Water Loss and Postharvest Quality Marita Cantwell, UC Davis micantwell@ucdavis.edu http://postharvest.ucdavis.edu Water Loss and Postharvest Quality Topics to cover How does water loss occur What are critical levels of water loss Where does water loss occur in handling How to control water loss Postharvest Water Relations Water loss Water gain 1
Fresh Produce and Water Loss Fresh produce contains 65% (garlic) to 95% (lettuce) water; water content for most products is 85 90% Harvested products begin to lose moisture immediately upon cutting from the plant Water loss = transpiration Water loss = weight loss (except if significant dry matter loss during storage) Water loss is water vapor movement from product to the environment Water loss is affected mainly by packaging, temperature, relative humidity and airflow Water loss Through stem end Through epidermis and stomates Through peel and lenticels Through damaged areas J.L.J. Bezuidenhout. 2005. Lenticels different plant species, Thesis. Univ. Pretoria., SA. Light microscopy mango lenticels 2
Water loss is Cumulative Impacts on Quality Loss of Salable Weight Loss Fresh Appearance Gloss Shrivel Pitting, sunken areas Loss of Texture, Turgidity Changes in Product Physiology Critical levels for many products <3% no visual effect, texture 3-5% visual quality affected >5% shrivel, lose salability These berries were kept cold and lost less than 1% weight and look fresh These berries were held at ambient temperature and lost more than 10% weight and look old and tired Romaine Lettuce is marketable until 5% weight loss 0.4% 5.2% 10.3% 13.9% Ripened at 15C Higher gloss Less weight loss Firmer Tomatoes Ripened at 20C 3
Iceless Broccoli Temperature-yellowing Moisture loss-softening Texture and Water loss 80 % Firmness loss vs % Weight loss % Firmness loss 60 40 y = 5.68x + 9.69 R 2 = 0.80 20 0 0 2 4 6 8 10 12 % Weight loss ICELESS BROCCOLI Minimize delay from harvest to cooling Use plastic liners with holes to reduce water loss Keep it cold About 3-4% weight loss = soft head Water Loss and Fruit Physiology Water Loss and Fruit Ripening Water loss during initial phase of ripening affects rates of ripening Water loss is a stress and caused increased synthesis of ethylene Therefore minimize water loss during initial 72 hours after harvest Stage when induce water loss Total % Water loss Days to ripen Pre-climacteric 5.6 14.1 Climacteric 5.3 15.7 Post-climacteric 5.2 17.0 Early season fruit; Induced water loss conditions: 20C with 20%RH Control, 20C 95%RH lost only 1.3% weight and required 16.4 days to ripen Decay was less on fruit from treatments with water loss than on control fruit Burdon, J. et al. 2005. Mode of action of water loss on fruit quality of Hass avocadoes. NZ and Australia Grower s Conf., 2005 4
Cluster Tomato Fruit Abscission Interaction of Water Loss and Fruit Ripening No abscission: store for 2 weeks at 20C & 95%RH No Abscission: 10 ppm ethylene 8days at 20C & 95%RH No abscission: store at 20C and 20%RH if fruit full red before sepal shrivel (cannot detach fruit without damage) Abscission occurred: storing fruit at 20C and 20% or 50%RH and if sepals shrivel before fruit is full red Weight loss during harvest and initial handling is most critical JK Brecht and KM Cordasco. 2006. HortScience 41(4) Abstract 979 Fruit 100% RH in air spaces Assume 20C 100% RH Skin/epidermis Environment Temperature Relative Humidity less than 100% Air velocity Assume 20C with 40%RH VPD increases exponentially with rising temperature VPD increases linearly with falling humidity Vapor pressure deficit 5
Water loss and temperature Wt loss (%/day) = product K x VPD Psychrometric Chart Thermodynamic properties of air Temperature and Water Content VPD increases exponentially with rising temperature VPD increases linearly with falling humidity Typical field and storage conditions Handling at harvest is critical for water loss management Basil Highly susceptible to water loss Very chilling sensitive Situation: Excellent quality crop Harvesting late in day High temperatures, ~30 C Low RH, ~50%; Little protection from ambient Long delays to packinghouse What can be done to improve this handling??? 6
