Walnut : Quality and Storage

Species and classificationSect. Juglans. Leaves large (20-45 cm) with 5-9 broad leaflets, hairless , margins entire

Juglans regia L. (J. duclouxiana Dode, J. fallax Dode, J. orientis Dode) - Persian Walnut, Carpathian, or Common Walnut Juglans sigillata Dode - Iron Walnut (doubtfully distinct from J. regia)

Sect. Rhysocaryon. Leaves large (20-50 cm) with 11-23 slender leaflets, finely pubescent, margins serratedJuglans australis Griseb. (J. boliviana Dode) - Argentine Walnut Juglans brasiliensis Dode - Brazilian Walnut Juglans californica S.Wats. - California Walnut Juglans hindsii (Jepson) R.E.Smith - Hinds' Walnut Juglans hirsuta Manning - Nuevo Leon Walnut Juglans jamaicensis C.DC. (J. insularis Griseb.) - West Indies Walnut Juglans major (Torrey) Heller (J. arizonica Dode, J. elaeopyron Dode, J. torreyi Dode) - Arizona Walnut

Juglans major var. glabrata Manning Juglans microcarpa Berlandier (J. rupestris Engelm.) - Texas Walnut or Little Walnut

Juglans microcarpa var. stewartii (Johnston) Manning Juglans mollis Engelm. - Mexican Walnut Juglans neotropica Diels (J. honorei Dode) - Andean Walnut Juglans nigra L. - Black Walnut Juglans olanchana Standl. & L.O.Williams - Juglans peruviana Dode - Peruvian Walnut Juglans soratensis Manning - Juglans steyermarkii Manning - Guatemalan Walnut Juglans venezuelensis Manning - Venezuela Walnut

Sect. Cardiocaryon. Leaves very large (40-90 cm) with 11-19 broad leaflets, softly downy, margins serratedJuglans ailantifolia Carr. (J. cordiformis Maxim., J. sieboldiana Maxim.) - Japanese Walnut Juglans cinerea L. - Butternut Juglans mandshurica Maxim. (J. cathayensis Dode, J. formosana Hayata, J. hopeiensis Dode, J. stenocarpa Maxim.) - Manchurian

Walnut or Chinese Walnut.

Persian Walnut• Persian (English) walnut (J. regia ) is a member of the family Juglandaceae. • Common Walnut, English Walnut, Carpathian Walnut, Persian Walnut• Archaeological finds the oldest walnut remains region that is now Iraq• Originates Iraq , Iran, Turkey, Afghanistan, southern Russia and India• The Persian walnut (J. regia L.) is the most widely cultivated species

and the most commercially important, as the nuts are larger, sweeter and easier to crack owing to their thin shell • Due to the heterozygote nature of walnut, there's a big variety among its

genotypes• Walnut is a kind of precious nut and oil economic species

Walnut FlowersStaminate ( male ) Pistallate ( female )

Pollination and fertilization

Walnut Fruit Diagram

Insect Problems• The major insect pest is the codling moth (Cydia pomonella)• Early codling moth damage can lead to more serious

infestation with navel orange worm (Amyelosis transitella ) and this is more difficult to detect if the nut is not shelled

• The walnut husk fly (Rhagoletis completa) is a serious pest in mid to late season. Larval feeding damages the husk tissues, leading to staining of the shell and failure of the husk to split mid to late July, and in cooler areas in early August

• In all cases, insect damage will tend to increase problems with pathogen infection

Maturity and Harvested• Kernels are considered mature when oil accumulation is complete• Indicated by browning of the internal packing tissue• The husk split and relatively dry at harvest

• Harvest period from late August to early November• Ethephon ( Ether ) applications are used to advance the harvest and make

nut maturation• If walnuts drop from the tree with the husk intact, leave them on the ground

until the husks become loose, usually in a week or two. Then remove the husk by hand

Approximate stage time in walnut fruit developmentWeek after bloom State of development

1 Fertilization of egg cell

2 Embryo consist of 2 – 8 cell , Copious endosperm present

3 Embryo consist of 8 – 32 cell

5 Embryo is globular and consist of up to several hundred cells

6 Cotyledons begin to grow. Tip hardening begins in shell

8 Total growth starts to slow relative to rapid , early stage

9 Kernel begins rapid growth as cotyledons start to fill locule

10 Final fruit size attained

12 – 15 Shell sclerification completed

15 Kernel growth ( weight ) resumes at a rapid pac

18 Maximum total weight

19 - 22 Approximate date of harvest

Walnut Oil Accumulation

Accumulation of oil in walnut kernels over a season of development

Degree of un saturation in oil being accumulated in walnut kernels during development

Dehydration

• Once harvested, start drying walnuts within 24 hours

• Shell moistures ˃ kernel moist. at both the start and end of drying• Dehydration benefit : stable weight , prevent deterioration, bleaching of the shell prolonged storage molding and darkness of kernel Gather husk-free walnuts as soon as possible after they drop, as nuts that remain on wet ground rapidly become discolored • 2 way for hydration : mechanical dryers and drying under sun light• The temperature of the drying air is kept low at < 43 °C • Check walnuts by occasionally cracking one open. • The nut halves breaks with a snap when bent , If the kernel is rubbery, it is not

dry

Walnut

Production

(FAO,2012 )

