1

Postharvest HandlingLeafy Vegetables

Marita Cantwell, UC Davis

micantwell@ucdavis.edu

http://postharvest.ucdavis.edu

Causes of Quality & Postharvest LossesCauses of Quality & Postharvest Losses

Leafy VegetablesLeafy VegetablesLettucesLettucesSpinachSpinachCabbageCabbageChardChardBroccoliBroccoliCeleryCeleryHerbsHerbsEndivesEndivesAsparagusAsparagusGreen OnionsGreen Onions

Water lossWater loss Mechanical damageMechanical damage Loss of chlorophyll and Loss of chlorophyll and

other nutrientsother nutrients Respiration ratesRespiration rates Microbial growthMicrobial growth Sensitivity to ethyleneSensitivity to ethylene

Relative Perishability

Relative Respiration Rate

NutsNutsDatesDates

CitrusCitrusGarlicGarlicPotatoPotato

AppleAppleCarrot Carrot OnionOnion

BananaBananaTomatoTomatoPeachPeach

ArtichokeArtichokeBroccoliBroccoliStrawberryStrawberry

AsparagusAsparagusPeasPeasSweet CornSweet Corn

10 Effect of Temperature on Deterioration

25422.51.540104

14715.02.03086

8137.52.52068

3333.03.01050

11001.0--032

Daily Loss (%)

Relative Shelf-life

Relative Velocity of Deterioration Q10

Temp. °C

Temp. °F

Q10 = rate of deterioration at T+10°rate of deterioration at T

Storage temperature

Da

ys

(to

in

itia

te y

ell

ow

ing

)

0

5

10

15

20

25

30

35 Broccoli Shelf-life & Temperature

032

2.536

541

7.545

1050

12.5 55

1559

20°C68°F

cv. Legacy

Fresh appearance

Green florets

Tender stem

No discoloration

No breakage

No decay

No off-odors

mg

/100

g F

W

0

5

10

15

20

25

mg

/100

g F

W

0

1

2

3

4

Days

0 5 10 15 20 25

mg

/100

g F

W

05

10152025303540

Days

0 5 10 15 20 25

mg

/100

gF

W

0

5

10

15

20

25

Chlorophyll Carotenoids

Ascorbic Acid Sugars

0°C (32°F)10°C (50°F)20°C (68°F)

Limit of Salability

Broccoli Compositional Quality and Storage Temperature

Cantwell, unpublished

2

Specialty Brassicas Comparative StudyGai-lanChoi-sumBroccoli raab, rapiniBroccolini

Stem TissueFlorets

888687112176235Vitamin C, mg/100g FW

32434792100117Antioxidant activitymg Trolox/100g FW

1.11.00.52.31.41.1Ammonia, µmole/100gFW

12.014.417.43.74.55.2Total sugars, mg/gFW

10C

8d

5C

8d

Initial10C

8d

5C 8d

Initial

Component

M. Cefola, G. Hong, M. Cantwell, R. Paiva e G. Colelli. 2009

Marketable qualityMarketable qualityCompositional qualityCompositional qualityResponse to TemperatureResponse to TemperatureResponse to atmospheresResponse to atmospheres

Broccoli raab

Iceless BroccoliTemperature-yellowingMoisture loss-softening

• 0°C with very high humidity

• MA: 5-8% O2 + 7-10% CO2

Broccoli Storage Conditions

Days at 7.5°C

0 1 2 3 4

% W

eig

ht lo

ss

0

1

2

3

4

5

6

7

8

Curve 1, y = 1.55x + 0.34; R2 = 0.98Curve 2, y = 1.72x + 0.36; R2 = 0.98

Curve 1 original firmness technique

Curve 2, modified technique, mark

A. % Weight Loss

Days at 7.5°C

0 1 2 3 4 5 6 7

% F

irmn

ess

loss

0

10

20

30

40

50

60

70

80

90

100

Curve 1 original firmness technique

Curve 2, modified technique, mark

B. % Firmness Loss

ICELESS BROCCOLIMinimize delay from harvest to cooling Use plastic liners to reduce water loss Keep it cold

About 4% weight loss results in 30% decrease in firmness and this is likely the point at which a buyer would consider the head soft.

