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 (%) --......... 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 (to initiate yellowing) Broccoli Shelf-life & Temperature... Storage temperature cv. Legacy C F mg/ g FW mg/ g FW Broccoli Compositional Quality and Storage Temperature Chlorophyll Limit of Salability Ascorbic Acid mg/g FW mg/ gfw Cantwell, unpublished Carotenoids C ( F) C ( F) C ( F) Sugars Iceless Broccoli Temperature-yellowing Moisture loss-softening % Firmness loss % Firmness loss vs % Weight loss y =.x +. R =. % Weight loss ICELESS BROCCOLI Minimize delay from harvest to cooling Use plastic liners with holes to reduce water loss Keep it cold About % weight loss = soft head
Broccoli Postharvest Quality and Variety Evaluations Maturity at harvest Protect from water loss Cool as soon as possible 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 Loss of green color by mature and immature Kale leaves stored at temperatures for up to days. Color score, =dark green, =yellow Mature Kale Leaves C ( F) C ( F) C ( F) C ( F) Immature Kale Leaves LSD. Leafy green grower, Singapore Aug Leaf maturity: Size, weight Leaf opening Uncurling of edges Color Width of midrib Leaf thickness Leaf wax C Air -MCP, C Air C C H -MCP, C C H Napa or Chinese cabbage Black Speck Disorder Collards C Air C Air C C H -MCP=-methyl-cyclopropene, SmartFresh, AgroFresh days; ppm CH; ppb -MCP
Black speck index Black Speck Disorder on Chinese Cabbage Air Ethylene Cv #= T- = Yuki = Spring Flavor = Southern King = New Summer = Chacha = China Express = Blues = WR- 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. Cauliflower Quality Color is cream white Freedom from mechanical injury Freedom from decay No discoloration on cut edges Cultivar Black speck index = black speck score multiplied by % extension. Cultivars vary greatly in their susceptibility to the black speck disorder. Cauliflower Discoloration (in relation to storage temperature) Opportunities related to more nutritious lettuces Constituent (fresh wt. basis) Romaine Iceberg Chlorophyll (mg/ g).. Carotenoids (mg/ g).. Sugar (mg/g).. Vitamin C (mg/ g).. Phenolics (A ).. Marita Cantwell Cantwell and Ermen 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 Vital Heat (BTU/ton-day) Iceberg (air) Romaine (air) Looseleaf (air) Iceberg (% O ) Temperature and Respiration Rate Oxygen and Respiration Rate Respiration rate (mg CO/kg-hr) C ( F) C ( F) From M. Cantwell, UC Davis C ( F) C ( F) C F Temperature
Immature Mature Overmature No. leaves Weight Firmness % Green Sweetness Bitterness Phenolics Russet Spotting Ethylene-induced Disorder on Lettuces Large differences among varieties in susceptibility Russet spot scores ~ (none),, and, respectively. Lettuce Maturity -MCP Prevents Russet Spot Disorder on Iceberg Lettuce Russet Spotting Score =none, =severe =Sonoma A. Iceberg Lettuces =Spreckles =Salinas =Raider =Salinas =Buena Vista =Stinger =Van Sal =Salinas =Ace =Champ =Salinas =Ridgemark Variety B. Romaine Lettuces =Paris Island Cos =Romo =Red Eye Cos =Gx =Corazon =Red Hot Cos =Nero Variety Russet spot score, =none, =severe Air ppm Ethylene -MCP, Air -MCP, ppm Ethylene LSD. Control + Ethylene -MCP + Ethylene Development of Russet Spot Disorder on Iceberg and Romaine Lettuces. Intact heads were stored in ppm ethylene at C ( F) plus week in air. at C Cantwell, UC Davis, unpublished 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 Romaine Symptoms of Freezing in Lettuce Freeze Injury Pink rib Heart Discoloration 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 Traditional Packing of Romaine: Do not place cut lettuce on the ground Waxed cartons or cartons with liners rather than crates days Naked lettuce Vertical shelving Open Simple packaging to reduce water loss. Need to cool product before packaging (room or hydrocool) or used vented packaging and vacuum cool (romaine lettuces).%.%.% weight loss Plastic Bag.%.%.% weight loss. C ( F) C ( F) C ( F)
Spinach Quality Parameters Manual harvest of bunched Spinach; vacuum cooled Note: no longer use slickers, use aprons Green and uniform color Minimum breakage No dirt ; Clean No decay Composition nitrates, oxalates Shelf-life Yellowing Rating Scale for Spinach Mechanical harvest of young spinach for washed and packaged product http://www.ramsayhighlander.com Color score L* Chroma Hue Chlorophyll mg/g FW Carotenoids mg/g FW......................... Color values measured in upper right hand corner of each leaf; data average - leaves per category =none, =severe =excellent, =unuseable Impact of Temperature on Quality Changes Visual Quality Decay =none, =severe =green, =yellow Color. C F C F. C F C F Off-odors Spinach: Commerical washed and bagged product stored at temperatures BUT. Target Temp. ºC (ºF) Cantwell, UC Davis 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
Changes in ammonium, chlorophyll and carotenoid concentrations in spinach after and days in air at C (F). Data averaged from spinach cultivars (Cantwell, ) g/g fresh weight mg/g fresh weight mg/g fresh weight................. A. Ammonium B. Chlorophyll at C ( F) LSD. =. LSD. =. C. Carotenoids LSD. =. AMMONIA INCREASE % Ammonia increases in spinach In response to temperature and Stressful atmospheres AMMONIA INCREASE GS TOT C C C days, Catalano and Cantwell, TOTAL GS ACTIVITY Figure Texture profile smooth spinach leaves Texture Profile of Spinach Leaves Smooth-No-Vein. ---- less fragile Wrinkled-No-Vein.. ---- more fragile.. µm... Force (N) Older Leaf.... Distance (mm) ppm N (% nitrate-%ammonia) Palisade cells Spongy mesophyll ppm N (% 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 (- 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 -% % 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 -% Quality score Asparagus: Deterioration and Temperature Excellent Good Fair Tip decay (bacterial) 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 C C C. C Poor storage Frozen and then thawed A. Visual Quality CILANTRO =none, =severe =green, =yellow =excellent, =unusable C F C F C F C F B. Color C. Decay LSD. C F C F C F C F L*..... Chroma..... Hue..... Chlorophyll..... mg/g FW Carotenoids..... mg/g FW 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 Paulenas and Cantwell, UC Davis, What can be done to improve this handling??? Chilling injury Score C ( F). C ( F) C ( F) Basil loses moisture very rapidly Basil is very chilling sensitive Chilling Score =no injury; =severe C ( F). C ( F) C C C F F F Basil stored days in plastic bags Shiso, a basil relative, is also chilling sensitive Cantwell, UC Davis, July,
days C C C C Exposed Covered Weight loss, % per day Weight loss in relation to VPD in products Strawberry y =.x +. R =. Broccoli y =.x +. R =. Romaine y =.x +. R =. Mushroom y =.x +., R =. Strawberry Romaine lettuce Broccoli Mushroom Vapor pressure deficit, mm Hg Cold and Dry F F F C Bacterial growth: temperature and moisture Belgian Endive-keep cold and away from light Celery hearts Trimmed, washed and packaged Mobile processing unit Chlorine rinse Drain and package in perforated bag T&A, June Production Conditions and Quality Implications Causes of Quality & Postharvest Losses Leafy & Related Vegetables China: row covers lettuces Belgium: Hortiplan, mobile gully system 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 Harvesting mache, Turin, Italy, China: nutrient film technique