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Measurement of lactose in “lactose-free” products.

D. Mangan




Measurement of lactose in “lactose-free” products.
D. Mangan*, R. Ivory, E. Delaney, C. Cornaggia, B. V. McCleary. Megazyme Bray, County Wicklow, Ireland.

The industrial production of “lactose-free” dairy products is typically achieved through the use of β-galactosidases to hydrolyze the lactose naturally present. This process not only generates glucose and galactose but also a range of lactose analogs and galactooligosaccharides (GOS) that are produced through concomitant transglycosylation reactions. As a result, “lactose-free” dairy products often contain a range of lactose analogs and GOS at concentrations comparable to or higher than the residual lactose content. The most prominent by-product in “lactose-free” samples is allolactose (1,6-β-D-galactosyl-glucose) which can often reach total concentrations of ~0.05 g/L when final concentration of lactose can in some cases be < 0.01 g/L. Traditional enzymatic lactose determination procedures involve the use of a β-galactosidase to hydrolyse the residual lactose in “lactose-free” products coupled with measurement of the glucose or galactose released. With these sample types, the selectivity of the β-galactosidase employed is of paramount importance since the non-selective enzymatic hydrolysis of the lactose analogs such as allolactose present in the sample also leads to additional glucose/galactose formation and results in the overestimation of lactose content. Briefly, this novel enzymatic procedure comprises a sample pre-treatment to enzymatically remove glucose, a selective b-galactosidase hydrolysis step, and a creep calculation to account for unselective hydrolysis. This method was fully characterized in terms of its linear range (2.3—113 mg lactose/100 g), limit of detection (LOD) (0.13 mg lactose/100 g), limit of quantification (LOQ) (0.44 mg lactose/100 g) and reproducibility (≤3.2% CV). A range of commercially available lactose-free samples was analyzed. The lactose values obtained compared favorably with those obtained using quantitative high-performance anion exchange chromatography — pulsed amperometric detection (HPAEC-PAD) analysis. This method achieved Official Method First Action Status at the AOAC annual meeting in September 2019.

Keywords: analytical method, lactose-free, enzymatic assay.

Biography: Dr. David Mangan was awarded his BSc (2006) and Ph.D. (2010) from Trinity College, Dublin, Ireland. He is the author of a number of patents and papers in the fields of carbohydrate chemistry and biocatalysis. He has been employed at Megazyme since 2012 and currently holds the position of Research Director under CEO, Professor Barry McCleary, who developed the Integrated Total Dietary Fiber method (AOAC 2009.01), along with CODEX approved methods for the measurement of resistant starch (AOAC 2002.02), β-glucan (AOAC 995.16) and fructooligosaccharides (AOAC 999.03).