Fruit Ripening & Retail Handling Workshop Cold Storage Disorders of Fruits and Vegetables Mikal E. Saltveit Mann Laboratory, Department of Plant Sciences University of California, Davis Why use cold storage? Shelf-life is inversely proportional to respiration (colder temp slower respiration longer shelf-life). The rate of respiration at least doubles for every 18 F (1 C) rise in temperature (a Q 1 of 2). Low temperatures reduce microbial growth. Low temperatures reduces water loss (air at 1 C can hold twice as much water as at C) Fruit ripening workshop Cold storage disorders 1 Fruit ripening workshop Cold storage disorders 2 Respiration and Temperature Ripe Strawberries After 7 days Respiration (mg CO2/kg h) 3 Asparagus spears Globe artichokes 1 Head lettuce 1 1 2 Temperature ( C) Q 1 = 1/4 = 2. Fruit ripening workshop Cold storage disorders 3 Heat production (1, BTU/Ton day) 4 Brussels sprouts 3 Shasta strawberry Wickson plum 1 4 1 1 2 3 Temperature ( C) A B C C C 1 C 32 F 41 F FSlide from Marita Cantwell Fruit ripening workshop Cold storage disorders 4 Effect of handling temperatures on strawberry deterioration Treatment (48 h period) Fruit condition (%) Sound Soft Rotted 1. 48 h at C (41 F) 9 4 1 2. 24 h each at C (41 F) 76 1 14 and C (68 F) 3. 2 x 12 h periods at C (41 F) 7 7 23 and C (68 F) 4. 48 h at C (68 F) 44 1 Slide from Marita Cantwell Mitchell et al., 1996 Handling Strawberries, UC Publ. 2442 Fruit ripening workshop Cold storage disorders The saturated water content of air (SVP) increases logarithmically with increasing air temperature The SVP doubles for every 11 C rise in temperature R.H. = VP * 1 SVP 1 atmosphere = 98 kpa =.1 mpa = 1.1 bars = 14.7 psi = 76 mm Hg = 33.9 ft H 2 O Wet bulb temperature ( C) Wet bulb lines Saturation ti Vapor Pressure (SVP) Constant Vapor Pressure -1 - Relative humidity lines Dry bulb lines 1 1 2 3 Relative humidity (%) 1 8 6 4 3-1 - 1 1 2 3 3 4 4 6 Dry bulb temperature ( C) Fruit ripening workshop Cold storage disorders 6 4 4 3 3 2 1 1 Vapor pressu ure (kpa) Page 1
Excessive water loss can occur at low relative humidity Relative humidity (%) 6 4 3 1 8 3.28 4 4 The Temperature window Coil temperature = C (32 F) Room temperature = C (41 F) RH = 7% Wet bulb temperature ( C) 1 1 2.24..16.12.8 Specific humidity (kg/kg) 3 3 2 1 Water vapor pressure (millibars) 1 -.4-1. - 1 2 1 3 4 4-1 3 6 Dry bulb temperature ( C) Fruit ripening workshop Cold storage disorders 7 Freezing Chilling Heat stress - 1 1 2 3 Fruit ripening workshop Cold storage disorders 8 Outside the Optimum Ripening of Tomato Fruit High temperature - scald, sunburn Non-freezing Temperatures - chilling sensitivity Sub-zero temperatures - frost injury, freezing Chilling injury Just right 1 1 2 3 4 High temperature injury Tomato fruit after 2 weeks at C. Softening and synthesis of pigments and aromas may be abnormal at cold (chilling injury) or high temperatures. Fruit ripening workshop Cold storage disorders 9 Fruit ripening workshop Cold storage disorders 1 Problems with cold storage Temperatures below 32 F ( C) can cause freezing (depends on the tissue s sugar content). Freezing usually reduces quality and shelf-life Non-freezing temperatures below about F (1 C) can cause chilling injury. Chilling injury may be hidden and only develop after the product is purchase by the consumer. A closed cold storage room allows accumulation of gasses: CO 2, C 2 H 4 Freezing Injury Water in the cell walls surrounding each plant cell contains less soluble solids (e.g., sugars) than does the cytoplasm in the cell, so ice crystals first form in the cell wall. The solution in the cell wall gets more concentrated t as ice crystals form. Water moves from the cell into the cell wall to re-establish osmotic equilibrium, and the cell dehydrates. Cellular dehydration, not ice crystal formation, causes cellular injury associated with freezing. Fruit ripening workshop Cold storage disorders 11 Fruit ripening workshop Cold storage disorders 12 Page 2
