Pertemuan ke 3 temperature effects on deterioration

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Pertemuan ke 3 temperature effects on deterioration

  1. 1. Temperature Effects on DeteriorationTemperature Effects on DeteriorationThere are six direct temperature effects onThere are six direct temperature effects ondeteriorationdeterioration The rate of respiration is determined by theThe rate of respiration is determined by thetemperature of the producttemperature of the product The rate of water loss from harvested produce isThe rate of water loss from harvested produce isdirectly influenced by the temperature of thedirectly influenced by the temperature of theenvironment that the product is held in.environment that the product is held in. The temperature of the product influences allThe temperature of the product influences allmetabolic activity in the tissue including the synthesismetabolic activity in the tissue including the synthesisof ethylene, its activity and its sensitivity if exposed toof ethylene, its activity and its sensitivity if exposed toan external source of ethylene.an external source of ethylene.
  2. 2. Lower temperature will offer some controlLower temperature will offer some controlover a lot the disease organisms that causeover a lot the disease organisms that causedecay.decay.Lower temperature will slow down the activityLower temperature will slow down the activityof insects and over prolonged periods, mayof insects and over prolonged periods, maykill the pest.kill the pest.The temperature of the environment and theThe temperature of the environment and theproduct will determine the amount of growthproduct will determine the amount of growthand development that occurs after harvestand development that occurs after harvest
  3. 3. Gaseous Environment Effects onGaseous Environment Effects onDeteriorationDeterioration There are four gases of importance in theThere are four gases of importance in thepostharvest phase, they are oxygen, carbonpostharvest phase, they are oxygen, carbondioxide, ethylene, and water vapor.dioxide, ethylene, and water vapor. The movement of gases into and out of aThe movement of gases into and out of aproduct is one of simple gas diffusion.product is one of simple gas diffusion. There will be a greater overall movement ofThere will be a greater overall movement ofwater vapor molecules out of the product towater vapor molecules out of the product toexternal environment than there will be form theexternal environment than there will be form theexternal environment to the product. This willexternal environment to the product. This willcontinue until there is an equilibrium (or balance)continue until there is an equilibrium (or balance)achieved between the two concentrations ofachieved between the two concentrations ofwater vapor.water vapor.
  4. 4. The rate of gas diffusion is governed by :The rate of gas diffusion is governed by :The concentrations gradient between theThe concentrations gradient between theinternal environment (in the product) and theinternal environment (in the product) and theexternal environment (in the package orexternal environment (in the package orcoolroom for example). The greater thecoolroom for example). The greater thedifference in concentration, then the greaterdifference in concentration, then the greaterthe rate of diffusion of the gas from highthe rate of diffusion of the gas from highconcentration to the low concentration.concentration to the low concentration.
  5. 5. Air movement will alter concentration of all ofAir movement will alter concentration of all ofthese gases adjacent to the surface of thethese gases adjacent to the surface of theproduct which may influence the direction ofproduct which may influence the direction ofthe diffusion.the diffusion.Air pressure influences the rate of diffusion.Air pressure influences the rate of diffusion.As air pressure decreases, then the rate ofAs air pressure decreases, then the rate ofdiffusion increase.diffusion increase.
  6. 6. Respiration EffectsRespiration Effects An oxygen supply must be maintained to theAn oxygen supply must be maintained to theproduct in the postharvest phase at all times soproduct in the postharvest phase at all times soas to sustain the living processes.as to sustain the living processes. As respiration is a reversible reaction, it isAs respiration is a reversible reaction, it ispossible to adjust the level of oxygen topossible to adjust the level of oxygen tomanipulate the rate of diffusion andmanipulate the rate of diffusion andconsequently, respiration.consequently, respiration. The amount of carbon dioxide in theThe amount of carbon dioxide in theenvironment around the product can beenvironment around the product can beincreased to reduce the rate of diffusion out andincreased to reduce the rate of diffusion out andpromote the backward direction of thepromote the backward direction of therespiration process.respiration process.
  7. 7. Ethylene EffectsEthylene EffectsEthylene is a natural plant hormone whichEthylene is a natural plant hormone whichis important in both senescence of freshis important in both senescence of freshproduce and the ripening of climactericproduce and the ripening of climactericfruit.fruit.Ethylene is involved in the ripening ofEthylene is involved in the ripening ofmany important commercial fruit that havemany important commercial fruit that havea climacteric pattern of respiration.a climacteric pattern of respiration.
  8. 8.  Ethylene has both beneficial and detrimentalEthylene has both beneficial and detrimentaleffects in the post harvest horticulture. The twoeffects in the post harvest horticulture. The twomost common benefits seen are controlledmost common benefits seen are controlledripening (bananas, tomatoes, avocados, andripening (bananas, tomatoes, avocados, andmangos) and the de-greening of citrus. Ethylenemangos) and the de-greening of citrus. Ethylenetreatments promote a faster, more uniform fruittreatments promote a faster, more uniform fruitripening.ripening. The detrimental effects are increased rate ofThe detrimental effects are increased rate ofsenescence, loss of chlorophyll, thesenescence, loss of chlorophyll, thedevelopment of abscission zones and prematuredevelopment of abscission zones and prematurewilting of flowers.wilting of flowers.
  9. 9. Water LossWater Loss Most horticultural products have a very highMost horticultural products have a very highwater content. They are susceptible to waterwater content. They are susceptible to waterloss after harvesting as they are removed fromloss after harvesting as they are removed fromtheir source of water.their source of water. Water loss result in both qualitative andWater loss result in both qualitative andquantitative losses in the product.quantitative losses in the product. Reduced appearance through wilting andReduced appearance through wilting andshriveling, and reduced succulence signified byshriveling, and reduced succulence signified bylack of turgidity, lack of crispness and loss oflack of turgidity, lack of crispness and loss ofjuiciness, are qualitative losses. For thosejuiciness, are qualitative losses. For thoseproducts that are sold by weight, water loss is aproducts that are sold by weight, water loss is aquantitative loss of saleable weight.quantitative loss of saleable weight.
  10. 10. The rate of water loss depends on :The rate of water loss depends on :The nature and condition of the surface of theThe nature and condition of the surface of theproductproductThe surface area to volume ratioThe surface area to volume ratioThe environmentThe environment
  11. 11. The environment around the productThe environment around the product Temperature, relative humidity, air movementTemperature, relative humidity, air movementand air pressure are the four components of theand air pressure are the four components of theenvironment that will influence the rate of waterenvironment that will influence the rate of waterloss from harvested produce.loss from harvested produce. High temperatures, low relative humidity, rapidHigh temperatures, low relative humidity, rapidair movement and/or a reduction in air pressureair movement and/or a reduction in air pressurewill all increase the rate of evaporation of waterwill all increase the rate of evaporation of watervapor from the product.vapor from the product.
  12. 12. Temperature and Relative HumidityTemperature and Relative Humidity Relative humidity (RH) is the commonly usedRelative humidity (RH) is the commonly usedterm describing the amount of water vapor heldterm describing the amount of water vapor heldin the air.in the air. The amount that can be held in the air dependsThe amount that can be held in the air dependson the temperature.on the temperature. Warmer air can hold more water vapor. ForWarmer air can hold more water vapor. Forexample, air at 30example, air at 30ooC and 905 RH is more dryingC and 905 RH is more dryingthan air at 20than air at 20ooC and 90% RH simply because itC and 90% RH simply because itcan hold more water vapor.can hold more water vapor.

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