1. Optimisation of Kernel Storage
Parameters and the Prediction of Shelf
Life for South African Macadamia Kernel
M.G. Penter, F.J. Kruger and A.D. Sippel
Agricultural Research Council - Institute for Tropical and Subtropical Crops
P/Bag X11208, Nelspruit, 1200, South Africa

2. Background
South African Industry
Export value for 2011
$ 103 660 000
R850 000 000
Slide Compliments of Rudolf Badenhorst

3. Background
Slide Compliments of Rudolf Badenhorst

4. Background
Slide Compliments of Rudolf Badenhorst

5. Background
SA Macadamia Tree Age Distribution (%)
13.4
18.8
0 - 5 yrs
6 - 10 yrs
> 11 yrs
31.5
Unknown
36.3
Slide Compliments of Andrew Sheard

6. Background
2012 2017 2022
34 500 t 41 800 t 50 000 t ?
Slide Compliments of Derek Donkin

7. Introduction
• Consequences of rapid industry growth include:
– NIH spending longer periods on the ground
– NIS being held on farm for longer periods
– NIS being held longer at processors
– Extended harvesting season (‘Beaumont’)
– Processed kernel being held for longer periods

8. Introduction
• Industry needs information:
– Extended shelf life (optimised storage)
– Accurate sell-by dates
– Export kernel required to have peroxide <
3meq/kg

9. Quality parameters
• Peroxide
• Breakdown products of peroxides

10. Peroxide production

11. Factors promoting peroxide formation
• Oxygen
• Lipoxygenases
• Light
• Metals (iron, manganese, copper)
• Water
• Heat
• Time (maturity, NIS holding period)
• Oil exposure to oxygen

14. Storage trials
• Procure commercially packed kernel (nitrogen
flushed, vacuum packed, 5.68kg)
• Examine the effect of:
– Storage period
– Storage temperature
– Style
– Seasonality
• Use peroxide analysis to monitor quality (react
with iodide, titrate iodine with Na2S2O3)

15. Early season Mid season Late season
-5C RT -5C RT -5C RT
5C 15C 5C 15C 5C 15C
6, 12, 18, 24 months 6, 12, 18, 24 months 6, 12, 18, 24 months
0, 2, 4, 6, 8, 12, 16, 20 weeks on shelf 0, 2, 4, 6, 8, 12, 16, 20 weeks on shelf 0, 2, 4, 6, 8, 12, 16, 20 weeks on shelf
Peroxide analysis Peroxide analysis Peroxide analysis

16. Early season kernel stored 6 months
14
12
10
Peroxide value (meq/kg)
8
6
4
2
0
E 6m 0w E 6m 2w E 6m 4w E 6m 6w E 6m 8w E 6m 12w E 6m 16w E 6m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

17. Mid season kernel stored 6 months
14
12
10
Peroxide value (meq/kg)
8
6
4
2
0
M 6m 0w M 6m 2w M 6m 4w M 6m 6w M 6m 8w M 6m 13w M 6m 16w M 6m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

18. Mid season kernel stored 6 months
14
12
10
Peroxide value (meq/kg)
8
0.24
0.12
0.12
6 0.12
12.83
0.12
4
2
0
M 6m 0w M 6m 2w M 6m 4w M 6m 6w M 6m 8w M 6m 13w M 6m 16w M 6m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

19. Late season kernel stored 6 months
14
12
10
Peroxide value (meq/kg)
8
6
4
2
0
L 6m 0w L 6m 2w L 6m 5w L 6m 8w L 6m 12w L 6m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

20. Late season kernel stored 6 months
14
12
10
Peroxide value (meq/kg)
8 2..51
9.73 0.25
0.25 7.14
0.37 0.87
3.25 0.12
6 7.99 5.12
7.60
4
2
0
L 6m 0w L 6m 2w L 6m 5w L 6m 8w L 6m 12w L 6m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

21. For kernel stored 6 months
• Ambient temperature not sufficient for late
season kernel – requires storage temperatures
of 15˚C or less
• Data variability is of concern – arises from
small quantities of poor kernel in otherwise
good batches