Cantwell lab, UCDavis, 2010

Leafy greengrower, SingaporeAug 2007 Leafy green

grower, SingaporeAug 2007

3

Days

0 2 4 6 8 10 12 14 16 18

Col

or s

core

, 5=

dark

gre

en, 1

=ye

llow

1

2

3

4

5

Mature Kale Leaves 20°C (68°F)15°C (59°F)10°C (50°F) 5°C (41°F)

Days

0 2 4 6 8 10 12 14 16 18

Immature Kale Leaves

LSD.05

Loss of green color by mature and immature Kale leaves stored at 4 temperatures for up to 18 days.

5 4 3 2 1

10°C Air 1-MCP, 10°C Air 10°C C2H4 1-MCP, 10°C C2H4

12 days; 8 ppm C2H4; 500 ppb 1-MCP

Collards

5°C Air 10°C Air 10°C C2H4

1-MCP=1-methyl-cyclopropene, SmartFresh™, AgroFresh

Broccoli ShelfBroccoli Shelf--life & Varietylife & Variety

Days 7.5°C Score 2

Cultivar Range Average % Head Rot PPPaaaccckkkmmmaaannn 111777---111999 111777...777 333333

LLLiiibbbeeerrrtttyyy 111222---111777 111555...111 000

PPPaaatttrrriiiooottt 111222---111777 111444...444 111000

GGGrrrnnn VVVaaallliiiaaannnttt 111333---111555 111444...111 000

BBBrrriiigggaaadddiiieeerrr 999---111222 111111...222 222000

MMMaaajjjeeessstttiiiccc 999---111444 111111...111 111111

AAAvvveeerrraaagggeee 111222---111555 111333...777 111111

M. Cantwell, Nov 1997

BacterialSoft rot

Napa or Chinese cabbageNapa or Chinese cabbageBlack Speck DisorderBlack Speck Disorder

Cultivar

1 2 3 4 5 6 7 8 9

Bla

ck s

pec

k in

dex

0

50

100

150

200

250

Air Ethylene

Cv #1= T-740 2= Yuki 3= Spring Flavor 4= Southern King 5= New Summer 6= Chacha 7= China Express 8= Blues 9= WR-70

Black speck development on Napa cabbage stored in air or in ethylene is the same. PAL enzyme levels similar; 1-MCP does not reduce black speck. Cultivars vary greatly in their susceptibility to black speck.

Black speck index = black speck score multiplied by %

extension.

Black Speck Disorder on Chinese CabbageBlack Speck Disorder on Chinese Cabbage

Cauliflower Qualitycolor is cream whitefreedom from mechanical injuryfreedom from decayno discoloration on cut edgesminimal number of small pieces; good integrity of cut florets good aroma and odor as fresh or microwaved foodretain high content of sugars and Vitamin C

4

Cauliflower Discoloration (in relation to storage temperature)

Marita Cantwell

0.220.44Phenolics (A320)

7.523.9Vitamin C (mg/100 g)

20.020.4Sugar (mg/g)

1.65.9Carotenoids (mg/100 g)

5.121.5Chlorophyll (mg/100 g)

IcebergRomaineConstituent (fresh wt. basis)

Opportunities related to more nutritious lettuces

Cantwell and Ermen 2006

Tot

al s

uga

rs (

mg

/g fw

t.)

0

5

10

15

0 days7 days

HeartInner

Young Midsize Full sizeOuter

Leaf Position

Total sugars

LSD.05

Leaf Position

Tot

al a

scor

bic

acid

(m

g/1

00g

fwt.)

