Analysis method for determination of nisin A and nisin Z in cow milk by using liquid chromatography-tandem mass spectrometry.

Nisin, a polypeptide with antimicrobial properties, is known as a natural preservative. It is used in various foods, including dairy products. This study validated a novel procedure using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the determination of nisin A and nisin Z in cow milk. An extraction solution of 0.1 M acetate buffer containing 1 M NaCl (pH 2.0) and MeOH (1:1) was used to extract nisin A and nisin Z from milk samples. After the addition of extraction buffers, the samples were homogenized and centrifuged. The supernatant was filtered and injected for LC-MS/MS analysis. The linearity of the analytical method had a high correlation coefficient (r≥0.9987). The limits of quantitation of nisin A and nisin Z were approximately 12.9 and 10.9 µg/kg, respectively. The accuracy of the analytical method in milk ranged from 90.6 to 103.4% for nisin A and from 83.8 to 104.4% for nisin Z. The coefficient of variation values of intra- and interday in milk determined to be less than 5% in both nisin A and nisin Z. Because the proposed method has comparatively high recovery and low coefficient of variation, it seems appropriate for the determination of nisin A and nisin Z in milk samples. As the quantification of nisin A and nisin Z in milk samples by using LC-MS/MS has only been rarely reported until now, this study provides a meaningful technological advance for the dairy industry.

Determination of Tinopal CBS-X in rice papers and rice noodles using HPLC with fluorescence detection and LC-MS/MS.

To date there have been no reports of methods to determine Tinopal CBS-X. We developed a rapid and simple method to determine the Tinopal CBS-X content in rice noodles and rice papers using HPLC equipped with fluorescence detection. Heating the rice noodles and rice papers to 80°C after adding 75% methanol solution induced the release of Tinopal CBS-X from processed rice products. Tinopal CBS-X was separated using an isocratic mobile phase comprising 50% acetonitrile/water containing 0.4% tetrabutyl ammonium hydrogen sulphate at pH 8.0. The samples suspected to be positive by HPLC analysis were then confirmed by LC-MS/MS analysis. This study also investigated the Tinopal CBS-X content of three rice noodle products and two rice papers. The limits of quantification for rice papers and rice noodles were 1.58 and 1.51 µg kg(-1), respectively, and their correlation curves showed good linearity with r(2) ≥ 0.9997 and ≥ 0.9998, respectively. Moreover, rice papers had recoveries of 70.3-83.3% with precision ranging from 5.0% to 7.9%, whereas rice noodles had slightly lower recoveries of 63.4-78.7% and precisions of 8.5-11.5%. Only one rice noodle product contained Tinopal CBS-X, at around 2.1 mg kg(-1), whereas it was not detected in four other samples. Consequently, Tinopal CBS-X from rice noodles and rice papers can be successfully detected using the developed pre-treatment and ion-pairing HPLC system coupled with fluorescence detection.