22. Early season kernel stored 12 months
14
12
10
Peroxide value (meq/kg)
8
6
4
2
0
E 12m 0w E 12m 2w E 12m 4w E 12m 6w E 12m 8w E 12m 12w E 12m 16w E 12m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

23. Mid season kernel stored 12 months
14
12
Peroxide value (meq/kg)
10
8
6
4
2
0
M 12m 0w M 12m 2w M 12m 4w M 12m 6w M 12m 8w M 12m 12w M 12m 16w M 12m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

24. Late season kernel stored 12 months
16
14
12
Peroxide value (meq/kg)
10
8
6
4
2
0
L 12m 0w L 12m 2w L 12m 4w L 12m 6w L 12m 8w L 12m 12w L 12m 16w L 12m 20w
-5˚C S1 -5˚C S5 5˚C S1 5˚C S5 15˚C S1 15˚C S5 Ambient S1 Ambient S5

25. For kernel stored 12 months
• Style 5 is of concern, particularly at ambient
temperatures
• Late season style 5 at all temperatures except -
5˚C approach 3meq/kg after 5 months on the
shelf
• Style 5 to be consumed within 3 months of
repacking or held below 0˚C if longer shelf life is
required
• Mid season kernel appears to be of better quality
than early or late season kernel

26. Early season kernel stored 18 months
12
10
Peroxide value (meq/kg)
8
6
4
2
0
E 18m 0w E 18m 2w E 18m 5w E 18m 8w E 18m 12w E 18m 16w E 18m 20w
-5C S1 -5C S5 5C S1 5C S5 15C S1 15C S5 Ambient S1 Ambient S5

27. Mid season kernel stored 18 months
12
10
Peroxide value (meq/kg)
8
6
4
2
0
M 18m 0w M 18m 2w M 18m 4w M 18m 6w M 18m 8w M 18m M 18m M 18m
12w 16w 20w
-5C S1 -5C S5 5C S1 5C S5 15C S1 15C S5 Ambient S1 Ambient S5

28. Late season kernel stored 18 months
12
10
Peroxide value (meq/kg)
8
6
4
2
0
L 18m 0w L 18m 2w L 18m 4w L 18m 6w L 18m 8w L 18m 12w L 18m 16w L 18m 20w
-5C S1 -5C S5 5C S1 5C S5 15C S1 15C S5 Ambient S1 Ambient S5

29. For kernel stored 18 months
• Style 5 again cannot be held at ambient
temperature – not even for mid season harvest
• For both style 1 and 5, 15˚C is inadequate for
storing late season kernel if 5 months shelf life
is required in retail packs

30. Predicting shelf life

31. Rancimat
• Also known as:
– Swift test
– Accelerated oxidation test
• Principle:
– At elevated temperatures and oxygen levels, poor
samples with existing oxidative damage will
degrade rapidly

33. Effect of style and harvest time on Rancimat
induction period
50
45
40
Induction period (hours)
35
30
25
20
15
10
5
0
Style 1 Style 5 Style 1 Style 5 Style 1 Style 5
Early season Mid season Late season
Style and harvest timing

34. Rancimat
• The rancimat test predicts:
– Kernel quality and shelf life declines as season
progresses
– Style 5 has lower storage potential than style 1
• Is this prediction accurate?

35. Conclusions
• Style 5 kernel has lower storage potential than
style 1 kernel (assume this applies to all styles
with fractured kernel
• For vacuum packed bulk kernel:
– For storage periods of up to 12 months, ambient
temperature is not suitable
– For storage periods of 18 months temperatures of
15˚C may not be adequate

36. Conclusions
• Kernel quality declines as season progresses
and there may be small quantities of poor
kernel in early season batches
– Is there old kernel picked up in the early season?
– Is late season kernel spending longer on the
orchard floor / drying bins?
• Rancimat may be able to predict shelf life –
further work required to correlate induction
times and shelf life

37. Thank You
• SAMAC
• ARC
• Bioservices cc
• Elvis Nkwana and Yvonne Nxundu