Figure 2: The molecular structure of α-lactose, as determined by X-ray crystallography

Sources of Lactose:⁶

Lactose is naturally found in milk and dairy products and is commonly added to processed foods.

Bread, baked goods, cereals, soups, and beverages often contain lactose, which is important for

lactose-intolerant individuals to monitor.

Some hidden sources of Lactose⁷:

Figure 3: Certain hidden sources of lactose

Figure 4: Lactose Sources

Lactose: Properties and Solubility⁸

1. Lactose and Lactose in Solution:

Lactose, a disaccharide of β-D-galactose and D-glucose, is a reducing sugar that accelerates chemical reactions. It exists as two anomers, α-lactose and β-lactose, distinguished by the orientation of the hydroxyl (-OH) group at the anomeric carbon. These anomers interconvert through a temperature-dependent process. Polarimetry differentiates them based on specific rotations: α-lactose (89.4°) and β-lactose (35.0°).

2. Solid form of Lactose:

Lactose exists in three solid forms: amorphous lactose glass, anhydrous β-lactose, and α-lactose monohydrate. α-Lactose monohydrate, the most common in milk powders, contains 5% water and is non-hygroscopic. Anhydrous α-lactose has two forms: unstable and stable, produced by heating α-lactose monohydrate above 100°C under vacuum. Mutarotation maintains equilibrium between α- and β-lactose until saturation. Amorphous lactose glass forms in spray-dried or freeze-dried milk and whey products.

3. Synthesis of Lactose and Role of Lactose in Secretion of Milk:

Lactose, the primary milk solid in cow's milk, is synthesized in the Golgi apparatus of secretory cells from glucose and galactose via lactose synthetase (α-lactalbumin + galactosyl transferase). High glucose demand supports lactation, with Holstein cows producing ~1,800–1,900g/day. Immune challenges (e.g., mastitis, infections) further increase glucose consumption.

4. Lactose In Dairy Products and by-Products:

Lactose content varies across dairy products. Milk and conventional yogurt retain full lactose, while cheese, Greek yogurt, and cultured products have lower levels due to whey drainage. Milk, whey, and buttermilk powders contain significant lactose for long-term storage. Amorphous lactose glass forms on powder surfaces due to rapid drying above 93.5°C.

Commercial Uses of Lactose:⁹

1. Infant Formula: Lactose is added to baby formula and used to produce galactooligosaccharides (GOS), prebiotics that enhance formula similarity to human milk and may reduce GI inflammation.

2. Pharmaceuticals: Lactose serves as an excipient in tablets and capsules, aiding in drug stability and bioavailability.

3. Animal Feed: UF permeate or high-lactose liquids are combined with nutrients for cost-effective livestock feed. Cheese whey is also used in cattle diets to reduce waste disposal issues

Analytical Methods for Lactose Measurement¹⁰:

In order to control lactose fractionation during processing, measure the amount of lactose in animal feeds to accurately calculate the dietary energy content, measure the amount of lactose output per cow per day to manage energy-related acne in dairy cows, label food products with nutritional information, and comply with regulations when claims regarding the lactose content of food products are made, lactose measurement is necessary. The way lactose is expressed and determined has not always been well defined; it can be expressed as anhydrous lactose, lactose monohydrate, or just a lactose value that is determined by subtracting the total solids of milk from the sum of the fat, protein, and ash factor. But according to their data, it is lactose without mentioning anhydrous lactose. Lactose by difference, or lactose monohydrate¹³. As a result, reported lactose levels for milk and milk products have become inconsistent. Below is a summary of the several analytical techniques that can be used to measure lac toes.

Polarimetry:

A very old technique for determining a compound's concentration is polarimetry. The traditional approach is polarimetry (AOAC International, 2016, method 896.01). Method for measuring lactose, but it is challenging to use and involves hazardous chemicals that cause problems with waste disposal and safety. Since 1896, the AOAC International Polarimetry method has not altered. The concentration of a chiral component in a sample can be linked to a compound's specific rotation. A measured rotation is converted to a specific rotation by dividing it by the travel length in decimetres and the concentration in g/mL. The following is the equation:

(α) =---------------

c-l

Where:

(α) is the specific rotation,

α is the observed rotation (in degrees),

c is the concentration of the solution (in g/mL),

l is the path length of the sample tube (in dm).

