Determination and study on refractive indices and viscosities of aqueous solutions of citric acid, (citric acid + glycerol), and (citric acid + d-sorbitol) at T = 293.15 K–323.15 K and atmospheric pressure
Introduction
The study on thermodynamic properties of liquid mixtures and solutions has direct applications in food, drug, petroleum, cosmetic and detergent industries (Singh et al., 2014, Bajić et al., 2013, Marmiroli et al., 2008, Kumar and Angural, 2016). In these industries, many chemical processes are done and components are normally handled in fluid form. The measurement of thermodynamic properties for these fluids is very important because using these data (viscosity, density, refractive index, and speed of sound), we can control these chemical processes (Rahul, Gowri Sankar, Krishna, & Ramachandran, 2016). On the other hand, investigations on the thermodynamic properties of binary and ternary liquids and mixtures have been done to gain information about intermolecular interaction and change in packing efficiencies with corn positions (Koohyar et al., 2013, Koohyar et al., 2013).
Organic acids and their aqueous solutions are widely used in food industry. There are two prevailing methods for production of organic acids. These two methods are fermentation and chemical synthesis (Soccol et al., 2008, Ali et al., 2016, Khan et al., 2017, Li et al., 2016, Saha, 2003, Lu et al., 2009, Dwivedi et al., 2011). Of course, fermentation is the method that are most commonly used in production of organic acid. In fermentation, some bacteria and yeasts consume sugar and produce organic acids, alcohols, and gases in the absent of oxygen.
Citric acid is widely used in many cases such as pharmaceutically active substances, pharmaceuticals, personal care and cosmetic products, food, flavoring agent, blood anticoagulant, environmental remediation, diuretic, and beverage (as an acidulant and pH stabilizer) (Ciriminna, Meneguzzo, Delisi, & Pagliaro, 2017). Citric acid is usually produced by surface or submerged fungal fermentation mainly with Aspergillus Niger. However the highest amount of citric acid is produced by the submerged fermentation method (Soccol et al., 2006, Max et al., 2010, Aboud-Zeid and Ashy, 1984, Kim et al., 2015). Citric acid has a high solubility in water because it has tree carboxylic groups (Fig. 1) and the Hydrogen bonds are generated between citric acid and water when it dissolves in water. Hydrogen bonding has key role for dissolving the acids in water. Hydrogen bonding systems is very interesting because hydrogen bonds play a vital role in chemical, physical, and biological processes (Jeffrey, 1997, Głowacki et al., 2013). All studied molecules in this research work have strong hydrogen bonds with water molecules.
d-sorbitol (d-glucitol) has six OH groups (Fig. 1). It dissolves in water in high amount (2350 g/L) due to production of hydrogen bonds between water molecules and its hydroxyl groups. d-sorbitol can be found in apples, pears, peaches, and prunes (Ortiz et al., 2013, Barbieri et al., 2014). d-sorbitol is produced from sucrose or glucose using a catalytic hydrogenation with hydrogen gas and nickel catalyst at high temperatures (Evrendilek, 2012, Kusserow et al., 2003). There are many industrial processes which are used to produce d-sorbitol but only a few microorganisms, including three yeast strains and bacteria like Zymomonas mobilis and Candida boidini, have been suggested as potential d-sorbitol producers (Jonas and Silveira, 2004, Ladero et al., 2007).
d-sorbitol gives a cooling sensation in the mouth due to having a negative heat of solution. It has a cool, pleasant, and sweet taste. Besides acting as a sweetener, it is also an excellent humectant, softener, texturizing and anti-crystallizing agent (Ergun et al., 2010, Patra et al., 2009). d-sorbitol has many applications in foods, pharmaceuticals, and cosmetics (Okesola, Vieira, Cornwell, Whitelaw, & Smith, 2015). For instance, d-sorbitol is used in products for special nutritional purposes designated for people with diabetes because it has non-cariogenic properties. In addition, it can be added to many products, such as sugar-free candies, chewing gums and sugar-free foods such as frozen desserts and baked goods.
Glycerol (glycerin) is a viscous liquid that is miscible in water because of having tree hydroxyl groups and its shape and size (Fig. 1). Glycerol is usually obtained from plant and animal sources where it occurs as triglycerides. It is widely used in the cosmetics as softener and moisturizing, in food industry as a sweetener and humectant and in pharmaceutical formulations. Glycerol is relatively good solvent for oil and helps prevent sugar crystallization (Adamenko, Zelinsky, & Korolovych, 2007).
Section snippets
Materials
d-sorbitol, citric acid, and glycerol were purchased from Merck Company. Purity of these chemicals was more 99 mass percent and they were used without further purification. To prepare these aqueous solutions, the deionized water was used. Binary mixtures were prepared from known masses of each liquid in air-tight stoppered glass bottles. All dilute solutions were prepared double – distilled water with specific conductivity equal to 1.3 ± 0.1µΏ−1·cm−1.
Apparatus and procedure
All solutions were prepared by weighing
Study on refractive index and viscosity data
The control of chemical processes is very important in various industries. The experimental thermodynamic properties of aqueous solutions have an important role in control of chemical processes. In addition, this data can be used in research works to lead us to better understanding interactions between species in various solutions.
In this research work, the experimental viscosities, ƞ, and refractive indices, nD, were measured for binary system of (water + citric acid) and also, ternary
Conclusion
In this study, the refractive index and viscosity were measured for aqueous solution of citric acid and ternary solutions of (water + citric acid + glycerol) and (water + citric acid acid + d-sorbitol) at temperatures T = (293.15, 303.15, 313.15, and 323.15) K in wide range of mass fraction of citric acid. Some equations were used for fitting refractive index and viscosity data. Parameters of these equations can lead us to better understanding of interactions between species in our studied
Declaration of interests
The authors declare that they have no known competing financialinterestsor personal relationships that could have appeared to influence the work reported in this paper.
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