Modified atmosphere packaging is now a prerequisite for many food products, extending shelf life, appearance and taste by preventing or retarding spoilage mechanisms. Quite simply, modified atmosphere packaging uses the main constituent gases that make up the Earth’s atmosphere – nitrogen, oxygen and carbon dioxide then alters the mix and or ratios to obtain beneficial qualities enabling extended food preservation.
Food grade nitrogen within Europe is given an additive number, E941, as it is classed as a food additive when used for modified atmosphere packaging applications. Many other legislative authorities globally also adopt the European standard or have a very similar specification.
Food additive E941 specification purity limits
- Nitrogen* ≥ 99% v
- Oxygen ≤ 1% v
- Water ≤ 0.05% v (500ppmV)
*99% including other inert gases such as noble gases (mainly argon)Impurities:
- Carbon monoxide ≤10 ppmV
- Methane and other hydrocarbons (as methane) ≤100 ppmV
- Nitrogen monoxide and nitrogen dioxide ≤ 10 ppmV
The main contaminant to consider within the specification is oxygen @ ≤1%, however, this is for the nitrogen gas itself whether produced from on-site generation or supplied via traditional methods such as high-pressure cylinders or bulk liquid. One important factor for gas generation is that the higher the acceptable level of maximum remaining oxygen content, (MROC), in the output N2 stream, the less compressed air is required to produce the gas and hence the lower the overall unit gas cost. Typically, to produce nitrogen from a gas generator at 10 ppm MROC is 3 times higher cost than at 0.5%.
Often the oxygen content within the finished gas flushed food pack is higher than 1% and the actual acceptable level is specified based on the type of food, designated shelf life, storage conditions and possible spoilage mechanisms.
Many food producers employ the services of expert independent food research establishments such as Campden BRI based in the UK for example. In these facilities, packing and storage conditions along with microbial assessment can be evaluated pertaining to the specific food product to establish the optimum modified atmosphere specification — including maximum remaining oxygen content within the finished pack.
A specific range of foods that have a long history of benefiting from modified atmosphere packaging are dried, powdered products such as coffee, infant formula and spices. These are routinely packaged using Vertical Form Fill and Seal, (VFFS), machinery, fitted with a dedicated nitrogen gas flushing system.
Parker has many nitrogen gas generators operating globally, employed for modified atmosphere packaging of dried powdered foods with VFFS machines. Establishing initial suitability can often be challenging if simple logic is not taken into consideration.
On-site nitrogen generation: a safe, low-cost alternative to traditional methods
Food producers that use MAP are rapidly realising the benefits of on-site generation as a safe, convenient, sustainable and low-cost alternative to traditional methods of supply. The change from purchased gas to self-produced might seem a little daunting to some and there is often insistence that the new generated supply must match the existing specification with regards to oxygen content.
MROC in purchased gas vs. a nitrogen generator
Sometimes an impasse is reached where a food producer wants to change to a Parker gas generator but insists on 99.999% (10ppm maximum remaining oxygen content) purity unless it can be proven that a slightly higher oxygen content gas will achieve exactly the same results, even though the acceptable oxygen level within the finished pack would typically be in the region of 2%.
Parker appreciates this stance and fully understands that for food producers there is a lot at stake in getting it right. However, considering using purchased gas at typically 10-20 ppm purity, does switching to generated gas at say 0.5% change the 2% MROC achievable in the finished pack?
In reality, it doesn’t and the reason for this is that it is almost impossible to flush all of the air out of the packs as they are rapidly and continuously formed within the packing machine, so some oxygen content from the residual ambient air always remains. Secondly, as the product is dropped into the pack from the multi-head weigher through the filling funnel, it pulls in ambient air, thus introducing a little more oxygen into the pack.
One possible way of confirming the suitability of an on-site supply of food grade nitrogen at various purities to establish the most suitable would be to install a small nitrogen generator system to run on a trial basis. This however in most instances is not logistically or physically viable.
Recently Parker UK was faced with the dilemma where a high-quality coffee producer desperately wanted to convert from an expensive and problematic long-standing bulk liquid supply to a NITROSource PSA on-site solution. The producer fully understood the huge cost savings that could be enjoyed by specifying 0.5% purity as opposed to 10ppm but wanted absolute proof that their reputation and produce would not be jeopardised by the change in purity.
To overcome the problems associated with the installation of a full-scale trial unit, Parker's nitrogen generation manufacturing GSFE Division UK and the Local UK Parker sales company devised a solution to introduce a small, fully variable quantity of food grade compressed air into the existing high purity nitrogen supply, thus enabling the ability to increase the MROC to any desired level. A calibrated independent oxygen analyser was installed at the device outlet to constantly monitor O2 levels.
A series of tests were carried out on one packing line where the device was installed and the producer’s quality assurance department was on hand to oversee the trial and sample the finished packs using a calibrated bench top pack analyser for MROC.
The machine was run at its standard 36 bags/min first with only the 10ppm liquid supply and then 2 levels of raised oxygen gas at 0.1% and 0.5% achieved through a small bleed in of food grade compressed air.
As can be seen from the table of results, there was virtually zero difference between the gas purities with regards to MROC in the pack and the target O2 level was maintained well below the limit.
The test was evaluated by the producer's decision-making team and a twin bank NITROSource PSA system was duly ordered and installed to fulfill the demand of the entire factory.
Interesting to note that on the day of change over from the existing liquid supply to Parker generated gas, the operatives and QA department were not informed so as to execute a blind test. We are happy to report that the system actually ran for 3 weeks without any detected difference before the parties concerned were eventually informed!
Considering the total cost of ownership including energy, maintenance and capital expenditure, the entire system is expected to realise pay-back within 2 years and reduce cost by up to 75% thereafter.
Now, watch this video to learn more about NITROSource:
For additional information on Parker NITROSource gas generators, download the product brochure. You can also contact Phil Green, the author, directly: firstname.lastname@example.org
This post was contributed by Phil Green, industrial gas application and training manager, Parker Gas Separation and Filtration Division EMEA.