Gelatin is a collagen in the skin, bone and tendons of animals. After partial hydrolysis, the protein product obtained by purification is also a good microbial culture medium under a certain water content. Therefore, microbial control of gelatin products is critical.

There are more than 20 kinds of preservatives added to internationally recognized foods. Among them, hydroxyphenyl esters (parabens) have become the first choice for many empty capsule manufacturers due to their broad-spectrum antibacterial activity and wide pH adaptability . There are four commonly used parabens, namely methyl ester, ethyl ester, propyl ester and butyl ester. By destroying the cell membrane of microorganisms, parabens denature proteins in cells and inhibit the activity of respiratory enzymes and electron transport enzymes of microbial cells to produce bacteriostatic action. The combination of parabens is usually used to reduce the amount of use and increase the antibacterial effect.

Countries have strict regulations on the amount of parabens in foods, and the total content of parabens in finished products is usually less than 0.05%. China's GB1760 stipulates that the total amount of parabens used alone or in combination should be less than 0.05%; the butyl ester commonly used in Japan, the maximum limit is 0.028%; the United States allows a small amount of heptyl ester for beer preservation, while the EU is in DIRECTIVE 95/2/EC Directive stipulates that no preservatives for parabens are allowed in dietary supplements; the United States and the European Union have mentioned in relevant regulations that preservatives cannot be used to lower the standards for GMP or raw materials. Products requiring chemical preservatives in the United States must be clearly labeled on the label as “addition of ××× as a preservative” or “use of ××× to inhibit bacterial growth”. CP 2010 edition "gelatin empty capsule" consultation draft has increased the detection of "hydroxyphenyl ester" content, the limit is 0.05%.