Computer-based on-site continuous custom gas mixing system for the modified atmosphere packaging of food products

Controlled and modified atmosphere packaging of agricultural products has often been used to provide an environment that will extend the freshness and quality of a product through the distribution chain. Strong emphasis has been placed on developing gas mixtures which will provide optimum environments for specific food products. Development and research into ways of administering these mixtures has been minimal. The purpose of this study was to continue research into the development of an efficient system for on-site custom mixing of three gases.

Flows of three gases suitable for controlled and modified atmosphere packaging (carbon dioxide, oxygen, and nitrogen) were controlled by plug valves. Control of these valves was accomplished by pneumatic actuators, electro-pneumatic positioners, and a D/A PC-bus card. A computer software program was developed to allow the percentages of the various gases in the mixture to be changed "on-line".

Experiments were conducted to verify the percentages of the various gases in a specified mixture. Gas samples were withdrawn using a 10-ml syringe. Gas chromatography was used to measure the concentration of each gas in the mixture. The gas mixing system consistently achieved three target mixtures within an 8.5% accuracy for the vacuum purge procedure. It was able to quickly altemate between the target mixtures without loss of accuracy.