The consumer demands food of high quality and nutritional availability, as well as safe from the microbiological point of view. For its part, the food industry requires effective treatments. The NOVAPACK project in which Grupo Riberebro, Gvtarra and AINIA Centro Tecnologico have participated has focused on developing new packaging materials on which to apply electrical pulse technology to packaged vegetables, thus trying to meet consumer requirements and the food industry.
Technological innovation in the food industry has provided the necessary tools to satisfy consumer demands for food with high quality and nutritional availability and, furthermore, safe from a microbiological point of view.
The most widely used food preservation method is based on heat treatments consisting of subjecting the food to temperatures between 60º and 100ºC for a short period of time.
To this day, heat treatments are the most appropriate to guarantee food safety, since they manage to considerably reduce the microbial flora. Even so, the food industry is exploring other ways of conservation that could have some additional advantage, such as a greater speed in the treatment or some improvement in the organoleptic variations (texture, flavor…) that the treatments cause on the food.
Faster treatments
Among the alternative conservation technologies based on non-thermal treatments available today, the application of electrical pulses stands out. This consists of the intermittent application of electric fields, generally of high intensity (1–40 kV/cm) and short duration (μs) to a food placed between two electrodes. These treatments produce the phenomenon known as electroporation, which results in the temporary or permanent permeabilization of cell membranes.
The electric pulse technology is very attractive because it presents short treatment times and minimizes the organoleptic changes caused by more severe treatments. The mechanism of action of the electrical pulses is that they cause the appearance of pores on the cytoplasmic membrane of the cells (electroporation) and this may have applications for the extraction of components or lead to the death of microorganisms. However, to achieve microbial inactivation, the application of high-intensity electrical pulses (PEAI) (of the order of 20-40 kV/cm) is required, resulting in the irreversible formation of pores. This requirement has meant that the effectiveness of the PEAIs could be verified experimentally only in liquid foods (juices, milk, purees).
Limitations on solid foods
Despite the fact that microbial inactivation by PEAIs has not been successfully applied to solid foods – mainly due to limitations in the experimental devices – electrical pulse treatments have been carried out on solid foods. In this case, they are limited to component extraction processes (for example, nutrients, phenolic compounds…), to facilitate the processing of solid foods (for example, facilitating the peeling of tomatoes, conditioning potatoes for peeling, cutting and frying …) or to improve the efficiency of fruit and vegetable dehydration processes (useful life extension). In these cases, electrical pulses of lower intensity are applied, which give rise to the generation of pores in the cell membranes and which favor the phenomena of extraction or dehydration.
The application of electrical pulses for food preservation is considered an emerging technology, and as such, it has not yet been implemented on an industrial scale. The main limitations that it presents are related to the high treatment intensities necessary to achieve effective microbial inactivation (>20 kV/cm) and to the technical problems derived from its application in solid products (high electrical power required, difficulty of continuous scaling, etc.). Likewise, advances are required in the treatment devices so that a greater flow of product is allowed (greater amounts of product treated) and migrations from the electrodes to the food are avoided.
In addition, the effectiveness of microbial inactivation by PEAIs depends on a large number of factors related to food, such as its pH, or the high variability in resistance between strains of the same pathogenic species. It is for this reason that the commercial application of this conservation technology requires an individualized study to guarantee the safety of the treated food by comparing it with the equivalent heat treatment.
New materials and packaging for vegetables
One of the limitations of the PEAIs technology for its industrial implementation is given by the treatment chambers, the need to avoid flow from the electrodes to the product and to design treatment chambers that guarantee the homogeneity of the processing. In this sense, the studies carried out have been carried out, mainly, on liquid foods that are passed continuously through small-diameter pipes, in special cells of larger diameter for solid products, but in no case have they been reached. carry out studies on packaged products.
The NOVAPACK project in which Grupo Riberebro, Gvtarra and AINIA Centro Tecnologico have participated, and which has been financed by the Ministry of Economy, Industry and Competitiveness through the Collaboration Challenges program (2014-1017) has effectively pursued this objective, design new packaging materials and containers on which to manage to treat vegetables and packaged vegetables through PEAIs. The fact of packaging the food as a step prior to the application of the treatment allows to contain the risk of contamination of the food by contact with the electrodes and, in addition, through the design of the containers it could be possible to achieve a more homogeneous application of the treatment.