preservation of nuts
TRANSCRIPT
PRESERVATION OF NUTS:
SCIENCE & TECHNOLGY
BY: PRATHAMESH KUDALKAR 13FET1011
GUIDE: PROF. SMITA LELE
INTRODUCTIONA 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
STRUCTURE OF NUTS
COMPOSITION OF NUTSAmount/100g Almonds Cashew Walnut Peanut
Energy (kcal) 576 553 654 570Total 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 16Carbohydrates (g) 22 30 13.8 21 Dietary Fiber (g) 12 3.3 6.7 9Protein (g) 21 18.2 15.2 25Calcium (mg) 264 37 98 62Magnesium (mg) 268 292 158 184Iron (mg) 3.72 6.68 2.91 2Water 4.7 5.2 4.07 4.26
*All values from USDA Database
FACTORS RESPONIBLE FOR SPOILAGE IN NUTS
Spoilage of Nuts
Pests
Microbial growth and
toxin production
Lipid Oxidati
on
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
Excreta
Eggs
Larvae
Pin holes
Webbing
Beetles
Navel orangeworm
Codling moth
Borer Microorganisms
PESTSType Pest Nuts Adverse Effects References
Field Navel orangeworm
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)
Storage
Indianmeal moth
All nuts Larvae can enter through cracks and holes as small as 0.4 mm, contamination of the product with silk, feces, cast skins, the insects themselves
Johnson (2013)
Almond moth
All nuts Feces, webbing Johnson (2013)
Red flour beetle
All nuts Feeding of larvae, cast skins, dead insects and feces.
Johnson (2013)
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
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 °CSource of contamination: SoilLimit: 15ppb
PathogensPathogens are the disease causing microorganisms.Don’t multiply on the surface of nuts but can survive.Cause nausea, vomiting, stomach cramps, diarrheaMicrobes: Salmonella enterica serovar Enteritidis PT 30, E. coliSource of contamination: SoilPrecaution: Pasteurization to ensure 4-log reduction of Salmonella enterica serovar Enteritidis PT 30
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
RhizopusPenicilllium
Salmonella enterica serovar Enteritidis PT 30
Almonds, Peanuts
Salmonellosis Danyluk, 2005
E. coli All nuts Nausea, vomiting, stomach cramps, diarrhea
Danyluk, 2005
Microbe Nuts Adverse Effects
Reference
METHODS OF PRESERVATION
Preservation of Nuts
Chemical
Non-thermal
Packaging &
Storage
Thermal
FUMIGATIONPropylene 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 strandsEffective against: Pests, microbesResult: 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
EDIBLE COATINGS
Butylated hydroxyanisole (BHA) Butylated hydroxytoluene (BHT)
BHA & BHT
E320 E321
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.
(Passone et al., 2009)
EDIBLE COATINGSWhey 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 0.5Glycerol 1.7BHT 0.2Distilled Water
97.6
Larrauri et al., (2016)
Lee and Krochta, (2002)
Constituent
% (w/w)
WPI 10Vitamin E 0.5
ORGANIC ACIDS Principle: Organic acids at high enough concentrations reduce the pH and bring about changes in protein configuration leading to cell lysis.
Shelling
Spraying
10% acid solution (1.6
ml/ 25g)
Air Drying2h, 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
STEAM PASTEURIZATIONSteam 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 pressureResult: 5-log reduction of Salmonella was achieved in 25s. No visual deterioration of quality. Increase in moisture content, secondary drying is needed. (Chang, 2010)
INFRARED PASTEURIZATIONAdvantages of Infrared heating:• High heat transfer
coefficients• Non-chemical method, no
flame• Easy temperature control
Lactic Acid Spray + NIREffective 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)
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
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 causes the material to rapidly heat volumetrically.
RADIO FREQUENCY HEATINGAlmonds
Walnuts
Amount 1.7 kg 11 kgTo inactivate Salmone
llaPests
Pretreatment Soaking NoneFrequency 27 MHz 27.12
MHzTime 2-4 min 5 minTemperature 75°C 55 °CPower 6 kW 25 kWElectrode Gap
13cm 28cm
Hot Air Yes YesReference Gao et
al. ,2011S. Wang et al., 2007
Advantages of RF Heating Deeper penetration than MW Uniformity in heating
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)
IRRADIATIONIrradiation 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 raysMode 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, carbohydrates, and pectins and can cause undesirable quality changes such as fat oxidation, pectin depolymerization, and development of off- flavors.
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;
PACKAGING & STORAGEVacuum 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.• Shelf life: > 3 yrs
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
• Shelf life at -18 °C: > 3 yrs
Gas %Nitrogen >80Carbondioxide
20
Oxygen < 0.5
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.
Methods for Preservation of NutsProcess
TypeTreatment Nuts Effective
AgainstFeatures 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 (BHA, BHT)
Peanuts Aflatoxin accumulation Inhibits Aspergillus flavus and A. A. parasiticus
Passone et al., 2009
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, 2010Infrared Heating Almonds Salmonella 109 degree Celcius followed
by slow cooling for 1 hBari, 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
CONCLUSIONSNuts 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.
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