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Technology applied to milk processing

The use of pulses electrical treatment of milk enables effective microbial inactivation with a small increase in temperature

The use of high voltage electrical pulses (Pulsed Electric Fields, PEF) is a good alternative to conventional heat treatment of liquid foods and semi-liquids. Pasteurization of milk is one of its potential applications. Despite some of the limitations of this process, as the high cost of facilities, offers great potential in the treatment of milk because it allows a food sensory and nutritional characteristics similar to the starting product and in the future could be an alternative to traditional pasteurization.

early twentieth century began to study the feasibility of using electrical treatments for the sanitization of milk. In those years it came to using this technology to process large quantities of milk that were intended for human consumption without affecting consumer health. Despite the satisfactory results achieved so far, this technology was no longer used, no clear reason, and has been in recent decades when there has been a growing interest to the PEF, probably due to further improvement of technology and, above all, the rise of minimally processed foods.

According to the results of studies carried out so far, the main advantage of using PEF for treatment of milk resides in the effective microbial inactivation obtained at the level of pasteurization, with a small increase in the temperature. This also provides a product suitable for consumption with good nutritional and sensory quality, similar to fresh food. An additional advantage of this technique is the low formation of deposits, compared with a traditional pasteurization.

Basics

A treatment followed by PEF pasteurization can potentially increase the shelf life of milk up to 60 days PEF treatment involves the application for short times (2-300 microseconds) of high intensity electrical pulses. This technology is based on the ability of fluid foods conduct electricity because of their high water content and nutrients that may be carriers of electric charges. During treatment with PEF energy, stored in a capacitor, is discharged into high intensity pulses very fast to a treatment chamber, where the food is confined. Although initially the process was carried out in static cameras, computers today are suitable for continuous flow treatments.

fundamental aspects to ensure the effectiveness of the process are the generation of high field strengths and chamber design that allows uniform treatment with minimal temperature rise, avoiding electrolysis. Therefore, the main process parameters to be considered include, besides the electric field intensity, treatment time (pulse duration by the number of pulses) and pulse rate. There are different types of pulses but the exponential decay and square wave are the most used. Effect

constituents on microorganisms and microbial

inactivation achieved by PEF refers to vegetative cells because, in general, inactivation of the spores is negligible. Studies have been conducted in major milk bacteria such as Escherichia coli , Pseudomonas spp. Bacillus spp. Staphylococcus aureus, Lactobacillus spp. Listeria spp. Salmonella Dublin and bacteria in raw milk themselves. Recently, it has proven the effectiveness of PEF in the inactivation of Enterobacteriaceae in infant formulas.

The main effect an electric field on microorganisms is an increase in membrane permeability due to compression and electroporation phenomena. When the values \u200b\u200bof field strength exceeds 25 kV / cm rupture of the membrane becomes irreversible, leading to cell lysis. In general we have seen that short pulses, high intensity and high frequency field are perhaps the most effective conditions for microbial inactivation. Has also been shown that square pulses are more effective than those of exponential decay. Other factors that affect microbial inactivation is the initial temperature of the food, the initial concentration of bacteria and their size, species and growth stage, with those in the logarithmic phase more susceptible than stationary phase and latency.

As regards the effect of PEF on enzymes, generally require more intensive treatment than are required for vegetative cells. The parameters affecting the effectiveness of inactivation are similar to those mentioned above for microorganisms. We have studied the influence of PEF on enzymes important in milk such as alkaline phosphatase, plasmin, lipase and peroxidase, as well as lipases and proteases of microbial origin, obtaining variable results.

Of the studies conducted so time on the inactivation of microorganisms and enzymes by PEF in buffer solutions, model systems and milk with different fat content, has been the medium (composition and pH) also exerts an important effect when considering the effectiveness of the process. Some authors have suggested that high fat content and / or proteins may have a protective effect against inactivation during treatment of milk.

As for the effect on the organoleptic and nutritional quality of processed milk with PEF, the bulk of the work have not shown a significant influence on chemical and sensory properties of milk, with similar characteristics organoleptic a PEF-treated milk to pasteurized milk in a traditional way. In the case of the nutritional value has been only a slight change in the vitamin C in milk treated with a high number of pulses. Very recently it has been observed that treatment of milk with PEF may affect casein, reducing viscosity and improving milk coagulation properties. Comparing the life of conventionally pasteurized milk and milk subjected to PEF was found to have similar life span (two weeks). Pasteurization treatment followed by PEF can potentially increase the shelf life of milk up to 60 days.

LIMITATIONS OF PEF

Treatment of milk with PEF is effective to inactivate vegetative forms but not spores and enzymes as required PEF treatment combined with other technologies. For example, PEF with mild heat or bacteriocins were obtained in this way, synergy between the combined technologies. Studies carried out so far with PEF were performed at laboratory scale and pilot plant. There is a large-scale plant with a capacity of 2000 L / h which allows the processing of liquid foods, particularly tomato juice.

The main problem that arises for the industrial application of PEF is the high cost of facilities. However, it has been shown that the application of this technology leads to more efficient use of energy than a conventional heat treatment, so in a timely manner, could be amortized capital originally invested in the plant. However, industrial applications of PEF require more studies to ensure the effectiveness and safety of the process, especially in foods such as milk, for its high concentration of microorganisms and enzymes that can impair their quality.

Another limitation of PEF is related to the formation of electrolytes in the food and release from the electrode material for the dielectric breakdown phenomenon. These aspects must be considered when designing a process by PEF. Despite these limitations, this type of process offers great potential in the treatment of milk, and you get a food sensory and nutritional characteristics very similar to the starting product and in the future, could provide an alternative to Traditional pasteurization.

http://www.consumer.es/seguridad-alimentaria/ciencia-y-tecnologia/2006/07/05/24173.php