In the 100-year history of capsules, gelatin has maintained its position as a mainstream capsule material due to its wide range of sources, stable physical and chemical properties, and excellent processing properties. With the increasing preference for capsules, hollow capsules are more widely used in the fields of food, medicine and health products.
However, the occurrence and spread of mad cow disease and foot-and-mouth disease has led to concerns about animal-derived products. The most commonly used raw materials for gelatin are bones and skins of cattle and pigs, and the risks are becoming more and more concerning. In order to reduce the safety risks of hollow capsule raw materials, industry experts continue to research and develop suitable plant-derived capsules.
In addition, with the increase of capsule varieties, the diversity of its contents has gradually made people realize that gelatin hollow capsules have compatibility problems with some contents with special properties. For example, contents containing aldehyde groups or reacting under certain conditions to form aldehyde groups may cause cross-linking reaction of gelatin, highly reducing contents may have a Maillard reaction with gelatin, and highly hygroscopic contents will cause the shell of the gelatin to lose water and lose its original toughness. The above-mentioned stability problems of gelatin hollow capsules have attracted more attention to the development of new capsules.
What plant-derived materials are suitable for the production of hollow hard capsules? There have been many attempts. Chinese Patent Application No. 200810061238. X applied for cellulose sodium sulfate as the main capsule, 200510013285.3 applied for starch or starch composition as the main capsule, Wang GM [1] reported the manufacture of hollow capsules from chitosan capsule raw materials, and Zhang Xiaoju et al. [2] reported products with konjac-soybean protein as the main capsule. Of course, the most studied is cellulose materials. Among them, hollow capsules made of hydroxypropyl methyl cellulose (HPMC) have formed large-scale production.
HPMC is widely used in the field of food and drugs, is a commonly used pharmaceutical excipients, and is included in the pharmacopoeia of various countries; FDA and the European Union approved HPMC as a direct or indirect food additive; GRAS is included as a safety substance, No. GRN 000213, included in the JECFA database, INS No.464, does not limit the maximum daily dose of HPMC, and was approved by the Ministry of Health of China in 1997 as a food additive, thickener (No. 20), suitable for all kinds of food, and added according to production requirements [2-9]. Due to the difference in properties with gelatin, the prescription of HPMC hollow capsules is more complicated, and some gelling agents need to be added, such as gum arabic, carrageenan (algin), starch, etc.