Reducing Sugar Method:

The ability of lactose to readily oxidize and reduce another chemical is the foundation of reducing sugar techniques. The techniques for decreasing sugar are colorimetric. That creates a colourful molecule by the reaction of lactose with a reagent. Drey wood’s reagent serves as an illustration of this. According to Beer's Law, which states that the concentration of the coloured compound formed is proportional to the concentration of lactose present in the sample, absorbance can then be measured using devices as basic as a spectrophotometer or a visual colorimeter to ascertain the lactose concentration. These techniques can also be used to examine lactose in samples that contain combinations of lactose and sucrose. Fehling's solution is another illustration of a lowering sugar technique. This process creates a potent oxidizing agent that can react with reducing agents by combining two distinct solutions. sugars, such as lactose, and produces a precipitate of copper oxide. The Munson and Walker method measures the amount of copper oxide produced using a traditional gravimetric technique. Due to their need for calibration standards, colorimetric and Fehling's solution are both considered secondary procedures. Due to the fact that the redox reactions upon which they are predicated depend on the existence of a reducing species—which might be any number of chemical substances other than lactose, including other monosaccharides, maltose.

Enzymatic Methods:

Spectrophotometric and differential pH are the two primary detection techniques used in conjunction with enzymatic tests for lactose. Regarding spectrophotometry Prior to the enzymatic analysis stage, the milk samples must be cleared (that is, the fat and protein must be removed) because any turbidity or particle matter could cause light scattering to skew the absorbance value. Cares solution or a low concentration of trichloroacetic acid is commonly used to precipitate fat and protein. With better within- and between-method performance, the former AOAC International (2016) method 984.15 was replaced with method 2006.06 for determining the lactose content of milk. The β-galactosidase enzyme hydrolyses lactose to produce d-glucose and d-galactose as the initial step in the spectrophotometric enzymatic assay. at 6.6 ph. At a pH of 8.6, the enzyme β-galactose dehydrogenase then converts d-galactose to d gala tonic acid while reducing NAD+ to reduced NADH. Radiation at 340 nm is absorbed by NADH, and the amount of lactose present has a stoichiometric relationship with NADH production. Thus, by applying Beer's Law, the change in the NADH absorbance can be used to calculate the lactose concentration.

HPLC:

Lactose in a sample is separated, identified, and quantified using high-performance liquid chromatography, which uses pressure to push a solvent through a confined column with tiny particles in it. Because various sugars elute from the column at different intervals, lactose can be separated from other sugars based on its interaction with the stationary phase (column particle materials) and mobile phase (solvent). A differential refractometer detector detects lactose after it has been separated from an internal standard using cation exchange column. Although the technology for HPLC detectors has improved (evaporative light scattering, electrochemical, and pulsed amperometry detectors are now available), interlaboratory research and method performance validation have prevented the addition of these detectors to official procedures. Because it depends on calibration using high purity lactose calibration standards, the HPLC is a secondary approach. HPLC, on the other hand, is very lactose specific. Unlike the lowering sugar approaches, this method offers very good distinction between carbohydrates.

Mid-Infrared Milk Analysis:

The measurement of absorbance of distinctive vibrational modes is the foundation of the mid-infrared (MIR) technique. a molecule of lactose. The OH groups are the vibrational modes of interest for lactose. But lactose is not the only substance in milk that has OH groups; hence, adjustments for background absorption by other substances are required. Additionally, background corrections must be applied for variations in water concentration from sample to sample due to the strong absorption of MIR light by water, the main component of milk. Since numerous other substances in milk can also contribute to the absorbance at the wavelengths where lactose is present, the MIR has very little specificity to lactose. Identified, hence the necessary adjustments need to be done (Lynch et al., 2006). However, due to its low cost and rapid speed, MIR is frequently used for routine milk analysis. It can overcome its poor lactose sensitivity because milk doesn't contain.

Use of Lactose:^11,12

1. Fluid Milk and Beverages:

Dairy products that are lactose-reduced or lactose-free can be produced by hydrolysing lactose, filtering out lactose, or a combination of the two methods, and all of these methods are now in use. Lactose and the products of lactose hydrolysis are measured. This is especially crucial for dairy-based drinks and milks that are lactose-free or reduced. Due to the requirement for a low limit of detection, low-lactose beverages can provide difficulties for analytical techniques. Additionally, it could be necessary to distinguish between different lactose, glucose, and galactose concentrations.

