Temperature management

1. Temperature management

2. Coolingthe harvested product • Temperature- the most important factor in maintaining the quality of the harvested product. Product temperature response: • Temperatures in the interim. • Low temperatures damage. • High temperatures damage.

3. Low temperature affects • The harvested product is transported in low temperature. The ideal temperature: • For chilling insensitive product - just above freezing point. • For chilling sensitive product - slightly above the chilling injury temperature. • The activity rate of various enzymes involved in the metabolism of the harvested products, usually rises exponentially with the increasing temperature. • By the Dutch chemist Van Hoff Chemical Reaction rate multiplied any 10oC. The value of Q10 decreases with increasing temperatures. 10 / (t2-t1) Q10 = (R2/R1)

4. Low temperature affects • Lowering the temperatureinhibits theexhaustionof the harvested product • Lowtemperaturecandelay thebeginning ofripeningin climacteric fruits (Onset of ripening.(Lowtemperaturesslowthe rate ofethyleneproductionandthe response to ethylene. • Therefore, a prolonged exposure toethyleneis necessarytostartripeningprocesses at low-temperature.

5. Low temperature affects • Ripening temperatures- 10-30oC, usually. • Some pear varieties will ripe at temperatures lower than 10oC, but prolong storage in low temperature might inhibit adequate ripening. • Maintaining products at low temperatures can inhibit developmental processes in various products, such as opening inflorescence of cut flowers, asparagus lignification and loss of sweetness of peas. • Exposure to low temperatures may occur during transport, storage ect.

6. Low temperatures injuries

7. Low temperature injuries • Freezing injury • Freezing injury is not due to disruption of metabolism similar to chilling injury. • Caused irreversible damage due to ice crystals created in the product. • Brief freezing of fleshy tissue affects the product. • Freezing temperature is different between the products, due to the content of different solutes. • The products’ moisture content influence its resistance to freezing. • water are not available to create ice crystals in products with very low humidity content. • Freezing: lettuce - 0.2oC, grapes - 2.0oC. • When defrosting – in most products, the tissue is thaw, the texture changes and water soaked areas appear. • Less sensitive products: a slow thaw of cabbage, onions and several varieties of pear. • Acclimatization of different products to low temperature may reduce their sensitivity to freezing injuries.

8. Freezing injuries

9. Chilling injury • Chilling injury is the result oftemperatureshigher than freezing temperatures. • The injury isdueunbalancedmetabolismanddamage to the cellular compartments Lowtemperaturedamagesare divided intotwo categories: Chilling injury and physiological disorders. • tropical and subtropicalfruits are particularlysusceptible tochilling injuries. • Chilling injury is the combinationof temperature andduration ofexposure. • Low temperaturefor a short time - may not develop any injury. • Low temperaturefor a long time - irreversible chilling injury maydevelop.

10. Chilling injury • Differentsensitivity toChilling injurymay occurbetweenvarieties of the same fruit, or a result of different growth region. • Sometimesthe damageis visible after transition of the product to higher temperature (shelf life) . Typicalsymptomsofchilling injuryin someproducts:

11. Chilling injury • Pitting- Collapse ofcellsbeneath the surface, leading topittingandchange of color. Might increasewater loss.

12. Chilling injury • Browning- Usuallyappearsaroundthe fruittransportorgans ( e.g. xylem).Browning ,might be the result of the action ofthe PPOenzyme oxidizing phenolsreleased from the vacuole as a result of the chilling damages.

13. Chilling injury • uneven ripening- early harvested fruit might not ripen properly after prolonged cold storage.

14. Chilling injury • De-greening- Slowingthe loss ofgreen colorevenbyslightcooling.

15. Chilling injury • water soaking- exposure to cold of leafy vegetables and some fruits like papaya.

16. Chilling injury • Increasing the sensitivity to pathogens- chilling injury damage the cellular compartments and results the release of amino acids, sugars, minerals and other factors that serves as excellent substrates to pathogens.

17. Chilling injury Developmentof off flavors, aftertasteandundesirable odors.

18. Chilling injury PreventingChilling injury • Cooling the product above its criticaltemperature. • Conditioning- exposure of the product torelativelylowtemperaturefor a short timefollowing by storageat higher temperaturemaypreventchilling injury. • This method iseffective inpreventingbrowningof pineapple, peach wooliness and plum internal browning. • Successful treatmentto preventchilling injury innectarinesand peachesisa combination ofintermediateheatingand controlledatmosphere. • ImmersioninCaCl2reducedlow temperature breakdown (LTB) in Jonathanapples.

19. The mechanism of chilling injury development Lipid hypothesis of chilling • Some lipidsundergo changesat lowtemperaturethat affects thephysical propertiesofcellmembranes. • As a result, membranepropertiesare affected, including: membraneintegrity, ionsandmetabolitespermeability, and the activity ofmembrane-anchoredenzymes. • Later, there may beeffectson the metabolismandcellularcompartment,leading tocell deathandthe known symptomsofchilling injury.

