Carbon dioxide(CO2), one of the naturally occurring gases in the atmosphere, is blamed by the environmentalists for the dreaded global warming phenomenon being faced by the modern world. It is true that CO2 is omnipotent because all living creatures inhale oxygen and exhale CO2 every second without which life is not possible. Plants absorb CO2 during day time to fix solar energy and synthesise starch using chlorophyll pigments present in green leaves. Normally atmospheric air contains 21% Oxygen, 0.038% Carbon Dioxide and 78% Nitrogen. Major sources of CO2 emission are fossil fuels which are burned to generate energy for driving modern civilization. Kyoto Protocol on green house gases calls on all countries to reduce these emissions in order to save the world from disaster due to uncontrollable and undesirable weather changes. Viewed from this angle CO2 is indeed a villain but branding this gas as such ignores the beneficial role it plays in many spheres of life to day.
The omnipotent fire extinguisher that is a part of to day's civil infrastructure is based on the principle that CO2 is a fire retardant and the soda-acid fire extinguishers generate CO2 that can be directed at the fire. As a refrigerant, dry ice or solid CO2 has no parallel as it is a clean refrigerant leaving no residue once sublimed. The temperature of pure dry ice is minus 109.8F which can be further lowered by mixing powdered dry ice with ether or acetone to minus 220F. CO2 is one of the raw materials in the manufacture of the most popular fertilizer Urea. CO2 under pressure is also widely used as a cleansing agent in many industries.
Food industry owes a lot to CO2 for its diverse portfolio of products. Most common use, as a common man can see, is in the manufacture of aerated drinks where the fizz is provided by this gas. CO2 under pressure and at low temperatures dissolves in aqueous phase lowering the pH and providing an atmosphere that inhibits almost all living contaminants in the product. Technologies like Modified Atmosphere Packaging (MAP), Controlled Atmosphere Storage (CAS), Equilibrium Modified Atmosphere Packing (eMAP), Modified Atmosphere/Modified Humidity Packing (MA/MH) owe their strength to the presence of CO2 in the gas mixture that protects commodities under ambient as well as reduced temperature conditions. CO2 at just 80% cause hypercarbia while Nitrogen beyond 98% concentration leads to hypoxia conditions, both inimical to most living things including microorganisms. CAS was being used since 1930 for transportation of fruits over long distances while MAP became prominent in 1970 for Bacon and Fish transport. To day MAP is widely used for distributing products like red meat, sea food, minimally processed fruits and vegetables, cheese, pasta, bakery goods, poultry, cooked and cured products, ready meats and dried foods. It is estimated that 25-40% of all fresh produce harvested does not reach the consumer table due to spoilage and emergence of the above technologies helps to reduce the waste to the minimum where CO2 plays a very significant role.
While meat and fish require very low gas permeability films or high barrier packing materials as they are non-respiring in nature, fruits and vegetables, being actively respiring and transpiring, call for use of films with certain permeability characteristics to allow for diffusion of O2 and CO2 for establishing equilibrium. They need O2 for respiration and emit CO2 as a by-product. Build up of too much CO2 can adversely affect the sensory quality of the product packed and that calls for its diffusion out of the pack. Depletion of O2 is also to be avoided and there fore O2 entry into such packs at desired rate is also necessary. There are excellent packaging materials available to day thanks to the innovative efforts of the packaging industry, meeting every need of the food packers. Both gas flushing and compensated vacuum methods are deployed in packing foods under MAP system. O2 levels of 3-5%, CO2 levels of 10% and rest N2 can be effective for packing fruits and vegetables. CO2 at concentrations of 10% or less is considered most effective in killing all microbes and pests. Grains stored under CO2 can stay in good shape for more than 5 years.
CO2 is a by-product of alcohol fermentation and is available in plenty, waiting to be harnessed for use by the food industry. In baking industry CO2 is an essential tool to impart the desired texture to the baked products. Baking powder, based on sodium bicarbonate and tartaric acid or calcium hydrogen phosphate which generates CO2 on heating is an integral part of the bakery industry and millions of kitchens around the world. The loaf volume, texture and other qualities of the bread are imparted by CO2 generated by yeast under aerobic conditions. The Super Critical CO2 Fluid Extraction Technology (SCFE), the high end process developed some time back has enabled the industry to obtain concentrated and purified products from flavor bearing materials like spices, herbs and aromatic plants. The decaffeinated coffee is made to day mostly by the SCFE technology which does not affect adversely the delicate flavor constituents present in coffee, unlike the solvent extraction technology and Caffeine is obtained as a valuable by-product.
Since the world is fighting against uncontrolled build up of CO2 to protect the environment, it is certainly an adversary but considering the diverse beneficial uses it has in the day day to day lives of people, CO2 is also a friendly partner that sustains the human civilization.