SPSFAM-FLAV-11 Based from Call for Methods 12-21-2011 PAYNE ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 93, NO. 1, 2010 89 DIETARY SUPPLEMENTS Determination of Total Procyanidins in Selected Chocolate and Confectionery Products Using DMAC MARK J. PAYNE,WILLIAM JEFFREY HURST,andDAVI D A. STUART Hershey Center for Health and Nutrition, The Hershey Co., 1025 Reese Ave, Hershey, PA 17033 BOXIN OU and ELLEN FAN Brunswick Laboratories (USA), 50 Commerce Way, Norton, MA 02766 HONGPING JI and YAN KOU Brunswick Laboratories (China), 218 Xing Hu Rd, Suzhou Industrial Park, China 215125 A simple, specific, high-throughput colorimetric which the monomers are linked through C4÷C8 or, less method based on the reaction of frequently, C4÷C6 linkages. In the less common A-type 4-dimethylaminocinnamaldehyde (DMAC) with procyanidins, the monomers are connected through C2÷O÷C7 flavan-3-ols was developed to determine total or C2÷O÷C5 linkages. Procyanidins are widely distributed in procyanidins in selected cacao-based products. plants and are found in significant quantities in foods such as Extracts of defatted samples were dispensed into a fruits, spices, tea, wine, nuts, and cocoa (1). Of the many types of 96-well plate and reacted with DMAC. The polyphenols, flavan-3-ols, flavonols, and anthocyanidins are the absorbance of the reaction products was most abundant classes found in plants (2). The interest in measured at 640 nm and compared to polyphenol antioxidants has increased dramatically due to their commercially available procyanidin B2 as a ability to scavenge free radicals and their association with a standard. The use of the 96-well plates and a plate wide range of positive health benefits, including vasodilation, reader dramatically improved sample throughput. antibacterial, anticarcinogenic, anti-inflammatory, and antiviral A standard protocol was established and used for effects (3–7). More specifically, for example, studies with cocoa further studies. The calibration was found to be and dark chocolate have shown improved cardiovascular linear from 1–100 ppm. The DMAC reagent reacted function (8, 9) and lower blood pressure (10, 11). relatively specifically to (–)-epicatechin, (+)-catechin, epigallocatechin, gallocatechin, the The growing interest in procyanidins has generated a need for gallates of catechin, epicatechin, gallocatechin, improved quantitative analytical methods to determine and epigallocatechin, oligomeric procyanidins of procyanidins, particularly in complex food matrixes. cocoa up to n = 4, and A-type procyanidins. Little These methods are useful for several purposes, including or no reaction occurred with cyanidins and quantitation of procyanidin changes that occur during representative compounds of phenolic acids, food processing, assessment of food-to-food and flavones, flavanones, flavonols, anthocyanidins, category-to-category comparisons, product development, and isoflavones, and stilbenes. Sample precision test material characterization in clinical tests. A variety of studies were carried out on 10 different test methods have been developed to address this need, and have materials over several weeks, and yielded RSD been reviewed (12–14). Conventional methods of analysis, such values of 4.0 to 9.5%. The method was ring-tested as the widely used colorimetric assays with Folin reagent, in three laboratories using blinded test materials vanillin, or reaction with acidic butanol, can provide quantitative including cocoa beans, cocoa powder, chocolate results but have limitations. For example, the Folin-Ciocalteu liquor, dark chocolate, and milk chocolate. reagent reacts with all polyphenols, as well as some nonphenolic There was excellent agreement of the results compounds (e.g., ascorbic acid), yielding an overestimation of between laboratories. the total procyanidin content in a sample. The vanillin assay is very sensitive to reaction conditions and is not specific for procyanidins. More recently, reversed-phase (15, 16) and rocyanidins are oligomeric and polymeric compounds normal-phase LC methods (17–20) have been developed to belonging to the flavonoid class of polyphenols (Figure 1). separate individual procyanidin oligomers. While LC allows P separation and identification of individual components, These consist of flavan-3-ol monomeric units, typically catechin or epicatechin. The B-type procyanidins are polymers in standards for most procyanidin oligomers, particularly N > 2, are not commercially available, making direct quantitation of total procyanidins untenable because of fluorescence quenching of Received February 20, 2009. Accepted by AP June 9, 2009. longer-chain oligomeric and polymeric procyanidins. An added Corresponding author’s e-mail: [email protected] complication resulting from