No. Country

2012

Tonnage Percentage

1 China 1 700 000 49.73

2 Iran 450 000 13.16

3 USA 425 820 12.46

4 Turkey 194 298 5.68

5 Mexico 110 605 3.20

6 Ukraine 96 900 2.80

7 India 40 000 1.17

8 Chile 38 000 1.10

9 France 36 425 1.00

10 Romania 30 546 0.9

11 Iraq 1 750 0.05

Nutrition Value of Persian walnut /100 gmContent Component Daily Value %

Energy ( kcal. ) 659 21.50

Moisture ( gm ) 4.1

Protein ( gm ) 15.5 27.67

Carbohydrate ( gm ) 13.8 10.61

Fat ( gm ) 65.9 65.9

sat. ( gm ) 6.2

mono. ( gm ) 9.0

poly. ( gm ) 47.6

Calcium ( mg ) 100 7.70

Iron ( mg ) 2.9 26.36

Magnesium ( mg ) 159.4 38.90

Potassium ( mg ) 445.0 35.60

Sodium ( mg ) 2.0 0.13

Zinc ( mg ) 3.1 28.20

Vit. A ( μg ) 1.0 0.11

Vit. E ( mg ) 0.7 4.67

Nutritional Value• Walnuts have the highest content of antioxidants• Rich source of PUFAs : linoleic acid : 49 to 72% , and linolenic acid : 8 to 25 %• Alpha-linolenic acid (omega-3) reduce : inflammation the risk of some chronic diseases the risk of cardiovascular disease the LDL cholesterol increase : the HDL cholesterol• improved working memory• Phytosterols such as Gallic acid and ellagic acid inhibit the intestinal absorption of cholesterol with the inhibition of cancer cell growth

Walnut Quality

Quality factor effecting nut value

1 . Nut size2 . Light kernel color Light-colored kernels earn a higher price because indicates that the kernel still has a relatively long shelf-life3 . Low internal damage from insect and mold4 . Low external damage such as broken shells and adhering hull tissue5 . “Processing quality" are ease of shelling and yield of intact kernel halves Sunlight intensity , rainfall during shell- hardening stages cause to hardening shell 6. High oil content that is free of off-flavors caused by oxidation of polyunsaturated fatty acids.

Hard Shell Genotype And

Thin Shell Genotype Walnut

Hard Shell genotype Thin Shell genotype

Weight range 12.18- 15.5 gm 05.65- 20.02 gm

Diameter 2.79 cm 3.28 cm

Length 3.33 cm 3.86 cm

kernel weight 10.25- 13.01 gram 11-13.25 gram

Average thickness shell 3.56 cm 3.17 cm

Factor Effect on Walnut Quality

• Variety : Serr and Hartley and Chandler : light color Eureka and Vina : Dark color

• Climate effect : cool-climate and light rain : hull and kernel are at same time warm and low humidity : kernel can mature up 2-3 week before the hull Varieties that have dark kernel in the hot region may produce very light colored kernel in the coastal region• Moisture - Kernel water content below 4% - The hull apparently causes heat buildup because it insulates the nut and reduce moisture loss

• Harvest time : - walnut kernels are mature and pellicle are lightest in color at picking tissue brown (PTB) stage - Harvest delay allow insects ( navel orengeworm …) and such as mold-causing fungi as Penicillium , Aspergillus and Rhizopus to enter the kernel. - After hullsplit , the greater percentage that becomes infected with navel orange worm and molds●Walnut damage : - Retention of light-color is influenced by the integrity of the seal between the two halves of the shell, because the shell is an important barrier to O2 entry

• Temperature : - Above 32 ⁰C increase the rancidity although, left in the shade - Exposure to sun

• Breeding : As the shoot length increased, shell thickness and skin weight increased and the kernel percentage decreased.• Total number of fruits per tree : Negative correlation is with fruit dimensions (width, length, height), shell thickness, and weight And positive correlation with the kernel percentage, trunk diameter, tree canopy volume, and yield per tree.

Postharvest Pathology• Most infections with pathogens are initiated in the orchard and transferred

to the postharvest environment. • In-shell product is protected unless the shell has been broken or penetrated

by insects.

