Pregnancy Cervix Diagram

Ohmic heating for food preservation

The application of ohmic heating in a wide range of foods provides products suitable organoleptic and nutritional

Ohmic heating occurs when a current electricity passes through a meal, causing the temperature rise inside as a result of the resistance offered to the passage of electrical current. The advantages of this process stem from the fact that the warming takes place inside the food. Thus, unlike what happens in conventional heating, no hot surface contact.

Ohmic heating is faster and has greater capacity penetration of microwaves, which makes it particularly useful in the case of particulate foods, sauces, fruit purees, liquid egg or meat products, among others. This type of treatment avoids overheating, allowing less deterioration in the constituents and reduced deposit formation, the latter being particularly important in foods rich in salts and proteins, for example, milk.

A large number of applications of ohmic heating include blanching, pasteurization, sterilization, thawing, evaporation, drying, fermentation and extraction, among others. One difference from the microwave is the lack of equipment in the home. Yes there is a pilot plant scale and industrial. In 2003 there were 19 plants for ohmic heating, with Japan, Italy, Greece, Great Britain, the USA and Mexico leading countries in the development of these plants. Among the various plants applying this treatment, are particularly notable that have been developed for continuous flow sterilization of fruits, fruit juices, soups, sauces or liquid egg.

The liquid egg is very appropriate for this type of process as ohmic heating can be very short time and without bleeding problems. Although equipment prices are falling, it's a technology whose initial costs can be high. However, profitability has assessed the long term because these are processes in which products are obtained with appropriate microbiological, organoleptic and nutritional conditions of low fouling and takes up little space and can be applied to a wide range of foods. Another advantage of this warming is related to operating costs. They are warm in that 95% of the energy is transformed into heat, while in a microwave heating is usually a 70% maximum. Effectiveness

density, size and shape of food are key factors in the effectiveness of ohmic heating of the heating effect depends on factors specific to the system as the food. There is evidence that the heating rate is directly proportional to the intensity of the electric field and electrical conductivity of the food. Food must be drivers but not much. The optimal values \u200b\u200bof conductivity at 20 ° C are in the range from 0.01 to 10 siemens / m. For example, a suitable food to be subjected to ohmic heating would milk the conductivity value is 0.5 siemens / m. Other factors that influence the effectiveness of warming are the density and specific heat of food as well as the size, shape and concentration of particles in the case of food particulates.

The main mechanism of microbial inactivation is thermal. Kinetic studies have been performed to compare the thermal treatments with conventional ohmic have shown no significant differences between the two processes. Some authors also consider that may occur in the cell membrane electroporation, although there are few studies and do not reach definitive conclusions.

An important aspect to be considered is the possible reactivation of microorganisms after the ohmic heating. Studies have been done in liquid egg show that after 12 weeks of storage there is a lower microbial counts in samples treated with ohmic heating, compared with a conventional heat treatment. In a study of pasteurized orange juice by both types of heating showed that, although the microbiological quality in the juice stored at 4 ° C after both heating was identical, the organoleptic quality was higher in the juice ohmic heating. Despite these promising results, further studies are needed. In general, it is true that the life of processed foods by ohmic heating to be comparable with that of conventionally processed foods.

EFFECT ON THE CONSTITUENTS

Although ohmic heating is a promising technology for the moment little is known about the effect of this type of heating in the constituents of food. In the case of enzymes, inactivation occurs, as happens with microorganisms by thermal effect.

Although few, there are works that demonstrate the suitability of this type of process in improving the functional properties of foods such as surimi from various fish. This effect could be related to ohmic heating uniformity.

Following the various studies conducted so far, the ohmic heating can be considered, among all emerging technologies, as one of the most promising in the food industry. As future prospects have to consider further studies on a microbiological level and constituents, not to mention the possible scaling optimizing domestic and industrial facilities to reduce initial costs.

http://www.consumer.es/seguridad-alimentaria/ciencia-y-tecnologia/2006/07/19/24373.php