0

10

20

30

40 0 days7 days

LSD.05

Vitamin C (Total Ascorbic Acid)

HeartInner

Young Midsize Full sizeOuter

Romainelettuce

Res

pir

atio

n r

ate

(ml C

O2 /

kg-h

)

0

5

10

15

20

25

30 Lettuces, EndivesSpinach, ChardsArugula , Brassicas

0°C (32°F) 10°C (50°F)

Immature Leaves

Iceberg LettuceRomaine LettuceLooseleaf Lettuces

Mature Heads

0°C (32°F) 10°C (50°F)

Respiration rates of specialty salad greens and full size lettucRespiration rates of specialty salad greens and full size lettuces.es.

From M. Cantwell, UC Davis 1998

Temperature

0 5 10 15 20

Res

pira

tion

rate (mg

CO

2 /kg-h

r)

0

15

30

45

60

75

90

Iceberg (air)Romaine (air)Looseleaf (air)Iceberg (2% O2)

32 41 50 59 68°F°C

3300

6600

9900

13200

16500

19800

Vit

al H

eat

(BT

U/t

on

-da

y)

1 2 3

4 5

Maturity Stages of Iceberg Lettuce

5

Russet SpottingRusset SpottingEthyleneEthylene--induced Disorder on Lettucesinduced Disorder on Lettuces

Large differencesLarge differencesamong varietiesamong varietiesin susceptibilityin susceptibility

Russet spot scores ~ 1 (none), 3, 6 and 9, respectively.

Variety

1 2 3 4 5 6 7 8 9 10 11 12 13

Rus

set

Sp

ottin

g S

core

1=n

one,

9=

seve

re

1

2

3

4

5

6

7

8

1=Sonoma 2=Spreckles 3=Salinas 521 4=Raider 5=Salinas 517 6=Buena Vista 7=Stinger 8=Van Sal 210 9=Salinas10=Ace11=Champ12=Salinas 8813=Ridgemark

A. Iceberg Lettuces

Variety

1 2 3 4 5 6 7

B. Romaine Lettuces

1=Paris Island Cos2=Romo3=Red Eye Cos4=Gx8005=Corazon6=Red Hot Cos7=Nero

Development of Russet Spot Disorder on Iceberg and Romaine Lettuces.Intact heads were stored in 5ppm ethylene at 5°C (41°F) plus 1 week in air.

Cantwell, UC Davis, unpublished

Days at 5°C0 2 4 6 8 10 12

Rus

set

spot

sco

re, 1

=no

ne,

9=se

vere

0

1

2

3

4

5

6

7

LSD.05

Air

5 ppm Ethylene

1-MCP, Air1-MCP, 5 ppm Ethylene

1-MCP Prevents Russet Spot Disorder on Iceberg Lettuce

Test#2, midribs; 1000 ppb 1-MCP; Tarraza and Cantwell, Nov 2002

Control + Ethylene

1-MCP + Ethylene

Brown StainBrown StainCO2 >3%CO2 >3%

Lettuce disordersLettuce disorders•• Brown stainBrown stain——CO2CO2•• Pink rib Pink rib ––overmatureovermature headsheads•• Heart leaf injuryHeart leaf injury–– O2/CO2O2/CO2

Pink ribHeart Discoloration

Symptoms of Freezing in Lettuce

Normal Frozen

Romaine

Freeze Injury

Lettuce Storage ConditionsLettuce Storage Conditions

•• 00°°C (32C (32°°F) but freezing point is F) but freezing point is --0.20.2°°C (31.5C (31.5°°F)F)

•• ShelfShelf--life:life:–– 00°°C (32C (32°°F): >4 weeksF): >4 weeks

–– 55°°F (41F (41°°F): ~3 weeksF): ~3 weeks

•• High relative humidity, avoid free moistureHigh relative humidity, avoid free moisture

•• Controlled atmospheresControlled atmospheres–– Low O2 beneficial, CO2 >3% damagingLow O2 beneficial, CO2 >3% damaging

