Comparative Researches On Contents And Thermal Stabilities Of Active Components Of Two Aloe Species

Four species of common aloes, i.e., Aloe vera, Aloe vera L var Chinesis(Haw) Berg, Aloe arborescens and Aloe ferrox Miller have been used for comparative research on their physical properties and chemical compositions. Among them Aloe vera and Aloe arborescens, more appropriate for industrial production, were selected for further investiment on the contents of active components in relation to leaf position and leaf part, isolation and purification of gel and skin polysaccharides, thermal stabilities of active components including polysaccharides, aloin and protein.Results show that there are no significant differences in the density, and pH values which range from 4.24 to 5.25, between the four aloe juices. The contents of active components measured such as soluble protein, polysaccharides and aloin in skin juice are markedly higher than those in gel juice. The viscosity and the polysaccharide content of Aloe vera L var Chinesis(Haw) Berg juice exhibit the maximum, next is Aloe vera. Aloe arborescens and Aloe ferrox Miller contain relatively high amount of aloin, and a large amount of monosaccharides also present in Aloe arborescens. Due to the little strain for Aloe vera L var Chinesis(Haw) Berg and low juice productivity for Aloe ferrox Miller, the two aloes are limited in the application of industry.There are much higher amounts of soluble protein, total saccharides and polysaccharides in skin juice in comparision to gel juice from Aloe vera and Aloe arborescens. The highest content of soluble protein is found to occur in middle-upper position of Aloe vera, but both total saccharides and polysaccharides over the highest in middle-lower position of Aloe vera, while the three substances mentioned above are the highest in middle-upper position of Aloe arborescens. The protein contents in skin juice from the terminal 1/3 part of the same leaf of Aloe vera and Aloe arborescens are the highest compared with the middle 1/3 part and the base 1/3 part. The base 1/3 part contains much more total saccharides and polysaccharides in skin juice than the other two parts. The presence of significant amounts of active constiuents in skin juice measured in Aloe vera. and/or Aloe arborescens is responsible for the distribution pattern of active components in the whole aloe plant.Crude gel and skin polysaccharides from the two aloes are isolated by a series of sequential steps including precipitation with ethanol multiple times, removal of protein by sevag method, dehydration by several organic solvents. Analysis of infrared spectra indicates that the highest content of acetyl group occurs in gel polysaccharides from Aloe vera, almostno acetyl group is observed in skin polysaccharides from Aloe arborescens, of which only a small amount of polysaccharides (around 1.05%), possibly high amount of cacium oxalate owing to the impurities thereof. Polysaccharides from Aloe ver& and Aloe arborescens consist of neutral and acidic polysaccharides, largely composed of neutral polysaccharides. In crude polysaccharides, there is a higher proportion of acidic polysaccharides in gel polysaccharides (1/3) and in skin polysaccharide (about 14%) from Aloe arborescens;of which less than 5% of acidic polysaccharides occurr in gel polysaccharides and skin polysaccharides from Aloe vera. Further fractionations of neutral and acidic polysaccharides by gel filtration reveal that the presence of single polysaccharide in skin neutral polysaccharides from Aloe vera and Aloe arborescens, 2 to 3 distinct polysaccharides according to molecular size in the gel neutral and acidic polysaccharides and in skin acidic polysaccharides from the two aloe species.Aloin is unstable when dissolved in methanol, acetyl acetate was appropriate for use as the solvent in standard solution. Heating promoted a remarkable decrease in aloin and protein contents depending on temperature and time, higher temperature and longer heating time, more loss. The polysaccharides from Aloe vera exhibit a maximal stability at 70 °C;the marked decrease at 80-90 °C may be due to the thermal degradation of the polysaccharide;the significant decrease at 50-60 °C is probably as a result of the presence of enzymes which could be responsible for the hydrolysis of large molecular polysaccharides into lower ones.