Review Gelatin structure and composition linked to hard capsule dissolution: A review Anne Duconseille a , Thierry Astruc a , Naira Quintana b , Filip Meersman b , V  eronique Sante-Lhoutellier a, * a INRA de Clermont-Ferrand-Theix, UR370 QuaPA, F-63122 St Gen es Champanelle, France b Rousselot NV, Meulestedekaai 81, 9000 Gent, Belgium article info Article history: Received 8 November 2013 Accepted 10 June 2014 Available online 17 June 2014 Keywords: Gelatin dissolution Collagen structure Aggregates Cross-links Gelatin molecular weights Hard capsules abstract Gelatin obtained from pig skin constitutes about 50% of world production and is mainly composed of collagen extracted from skin by acidic baths and thermal treatments. The gelatin is used to make various products, notably hard gelatin capsules (HGC) which of varying solubility in water. This issue has been known for many years and has been, and remains, a subject of study and debate. The main reason for low gelatin dissolution rates is its tendency to form cross-links in the denatured collagen chains under specific conditions which stabilize the gel network and prevent dissolution. As it is extracted from animal tissues, gelatin may contain molecules other than collagen (sugars, lipids and other proteins) which may react with collagen chains to form covalent bonds. Although this biopolymer has been the subject of numerous publications, its structure and composition is not well defined. Indeed, there are many dif- ferences from an article to another. Consequently, the causes of HGC dissolution are not well identified and controlled. © 2014 Elsevier Ltd. All rights reserved. Contents 1. Introduction ...................................................................................................................... 361 2. Collagen composition and structure ................................................................................................. 361 3. Gelatin composition ........................................................... ................................................... 362 4. Gelatin structure and gelation mechanism ........................................................................................... 363 4.1. Gelatin structure ............................................................................................................ 363 4.2. Nature of interactions ....................................................... ................................................ 365 4.2.1. Hydrogen bonds ..................................................................................................... 365 4.2.2. Hydrophobic interactions .................................................. ........................................... 365 4.2.3. Electrostatic interactions ............................................................................................... 366 4.2.4. Covalent bonds ....................................................... ............................................... 366 4.3. Parameters affecting cross-link formation ....................................................................................... 369 5. Mechanisms and factors influencing dissolution ....................................................................................... 370 5.1. Effect of the physicochemical environment on gelatin swelling behavior ........................................................... 370 5.2. Parameters influencing solubility ............................................................................................... 371 5.2.1. Origin of raw material and concentration ................................................................................ 371 5.2.2. High molecular weight ............................................................................................... 371 5.2.3. Aggregates .......................................................................................................... 373 5.2.4. Impact of the manufacturing process ................................................................................... 373 5.2.5. Dissolution test ...................................................... ............................................... 373 * Corresponding author. Tel.: þ33 4 73 62 47 08; fax: þ33 4 73 62 42 68. E-mail address: veronique.sante@clermont.inra.fr (V. Sante-Lhoutellier). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd http://dx.doi.org/10.1016/j.foodhyd.2014.06.006 0268-005X/© 2014 Elsevier Ltd. All rights reserved. Food Hydrocolloids 43 (2015) 360e376