2. Dried Milk and Whey Products:

Both domestically and globally, dried milk and whey products are significant commodities. The protein content of these goods is often specified as a percentage of total protein (TS) in the product, according to composition guidelines. The majority of the leftover milk solids in these dried goods are lactose, although protein is the main, highly valuable milk component.

While lactose makes up the majority of the leftover milk solids in these dry products, protein is the key milk component with the highest value. Therefore, maintaining control over the protein and lactose level of these products is essential for the processor's financial performance as well as the consistency of the dried milk ingredient's functioning and nutritional profile. UF removes lactose during the manufacturing of WPC, WPI, milk protein concentrates, and milk protein isolates. Thus, it is crucial to regulate the liquid product's protein to anhydrous lactose ratio throughout processing prior to drying. The protein concentration may be too high if the lactose level is too low; if the product is sold based on minimum protein content, and if the protein content is higher than the minimum, no premium is given.

3. Cultured Products:

Over the past 40 years, cheese production and consumption have grown dramatically in the United States (International Dairy Foods Association, 2016). Consumption of yogurt and the variety of cultured goods sold in stores have also increased dramatically. Cheese is used extensively in food service in the United States, and it is therefore crucial to carefully control its composition to ensure that it has a chilled shelf life for distribution and functions properly when used as a component.

4. Milk Production and Dairy Cattle Management:

Though it contains the largest concentration of any of the three major components of milk (lactose, protein, and fat), lactose has the lowest commercial value per unit weight. The low value of lactose has led to a lack of focus on the quality of lactose data from dairy herd improvement and payment laboratories. Lactose has been more widely available commercially as milk production has grown. Finding economically feasible applications for lactose has been difficult, especially as it is a by-product of the production of cheese, high-protein milk, and whey powder. The industry must so concentrate more on increasing the production of high-value milk components (such as fat and protein) per unit.

Metabolism:

Infant mammals produce lactase (β-D-galactosidase) in intestinal villi to hydrolyze lactose into glucose and galactose for absorption. In most mammals, lactase production declines post-weaning due to reduced dietary lactose. However, in populations with a history of dairy consumption (Europe, West Asia, South Asia, and parts of Africa), genetic selection has favored lactase persistence into adulthood. Over 70% of Western Europeans retain lactase activity, while less than 30% of individuals from Africa, East/Southeast Asia, and Oceania do. Lactose intolerance results in undigested lactose fermenting in the gut, causing gastrointestinal symptoms like bloating and diarrhea.

There are some methods of Metabolism as follow¹³:

1. Absorption: The small intestine is where lactose is processed. It is made up of two simpler sugars, glucose and galactose1, making it a disaccharide. The small intestine's lining contains the enzyme lactase, which is essential for breaking down lactose into these simpler sugars.

2. Genetic Regulation: Genetic variations cause individual variances in lactase activity. Lactose intolerance1 can result from decreased lactase activity in some persons, while others may have a genetic predisposition that permits them to maintain high lactase activity throughout adulthood.

3. Gut Microbiota: Our gut microbiota can also affect how well lactose is digested. Some bacterial strains generate lactase-like enzymes, which aid in the more effective digestion of lactose by those with decreased enzyme activity.

4. Clinical Implications: Treating diseases like lactose intolerance requires an understanding of lactose metabolism. A low-lactose diet, lactase supplements, and maybe prebiotic use to support good gut flora are treatment possibilities for lactose intolerance. Consequently, the enzyme known as lactase metabolizes lactose. Therefore, galactose and glucose are the products that are formed when an enzyme and lactose interact. The small intestine breaks down and absorbs lactose as part of its metabolism. The enzyme lactase breaks down lactose, a disaccharide, into its constituent sugars, galactose and glucose. The circulation then absorbs these simple carbohydrates. To break down the lactose in milk, the small intestine of newborns and young mammals produces the enzyme lactase. However, since lactose is no longer a major component of the diet after weaning, lactase synthesis declines in many mammals. Some individuals, especially those from areas where dairy consumption has historically occurred, continue to produce lactase, which enables them to digest lactose throughout their lives. When lactose is ingested, people with lactose intolerance experience digestive problems such bloating, gas, and diarrhoea because their bodies do not produce enough lactase. Figure. 6 shows the lactose metabolism process.

