A brief overview on preservation of nuts using modern techniques.

1. PRESERVATION OF
NUTS:
SCIENCE &
BY: PRATHAMESH
KUDALKAR
13FET1011
GUIDE: PROF. SMITA
LELE

2. INTRODUCTION
A nut is a fruit composed of a hard shell and a seed, which is
generally edible.
Most of the products we call nuts are not nuts in botanical
sense.
Tree nuts have become increasingly popular as a component of
healthy diets throughout the world.
Nuts are associated with a reduction in the risk of heart disease
and have been shown to contain high levels of antioxidants.
The United States leads the world in tree nut production with
2.4 million tons of in-shell nuts produced during 2010.
Due to their exclusivity, nuts are highly valued agricultural
products.
Almonds Walnuts Cashew Peanut
Price/kg (Rs) 1200-1400 1400-2000 1100-1400 150-200

3. STRUCTURE OF NUTS

4. COMPOSITION OF NUTS
Amount/100g Almonds Cashew Walnut Peanut
Energy (kcal) 576 553 654 570
Total Fat (g) 49 44 65.2 48
Saturated Fat (g) 3.7 7.8 6.1 7
PUFA (g) 12 7.8 47 24
MUFA (g) 31 23.8 9 16
Carbohydrates (g) 22 30 13.8 21
Dietary Fiber (g) 12 3.3 6.7 9
Protein (g) 21 18.2 15.2 25
Calcium (mg) 264 37 98 62
Magnesium (mg) 268 292 158 184
Iron (mg) 3.72 6.68 2.91 2
Water 4.7 5.2 4.07 4.26
*All values from USDA Database

5. FACTORS RESPONIBLE FOR
SPOILAGE IN NUTS
Spoilage
of Nuts
Pests
Microbial
growth and
toxin
production
Lipid
Oxidation

6. PESTSA destructive insect or other animal that
attacks crops, food, livestock, etc. is termed
as a pest.
Field Pests
Storage
Pests
Don’t multiply
during storage
Multiply during
storage
Indianmeal moth
Almond moth
ExcretaEggs
Larvae
Pin
holes
Webbin
g
Beetles
Navel orangeworm
Codling moth
Borer Microorganism
s

7. PESTS
Type Pest Nuts Adverse Effects References
Field Navel
orangewor
m
walnuts,
almonds,
pistachios
Deposit eggs, hatched
larvae feed directly on
nutmeats, increased
aflatoxin levels
Campbell et
al (2002),
Johnson
(2013)
Codling
moth
walnuts Larvae bore into nuts
and deposit feces
Strand
(2003),
Johnson
(2013)
Peach twig
borer
Almonds Larvae feeds on
nutmeat
Strand
(2002),
Johnson
(2013)
Storag
e
Indianmeal
moth
All nuts Larvae can enter
through cracks and
holes as small as 0.4
mm, contamination of
the product with silk,
Johnson
(2013)

8. LIPID OXIDATION
Mechanism
Initiation: It is the step in which free radicals react
with Fatty acids to produce lipid radical. Reactive
oxygen species are the most common initiators.
Propagation: Lipid radical reacts with oxygen to
form lipid peroxyl radical. This radical is also an
unstable species that reacts with another free fatty
acid, producing a different fatty acid radical and a
lipid peroxide, or a cyclic peroxide if it had
reacted with itself.
Termination: The radical reaction stops when two
radicals react and produce a non-radical species.
• More than 80% lipids in nuts are unsaturated.
• Produces undesirable flavours and odours. Loss of
nutrients

