Poor eating habits and lifestyle of our society have led to a growing public health problem. Within the current disintegration in reference to the recommended pyramid of daily food intake, the most critical points are found in excessive consumption of saturated fatty acids and cholesterol. 7% of saturated fatty acids in respect of the energy intake and <250 mg/day of cholesterol are recommended, while reality reaches values of 15% and 350 mg/day respectively. Excess in energy intake is mainly due to excessive consumption of saturated fats, while excessive intake of cholesterol is caused by to excessive consumption of animal products.
All epidemiological studies agree that the overindulgent consumption of fat-rich food concomitant with a decrease in energy expenditure by physical activity leads to a number of prevalent health disorders, overweight/obesity and hypercholesterolemia counted among the most serious ones. In addition to the impairment of the quality of life, overweight and obesity have been linked as causative factors with serious adverse health conditions that include cardiovascular diseases, type 2 diabetes, muscle-skeletal problems, and cancer. Hypercholesterolemia on the other hand, by leading to atherosclerosis, is believed to be a major risk factor for coronary heart diseases, the leading cause of death in developed countries.
In view of the above, non prescription lipid-lowering agents that could help to reduce body weight and lower cholesterol are being increasingly sought. As a result, irrespective of their varying and not always fully substantiated effectiveness, a multitude of over-the-counter lipid-lowering dietary supplements are being marketed. Among them chitosan, available in the form of capsules and tablets, is advertised to be able to both lower cholesterol and produce rapid weight loss.
Chitosan is a polyaminosaccharide derived from chitin. Chitin, one of the most plentiful renewable organic resources in nature, found mainly in the exoskeleton of crustaceans, is chemically a linear polymer composed of N-acetyl-D-glucosamine units and D-glucosamine units linked with β-(1-4)-glycosidic bond, wherein N-acetyl-D-glucosamine units are predominant in that polymer chain. The deacetylated form of chitin refers to chitosan. Chitin usually refers to a copolymer with a degree of acetylation of more than 40% [i.e., number of N-acetyl-D-glucosamine more than 40% and number of D-glucosamine less than 60%] and insoluble in dilute acids. The name chitosan is used for a copolymer with less than 40% DA [i.e., more than 60% DD (degree of deacetylation), number of N-acetyl-D-glucosamine less than 40% and number of D-glucosamine more than 60%] that, in most cases, will be soluble in dilute acid. Chitin and chitosan can be chemically considered to be analogues of cellulose in which hydroxyls at carbon-2 have been replaced by acetamido and amino groups, respectively. Chitosan possesses distinct chemical and biological properties attributable to the presence of multiple amino groups in its molecules. This can be exploited in a variety of processes, medical treatments included, and these are possible due to excellent biocompatibility and physiological inertness of chitosan.
Chitin and chitosan are found as supporting materials in many aquatic organisms (shells of shrimps and crabs and bone plates of squids and cuttlefishes), in many insects, in terrestrial crustaceans (Armadillidium vulgare, Porcellio scaber), in nematode, in mushrooms and in some of microorganisms (yeast, fungus and algae).
The aquatic shells contain approximately 30-40% protein, 30-50% calcium carbonate, and 20-30% chitin on a dry basis. These portions vary with crustacean species and seasons. Traditionally chitin is manufactured by the decalcification and deproteination of crab or shrimp shells, which involves the dissolution of calcium carbonate with acid solution and the removal of proteins in alkaline medium or with enzymes, respectively. Chitosan can then be obtained by deacetylating chitin with a hot alkali solution, and a decolorization step. This chitosan production process has a number of unfavorable characteristics. For example, the process requires expensive heat energy and caustic alkali, which is a potential health hazard. The process also produces large amounts of waste, thereby necessitating significant disposal costs. In addition, the supply of shrimp or crab shells is highly dependent upon seasonal and environmental factors, leading to unpredictable limitations on production capacity and to inconsistent physico-chemical characteristics in final products to be used for medical and agriculture applications. Moreover, chitosan from shells of shrimps can present antigens in the final product which could cause allergies to the consumer. Thus, although chitosan has been clinically well tolerated, it cannot be recommended to people allergic to crustaceans. These problems may be circumvented by extracting chitosan from different sources.