Figure 5: Metabolism of Lactose

Biological Properties of Lactose:¹⁴

Sweetness and energy Value

Lactose has 20–40% of sucrose’s sweetness. It provides 4kcal/g upon complete digestion, though its caloric value may drop to 2–4kcal/g if partially digested. Undigested lactose enhances mineral absorption (e.g., calcium, magnesium) and has a glycemic index (GI) of 46–65, lower than glucose (100–138) and sucrose (68–92).

Functional Roles:

· Energy Source: Lactose is hydrolyzed in the small intestine or fermented by lactic acid bacteria in dairy products.

· Mineral Absorption: Facilitates calcium and magnesium uptake, aiding bone health.

· Osmotic Pressure Regulation: Maintains milk stability, ensuring efficient nutrient delivery in infants.

· Low Cariogenicity: Unlike fermentable sugars, lactose minimally contributes to dental plaque formation.

Lactose Intolerance & Industrial Applications:¹⁵

Lactose intolerance arises from insufficient lactase activity, leading to GI symptoms. Despite this, lactose remains vital in:

· Pharmaceuticals: Used as an excipient in tablets, capsules, and dry powder inhalers due to its stability and compatibility.

· Food Industry: Enhances texture, viscosity, and crystallization in chocolate and baked goods while serving as a carrier for flavors and supplements.

· Fermentation: Certain Kluyveromyces yeasts ferment lactose to ethanol, making it useful for biofuel and brewing (e.g., milk stout).

· Animal Feed: Whey-derived lactose is used in livestock diets to optimize nutrient efficiency.

Food Additive and Nutritional Use:

Lactose is a key carbohydrate in infant formula, maintaining a close resemblance to human milk. It also plays a role in protein standardization in dairy powders and contributes to nutritional supplements.

CONCLUSION:

Lactose plays a vital role in dairy production, pharmaceuticals, and nutrition. Understanding its properties, metabolism, and industrial applications enhances its effective utilization. Despite its reduced digestibility in lactose-intolerant individuals, its role in infant nutrition, excipient formulations, and food processing remains significant. The accurate measurement and regulation of lactose content are crucial for maintaining dairy quality, pharmaceutical formulation efficiency, and food safety standards.

REFERENCES:

1. Hebb GA, Dickhoff BH. Application of lactose in the pharmaceutical industry. In: Lactose. Academic Press; 2019. p. 175–229.

2. Swagerty DL Jr, Walling AD, Klein RM. Lactose intolerance. Am Fam Physician. 2002; 65(2): 1845–51.

3. Fox PF, Uniacke-Lowe T, McSweeney PL, O'Mahony JA. Lactose. Dairy Chem Biochem. 2015; 3:21–68.

4. Holsinger VH. Lactose. In: Fundamentals of Dairy Chemistry. Boston, MA: Springer US; 1988. p. 279–342.

5. Suarez FL, Savaiano DA, Levitt MD. Review article: The treatment of lactose intolerance. Aliment Pharmacol Ther. 1995 Dec; 9(5): 589–97.

6. de Verse M, Sieber R, Stransky M. Lactose in der menschlichen Rearing [Lactose in humannutrition]. Schweiz Med Wochenschr. 1998 Sep 19; 128(6):1393–400. German.

7. Kretchmer N. Lactose and lactase. Sci Am. 1972 Oct; 227(7): 71–8.

8. Kou X, Chan LW, Steckel H, Heng PW. Physico-chemical aspects of lactose for inhalation. Adv Drug Deliv Rev. 2012 Mar 15;64(8):220–32. doi: 10.1016/j.addr.2011.11.004. Epub 2011 Nov 15.

9. Janssen PHM, Berardi A, Kok JH, Thornton AW, Dickhoff BHJ. The impact of lactose type on disintegration: an integral study on porosity and polymorphism. Eur J Pharm Biopharm. 2022 Nov; 180:251–9. doi: 10.1016/j.ejpb.2022.10.012.

10. Torres JKF, Stephani R, Tavares GM, de Carvalho AF, Costa RGB, de Almeida CER, Almeida MR, de Oliveira LFC, Schuck P, Perrone ÍT. Technological aspects of lactose-hydrolysed milk powder. Food Res Int. 2017 Nov; 101:45–53.