9. MICROBIAL SPOILAGE
Mycotoxins
Mycotoxins are toxic secondary
metabolites of filamentous
fungi that can grow and
produce such toxins on a wide
range of food plants.
Aflatoxins are the most toxic
mycotoxins with hepatotoxic,
mutagenic, teratogenic and
carcinogenic effects on humans
and animals.
Aspergillus flavus is the most
prominent microbe producing
aflatoxins.
Conditions: High relative
humidity of around 97-99% and
temperatures between 25-30 °C
Source of contamination: Soil
Pathogens
Pathogens are the disease
causing microorganisms.
Don’t multiply on the
surface of nuts but can
survive.
Cause nausea, vomiting,
stomach cramps,
diarrhea
Microbes: Salmonella
enterica serovar Enteritidis
PT 30, E. coli
Source of contamination:
Soil
Precaution: Pasteurization
to ensure 4-log reduction

10. MICROBIAL SPOILAGE
Aspergillus
species
All nuts Hepatotoxic
aflatoxins,
ephrotoxic
ochratoxins.
Permissible up to
10 μg/kg in EU.
Molyneux
R. J. 2007;
D. Clavel
and C.
Brabet.
2013
Rhizopus
Penicilllium
Salmonella
enterica serovar
Enteritidis PT 30
Almond
s,
Peanuts
Salmonellosis Danyluk,
2005
E. coli All nuts Nausea, vomiting,
stomach cramps,
Danyluk,
2005
Microbe Nuts Adverse
Effects Reference

11. METHODS OF
PRESERVATION
Preservatio
n of Nuts
Chemical
Non-
thermal
Packaging
& Storage
Thermal

12. FUMIGATION
Propylene Oxide
• Flammable liquid
• Boiling Point: 34.238 °C
Mode of action: Propylene
Oxide targets the DNA and
causes alkylation of DNA
guanine, which results in
breaking of DNA strands
Effective against: Pests,
microbes
Result: 5-log reduction of
Salmonella
The U.S. Environmental Protection Agency
(EPA) guidelines:
(i) exposure temperature must not exceed
51.68°C
(ii) exposure time shall be no more than 4
h
(iii) PPO residue in the product shall not
exceed 300 ppm.
Preheating of
Nuts
48°C, 2 days
Vacuum
10 kPa
PPO Spraying
0.5 kg/cu.m
Aeration
Cycles
Tempering
15-18°C, 5
days
Danyluk, 2005

13. EDIBLE COATINGS
Butylated hydroxyanisole (BHA) Butylated hydroxytoluene (BH
BHA & BHT
E320 E321

14. BHA & BHT
• Well known antioxidants
• Found to cause Aspergillus inhibition
at in vitro level (Passone et al.,
2007a).
• Suggested Mechanism: BHA affects
the cell membrane by changing pH
values and affecting transduction
energy and substrate transport.
• Nut tested: In-pod Peanuts
• Level: 1802 and 2204 μg g−1 of BHA
and BHT respectively
• Results: After 5 months, close to 2-
log reduction in Penicillium spp. and
1-log reduction in Aspergillus spp.
was observed.

15. EDIBLE COATINGS
Whey Protein +
Tocopherol
CMC + BHT
• Tested for: Peanuts
• Effective Against: Oxidative
Rancidity
• Principle: Films based on heat-
denatured whey-protein-isolate
(WPI) have been found to be
excellent oxygen barriers.
• Result: Accelerated shelf life
studies estimated shelf life of 330
days at 25 °C
• Tested for: Almonds
• Effective Against: Oxidative
Rancidity
• Principle: BHT is well known
antioxidant. CMC has good film
forming qualities and is a
stabilizer.
• Result: Peroxide Value of coated
sample was found to be half of the
control sample
Constituent %
CMC 0.5
Glycerol 1.7
BHT 0.2
Distilled
Water
97.6
Larrauri et al.,
(2016)
Lee and Krochta,
(2002)
Constitue
nt
% (w/w)
WPI 10
Vitamin E 0.5

16. ORGANIC ACIDS
Principle: Organic acids at high enough concentrations
reduce the pH and bring about changes in protein
configuration leading to cell lysis.
Shelling
Sprayin
g
10% acid
solution (1.6
Air
Drying
2h, 25 °C
Storage
24 °C,3 days
Acetic Acid
Citric Acid
• Safe
• 5-log reduction
of Salmonella
Pao et al., (2006)
• High Cost
• May have an
effect on
product quality

