The word Aloe has two different meanings - One is an invented term that refers to the generic name of the Asphodelaceace subfamily. The second one is used to refer to pharmaceutical products obtained from the juice of certain Aloe species.
The true aloe, lat. Aloe Vera, belongs to the subfamily of Asphodeloideae (Affodilaceae) and further to the family of Xanthorrhoeaceae. The genus of Aloe plants includes more than 250 species, although only a few are used for commercial cultivation. They are water-storing xerophytes adapted to warm desert regions where water is scarce. Like the agave plants, the aloe plant belongs to the succulents (sap-rich plants). Its growth habit resembles a hybrid of shrub, herb and tree. Its fleshy, leathery leaves are usually toothed and often end with a spiny tip. The leaves can grow 50 cm long and without or with a small stem in dense groups (rosette-like growth habit). Their height can be up to 3 meters, although a lower height is preferred in plantation cultivation.
The anatomy of the leaves is decisive for the respective intended use: for example, different parts of the leaf are required in the pharmaceutical industry other than in the cosmetic industry. Roughly, the leaf is divided into two parts: The leaf bark with the underlying latex layer and the leaf gel. Each area contains specific chemical substances that can be used for different purposes. For example, the pharmaceutical industry is increasingly targeting the leaf bark and latex layer. The anthranoids contained there, a chemical class of substances, is suitable for medicinal applications and should never be included in cosmetic products. Careful selection of the right plants with appropriate processing procedures is therefore very important. Only the aloe gel obtained from the aqueous leaf gel/pith is used in cosmetics.
The exact origin of the plant is unknown but an origin in Africa is suspected. Its good adaptability to dry areas allows its cultivation in almost all tropical and subtropical regions worldwide. The plant prefers low annual precipitation combined with high average temperature around 23 degrees Celsius. Main cultivation areas are found in the USA, Mexico, Africa and the Mediterranean region. There, the plants are cultivated in plantations, although wild collections can also be found. Depending on the quality requirements, locations with high sunlight and good soils can be advantageous: these include small farms in Greece, Spain and the Canary Islands in particular. After two to three years, the plant forms yellow and red flowers.
Three to four years old leaves are harvested from the outside to the inside. For this purpose, the mature leaves are separated individually by hand at the base. Since it immediatley leaks anthranoid-containing sap from the base, a certain amount of time should pass for this leaking process to be completed before further processing (see below).
Aloe vera gel occupies a position between the classical mucilages or mucilage drugs and gums (e.g. gum arabic).
Aloe gel is a colorless mucilage obtained from the anthranoid-free parenchymatic tissues (=peeled leaves). This gel consists of almost 95% water and contains, among other things, chemical agents such as glucomannans, glycoproteins and aloeins. Due to the high water content, microbial decay occurs very quickly, making chemical preservation, stabilization or thermal preservation necessary.
The leaf consists of the leaf bark with the spines and the characteristic thorn, the latex layer and the leaf gel. The main component is the hydrous pith with the characteristic mucilaginous, transparent gel.
In production, it is necessary to distinguish between two indications: pharmaceutical and (mostly) cosmetic (also food). In the following, the cosmetic indication will be emphasized.
In order to reduce dirt and possible impurities on the outside of the leaf, the leaves are washed (mechanically) after harvesting for subsequent processing. Due to the juice escaping directly after the plant is cut, a waiting period must be observed to reduce residual anthranoids in the leaves. Due to the increasing demand worldwide, four major production processes have been established: whole leaf, rolling, filleting and mechanical peeling.
As the name suggests, in the whole-leaf process the entire leaf is crushed and the obtained pulp is then pressed. All substances, including the unwanted anthranoids, are separated at the same time. In order not to have these substances in the final product, special activated carbon filters are used: these remove anthranoids, but also a large part of bioactive substances. This results in high quality substances but with (too) few ingredients. The advantage is an adjusted product that can be easily further processed and contains only a small amount of anthranoids.
The rolling process differs from the whole-sheet process only in the preparation of the leaves: in the rolling process, the sheet is first cut open on one side and then passed through a roller. Starting from the closed side of the leaf it is passed through the roller and the gel contained in the leaf flows out through the previously cut side. Since the undesirable anthraquinones are also extracted here, subsequent filtering must take place with the disadvantage/advantage mentioned above.
The filleting of the leaves is reminiscent of fish preparation: the leaves are cut open individually by hand in order to gently remove the leaf pulp or gel. Through clean cuts, the gel can thus be carefully removed from the leaf without damaging the anthraquinone-containing cells. Contamination can thus be greatly reduced. The "gel fillets" still need to be washed and can then be further processed (see below). After filleting there is usually no need for further processing steps, which is why desirable bioactive substances remain in the gel. The quality of this process is therefore at its highest.
In the case of mechanical peeling, attempts are made to make the advantages of filleting even more efficient. For this purpose, the leaves are passed over a type of milling machine that mechanically removes the outer skin. Since the leaves have different sizes and characteristics, this can lead to increased anthranoid contamination. These substances still have to be removed with filters. The advantage is a qualitatively higher starting substance in relation to the whole-sheet process. The downstream treatment processes are thus more cost-effective.
