NUTRITIVE SWEETENERS

III. NUTRITIVE SWEETENERS

A. Fructose

1. History Fructose is a hexose monosaccharide that is one of the most commonly occurring natural

sugars. It is often called fruit sugar or levulose. Free fructose is found in almost all fruits and berries and in most vegetables. Fructose was earlier very difficult to produce and therefore remained unavailable for food use until the late 1960s.

Crystalline fructose has been commercially available for only a decade, and therefore it is not commonly known in all parts of the food industry. However, its use has increased significantly due to its properties in diabetic and other special dietary foods. Also the interest in natural sweeteners has centered on fructose. Therefore, fructose may have sig- nificant applications in dietetic and health foods in the future.

2. Properties and Uses Commercially crystalline fructose is produced from sucrose by inversion or from glucose

by enzymatic isomerization. One of the major advantages of the use of crystalline fructose is its relative sweetness, which is about 1.5 times that of sucrose. Fructose is the only carbohydrate with a sweetness higher than that of sucrose on a weight basis. Usually smaller amounts of fructose are needed for the same sweetness in food products, and this often results in reduction of energy content. Fructose is also more slowly absorbed than glucose or sucrose, and it does not stimulate insulin per se. Fructose does not increase serum triglycerides in normal subjects. Therefore, fructose has been recommended as a sweetener for diabetics and is presently included in the diabetic diet recommendations in many countries. However, one must take into account the calories in fructose.

Results of clinical dental trials on fructose have indicated that fructose is signifi- cantly less carcinogenic than sucrose (Scheinin and Ma¨kinen, 1975). Later studies appear to have verified the findings as reviewed by Grenby (1983).

Fructose is readily soluble in water, and it is sweetest in cold solution. Fructose also tends to enhance the flavor of fruits and berries, which makes it suitable as a sweetener for fresh fruits, iced tea, and lemonade. As a ketose-type sugar, fructose undergoes Mail- lard reactions with amino groups at even lower temperatures than sucrose; therefore, brow- ning reactions in baked or cooked foods can be obtained at lower temperatures. The ratio- nale for fructose use has been extensively reviewed by Doty (1980) and Wu¨rsch and Daget (1987).

In a food technological sense, fructose has its major applications in dietetic and diabetic foods, where its slow absorption and greater sweetness are of value. Good applica- tions for fructose can be found in presweetened cerals, canned fruits, cakes, biscuits, and ice cream. Fructose is also ideal for powdered juices and frozen products.

3. Regulatory Status The regulatory status of fructose in the United States has been reviewed by Frattali (1982),

particularly with respect to its use in special dietary foods. Fructose is a natural sugar that has been tested in many clinical situations as indicated by Scheinin and Ma¨kinen (1975). No side effects have been observed, and therefore most countries consider fructose an ingredient rather than an additive. There are usually no restrictions on fructose use.

B. Xylitol

1. Chemistry Xylitol is a pentitol that can be found in most fruits and berries as well as vegetables

(Washu¨ttl et al., 1973). Commercially xylitol is produced from xylan-containing plant material by acid hydrolysis, hydrogenation, and purification. Xylitol can also be produced by microbiological methods (Aminoff et al., 1978). At room temperature xylitol is equis- weet with sucrose and therefore twice as sweet as sorbitol and three times as sweet as mannitol (Aminoff et al., 1978; Ma¨kinen, 1978). Xylitol is a sweetener with the same caloric content as sucrose. It is supplied as a colorless, nonhygroscopic crystal and has a caloric content equal to sucrose ( Table 3 ). Xylitol is shown to be a noncariogenic sweet- ener, and it is also suitable for diabetic and dietetic foods (Ma¨kinen, 1978; Alanen et al., 2000).

