The dairy industry has traditionally relied on thermal processing techniques like high-temperature short-time (HTST) pasteurization, low-temperature long-time (LTLT) pasteurization, and ultra-high temperature (UHT) processing to ensure food safety and extend shelf life. While these methods effectively reduce microbial contamination, they often lead to undesirable effects such as nutritional degradation, cooked or burnt flavors, and caramelization of natural sugars.
A novel alternative, Ohmic heating, also known as Joule heating or electrical resistance heating, is gaining popularity in the dairy processing industry due to its advantages in heating efficiency, uniformity, and preservation of nutritional and sensory qualities.
What is Ohmic Heating?
Ohmic heating is an advanced thermal processing technology where an alternating electrical current (AC) passes through a food product, generating heat due to its electrical resistance. This method ensures rapid, uniform heating, which minimizes thermal degradation and improves the quality of dairy products.
Key Advantages of Ohmic Heating
- Faster heating times, reducing thermal damage to nutrients
- Even heat distribution, preventing localized overheating
- Minimal impact on flavor and texture
- Reduced fouling, as no direct heat transfer surface is involved
- Energy-efficient and cost-effective
Principles of Ohmic Heating
Ohmic heating operates based on the electrical conductivity of food. Since milk contains water, ions, minerals, and salts, it conducts electricity while also resisting it to generate heat. The process allows short-time, high-temperature processing, reducing the risk of browning reactions while effectively inactivating microorganisms and enzymes.
Factors Affecting Ohmic Heating in Dairy Processing
1. Electrical Conductivity of Milk
- The composition of milk, including water, minerals, and salts, determines its electrical conductivity.
- Cow’s milk has a conductivity of 4-6 mS/cm at 18°C.
- Higher temperatures increase electrical conductivity, leading to faster heating.
2. Orientation of Particles
- Parallel orientation of particles in an electric field enhances heating efficiency.
- Smaller particles contribute to more uniform heating.
3. Field Strength
- Higher field strength leads to shorter processing times.
- However, higher solid concentrations in milk can affect heating efficiency.
4. Heater Arrangement
- Electrode placement and heater configuration impact heating uniformity.
- Graphite electrodes are preferred over stainless steel or tin, as they are less prone to fouling.
5. Product Characteristics
- Specific heat capacity, viscosity, density, water content, protein, fat, and carbohydrates all influence temperature rise during Ohmic heating.
Impact of Ohmic Heating on Dairy Products
Ohmic heating has been successfully applied to various dairy products, demonstrating promising results in quality retention and microbial control.
1. Kefir
- Study by Mainville et al. (2001): Ohmic heating at 72°C effectively reduced microbial counts in kefir without altering its composition.
- However, structural changes in proteins and lipids were observed.
2. Whey Processing
- Ayadi et al. (2004) found that Ohmic heating led to protein fouling due to denaturation of whey proteins at high temperatures.
3. β-Galactosidase Enzyme Stability
- Pereira et al. (2008) tested goat milk pasteurization using Ohmic heating and found no lipid hydrolysis or significant changes in free fatty acid content compared to conventional methods.
Challenges and Limitations of Ohmic Heating
1. Electrode Fouling
- Although Ohmic heating eliminates surface fouling, electrode deposits can form due to high power supply and temperature.
- Using higher frequency currents for shorter durations minimizes deposits.
2. Need for Further Research
- Temperature distribution in dairy products requires more investigation to optimize processing parameters.
- Potential applications in dehydration, evaporation, blanching, and extraction need further development.
Future Scope of Ohmic Heating in Dairy Processing
With growing demand for efficient, energy-saving, and high-quality processing methods, Ohmic heating has significant potential in food technology consulting and dairy plant engineering. Its application in sustainable food processing, nutrient preservation, and alternative dairy products could revolutionize modern dairy production.
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