**4.1 Chemical and crystalline forms**

In solid-state, lactitol can exist in different crystalline forms, having different melting points. Early observations showed the existence of two forms of anhydrous lactitol having different melting points [8, 9]. XRD and IR-spectra revealed three hydrate forms (mono-, di-, and tri-hydrate), two anhydrate (A and B), and one amorphous form [3, 26, 27]. The most common form of lactitol is monohydrate, which is obtained through slow crystallization of the lactitol slurry. Lactitol is a monoclinic polyol with one intra- and eight inter-molecular hydrogen bonds in its chemical structure [27]. All hydroxyl H-atoms form hydrogen bonds, which give rise to an eight-membered ring, chair conformation of the galactopyranosyl ring. The crystalline form of lactitol dihydrate is tetragonal with 3 intra- and 12 inter-molecular hydrogen bonds in its chemical structure [28]. Similar to lactitol monohydrate, all hydroxyl H-atoms form hydrogen bonds resulting in a chair configuration of the galactopyranosyl ring.

## **4.2 Solubility**

Lactitol is found commercially as a crystalline powder. Interestingly, lactitol properties and therefore its potential application depend on the given crystalline form. Lactitol is recovered after hydrogenation, where the spent catalyst is removed via ion-exchange. Then, the slurry is evaporated under vacuum, and subsequently crystallized under prescribed protocol. Once the crystals are formed, the lactitol slurry is centrifugated and dried. Crystallization is the key step during the formation of a given crystal form. The crystallization of carbohydrates can be used as a general guideline of the crystallization of lactitol. Nurmi and Kaira [29] provided the most accurate guides in the literature for the crystallization of lactitol. Solubility curves of the lactitol crystals are illustrated in **Figure 6**. For simplicity, the solubility curve was divided into four regions.

The region IV illustrates the required conditions to yield lactitol in anhydrous form. This has been illustrated by Nurmi and Kaira [29], who crystallized a 91%

**43**

*Hundred Years of Lactitol: From Hydrogenation to Food Ingredient*

mother liquid at temperatures lower than 10°C [29].

**4.3 Caloric value**

**4.4 Sweetness**

**4.5 Health claims**

48–40% with respect to sucrose.

cally reduce the sucrose concentration.

lactitol solution to obtain lactitol anhydrous. The solution was cooled from 95 to 75°C within 10 h, inducing the crystallization from solution. Similarly, Heikkila et al. [30] obtained lactitol anhydrous by cooling from 90 to 80°C a 90% lactitol solution. The working conditions for yielding lactitol monohydrate are exemplified in region II. Heikkilä et al. [30] obtained lactitol monohydrate using a four-step crystallization. Heikkilä's protocol involved the cooling of a 82% seeded lactitol solution from 70 to 40°C in 16 h. Wijnman et al. [31] obtained lactitol in the form of monohydrate by seeding a 80% solution of lactitol, and cooled it from 75 to 50°C in 18 h. The remaining mother liquid from this protocol was seeded and cooled down to 18–15°C to obtain lactitol dihydrate, indicated in region II. Wijnman et al. [31] followed a similar protocol to obtain 60% yield of lactitol dihyrate. Lactitol trihydrate, which is illustrated in region I, is obtained by further crystallization of the

Evidence of the reduced-calorie value of lactitol dates back to the 1930s, where the enzymatic hydrolysis of lactitol was found to be significantly slower than that of lactose [32]. This observation pointed out the possibility of a reduced calorie effect of lactitol. Indeed, Hayashibara and Sugimoto [33] measured the concentration of lactitol in the intestines of rabbits injected with a 20% solution of lactitol. After hours of injection, the lactitol concentration did not, while the concentration of glucose was reduced by 85%. Van Es et al. [34] analyzed the metabolized energy derived from lactitol and sucrose. They found that the energy contribution to the body was 60% less than for sucrose. European labeling considers a blanket caloric value of lactitol as 2.4 kcal g−1 [5]. At the same time, the Food and Drug Administration (FDA) establishes a general value of 2.0 kcal g−1, a reduction of

