Postharvest Handling Leafy & Related Vegetables Marita Cantwell, UC Davis micantwell@ucdavis.edu http://postharvest.ucdavis.edu Postharvest Technology Short Course June Ch. Postharvest Technology Book Causes of Quality & Postharvest Losses Leafy & Related Vegetables Lettuces Spinach Cabbage Chard Broccoli Celery Herbs Endives Asparagus Green Onions Mushrooms 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. Relative Velocity C Q of Deterioration Relative Shelf-life Daily Loss (%) --... 68. 7. 8 86.. 7.. Q = rate of deterioration at T+ rate of deterioration at T Fresh appearance Green florets Tender stem No discoloration No breakage No decay No off-odors Days (to initiate yellowing) Broccoli Shelf-life & Temperature cv. Legacy. 6 7.. 9 C 68 F Storage temperature
Broccoli Compositional Quality and Storage Temperature Chlorophyll Carotenoids mg/ g FW mg/ g FW Days Limit of Salability Ascorbic Acid mg/g FW mg/ gfw Cantwell, unpublished Days C ( F) C ( F) C (68 F) Sugars Broccoli Quality and Variety Evaluations Head Size, floret uniformity Floret/Head Color Head Firmness, Stem Texture Water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
This image cannot currently be displayed. 6/9/ % Firmness loss 6 % Firmness loss vs % Weight loss y = 7.8x; R =.98 Broccoli held at 7.C 6 7 % Weight loss 8 Loss of Broccoli Head Firmness is Correlated to Water Loss About % weight loss results in % decrease in firmness and this is likely the point at which a buyer would consider the head soft. % Firmness loss vs % Weight loss ICELESS BROCCOLI Minimize delay from harvest to cooling Plastic liners with holes reduce water loss Keep it cold About % weight loss = soft head % Firmness loss 6 y =.68x + 9.69 R =.8 Broccoli held at,,, and C 6 8 % Weight loss Respiration rate, µl/g-h 8 6 Control min hydrate hour hydrate % weight loss % wt. loss + min hydrate Water loss and water gain do have an effect on broccoli respiration rates and shelf life 8 6 8 6 8 Days at C cv Ironman Melo and Cantwell, Treatment Shelf life C. Control.8. min hydrate.. hr hydrate.. % weight loss 6.7. % weight loss + min hydrate 6.9 LSD..6
Weight loss, % 8 6 8 6 A. % Weight loss, bags folded over No Bag, waxed carton Lettuce bag, folded over Extend bag, folded over New Peak Fresh bag, folded over Smart bag, folded over LSD. Broccoli weight loss and firmness loss can be minimized with plastic liners. Simple perforated PE lettuce or basil liners perform as well as more expensive plastic films. B. Firmness, bags folded over Firmness, N force to compress 9 8 7 6 LSD. 6 8 Days at C ( F) Cantwell, UC Davis, 9 Maturity at harvest Protect from water loss Cool as soon as possible
Leafy green grower, Singapore Aug 7 Loss of green color by mature and immature Kale leaves stored at temperatures for up to 8 days. Color score, =dark green, =yellow Mature Kale Leaves C (68 F) C (9 F) C ( F) C ( F) Immature Kale Leaves LSD. 6 8 6 8 Days 6 8 6 8 Days Leaf maturity: Size, weight Leaf opening Uncurling of edges Color Width of midrib Leaf thickness Leaf wax 6
C Air -MCP, C Air C C H -MCP, C C H Collards C Air C Air C C H -MCP=-methyl-cyclopropene, SmartFresh, AgroFresh days; 8 ppm CH; ppb -MCP Napa or Chinese cabbage Black Speck Disorder 7
Black speck index Black Speck Disorder on Chinese Cabbage Air Ethylene Cv #= T-7 = Yuki = Spring Flavor = Southern King = New Summer 6= Chacha 7= China Express 8= Blues 9= WR-7 Black speck development on Napa cabbage stored in air or in ethylene is the same. PAL enzyme levels similar; -MCP does not reduce black speck. 6 7 8 9 Cultivar Black speck index = black speck score multiplied by % extension. Cultivars vary greatly in their susceptibility to the black speck disorder. Cauliflower Quality Color is cream white Freedom from mechanical injury Freedom from decay No discoloration on cut edges 8
Cauliflower Decay/Discoloration (in relation to storage temperature) Marita Cantwell Cauliflower and Modified Atmospheres 9
Opportunities related to more nutritious lettuces Constituent (fresh wt. basis) Romaine Iceberg Chlorophyll (mg/ g).. Carotenoids (mg/ g).9.6 Sugar (mg/g).. Vitamin C (mg/ g).9 7. Phenolics (A ).. Cantwell and Ermen 6 Respiration rates of specialty salad greens and full size lettuces. Respiration rate (ml CO/kg-h) Immature Leaves Lettuces, Endives Spinach, Chards Arugula, Brassicas Mature Heads Iceberg Lettuce Romaine Lettuce Looseleaf Lettuces C ( F) C ( F) C ( F) C ( F) From M. Cantwell, UC Davis 998
