Alternative method for lactulose quantification in the presence of lactose in milk using HILIC with refractive index detection

Abstract

An alternative chromatographic method, HILIC-RID, has been developed for lactulose quantification in the presence of lactose in milk samples. Eighteen commercial UHT milk samples were analyzed. The best separation results were achieved with a mobile phase composed of acetonitrile–water (75 : 25) using an isocratic flow of 1 mL min⁻¹. The limits of detection and quantification were 22.68 ± 8.10 and 75.61 ± 27.01 mg L⁻¹, respectively. Recovery ranged from 98.5 to 103.6% for three lactulose fortification levels. All samples presented low coefficients of variation (0.31–2.16%) for lactulose quantification, indicating good method reproducibility. ANOVA test showed all samples differ from the others at the 99% confidence level and allowed an inference about the lack of uniformity in Brazilian UHT milk. A lactulose amount above 600 mg L⁻¹ found in a specific sample indicated a possible recirculation occurrence during its processing. The results attested the applicability of the HILIC-RID method as an alternative tool for quality control, heat damage investigation and food inspection.