•• Ethylene sensitiveEthylene sensitive

6

Field Pack & PalletizeField Pack & PalletizeVacuum CoolVacuum CoolNaked, Liner, Head wrappedNaked, Liner, Head wrapped

Traditional Packing of Romaine:Do not place cut lettuce on the groundWaxed cartons or cartons with liners rather than crates

Simple packaging to reduce water loss.Need to cool product before packaging (rooms or hydrocool)or used vented packaging and vacuum cool (romaine lettuces)

Open

Bag

8 days

0.5°C (33°F) 5°C (41°F) 10°C (50°F)

5.2% 10.3% 13.9% weight loss

0.4% 0.5% 0.7% weight loss

Naked lettuceVertical shelving

Spinach Quality ParametersSpinach Quality Parameters

•• Green and uniform colorGreen and uniform color

•• Minimum breakageMinimum breakage

•• No dirt ; Clean and disinfectedNo dirt ; Clean and disinfected

•• No decayNo decay

•• CompositionComposition–– nitrates, oxalatesnitrates, oxalates

•• ShelfShelf--lifelife

7

Manual harvest of bunchedSpinach; vacuum cooledNote: no longer use slickers, use aprons

http://www.ramsayhighlander.com

Mechanical harvest of young spinachfor washed and packaged product

1 2 3 4 5

110.9

121.4

123.4

126.6

129.5

Hue

0.22

0.50

0.75

1.17

1.49

Chlorophyllmg/g FW

0.10

0.16

0.18

0.26

0.29

Carotenoidsmg/g FW

5

4

3

2

1

Color score

44.659.8

31.347.6

27.545.0

21.640.7

18.139.2

ChromaL*

Color values measured in upper right hand corner of each leaf; data average 4-6 leaves per category

Yellowing Rating Scale for Spinach Marita Cantwell

9=ex

celle

nt,

1=

un

use

ab

le

1

2

3

4

5

6

7

8

9

5=g

reen

, 1=

yell

ow

1

2

3

4

5

Days

0 3 6 9 12 15 18

1=n

on

e, 5

=se

vere

1

2

3

4

5

Days

0 3 6 9 12 15 18

1=n

on

e, 5

=se

vere

1

2

3

4

5

Visual Quality Color

Decay Off-odors

2.5°C 36°F5°C 41°F

7.5°C 45°F10°C 50°F

Spinach: Spinach: CommericalCommericalwashed and baggedwashed and baggedproduct stored at 4 product stored at 4 temperaturestemperatures

Cantwell, UC Davis

BUT….Target Temp.0ºC (32ºF)

Impact of Temperature on Quality Changes

Quality categories (leaf damage)

for commercial packaged spinach

Leaf pieces comprised of <25% of leaf areaLeaf Pieces5

4

3

2

1

Category number and name

Partial leaves and partial leaves with numerous damaged areas

Severe damage

Intact or near intact* leaves with several damaged areas Moderate damage

Intact or near intact* leaves with 1 notable damaged area (tear, fracture)

Slight damage

Intact leaves with no or only minor damageNo damage

Category Description

*Near intact refers to leaves cut at the base with mechanical harvester

DEFECTS ON FIELD-GROWN PACKAGED LEAFY GREENSDAMAGE FOLLOWED BY DECAY, MOSTLY BACTERIALAugust 2008

Stored 7d 5C

White chardGreen romaine

Red romaine

Red chard

Tango

8

g/g

fre

sh w

eig

ht

0 .0

0.5

1.0

1.5

2.0LSD .05 = 0.32A. Am monium

mg

/g fr

esh

we

ight

0 .0

0.2

0.4

0.6

0.8

1.0

Days at 5°C (41°F)

mg

/g fr

esh

we

ight

0 .00

0.05

0.10

0.15

0.20

0.25

0 21

B. Chlorophyll

C . Carotenoids LS D.05 = 0.027

LS D.05 = 0.092

Changes in ammonium, chlorophyll Changes in ammonium, chlorophyll and and carotenoidcarotenoid concentrations concentrations in spinach after 0 and 21 days in airin spinach after 0 and 21 days in airat 5C (41F). Data averaged from at 5C (41F). Data averaged from 11spinach cultivars (Cantwell, 2001)11spinach cultivars (Cantwell, 2001)

