Analysis of Functional Sugars in Foods Using HILIC Mode

TM Technical Article No. 010

Introduction Results and Discussion Recently, the effects of functional sugars in foods are 1. Analysis of Lactulose gaining scientists’ interests, and thus their analytical Lactulose is a functional sugar found in dairy products methods are called for. and it regulates intestinal health of humans. Lactulose Shodex™ HILICpak™ VG-50 series used in this remains undigested and reaches the intestine application is a set of polymer-based amino columns which unabsorbed, and then Bifidobacterium uses the sugar effectively separate various saccharides. The packing for its proliferation. The structures of lactulose, lactose, material consists of a polyvinyl alcohol base with a and epilactose are very similar, which makes their hydrophilic functional group, a modified tertiary amine chromatographic separation challenging. (Fig. 1) A mixture of acetonitrile and water (or buffer) eluent is generally used in HILIC mode separation. We used a mixture of acetonitrile and water as a starting eluent to separate three above mentioned disaccharides. Figure 2 shows the obtained results. We tested different ratios of acetonitrile and water, however, none were able to separate the three saccharides completely. Higher acetonitrile ratio made the retention time longer and increased the baseline Fig. 1. Schematic diagram of VG-50 packing material noise. This resulted in lowering the signal to noise With some columns, reducing sugars form a Schiff base ratio (S/N). with the packing material and are retained in the column. This does not occur with the HILICpak™ VG-50 series columns, leading to the series’ ability to achieve a high recovery rate. Moreover, column bleeding (elution of column packing material related debris) that is often 1. Lactulose observed with silica-based amino columns is rarely found 2. Epilactose with the HILICpak™ VG-50 series columns, and 3. Lactose consequently the related problems of increased

background and/or ion suppression in MS are less likely to H2O/CH3CN = 20/80 occur. Another advantage of this column over the silica- based amino column is that the HILICpak™ VG-50 series columns can be used under alkaline conditions (working pH H2O/CH3CN = 15/85 range, 2 to 13). 0 5 10 15 20 25 min In this work, we optimized analytical conditions for the Sample : 5 mg/mL each in H2O/CH3CN = 1/1, 5 μL analysis of functional sugars in foods using HILICpak™ Column : Shodex HILICpak VG-50 4E VG-50 4E (4.6 mm I.D. x 250 mm; particle size 5 μm), Eluent : H2O/CH3CN = 20/80 or 15/85 including the preparation methods for actual food products. Flow rate : 1.0 mL/min Detector : RI Column temp.: 40 ºC

Fig. 2. Optimization of LC conditions for lactulose analysis (1)