% Water Loss From G. Mitchell, UC Davis 7 6 Table Grapes Ideal vs Poor Postharvest Handling 5 Load at 40 F, Transport at 40 F 4 3 Cooled at 40 F, 75% RH Stored at 32 F, 75% RH air at 2 mph 2 1 0 6 hrs 80 F 20% RH 1 hr Delay Before Cooling 32 F, 95% RH 6 hours Cooling 32 F 95% RH, air at 0.5 mph 7 day Storage Load at 32 F, Transport at 40 F 7 day Transit Weight loss of Tuscan melons held for different periods at 37 C (99 F) before cooling, storage and shelf-life. Cooling delay 3.0 2.5 Water loss is Cumulative % weight loss before cool % weight loss storage 10D 5 C Tuscan melon weight loss and time at 37 C (99 F) 20%RH % weight loss shelf-life 4D 20 C Total Weight loss % Suture browning Tuscan melons Suture browning score 0 h delay control 0.00 2.14 0.97 3.08 1.2 4 h delay 0.38 1.95 0.96 3.25 1.3 8 h delay 0.85 1.85 0.78 3.45 1.3 12 h delay 1.19 1.62 0.79 3.56 1.4 16 h delay 1.50 1.32 0.85 3.63 2.8 20 h delay 2.06 1.47 0.68 4.15 4.0 24 h delay 2.80 1.41 0.71 4.85 4.2 LSD.05 0.21 0.42 ns 0.60 0.8 1=none 5=severe % weight loss 2.0 1.5 1.0 0.5 0.0 y = 0.1068x -0.049 R 2 =0.99 0 4 8 12 16 20 24 Hours at 37 C (99 F) Cantwell, UC Davis 7
Delays to cool of Tuscan Melons; fruit held at 37 C (99 F) 0 h 0.0% 8 h 0.8% Weight loss 16 h 1.5% 24 h 2.8% Melon visual quality after delays to cool, storage 10d 5 C (41 F) + 4d 20 C (68 F) 0 h 3.0% 8 h 3.2% Total Weight loss 16 h 4.0% 24 h 4.8% 8
Stems as freshness indicators Initially stems contribute 40% to weight loss As stems dry, less water loss through them Weight and water content cherries and stems. 21 C, 66%RH, restricted natural convection, 6days Parameter Fruit with Fruit Stems stems bodies Initial fresh weight, g 11.89 11.76 0.14 Final fresh weight, g 11.02 10.95 0.06 Water loss, % 7.4 6.8 54.4 Initial water content, % 80.98 81.11 69.37 Final water content, % 73.58 74.28 14.72 Linke et al. 2010. Green peduncles may indicate postharvest freshness of sweet cherries. Postharvest Biol. Tech. 58: 135-141. Litchi Browning: Water loss is a major contributor: 8% water loss for peel browning. Mechanical damage, senescence, improper storage temperature, and postharvest pathogens also contribute. Predicted postharvest moisture loss from litchi with idealized handling. Stage Temp. ( C) RH (%) Wind speed (m s 1 ) Duration (h) Predicted moisture loss (%) Cumulative moisture loss (%) Harvest 30 65 1.5 3 1.87 1.87 Pre-cooling 5 75 1 5 0.38 2.25 Storage 5 75 0 5 0.06 2.31 Transport 7 66 0 12 0.23 2.54 Wholesale 5 75 0 3 0.04 2.58 Wholesale display 25 22 0 2 0.27 2.85 Transport 7 66 0 2 0.04 2.89 Retail 20 50 0.5 6 0.90 3.79 38h Bryant, P.H. 2012. A model of postharvest moisture loss under air currents to reduce pericarp browning of litchi. Postharvest Biol. Tech. 73: 8-13. 9
Wind speed and weight loss Litchi ~8% weight loss = desiccation browning Harvest Conditions Temp. ( C) RH (%) Wind speed (m s 1 ) Duration (h) Predicted moisture loss (%) Standard 30 65 1.5 3 1.9 No wind 30 65 0 3 0.3 Delay 30 65 1.5 6 3.6 Extreme 35 50 1.5 6 6.3 Bryant, P.H. 2012. A model of postharvest moisture loss under air currents to reduce pericarp browning of litchi. Postharvest Biol. Tech. 73: 8-13. Minimize Weight loss and Firmness Loss in Peppers Water loss and Cultivars 14D 7.5 C + 3D 20 C Variety % Weight loss % Firmness loss Allegiance 3.9 35.0 Baron 6.4 60.2 Classic 4.7 56.8 Cypress 5.1 53.5 Double Up 5.8 52.4 Excel 6.3 37.7 Karisma 4.0 45.6 Patriot 4.4 53.5 RPP 22984 6.4 67.3 Wizard 4.9 45.8 Average 5.2 50.8 LSD.05 0.6 8.2 10
Role of cultivar in postharvest quality loss Example: Grape tomatoes and weight loss 12days 20C 50%RH Cultivar Shrivel * % weight loss Ahern 299 3.5 13.2 Amsterdam 3.2 15.2 Harris LI-34 4.6 15.6 Hazera 1319 4.3 18.0 Rotterdam 2.4 11.8 TC 1260 3.6 14.9 LSD.05 0.6 1.5 *Shrivel score -1-5 scale, 1=none, 2=slight, 3=moderate, 4=moderately severe, 5=severe 1 2 3 4 5 Cantwell, UC Davis 2004 Simple packaging to reduce water loss. Need to cool product before packaging (room or hydrocool) or used vented packaging and vacuum cool (romaine lettuces) 11