17. STEAM PASTEURIZATION
Steam pasteurization is effective for reducing
naturally occurring and pathogenic bacteria in foods
(Nutsch et al. 1998)
Effective against: Salmonella and other microbes.
Advantages:
Large amount of heat transferred to targeted foods
when steam condenses, increasing the surface
temperature promptly.
It can effectively penetrate cavities, crevices and
feather follicles that may provide protection for
surface-attached micro-organisms.
Process Conditions: Steam valve maintaining 143kPa
constant pressure
Result: 5-log reduction of Salmonella was achieved in
25s.
(Chang, 2010)

18. INFRARED PASTEURIZATIONAdvantages of Infrared
heating:
• High heat transfer coefficients
• Non-chemical method, no
flame
• Easy temperature controlLactic Acid Spray + NIR
Effective Against: Salmonella
spp.
Process Parameters: 10ml 2%
Lactic Acid solution spray+ NIR
(1300nm/ 500W)+ 23 rpm+ 5
min (80 °C)
Results: 5-log reduction of
Salmonella
No effect on sensory
qualities
(Ha and Kang, 2015)

19. INFRARED
PASTEURIZATIONSequential Infrared and Hot Air (SIRHA) Dry
Roasting
Objective: Inactivate Salmonella
Achieve roasted flavor
Process: Infrared Heating [6
min/(11000W/sq.m)]+
Hot Air Roasting(10s).
Temperature: 140°C
Results: 5.8-log Salmonella reduction
Desirable sensory characteristics
40% time reduction
Yang et al. 2010

20. RADIO FREQUENCY
HEATING
Introduction:
Radio-frequency heating is the process of
heating materials through the application of
radio waves of high frequency—i.e., above
70,000 hertz
Working:
In a radio frequency heating system the RF
generator creates an alternating electric field
between two electrodes.
The material to be heated is conveyed between the
electrodes causing polar water molecules in the
material to continuously reorient to face opposite
electrodes.
Friction resulting from this molecular movement

21. RADIO FREQUENCY
HEATING
Almonds Walnuts
Amount 1.7 kg 11 kg
To inactivate Salmonel
la
Pests
Pretreatment Soaking None
Frequency 27 MHz 27.12
MHz
Time 2-4 min 5 min
Temperature 75°C 55 °C
Power 6 kW 25 kW
Electrode Gap 13cm 28cm
Hot Air Yes Yes
Advantages of RF Heating
 Deeper penetration than MW
 Uniformity in heating

22. COLD PLASMA• Cold plasma is a collection of partially ionized gases
considered to be the fourth state of matter.
• Cold plasma can be generated by passing gas between two
electrodes and product can either be placed between the
electrodes to achieve contact with the plasma or the plasma
can be moved to a site distant from the electrodes
Mechanism: Low temperature plasma generates highly reactive
chemical species of molecular oxygen such as ozone, atomic
oxygen, hydroxyl, nitric oxide and super oxide radicals as well as
other free radicals which are the primary agents of antimicrobial
action.
Experimental Results: A 30 s treatment at 30 kV and 2000 Hz
reduced E. coli counts by almost 5 logs.
Advantages: No residues.
Disadvantages: Enhanced lipid oxidation, Nitrogen gas is not as
effective as dry air.
Brendan A. Niemira ,(2012)
Deng, (2007)

23. IRRADIATION
Irradiation is highly effective against pathogenic and spoilage
organisms and insects.
The term ‘food irradiation’ refers to exposure of food to one of three
types of ionizing radiation: gamma rays, X- rays, or electron beams ( β
particles).
The penetration depth for electron beams is lower than that for gamma
rays
Mode of Inactivation:
High energy electromagnetic radiation can directly destroy the
microorganism by damaging the DNA of the microorganism as well as
the cell membrane thus disrupting cellular processes and causing cell
death.
Merits: Can inactivate microorganisms and pests at the same time.
Demerits: Free radicals also react with large molecules such as proteins,

