**2. Historical timeline**

**Figure 1** illustrates selected milestones of lactitol over the past 100 years. A comprehensive review of the technological advancements of lactitol can be found elsewhere [1]. Chemical catalysis was perhaps the first great contributor to the advancement of lactitol. In 1920, Senderens [6] hydrogenated lactose over activated nickel. Senderens' catalysis was very unstable, making unrealistic any kind of large-scale production. The stability of nickel-based catalysts became a reality with the invention of the sponge nickel by Raney in 1925 and 1926 [7]. Raney's invention consisted of crystalline particles of active nickel embedded within an inactive metal. In subsequent years, the reaction kinetics of hydrogenation was elucidated, which allowed the production of lactitol at high yields and selectively.

Early production of lactitol was aimed at research facilities, where potential applications were investigated throughout 1930–1970. In 1938, the crystalline structure of lactitol was elucidated by purification and crystallization of the hydrogenated slurry [8]. A second anhydrous crystalline form of lactitol, dihydrate, was discovered by 1952 [9]. In subsequent years, lactitol entered the fields of nutrition, material science, and biotechnology. Fortification of infant food, synthesis of lactitol-based polyethers, sweetening agent, and animal feed are examples of applications of lactitol.

**37**

**Figure 2.**

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

In 1977, the sweetness intensity of lactitol was established by the development of the sweetness scale using sucrose as a reference [10]. Soon after, lactitol was incorporated in confectionary formulations and chewing gum. In the 1980s, lactitol found applications in the field of hygiene and medicine, where it was used to formulate toothpaste, mouthwashes, and aseptic products. Metabolic concerns related to the consumption of lactitol were studied in 1981 [11]. In years thereafter, lactitol was used for the treatment of liver disease [12]. In 1993, the Food and Drug Administration (FDA) granted the status of Generally Recognized as Safe (GRAS) [13]. The current literature on applications of lactitol reveals about 3000 patents, ranging from a low-calorie sweetener to a surfactant and stabilizer agent. Nowadays, lactitol and other sugar alcohols represent a significant global market with various applications, and its production is projected to reach 1.9 million metric

Lactitol is not found in nature, and it can only be produced through catalytic hydrogenation of lactose. Thus, the transition state theory of catalytic surface reactions is the foundation of lactitol synthesis. The actual synthesis consists of a sequence of elementary reactions, namely adsorption, surface reaction, and desorption [14]. Collectively, all these reactions are known as the Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetics [2]. **Figure 2** illustrates the LHHW kinetics that is formulated from a presumed elementary step. Then, the rate is derived through the different elementary steps with the assumption of one of them is the rate-determining step, while the others are achieved the equilibrium. The overall reaction rate is strongly affected by temperature and pressure since

Lactose and hydrogen are adsorbed through chemisorption, where the exchange

of electrons with surface sites leads to the formation of a chemical bond [15]. Lactose is adsorbed from the bulk solution, a process that overcame the interaction forces of the solvent. A molecular mechanism is responsible for adsorbing the

*Illustration of Langmuir-Hinshelwood-Hougen-Watson kinetic. Adapted from [2]. Numbers 1, 2, and 3* 

*represent adsorption, surface reaction, and desorption, respectively.*

these variables determine the equilibrium of the elementary reactions.

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

tons by 2022.

*3.1.1 Adsorption*

**3. Production of lactitol**

**3.1 Catalytic hydrogenation**

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

In 1977, the sweetness intensity of lactitol was established by the development of the sweetness scale using sucrose as a reference [10]. Soon after, lactitol was incorporated in confectionary formulations and chewing gum. In the 1980s, lactitol found applications in the field of hygiene and medicine, where it was used to formulate toothpaste, mouthwashes, and aseptic products. Metabolic concerns related to the consumption of lactitol were studied in 1981 [11]. In years thereafter, lactitol was used for the treatment of liver disease [12]. In 1993, the Food and Drug Administration (FDA) granted the status of Generally Recognized as Safe (GRAS) [13]. The current literature on applications of lactitol reveals about 3000 patents, ranging from a low-calorie sweetener to a surfactant and stabilizer agent. Nowadays, lactitol and other sugar alcohols represent a significant global market with various applications, and its production is projected to reach 1.9 million metric tons by 2022.