20. Physiological disorders during cold storage • Physiological disorders during cold storage are mainly deciduous (apples, pears), stone fruits (peaches, plums) and in most citrus. • The damage might affect only the surface of the product or the flesh and core sections as well. • The metabolic process that results the damage is usually unknown, and perhaps different symptoms caused by different malfunctioning of the metabolic pathway. • Physiological response to cold damage have been studied mainly on apples.Most damages are developing during exposure to temperatures lower than 5oC.

21. Physiological disorders during cold storage

22. Physiological disorders during cold storage Factors affecting thesusceptibility tothe damage:ripeningstage at harvest, orchard treatments,the climateduringfruitdevelopment, fruit size, method ofharvest. storage methodsfor chilling sensitivefruit: • shortstorage period. • Gradualcoolingat the firststages ofstorage. • Heatingintermediate20oCfor several daysduring storagereducedthis disorder in applesandstone fruits, butproblematic incommercial terms:It is difficult toquickly elevate thetemperaturein the storage roomwith large amount offruit.

23. Physiological disorders during cold storage Prevention of chilling injuries: Brief exposureto high temperatureprevented: • Superficial scald in apples • Pitting in avocado, citrus andcucumber. • Brown spotsin prickly pear. • Grapefruit - after harvest:48 hoursat 27-29oC, or 7days in 21oC,followed by storageat 10-16oC.

24. Physiological disorders during cold storage Controlled atmosphere conditions: • Jonathan spots prevention, reduction of core browning and internal breakdown of apples. • On the other hand, an increase of internal breakdown was reported in controlled atmosphere storage due to: High humidity, lack of air movement, accumulation of fruit volatiles. • Low oxygen levels and high carbon dioxide levels: core browning in apples and pears.off flavors- anaerobic metabolism.

25. Physiological disorders during cold storage • Fruit peel blemishes might affect its appearanceand reduce its marketability. • Internalblemishes - morecommercially " tolerable". • It is possible to reduce these blemishes by chemical and physical treatments, or by choosingless sensitivevarieties.

26. High temperatures damages Exposureto high temperatures: • Exposureto direct sunlight • Hotwind. Heattreatmentto preventpathogens: • Immersionin hot water, evaporation, anddryheat. • Enzymaticactivitydecreasesin mostharvested productsabove 30oC, andabove 40oCare inactivedue todenaturation.

27. Additional use of different temperature exposures High temperatures: • Prolongedexposureto heatofclimacteric fruitsadvancedfruit ripening, butdelayedthe colorchange. E.g. yellowing of banana peel or redness of tomato. • The metabolism is disrupted over 35oCresulting inimpairedmembraneintegrityleading tocellularcompartment damagesexpressedas loss ofpigmentand transparency of the product.

28. Additional use of different temperature exposures Prevention ofpests: • Essential topreventtheirspreadingto new areas. • Temperaturetreatmentscanpreventvarious insectsin fruits, vegetables, nuts, flowers and more. • For example, 125 minutesat 51.5oCpreventsCaribbeanfruitflyin mangoes.

29. Additional use of different temperature exposures Prevention ofpests: • Low temperature - delaythe development ofpathogens including bacteria and fungiandalsodelaythe development ofinsects. • High temperature - short-termexposure iseffectiveforpathogeninhibition, for example: 3 secondsof steam(100oC) reduced decay incarrots.Shortexposure of mangoes to 55oCreduced decay.Immersion of papayain waterat 49oCfor 20minutesreduceddecay.

30. Additional use of different temperature exposures Conditioning • Conditioning before storageormarketingcan affecta variety offruittraitssuch asincreasedfirmnessof apples, delay of asparagusgravitropism, delayof sprouting ofpotatoes. • Conditioning afterstorage canspeed upgerminationandfloweringofgladiolibulbsorlilybulbs.

31. Additional use of different temperature exposures Curing • Exposureto conditionsthat allowhealingof woundsorthe developmentofa protective layer. • Brief exposure tohightemperatureafter harvest: potato - Exposureto 29oCfor 5-7 days (80-90% R.H.) accelerating the creation of periderm layer at the site of injury which reducedecay.Kiwi - stayin the shedfor 24-48hours afterimmersionbefore storage.

32. the affects of temperature on starch and sugar balance • Storageat low temperaturescan affect thebalance ofsugarandstarch invariousvegetablessuch aspotatoes, sweet potatoes,green peas,cornand more. starch↔sugar→CO2 • Ambient temperatures: starch←sugar • Respiration decrease in low temperatures: starch↔sugar→CO2 • Sugaraccumulationbeginsat typicaltemperaturecriticalfor the product:potato 10oC, sweet potato 15oC.

33. the affects of temperature on starch and sugar balance Due to theaccumulationof sugar: • Inferiortextureandsweetnessin cooking. • Browningdue to caramelization during frying. • Maillardreactions as aresult ofinteraction betweenamino acidsandsugars. • Typically,raising the temperatureto15-20oCreturns thesugarto its previous level.