2. Technology Interest in xylitol is primarily due to its properties and potential uses as a noncariogenic

sugar substitute (Ma¨kinen, 1978). Xylitol can be incorporated successfully into a wide range of foods. Usually it is possible to produce confections, sweet snacks, chocolate, and chewing gum using the common recipes with xylitol replacing sucrose (Aminoff et al., 1978; Voirol, 1978). The main application of xylitol appears to be in confectionery, espe- cially in sugar-free products and noncariogenic chewing gum. Xylitol can also be utilized in diabetic and dietetic foods provided its energy value is taken into account (Ma¨kinen, 1978). Xylitol has also been suggested for functional food use for the prevention of acute otitis media in children (Uhari et al., 1996). A review on the safety and efficacy of xylitol as a functional food ingredient is available (Salminen and Ahukas, 2000).

3. Toxicology The toxicological properties of xylitol have been extensively studied, and all tests have

proved xylitol to be safe at dietary levels likely to be consumed. Xylitol is absorbed slowly, and therefore a major part of the substance may be metabolized by intestinal microorgan- isms (Salminen et al., 1986). Otherwise xylitol is metabolized by the liver. Salminen et al. (1982, 1986) have shown that xylitol can be consumed without ill effects when the single dose does not exceed 30 g. A 30-g dose does not cause significant increases in blood glucose or insulin secretion (Salminen et al., 1982). Larger doses are often likely to cause diarrhea; this may be due to the intestinal bacteria, which are not able to metabo- lize large xylitol doses (Salminen et al., 1986). The toxicological studies include studies on carcinogenicity, mutagenicity, and teratogenicity. All these studies have indicated that xylitol is safe for food use. A comprehensive review is available from the World Health Organization (WHO, 1983).

4. Regulatory Status The Joint FAO/WHO Expert Committee on Food Additives has established an acceptable

daily intake of ‘‘not specified’’ for xylitol (WHO, 1983). This means that on the basis of the available data, the potential daily intakes do not represent a hazard to health.

The regulatory status of xylitol varies from country to country. In Europe, xylitol is used as a sweetener and food additive according to the directive on sweetening agents.

Table 3 Some Properties of Polyol Sweeteners

Melting

Solubility

Laxative ADI b Polyol

Impact on

effect a (year of evaluation) Xylitol

E code

(g/100 g H 2 O)

blood sugar

Not specified (1985) Sorbitol

64 Very low

Not specified (1982) Mannitol

Mannit, mannose

⫹⫹⫹ Not specified (1987)

sugar

Not specified (1983) Maltitol

Lactitol E 966

149 c None

Not specified (1985) Isomaltitol

Easily soluble

Low

⫹⫹⫹ Not specified (1985) a Gradual adaptation to large xylitol, sorbitol, mannitol, and lactitol doses occur in most humans during prolonged consumption; initial laxative threshold varies between 20 and

40 g/day. b WHO.

c As a monohydrate.

C. Sorbitol

1. Chemistry Sorbitol is a six-carbon sugar alcohol that was originally found in the berries of mountain

ash. It occurs in many fruits and vegetables (Washu¨ttl et al., 1973). Sorbitol has the same steric configuration as glucose, and it is chemically synthesized from glucose or dextrose for commercial use. Sorbitol has about half the sweetness of sucrose. Some properties of sorbitol are listed in Table 3 .

2. Technological Properties Sorbitol is used mainly as a sweetening agent for dietetic foods, where it combines moder-

ate sweetening power, specific flavor characteristics, and pleasant viscosity in liquids. It is used in sugar-free candies and chewing gum and in diabetic foods. In mixtures with other sugars, sorbitol modifies the crystallization properties of foods. When added to syr- ups containing sucrose it reduces crystal deposition during storage. Sorbitol also has some uses as a humectant and stabilizer, and it can be used as a substitute for glycerol. Small amounts of sorbitol have been added to low-calorie drinks to mask the aftertaste of saccha- rin and to provide the normal mouth-feel (Grenby, 1983). Typical products in Europe include confectionery, pastilles, diabetic jam and cookies, ice cream, chocolates, and past- ries.

