relative humidity (RH). At 80% RH, theEMC is 1.5% and at 85% the moisturepickup increases to an extent whichpractically liquifies the crystals. Athigher temperatures, the inflectionpoint occurs at lower relative humidi­ties. For practical purposes, these find­ings show xylitol to be unsuitable as ahumectant at low temperature/highhumidity combinations, while storageof xylitol or high-xylitol products maypresent packaging problems in moisttropical climates.

Two crystalline structures have beenreported for xylitol, a stable orthorhom­bic form, melting at 94°C and a metasta­ble monoclinic form, melting at 61dc.No melting point depression was foundin a mixture of the two forms and thelow-melting form seems to be very eva­sive, changing into the stable formwhen left to stand. Commerciallyproduced xylitol is orthorhombric, witha melting range of 92°C to 96°.c.

Crystallization properties of xylitoldiffer remarkably from those of mono­saccharides, disaccharides and fromother polyols. The pure material formsa clear melt of low viscosity, which boilsat 216°C with little if any discolorationand in sealed containers, the cooled­down melt is stable. Xylitol gives solu­tions of relatively low viscosity. At satu­ration (63%) and at 25°C, the viscosityis 0.3 cps (0.03 Pa's). The density ofcrystals at 20°C is 1.52, that of melt at20°C, 1.42. Dust particles have beendemonstrated to trigger crystallizationin open containers, but not whenenclosed in a container before melting.The rate of crystallization in open con­tainers does not change in a pure oxy­gen or saturated water vapour atmos­phere. Five percent sorbitol or mannitolmelted with xylitol did not cause crytal­lization in sealed containers. Additionof 5-20% water to the melt increased thepropagation rate of crystals because ofreduced viscosity; however, thesesupersaturated solutions are also stablewhen kept in closed systems.

Crystallization can be initiated fromoutside thin-walled containers by ultra­sonic cavitation or more rapid re­crystallization of the melt can beobtained by seeding the melt withmilled xylitol crystals. The process ofmelting and crystallization has beenrepeated up to ten times, with noapparent change in xylitol composition.The specific heat ofaxylitol melt wasdetermined as 40 kcal/kg (167.8 J/kg)between the melting point and 25°C. Apure melt, when seeded with xylitolmicro-crystals, will heat up to 92°C inan insulated container when re-crys­tallization sets in.

Can. Ins!. Food Sci. Technol. J. Vol. 18. No. I, 1985

The lack of aldo or keto groups inxylitol reduces its chemical reactivitysubstantially. Maillard-type reactionswith amino acids do not occur, therebyallowing the formulation of heat­processed sweetened foods or infusionin the presence of proteins. Essentialamino acids, such as lysine, are notblocked but will remain biologicallyactive. A melt heated to 316°C will boilwithout immediate discolouration.Polymerization does occur to a minordegree with prolonged heating above300°C. Upon cooling to room tempera­ture, the melt can still be recrystallized.Furthermore, no esterification of xylitolhas been shown to take place in thepresence of 0.5% citric or acetic acid ina 5% aqueous solution at 120°C for onehour.

The metabolism of ingested xylitoloccurs independently of insulin.Although xylitol is of the same caloricvalue and has the energetic functionsof carbohydrates, it does not producehyperglycemic peaks or hypoglycemicfatigue. Despite the fact that its intakedoes not influence the blood glucoselevel, its use is not normally consideredfor the purpose of formulating diabeticfoods. Fructose, which is also metabo­lized insulin-dependent, which costsless and which carries additionalbenefits (e.g., better tolerance in higherdoses), is, therefore, preferred.

The reason for the food industry'sincreasing use of xylitol is, no doubt, itsnonfermentability by cariogenic oralmicro-organisms. Based on this evi­dence and on reports indicatingincreased shelf life in the xylitol foodsproduced for the Turku Sugar Studies,a series of preliminary in vitro tests withmicro-organisms causing food spoilage,was initiated. The growth of variousmicro-organisms on beef broth/yeastextract substrate with either 0.5%xylitol, 0.5% glucose or with no addedcarbohydrate, was determined by lighttransmission using 530 nm filter. Fer­mentability was determined by the pHdifference between untreated andinoculated substrates after incubation ata specific temperature and duration. In9 of the 13 strains of bacteria, mouldsand yeasts, growth was virtuallystopped and no acid was formed in thepresence of xylitol, wheres variablegrowth and acid formation wereobserved with glucose.

It is hardly surprising that many ofthe foodspoilage micro-organisms aswell as cariogenic streptococci are notcapable of utilizing xylitol as the solesource of energy. One hypothesisattempts an evolutionary explanation.Virtually all carbohydrates, serving

since millennia as energy sources forbacteria, are molecules based on six­carbon atoms or multiples of sixwhereas xylitol is based on a five-carbonatom structure. Most micro-organismsdo not have the enzyme system neces­sary to metabolize pentilols. Providedwith xylitol as the only source of energyin their substrate, they are unable tometabolize it and are"starved".

To date, xylitol is considered byexperts safe for human consumptionwith reasonable limits of intake. As inall polyols, excessive consumption inthe unadapted state may cause osmoticdiarrhea. As a conservative recommen­dation, the initial dose for adults shouldnot exceed 30g xylitollday. After adap­tation, doses of 200 to 300g/day havebeen tolerated.

Twenty-eight countries now havepositive regulations towards xylitol. Inaddition, the 27th Report of the JointFAO/WHO Expert Committee on FoodAdditives has qualified xylitol with anADI (acceptable daily intake) "notspecified". The two most notableexceptions are France (permission onlyin pharmaceuticals) and Japan (permit­ted in infusion solutions).

Contributed by Felix Voirol of Xyrofin Ltd.Clara-Strasse 12, CH 4058 Basel. Switzerland

News

u.s. Survey on Vitamin Supple­ments

The results of a 1982 Gallup study ofvitamin use in the United States haverecently been released. In 1982, 37% ofthe American adults surveyed took vita­min supplements. Vitamin supplementusers were most likely to be women,had higher education levels, and weremore often from the $10,000 or moreannual income bracket. Vitamin userswere characterized as having greaterconcern for their overall health. About41% of the female respondents reportedgiving vitamin supplements to theirchildren on a regular basis. Multivita­mins supplements were the most com­mon type of supplement used. Whenasked why they took vitamin supple­ments, most respondents indicated thereason as being to supplement their dietor to be healthy.

Source: Lachance, P. and Fisher, M. 1984. Vitamin usage:rampant or reasonable? Food, Nutrition and HealthNewsletter. June.

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