24. IRRADIATION
• D-value of Salmonella Enteritidis
Phage Type PT 30 is around 1.25
kGy.
• 4-log reduction would require 5 kGy
treatment which will make nuts
sensorily unacceptable
Recommended Dosage: 1-1.5
kGy
 D- value of most pests is around
0.2-0.3 kGy
 2-3 log reduction is acceptable as a
part of most quarantine treatments.
Dosage above 3 kGy rendered
almonds unacceptable
Prakash, A, 2010;

25. PACKAGING & STORAGE
Vacuum Packaging
• Most widely used
preservation
technique.
• Objective is to reduce
the oxygen exposure
and inhibit oxidation
and aerobes.
• Shrink film is used to
have a tight fit.
• Retains quality.
MAP
• Modifying the in
package atmosphere
to reduce the
respiration of nuts.
• Carbondioxide also
has antimicrobial
activity.
• Gas Composition:
Cooling
• Reduces the rate of
breathing.
• Microbes are
inactivated at low
temperatures.
•
• Shelf life at 4°C: >
1yr
Gas %
Nitrogen >80
Carbondioxi
de
20
Oxygen <
0.5

26. PACKAGING & STORAGE
Oxygen Absorbers
•Absorbs the headspace oxygen.
•Reduce oxygen levels to less
than 0.1%
•Shelf life: >12 months
•Eg: Silica Gel
Barrier Films
•Polymer films with high oxygen
barrier properties extend the
shelf life.
•Oxygen permeability should be
lesser than 10 cc/sq.m.
•Eg: Polyvinylidiene chloride,
Ethylene vinyl alcohol
Bulk Shipping & Storage
•Vacuum packaging in shrink
wraps.
•These packages are shipped in
enclosed wooden crates or
metal containers.
•Stored in chambers with
controlled relative humidity.

27. Methods for Preservation of Nuts
Process Type Treatment Nuts Effective Against Features References
Chemical Propylene
Oxide
Fumigation
Almonds,
Walnuts
Salmonella, yeast,
bacteria, mold, pests
Concentartion:0.5
kg/m3 for 4 h in
Chamber, 5 days
storage, Batch Process,
<300 ppm.
Danyluk, 2005
Lactic Acid
Spray
Almonds Salmonella Safe, 10ml 2% vol/vol,
Combined with NIR
heating (1300nm),
Temperature rises to 80
degree C, 5min, No
effect on sensory
attributes.
Ha and Kang,
2015
Citric Acid
Spray
Almonds Salmonella 1.6mL Citric Acid / 25g
Almonds, Shelling and 3
sprayings, 5-log
reduction of Salmonella
Pao et al.,
2006
Whey Protein
Edible
Coating
Peanuts Oxidative rancidity 5% weight addition,
Shelf life of 330 days at
25 degree Celcius.
Lee and
Krochta, 2002
CMC+ BHT
Edible
Coating
Almonds Oxidative rancidity 0.5% CMC+ 0.02% BHT
Solution followed by
drying. PV half that of
control sample after
120 days.
Larrauri et al.,
2016
Phenolic
Antioxidants
Peanuts Aflatoxin accumulation Inhibits Aspergillus
flavus and A. A.
Passone et al.,
2009

