Carbon Dioxide Processing and Milk

Thermal treatment of food product is always related to high impact on their nutritional and organoleptic values and a times are not desirable specially in case of thermally sensitive food products. Most general practice in dairy industry is having high temperature short time (HTST) pasteurization practice where the liquid milk is subjected to high temperature having range of 70-78 Deg. C, which although reduce microbial load in milk but the milk is in risk of losing thermally sensitive nutrients and enzyme, off flavor development due to overheating and other changes in organoleptic factors.

High pressure carbon dioxide, also known as HPCD is an emerging technology being used for thermally sensitive food product. A type of pasteurization that can be an alternative to thermal pasteurization in food industry. This technique is considered as an alternate to pasteurization as this process has been known for bactericidal effect.

Solubility of Carbon Dioxide-

The amount of carbon dioxide in any solution is known as the concentration of carbon dioxide. There is always saturation level, i.e., the maximum amount of carbon dioxide that can be dissolved in any liquid, present which is exploited during processing. Carbonation is the term given to the process of addition of carbon dioxide in liquid.

During the milking stage, milk already consists of certain percentage of CO₂ ~5 millimole but with time, the concentration drops as it equilibrate with the atmospheric CO_2. The solubility of CO₂ in milk is controlled by temperature and product viscosity. The more the temperature, less the diffusion of CO₂ in milk but increase in viscosity helps in diffusing more gas in higher temperature product. With slight infusion of CO_2, freezing point of milk can be brought down but is reversible until the infusion is moderate.

How Microbes react to HPCD-

What makes the CO₂ to be antimicrobial? Well, the acidification property and solvent properties helps in attaining the goal, and maximum effect can be attained in the supercritical state. The liquid form of CO₂ has greater solubility and can penetrate through the microbes and disrupts the cells. The acidifying property when is doubled with pressure the bactericidal effect. Depending on applying temperature and pressure, impact on microorganism can be altered

1. At low pressure and low temperature carbon dioxide can inhibit the growth of pathogenic microbes and alters the pH of the medium which infers double attach to the growth of microbes.
2. At high pressure and moderate temperature, carbon dioxide tends to attack the microorganism and inactivates by destroying its cells.

Parameter influencing –

The process parameters such as temperature, pressure, time of exposure and agitation affects the overall shelf life of product in case of carbon dioxide processing.

1. Temperature- Higher temperature facilitates the higher diffusion and penetration of carbon dioxide in the microorganism cells leading to more lethal effect on present microorganisms. But the optimal range is to be kept in mind while providing heat to the product as the higher temperature leads to less solubility of carbon dioxide in product. From past research it has been evident that temperature range of about 20- 45 Deg. C is optimal for carbon dioxide treatment.
2. Pressure- When pressure is increased it has been noted that less exposure time is required for the deactivation of microorganism. Also fast depressurization also helps in the cause.
3. Agitation- In case of no agitation, only the periphery microorganism shall come in contact with the carbon dioxide present in product hence, constant agitation facilitates the contact of carbon dioxide and microorganism hence high chances that the all microorganism in product is deactivated.

There has been almost hundreds of bacteria identified in the raw milk. All have different characteristics, and each have differently impacted when subjected to various processing conditions. The product composition also have important role to play on the shelf life and treatment effects. The statement is backup with various previous and ongoing studies. Addition of certain amount of starch didn’t affected the bactericidal effect of CO₂ while presence of whey protein affects negatively on the efficiency of carbon dioxide processing. Also lower water content also reduces efficiency of CO₂ treatment as it act as a protective barrier for microbial cells. Salt also affects the kill efficiency- Lower salt reduces the potency while higher salt concentration facilitates the kill efficiency of carbon dioxide processing.

To conclude, listing some of the attributes that can benefit the commercializing of carbon dioxide processing of food products.

1. Low fat content
2. High Water activity
3. Low to moderate sugar content
4. Alcohol and protein content
5. Low pH and
6. Low viscosity

Skimmed liquid milk fits precisely in this category and thick dairy products are hard to treat with the carbo dioxide pasteurization technique.

All studies till date conducted, including product shelf life, effect on food product, and others are of laboratory level which is the holding back point for this technology. Need of the time is to carry out extensive research on the utilization in commercial level so that the benefits can be fully commercialized.