Since the obtained gels have a high sugar content they must be processed quickly to reduce microbial deterioration. The majority is usually chemically preserved: on the one hand, this has the advantage of largely preserving the natural ingredients. On the other hand, the chemical structure of the mucilage is not destroyed. Possible preservatives that can be added include vitamins C and E as well as citric acid, benzoates and alcohols. Depending on the application, the gels can then be pressed and filtered to remove residual plant fibers. The final products are often transported and stored refrigerated or even frozen to reduce microbial deterioration.
Preservation by heat destroys the rheological properties of the mucilage and thus of the complete end product. For this purpose, the obtained gel is pasteurized for a short time or even concentrated. The heat destroys bioactive substances and the structure of the sugars/mucilage: the gel exhibits completely new haptic properties. Additional gelling agents such as carbopol, xanthan or cellulose are used to restore the product to its original properties. The advantages of heat sterilization are the specially adjustable properties and the longer shelf life with low preservative content. In addition to heat sterilization, another option is to concentrate the gel: thermal energy is used to extract more and more water from the substance until a critical concentration is reached. This concentration allows the reversible process: mixing with water or other substances to restore the original properties. Concentration can increase shelf life and reduce transportation costs.
Aloe vera gel consists largely of D-glucose and D-mannose built polysaccharides (55%) which allow a high concentration of water. In addition, freshly obtained gels contain simple sugars (17%), minerals (16%), vitamins (A, E, C), amino acids, proteins, and enzymes. These substances are often degraded by the manufacturing process, preservatives, or excessive storage. Aloe vera gel is believed to have anti-inflammatory, immune system stimulating, irritation reducing and wound healing effects.
Due to great media attention, the product is used in large quantities externally and increasingly also internally, although there is still no clear evidence. Several studies present partly controversial substances which still need to be reviewed. Especially the plant origin, the starting material and the form of application bring a large part of interfering factors into these studies. Commercial application is found in the cosmetic industry, where it is a component of body lotions, shampoos, shaving creams, toothpastes, antiperspirants and creams. Due to its possible anti-inflammatory effect, it is also used in acne, sunscreen and sunburn products. For external applications, the species Aloe Barbadensis Mill. is often used, which is cultivated in large plantations. External use is obvious simply because of its high water content: evaporative cooling produces a pleasant sensation on the skin. Together with the polysaccharides (anti-irritant and immunostimulant) and glycoproteins (antiphlogistic effect), positive effects can thus result. The enzymes contained are also said to have an irritation-reducing effect: their activity can reduce inflammatory processes and thus lead to an immune-stimulating and wound-healing effect.
Increasingly, products for oral ingestion are also coming onto the market. These tonics or fitness drinks are offered in the form of juice, shakes, cocktails or shots. Since the gel is a mucilaginous drug, dilutions may be necessary depending on the area of application. This can be implemented with various substances such as water or alcohol to obtain a juice, for example. The application should not be longer than 2 weeks, as not to exceed the daily requirement of aloin of 30mg per day. Special attention is paid to the substance acemannan, also called aloverose, in aloe vera products. It is a (muco-) polysaccharide which is said to have immunostimulating, antiviral and antineoplastic effects. Often this substance serves as the marker for the quality of a gel. Aloverose content, similar to sugar content in grapes/fruit, reflects the ripeness of the leaves. A good Aloe Vera has about 800 mg /ltr Aloverose, very good products 1000, top juice brings it to 1200. Here it should be noted that you can not compare whole leaf juice with filleted quality. A whole leaf juice can easily bring it up to 2000 mg because the polysaccharides lie under the leaf skin and you can not extract them completely when filleting. In addition, the whole leaf juice is very highly enriched with aloin due to the use of the leaf shells and must be filtered with a large amount of activated carbon. Customers who buy the juice to drink do not want whole leaf.
Depending on the area of application, different concentrations are offered: the ratio of fresh plant to end product is important. A ratio of 200:1, for example, indicates that 200kg of starting material was processed to produce 1kg of end product. The preservatives contained are also important for the subsequent areas of application and should be in line with the product philosophy (e.g. no citric acid in cosmetics, as this can cause irritation to the skin). In general, the fresher the starting material and the lesser the preservation, the more attention must be paid to microbial contamination.
It is precisely the media presence that aloe products owe a great deal of hype which continues to this day: according to a study, 71% of the surveyed people attribute a particularly caring effect to aloe products.
The anthranoids, which are found in the leaf bark and underlying latex layer, have already been replaced by more controllable laxatives. The manufacturing process and the preparation steps are important in order to avoid having this substance class in cosmetic products. Several chemical markers have been introduced to detect the impurities, including the anthranoid aloin. If its content is too high, the product should not be ingested or applied (the BFARM recommends no more than 30mg of the substance per day, with a maximum application period of 2 weeks). Often customers try to prepare the leaves fresh (e.g. as a drink or to apply to the skin) and damage the latex layer when cutting it open. This results in the leakage of anthranoids onto the filleted gel. By experiments it was found that in extracted gels rinsed with water still higher amounts of aloin (factor 300) were ingested than in industrially produced products. Thus, only industrially manufactured or tested products should be used.
Aloe vera gel may take on a slight brown tint over time, as this is a natural aging process. This does not reduce the quality of the gels in the first place, but can be reduced by storing them away from light and in a cool place.