or because the first was processed WLE which had an anthraquinone content 50 times greater than the second material, which is gel carefully hand filleted from large leaves and therefore low in anthraquinones.
The relationship between time of adsorption and activated charcoal concentration is reciprocal. If a more prolonged adsorption period can be tolerated, then lower amounts of charcoal can be used, although the ratio must be maintained between limits. If, on the other hand, it is desired to keep the adsorption period down to 15 minutes, larger quantities must be used. Thus there are four sets of parameters to be optimized for successful adsorption: (i) time, in the range of 15—60 minutes; (ii) temperature: in the range of 4° to 60 °C; (iii) amount of color change potential; and, (iv) amount (0.05 to 2% w/v) and type of activated carbon employed.
Once adsorption is finished, the activated charcoal must be removed. This is generally done with a filter press (Figure 8.8, Process O) using paper with a nominal pore size of 20 ^m, rather than by sedimentation or centrifugation. The most active carbon systems generally have a small particle size, in order to maximize surface area. When particle size is significantly below 50 ^m, it is advisable to employ 0.05 to 0.5% of a clarifying agent such as Celite Filteraide (diatomateous earth) to minimize filter clogging. With a properly designed and operated filtering system, a throughput sufficient to clarify 2,000 to 10,000 liters per hour is feasible.
Technologies encompassing pellicular activated charcoal, ranging from 50—100 ^m up to several mm, are widely employed in water treatment facilities. Some of these systems pack the activated charcoal beads in columns through which the process liquid circulates. These systems offer the possibility of continuous processing that is compatible with HTST pasteurization. Furthermore, carbon columns are amenable to regeneration, which may help offset their initial higher capital cost. To our knowledge, columns of activated charcoal (Figure 8.8, Process P) have not yet been employed at the production level in the aloe industry.
The product that emerges after activated charcoal treatment (Figure 8.8, Product Q) is decolorized '1:1 Aloe vera Gel' according to the IASC nomenclature (IASC, 2001). This 'gel' material makes up almost all of the remainder of the output of non-concentrated aloe 'gels', the remainder being raw aloe gel and pasteurized aloe gel. During the last decade, because of problems with color change and concerns about the carcinogenicity of anthraquinones in Europe, there has been a shift away from natural 'non-decolorized' to 'decolorized gel.' The ARF reference material for this type of product is termed ARF Process C 'Decolorized Gel.' This material is universally referred to in the aloe industry as 'Gel.' This A. barbadensis material, carefully prepared from fillets, without exogenous cellulase, when treated by adsorption with DARCO activated charcoal and filtered through a 20 ^m paper filter press with Celite Filteraide, has pseudoplasticity slightly greater than water. It should not be referred to by the physical-chemical term, gel. The pseudoplasticity is lost, not solely because of the adsorption of polysaccharide on activated charcoal but because of physical entrapment of native polysaccharide into the complex of charcoal, diatomaceous earth, and 20 ^m pore size paper filter. In the ARF 1993 Processing Study treatment of A. barbadensis gel with activated charcoal resulted in the loss of 19 to 23% of the polysaccharide content, (see Figure 8.11). Furthermore, the nature of the polysaccharide is changed by this process from native polysaccharide-like to Acemannan-like substances (Figure 8.3). There are some suggestions that processes other than entanglement and simple adsorption may be involved.
What is actually adsorbed on to charcoal?
Activated carbon adsorption is the first processing step where gel is intentionally subjected to chemical alteration — all the previous processing steps, washing, filleting, depulping, pasteurization, were extractive or sanitation-related. Charcoal adsorption results in a radical change in the chemical composition. Since the aloe industry regards activated charcoal adsorption as a standard and usual procedure, those molecules removed during this process cannot be regarded as part of the IASC general definition of aloe. This restriction explains the selective bias in the IASC certification standards towards solids, mineral cations and organic acids, since none of these are changed radically by activated charcoal adsorption. Molecules such as barbaloin, aloesin and aloe emodin, long associated with A. barbadensis, are not IASC certification analytes because their content changes during legitimate processing. This emphasis on certification parameters that do not change with processing explains why the IASC has grappled for 20 years with polysaccharide tests, because polysaccharide levels and chemistry change with industry-accepted processing. Thus we have diametrically opposed definitions of aloe. The European definition of aloe (e.g. Reynolds, 1994) focuses on the exudate with its mixture of almost 50 chromones and anthraquinones, which are adsorbed on to activated charcoal. The American definition, exemplified by the IASC, focuses on parameters such as solids, salts and organic acids that do not change with processing.
We have developed a different way of looking at what adsorbs on activated charcoal, not what is lost from aloe but what can be eluted from a mixture of carbon and diatomaceous earth. Figure 8.9 illustrates that what goes on activated charcoal can be eluted off. About 6.5% of the dry weight of charcoal with adsorbed material can be eluted using mixtures of organic solvents. We have used mixtures of chlorinated hydrocarbons with acetone or alcohols under refluxing conditions to elute adsorbed aloe materials. The eluate resembles the acetone extract of A. barbadensis gel (compare Figure 8.9 with Figure 8.7, lanes 1 and 2). In some cases the eluate resembles the exudates of Reynolds. The complex of 7-, 5- and 4-hydroxyaloins with Rfs between those of aloin and aloesin are greatly reduced in the activated charcoal eluates, as they are in exudate. This may be due to oxidation of some of these THA compounds to the 'red compound(s)'. The red compound(s) are intermediates.
Finally, these extracts of aloe-adsorbed on charcoal/diatomaceous earth contain a significant amount, up to 37%, of hexose. This appears to be a mixture of sugars resulting from the breakdown of polysaccharide trapped on the complex of the adsorbant. In this respect the charcoal eluates further resemble the leaf exudates which are rich in breakdown products of simple and complex sugars.
The above description give a plausible suggestion as to why aloe undergoes color change. The THA are oxidized to compounds which undergo polyphenolic condensation to a brown/black insoluble residue. Color change can be prevented by removing the THA before they oxidize. On the other hand it is possible that the oxidative method of aloe stabilization (e.g. Cobble, 1975; Coates, 1979; etc.) may prevent color change by converting the THA to insoluble polyphenolics, which are removed during filtration. Whatever the mechanism of 'decolorization' used, experience in the aloe industry
Short Wavelength UV Light
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