Lactitol is known for its mild and clean sweet taste [4]. Relative sweetness is measured in relation to a reference value of 1, which corresponds to the sucrose sweetness at a given concentration [5]. Lactitol possess a relative sweetness from 0.3 to 0.42. Generally, lactitol sweetness is considered to be 30–35% of the sucrose sweetness. Thus, simply replacing sucrose with lactitol requires substantial amount of lactitol. Alternatively, lactitol is combined with other sweeteners to synergisti-

Lactitol is not considered as essential nutrient, but its consumption has been clinically linked to a number of health benefits. Health benefits and claims associated with the consumption of sugar alcohols have been reviewed elsewhere [35, 36]. Overall, sugar alcohols are a limited source of energy for oral bacteria that results in less production of acid. van der Hoeven [37] studied the cariogenicity of lactitol in fed rats, and observed that lactitol significantly reduced caries development when compared with sucrose. This observation was in agreement with the rate of fermentation by oral bacteria. Acid production from lactitol occurred at much lower rate than the acid production of sucrose. Clinical evidence demonstrated a reduction in the incidence of caries by the substitution of sucrose with sugar alcohols in chewing gum and candies. van Loveren [38] postulated that the preventive effects against caries in gums and candies formulated with sugar alcohols are due to a stimulation

*DOI: http://dx.doi.org/10.5772/intechopen.93365*

**Figure 6.** *Solubility curves of lactitol anhydrous, monohydrate, dihydrate, and trihydrate.*

*Hundred Years of Lactitol: From Hydrogenation to Food Ingredient DOI: http://dx.doi.org/10.5772/intechopen.93365*

lactitol solution to obtain lactitol anhydrous. The solution was cooled from 95 to 75°C within 10 h, inducing the crystallization from solution. Similarly, Heikkila et al. [30] obtained lactitol anhydrous by cooling from 90 to 80°C a 90% lactitol solution. The working conditions for yielding lactitol monohydrate are exemplified in region II. Heikkilä et al. [30] obtained lactitol monohydrate using a four-step crystallization. Heikkilä's protocol involved the cooling of a 82% seeded lactitol solution from 70 to 40°C in 16 h. Wijnman et al. [31] obtained lactitol in the form of monohydrate by seeding a 80% solution of lactitol, and cooled it from 75 to 50°C in 18 h. The remaining mother liquid from this protocol was seeded and cooled down to 18–15°C to obtain lactitol dihydrate, indicated in region II. Wijnman et al. [31] followed a similar protocol to obtain 60% yield of lactitol dihyrate. Lactitol trihydrate, which is illustrated in region I, is obtained by further crystallization of the mother liquid at temperatures lower than 10°C [29].

### **4.3 Caloric value**

*Lactose and Lactose Derivatives*

**4. Properties of lactitol**

galactopyranosyl ring.

**4.2 Solubility**

**4.1 Chemical and crystalline forms**

In solid-state, lactitol can exist in different crystalline forms, having different melting points. Early observations showed the existence of two forms of anhydrous lactitol having different melting points [8, 9]. XRD and IR-spectra revealed three hydrate forms (mono-, di-, and tri-hydrate), two anhydrate (A and B), and one amorphous form [3, 26, 27]. The most common form of lactitol is monohydrate, which is obtained through slow crystallization of the lactitol slurry. Lactitol is a monoclinic polyol with one intra- and eight inter-molecular hydrogen bonds in its chemical structure [27]. All hydroxyl H-atoms form hydrogen bonds, which give rise to an eight-membered ring, chair conformation of the galactopyranosyl ring. The crystalline form of lactitol dihydrate is tetragonal with 3 intra- and 12 inter-molecular hydrogen bonds in its chemical structure [28]. Similar to lactitol monohydrate, all hydroxyl H-atoms form hydrogen bonds resulting in a chair configuration of the