0

200

400

600

800

1000

1200

1400

1600

0°C 5°C 10°C

AMMONIA

INCR

EASE

%

25

27

29

31

33

35

37

39

TOTA

L GS

ACT

IVIT

Y

AMMONIA INCREASE GS TOT

6 days, Catalano and Cantwell, 2007

Ammonia increases in spinachIn response to temperature andStressful atmospheres

100µm

50ppm N (80% nitrate-20%ammonia) 200ppm N (80% nitrate-20%ammonia)

OlderLeaf 8

(only part of leaf)Palisadecells

Spongy mesophyll

High N results in more fragile leaves with larger cells; can be more breakage during harvest and handling, resulting in increased decay and reduced shelf-life

Greenhouse spinach, Gutierrez and Cantwell 2007

Figure1 Texture profile of smooth spinach leaves

00.20.40.60.8

11.21.41.61.8

2

0 0.5 1 1.5 2 2.5 3 3.5 4

Distance (mm)

Fo

rce

(N

)

Smooth-No-Vein1

Wrinkled-No-Vein1

Texture Profile of Spinach Leaves---- less fragile

---- more fragile

•• Young and mature spinach leaves respond Young and mature spinach leaves respond similarly to storage conditionssimilarly to storage conditions

•• Young leaves have less physical damageYoung leaves have less physical damage•• Excessive N fertilization results in weaker leavesExcessive N fertilization results in weaker leaves•• Low temperatures are essential for adequate Low temperatures are essential for adequate

shelfshelf--lifelife–– 00°°C (32C (32°°F): 3 weeksF): 3 weeks–– 55°°C (41C (41°°F): 2 weeksF): 2 weeks

•• Modified atmospheres, keep CO2 at 5% or lessModified atmospheres, keep CO2 at 5% or less•• High COHigh CO22 atmospheres stressful to spinachatmospheres stressful to spinach

Spinach StorageSpinach Storage

2-3°C (34-36°F) best temperature; Asparagus is slightly chill sensitiveCA with high CO2 is beneficial

Asparagus

AsparagusAsparagus

M. Cantwell, UC Davis

TTIIPP Cell DivisionCell Enlargement

Sugars LOWProtein & Acidity HIGHSlight Lignification

MIDDLE Cell ElongationHydration

Total Solids 8-14%% Water High

BASE Cell WallThickening

Sugars HIGHProtein & Acidity LOWMaximum Lignification

Asparagus packinghouse in Peruhttp://www.freshplaza.com/fotoarchief/apr11.htm

9

Asparagus storage conditions• 2.5°C (slightly chilling sensitive

• High humidity

• 1-2 weeks; 3 weeks MA

• Modified atmospheres

– O2 5-10%

– CO2 7-10%

Days storage

0 3 6 9 12 15 18 21 24 27 30 33 36

Qu

alit

y sc

ore

1

2

3

4

5

6

7

8

9

Asparagus: Deterioration and Temperature

Excellent

Good

Fair

Poor2.5°C15°C 10°C 5°C

Tip decay (bacterial)

Frozen and then thawed

mg

/10

0g

fre

sh w

eig

ht

5

6

7

8

9

10

11

12

mg

/10

0g

fre

sh w

eig

ht

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Days 2.5°C (36°F)

0 7 14 21

mg

/g f

resh

we

igh

t

6

8

10

12

14

Days 2.5°C (36°F)

0 7 14 21

µg

/g f

resh

we

igh

t

20

40

60

80

100

120

E. Chlorophyll F. Carotenoids

G. Sugars H. Ammonia

UC115

UC157

UC115UC115 compared to UC157. UC157. Asparagus stored at 2.5°C (36°F) up to 21 days.