11. Seki N, Saito H. Lactose as a source for lactulose and other functional lactose derivatives. Int Dairy J. 2012; 22(12): 110–5.

12. Seki N, Saito H. Lactose as a source for lactulose and other functional lactose derivatives. Int Dairy J. 2012; 22(13):110–5.

13. Barbano DM, Lynch JM, Fleming JR. Direct and indirect determination of true protein content of milk by Kjeldahl analysis: collaborative study. J Assoc Off Anal Chem. 1991; 74(14):281–8.

14. Haque K, Roos YH. Crystallization and X-ray diffraction of spray-dried and freeze-dried amorphous lactose. Carbohydr Res. 2005; 340(2): 293–301.

15. Whittier EO. Lactose: a review. Chem Rev. 1925;2(1):85–125.

16. M. Kranthi Kumar Reddy, B. Narasimha Rao, K. Ravindra Reddy. Study on Effect of Excipients in Enhancing the Solubility of Nateglinide by Solid Dispersions. Asian J. Pharm. Res. 2012; 2(4): 144-147.

17. Keerthi Manukonda, Rama Rao N, Santhosh Aruna M, Lakshmi Prasanna J. Solid Dispersions-An Approach to Enhance the Dissolution Rate of Clopidogrel Bisulphate. Asian J. Res. Pharm. Sci. 2014; 4(4): 165-168.

18. Salma Banu S.K., Venkateswara Rao T. Design and Development of Sustained Release Bilayered Tablets of Glipizide. Research J. Pharma. Dosage Forms and Tech. 2012; 4(1):24-31.

19. Patel Chirag J, Asija Rajesh, Asija Sangeeta, Mangukia Dhruv K, Patel Jaimin R, Kanu Patel. Development and Evaluation of Self Pore Forming Osmotic Tablets of Nifedipine. Research J. Pharma. Dosage Forms and Tech. 2012; 4(4): 207-210.

20. Praveen Kumar Uppala, K. Atchuta Kumar, Murali Krishna, U. Upendra Rao. Formulation and Evaluation of Israpidine Extended-Release Matrix Tablets. Res. J. Pharm. Dosage Form. & Tech. 2016; 8(4): 277-291.

21. R. R. Shah, M. S. Kondawar, S. S. Shinde, N. D. Shah. Formulation and Evaluation of Spray-dried Combination Respirable Powder Based on Selection of Excipients for Pulmonary Delivery: Comparison between Lactose and Mannitol. Research J. Pharm. and Tech. 2011; 4(10): 1604-1614.

22. T. Sonica, T. E. G. K. Murthy. Studies on the Influence of Different Coprocessing Excipients on the Flow and Dissolution kinetics of Donepezil HCl. Research J. Pharm. and Tech. 2013; 6(8): 868-873.

23. Bonshikachatterjee, Nivetha. A, Mohanasrinivasan. V. Immobilization of β-galactosidase in Chitosan-Alginate composite scaffolds and optimization of lactose hydrolysis. Research J. Pharm. and Tech. 2018; 11(4): 1480-1485.

24. P. Jitendra kumar, Y. Indira Muzib, Gitanjali Misra. Formulation and Evaluation of Pulsatile Drug Delivery of Lovastatin. Research J. Pharm. and Tech. 2018; 11(7): 2797-2803

25. Gaviraj EN, Ramarao A, Veeresham C, Shivakumar B, Kalyane NV, Biradar SM. Inhibitory activities of some Folklore remedies on Aldose reductase of rat lens and generation of advanced glycation end products. Research J. Pharm. and Tech. 2019; 12(4): 1947-1952.

26. Sriram B. S, Ravichandra.V, Rajendra Holla, Shailaja Moodithaya, Kishan Prasad. An Experimental Study Evaluating the dose of oral D-Galactose on aging Induction in wistar albino male Rats. Research J. Pharm. and Tech. 2020; 13(7): 3289-3292.

Received on 17.02.2025 Revised on 22.03.2025

Accepted on 23.04.2025 Published on 09.05.2025

Available online from May 12, 2025

Res. J. Pharma. Dosage Forms and Tech.2025; 17(2):130-136.

DOI: 10.52711/0975-4377.2025.00019

This work is licensed under a Creative Commons Attribution-Non Commercial-Share Alike 4.0 International License. Creative Commons License.