It was striking to read a claim in the print media recently that a scientific group in India was able to get an international patent covering 120 countries for a process "sterilization of liquid foods by pulsed electric fields". If technically and commercially feasible, beyond any shadow of doubt, this process can revolutionize the milk and juice industry in the country. What practical problems that may arise can be known only when the process is scaled up into a fully baked industrial scale technology with necessary engineering designs for the critical original equipment necessary for its success. According to the claims by the Indian scientists a liquid food like juice or sauce, when passed through a specially designed fluid treatment chamber with provision for generating a short pulse at very high voltage, it was able to kill bacteria, molds and their spores and viruses. Basically the high voltage is supposed to disrupt the cell membrane through the phenomenon of electroporation.
In Pulsed Electric Field processing (PEF), a substance is placed between two electrodes and pulsed electric field is applied. The effect is to enlarge the pores on the cell membrane which kills the cells and releases their contents into the environment. All cells have pores which control the flow of nutrients into, and metabolic wastes out of, the cell. If these pores become wider and larger, the contents can leak into the medium, eventually killing the cell. The temperature rise in such a system due to the electric field is less than 30C and therefore the material treated does not even attain the pasteurization temperature sufficient to kill pathogens by heat alone, The voltage applied can be between 15000 to 30000 volts, where the lower voltage can kill plant cells while the higher voltage brings about the death of bacterial and fungal cells. How this technology can immobilize viruses, as claimed by the Indian scientists is not clear. Also in doubt is the ability of this process to obtain 100% kill of the spores which have very tough membranes that can survive high voltages.
Though useful information about PEF technology started emerging in 1991 and early patents on pulse electric field for sterilization and preservation of liquid foods (US Patents5235905, 5690978 and 6746613) were already granted in the US, it has failed to take off due to certain practical problems when tried on a commercial scale. This technology is used to a very limited extent by the fruit juice industry in the US. Most enzymes are not affected by pulsed electric field which can cause deterioration in the juice under ambient conditions and therefore to preserve the organoleptic quality, the treated products will have to be refrigerated during marketing, up to the point of consumption. Gas bubbles which are trapped in the juice during extraction tend to allow electric arcing between the electrodes causing burning of the substances being processed and consequent generation of potential carcinogenic artifacts.
The media reports convey the impression that PEF technology has been perfected for the first time in India and is ready for commercial use. On the contrary much more work needs to be done to standardize the process for tropical fruit and vegetable products popular in the country. Milk could be the most eligible candidate for mass application of this technology but practically no information is available regarding its suitability in a complex protein-fat matrix like milk. Stray reports do indicate that application of PEF in tandem with heating can extend shelf life of milk up to 24 days. Imagine the advantages for a middle class consumer when the milk sachet which arrives unfailingly every day in front of his house, can be kept under ambient condition or even in a refrigerator for at least a week or more. This is where efforts are called for as India is world's largest milk producer and a major portion is consumed as fluid milk in millions of house holds across the country. Here is a typical example of a patent being touted as the ultimate in non-thermal sterilization but with out any solid data regarding its applicability, efficacy and safety on Indian products. It is sad that good scientific work like this, with potential for far reaching benefits to the society, gets trivialized by premature publicity and bloated claims.