Nowadays research is focused on extracting pure chitosan from fungal cell wall components. To this aim, N. Nwe et al. studied the bond between chitosan and glucan in fungal cell wall to develop an enzymatic method for the production of very pure chitosan from fungus Gongroella butleri in a high yield (N. Nwe et al. 2010, “Production of fungal chitosan by enzymatic method and applications in plant tissue culture and tissue engineering: eleven years of our progress, present situation and future prospects” Biopolymers, edited by Magdy Elnashar, published: Sep. 28, 2010, chapter 7 pp. 135-162).
EP 1483299 describes a method that allows separating chitin from β-glucans in a controlled way without degradation or transformation of the chitin chains. The method is based on contacting fungal cells of Aspergillus niger with a basic solution, contacting the alkali-insoluble fraction with an acidic solution, whereby obtaining a suspension of acidified alkali-insoluble fraction comprising said cell wall derivatives, and finally contacting it with β-glucanase enzymes to obtain a chitin product or with a chitin deacetylase to obtain a chitosan product.
One application of chitosan is as a dietary antilipidemic supplement where, owing to limited hydrolysis by human digestive enzymes, chitosan passes along the digestive system up to the large intestine practically intact, acting effectively like a dietary fiber. Chitosan is thought to reduce fat absorption from gastrointestinal tract by binding with anionic carboxyl groups of fatty and bile acids, and interferes with emulsification of neutral lipids (i.e., cholesterol, other sterols) by binding them by hydrophobic bonds. The antihyperlipidemic potential of chitosan has been studied both in vivo and in vitro. In vivo studies include trials carried out both on animals and humans and consisted of a variety of determinations, mainly body weight, serum lipid levels, and lipid concentrations in feces. Remarkably, the data reported are conflicting. Although animal trials mostly showed reducing effects of chitosan on body weight and cholesterol levels (H. Yao et al., “Effect of chitosan on plasma lipids, hepatic lipids, and fecal bile acid in hamsters human trials failed to show these effects” J. Food Drug Anal. 2006, vol. 14, pp. 183-189), human trials failed to show these effects (M. D. Gades et al., “Chitosan supplementation and fat absorption in men and women” J. Am. Diet. Assoc. 2005, vol. 105, pp. 72-77, C. N. Mhurchu et al., “Effect of chitosan on weight loss in overweight and obese individuals: a systematic review of randomized controlled trials” Obes. Rev. 2005, vol. 6, pp. 35-42).
Chitosan supplement formulations are similar but not identical. Chitosan itself is the product of chemical deacetylation of the raw material chitin, and the degree of deacetylation in the product varies with reaction conditions. Some factors during processing such as the degree of deacetylation and molecular weight of the molecules, chitin/chitosan ratio, solubility, ionic strength, pH, particle size, and temperature affect the production of chitosan and its properties. One may expect the efficiency of chitosan to depend on their physicochemical properties. However, no correlation has been established between the binding capacity and the measured physicochemical properties of chitosan. This is indicated in a study, among others, which reported the bile acid-binding capacity, fat-binding ability, swelling capacity, deacetylation degree, and solution viscosity of 11 selected chitosan preparations (K. Zhou et al., “In vitro binding of bile acids and triglycerides by selected chitosan preparations and their physico-chemical properties” Food Science and Technology 2006, vol. 39, pp. 1087-1092).
Chitosan-based supplements are sold as “oil” trappers” and “oil magnets”. Advertising claims for some of these supplements may give consumers unrealistic expectations. While it is advertised to be able to both lower cholesterol and produce rapid weight loss, they can at the same time cause anti-nutritional effects due to their ability to trap also lipid-based molecules which are beneficial for human health, such as fat-soluble vitamins A, D, E, K, HDL cholesterol, vegetal sterols, and polyunsaturated fatty acids such as omega 3 and 6 fatty acids.