Firmness, N force to compress Weight loss, % 18 16 14 12 10 8 6 4 2 0 100 90 80 70 60 50 40 30 20 10 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 B. Firmness, bags folded over LSD.05 LSD.05 Broccoli weight loss and firmness loss can be minimized with plastic liners. Liners placed in field And product vacuum cooled Simple perforated PE lettuce or basil liners perform as well as more expensive plastic films. 0 0 2 4 6 8 10 Days at 10 C (50 F) Cantwell, UC Davis Condensation worse than water loss for many products Strawberries do not tolerate free moisture Dew point Salad kale does not tolerate free moisture 12
A small amount of controlled water loss leads to longer postharvest life; Avoid free moisture Weight loss, % per day 24 Weight loss in relation to VPD in 4 products Mushroom y = 1.66x - 1.29; R 2 = 0.98 21 Broccoli y = 1.15x -0.68; R 2 = 0.98 Romaine y = 0.70x -0.23; R 2 = 0.97 18 Strawberry y = 0.583x - 0.25; R 2 = 0.95 15 12 9 6 3 0 Products at 0, 10, 20 and 30C exposed or in vented plastic bags 0 2 4 6 8 10 12 14 Vapor pressure deficit, g moisture/kg dry air Cold and Dry Bacterial growth: temperature and moisture Cold and Dry Handling Leafy green grower, Singapore. Product harvested in afternoon, cooled overnight in marine container, slightly dehydrated (5-10% weight loss) and then consumer packaged the following day. 13
Washed Baby Spinach Humidity controlled Pre-wash and Storage 36h 15 C prewash; 19.7, 11.0 and 0.5% wt. loss 12d 7 C storage in MAP (~5%O2+8%CO2) Overall Visual Quality Leaf damage causes decrease in shelf-life and increase microbial load. Low =72%RH Medium =85%RH High =99%RH Percent Damaged Leaves Medina et al. 2012. Postharvest Biol. Tech. 67: 1-9. Water loss control Low temperature Packaging appropriate Minimize time 14
Water loss and Retail Handling Display ready reusable packaging What are advantages and disadvantages? Display ready reusable crates-what are advantages and disadvantages For product to tolerate such conditions at retail, must minimize water loss at earlier steps in handling chain Additional paper or plastic packaging can notably reduce water loss 1.2 Retail Spinach Bags: Weight Loss % weight loss 1.0 0.8 0.6 0.4 2.5 C 36 F 5 C 41 F 10 C 50 F 0.2 0.0 Weight loss rate per day: 2.5 C = 0.03% 5 C = 0.06% 10 C = 0.085% 0 2 4 6 8 10 12 14 16 18 Days storage 8 days Exposed 5.2% 10.3% 13.9% weight loss Bag with perforations 0.4% 0.5% 0.7% weight loss 0.5 C (33 F) 5 C (41 F) 10 C (50 F) 15
Water Loss and Postharvest Quality Water loss occurs through natural pores and damaged areas Environmental conditions at harvest cause high rates of water loss Harvest when cool Protect and shade in the field Reduce delays from harvest to start cooling Cool efficiently, then reduce air flow over product Manage Temperature, RH, air flow during storage and transport Use protective packaging Use protective treatments in some cases (waxes, coatings) Weight loss is cumulative, store only as long as necessary Controlled weight loss may be beneficial to shelf-life Problem conditions are at the beginning and end of the value chain REFERENCES Ben-Yehoshua, S. and V. Rodov. 2003.Transpiration and water stress. In: J.A. Bartz and J.K. Brecht. (Eds.). Postharvest Physiology and Pathology of Vegetables. 2nd ed., Marcel Dekker, Inc., NY. Pp. 111-159. Rodov, V., S. Ben-Yehoshua, and N. Aharoni. 2010. Modified Humidity Packaging of Fresh Produce. Horticultural Reviews 37: 281-329. Thompson, J.T. 2002. Psychrometrics and perishable commodities. Ch13. In A.A. Kader (ed.). Postharvest Technology of Horticultural Crops. Publication 3311, Univ. California Agriculture and Natural Resources, Oakland. pp. 129-134. Tijskens, L.M.M., S. Jacob, R.E. Schouten, J.P. Fernández-Trujillo, N. Dos-Santos, E. Vangdal, E. Pagán and A. Pérez Pastor. 2010. Water Loss in Horticultural Products - Modelling, Data Analysis and Theoretical Considerations. Acta Horticulturae 858: 465-471. 16