Method development for the quantitative determination of lactulose in heat-treated milks by HPAEC with pulsed amperometric detection.
A robust, rapid, and sensitive high-performance anion-exchange chromatographic method for the separation and quantitative determination of lactulose in heated milks, along with other common milk carbohydrates, has been developed. Complete separation of galactose, glucose, N-acetylgalactosamine, lactose, lactulose, and epilactose was isocratically accomplished in about 22 min by an anion-exchange column eluted with 10 mM NaOH spiked with 2 mM Ba(OAc)2. The within-day repeatability was lower than 2.1% for 10 repetitive injections. Under optimized conditions, there was no need either of post-column addition of strong bases to the eluent for enhancing detection sensitivity or, even more important, for column regeneration between chromatographic runs. Upon 100-fold sample dilution, the amperometric response of lactulose in milk samples was found to be linear up to 100 microM (r = 0.99935) with a limit of detection equal to 1.2 microM (S/N = 3). The lactulose content in ultrahigh-temperature (UHT) and sterilized milks was evaluated by a calibration graph using 2-deoxyglucose as the internal standard, making the proposed method very useful in discriminating among heat-treated milks. Whereas the mean value of lactulose in skimmed, partially skimmed, and whole UHT milks ranged from 10 to 90 mg/100 mL, lactulose content in bottle-sterilized whole milk (two samples) was higher than 140 mg/100 mL. The presence of epilactose, which is another isomer of lactose, was also ascertained in sterilized milk.
Cataldi
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Dipartimento di Chimica, Università della Basilicata, Potenza, Italy. cataldi@unibas.it
Angelotti
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Bufo
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SA
D000818:Animals; D017609:Barium Compounds / Q000737:chemistry; D002241:Carbohydrates / Q000032:analysis; D002852:Chromatography, Ion Exchange / Q000379:methods*; D004563:Electrochemistry / Q000379:methods*; D006358:Hot Temperature; D007785:Lactose / Q000737:chemistry / Q000378:metabolism; D007792:Lactulose / Q000032:analysis*; D008892:Milk / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013242:Sterilization
D017609:Barium Compounds; D002241:Carbohydrates; D007792:Lactulose; D007785:Lactose