1

Postharvest Handling Leafy & Related

Vegetables

Marita Cantwell, UC Davis

micantwell@ucdavis.edu

http://postharvest.ucdavis.edu

Postharvest Technology Short Course June 2012Ch. 34 Postharvest Technology Book

Causes of Quality & Postharvest Losses

Leafy & Related VegetablesLettucesSpinachCabbageChardBroccoliCeleryHerbsEndivesAsparagusGreen OnionsMushrooms

Water loss Mechanical damage Loss of chlorophyll and

other nutrients Respiration rates Microbial growth Sensitivity to ethylene

Effect of Temperature on Deterioration

Temp. °F

Temp. °C Q10

Relative Velocity of Deterioration

Relative Shelf-life

Daily Loss (%)

32 0 -- 1.0 100 1

50 10 3.0 3.0 33 3

68 20 2.5 7.5 13 8

86 30 2.0 15.0 7 14

104 40 1.5 22.5 4 25

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Cantwell, unpublished

% Weight loss

0 2 4 6 8 10 12

% F

irmne

ss lo

ss

0

20

40

60

80

y = 5.68x + 9.69R2 = 0.80

% Firmness loss vs % Weight loss

Iceless BroccoliTemperature-yellowingMoisture loss-softening

ICELESS BROCCOLIMinimize delay from harvest to cooling Use plastic liners with holes to reduce water loss Keep it coldAbout 4% weight loss = soft head

2

• Head Size, floret uniformity

• Floret/Head Color

• Head Firmness and Stem Texture

• Water loss and firmness loss

• Decay susceptibility

• Discoloration cut ends

• Shelf-life

• Composition– % dry weight

– Sugars

– Vitamin C

– Pigments

– Glucosinolates (glucoraphanin)

– Antioxidant activity

Broccoli Postharvest Quality and Variety Evaluations

Maturity at harvestProtect from water lossCool as soon as possible

Leafy greengrower, SingaporeAug 2007

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 Leaf maturity:Size, weightLeaf openingUncurling of edgesColorWidth of midribLeaf thicknessLeaf wax

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

Napa or Chinese cabbageBlack Speck Disorder

3

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 the black speck disorder.

Black speck index = black speck score multiplied by % extension.

Black Speck Disorder on Chinese Cabbage

Cauliflower Quality• Color is cream white• Freedom from mechanical injury• Freedom from decay• No discoloration on cut edges

Cauliflower Discoloration (in relation to storage temperature)

Marita Cantwell

Constituent (fresh wt. basis) Romaine Iceberg

Chlorophyll (mg/100 g) 21.5 5.1

Carotenoids (mg/100 g) 5.9 1.6

Sugar (mg/g) 20.4 20.0

Vitamin C (mg/100 g) 23.9 7.5

Phenolics (A320) 0.44 0.22

Opportunities related to more nutritious lettuces

Cantwell and Ermen 2006

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 lettuces.

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)

Temperature and Respiration RateOxygen and Respiration Rate

4

ImmatureMatureOvermature

No. leavesWeightFirmness% GreenSweetnessBitternessPhenolics

Lettuce Maturity

Russet SpottingEthylene-induced Disorder on Lettuces

Large differencesamong varietiesin 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 StainCO2 >3%

Lettuce disorders• Brown stain—CO2• Pink rib –overmature heads• Heart leaf injury– O2/CO2

Pink ribHeart Discoloration

Symptoms of Freezing in Lettuce

Normal Frozen

Romaine

Freeze Injury

5

Lettuce Storage Conditions

• 0°C (32°F) but freezing point is -0.2°C (31.5°F)

• Shelf-life:– 0°C (32°F): >4 weeks

– 5°F (41°F): ~3 weeks

• High relative humidity, avoid free moisture

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

• Ethylene sensitive Field Pack & PalletizeVacuum CoolNaked, Liner, Head wrapped, Clamshells

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 (room or hydrocool)or used vented packaging and vacuum cool (romaine lettuces)

Open

PlasticBag

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

6

Spinach Quality Parameters

• Green and uniform color

• Minimum breakage

• No dirt ; Clean

• No decay

• Composition– nitrates, oxalates

• Shelf-life

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

Color score L* Chroma Hue Chlorophyllmg/g FW

Carotenoidsmg/g FW

1 39.2 18.1 129.5 1.49 0.29

2 40.7 21.6 126.6 1.17 0.26

3 45.0 27.5 123.4 0.75 0.18

4 47.6 31.3 121.4 0.50 0.16

5 59.8 44.6 110.9 0.22 0.10

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

Yellowing Rating Scale for Spinach

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: Commerical washed and baggedproduct stored at 4 temperatures

Cantwell, UC Davis

BUT….Target Temp.0ºC (32ºF)

Impact of Temperature on Quality Changes

Quality categories (leaf damage)

for commercial packaged spinach

Category number and name Category Description

1 No damage Intact leaves with no or only minor damage

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

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

4 Severe damage Partial leaves and partial leaves with numerous damaged areas

5 Leaf Pieces Leaf pieces comprised of <25% of leaf area

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

7

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 and carotenoid concentrations in spinach after 0 and 21 days in airat 5C (41F). Data averaged from 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 et al

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 similarly to storage conditions

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

shelf-life– 0°C (32°F): 3 weeks– 5°C (41°F): 2 weeks

• Modified atmospheres, keep CO2 at 5% or less• High CO2 atmospheres stressful to spinach

Spinach Storage

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

Asparagus

Asparagus

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

8

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

Storage Conditions for Fresh Herbs

• 0°C (32°F) but freezing point is -0.2°C (31.5°F)– Shelf-life at 0°C (32°F): 3-4 weeks– Shelf-life at 5°C (41°F): 2-3 weeks - Shelf-life based on aroma quality: 1-2 week- Exception: chilling sensitive basil 12.5°C (55°F) best

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

• Modified atmospheres can be beneficial

• Ethylene sensitive: yellowing, abscission, epinasty

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

1 2 3 4 5

L* 49.5 52.4 62.2 68.1 71.7

Chroma 23.9 28.2 41.5 44.4 46.2

Hue 125.5 125.1 118.3 111.1 108.1

Chlorophyll mg/g FW

1.77 1.61 0.85 0.60 0.40

Carotenoidsmg/g FW

0.28 0.25 0.17 0.12 0.06

Paulenas and Cantwell, UC Davis, 2008

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???

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

Cantwell, UC Davis, July, 2006

Shiso, a basil relative, is alsochilling sensitive

9

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

We

igh

t lo

ss,

% p

er

day

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

“Cold and Dry”

Bacterial growth: temperature and moisture

Belgian Endive-keep cold and away from light

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

T&A, June 2007

Belgium: Hortiplan, mobile gully system

Production Conditions and Quality Implications

China: nutrient film technique

China: row covers lettuces

Harvesting mache, Turin, Italy, 2011

Causes of Quality & Postharvest Losses

Leafy & Related VegetablesLettucesSpinachCabbageChardBroccoliCeleryHerbsEndivesAsparagusGreen OnionsMushrooms

Water loss Mechanical damage Loss of chlorophyll and

other nutrients Respiration rates Microbial growth Sensitivity to ethylene