By Dakshayani. R and Abimanyou. A
Dairy products and by-products are more sensitive to thermal processing, which can lead to various nutritional degradation of products and question the safety of the product with respect to microbial contamination. To address these challenges, the dairy industry has turned to non-thermal methods, which have been proven to provide health benefits and provide an eco-friendly environment. The industry began to search for alternatives which were non-invasive with respect to quality and highly nutritive in nature. Non-thermal technologies have been proven to be effective in microbial inactivation and preserve the functionality and nutritive quality of milk and milk products. The majorly utilized non-thermal technologies in dairy products were Ultraviolet (UV-C), High-Pressure Homogenization (HPH) and High-Pressure Processing (HPP), Cold Plasma (CP), Ultrasound (US) and Pulsed Electric field (PEF) respectively given in figure 1.
Non-ionizing radiation in the range of 200-280 nm falls under UV-C, which is non-toxic and uses physical energy, where light photons are absorbed by the product. The longer exposure time causes damage to the DNA and RNA of microbes and leads to death. The UV-C effect on milk nutrition was studied and found to increase the vitamin D3 content. A study on American cheeses (packed and unpacked) with UV-C reported that treatment was proven to be effective against Listeria monocytogenes and Penicillium roqueforti. There was a significant colour difference found in the treated cheese, though when subjected to sensory evaluation, the judges could not find the difference. Even though, the process of UV-C is effective, the penetration depth and lamp sources were the constrain of this technique but are cost-effective.
HPP works under the principle of Le-chatelier principle and isostatic rule to inactivate microorganisms. HPP (milk) at 600 MPa for 3 minutes reduce log reduction of 5 for Listeria monocytogenes, Escherichia coli, and Samonella spp. HPP was found effective against Enterobacteriaceae, LAB and pseudomonas in comparison with pasteurized milk, which ultimately increases the shelf life of the product. The HPP preserves the product quality similar to that of the original matrix and have very minimal impact on vitamins and volatile compounds. It could also be used as allergen reduction namely beta-lactoglobulin in bovine milk, a suitable alternative to homogenization and pasteurization of milk. In cheese, the enzyme reduction by HPP is noteworthy, and functionality improvement in probiotic milk beverages was also remarkable. The colour value of both the thermal and HPP-treated milk were observed to be similar in various case studies. The major drawback was the huge installation cost and low capacity of processing.
CP approach in milk is quite emerging, where plasma being the fourth state of matter works on ionization of gas and thermodynamic equilibrium amid the product. The CP treatment of milk found to be effective against Escherichia coli, Listeria monocytogenes, and Salmonella typhimurium with about log reduction of 2 to 5 log CFU/ml in the treatment time range of 5 to 20 minutes. The CP found effective in retaining the fatty acid concentration of dairy products as that of fresh dairy products, it also improves the nutritive quality in comparison with pasteurized products. The sensorial attributes of CP have very less impact on flavour and aroma, though could be eliminated by process optimization. Currently, plasma systems were not available in a commercial form for decontamination in the food industry, still further exploration is needed in this field.
US being sound waves which was beyond human hearing (>20 kHz) were used with the principle of cavitation. US found effective against pathogens namely Escherichia coli, Pseudomonas fluorescens, Staphylococcus aureus, Debaryomyces hansenii in milk with 4.61,2.75 and 2.09 reduction log CFU/ml. The operating parameter influences the decontamination includes frequency, power and treatment time. US in dairy beverages have notable functions namely microbial reduction, kinetic stabilization and homogenization. The US increase the bioactive peptides in fermented milk and there needs research for optimizing the process condition of US on milk and milk products. US on dairy products were complex and hard to understand for commercialization in future, but could be an effective energy saving technique if scaled up.
PEF application in dairy firms is based on microbial destruction and shelf-life enhancement. PEF works on the principle of electroporation leads to microbial cell damage. PEF was recognized for sublethal effect on microbial destruction and enzyme inactivation. PEF have a positive impact on microbes such as E. coli, S. aureus, and L. monocytogenes in milk with a log reduction of 2.8,3 and 5 CFU/ml in milk. PEF in whey protein isolate formulation have no negative impact on vitamin A and vitamin C, it also has very little effect on the concentration of immunoglobulins available in Whey Protein Isolate formulation. The influence of PEF on dairy products is a less explored area of research which has to be focused on in order to commercialize the technology. It is complex to scale up this technology for commercialization and the energy required is high.
The non-thermal techniques have huge advantages on milk and milk products over thermal technology. Over the past decades, numerous studies were performed in novel non-thermal processing and its time to scale up these techniques. Each technique has its own advantages and disadvantages and has to be observed carefully to implement these techniques on a large scale to overcome the drawbacks of thermal processing as well as to ensure the quality and safety of the product. Further studies have to be performed to cut down the production cost of these technologies for scale-up.
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