• Fungi such as Aspergillus flavus and Asp. parasiticus and Penicillium sp. which can produce aflatoxins that are both toxic and carcinogenic

• Mold growth

• Insect damage

Grades and Sizes:• The morphology and size distribution of walnuts and kernels is essential

for the accurate design of equipment for cleaning, grading and separation

• Gravimetric properties are important in the design of equipment related to aeration, drying, storage and transport • Bulk density determines the capacity of storage and transport systems

• In-shell and shelled grades exist and are primarily determined by size, degree of kernel fill, color and freedom from defects and foreign material. Freedom from off-flavors (rancidity) is important

• kernel percentage is proportional with kernel weight Kernel opposite with shell thickness

Standard Quality of shell Walnut in Iraq ( 1993 )

Large size : 3.0 - ≥ 3.5 cmMedium size : 2.5 - 3.0 cm

Small size : ≤ 2.5 cm

Grade Defect No. % Shrivel %( mass )

Foreign Material %( mass )

Insect and Mold % ( mass 0 Size

No. 1 0.0 – 5.0 0.0 – 5.0 0.0 0.0 – 1.0 Large

No. 2 6.0 – 8.0 6.0 – 15.0 0.0 – 0.5 1.0 – 2.0 Medium

No. 3 9.0 – 10.0 16.0 -25.0 0.5 – 1.0 2.0 – 3.0 Small

• In-shell walnut ( kernel walnut ) The percentage of moisture ≤ 4.0% by mass The ratio of infected pests ≤ 4.0% by mass Foreign material ≤ 5.0% by mass Shrivel and immature of kernel ≤ 5.0% by mass Small pieces of kernel ( lower 3mm ) ≤ 5.0% by mass The proportion of the dust ≤ 1.0% by mass Free of living pests (in all stages of its life)

Walnut Rancidity* The skin covering the kernel ( Pellicle ) contains chemicals that protect fatty acids in the kernel from becoming rancid* Rancidity. "Rancidity" means the stage of deterioration in which the kernel has developed a rancid flavor.* Hydro peroxides have no favor or odor but break down rapidly to form aldehydes, which have a strong, disagreeable favor and odor• Hexanal are present at the highest levels, and they are considered to be the degradation products of the decomposition of linoleic acid. Hexanal has been shown to greatly increase in oxidized walnuts, and is an important marker of oxidative flavor.

Rancidity :

A - Hydrolytic Rancidity

1-Lipase enzyme reaction 2-Lipoxygenases (LOX) are capable of oxidizing the PUFA to lipohydroperoxides which can then spontaneously decompose to generate rancid products

B- Oxidative Rancidity

Factors effect on rancidity :1. Genetic Are differences among varieties in rate of rancidity development due to chemical differences or to variation in the gas exchange characteristics of the nut shell and pellicle2. Preharvest and harvest factors , include: exposure to high temperatures while the nuts are on the orchard floor, delays between harvest and hulling, etc.3. Postharvest factors , include: delays between harvest and drying , drying temperature, moisture content , exposure to light temperature and relative humidity of storage , shelling waxing as a barrier to gas exchange,

Storage Conditions and Packaging* Low water content and high fat content of the kernel make it relatively metabolically stable and able to tolerate low temperatures* The primary objectives of storage are to maintain the low water content attained after preliminary drying for : enzyme activity suppression retention of texture reduction of microbial activity limit exposure to O2 to minimize rancidity * Chilling Sensitivity: Walnuts are not sensitive to chilling; storage may be at or below freezing * The optimum temperature range for storage is 0 - 10 °C

* Within this temperature range, a 50 to 65% RH will maintain walnuts at 4% moisture * For walnut kernels optimum stability and texture were retained in a storage environment of 10 °C (50 °F) and 60% RH in air

* It is important that damaged kernels be discarded prior to storage and that the low temperature and RH conditions discussed earlier be maintained in order to reduce the chance for mold growth

* Respiration Rates: The low water content of properly stored walnuts makes them relatively inert metabolically. Respiratory rates are very low.

• * (BHA) and butylated hydroxytoluene (BHT) can be applied to the kernels

• Fumigation with methyl bromide or phosphine has been used for disinfestation

• Radiation : heating to short time

• Controlled Atmosphere Considerations: Shelf-life can be extended by storage in < 1% O2. O2 < 0.5% (balance N2) or CO2 levels above 80% in air can be effective in insect control• Packaging should be moisture-proof • Shelled products should be packaged in airtight, moisture-proof, opaque or foil

packages to maximize shelf-life

•Reference

• Walnut production manual , (1998) , 2nd edition

• Whitney Ellie , Rolfes R. Sharon , (2011), Understanding Nutrition, Twelfth Edition , Wadsworth, Cengage Learning

• California Walnuts nutrition & scientific research

• UNITED NATIONS , (2002) EDITION , WALNUT KERNELS , New York and Geneva

• DRYING WALNUTS , Washington State University, U.S. Department of Agriculture

• LI LI , RONG TSAO, (2007) , Fatty Acid Profiles, Tocopherol Contents, and Antioxidant , Activities of Heartnut (Juglans ailanthifolia Var. cordiformis),and Persian Walnut (Juglans regia L.), J. Agric. Food Chemistry , Vol. 55, 1164−1169

النوعية • والسيطرة للتقييس المركزي الجهاز التخطيط ، وزارة(1993 )، العراقية جمهورية (1808رقــم )،

• Persian Walnut Production , Perennial new idea / 2013• Sze-Tao and Shridhar K Sathe , (2000), Walnuts (Juglans regia L): proximate

composition, protein solubility, protein amino acid composition and protein in vitro digestibility , Journal of the Science of Food and Agriculture• http://faostat.fao.org/