this quenching is that errors in SPSFAM-FLAV-11 Based from Call for Methods 12-21-2011 90 PAYNE ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 93, NO. 1, 2010 reagent for plant tissues (30–32), and as a LC postcolumn derivatization reagent (33–38). Although some initial DMAC method validation work was carried out in plasma (28), no thorough analytical method has been published on cocoa-containing materials. This report describes method validation studies and application of the DMAC assay to the determination of procyanidins in cacao-based products. Experimental Figure 1. Flavanol ring structure. Reagents (a) p-(Dimethylamino)cinnamaldehyde (DMAC, ³98% measurement of individual oligomers are compounded when purity by TLC per vendor’s certificate of analysis), large correction factors are applied and summed. (+)-catechin hydrate, (–)-epicatechin, (–)-gallocatechin, One of the more potentially useful colorimetric procedures, (–)-epigallocatechin, (–)-catechin gallate, (–)-epicatechin first applied by McMurrough and McDowell in 1978 (21) for gallate, (–)-gallocatechin gallate, (–)-epigallocatechin quantitation of flavanols in barley and hops, employs the gallate, apigenin, caffeic acid, chlorogenic acid, p-coumaric reagent 4-dimethylaminocinnamaldehyde (DMAC). The acid, daidzein, ferulic acid, gallic acid, genistein, hesperidin, ± DMAC condensation reaction with flavanols has been shown luteolin, myricetin, ( )-naringenin, quercetin hydrate, to be quite specific (12). The structural requirements for resveratrol, procyanidin B2.—Sigma-Aldrich (St. Louis, reaction are: (1) meta-substituted dihydroxybenzene rings, such MO). as the 5,7-dihydroxy substituted A-ring of catechin and (b) Cyanidin chloride, delphinidin chloride.— epicatechin; (2) a single bond between C2 and C3; and (3)the ChromaDex (Irvine, CA). lack of a carbonyl at C4 (12). In comparison to the vanillin (c) Procyanidin B1, procyanidin B2.—Indofine Chemical assay, the DMAC assay provides improved specificity, Co. (Somerville, NJ). sensitivity, is easier to perform, and reaction products do not (d) Procyanidin B2.—Planta Analytica (Danbury, CT). degrade (12). Since the McMurrough paper, the DMAC (e) Hexanes (LC grade), reagent alcohol (histological reaction has been extended to other applications, including grade), glacial acetic acid (LC grade), hydrochloric acid, determination of flavanols in beer (22), wine (23–27), 37% (ACS Plus grade), methanol (LC grade).—Thermo plasma (28), and cranberry products (29), as a flavanol-staining Fisher Scientific (Waltham, MA). Figure 2. Reaction of (+)-catechin, (–)-epicatechin, procyanidin B2 dimer (from three vendors), trimer, and tetramer standards with DMAC. SPSFAM-FLAV-11 Based from Call for Methods 12-21-2011 PAYNE ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 93, NO. 1, 2010 91 Figure 3. Calibration plot comparison showing four different lots of procyanidin B2 standard from vendor Y. Apparatus (d) 25 mm, 0.45 mm, PTFE filter disk.—Millipore (Billerica, MA) or equivalent. (a) 96-Well plate reader capable of reading at 640 nm with KC4 data acquisition and reporting software.—BioTek Operating Conditions Instruments, Inc. (Winooski, VT). The temperature of the plate reader was set to 25°Cand (b) 96-Well plate, flat-bottomed, polystyrene.—Thermo allowed to equilibrate for at least 15 min prior to use. The Fisher Scientific or equivalent. UV-Vis detector in the reader was set to 640 nm. The software (c) 12-Channel digital pipettor.—Thermo Fisher was programmed to shake the 96-well plate for 3 s, then read Scientific. the wells at 1 min intervals for 12 min. Figure 4. Response of selected polyphenolic compounds (at 10 ppm) after reaction with the DMAC reagent. SPSFAM-FLAV-11 Based from Call for Methods 12-21-2011 92 PAYNE ET AL.: JOURNAL OF AOAC INTERNATIONAL VOL. 93, NO. 1, 2010 Table 1. Determination of sample precision Test material Fat, % n Mean, mg/ga SD RSD, % Cocoa bean (Ivory Coast) 54.4 7 14 1.11 7.8 Liquor A 53 15 16 1.27 8.0 Liquor B 54.9 8 19 0.64 3.4 Cocoa powder, natural 10.5 10 47 1.88 4.0 Alkalized cocoa powder 11 6 1.7 0.07 4.1 Dark chocolate A 35.2 10 9.4 0.34 3.7 Dark chocolate B 34.4 10 11 0.63 5.7 Dark chocolate C 42.4 6 7 0.66 9.5 Dark chocolate D 30 44 5.2 0.46 8.6 Milk chocolate 29.3 10 2.5 0.15 5.9 a Total procyanidins, B2 equivalents, on a whole product basis. Preparation of DMAC Solution Analysis For each full 96-well plate to be analyzed, 24 mL DMAC All blanks, standards, and samples were plated in triplicate. m solution was required. To prepare 30 mL DMAC solution, The 96-well plate was prepared by dispensing 50 L alcohol m HCl (3.0 mL) was added to 27 mL reagent alcohol, stoppered (which serves as the blank and zero-level standard), 50 L m with a glass or plastic stopper, and the solution was