Product spoilage can occur from the moment a food item has been produced. Increased consumer demand for fresh, high quality preservative-free foods has led to the development of modified atmosphere packaging (MAP). MAP or ‘gas flushing’ as it is also known, is an increasingly popular technique used to easily and economically improve product quality and extend shelf-life. Flushing packaged foods with inert high purity nitrogen retards aerobic spoilage and oxidative deterioration by typically reducing the oxygen level in packaged foods to below 1% so that food tastes as good as the day it was made. Nitrogen is primarily used to reduce the oxygen content within food packaging and to avoid product deterioration. A secondary reason for using nitrogen is as a filler gas to provide a pressurized atmosphere that prevents package collapse, this is an important consideration for consumer brands.
Nitrogen gas plays an essential role in many industries, with a broad range of applications ranging from packaging to fire suppression in an obviously volatile manufacturing environment. With recent technological advancements, on-site nitrogen generation equipment can now provide purity levels equal to that of liquid nitrogen, helping manufacturers lower costs without sacrificing quality or efficiency or quality.
Unlike most food products, fresh fruits and vegetables continue to ‘breathe’ or respire after they have been harvested.
This process consumes oxygen and produces carbon dioxide and water vapour. The key to keeping these packaged products fresh for as long as possible is to reduce the respiration rate without harming the quality of the product – its taste, texture and appearance. In general, the rate of respiration can be reduced by keeping the temperature low, having lower levels of oxygen in the packaging atmosphere and increased levels of carbon dioxide. However, things are not straightforward. For example if there is too little oxygen in the packaging atmosphere, a process called anaerobic respiration will kick in. This produces unwanted tastes and odours in the product and will cause the food to deteriorate. Furthermore, excessively high carbon dioxide can damage some varieties of product. As well as these considerations, the high water content of this class of food, plus the fact that fruit are intrinsically acidic, can lead to spoilage from yeasts and mould. Also, the flesh can become soft because of attack by enzymes from microbes, eventually resulting in rotting. The packaging material used for fruit and vegetables is especially crucial and in particular how permeable or breathable the material is. If the products are sealed in an airtight package, oxygen will soon become depleted and undesirable anaerobic conditions could develop. On the other hand if the material is too porous, the modified atmosphere will escape and no benefit will be derived.