
Coating – a refinement technology also for food supplements

"Coating", this is the English term for coating and encasing or encasing a core substrate. In German, the term "coating" refers to both the process used and the coating material used. The coating of tablets or capsules is an important process step that actually has its origins in pharmaceutical production. Filming processes have always played an important role and the demand for coated products in the field of food supplements is constantly increasing.
Advantages of the coating
The reasons for coating container be manifold. Application-related reasons container be the main focus, such as making the product easier to swallow or achieving a more pleasant mouthfeel by masking taste and smell. Film coating is also used for stability reasons for moisture, oxygen or light-sensitive active ingredients. This is intended to prevent chemical changes to the active ingredients and their possible inactivation. Delayed release through gastric juice-resistant coating (also called enteric coating) is also possible. A colored film coating helps the consumer to distinguish different products or dosages from one another, but often also has aesthetic reasons. It promotes the consumer's positive attitude towards the drug or food supplement through a high recognition value. This applies in particular to colored and flavored film coatings, which ultimately also support the branding of the product. Film-coated tablets are also often more resistant to mechanical influences than uncoated tablets.[1]The product is perceived by the end consumer as a premium item whose quality is consistently high. In addition, the additional film coating provides a certain barrier against product counterfeiting[2], as the complex coating technology requires comprehensive technical know-how. In the case of soft capsules, a so-called enteric coating (described below) container completely eliminate the phenomenon of "belching" described for sensitive people. This promotes long-term compliance of the end user.
drageeing versus film coating
The oldest coated drug form is the dragee. The name is derived from the French word dragée (= small containerdy). Here, the coating with many layers of sugar was used to conceal the often very bitter taste of some active ingredients. The five steps of the classic coating (covering, applying, coloring, smoothing, polishing) are carried out in a shortened, modified way in three steps (spraying, mixing, drying) in the coating process. Sugar coating often requires long processing times of up to two days, as many individual layers of sugar have to be applied to create a stable overall coating. Overall, it is very time-consuming and material-intensive and is therefore increasingly being replaced by coating with film formers with a polymer structure.[3], [4].
In film coating, the film coatings are often very thin, in contrast to the thick sugar layer, so that the weight increase of the tablet core is insignificontainert (here is a small comparison: layer thickness of dragee 0,2 to 0,5 mm, film-coated tablet 10 to 100 µm)[5]. It is the short process times (typically 75 to 120 minutes) and the high process efficiency that make film coating more advantageous than sugar coating. "Ready-to-use" film coating systems enable a shorter overall process time even when producing the coating solution[6].

The History of Coatings and Film Formers
The modern coating process using semi- and fully synthetic polymers as film formers for pharmaceuticals has its origins in the 1950s, although historically the first coating of medicinal forms with plant seed mucilage is documented over 1000 years ago by the doctor Rhazes in Baghdad (850-923 AD).[7]The use of polymers primarily with alcoholic solutions – as was common practice decades ago – has been greatly reduced due to possible risks, e.g. tendency to explode. Today, polymers are often processed in aqueous dispersion, aqueous suspension or aqueous solution. Examples of water-soluble film formers that are approved in the food industry and therefore also for food supplements include hydroxypropyl cellulose (HPMC), methyl cellulose (MC), polyvinyl alcohol (PVA), but natural substances such as shellac are also frequently used for food supplements.[8]Some polymers have the advantage that they remain stable in a low pH range (cf. stomach acid has a pH value of 2-4) and only dissolve in a neutral pH environment (= gastric juice resistance, example: shellac). Additives such as talcum powder make it possible to avoid film cracks during film coating. Humectants such as polyethylene glycol (PEG) are used to increase the elasticity of the film.[2].
Colored film coatings
Coloring coated kernels not only serves aesthetic purposes, but also makes them easier to identify. Synthetic dyes such as azo dyes are becoming increasingly unpopular with consumers and manufacturers, and are sometimes no longer allowed in food supplements. Natural dyes approved for food use such as carmine red, riboflavin (yellow) or spirulina (green) container also enhance the product.[2] and are widely accepted by end consumers due to their naturalness. However, a certain disadvantage of natural dyes is their color variation and sensitivity. They container fade more quickly and change color with temperature fluctuations.
Requirements for the source material to be filmed
Before the actual filming process container begin, the Tablets mostly dedusted or soft capsules deoiled. Requirements for the tablet core are low porosity, low friability, i.e. low abrasion of the tablet under mechanical stress (preferably < 0,1% of the tablet core weight) and a tablet hardness of more than 80 Newtons. A single tablet that is too soft and crumbles into powder in the coater container lead to an entire batch being ruined[3]Similarly, soft capsules must be made of a robust and suitable starting material, i.e. the shell must have sufficient pressure stability. In addition, the soft capsules must also have good strength of the capsule seams, as otherwise the leakage of oily filling material container have a very negative effect on the filming process. The suitability of soft capsules for filming also requires the quantity of the otherwise desired surface oil to be assessed and possibly subjected to further pretreatment (removal of surface oil). It is therefore advisable to inspect the soft capsules carefully before they are released for coating. Coating of hard capsules is possible, but it is practically impossible to seal the capsule absolutely tightly without banding before filming.