Lactitol is found commercially as a crystalline powder. Interestingly, lactitol properties and therefore its potential application depend on the given crystalline form. Lactitol is recovered after hydrogenation, where the spent catalyst is removed via ion-exchange. Then, the slurry is evaporated under vacuum, and subsequently crystallized under prescribed protocol. Once the crystals are formed, the lactitol slurry is centrifugated and dried. Crystallization is the key step during the formation of a given crystal form. The crystallization of carbohydrates can be used as a general guideline of the crystallization of lactitol. Nurmi and Kaira [29] provided the most accurate guides in the literature for the crystallization of lactitol. Solubility curves of the lactitol crystals are illustrated in

The region IV illustrates the required conditions to yield lactitol in anhydrous form. This has been illustrated by Nurmi and Kaira [29], who crystallized a 91%

**Figure 6**. For simplicity, the solubility curve was divided into four regions.

**42**

**Figure 6.**

*Solubility curves of lactitol anhydrous, monohydrate, dihydrate, and trihydrate.*

Evidence of the reduced-calorie value of lactitol dates back to the 1930s, where the enzymatic hydrolysis of lactitol was found to be significantly slower than that of lactose [32]. This observation pointed out the possibility of a reduced calorie effect of lactitol. Indeed, Hayashibara and Sugimoto [33] measured the concentration of lactitol in the intestines of rabbits injected with a 20% solution of lactitol. After hours of injection, the lactitol concentration did not, while the concentration of glucose was reduced by 85%. Van Es et al. [34] analyzed the metabolized energy derived from lactitol and sucrose. They found that the energy contribution to the body was 60% less than for sucrose. European labeling considers a blanket caloric value of lactitol as 2.4 kcal g−1 [5]. At the same time, the Food and Drug Administration (FDA) establishes a general value of 2.0 kcal g−1, a reduction of 48–40% with respect to sucrose.

#### **4.4 Sweetness**

Lactitol is known for its mild and clean sweet taste [4]. Relative sweetness is measured in relation to a reference value of 1, which corresponds to the sucrose sweetness at a given concentration [5]. Lactitol possess a relative sweetness from 0.3 to 0.42. Generally, lactitol sweetness is considered to be 30–35% of the sucrose sweetness. Thus, simply replacing sucrose with lactitol requires substantial amount of lactitol. Alternatively, lactitol is combined with other sweeteners to synergistically reduce the sucrose concentration.

#### **4.5 Health claims**

Lactitol is not considered as essential nutrient, but its consumption has been clinically linked to a number of health benefits. Health benefits and claims associated with the consumption of sugar alcohols have been reviewed elsewhere [35, 36]. Overall, sugar alcohols are a limited source of energy for oral bacteria that results in less production of acid. van der Hoeven [37] studied the cariogenicity of lactitol in fed rats, and observed that lactitol significantly reduced caries development when compared with sucrose. This observation was in agreement with the rate of fermentation by oral bacteria. Acid production from lactitol occurred at much lower rate than the acid production of sucrose. Clinical evidence demonstrated a reduction in the incidence of caries by the substitution of sucrose with sugar alcohols in chewing gum and candies. van Loveren [38] postulated that the preventive effects against caries in gums and candies formulated with sugar alcohols are due to a stimulation

of the salivary flow, providing a buffer capacity that washes away soluble carbohydrates. However, there is no consensus regarding the minimal dose required to reduce caries. Nevertheless, van Loveren [38] suggested that chewing of sugar-free chewing gum at least 3 times per day may reduce caries incidence.

Lactitol is frequently prescribed as a laxative agent for the treatment of chronic constipation [39]. As a laxative agent, lactitol is minimally absorbed in the small intestine, and when it reaches the large intestine, it creates an osmotic gradient that increases the water retention in the stool, enhancing its passage. Miller et al. [40] performed a meta-analysis on the efficacy and tolerance of lactitol for adult constipation. It was found that lactitol supplementation was not only well tolerated but also significantly improved symptoms of constipation.
