Downloaded 198 times
More Related Content
Ohmic heating
- 1.
- 2. BYBY ASHISHASHISH NIROULANIROULA OHMIC HEATING:A NOVEL THERMAL FOOD PROCESSING TECHNIQUE
- 3. Table of contentTableof content Introduction Objective Literature review History Instrumentation Microbial inactivation by OH Factors affecting OH Current application Future use Advantages Current limitation Conclusion 3
- 4. Ohmic heating: ANovel Thermal Food Processing Technique Introduction Ohmic heating is advanced thermal processing method wherein the food material which serve as electrical resistor, is heated by passing electricity through it. Here heating occurs due to transformation of electrical energy into heat inside the food material which causes rapid and uniform heating. heating rate in the region of 1-100 C/s can be observed during ohmic heating. It is also called joule heating, electrical resistance heating or electro-heating. 4
- 5. Introduction contd…….. Basicprinciple It is based on joules effect of heating. Heating rate is directly proportional to electrical conductivity and squire of applied electric field i.e. q = E2 σ Where, E= electric field = electrical conductivityσ q= energy generation rate 5 Ohmic heating: A Novel Thermal Food Processing Technique
- 6. Ohmic heating: ANovel Thermal Food Processing Technique Objectives To introduce the importance of ohmic heating in food processing To understand the instrumentation of ohmic heating system To understand the mechanism of microbial inactivation To discuss the limitation of ohmic processing of food To highlight briefly the future of ohmic processing system 6
- 7. Literature review History In early20th century, electric pasteurization of milk was achieved and 6 states in US had commercial pasteurizer. Between 1950’s-70’s researchers were focused to use ohmic heating for thawing and blanching process. In 1988, The Electricity Council of Great Britain had patented a continuous-flow ohmic heater and licensed the technology to APV Baker. Within the past two decades, new and improved materials and designs for ohmic heating have become available. Now, OH heater has been developed by APV baker using a licensed design by EA Technology. 7 Ohmic heating: A Novel Thermal Food Processing Technique
- 8. Instrumentation A ohmicheating processing system consists of Heating chamber Electrode Power source Power source A three phase AC of voltage and frequency ranges from 120-240V and 50-60Hz respectively are used .8 Ohmic heating: A Novel Thermal Food Processing Technique
- 9. Instrumentation contd…. Heating chamber OHchamber is rectangular tank with two electrode mostly fixed on length side. Its dimension is determined by distance between electrode. Commercial OH chamber are generally made from glass material, stainless steel e.t.c. Electrode Previously graphite and aluminium electrodes were used, but they are limited because of corrosion. recently APV ohmic process discovered that use food compatible electrode i.e. silver electrode to eliminate electrolytic problem. 9 Ohmic heating: A Novel Thermal Food Processing Technique
- 10. Instrumentation contd….. metal Leaching(concn.In ppm) silver 0.18 titanium 0.11 chromium 1.10 10 Table: metal satiability leaching data Silver and titanium has least leaching property as compare to chromium. But silver has greater antimicrobial property so, silver electrodes are more preferably used in OH Equipment.
- 11. Ohmic heating: ANovel Thermal Food Processing Technique Mechanism of microbial inactivation Two mechanism has been proposed Thermal inactivation Damage to outer membrane: loss of lipopolysaccharide, release of periplasmic protein. Damage to cytoplasmic membrane: lipoprotein denatures, membrane lipid melts. Ribosome, RNA and DNA degradation: degradation of 30s ribosomal subunit , oxidation of DNA. Protein denaturation: 11
- 12. Mechanism contd….. Electroporation Electroporationis the formation of holes in a cell membrane due to individual ion pressure, which cause change in permeability of cell membrane. The low frequency used in ohmic heating (50-60Hz) allows cell wall to build up charges and form pores. 12 Ohmic heating: A Novel Thermal Food Processing Technique
- 13. Mechanism contd… S.N. D-valuesfor conventional heating K values for conventional heating D-values for ohmic heating K value for ohmic heating 1 17.1 0.002245 14.2 0.002703 2 9.2 0.004172 8.5 0.004516 13 Fig: D- values and reaction rate constant for inactivation of B. subtilis spore at 90C during ohmic and conventional heating. Thermal effect and electroporation combine during ohmic heating to produce combine or synergy effect that reduce processing time significantly and hence increase quality of processed product. Ohmic heating: A Novel Thermal Food Processing Technique
