Short communication: Development of a novel method for the extraction of norbixin from whey and its subsequent quantification via high performance liquid chromatography

Norbixin is the primary carotenoid in annatto coloring, which imparts the desired orange color in Cheddar cheese. However, a portion of the colorant remains in the cheese whey and is undesirable; therefore, a bleaching step is often applied. Restrictions exist for norbixin concentrations in products destined for infant formula. As such, evaluation of norbixin concentrations in whey and whey ingredients is desirable. Current extraction methods are laborious and require solvents that are banned in many countries. The objective of this study was to develop a fast and inexpensive norbixin extraction and quantitation technique using approved solvents with similar sensitivity to current established methods. Instead of solvent extraction and column purification, acetonitrile was added directly to fluid wheys, retentates, and rehydrated whey protein concentrates. An isocratic mobile phase [70% acetonitrile and 30% water with 0.1% (wt/vol) formic acid] was used and, to increase sensitivity, a large volume (50 μL) was injected onto the column. The column used was a C18 column with a particle size of 2.6 μm and column length of 10 cm. The column inner diameter was 4.6 mm and the pore size was 100 Ǻ. All of the previously described conditions allowed the run time to be only 4 min. The sample was sent through a photodiode array detector and quantified at 482 nm. Norbixin was quantified using external standard curves. The developed method had a >90% norbixin recovery in both milk and whey (9.39 μg/L-2.35 mg/L). The limit of detection of norbixin in fluid whey was 2.7 μg/kg and the limit of quantitation was 3.5 μg/kg, both of which are significantly lower than in previously described methods. The extracts were stable over 30 min at 21°C and stable over 24 h at 4°C. Repeatability and precision of the method had relative standard deviations of less than 13%. The developed method provides time and cost savings for evaluation of norbixin concentration in whey and whey products.