Postharvest Technology of Horticultural Crops Short Course // Causes of Quality & Postharvest Losses Leafy & Related Vegetables Postharvest Handling Leafy & Related Vegetables Marita Cantwell, UC Davis micantwell@ucdavis.edu http://postharvest.ucdavis.edu 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 cv. Legacy... Storage temperature 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Compositional Quality and Storage Temperature Chlorophyll Limit of Salability Ascorbic Acid mg/g FW mg/ gfw Cantwell, unpublished Carotenoids C ( F) C ( F) C ( F) Sugars Broccoli Quality and Variety Evaluations Head Size, floret uniformity Floret/Head Color Head Firmness, Stem Texture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
Postharvest Technology of Horticultural Crops Short Course // % Firmness loss % Firmness loss vs % Weight loss y =.x; R =. Broccoli held at.c % 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 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 y =.x +. R =. % Weight loss Broccoli held at,,, and C Firmness, N force to compress Weight loss, % 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. B. Firmness, bags folded over LSD. at C ( F) 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. Cantwell, UC Davis, Maturity at harvest Protect from water loss Cool as soon as possible Leafy green grower, Singapore Aug 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. C Air -MCP, C Air C C H -MCP, C C H Collards Leaf maturity: Size, weight Leaf opening Uncurling of edges Color Width of midrib Leaf thickness Leaf wax C Air C Air C C H -MCP=-methyl-cyclopropene, SmartFresh, AgroFresh days; ppm CH; ppb -MCP
Postharvest Technology of Horticultural Crops Short Course // Napa or Chinese cabbage Black Speck Disorder 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. 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 Cauliflower Decay/Discoloration (in relation to storage temperature) Marita Cantwell Opportunities related to more nutritious lettuces Cauliflower and Modified Atmospheres Constituent (fresh wt. basis) Romaine Iceberg Chlorophyll (mg/ g).. Carotenoids (mg/ g).. Sugar (mg/g).. Vitamin C (mg/ g).. Phenolics (A ).. Cantwell and Ermen
Postharvest Technology of Horticultural Crops Short Course // 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
Postharvest Technology of Horticultural Crops Short Course // 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 Roots on heads effect on product quality? Simple packaging to reduce water loss. Need to cool product before packaging (room or hydrocool) or used vented packaging and vacuum cool (romaine lettuces)
Postharvest Technology of Horticultural Crops Short Course // 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 http://www.ramsayhighlander.com Mechanical harvest of young spinach for washed and packaged product Spinach Damage Increases Water Absorption in Wash Flume C water min % weight increase No damage Cut Cuts Young Leaves Older Leaves Yellowing Rating Scale for Spinach Quality categories (leaf damage) for commercial packaged spinach Category number and name Category Description 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 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
Postharvest Technology of Horticultural Crops Short Course // =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 Typical defects (% damaged leaves) in spinach from commercially processed and packaged product. Defect level Food Service Retail None or slight.. Moderate.. damage Severe damage.. Leaf Pieces.. cv Space; data average bags (for foodservice packaging, % of bag was evaluated; product was prepared on same line. Cantwell, UC Davis g/g fresh weight mg/g fresh weight mg/g fresh weight................. A. Ammonium B. Chlorophyll at C ( F) LSD. =. LSD. =. C. Carotenoids LSD. =. 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 in spinach and other leafy greens in response to temperature and stressful modified atmospheres AMMONIA INCREASE % AMMONIA INCREASE GS TOT C C C days, Catalano and Cantwell, TOTAL GS ACTIVITY Off-odor score...... Spinach stored in produce bags at C (no atmosphere modification) Spinach off-odors vs Ammonia y =.x +. R =. Ammonia, µg/g FW µmole/g fresh wt. Ammonia increases are associated with senescence and stress (storage time and temperature, modified atmospheres) in spinach and other green leafy vegetables. Ammonia Air % O %O + %CO %O + %CO Air + %CO at. C ( F) + % Controlled or modified atmospheres appear to maintain visual quality of spinach but may also cause darkening of the leaves 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.... ppm N (% nitrate-%ammonia) Palisade cells Distance (mm) Spongy mesophyll ppm N (% nitrate-%ammonia) (only part of leaf) 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.
Postharvest Technology of Horticultural Crops Short Course // Spinach =excellent, =unusable mg/g FW A. Visual quality LSD. C ( F) C ( F) C ( F) D. Vitamin C E. Antioxidant activity LSD. =none, =severe mg Trolox/g FW B. Decay or deterioration LSD. LSD. C ( F) C ( F) C ( F) =none, =severe C. Yellowing LSD. C ( F) C ( F) C ( F) Spinach leaves are perishable and respond to storage temperature Decay can be an important factor in shelf life Nutrient levels are relatively high and also responsive to storage temperature Temperature to limit of marketability Spinach to % Vitamin C to % Antioxidant activity C ( F) > > > C ( F) C ( F). CONCLUSIONS: Buying spinach based on visual appearance would ensure good nutritional quality.. Is postharvest visual appearance a good indicator of nutritive value for vegetables? Generally YES! Vegetable Conclusion Artichoke Arugula Asparagus Bean, green Broccoli Cauliflower Kale Snap Pea Spinach Zucchini Partially Partially yes Used % retention of Vitamin C and Antioxidant Activity at the limit of marketability (score out of ) as criteria to answer the question. WIC Study,. Cantwell et al. 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 Asparagus TIP Cell Division Cell Enlargement Sugars LOW Protein & Acidity HIGH Slight Lignification MIDDLE Cell Elongation Hydration Total Solids -% % Water High - C (- F) best temperature; Asparagus is slightly chill sensitive CA with high CO is beneficial BASE M. Cantwell, UC Davis Cell Wall Thickening Sugars HIGH Protein & Acidity LOW Maximum Lignification
Postharvest Technology of Horticultural Crops Short Course // Asparagus storage conditions. C (slightly chilling sensitive) High humidity - weeks; weeks MA Modified atmospheres O -% CO -% Asparagus: Deterioration and Temperature Tip decay (bacterial) Excellent Good Quality score Fair C C C. C Poor 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 =none, =severe =green, =yellow =excellent, =unusable A. Visual Quality CILANTRO C F C F C F C F B. Color C. Decay C F C F C F C F LSD. L*..... Chroma..... Hue..... Chlorophyll..... mg/g FW Carotenoids..... mg/g FW Paulenas and Cantwell, UC Davis, 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??? Basil loses moisture very rapidly Basil is very chilling sensitive Chilling Score =no injury; =severe C ( F). C ( F) Chilling injury Score C ( F) C ( F). C ( F)
Postharvest Technology of Horticultural Crops Short Course // days C C C C Exposed Covered C C C F F F Basil stored days in plastic bags Shiso, a basil relative, is also chilling sensitive F F F C Cantwell, UC Davis, July, Belgian Endive-keep cold and away from light 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 Bacterial growth: temperature and moisture 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