3. Toxicology and Safety The toxicology of sorbitol has been reviewed recently by WHO. The Joint FAO/WHO

Expert Group on Food Additives has given sorbitol an ADI of ‘‘not specified,’’ which means that no health hazards are foreseen (WHO, 1982). Since sorbitol is absorbed slowly, foods sweetened with sorbitol are thought to be suitable for diabetics provided that the calories are taken into account. However, large amounts of sorbitol can cause flatulence, diarrhea, and abdominal distension. Gradual addition of sorbitol into the diet may increase the tolerance of the individual (Salminen et al., 1985a,b).

4. Regulatory Status In most countries sorbitol is approved as an ingredient when used for sweetening purposes.

In the United States sorbitol is permitted for use as a food additive by the U.S. Food and Drug Administration. Sorbitol is also considered GRAS for use as a nutrient and dietary supplement (FASEB/SCGOS, 1973a).

D. Mannitol

1. Chemistry Mannitol is a hexitol that is stereoisomeric to sorbitol. It is commonly found naturally in

some plant foods, including beets, celery, olives, and seaweed. Mannitol has about 0.4–

0.5 the sweetness of sucrose, and its properties are fairly similar to those of sorbitol (Table 3). Only the solubility of mannitol is poor compared to sorbitol. Mannitol is produced from sucrose or dextrose and can also be obtained as a byproduct of some fermentations.

2. Technological Properties Mannitol is used in sugar-free dietary foods, sugar-free chewing gum, sweets, and ice 2. Technological Properties Mannitol is used in sugar-free dietary foods, sugar-free chewing gum, sweets, and ice

3. Toxicological Studies and Safety Mannitol is slowly absorbed from the intestinal tract and may cause diarrhea and flatu-

lence. In experimental animals an adaptation to mannitol can be seen (Salminen et al., 1985b). In humans a laxative effect is observed after intakes of 20–30 g of mannitol. Toxicity studies have not indicated any adverse effects other than diarrhea. Therefore mannitol is considered safe for use in foods. Mannitol is also on the U.S. FDA GRAS list. An evaluation of its health effects has been conducted (FASEB/SCOGS, 1973b). An acceptable daily intake of ‘‘not specified’’ has been allocated for mannitol (WHO, 1986).

E. Lactitol

1. Chemistry Lactitol is a disaccharide alcohol [(4-O- β-D-galactopyranosyl)-D-glucitol] produced by

the hydrogenation of lactose or lactulose. Lactitol has been known since 1912, and its manufacture was mentioned by Aminoff in 1974, but attention has been directed to its properties only lately (Linko et al., 1980). Lactitol has a low sweetness ( Table 3 ), and therefore its major use is not as a sweetener. More recent biological research cited by WHO (1983) indicates that lactitol may have a lower energy value than other carbohydrate sweeteners.

Commercially available lactitol has a molecular weight of 344 and crystallizes as

a colorless and odorless monohydrate with a pleasant mild sweetness (Saijonmaa et al., 1978; Linko et al., 1980). Since lactitol does not have a carbonyl group it cannot undergo Maillard reactions. In general use, lactitol is more stable than lactose. Its relative sweetness is about 50% that of glucose (Linko et al., 1980). Like lactulose lactitol also promotes the amount of bifidobacteria and lactic acid bacteria in the human colon. Thus, lactitol can be considered a bifidogenic factor or a prebiotic substance (Ballongue et al., 1997; Salminen and Salminen, 1997).

2. Technological Uses Lactitol as well as most polyols can be applied to special dietary foods that can be con-

sumed by diabetics provided that the calories are taken into account. Lactitol can be used as a sweetener in most foods, but due to its low sweetness it is not very attractive. However, it may have other uses as a sweet bulking or texturizing agent in the future because of its low energy value (WHO, 1983). The products that are manufactured with lactitol have excellent palatability, and no unpleasant aftertaste is associated with lactitol. Lactitol also has uses as an ingredient for the pharmaceutical industry. Lactitol can also be utilized instead of lactulose for some therapeutic applications and special dietary foods (Patil et al., 1987) and as a prebiotic in functional foods (Salminen and Salminen, 1997).