Vital Heat (BTU/ton-day) 98 6 99 66 Iceberg (air) Romaine (air) Looseleaf (air) Iceberg (% O ) Temperature and Respiration Rate Oxygen and Respiration Rate 9 7 6 Respiration rate (mg CO/kg-hr) C 9 68 F Temperature Immature Mature Overmature No. leaves Weight Firmness % Green Sweetness Bitterness Phenolics Lettuce Maturity
Russet Spotting Ethylene-induced Disorder on Lettuces Large differences among varieties in susceptibility Russet spot scores ~ (none),, 6 and 9, respectively. Russet Spotting Score =none, 9=severe 8 7 6 =Sonoma =Spreckles =Salinas =Raider =Salinas 7 6=Buena Vista 7=Stinger 8=Van Sal 9=Salinas =Ace =Champ =Salinas 88 =Ridgemark A. Iceberg Lettuces B. Romaine Lettuces =Paris Island Cos =Romo =Red Eye Cos =Gx8 =Corazon 6=Red Hot Cos 7=Nero 6 7 8 9 Variety 6 7 Variety Development of Russet Spot Disorder on Iceberg and Romaine Lettuces. Intact heads were stored in ppm ethylene at C ( F) plus week in air. Cantwell, UC Davis, unpublished
-MCP Prevents Russet Spot Disorder on Iceberg Lettuce 7 Russet spot score, =none, 9=severe 6 Air ppm Ethylene -MCP, Air -MCP, ppm Ethylene LSD. Control + Ethylene -MCP + Ethylene 6 8 Days at C Test#, midribs; ppb -MCP; Tarraza and Cantwell, Nov Brown Stain CO >% Lettuce disorders Brown stain CO Pink rib overmature heads Heart leaf injury O/CO Pink rib Heart Discoloration
Symptoms of Freezing in Lettuce Romaine Freeze Injury Normal Frozen Lettuce Storage Conditions C ( F) but freezing point is -. C (. F) Shelf-life: C ( F): > weeks F ( F): ~ weeks High relative humidity, avoid free moisture Controlled atmospheres Low O beneficial, CO >% damaging Ethylene sensitive
Field Pack & Palletize Vacuum Cool Naked, Liner, Head wrapped, Clamshells
Simple packaging to reduce water loss. Need to cool product before packaging (room or hydrocool) or used vented packaging and vacuum cool (romaine lettuces) Spinach Quality Parameters Green and uniform color Minimum breakage No dirt ; Clean No decay Composition nitrates, oxalates Shelf-life 6
Manual harvest of bunched Spinach; vacuum cooled Note: no longer use slickers, use aprons Mechanical harvest of young spinach for washed and packaged product http://www.ramsayhighlander.com 7
Water uptake by undamaged spinach leaves % water uptake ( min C) Cultivar st group* nd group** AM harvest Whale.7.9 PS 7.6. Space.6. Average.6. PM harvest Whale.8.7 PS 7.6. Space.. Average.6. Spinach plants dug up with roots, placed in polyethylene bags inside coolers and transported to lab where held overnight* or. days** at. C. Leaves of commercial size cut for testing. Spinach in moving water at C for min. 7 6 Spinach Damage Increases Water Absorption in Wash Flume C water min % weight increase 8 No damage Cut Cuts Young Leaves Older Leaves 8
Yellowing Rating Scale for Spinach Color score L* Chroma Hue Chlorophyll mg/g FW Carotenoids mg/g FW 9. 8. 9..9.9.7.6 6.6.7.6. 7...7.8 7.6....6 9.8.6.9.. Color values measured in upper right hand corner of each leaf; data average -6 leaves per category 9=excellent, =unuseable Impact of Temperature on Quality Changes 9 8 7 6 Visual Quality =green, =yellow. C 6 F C F 7. C F C F Color Spinach: Commerical washed and bagged product stored at temperatures Decay Off-odors =none, =severe 6 9 8 Days =none, =severe 6 9 8 Days BUT. Target Temp. ºC (ºF) Cantwell, UC Davis 9
Quality categories (leaf damage) for commercial packaged spinach Category number and name Category Description No damage Intact leaves with no or only minor damage Slight damage Intact or near intact* leaves with notable damaged area (tear, fracture) Moderate damage Intact or near intact* leaves with several damaged areas Severe damage Partial leaves and partial leaves with numerous damaged areas Leaf Pieces Leaf pieces comprised of <% of leaf area *Near intact refers to leaves cut at the base with mechanical harvester Typical defects (% damaged leaves) in spinach from commercially processed and packaged product. Defect level Food Service Retail None or slight.7.7 Moderate 7.9. damage Severe damage.. Leaf Pieces.. cv Space; data average bags (for foodservice packaging, % of bag was evaluated; product was prepared on same line.
