Looking beyond thermal processing-Emerging new technologies for the food industry

Who does not want to enjoy a safe and tasty meal? The food we eat is as precious to creatures as it is to us, who live along with us in this planet and therefore competing with man to have a share of the pie is quite natural, But man in his perpetual fight for ensuring continuous supply of food for himself and his fellow denizens innovate tirelessly to protect the food supply through "killing" technologies which are widely deployed through out the entire spectrum of food chain. By far his fight has been of epic proportions when it comes to eliminating vectors and pathogenic bugs. Many of them, besides eating the food which man considers as his, they also contribute a host of diseases with mass destruction potential. Once this is achievable the next focus is keeping the food as fresh as possible to utilize the nutrients present in them fully and enjoying the unique flavor and taste associated with fresh foods.

Historically food preservation was accomplished by using natural substances like salt and sugar both of them being injurious to pathogenic microorganisms at high concentrations raising the osmotic pressure of the medium to intolerable levels. Fermentation to lower the pH of the food system was also as old as human civilization. Use of heat to cook the foods achieved destruction of undesirable microbes besides imparting highly palatable qualities to the food. Pasteurization and sterilization became common place to prolong the life of many foods and thermally processed foods in bottles and cans supported human lives especially during stress times like wars, famine, drought, epidemics etc. Even to day heat is used in some modern processes like aseptic packing, HTST and UHT technologies and in-package sterilization. Advent of chemical preservatives like sulfur dioxide, benzoates, sorbates and many other chemical substances provided an easier option to thermal processing. But to day's consumer is not willing to accept any chemically tainted foods because of the unknown consequences, especially in the long run,  of ingesting them on his health.   

Under such an environment it is no wonder that food scientists and the processing industry are looking for new technologies that will be more efficient and less intrusive as far as flavor and texture of the food is concerned. Consumer is fully justified in demanding more and more fresh , improved quality and healthy foods for him as well as his family and this demand from the market place is the driving force for novel technologies that can provide chemically free, palatable and healthy foods. Here comes the challenge because severe processing conditions can irrevocably change the characteristics of the natural food giving the consumer some thing like a pale shadow of the original food. Also environment friendly processes with minimum power and water use and less and less pollution potential are inevitable. New emerging technologies such as high-pressure processing (HPP), pulsed electric field (PEF) and cold plasma are considered very promising and can be expected to be main stream processes in the coming years..

HPP does not use heat for achieving disinfection of products and is in the forefront as a choice for a non-thermal pasteurization technique. Here products are subjected to high pressures between 300 and 600 MPa for a duration of about 10 minutes. The advantages of HPP over the conventional thermal processing techniques can be manifold, most important ones being significantly reduced process times, very low heat damage to the product and retention of product flavor, texture, color and heat labile nutrients. But HPP cannot be effective in achieving destruction of dangerous spores of some bacteria if used alone, though it can be used in conjunction with low acidity of the medium or use of refrigeration. HPP is versatile in that it can inactivate pathogenic and spoilage bacteria, yeasts, molds and viruses but not effective when it comes to inactivation of undesirable enzymes. Its application is linked to factors such as the type of microorganism, food composition, pH and water activity of the food system. Its use world wide  by industrial establishments is reported to be wide spread during the last few years. HPP is excellently suited to liquid and semi-solid food products such as fruit juices, purees, smoothies, jellies etc. Major constraints for its growth are high capital expenditure, low productivity and batch type of operations. 

PEF is a unique process which can kill bacteria present in liquid food products at low temperatures within a short period of time. Here the food is exposed to a pulsed high voltage field for less than 1 second and this process ensures better retention and storage stability of phytochemicals like carotenoids, phenolic compounds and flavonols, in comparison to thermal processing. Combining the PEF treatment at moderate temperatures with the presence of an antimicrobial, effective against both Gram-positive and -negative pathogenic bacteria, would significantly enhance process efficiency, reduce the number of pulses and outlet temperature and lead to significant energy cost savings. A major limitation of PEF is that it is not suited to foods with high conductivity, high salt content and liquid foods with high particulate content. Research efforts are in progress to further refine the technology for as wide applications as possible and fool proof with 100% kill efficiency against most food borne pathogens.   .  

Cold plasma technology is another choice when it comes to processing foods without using high temperatures. Plasma is considered the fourth state of matter that is energetically distinguishable from solids, liquids and gases. Plasma is a source of different antimicrobial substances including UV photons, charged particles, and reactive species such as superoxide, hydroxyl radicals, nitric oxide and ozone. Non-thermal plasma which does not use high temperature and power can be generated by electric or magnetic discharges at lower pressures, Cold plasma can be effective in the sanitization of the surface of fresh produce like fruits and vegetables, liquid products like juices and still beverages besides decontamination of processing equipment  in food industry. It may take more efforts for the cold plasma processing to become a fool proof method for the food processing industry as there is no assurance that it can achieve a 100% kill rate in all food systems.  

Though the on-going public interest in non-thermal process technologies is very high, investments sufficient to fast track these developments are not forthcoming due to many reasons, the major one being the high capital cost involved in fabricating industrial capacity machinery with high productivity. One example of a non-thermal process that remains untapped fully is irradiation technology, in spite of high investments made over the last three decades in evolving industrial scale plants for treating a variety of food products with assured decontamination efficiency and minimum damage to the products processed. Probably this may be the non-motivating factor that is impeding development of many non-thermal food processing technologies at a pace commensurate with the growth of food industry world over.

V.H.POTTY
http://vhpotty.blogspot.com/
http://foodtechupdates.blogspot.com

PULSED ELECTRIC FIELD-APPLICATION IN FOODS

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.

V.H.POTTY
http://vhpotty.blogspot.com/