34. the affects of storage temperature on starch and sugar balance • highsugar content is desirable in cornandpeas. • Those are pickedat early stage of maturity (immature)whensugar contentis highest. • Faststorage at low temperatureis neededtopreventacceleration of starch sugar conversion.

35. The benefits of cold storage • Decreases the rate of respiration. • Low respiration rate → long shelf life • Reductionof 10oCmay decrease the respiration rate by 2-3 folds. • shelf lifeincreases by 2-3 folds.

36. The benefits of cold storage • Reducing water loss. • hot product has the largest water loss. • Fast cooling → less water loss. • In some products the water loss during 1 hour in hot and dry air is similar to 1 week in cold storage with high humidity.

37. The benefits of cold storage • Reducing decays. • Harvest temperatureis optimalfor manypathogens. • Low temperatures significantlyreducesthe development ofpathogens.in the product.

38. What are theheat sources? • Fieldheat (sensible heat). • Metabolicheatgeneratedduring the respiration process (vital heat). • Passingheatconductionthrough walls, floorsetc. • Heatexchange ofairor leaks. • Other sources: lights, motorsand more.

39. What are theheat sources? • 47%- Field. • 37%- The fansin the storage facility. • 8%- Forklifts. • 7%- Conductionthrough walls, roof, and air. • 1%- lights, labor, and more.

40. Half cooling timeor 7/8 cooling time • Halfcoolingtime- time requiredto reduceby halfthetemperature differencebetween the product andthe environment. • coolingrate is higher as thetemperature differencebetween the product and the environmentis larger, although half-coolingtimeremains constant. • Three coolingcycles ofthe productwill allowcoolingin 7/8 of thetemperature differencebetween the product andthe surrounding environment (1/2 ← 1/4 ← 1/8).

41. Heat removal • Conduction • Convection • Evaporation • Radiation

42. Coolingmethods Cold air • air is simpleand accessiblemediumeasy tomove. • Lowthermalcapacity. Ways of cooling with coldair: • Coldroom. • Forced aircooling.

43. Coolingmethods Coldroom • Coolingmethodwhichrequireslesscoolingcapacitythanothercoolingmethodsbecauseheat removallastsa relativelylong time (e.g.overnight) • The product canbe storedwhere itis cooled. • The process is slow.

44. Coolingmethods Forced aircooling • Much fastercompared withpassive cooling (4 - 10 fold times faster). • This method allowsrapidmobilizationof the productto the marketswithoutextensive use ofthe storage rooms. • High coolingcapacityrequiredto dealwithheat peaks.

45. Factorsthat affect thespeedandefficiency ofcooling • Cooling capacity:Impropercooling- air temperaturemay riseby addingwarm product.The initialproducttemperature: Asproducttemperature ishigher→ more time will taketocool it. • Air temperaturein the storage room:If theair temperaturewill increase especiallytowards the end ofcooling, the whole processwould be prolong. • Air velocityoverthe product:The airtakes theheatfrom the product, therefore if there is nomovement ofcoolingairthe process will be very slow. • Fanspeed:Coolingunitsare designedto coolefficiently.doubling theflow velocitycancausecoolingto be 40% faster.

46. Unevencooling • Product near cooling diffusers will cool quickly than remote product. • product at the top of the packaging cools faster than the product at the bottom. • space between the containers is important for air flow and effective cooling. • The first product in contact with cold air would cool faster.

47. Importance ofpackagingdesign • cooling holes at the packaging are required for proper cooling rate. • 5% - recommended ventilation area. • Large ventilation holes are better than many small ones. • There is high importance for hole punching method and locatin in the cardboard for achieving effective ventilation and to maintain its strength. • Other packaging materials in the carton (plastic containers, for example) will significantly reduce air flow and cooling efficiency.

48. Coolingsensing • temperature reading is recommended after a few thrusts of the thermometer in the fruit depth to Equilibrate temperatures with fruit. • Temperature measurement should be made in the fruit which is expected to cool the slowest. • Typically, the warmest fruit is far from the fan and at the bottom of the box.

49. Hydro cooling The advantages of usingwaterfor cooling: • water has highcoolingcapacity (1kcal/kg/oC), therefore waterabsorbmore energybeforethe temperature rise. • water has highheat conductivity (5.2 cal/g/h/oC), thereforethere is fasterheat loss to the water. • Use of waterfor coolingthe productpreventsloss ofwaterduringthe coolingprocess.

50. Hydro cooling • A wide varietyoffruits andvegetables are suitableto coolin cold water. • This is one ofthe fastestmethodsfor cooling. productswhich are not suitablefor this coolingmethod: • products sensitive to freewater : grapes, flowersandmostberries. • Productsthat can becooledmore efficientlywith othermethods:for example, vacuumcooling of leafy vegetables.