28. Thermal Dry Roasting Almonds, Peanuts,
Cashew
Salmonella Most primitive method Sanders 2014;
Yang et al., 2010
Oil Roasting Almonds, Peanuts,
Cashew
Salmonella Oil roasting for 1.5 min at
150 C resulted in greater than a
6.0 log CFU/g reduction of
Salmonella.
Sanders, 2014; Abd
S. J. ,2012
Steam Almonds Salmonella 25s for 5-log reduction Chang, 2010
Infrared Heating Almonds Salmonella 109 degree Celcius followed by
slow cooling for 1 h
Bari, 2009
Sequential
infrared and hot
air (SIRHA)
roasting
Almonds Salmonella Effective than infrared heating Yang et al. 2010
RF heating Almonds,
Walnuts
Pests, Microbes 25kW, 27Mhz, 5 min, 100%
destruction of pests
S. Wang et al.,
2007;
Gao ,2011
Non- Thermal Electron beam
irradiation
Cashew,
Almonds
Pests 1 kGy dose. Lipid oxidation at
high doses.
Singhal R. S., 2005;
Mexis, 2009
Irradiation
(Gamma rays)
Almonds, Walnuts Pest, Microbes 1 kGy dose. Lipid oxidation at
high doses.
Prakash, A, 2010;
Wilson-Kakashita,
1995
Cold Plasma Almonds Salmonella 30-sec treatment at 30 kV and
2000 Hz
Brendan A. Niemira
,2012; Deng, 2007
Packaging &
Storage
Vacuum
Packaging,
Nitrogen Flushing,
Packaging Films,
MAP
Cashew, Almonds,
Shelled Walnuts,
Peanuts
Oxidative rancidity, Microbes < 0.5% Oxygen L.G.M. Gorris,1992;
Mexis, 2009;
Raquel P. F et al,
2014

29. CONCLUSIONS
Nuts are extremely valuable agricultural products with moderate
risk of spoilage.
Good Agricultural Practices (GAP) should be strictly implemented in
fields.
Only thermal treatments full-proof inactivation of microbes.
Newer techniques like infrared heating should be practiced.
Non-thermal treatments entail high cost.
Spoilage due to oxidative rancidity can be minimized by proper
packing and storage.
Sprays of organic acids should be encouraged instead of chemical
fumigants.
Combination of techniques should be investigated.

30. REFERENCES
CAMPBELL J F , MULLEN M A , and DOWDY A K ( 2002 ), ‘ Monitoring stored- product pests in
food processing plants with pheromone trapping, contour mapping, and mark- recapture ’, J
Econ Entomol , 95 , 1089 – 1101 .
STRAND L ( 2002 ), Integrated Pest Management for Almonds . Oakland, CA , University of
California Agricultural and Natural Resources .
STRAND L ( 2003 ), Integrated Pest Management for Walnuts . Oakland, CA , University of
California Agricultural and Natural Resources.
J. Johnson. 2013. Pest Control in Postharvest nuts. In: Improving the quality and safety of nuts.
Linda Harris (ed.). Woodhead Publishing. 59-77
Danyluk, M. D., A. R. Uesugi, and L. J. Harris. 2005. Survival of Salmonella Enteritidis PT 30 on
inoculated almonds after commercial fumigation with propylene oxide. J. Food Prot. 68:1613–
1622.
Ha, J.-W., and D.-H. Kang. 2015. Combining lactic acid spray with NIR radiant heating to
inactivate Salmonella enterica serovar Enteritidis on almond and pine nut kernels. Appl. Environ.
Microbiol. DOI: 10.1128/AEM.00943-15.
Pao, S., A. Kalantari, and G. Huang. 2006. Utilizing acidic sprays for eliminating Salmonella
enterica on raw almonds. J. Food Sci. 71:M14–M19.
Lee S.Y., and Krochta J.M. 2002. Accelerated Shelf Life Testing of Whey-Protein-Coated Peanuts
Analyzed by Static Headspace Gas Chromatography. J. Agric. Food Chem. 2002, 50, 2022-2028
Passone et al. 2009. Postharvest control of peanut Aspergillus section Flavi populations by a
formulation of food-grade antioxidants. International Journal of Food Microbiology 131: 211–
217
T. H. Sanders and R. S. Calhoun. (2014). Effect of Oil and Dry Roasting of Peanuts at Various

