Abstract:
This invention relates to a method for stabilizing quercetin by placing it in a solution containing vitamin B3 and vitamin C and assessing stability of the quercetin in the mixture.

Description:
BACKGROUND 
       [0001]    It is known that certain natural antioxidants, such as quercetin, inhibit both acute and chronic phases of free-radical induced diseases. Further, some natural antioxidants exhibit synergy in their reactions with biologically relevant oxygen species, e.g., hydroxyl radicals, superoxides, oxysulfurs, sulfur dioxide, and nitrogen dioxide. 
         [0002]    However, quercetin is unstable when placed in an aqueous solution. It is therefore desirable to develop a method to increase quercetin stability. 
       SUMMARY 
       [0003]    The present invention is based on the unexpected finding that quercetin is much more stable in a solution also containing vitamins B3 and C than in a solution containing only quercetin. 
         [0004]    Accordingly, this invention features a method for stabilizing quercetin by placing it in a solution (e.g., an aqueous solution) containing vitamin B3 and vitamin C to form a mixture and then assessing the stability of the quercetin in the mixture after an extended period of time (e.g., two weeks, two month, or one year). In the mixture, which can be in suspended form, quercetin, vitamin B3, and vitamin C preferably have a weight ratio of 1:0.02-1:0.2-2.5 (e.g., 1:0.08:1). The concentration of quercetin can range from 20 mg/L to 10 g/L (e.g., 500 mg/L to 2 g/L). 
         [0005]    The details of one or more embodiments of the invention are set forth in the description below. Other features or advantages of the present invention will be apparent from the following drawing and detailed description of several embodiments, and also from the appending claims. 
     
    
     
       DESCRIPTION OF THE DRAWING 
         [0006]      FIG. 1  is a chart showing stability of quercetin in two aqueous solutions containing quercetin alone (QP2-Q), and quercetin, vitamin B3, and vitamin C (QP1-QB3C), respectively, and an acidic solution containing quercetin alone (QP3-Q). 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    One can stabilize quercetin by either dissolving or suspending it in a solution containing vitamin B3 and vitamin C to form a mixture. 
         [0008]    The weight ratio between quercetin, vitamin B3, and vitamin C in the mixture can be 1:0.02-1:0.2-2.5, or any ratio in between. For example, the weight ratio can be 1:0.04-0.5:0.3-2.0, 1:0.05-0.3:0.4-1.5, 1:0.05-0.2:0.5-1, and 1:0.1-0.2:0.5-1. Preferred ratios include 1:0.02:1, 1:0.04:1, 1:0.08:1, 1:0.05:1.5, and 1:0.16:1. The term “quercetin” refers to both quercetin aglycon and quercetin derivatives, e.g., quercetin-3-O-glucoside, quercetin-5-O-glucoside, quercetin-7-O-glucoside, quercetin-9-O-glucoside, quercetin-3-O-rutinoside, quercetin-3-O-[α-rhamnosyl-(1→2)-α-rhamnosyl-(1→6)]-β-glucoside, quercetin-3-O-galactoside, quercetin-7-O-galactoside, quercetin-3-O-rhamnoside, and quercetin-7-O-galactoside. After digestion, quercetin derivatives are converted to quercetin aglycon and other active derivatives, which are absorbed in the body. The quantity of quercetin mentioned above refers to that of quercetin aglycon or the quercetin moiety of a quercetin derivative. Quercetin can be added to the composition either in a pure form or as an ingredient in a mixture (e.g., a plant extract). Examples of commercially available quercetin include QU995 (containing 99.5% quercetin) and QU985 (containing 98.5% quercetin) from Quercogen Pharma LLC (Newton, Mass.) and Merck KGaA (Brazil). “Vitamin B3” mentioned herein includes vitamin B3 in its various forms, including niacinamide, nicotinic acid, nicotinamide, inositol hexaniacinate. “Vitamin C” mentioned herein includes vitamin C (i.e., L-ascorbic acid, D-ascorbic acid, or both) and its salts (e.g., sodium ascorbate). 
         [0009]    The vitamin B3/vitamin C solution can be prepared by dissolving vitamin B3 and vitamin C in a suitable solvent, such as a pure solvent (e.g., water) or a mixture of two or more solvents. One or more quercetins are then dissolved or suspended in the vitamin B3/vitamin C solution to form a mixture. The mixture can be stored at a suitable temperature (e.g., 20 or 25° C.) for an extended period of time (e.g., two weeks or two month). During the storage, the quercetin content in the mixture is determined periodically (e.g., every 24 hours or every week) via conventional methods, e.g., HPLC, to assess quercetin stability. 
         [0010]    Without further elaboration, it is believed that the above description has adequately enabled the present invention. The following example is, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
       Stability of Quercetin and Quercetin/Vitamine B3/Vitamine C in Aqueous Solutions 
       [0011]    An aqueous solution containing 0.1% (w/v) quercetin (coded “QP2-Q”) was prepared, kept in 12 sealed 60-ml glass bottles, i.e., bottles 1-12, and incubated at 75° C. More specifically, 50 ml of the solution were placed in each glass bottle. Quercetin contents in bottles 1-12 were determined by HPLC on day 1 to day 12, respectively. They were compared with the quercetin content on day 0 to obtain “% Recovery Relative to Control,” shown in  FIG. 1 . as follows: 
         [0000]      % Recovery Relative to Control=(Quercetin content on day  X )/(Quercetin content on day 0) 
         [0012]    The same analysis as described above was applied to an aqueous solution containing quercetin, vitamin B3, and vitamin C at a ratio of 1:0.08:1 by weight (coded “QP1-QB3C”) and to an acidic solution (pH 2.6) containing 0.1% (w/v) quercetin (coded “QP3-Q”). Based on the results thus obtained, stability curves were prepared. Also see  FIG. 1 . 
         [0013]    The quercetin contents in QP1-QB3C remained unchanged during the 12-day incubation period. By contrast, the quercetin contents in QP2-Q and QP3-Q decreased by about 15% and 10% respectively during the 12-day incubation. These results indicate that quercetin was stabilized by the presence of vitamin B3 and vitamin C in the solution. 
       Other Embodiments 
       [0014]    All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features. 
         [0015]    From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the scope of the following claims.