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preservationbyheattreatment-blanching-200218125127.pptx

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Arti Mahajan

Blanching is a heat treatment used to inactivate enzymes in plant tissues prior to freezing, drying, or canning. It involves briefly heating the food in boiling water or steam. The major function is to stop enzymatic reactions that can degrade qualities like color, flavor, and nutrients. Blanching helps clean and reduce microorganisms on surfaces. It is important for many vegetables that cannot be eaten raw. There are three main methods - hot water blanching, steam blanching, or a combination of both - each with advantages and disadvantages related to factors like nutrient loss, contamination risk, and costs.

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preservationbyheattreatment-blanching-200218125127.pptx
Blanchin g: Blanching is used for variety of purpose. It is defined as a mild heat treatment applied to tissue (usually plant) primarily to inactivate enzymes prior to freezing, drying or canning.
Functions of blanching: 1.Inactivate most enzymes. 2.Some cleaning action. 3.Remove substances in some products. 4.Activate some enzymes(if controlled). 5.Removes undesirable odours/flavours. 6.Softens fibrous material and decreasesvolume. 7.Exples air and respiratorygases.
8.Preheating of product prior tocanning. 9.Reduces number of microorganisms
Major function of blanching is inactivation of enzymes. Enzymes can cause rapid change in colour, flavour and nutritive value of such food products. Blanching as a pretreatment before drying has many advantages. Its helps in cleaning the material and reducing the amount of micro-organisms present on the surface. Blanching does not allow effective autoclaving,and stops the activity of autolytic enzymes. Fruits are not blanched. As a thumb rule, all those vegetables which cannot be eaten raw are blanched. Ex: potatoes
Methods of blanching: Blanching is a delicate processing step. It requires carefull monitoring of time, temperature and the other conditions. There are mainly two typical methods of blanching based on type of heating medium viz. Hot water blanching and steam blanching use hot waterand steam as heating medium, respectively. A third type of blanching system exists which is a combination of hot water and steam blanching.
Hot water Blanching: In this method, the cleaned food is subjected to hot water(85 to 100*c) until the enzymes areinactivated. Pot blanchers are used at home scale. Generally hot water blanching is done because of low capital costs and better energyefficiency.
Disadvantages associated with hot water blanching include loss of water-soluble constituents, risk of contamination and higher cost of water and disposalof effluent.
Steam blanching: In case of steam blanching, the food products isdirectly exposed to steam, which avoids the loss of food soluble solids (flavours, vitamins, acids, sugars etc.) to blanching medium as well as solves the problem of disposing blanching medium after processing.
Steam blanching is advantageous as it results in less loss of water –soluble constituents, less volume of waste, easy to clean and sterilize. But it has some disadvantages such as higher capital costs, uneven blanching,and lowefficiency.
Blanchers with hot water and steamsystem: This type involves three step process viz. Product on conveyer belts is exposed to steam consecutively followed by contact between food and hot waterand finally immersion in hot water.
Efficacy of blanching: There are various types of enzymes such aslipoxygenase, polyphenolase, polygalacturonase and chlorophyllase, which cause loss of quality and therefore, must be inactivated. Normally, two heat resistant plant enzymes such as catalase and peroxidase, are used to evaluate blanching efficacy, as appropriate time and temperature is required to inactivate them.

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preservationbyheattreatment-blanching-200218125127.pptx

  • 2. Blanchin g: Blanching is used for variety of purpose. It is defined as a mild heat treatment applied to tissue (usually plant) primarily to inactivate enzymes prior to freezing, drying or canning.
  • 3. Functions of blanching: 1.Inactivate most enzymes. 2.Some cleaning action. 3.Remove substances in some products. 4.Activate some enzymes(if controlled). 5.Removes undesirable odours/flavours. 6.Softens fibrous material and decreasesvolume. 7.Exples air and respiratorygases.
  • 4. 8.Preheating of product prior tocanning. 9.Reduces number of microorganisms
  • 5. Major function of blanching is inactivation of enzymes. Enzymes can cause rapid change in colour, flavour and nutritive value of such food products. Blanching as a pretreatment before drying has many advantages. Its helps in cleaning the material and reducing the amount of micro-organisms present on the surface. Blanching does not allow effective autoclaving,and stops the activity of autolytic enzymes. Fruits are not blanched. As a thumb rule, all those vegetables which cannot be eaten raw are blanched. Ex: potatoes
  • 6. Methods of blanching: Blanching is a delicate processing step. It requires carefull monitoring of time, temperature and the other conditions. There are mainly two typical methods of blanching based on type of heating medium viz. Hot water blanching and steam blanching use hot waterand steam as heating medium, respectively. A third type of blanching system exists which is a combination of hot water and steam blanching.
  • 7. Hot water Blanching: In this method, the cleaned food is subjected to hot water(85 to 100*c) until the enzymes areinactivated. Pot blanchers are used at home scale. Generally hot water blanching is done because of low capital costs and better energyefficiency.
  • 8. Disadvantages associated with hot water blanching include loss of water-soluble constituents, risk of contamination and higher cost of water and disposalof effluent.
  • 9. Steam blanching: In case of steam blanching, the food products isdirectly exposed to steam, which avoids the loss of food soluble solids (flavours, vitamins, acids, sugars etc.) to blanching medium as well as solves the problem of disposing blanching medium after processing.
  • 10. Steam blanching is advantageous as it results in less loss of water –soluble constituents, less volume of waste, easy to clean and sterilize. But it has some disadvantages such as higher capital costs, uneven blanching,and lowefficiency.
  • 11. Blanchers with hot water and steamsystem: This type involves three step process viz. Product on conveyer belts is exposed to steam consecutively followed by contact between food and hot waterand finally immersion in hot water.
  • 12. Efficacy of blanching: There are various types of enzymes such aslipoxygenase, polyphenolase, polygalacturonase and chlorophyllase, which cause loss of quality and therefore, must be inactivated. Normally, two heat resistant plant enzymes such as catalase and peroxidase, are used to evaluate blanching efficacy, as appropriate time and temperature is required to inactivate them.