ONION DRYING

BLESSY .V. A2011-02-014S6

ONION DRYING

BLESSY V.A.2011-02-014

INTRODUCTION

• Scientific name - Allium cepa

• Pungency - allyl-propyl disulphide

• Contains vitamineB,vitamineC,iron and calcium

• Medicinal value – antimicrobial,

antiasthmatic,antitumor and anticancer effect

IMPORTANCE OF DRYING• Third rank in the world production

• World production - 64.48 million tone

• Highest production is in Ireland (58t/ha)

• Maharashtra is the leading producer In India (5.04 MMT )

• India is the second largest producer of dehydrated

onion(700 tone)

COMPOSITION

Particulars(g) Before drying(per 100g)

After drying(per 100g)

moisture 86.6 4.6protein 1.2 10.6fat 0.1 0.8minerals 0.4 3.5fiber 0.6 6.4carbohydrate 11.1 74.1

DRYING OF ONION• Drying of onion helps to increase shelf life

• Onion dried from initial moisture content of 86%(wb) to

7%(wb) or less

• Storage temperature(0-2.3°C)

• Storage relative humidity(30-70%)

ONION DRYERS• Solar onion dryer• Convection air dryer• Fluidized bed dryer• Infrared dryer• Vacuum dryer• Freeze dryer• Microwave dryer• Osmotic dehydration

SOLAR ONION DRYER

• Forced convection type

• Drying is due to convection and conduction

• Solar dryer developed at Sardar Patel renewable energy research institute(SPRERI)

Loading capacity 100kg/batch

Moisture content Initial 85% to final 2-5%Operating temperature

65°C

Source of heat Glazed solar air heating collectors(72m²)

Drying duration 4hrsInstalled in 1995

CONVECTION AIR DRYER

• Used Commercially

• Keep organoleptic characteristics of onion

• Excessive thermal damage is the main problem

• Air temperature range - 50°C to 80°C

• Relative humidity of air - below 20%

• Air velocity - 27m/min

• Slice thickness - 3mm

• Duration - 1 hour

FLUIDIZED BED DRYER

• Used for - onion flakes, slices • It permits continuous, large scale drying of food materials

without over drying.• High rate of heat transfer• Low maintenance cost• vibrated type fluid bed is used

• High heat and mass transfer rate • Duration - 15 minutes• Depth of onion bed - 75mm• Thickness of onion slice - 1 to 5mm

INFRARED DRYING• Heat energy is produced due electromagnetic radiation• Catalytic infrared dryer is used• Natural gas used - propane Advantages • High quality • Product - white in color• Rehydration is very easy

• Drying temperature - 80 °C to 70°C

• Initial temperature - 80°C

• Thickness of slice - 6mm

• Mainly infrared power level affect Drying rate

• Air circulation do not affect the drying rate

VACCUM DRYING

• Drying - low pressure , low temperature , low oxygen environment

• Thickness of the onion layer - 1 to 5mm• Drying temperature - 50°C to 70°C• High quality product

VACCUM TRAY DRYER

FREEZE DRYING

• Moisture removal due to sublimation• Laboratory purpose : -30 °C to -40°C• Commercial purpose : -20°C• Onion thickness : 4 to 6mm• Duration : 7 to 8 hours• Pressure : 6.1mm Hg

FREEZE DRYER

MICROWAVE DRYING

• Low energy consumption• Heating is more rapid

OSMOTIC DEYDRATION• Drying due to osmotic pressure difference• Salt concentration – 20%• Temperature - 28°C• Duration – 1 hour

CONCLUSION

“For the purpose of onion drying we can use different dryers but the cost , time of operation , product quality is varying with different type of dryers”

THANK YOU