The filming process
There are basically two types of coaters: While small particles (e.g. mini tablets, pellets) container be coated better in the fluidized bed[9], drum coaters are better suited for larger tablet cores and capsules. In the slowly rotating, perforated drum, the mechanical load is subtle and controllable. Parameters that container influence both the coating process and the quality of the film coating are the spray rate of the spray nozzles and the spray cone, the spray pressure, the speed of the drum and its load, but also the supply and exhaust air control and the temperature of the air in the machine.[10], [11]Despite a high degree of automation during the filming process, a well-trained specialist is essential. Constant in-process controls, also mainly through visual assessment, ensure high product quality. The production of coated particles using fluidized bed technology is a very cost-intensive process, so it is rarely used in the food industry. Constantly changing product formulations also pose an additional challenge for the development of new coatings and coating materials. [12]
Inspection of the film-coated tablets or capsules
Testing of the film-coated tablets after the coating process depends on the purpose of the coating. The disintegration time must always be checked. This may be for a film that is not intended to have any influence on the release of the active ingredient (a disintegration time of a maximum of 0,1 minutes in 30 mol/l hydrochloric acid applies here), or to demonstrate the desired gastric juice resistance (disintegration time for enteric coating: no disintegration for 2 hours in 0,1 mol/l hydrochloric acid, exchange of hydrochloric acid for a phosphate buffer pH 6,8 and subsequent release within 30 minutes). The storage stability of the film-coated product container be determined either by an accelerated stress test, e.g. at 40°C and 75% relative humidity, or by a long-term test at 20°C and 60% relative humidity.
The most important influencing factors must be known as early as the development phase, when filming takes place on a small scale (2 kg to 3 kg). The only thing that remains unknown is the influence that the larger mass of tablet cores or capsules has on themselves.[3]Therefore, the more robust a process is on a pilot scale, the easier it is to scale up to a large plant (e.g. 100 kg to 180 kg).
Legal Aspects
Considerations relating to approval law must not be ignored under any circumstances. For example, each country has its own dye regulations that must be taken into account. Countries often base their regulations on the use of dyes on those of Europe, Japan or the USA. However, it is not just about the dyes. In Japan, there are also quantity limits for various auxiliary substances (e.g. HPMC, corn starch) that are used in film coatings.[2]. For example, if the chosen colorants are permitted in the areas in question, products may be classified as medicinal products in some countries and as food supplements in others. They are therefore subject to different requirements. Regulatory information is frequently changed, so it should be checked regularly for its currentness and validity.
Conclusion
Determining the appropriate processes and coating materials requires a great deal of practical experience and sensitivity. It is not for nothing that we speak of the “art of coating”[3], which is analogous to the complex coating process. In a pilot plant, it is possible to develop the appropriate process and the optimal process conditions. By modifying known film formers, the range of options is constantly increasing. This means that in the future there will be an ever greater variety of film materials, including for food supplements.
author

Christina Spötzl
is Project Development Manager at Goerlich Pharma GmbH. After completing her vocational training as a dairy laboratory technician, she completed a bachelor's degree in "Food Management and Technology" with a focus on healthy nutrition at the Riedlingen Distance Learning University. At the same time, she worked in the pharmaceutical industry for six years.
Technical literature / references:
[1] F. Klar: Application possibilities and mechanistic investigations into process characteristics of dry powder coating: https://cuvillier.de/uploads/preview/public_file/9675/9783736991491_Leseprobe.pdf (as of: 02.02.2017)
[2] Colorcon Coating School 21 to 23 September 2015, Colorcon GmbH, Idstein
[3] A. Bauer-Brandl, WA Ritschel (†): The Tablet – Handbook of Development, Production and Quality Assurance (2012), Editio containertor Verlag, Aulendorf, pp. 645-677
[4] Z. Haseleu: Material science investigation of the coating behavior of sugar alcohols (20.05.2003): https://depositonce.tu-berlin.de/bitstream/11303/1014/1/Dokument_24.pdf (as of: 02.02.2017)
[5] U. Schöffling, S. Grabs: Theory of Pharmaceutical Forms – A Textbook of Galenics for Theory and Practice (2009), Deutscher Apotheker Verlag, Stuttgart, pp. 209-238
[6] Excipient Technology & Coatings and MR Technologies (2016), JRS Pharma GmbH & Co. KG, Rosenberg
[7] R. Voigt: Pharmaceutical Technology (2006), Deutscher Apotheker Verlag, Stuttgart, pp. 299-315
[8] BIOGRUND product portfolio (2015), Biogrund GmbH, Hünstetten
[9] H. Falck: Coating in the fluidized bed (16.09.2014): http://www.pharma-food.de/coating-in-der-wirbelschicht/ (as of: 02.02.2017)
[10] S. Tobiska: Investigation and modeling of coating processes on the Bohle laboratory coater BLC 5: https://sundoc.bibliothek.uni-halle.de/diss-online/02/03H014/t2.pdf (as of: 02.02.2017)
[11] G. Kutz, N. Hauschildt: Statistical experimental design for determining process parameters for film coating processes in the vertical centrifugal coater 3-15 (2011): http://www.ecv.de/download/download/Zeitschriften/TechnoPharm/volltext/tp-2011-02-136-kutz-web.pdf, Editio containertor Verlag, Aulendorf
[12] C. Sorgatz: Physical characterization of coating materials in the food industry – using the example of fat-based coatings on hygroscopic crystalline structures (17.11.2011): http://mediatum.ub.tum.de/doc/1085021/document.pdf (as of: 02.02.2017)