- 14. Factors tobe consider during OH 14 Electrical conductivity • Rate of heating is directly proportional to electrical conductivity. • It strongly affected by ionic content, moisture mobility, physical structure and heating process • Conductivity of food increase by 2-3 times over a temperature rise of 120ºC. Frequency • In food with non cellular structure, heating rate increase with increase in frequency. • For food with cellular structure, initial rise in temperature was obtained with low frequency Ohmic heating: A Novel Thermal Food Processing Technique
- 15. Factors contd…… Voltage andElectric field Rate of heat generation is directly proportional to squire of applied voltage. Heating time decrease approx. 78% when voltage gradient was increased by 2V/cm. Starch gelatinization It cause decrease in EC and hence slow down the heating rate. Fouling effect As temperature increases, protein undergoes denaturation. These denatured protein adhere to the electrode and hence fouling occurs. This cause power to drop and electrode temperature increase rapidly.15 Ohmic heating: A Novel Thermal Food Processing Technique
- 16. Current Application Meatprocessing: The Cooking time of brine cured meat was reduced by great extent (>0.5Kg/min). Quicker and uniform thawing with good sensory properties can be obtain by ohmic thawing of meat (Wang et al., 2002). Milk product processing: HTST ohmic pasteurization on quality of goat milk is comparable with conventional pasteurization. The physical and chemical properties of milk is not affected by ohmic heating as compare with conventional heating. 16 Ohmic heating: A Novel Thermal Food Processing Technique
- 17. Fruit and vegetableprocessing; Loss of solid during processing was reduced by great extent ( 50% in some case) with ohmic pretreated potato cubes as compared to conventional pretreatment. Studies found that, ohmic blanching enhance water and sugar transfer, since ohmic heating cause electroporation of cell membrane. 17 Application contd..... Ohmic heating: A Novel Thermal Food Processing Technique
- 18. Future use Extraction Beetdye extraction was enhances as much as 40% during ohmic heating and is prop. To electric field. Ohmically heated apple produce more juice than non-treated apple during mechanical juice extraction. Thawing Food can be thawed rapidly from -30 C to 30 C and the time is reduced by 1/4th to 1/5th tim.es that of conventional one. Cell damage and softening were prevented by ohmic heating which reduce drip loss. 18 Ohmic heating: A Novel Thermal Food Processing Technique
- 19. Future use contd…. Blanching Thequick process time and no dicing reduce solute losses during blanching. It was also found that ohmic blanching at 50V/cm give shortest critical inactivation time of 54s with best color quality. Fermentation Ohmic heating of a fermentation vessel containing L. acidophilus reduced the lag period of the bacteria Waste water treatment The lab scale ohmic heating system possessed good performance to coagulate protein (60 %) from waste water. 19 Ohmic heating: A Novel Thermal Food Processing Technique
- 20. Advantages ofohmic heating High energy efficiency (90% electrical energy is converted into heat). Rapid (1-100 C/s) and uniform heating i.e. the product doesn’t experience large temperature gradient. Better nutrient and vitamins retention No theoretical upper temperature limit. No hot surface for heat transfer; less risk of surface fouling and burning of the product. Reduced maintenance cost because of the lack of moving parts. Process can simply be controlled with switch on and off. Environmentally friendly. Product with large size (15mm) and high concentration of solid (up to 80%) can easily be processed.20 Ohmic heating: A Novel Thermal Food Processing Technique
- 21. Current limitation Someof most important current drawbacks are as follows:- Electrolysis of product and corrosion of electrode occur at low frequency that may result in metal contamination to food which may be hazardous at high concentration. Too high installation and initial operating cost. This system is unable to heat a product with high fat and oil and dried food system. Since fats are non-conductive (due to absence of water and ions), it may bypass current and slow heating may occurs. Runaway heating may occur at high temperature due to increase in electrical conductivity. 21 Ohmic heating: A Novel Thermal Food Processing Technique
- 22. Conclusions From above, followingconclusion can be drawn;- Ohmic heating is excellent method for processing both particulates and liquid. Some possible applications are blanching, extraction, thawing, fermentation, peeling, e.t.c High rate of heating during ohmic processing results in short processing time and higher retention of nutrients and vitamins. Electric fields in combination with heat produce synergy effect that exert more pronounce effect to enzyme and microorganism. Ohmic heater has simple arrangements (basically consist of electrodes, treatment chamber and power source). Further research have to be carried out in order to identify cold-spot, decrease cost and improve electrode so that electrolysis is prevent. 22 Ohmic heating: A Novel Thermal Food Processing Technique
- 23.