Juice production: electric field sterilization instead of heat sterilization

Pulsed electric field technology for the production of high quality (green) juices - The demand for fresh juice products has been steadily increasing. In particular, fruit shakes are very popular due to their high health properties. There are more and more products in the market called green smoothies, which contain spinach, kale or various salad leaves. These green smoothies are rich in vitamins and minerals. The extract that gives the fresh produce a bright green color is the secondary plant compound chlorophyll. Since chlorophyll is similar in structure to hemoglobin in the blood, it has a supporting effect on the formation of new blood cells. In addition, secondary metabolites also contribute to human health.

Fresh produce has the highest concentration of healthy ingredients. Due to the source of the fruit shake products and the process of making the smoothies, the shelf life of these products is very short. In order to achieve commercial applications, it is necessary to add a preservation process. Traditionally, such products are heated and maintained at a specific temperature. This pasteurization process reduces microbial concentration and extends the shelf life of the product.

However, not only the microorganisms in the juice or the fruit juice are affected by the heat treatment process, but also the ingredients that have health promoting effects, such as chlorophyll in the green fruit product. Some vitamins are also destroyed and their numbers are adversely affected. The color of the fruit will become darker. For example, after heat treatment, the bright green color of the freshly produced fruit will be destroyed, the basic reason is the oxidation of secondary metabolites.

An alternative to pasteurization is the pulsed electric field (PEF) technique. PEF treatment can replace heat treatment and can be used to produce high quality juice and smoothie products that remain stable during storage. In this process, the liquid product is pumped through the electrode and subjected to high voltage electrical pulse processing at the electrode for several seconds. These electrical impulses induce electroporation in the microbial cell membrane, that is, the cells are perforated.

Different methods, the same effect

After the perforation occurs, the cells are deactivated, the concentration of microorganisms in the liquid product is lowered, and the storage of the product becomes more stable. PEF uses a different inactivation mechanism than heat treatment in which the inactivation mechanism relies on cellular protein and enzyme denaturation. Despite the different mechanisms, the two treatments have the same effect on the microbial community and can give the product a certain shelf life.

Microbial concentration during untreated, heat treated and PEF treated orange juice at 4 °C

As an example, Figure 1 shows the total plate count (TPC) of PEF treated and heat treated orange juice versus untreated orange juice. During storage under refrigerated conditions, the microbial concentration of untreated orange juice increased very rapidly, while the growth rate of orange juice treated with low-intensity PEF was slower. In general, longer shelf life requires more intense processing.

Energy input determines the shelf life

When heat treatment is employed, the treatment strength is adjusted by the temperature and humidity for the length of time. For PEF processing, intake air temperature, energy, and electric field strength are the primary process parameters used to describe process strength.

A low energy input in the range of 60 kJ/kg gives a 21 day shelf life and depends on the manufacturer's microbiological limits. And about 100 kJ / kg of energy can give the product a shelf life of more than 3 months. As can be seen from Figure 1, a longer shelf life can be obtained with a more intense PEF treatment, and no microbial growth is detected in juices over a period of more than 60 days.

In summary, Elea PEF technology is effective in inhibiting microbial concentrations and can be used to produce juices and vegetable juices with stable shelf life. The main difference between this technique over heat treatment is the quality after treatment. The working principle of heat treatment is based on denaturation, which destroys some or all of vitamins and Other healthy ingredients. The PEF treatment mechanism only affects microorganisms that cause spoilage in liquid products, and the compounds that reflect quality remain active.

Green juice: fresh juice, heat-treated juice and Elea PEF technology treated juice

For example, one of the main quality attributes of green smoothies is the secondary metabolite chlorophyll, which gives the product a bright green color, as shown in Figure 2. After the heat treatment, the chlorophyll was destroyed and the product appeared brown. The heat generated by the PEF process is much less than that of the conventional pasteurization process, so the chlorophyll remains active. Thus, the use of PEF technology can produce green fresh fruit smoothies with stable shelf life.

PEF works not only for green smoothies, but also for other fresh juices, dairy products or shakes. The Elea CoolJuice® and Cool- Dairy® systems are available in a range of production capacities from 50 L/h for small batch production and test production facilities up to 10,000 L/h for industrial production.

to sum up

All in all, PEF technology has the advantage of ensuring microbial stability while maintaining high quality, almost fresh flavors, vitamin and mineral content and other healthy ingredients. In addition to the benefits of high quality products, longer shelf life has a significant impact on the scope of supply. A longer shelf life of freshly prepared untreated products can achieve greater market coverage than freshly made PEF-treated products. In addition, the cost of shipping and product handling is reduced, meaning that the rate of returning products is lower. In terms of production, Elea PEF technology is more flexible in terms of production logistics. By dividing into small batch production, it is possible to produce larger batches of products, reducing management overhead costs and production costs. Ultimately, PEF's innovative technology offers an opportunity for manufacturers to produce juice products with stable shelf life and highest quality standards.

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