Food preservation by controlling the Redox potential

azaquar's picture
Submitted by azaquar on Tue, 10/05/2011 - 10:21

Overview

Redox potential (Eh expressed in volts) measures the ease with which a win or lose electrons. An oxidizing environment is when it picks up electrons (the Eh is positive) and it is simplistic when it loses electrons (the Eh is negative).

A medium containing substances heavily hydrogenated,-SH radicals, reducing sugars or other compounds such as ascorbic acid (vitamin C) or tocopherols (vitamin E) is reductive. This is the case with many food products. The effect of an oxidative environment is mainly due to the presence of atmospheric oxygen or surface (meat) or mass (plants: parenchyma through the gaps and stomata).

The redox potential affects the speed of weathering reactions and the growth of microorganisms. Depending on their requirements in oxygen, microorganisms are classified into four categories:

  1. The strict aerobes (Pseudomonas, Micrococcus, Bacillus) are microorganisms that can grow in the presence of oxygen.
  2. The aerobic optional (Enterobacteria, Staphylococcus) are microorganisms that can grow in the presence and absence of oxygen.
  3. Strict anaerobes (Clostridium, Bacteroides, ...): Are the microorganisms that can grow in the presence of oxygen.
  4. Micro-Aérophile (Lactobacillus, Streptococcus, ...): Are the microorganisms that can grow in the presence of low amounts of oxygen.

The redox potential of a food depends on its physicochemical characteristics, presence or not of a package, the partial pressure of oxygen and atmosphere storage.

Control of redox potential

Besides oxygen, other gases in the atmosphere storage (water vapor, nitrogen, CO2) may modify the redox potential of a food.

The CO2 used for packaging atmospheres (conservation of apples, pears, cereals, etc..), Has in addition a bacteriostatic action: under high pressure, it improves the preservation of soft drinks. As for nitrogen, it is generally regarded as an inert gas.

For the control of redox potential of a product, on a case to control the gaseous environment around him. For this reason, several techniques are used, the most important are: vacuum packaging, packaging in modified atmosphere packaging and controlled atmosphere.

Vacuum packaging

The vacuum packaging is packaging associated with an exhaust gas and thus a reduction of oxygen in the environment of the product. It allows you to remove the adverse effects caused by the presence of oxygen.

This type of packaging may still present some disadvantages. Atmospheric pressure exerted on the outside packaging, but not inside, gives rise to a compression of the food: this compression can lead to the production of juices by the food or make difficult the separation of the slices s it is a food decision. In addition, this technique can not be very sensitive to foods (eg, food covered with a lining).

Modified atmosphere packaging

In contrast to the vacuum packaging, modified atmosphere packaging, also known as modified atmosphere packaging, is to change the environment of the gas produced by a reinjection of gases such as CO2 and nitrogen.

This technique improves the keeping quality of food. However, products packaged and can be considered microbiologically stable, this technique must obviously be associated with a conservation plan under cold, or combined with another barrier to counter the growth of microorganisms.

Today this technique is applied to a large number of foods such as fresh or processed meat, poultry, fish, shellfish, dairy products, vegetables, fruits, fresh pasta, pastries, cookies , snacks, coffee, tea. For some products, fresh pasta, for example, modified atmosphere packaging accounts for almost the entire market.

Controlled atmosphere storage

In the case of storage of fresh vegetable products such as apples and pears, we can not simply change the atmosphere surrounding the product once and for all. Indeed, the activity of respiration and transpiration of the cells causes a change of the environment gas. We must therefore intervene regularly to maintain the gas in the desired proportions: It is the controlled atmosphere storage.

The controlled atmosphere storage is used for preservation and also for controlling the ripening of fruit in bulk. Indeed, it is interesting not only to keep the fruit, but also to better control their maturation: the slow down when demand is low and the large stocks, the speed when demand is high.

Conservation of fruit can be done in controlled thermo-speakers in which the gas mixture is modified and controlled: a few% of oxygen and carbon dioxide, the rest of the atmosphere consists of nitrogen. The chamber may also be coupled to an ethylene absorber. Indeed, the ethylene produced naturally by fruit accelerates their maturation. It is interesting to reduce the concentration if it wants to delay maturation and therefore keep the fruit longer. This is preferable to the use of chemical inhibitors.