Determination of lactose and lactulose isomers in UHT milk by CZE-UV

Abstract

A capillary zone electrophoresis method with indirect detection in ultraviolet region (CZE-UV) for determination of lactose and lactulose in seventeen UHT milk brands using single-point standard addition was proposed. An average lactulose content of 455.52 mg L−1 and a relative standard deviation (RSD) of 45% were found, while ca. 23% of brands showed lactulose concentrations above 600 mg L−1. High RSD values were found in intra-brands analysis (17–49%) indicating the existence of many variations in UHT thermal processing. The mean lactose content was 4.45 g 100 mL−1 with a RSD of 9.2%. Validation results appointed good precision (RSD of 3.19% and 3.82%), and low limits of quantification (62.53 ± 4.32 mg L−1 and 0.083 ± 0.003 g 100 mL−1) for lactulose and lactose, respectively. Recoveries rates for lactose were found considering three concentration levels (96.5–102.2%) and for standard added in all samples during quantification step (100.02 ± 1.39)%. Lactulose recovery average of standard added was (99.24 ± 1.46)%. The method can be useful for thermal processing quality control as well lactose hydrolysis monitoring.