Data averaged over 2 Tests & 2 Fields, 2004

UC157 UC115

Storage Conditions for Fresh HerbsStorage Conditions for Fresh Herbs

•• 00°°C (32C (32°°F) but freezing point is F) but freezing point is --0.20.2°°C (31.5C (31.5°°F)F)–– ShelfShelf--life at 0life at 0°°C (32C (32°°F): 3F): 3--4 weeks4 weeks–– ShelfShelf--life at 5life at 5°°C (41C (41°°F): 2F): 2--3 weeks 3 weeks -- ShelfShelf--life based on aroma quality: 1life based on aroma quality: 1--2 week2 week-- Exception: chilling sensitive basil Exception: chilling sensitive basil 12.512.5°°C (55C (55°°F) bestF) best

•• High relative humidity, protective packaging, but avoid High relative humidity, protective packaging, but avoid free moisture condensationfree moisture condensation

•• Modified atmospheres can be beneficialModified atmospheres can be beneficial

•• Ethylene sensitiveEthylene sensitive

9=ex

celle

nt,

1=

unus

able

1

2

3

4

5

6

7

8

9A. Visual Quality CILANTRO

1=

gre

en, 5

=ye

llow

1

2

3

4

Days

0 2 4 6 8 10 12 14

1=

non

e,

5=se

vere

1

2

3

4

0°C 32°F5°C 41°F10°C 50°F15°C 59°F

0°C 32°F5°C 41°F10°C 50°F15°C 59°F

B. Color

C. Decay

LSD.05

1

2 4

3 5

0.060.120.170.250.28Carotenoidsmg/g FW

0.400.600.851.611.77Chlorophyll mg/g FW

108.1111.1118.3125.1125.5Hue

46.244.441.528.223.9Chroma

71.768.162.252.449.5L*

54321

Paulenas and Cantwell, 2008

Detrimental ethylene effectsDetrimental ethylene effectsYellowingYellowingEpinastyEpinastyAbscission Abscission

BasilHighly susceptible to water lossVery chilling sensitive

Situation:Excellent quality cropHarvesting late in dayHigh temperatures, ~30°CLow RH, ~50%; Little protection from ambientLong delays to packinghouse

What can be done to improve this handling???

10

Days

1 2 3 4 5 6 7 8 9

C

hill

ing

Sco

re0=

no

inju

ry; 8

=se

vere

0

1

2

3

4

5

6

7

8 0°C (32°F)

2.5°C (36°F) 5°C (41°F)

7.5°C (45°F)

10°C (50°F)

Basil loses moisture very rapidly

Basil is very chilling sensitive

Chilling injuryScore 3

Basil stored 2 days in plastic bags

0°C 5°C 10°C32°F 41°F 50°F

July 31, 2006

Shiso, a basil relative, is alsochilling sensitive

Exposed

Covered

0°C 10°C 20°C 30°C

32°F 50°F 68°F 86°C

2 days

Vapor pressure deficit, mm Hg

0 2 4 6 8 10 12 14 16

Wei

ght

loss

, %

pe

r da

y

0

3

6

9

12

15

18

21

24

Strawberry y = 0.506x + 0.35 R2 = 0.91

Broccoli y = 1.01x + 0.34 R2 = 0.97

Romaine y = 0.64x + 0.43 R2 = 0.94

Mushroom y = 1.48x + 0.21, R2 = 0.98

Strawberry

Broccoli

Romaine lettuce

Mushroom

Weight loss in relation to VPD in 4 products

Belgian Endive-keep cold and away from light

Celery heartsTrimmed, washed and packagedMobile processing unitChlorine rinseDrain and package in perforated bag

With permission from T&A, June 2007

Harvesting equipment for fennelD’Arrigo Brothers, Castroville CA

Belgium: Hortiplan, mobile gully system

Production Conditions: Quality Implications

China: nutrient film technique

China: row covers lettuces