3 Ice Crystal Formation Volume change upon Freezing Ice crystals form by the accretion of water molecules on the surfaces of an existing surface. No motive force can be exerted by a growing g crystal. Water at C (32 F) =.9998 g/cm 3 1 g water = 1.2 cm 3 Water is most dense at 4 C (32 F) 1 g ice = 1. cm 3 Ice at C (32 F) =.9167 g/cm 3 1 g ice = 1.99 cm 3 WATER The volume of an ice crystal actually decreases as it cools.917 Decreasing volume Ice takes up more volume than an equal weight of water, so ice floats. D = 12.94, same weight, but now larger volume D = 1 V = 4/3 r 3 Fruit ripening workshop Cold storage disorders 13 Fruit ripening workshop Cold storage disorders 14 Sugars and Freezing Susceptibility Why does fruit tissue close to the pit freeze first, and not tissue in the flesh? Core tissues freeze before outer flesh tissues because of differences in soluble solids content within the fruit. Examples of Freezing Injury Why did it freeze on just those edges? Freezing point depression; dependent on the number of molecules or ions and their ability to organize water. Tissue collapse Water logging Fruit ripening workshop Cold storage disorders 1 Fruit ripening workshop Cold storage disorders 16 Examples of Freezing Injury Most Fruits and Vegetables are chilling tolerant Water logging But many are chilling sensitive Fruit ripening workshop Cold storage disorders 17 Fruit ripening workshop Cold storage disorders 18 Page 3
Chilling Injury Chilling injury is a physiological disorder; however, symptom development can involve increases susceptibility to specific microbes. Chilling injury develops after exposure to non-freezing temperatures below a critical temperature. The severity of the injury depends on the temperature of exposure, and the length of exposure. The critical of threshold temperature varies with: crop, cultivar, growing conditions, pre-treatments, etc. Symptoms usually develop upon return to room temperature. The post-chilling environment can mitigate or accentuate symptom development. Flowering plants originated in the tropics Flowering plants evolved in the tropics and most tropical and semi-tropical plants are chilling sensitive. Tropical, sub-tropical, and even some temperature fruit are chilling sensitive and damaged by non-freezing temperatures below 1 C ( F) Fruit ripening workshop Cold storage disorders 19 Fruit ripening workshop Cold storage disorders Bell pepper Grapefruit Internal and external tissue browning Fruit ripening workshop Cold storage disorders 21 Surface pitting & discoloration Fruit ripening workshop Cold storage disorders 22 Chilling of Bananas Control Chilled Browning of inner side of peel Dracaena Cucumber String beans Tissue necrosis followed by attack by specific pathogens Fruit ripening workshop Cold storage disorders 23 Skin discoloration, Failure to ripen Chilled bananas develop a dull gray smoke appearance upon ripening. Fruit ripening workshop Cold storage disorders 24 Page 4
Chilling of Pineapples Endogenous Brown Spot Internal Breakdown of Stone Fruit Mealiness (soft but not juicy) Flesh Browning Lack of Flavor Failure to Ripen Internal Breakdown is induced by intermediate storage temperatures (2-8 C, 1-6 weeks) 7.2 C (4 F). C (42 F) 3 C (38 F) Fruit ripening workshop Cold storage disorders 2 Crisosto et al., 1999. Susceptibility to chilling injury of peach, nectarine, and plum cultivars in California. HortScience 34(6): 1116-1118. Crisosto et al. 4. Increasing Blackamber (Prunus salicina Lindell) plum consumer acceptance. Postharvest Biol. Tech 34: 237-234. Lurie, S and C. Crisosto.. Chilling injury in peach and nectarine. Postharvest Biol. Tech. 37: 19-8. Fruit ripening workshop Cold storage disorders 26 Susceptibility Varies with Cultivar Category Cultivar C C A Betty Anne October Sun Flavor Rich Joanne Red B Angeleno 3 Fortune 3 Hiromi Red 3 Black Amber 2 Purple Majesty 3 C Show Time 4 2 Friar 4 2 Earliqueen 3 2 Plum market life (in weeks) held at 2 storage temperatures based on chilling injury symptom development Fruit ripening workshop Cold storage disorders 27 Crisosto et al., 8. Adv. Hort. Sci. (Italy) 22(3): 1-4. Conditioning or Delayed Cooling (1% Mealy) ºC Days (% Mealy) (43% Mealy) ºC Days Crisosto, et al. 4. Controlled delayed cooling ºC 48 Hours + ºC Days extends peach market life. HortTechnology 14:99-14. Fruit ripening workshop Cold storage disorders 28 Variation in Chilling Sensitivity Diurnal changes in chilling sensitivity Cool mornings, hot afternoons, carbohydrate status Tomato seedlings are very chilling sensitive in the early morning and less sensitive later in the day. Tomato fruit also exhibit diurnal changes in chilling sensitivity. Changes can be duplicated with postharvest temperature conditioning. Preventing Chilling Injury Are we preventing injury or symptom development? Don t chill Controlled atmospheres Conditioning High temperature pre-treatment Low temperature treatment (above threshold) Intermittent warming Fruit ripening workshop Cold storage disorders 29 Fruit ripening workshop Cold storage disorders 3 Page