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relative humidity (RH). At 80% RH, the EMC is 1.5% and at 85% the moisture pickup increases to an extent which practically liquifies the crystals. At higher temperatures, the inflection point occurs at lower relative humidi- ties. For practical purposes, these find- ings show xylitol to be unsuitable as a humectant at low temperature/high humidity combinations, while storage of xylitol or high-xylitol products may present packaging problems in moist tropical climates. Two crystalline structures have been reported for xylitol, a stable orthorhom- bic form, melting at 94°C and a metasta- ble monoclinic form, melting at 61 dc. No melting point depression was found in a mixture of the two forms and the low-melting form seems to be very eva- sive, changing into the stable form when left to stand. Commercially produced xylitol is orthorhombric, with a melting range of 92°C to 96°.c. Crystallization properties of xylitol differ remarkably from those of mono- saccharides, disaccharides and from other polyols. The pure material forms a clear melt of low viscosity, which boils at 216°C with little if any discoloration and in sealed containers, the cooled- down melt is stable. Xylitol gives solu- tions of relatively low viscosity. At satu- ration (63%) and at 25°C, the viscosity is 0.3 cps (0.03 Pa's). The density of crystals at 20°C is 1.52, that of melt at 20°C, 1.42. Dust particles have been demonstrated to trigger crystallization in open containers, but not when enclosed in a container before melting. The rate of crystallization in open con- tainers does not change in a pure oxy- gen or saturated water vapour atmos- phere. Five percent sorbitol or mannitol melted with xylitol did not cause crytal- lization in sealed containers. Addition of 5-20% water to the melt increased the propagation rate of crystals because of reduced viscosity; however, these supersaturated solutions are also stable when kept in closed systems. Crystallization can be initiated from outside thin-walled containers by ultra- sonic cavitation or more rapid re- crystallization of the melt can be obtained by seeding the melt with milled xylitol crystals. The process of melting and crystallization has been repeated up to ten times, with no apparent change in xylitol composition. The specific heat ofaxylitol melt was determined as 40 kcal/kg (167.8 J/kg) between the melting point and 25°C. A pure melt, when seeded with xylitol micro-crystals, will heat up to 92°C in an insulated container when re-crys- tallization sets in. Can. Ins!. Food Sci. Technol. J. Vol. 18. No. I, 1985 The lack of aldo or keto groups in xylitol reduces its chemical reactivity substantially. Maillard-type reactions with amino acids do not occur, thereby allowing the formulation of heat- processed sweetened foods or infusion in the presence of proteins. Essential amino acids, such as lysine, are not blocked but will remain biologically active. A melt heated to 316°C will boil without immediate discolouration. Polymerization does occur to a minor degree with prolonged heating above 300°C. Upon cooling to room tempera- ture, the melt can still be recrystallized. Furthermore, no esterification of xylitol has been shown to take place in the presence of 0.5% citric or acetic acid in a 5% aqueous solution at 120°C for one hour. The metabolism of ingested xylitol occurs independently of insulin. Although xylitol is of the same caloric value and has the energetic functions of carbohydrates, it does not produce hyperglycemic peaks or hypoglycemic fatigue. Despite the fact that its intake does not influence the blood glucose level, its use is not normally considered for the purpose of formulating diabetic foods. Fructose, which is also metabo- lized insulin-dependent, which costs less and which carries additional benefits (e.g., better tolerance in higher doses), is, therefore, preferred. The reason for the food industry's increasing use of xylitol is, no doubt, its nonfermentability by cariogenic oral micro-organisms. Based on this evi- dence and on reports indicating increased shelf life in the xylitol foods produced for the Turku Sugar Studies, a series of preliminary in vitro tests with micro-organisms causing food spoilage, was initiated. The growth of various micro-organisms on beef broth/yeast extract substrate with either 0.5% xylitol, 0.5% glucose or with no added carbohydrate, was determined by light transmission using 530 nm filter. Fer- mentability was determined by the pH difference between untreated and inoculated substrates after incubation at a specific temperature and duration. In 9 of the 13 strains of bacteria, moulds and yeasts, growth was virtually stopped and no acid was formed in the presence of xylitol, wheres variable growth and acid formation were observed with glucose. It is hardly surprising that many of the foodspoilage micro-organisms as well as cariogenic streptococci are not capable of utilizing xylitol as the sole source of energy. One hypothesis attempts an evolutionary explanation. Virtually all carbohydrates, serving since millennia as energy sources for bacteria, are molecules based on six- carbon atoms or multiples of six whereas xylitol is based on a five-carbon atom structure. Most micro-organisms do not have the enzyme system neces- sary to metabolize pentilols. Provided with xylitol as the only source of energy in their substrate, they are unable to metabolize it and are" starved". To date, xylitol is considered by experts safe for human consumption with reasonable limits of intake. As in all polyols, excessive consumption in the unadapted state may cause osmotic diarrhea. As a conservative recommen- dation, the initial dose for adults should not exceed 30g xylitollday. After adap- tation, doses of 200 to 300g/day have been tolerated. Twenty-eight countries now have positive regulations towards xylitol. In addition, the 27th Report of the Joint FAO/WHO Expert Committee on Food Additives has qualified xylitol with an ADI (acceptable daily intake) "not specified". The two most notable exceptions are France (permission only in pharmaceuticals) and Japan (permit- ted in infusion solutions). Contributed by Felix Voirol of Xyrofin Ltd. Clara-Strasse 12, CH 4058 Basel. Switzerland News u.s. Survey on Vitamin Supple- ments The results of a 1982 Gallup study of vitamin use in the United States have recently been released. In 1982, 37% of the American adults surveyed took vita- min supplements. Vitamin supplement users were most likely to be women, had higher education levels, and were more often from the $10,000 or more annual income bracket. Vitamin users were characterized as having greater concern for their overall health. About 41% of the female respondents reported giving vitamin supplements to their children on a regular basis. Multivita- mins supplements were the most com- mon type of supplement used. When asked why they took vitamin supple- ments, most respondents indicated the reason as being to supplement their diet or to be healthy. Source: Lachance, P. and Fisher, M. 1984. Vitamin usage: rampant or reasonable? Food, Nutrition and Health Newsletter. June. Institute Affairs / xiii