3. Toxicology and Safety Lactitol has gone through extensive toxicological studies. All required toxicology studies

have been completed, including long-term and carcinogenicity studies. Also, short studies on the gut microflora changes have been completed (Salminen and Salminen, 1986b).

These studies indicate that apart from diarrhea after consumption of large lactitol doses no toxicologically significant adverse effects have been noted (WHO, 1983). The EEC Scientific Committee on Food has accepted lactitol and most other polyols for use in food. However, it was pointed out that laxation may occur at high intakes.

4. Regulatory Status Since lactitol has been made commercially available only recently, most countries have

not classified it as an ingredient or a food additive. JECFA has given lactitol an ADI of ‘‘not specified,’’ indicating that it is considered safe for food use (WHO, 1983). Food additive and ingredient petitions have been filed in most countries; lactitol has been ap- proved for special dietary foods in the Netherlands, and a lactitol preparation is used as

a pharmaceutical in Switzerland.

F. Lactulose

1. Chemistry Lactulose (4-O- β-D-galactopyranosyl)-D-fructose is a keto analog of lactose. Unlike lac-

tose, it resists the hydrolytic action of intestinal β-galactosidases and therefore is not ab- sorbed from the small intestine. Lactulose is mostly available in syrup containing 67% lactulose, but recently a crystalline form has also been produced. Lactulose has a relative low sweetness, but it is stable in most foods.

2. Technological Properties Lactulose can be utilized in most liquid foods, but due to its low sweetness it does not

have many food applications. In addition it has laxative properties that prevent its use in most common foods. Only special dietary foods that are intended for people suffering from constipation have utilized lactulose as a sweetener. It has been claimed that lactulose in infant foods and formulas enhances the development of intestinal flora containing lactic acid bacteria and bifidobacteria (Bifidobacterium bifidum) that mimic the flora of breast- fed infants (Mendez and Olano, 1979). Lactulose may also act as a nonabsorbable substrate for colonic bacteria, thereby causing other favorable changes in the microflora and making lactulose suitable for special dietary foods in this area. Lactulose also has a number of applications in pharmaceutical preparations. During the fermentation short chain fatty acids (e.g., acetic, lactic, and butyric acids) are formed with consequent lowering of the colon pH and modification of the microflora of the intestinal contents. It has been reported that lactulose promotes the growth of lactobacilli and especially Lactobacillus acidophilus in the colon. In addition to lactulose also the ingestion of dairy products fermented with lactic acid bacteria and lactitol have been shown to lower colonic pH and to relieve abnor- malities in intestinal transit (Ballongue, 1997; Salminen and Salminen, 1997).

3. Toxicology The toxicity of lactulose has not been studied according to present guidelines. However,

lactulose has been utilized for over 30 years in the treatment of chronic constipation and portal-systemic encephalopathy, and the patients have received large lactulose doses for long treatment periods. It is apparent that microflora changes in the intestinal tract occur during lactulose ingestion (Salminen and Salminen, 1997; Salminen et al., 1988). How- lactulose has been utilized for over 30 years in the treatment of chronic constipation and portal-systemic encephalopathy, and the patients have received large lactulose doses for long treatment periods. It is apparent that microflora changes in the intestinal tract occur during lactulose ingestion (Salminen and Salminen, 1997; Salminen et al., 1988). How-

4. Regulatory Status In most countries lactulose is utilized as a pharmaceutical preparation, and occasionally

it is used in special dietary foods.

G. Hydrogenated Glucose Syrups

1. Chemistry There are a number of hydrogenated glucose syrups that consist of 2–8% sorbitol, 50–

55% maltitol, 15–20% maltotriol, and 20–30% hydrogenated tri- or heptasaccharides. Hydrogenated glucose syrups are usually marketed as syrups containing about 75% solids that do not crystallize at high concentrations. No brown pigments are formed in the Maillard reaction because there are no aldehyde groups. Hydrogenated glucose syrup is used as a substitute for glucose, sucrose, or sorbitol. It has reduced cariogenicity com- pared to glucose, sucrose, or sorbitol and reduced laxative effect (Food Additives and Contaminants Committee, 1982).