31. REFERENCES
Abd, S. J., K. L. McCarthy, and L. J. Harris. 2012. Impact of storage time and temperature
on thermal inactivation of Salmonella Enteritidis PT 30 on oil-roasted almonds. J. Food Sci.
71:M42–M47.
Yang, J., G. Bingol, Z. Pan, M. T. Brandl, T .H. McHugh, and H. Wang. 2010. Infrared
heating for dry-roasting and pasteurization of almonds. J. Food Eng. 101: 273–280.
Chang, S.-S., A. R. Han, J. I. Reyes-De-Corcuera, J. R. Powers, and D.-H. Kang. 2010.
Evaluation of steam pasteurization in controlling Salmonella serotype Enteritidis on raw
almond surfaces. Lett. Appl. Microbiol. 50:393–398.
Bari, M. L., D. Nei, I. Sotome, I. Nishina, S. Isobe, and S. Kawamoto. 2009. Effectiveness of
sanitizers, dry heat, hot water, and gas catalytic infrared heat treatments to inactivate
Salmonella on almonds. Foodborne Path. Dis. 6:953–958.
S. Wang et al. 2007.Industrial-scale radio frequency treatments for insect control in
walnuts I: Insect mortality and product quality Postharvest Biology and Technology 45
(2007) 247–253
S. Wang et al. 2007.Industrial-scale radio frequency treatments for insect control in
walnuts I: Insect mortality and product quality Postharvest Biology and Technology 45
(2007) 247–253
Gao, M., J. Tang, R. Villa-Rojas, Y. Wang, and S. Wang. 2011. Pasteurization process
development for controlling Salmonella in in-shell almonds using radio frequency energy.
J. Food Eng. 104:299–306
Sajilata, M., & Singhal, R. (2006). Effect of irradiation and storage on the antioxidative
activity of cashew nuts. Radiation Physics and Chemistry, 75, 297–300.
S.F. Mexis, M.G. Kontominas. 2009. Effect of g-irradiation on the physicochemical and

32. REFERENCES
Prakash, A., F. T. Lim, C. Duong, F. Caporaso, and D. Foley. 2010. The effects of ionizing irradiation on Salmonella
inoculated on almonds and changes in sensory properties. Radiat. Phys. Chem. 79:502–506.
Wilson-Kakashita, G., D. L. Geredes, and W. R. Hall. 1995. The effect of gamma irradiation on the quality of English
walnuts (Juglans regia). Lebensm. Wiss. Technol. 28:17–20.
Brendan A. Niemira.(2012).Cold Plasma Reduction of Salmonella and Escherichia coli O157:H7 on Almonds Using
Ambient Pressure Gases, Journal of Food Science, M171-M175
Deng, S., R. Ruan, C. K. Mok, G. Huang, X. Lin, and P. Chen. 2007. Inactivation of Escherichia coli on almonds using
nonthermal plasma. J. Food Sci. 72(2):M62–M66.
L.G.M. Gorris and H.W. Peppelenbos. (1992). Modified Atmosphere and Vacuum Packaging to Extend the Shelf Life of
Respiring Food Products. HortTechnology , 303-309
S.F. Mexis, A.V. Badeka, M.G. Kontominas. 2009. Quality evaluation of raw ground almond kernels (Prunus dulcis):
Effect of active and modified atmosphere packaging, container oxygen barrier and storage conditions. Innovative
Food Science and Emerging Technologies 10 (2009) 580–589
S.F. Mexis, A.V. Badeka, M.G. Kontominas. Effect of packaging and storage conditions on quality of shelled walnuts.
Food Control 20 (2009) 743–751
Raquel P. F. Guiné, Cátia F. F. Almeida1, Paula M. R. Correia. 2014. Effect of Packaging and conservation conditions
on some physical and chemical properties of almonds. Journal of Hygienic Engineering and Design
J. Johnson. 2013. Pest Control in Postharvest nuts. In: Improving the quality and safety of nuts. Linda Harris (ed.).
Woodhead Publishing. 59-77
Molyneux R. J et al. (2007). Mycotoxins in edible tree nuts. International Journal of Food Microbiology 119 (2007) 72–
78
D. Clavel and C. Brabet. (2013). Mycotoxin contamination of nuts. In: Improving the quality and safety of nuts. Linda
Harris (ed.). Woodhead Publishing. 88-111