Analysis of Menaquinone-7 Content and Impurities in Oil and Non-Oil Dietary Supplements

Abstract

Rapid, global technological development has caused the food industry to use concentrated food component sources like dietary supplements ever more commonly as part of the human diet. This study analysed the menaquinone-7 (MK-7) content of dietary supplements in oil capsule and hard tablet forms. A novel method for separating and measuring geometric isomers of MK-7 in dietary supplements was developed and validated. Eleven different isomers of cis/trans- menaquinone-7 were identified. Identification of cis/trans isomers was performed by combination of HPLC, UPLC and HRMS-QTOF detection, whereas their quantities were determined by DAD detection. The content of menaquinone impurities was ascertained, including cis/trans- menaquinone-6 isomers (5.5–16.9 µg per tablet/capsule) and cis/trans-menaquinone-7 isomers (70.9–218.7 µg tablet/capsule), which were most likely formed during the chemical synthesis of the menaquinone-7. The all-trans MK-7 content was lower than the isomeric form and often lower than what the labels declared. A new method of quantification, developed and validated for menaquinones in oil capsules, provided on average 90% recovery and a limit of quantification (LOQ) of approximately 1 µg mL−1.

Optimisation of the fermentation media to enhance the production of the bioactive isomer of vitamin menaquinone-7

“…Relative to traditional MK-7 analytical techniques, which do not consider the isomer composition of samples, the analysis and measurement of MK-7 isomers present various difficulties. The fundamental issue is the absence of specific analytical standards for the potential cis forms of the vitamin, as only the all-trans MK-7 standard is commercially available [8,36]. As a result, the identification and quantification of cis MK-7 pose a challenge due to the lack of appropriate reference standards.…”

“…However, it is essential to note that, like most biological molecules, MK-7 can exist as geometric isomers, of which only the naturally occurring all-trans isomer is bioactive [6,8,36]. The double bond arrangement in the isoprenoid side chain of MK-7 molecules determines its shape and, consequently, its biological activity [6,37].…”

“…The concept of MK-7 isomers is a relatively recent and emerging area of interest; thus, insufficient research has been conducted on this aspect, and a great deal is yet to be explored. MK-7 can be produced from fermentation [15,41] or through chemical reaction methods [13,[42][43][44][45], and the isomer composition that is obtained is dependent on a variety of factors, primarily the methods used for the synthesis of the vitamin and purification of the post-reaction mixture [6,8,36,38]. The molecular structure of MK-7 comprises seven double bonds, and in the all-trans isomer, all seven double bonds have the trans configuration.…”

“…Moreover, the number and type of different cis isomers that can potentially be achieved are ambiguous, as very few studies have considered this aspect and often present conflicting information. The majority of investigations that have focused on analysing the MK-7 isomer composition have explored dietary supplements or similar formulations [6,8,36,46], and thus far, studies examining fermented samples have not been carried out. Additionally, the number and type of cis isomers that can be obtained from fermentation are unknown, as although fermentation is believed to produce the all-trans isomer selectively, the MK-7 isomer profile of fermented samples is yet to be elucidated.…”

Simultaneous Determination of Vitamins D3 (Calcitriol, Cholecalciferol) and K2 (Menaquinone-4 and Menaquinone-7) in Dietary Supplements by UHPLC

“…The regression coefficient for all calibration curves was greater than 0.999 (Figure 2a-d). The obtained results were better than those found in the literature, which considers that a regression coefficient above 0.99 is satisfactory [15][16][17][18][19][20][21][22][23]. The LOD and LOQ of the target analytes are presented in Table 2.…”