. A. Ammonium LSD. =. g/g fresh weight..... B. Chlorophyll LSD. =.9 Ammonia increases in spinach In response to temperature and Stressful atmospheres mg/g fresh weight mg/g fresh weight.8.6......... C. Carotenoids LSD. =.7 Days at C ( F) AMMONIA INCREASE % 6 8 6 AMMONIA INCREASE GS TOT C C C 6 days, Catalano and Cantwell, 7 9 7 9 7 TOTAL GS ACTIVITY Changes in ammonium, chlorophyll and carotenoid concentrations in spinach after and days in air at C (F). Data averaged from spinach cultivars (Cantwell, ) Ammonia increases are associated with senescence and stress (storage time and temperature, modified atmospheres) in spinach and other green leafy vegetables. Ammonia µmole/g fresh wt. Air % O %O + %CO %O + %CO Air + %CO + % 6 9 Days at 7. C ( F)
Controlled or modified atmospheres appear to maintain visual quality of spinach but may also cause darkening of the leaves O +CO Figure Texture profile smooth spinach leaves Texture Profile of Spinach Leaves Smooth-No-Vein.8 ---- less fragile Wrinkled-No-Vein.6. ---- more fragile..8 µm.6...... Distance (mm) Force (N) Older Leaf 8 ppm N (8% nitrate-%ammonia) Palisade cells Spongy mesophyll ppm N (8% nitrate-%ammonia) (only part of leaf) Greenhouse spinach, Gutierrez et al 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
Spinach Storage 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 C ( F): weeks C ( F): weeks Modified atmospheres, keep CO at % or less High CO atmospheres stressful to spinach Asparagus - C (-6 F) best temperature; Asparagus is slightly chill sensitive CA with high CO is beneficial
Asparagus TIP MIDDLE BASE Cell Division Cell Enlargement Cell Elongation Hydration Cell Wall Thickening Sugars LOW Protein & Acidity HIGH Slight Lignification Total Solids 8-% % Water High Sugars HIGH Protein & Acidity LOW Maximum Lignification M. Cantwell, UC Davis
Asparagus storage conditions. C (slightly chilling sensitive) High humidity - weeks; weeks MA Modified atmospheres O -% CO 7-% Asparagus: Deterioration and Temperature Tip decay (bacterial) 9 Excellent 8 7 Good Quality score 6 Fair C C C. C Poor 6 9 8 7 6 Days storage Frozen and then thawed Storage Conditions for Fresh Herbs C ( F) but freezing point is -. C (. F) Shelf-life at C ( F): - weeks Shelf-life at C ( F): - weeks - Shelf-life based on aroma quality: - week - Exception: chilling sensitive basil. C ( F) best High relative humidity, protective packaging, but avoid free moisture condensation Modified atmospheres can be beneficial Ethylene sensitive: yellowing, abscission, epinasty
9 A. Visual Quality CILANTRO 8 9=excellent, =unusable 7 6 B. Color C F C F C F C 9 F =green, =yellow L* 9.. 6. 68. 7.7 =none, =severe C. Decay LSD. C F C F C F C 9 F Chroma.9 8... 6. Hue.. 8.. 8. Chlorophyll.77.6.8.6. mg/g FW Carotenoids mg/g FW.8..7..6 6 8 Days Paulenas and Cantwell, UC Davis, 8 Basil Highly susceptible to water loss Very chilling sensitive Situation: Excellent quality crop Harvesting late in day High temperatures, ~ C Low RH, ~%; Little protection from ambient Long delays to packinghouse What can be done to improve this handling??? 6
Chilling injury Score Basil loses moisture very rapidly Basil is very chilling sensitive Chilling Score =no injury; 8=severe 8 C ( F). C (6 F) 7 6 C ( F) C ( F) 7. C ( F) 6 7 8 9 Days C C C F F F Basil stored days in plastic bags Shiso, a basil relative, is also chilling sensitive Cantwell, UC Davis, July, 6 7
days C C C C Exposed Covered F F 68 F 86 C Weight loss in relation to VPD in products Weight loss, % per day 8 9 6 Strawberry y =.6x +. R =.9 Broccoli y =.x +. R =.97 Romaine y =.6x +. R =.9 Mushroom y =.8x +., R =.98 6 8 6 Vapor pressure deficit, mm Hg Strawberry Romaine lettuce Broccoli Mushroom Cold and Dry Bacterial growth: temperature and moisture 8
Belgian Endive-keep cold and away from light Production Conditions and Quality Implications China: row covers lettuces Belgium: Hortiplan, mobile gully system Harvesting mache, Turin, Italy, China: nutrient film technique 9
Causes of Quality & Postharvest Losses Leafy & Related Vegetables Lettuces Spinach Cabbage Chard Broccoli Celery Herbs Endives Asparagus Green Onions Mushrooms Water loss Mechanical damage Loss of chlorophyll and other nutrients Respiration rates Microbial growth Sensitivity to ethylene