2. Toxicology Short-term studies in the rat and dog together with metabolic data, mutagenicity data, and

human tolerance studies do not give any reason to doubt the safety of hydrogenated glucose syrups as sweetening agents. However, no long-term studies are available. In the light of evidence that hydrogenated glucose syrup breaks down to glucose and sorbitol, it is possi- ble to consider their safety according to the results on sorbitol (WHO, 1980a,b).

3. Regulatory Status An acceptable daily intake (ADI) of ‘‘not specified’’ has been allocated to hydrogenated

glucose syrups (WHO, 1985).

H. Maltitol

1. Chemistry The maltitol molecule, 4-O- β-D-glucopyranosyl-D-glucitol, consists of a glucose and a

sorbitol unit linked 1,4 (1,4-glucosyl-glucitol). Maltitol is produced by enzymatic hydrolysis of starch (potato or corn) to obtain a high maltose syrup, which is hydrogenated to the corresponding high maltose syrup, from which crystalline maltitol is obtained. Both liquid and crystalline maltitol are used. They are soluble in water and are very stable both at different pH conditions and thermally. The sweetening power for crystalline maltitol is 0.9 and for liquid 0.6 (sucrose ⫽ 1).

2. Metabolism Maltitol is more slowly hydrolyzed to glucose and sorbitol by maltase than maltose, which

is a natural substrate. More than 50% of the ingested dose remains unsplit and enters the

3. Toxicity Maltitol has a low acute toxicity by oral administration (LD 50 ⬎ 24 g/kg body weight).

Maltitol is not mutagenic. Teratogenic studies have also been negative. Subscute and long- term toxicological studies with maltitol in various animal species failed to reveal any differences in behavior and biochemical patterns between control and maltitol-fed animals. Only a moderately decreased growth rate was observed in fed animals due to the reduced caloric intake (Yamasaki et al., 1973a,b; Shimpo et al., 1977).

I. Isomalt

1. Chemistry Isomalt is also called hydrogenated isomaltulose or hydrogenated palatinose. It is an equi-

molar mixture of 6-O- β-D-glucopyranosyl-D-glucitol and 1-O-β-D-glucopyranosyl- D-mannitol. Isomalt is produced by the enzymatic trans-glucosidation of sucrose to iso- maltulose followed by dehydrogenation. It is about 0.5 times as sweet as sucrose. It is stable in acid and alkaline media under conditions normally occurring in food production (Siebert, 1975).

2. Use Isomalt can be used as a sugar substitute in confectioneries, chewing gum, soft drinks,

and desserts. It is claimed to be less cariogenic than sucrose and less laxative than sorbitol or xylitol.

3. Toxicology Only 50% of isomalt is metabolized in humans. It is broken down initially in the gastroin-

testinal tract to form sorbitol, mannitol, and glucose. Some metabolic and tolerance studies in animals are available. The only effect seen in short-term studies in the rat and dog is

a dose-related increase in bilirubin level in the study of the rat. There are no long-term studies available on isomalt. Long-term studies have not been considered necessary be- cause the breakdown products are glucose, sorbitol, and mannitol (WHO, 1981).

4. Regulatory Status Isomalt was evaluated by the WHO expert group in 1981. Safety documentation was

inadequate with respect to long-term feeding studies. A temporary ADI of 0–25 mg/kg body weight was allocated. In 1985 an ADI of ‘‘not specified’’ was allocated (WHO, 1985).

J. Fructose Syrups

Fructose syrups should not be misunderstood to be similar to crystalline fructose (Doty, 1980). The amount of fructose in fructose syrup products varies from 40 to 90%. Relative sweetness compared to 15% saccharose solution is related to fructose content. In 40–90% fructose-containing products, the relative sweetness is 100–160. Fructose syrups are very hygroscopic, and the tendency to absorb moisture increases with increasing amounts of fructose. Fructose syrups are used to reduce saccharose intake. Their main use is in prod-