Comparative Determination of Lactose Content in Lactose-Free Milk Using Chemical and Electronic Methods
Keywords:
Lactose-free milk, Lactose determination, UV–Vis spectrophotometry, Colorimetric method, TCA precipitation, Electronic determination, Quality controlAbstract
Lactose-free milk products are widely consumed by individuals with lactose intolerance; however, regulatory standards vary globally, and residual lactose may persist after industrial processing. This study aimed to determine lactose concentrations in 20 commercial lactose-free milk samples—14 flavored and 6 unflavored—collected from local markets in Tripoli and Misurata, Libya. Two colorimetric methods based on UV–Vis spectrophotometry were employed: (Method I) using zinc sulfate and barium hydroxide for protein precipitation with Tollen’s reagent at 520 nm, and (Method II) using 24% trichloroacetic acid (TCA) with modified Tollen’s reagent at 482 nm. In addition, lactose was measured electronically using a TOUCH Master PRO ( ultrasonic milk analyzer). The findings revealed significant variability in lactose content, ranging from 0.22% to 2.24 % by Method I and 0.0249% to 0.123% by Method II, while electronic determination yielded overestimated values of 2.40% to 9.45% in flavored samples and 6.34% to 6.62% in unflavored samples. Several samples exceeded international regulatory limits of 0.01% (EU) and 0.1% (FDA) for lactose-free labeling. Method II demonstrated higher consistency and sensitivity for detecting trace lactose levels, while Method I was more susceptible to matrix interference. The electronic method proved unsuitable for flavored samples due to interference from other reducing sugars. The study highlights the need for stricter quality control and harmonized labeling standards to ensure consumer safety.
References
Pereira, P. C. (2014). Milk nutritional composition and its role in human health. Nutrition, 30(6), 619-627.
Husain, Q. (2010). Β Galactosidases and their potential applications: a review. Critical reviews in biotechnology, 30(1), 41-62.
OSGOOD, M. P., & JOHNSON, A. O. (2007). Lactose Intolerance. Clinical Studies in Medical Biochemistry, 266.
Walstra, P., Walstra, P., Wouters, J. T., & Geurts, T. J. (2005). Dairy science and technology. CRC press.
Perati, P., De Borba, B., & Rohrer, J. (2016). Determination of lactose in lactose-free milk products by high-performance anion-exchange chromatography with pulsed amperometric detection. Thermo Fisher Scientific, Application Note, 1-8.
AOAC INTERNATIONAL. (2018). _SMPR 2018.009: Standard method performance requirements for determination of lactose in lactose-free dairy products_. https://www.aoac.org/wp-content/uploads/2019/08/SMPR_2018_009.pdf.
Mayer, H. K., & Fiechter, G. (2012). Physical and chemical characteristics of lactose-free milk and milk products with TCA pretreatment. _International Dairy Journal, 22_(1), 27–36. https://doi.org/10.1016/j.idairyj.2011.07.003.
McKie, A., Delaney, E., & Kargelis, T. (2018). A novel enzymatic method for the measurement of lactose in lactose-free products. _Sigma-Aldrich Technical Bulletin_. https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma-Aldrich/Technical_Document/lolac-technical-bulletin.pdf.
U.S. Food and Drug Administration. (2020). _Lactose-free claims guidance for industry_. https://www.fda.gov/media/136215/download.
AOAC INTERNATIONAL. (1990). _AOAC Official Method 984.15: Lactose in milk, enzymatic method_. https://www.aoac.org/wp-content/uploads/2019/08/984_15_lactose.pdf.
Marshall, K. R. (2005). Enzymatic determination of lactose in milk and dairy products with protein precipitation. _Journal of AOAC International, 88_(4), 1146–1152. https://doi.org/10.1093/jaoac/88.4.1146.
Tollen, B. (1883). On the use of ammoniacal silver solution for the detection of reducing sugars. _Berichte der Deutschen Chemischen Gesellschaft, 16_(2), 2635–2636. https://zenodo.org/record/1427365.
Somogyi, M. (1952). Notes on sugar determination. _Journal of Biological Chemistry, 195_(1), 19–23. https://www.jbc.org/article/S0021-9258%2818%2950995-6/pdf.
Queiroz, J. H., Silva, M. E., & Stringheta, P. C. (2013). Adaptation of Tollen’s reagent for lactose quantification in dairy matrices. _Food Chemistry, 141_(3), 2181–2185. https://doi.org/10.1016/j.foodchem.2013.04.107.
Carlsberg Research Laboratory. (2021). _Touch Master Pro Lactose Analyzer: User manual and technical specifications. https://www.carlsberglab.com/touchmaster-pro.
AOAC INTERNATIONAL. (2020). _Determination of lactose in low-lactose and lactose-free milk – LactoSens® amperometry method_. https://www.aoac.org/wp-content/uploads/2020/02/2020_01_Lactose_Lactosens.pdf.
Singh, M., et al. (2020). Recent advances in lactose biosensors for food analysis. _Trends in Food Science & Technology, 105_, 390–401. https://doi.org/10.1016/j.tifs.2020.09.023.
Bollella, P., et al. (2019). Lactose biosensors for food and clinical applications. _Electroanalysis, 31_(3), 424–434. https://doi.org/10.1002/elan.201800669.
ISO/IDF. (2007). _ISO 22662 | IDF 198: Milk and milk products — Determination of lactose content by HPLC . https://www.iso.org/standard/38151.html.
Petrucelli, D., et al. (2015). Simultaneous determination of lactose, lactulose and galactose in milk by HPAEC-PAD. _Journal of Chromatography A, 1412_, 84–91. https://doi.org/10.1016/j.chroma.2015.08.001.
EP4389886A1. (2022). _Lactase enzymes and method of producing a milk-based product_. European Patent Office. https://patents.google.com/patent/EP4389886A1.
EP2234501B1. (2010). _Method for producing a low-lactose dairy product_. European Patent Office. https://patents.google.com/patent/EP2234501B1.
Schuck, P., et al. (2016). Matrix effects in lactose determination by spectroscopic methods. _International Dairy Journal, 58, 1–8. https://doi.org/10.1016/j.idairyj.2016.02.024.
Javed, S., et al. (2015). Kinetic parameters of β-galactosidase from various sources. _Enzyme and Microbial Technology, 70_, 45–52. https://doi.org/10.1016/j.enzmictec.2014.12.003.
Teles, F. F. F., Young, C. K., & Stull, J. W. (1978). A method for rapid determination of lactose. Journal of Dairy Science, 61(4), 506–508.
Sen, S., Himaja, D., Manoj Kumar, & Manjunath, S. Y. (2023). Colorimetric method development and validation for estimation of lactose in milk. International Journal of Pharmaceutical Technology Letters, 13(1), 27–32.
