The dissolved oxygen concentration in food matrices and that present in the headspace of packaging can give rise to degradative phenomena during the food’s storage period, or its shelf life. Maintaining low levels of this gas concentration certainly allows to preserve the organoleptic and microbiological characteristics of the food.
Oxygen reactions in packaging
It is well known that oxygen is involved in oxidation reactions, both chemical and enzymatic, in the degradation of pigments and aromas, aerobic respiration, and the proliferation of aerobic bacteria, molds, and yeasts.
Rancidity, for example, is a process affecting fatty food products that can develop through various mechanisms (hydrolysis, lipolysis, and oxidation reactions), while in products containing large amounts of sugars, chemical hydrolysis reactions occur that reduce sweetness.
For all these reactions and metabolisms, the oxygen concentration is proportional to the rate of the phenomenon and any system capable of reducing it is appropriate for extending shelf life.
How to reduce oxygen concentration
From an operational point of view, there are several ways to achieve a reduction in oxygen concentration in the headspace of packaging and/or in the liquid matrix:
- Use of oxygen scavengers (OS)
- Deaeration of food matrices before packaging.
- Hot filling of packaging and/or in a controlled atmosphere using an inert gas.
- Use of antimicrobial peptides.
Use of oxygen scavengers (OS)
Oxygen scavengers (OS) are among the most studied and established solutions in active packaging.
Indeed, the high reactivity of oxygen allows the creation of various OS systems where a chemical reaction (not an adsorption) ensures the reduction of concentration.
In the case of fat-rich foods, degradation phenomena tend to prevail during storage due mainly to the presence of oxygen in the headspace of the packaging. In this case, the use of “ageless” packaging—i.e., packaging containing small amounts of oxygen scavengers enclosed in permeable sachets or embedded directly in the polymer film, currently available on the market—could be used.
It is important to highlight that, in recent years, attention has shifted towards the use of recyclable materials.
According to European Union directives, all plastic packaging in circulation within the EU must be either reusable or economically recyclable by 2030.
In this regard, companies are gradually eliminating the use of materials with OS, as they are not recyclable. There is a move towards the use of recyclable and therefore eco-sustainable materials, and in the coming years, towards the use of recycled materials; this last step represents a challenge especially for the food packaging sector.
Deaeration of food matrices before packaging
A possible solution to reduce the oxygen concentration in the food matrix could be represented by pretreatment of the finished product or, in some specific cases, semifinished products, within a deaeration section.
Deaeration can occur by increasing temperature, reducing pressure, or by replacing with an inert gas. In the latter case, nitrogen bubbling countercurrent through the liquid phase is usually used.
Hot filling of packaging
Hot filling of packaging is undoubtedly a simple solution to naturally reduce the oxygen concentration in the liquid matrix.
According to physical laws (Henry’s Law), gas solubility in liquids is favored at low temperatures, so, consistent with the chemical characteristics of the product, the higher the temperature, the lower the dissolved oxygen concentration. Obviously, the maximum operating temperature is the one that allows the nutritional and organoleptic characteristics of the food to remain unchanged.
To reduce the oxygen concentration in the headspace, foods are generally packaged in “controlled atmosphere”, meaning that the headspace of the packaging is washed, for example, by flushing with nitrogen immediately before hermetically sealing the packages.
Use of antimicrobial peptides
The last technique used to reduce the oxygen concentration in the packaging headspace is the use of specific antimicrobial peptides. The use of this particular type of molecules represents an innovative approach to prolonging food shelf life without the use of chemicals.
The importance of oxygen concentration analysis for shelf life
To evaluate the oxidative phenomena of a food matrix, it is very useful to analyze the oxygen concentration in the headspace of the food packaging and/or in the liquid matrix.
This analysis can provide important information *on the packaging process, on the characteristics of the chosen packaging material, and on the formulation* and is essential both to monitor the stability of the standardized process and to verify if a modification was made due to regulations, marketing, or technological innovation.
In particular, the evaluation of the oxygen concentration profile during the product’s shelf life allows to understand and predict * (through accelerated shelf life application) * the oxidative pathway of the food matrix and correct any deviations from expectations by *intervening on the process, packaging material, and/or formulation*.
The study of oxygen concentration in shelf life is normally conducted *in parallel* at the *normal food storage temperature* and at a *higher temperature to accelerate the usual oxidative processes*; the temperature is chosen based on the chemical-physical characteristics of the matrix and its ingredients. Furthermore, currently, due to the growing trend to package wet foods with transparent materials, it is useful to conduct *comparative studies on packages stored both in light and in the dark*: light catalyzes and accelerates oxidative reactions.
Oxygen analysis at time zero
The oxygen analysis performed at time zero, just after packaging, allows an immediate assessment of the starting concentration and to develop any corrective strategies to modify the packaging filling process, by introducing *a nitrogen flow*, modifying the *filler filling heads*, modifying the *machine geometry*, or intervening on the *package geometry*.
Oxygen protocol for food matrices
To perform the analysis, it is necessary to use a specific protocol developed and optimized specifically for food matrices which mostly belong to the category of non-Newtonian fluids.
The phase of protocol definition requires a preliminary experimental study to understand *oxygen-food matrix interactions* depending on the food composition and a design study to modify commercially available instrumentation in order to make analytical operations more effective and applicable in an industrial context.
Finally, an optimized and flexible protocol is defined that can be applied to different types of foods.
Conclusions
In this article, we wanted to share an aspect of the product packaging process, and more generally of shelf life, which we consider fundamentally important but not always explored in depth. In the next article, we will present a case study of one of the works carried out by I.T.P. srl in this field, to show how the process takes place and what benefits the client received from the project we realized.
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