4):440-6.
*

22.  Gastric digestion was increased
significantly when green kiwifruit were
consumed with meat
≈ 50% ↑ in digestion
 Stomach emptying rate was faster when
green kiwifruit were consumed with meat
≈ 20% ↓ in T1/2
Pigs were fed diets containing beef-muscle
protein, together with either green
(Hayward) or gold (HORT 16A; no actinidin)
kiwifruit.
4. In vivo (growing pig model):
Actinidin-containing kiwifruit enhances protein digestion and stomach emptying
Green KF (+ actinidin) Hort 16A KF (- actinidin)
Like human digestive enzymes, actinidin is
active at low pH over the time course of
normal digestion.
Montoya et al. (2014) British Journal of Nutrition. 111: 957-967

23. 10 healthy adult males:
 Aged 21-48 years
 67-106 kg
 BMI 21 – 29
Gearry et al. (unpublished)
6. Human clinical trial
Actinidin contributes to gastric comfort after a high protein meal:
Test meals:
 400g lean steak +200g Green (+ actinidin)
 400g lean steak + 200g Hort16A Gold
(- actinidin)
Results:
For all measures of gastric comfort (pain in upper abdomen, rumbling
in stomach, bloating, belching, and flatulence):
Green kiwifruit (+ actinidin) → less symptoms reported
Reported bloating was significantly less when the subjects ate green
kiwifruit (+ actinidin) with their protein meal (p = 0.026)

24. 1. stomach
2. small
intestine
3. large
intestine
How does kiwifruit impact digestive comfort?
4. rectum
4-8 hours
18-64 hours
Laxation
Functional gut
‘motor’ for optimal
transit time
Stool characteristics
Guttransittime
Digestion
Enzyme function
Microbiota
Gut physiology

25. Actinidin
↑ Protein
digestion
Stomach
Emptying Rate
WHC,
swelling
Bulking
Microbiota
SCFAs
Polyphenols
1. stomach
2. small
intestine
3. large
intestine
4. rectum
Guttransittime
Fibre
Mucous layer
Raphides
Mechanisms underlying benefits of
kiwifruit for digestive health and comfort:
Supported by experimental
evidence
Requires further investigation
KEY:
Component of kiwifruit
Mechanism

26.  Kiwifruit is well-known to
promote laxation
 Fibre is only one part of the laxation
story
 Beyond laxation, there are many other
digestive health and comfort benefits, including protein digestion,
prebiotic activity and mucin production
Take Home Message:
Cutting-edge in vitro and in vivo evidence shows that
kiwifruit enhances digestive health and comfort

27. Acknowledgements
The Zespri Scientific Research Strategic Advisory (SRSA) Board especially:
Lynley Drummond
Drummond Food Science Advisory
Juliet Ansell
Zespri
Zespri Ltd for supply of fruit and funding.