Blanching

Blanching is a preservation technique mainly done to fruit and vegetables

1. BLANCHING Submitted by Muneeb 18msfood07 Central University of Punjab

2. Blanching Blanching is a mild heat treatment prior to freezing, canning or drying for fruit and vegetable Hot water or steam are mainly used heating media in industry. Not a final method of preservation it is a pre treatment Blanching is the scalding of fruit or vegetables in boiling water or steam It is combined with cleaning and/ or peeling

3. Blanching Blanching is a unit operation prior to freezing, canning , or drying in which fruits or vegetables are heated for the purpose of inactivating enzymes To achieve adequate enzyme inactivation, food is heated rapidly to a pre-set temperature, held for a pre-set time and then cooled rapidly to near ambient temperatures.

4. Objective Inactivating enzyme Modifying texture Preserving colour, flavour and nutritional value Removing trapped air Cleaning Reduction of microbial load

5. Factors Influence blanching time T ype of product S ize of the pieces of food B lanching temperature M ethod of heating.

6. Theory Unsteady state heat transfer by conduction and convection The maximum processing temperature in freezing and dehydration is insufficient to inactivate enzymes In canning, the time taken to reach sterilizing temperatures , particularly in large cans, may be sufficient to allow enzyme activity to take place Under-blanching may cause more damage to food than the absence of blanching does

7. Enzymes are Lipoxygenase Polyphenoloxidase Polygalacturonase Chlorophyllase Heat resistant enzyme present in most vegetable are Catalases and peroxidase – used for determining success of blanching. Adequate blanching also reduces number of contaminating micro organism on surface of food Blanching can soften tissue Food processing and preservation by Dhir Singh , Dheer Singh

8. Blanching Wet Blanching Dry Blanching Hot water Steam Hot gas Infra red Micro wave High pressure

9. Water blanching Performed at hot water, Temperature for water blanching is from 70 to 100 o c For a specified time and then cooled It results in a uniform treatment. Water is heated indirectly by steam In the widely used reel blancher , food enters a slowly rotating cylindrical mesh drum which is partly submerged in hot water Cooling is done by cold air, cold water , spray HTST or LTLT or combination of are used https://fpequipment.com/product/reel-blancher-5/

10. Advantages Lower capital cost Better energy efficiency Uniform treatment. Disadvantages L eaching of minerals and nutrients such as vitamins Produce effluents with large biological oxygen demand Risk of contaminating by thermophilic bacteria

11. Steam blanching. Product is transported by a chain or belt conveyer through a chamber where food grade steam is directly injected. Approximately 100 o c is used Steam blanching is recommended for a few vegetable like Broccoli, pumpkin, sweet potatoes and winter squash. Combination of both steam and water blanching is also in practise. Requires more time than water blanching.

12. https://www.slideshare.net/bavaneethan/blanching-83286088

13. Advantages Small loss of water soluble components Smaller volume of waste Lower disposal charge Easy to clean and sterilise Disadvantages Uneven blanching if the food is piled too Some Loss of mass in the food

14. Blancher-cooler Pre-heating, blanching, cooling sections. Food on a single conveyer belt throughout each stage, not to suffer from physical damage due to turbulence of conventional hot water blanchers. Food is pre heated with water After blanching, 2 nd recirculation system cools the food. A recirculated water steam mixture to blanch food and final cooling is done cold air.

15. Food processing and preservation by Dhir Singh , Dheer Singh

16. IQB It occurs in 2 stages Food is heated in a single layer to a sufficient temperature to inactivate enzymes. Adiabatic holding- a deep bed of food is held for sufficient time to allow temperature at centre of each piece to increase to that needed for enzyme inactivation Cooling stage 25s for heating and 50s for holding 1cm diced carrot compared with 3 min for conventional blanching.

17. Food processing technology principle and practise by P J Fellows.

18. Dry blanching Microwave Microwave blanching was started at 1940s. In which electromagnetic energy is converted into heat energy in matter. It is the best method of blanching. Little or no leaching of vitamins, volatiles, pigments, Carbohydrates. Less processing time It improve product quality and minimise waste. Heat is uniformly distributed in material and very faster heating rate. Main advantages is capable of producing heat internally and it have a high penetration power.

19. Infrared Infrared radiation penetrates in to the food and directly heats the food Water in food absorb heat energy efficiently in the range of medium and far infrared wavelength with peak wave length at 3,4,7 and 6 μ m Useful range of wave length for IR in range of 0.7 to 10 μ m Main disadvantage of IR is cell wall rupture, blackening and undesired structural changes .

20. High pressure The pressure ranges between 50 and 700 MPa. Generally between 100 and 200 MPa is recommended The product is generally contained in heat sealed container. It reduce drying time and increases rate of drying. Inactivation of peach polyphenoloxidase enzyme in peaches.

21. Blanching time of vegetables Vegetable Time Green beans 3 minutes Broccoli, Chopped or stalks 3 minutes Beets Small medium 25 to 30 minutes 45 to 50 minutes Carrots Tiny whole Diced or strips 5 minutes 2 minutes Greens like spinach 2 minutes Shelled peas 1.30 minutes Snow or sugar snap peas 2 to 3 minutes Summer squash like zucchini Slice or chunks Grated 3 minutes 1 to 2 minutes Source: food processing and preservation by Dhir singh & Dheer singh

22. Processing time & temperature Type Radiation or temperature Time Infrared Medium IR (peak) 3,4,7 μ m Far IR (peak) 6 μ m 3000 – 4000 W/m2 20 min Microwave 2450 – 50 MHz 85- 87 o c 10 – 11 minute High pressure blanching 100 and 200 MPa 22 to 24 (100 MPa) 24 to 26 (200 MPa) 10 minute 20 minute Hot water 70 o c and 80 o c 90 o c 1 minute 2.5 minute Steam blanching 100 o c 15-20 seconds Source: microwave blanching an emerging trend in food engineering and its effects on capsicum by Shivendu Ranjan

23. Effects of blanching on food quality Undesirable texture changes during wet blanching. Some times Undesirable color change occurs. Nutritional Quality Blanching reduces the nutritional value of food. Nutrients leach out from the product especially during water blanching. Water soluble vitamins are lost during wet blanching. Loss (%) of ascorbic acid Treatment Peas Broccoli Green beans Water blanch water cool 29.1 38.7 15.1 Water blanch air cool 25.0 30.6 19.5 Steam blanch water cool 24.2 22.2 17.7 Steam blanch air cool 14.0 9.0 18.6 Source: food processing and preservation by Dhir singh & Dheer singh

24. Thank you.

25. Reference https:// www.slideshare.net/bavaneethan/blanching-83286088 F ood processing and preservation by Dhir singh & Dheer singh Food processing technology principle and practise by P J Fellows. https://en.wikipedia.org/wiki/Blanching_(cooking ) Journal of food processing engineering microwave blanching : an emerging trend in food engineering and its effects on capsicum Shivendu Rajan , Nandita Dasgupta , Niharika Walia , Thara chand and Chidambaram Ramalingam