2. Analysis of Rare Sugars As a next step, we added methanol to the eluent. Figure 3 Rare sugars slow down the blood sugar level elevation shows the result of analyzing the three disaccharides using after a meal and inhibit the accumulation of visceral fat. The an eluent mixture of water, acetonitrile, and methanol. The use of rare sugars in commercial food products have been addition of methanol to the eluent effectively separated the recently increasing. Moreover, as rare sugars are known to disaccharides that have very similar structures. Good provide various bioactive effects, their potential applications linearity was obtained for the calibration curves of all in medicinal products, functional foods, and cosmetics have sugars, showing the method’s applicability for the been studied. In this work, we developed a method for quantification of the three disaccharides. separating six rare sugars, the ones fulfilling the International Institute of Rare Sugar Research and 1. Lactulose 2. Epilactose 600,000 Education’s definition of rare sugars (L-ribose, D-psicose, 3. Lactose Lactulose R2 = 0.9995 Epilactose R2 = 0.9994 xylitol, D-tagatose, D-allose, and L-glucose). 400,000 Lactose R2 = 0.9991 First, similar to the approach we took in “1. Analysis of peak area 200,000 Lactulose”, we used water/acetonitrile eluent for the separation of six rare sugars. Figure 5 shows the resulting 0 0 0.1 0.2 0.3 0.4 0.5 0 5 10 15 min concentration (%) chromatograms. Increase of acetonitrile ratio again lowered the S/N, and we concluded that the use of water/acetonitrile Sample : 5 mg/mL each in H2O/CH3CN = 1/1, 5 μL eluent cannot provide complete separation of all six rare Column : Shodex HILICpak VG-50 4E Eluent : H2O/CH3CN/CH3OH = 5/75/20 sugars. Flow rate : 1.0 mL/min Detector : RI 1. L-Ribose 2. D-Psicose Column temp.: 40 ºC 3. Xylitol 4. D-Tagatose Fig. 3. Optimization of LC conditions for lactulose analysis (2) 5. D-Allose 6. L-Glucose H2O/CH3CN = 20/80 To examine its feasibility of analyzing the real samples, we applied the method to analyze a commercial probiotic milk beverage that claims to contain lactulose. As a sample H2O/CH3CN = 15/85 pretreatment, we used the following procedures to remove the protein. Take 1 mL of the probiotic milk beverage and 0 5 10 15 min add 1 mL of acetonitrile. Centrifuge the mixture at 890 g for Sample : 5 mg/mL each in H2O/CH3CN = 1/1, 5 μL 10 minutes, and then filter the supernatant with a 0.45-μm Column : Shodex HILICpak VG-50 4E Eluent : H2O/CH3CN = 20/80 or 15/85 membrane filter. The obtained solution was used for the Flow rate : 1.0 mL/min analysis. Figure 4 shows the result of analyzing lactulose in Detector : RI : 40 ºC probiotic milk beverages. Lactulose was detected in the two Column temp. test samples analyzed, and it was well separated from other Fig. 5. Optimization of LC conditions for rare sugar analysis (1) saccharides. This demonstrated the effectiveness of the VG-50 for the analysis of lactulose in milk beverages. Next, we tested the eluent containing water, acetonitrile, and methanol (Fig.6). The addition of methanol to the eluent

Sample: 5 μL effectively separated the six rare sugars. Good lineality 1. Fructose 5. Epilactose 2. Galactose 6. Sucrose was obtained for the calibration curves of all rare sugars, 3. Glucose 7. Lactose indicating its feasibility for the quantification of those 4. Lactulose sugars.

Probiotic milk beverage (A)

Probiotic milk beverage (B)

Standards

0 5 10 15 min Refer to Fig.3 for analytical conditions used.

Fig. 4. Analysis of lactulose in probiotic milk beverages

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3. Analysis of Ethyl α-D-glucoside

1. L-Ribose 4. D-Tagatose Ethyl α-D-glucoside is an umami component specifically 2. D-Psicose 5. D-Allose found in sake (Japanese rice wines). Recent studies show 3. Xylitol 6. L-Glucose that it has a moisturizing effect, and the effects have been focused upon for cosmetic uses. In this study, we developed a method to simultaneously analyze ethyl α-D-glucoside and several saccharides generally present in sake. We used a 0 5 10 15 20 min mixture containing four saccharides and ethyl α-D-glucoside as a standard. Using an eluent containing water/acetonitrile Sample : 5 mg/mL each in H2O/CH3CN = 1/1, 5 μL = 20/80 effectively separated the target compounds (Fig. 8). Column : Shodex HILICpak VG-50 4E Eluent : H2O/CH3CN/CH3OH = 5/75/20 Good linearity was obtained for all analytes, showing the Flow rate : 1.0 mL/min method’s feasibility for the quantification of saccharides and Detector : RI ethyl α-D-glucoside. Column temp.: 40 ºC 1. Ethyl α-D-Glucoside Fig. 6. Optimization of LC conditions for rare sugar analysis (2) 2. Fructose 3. Glucose To examine its feasibility of analyzing the real samples, 4. Sucrose 5. Maltose we applied this method to analyze a commercial syrup containing rare sugars. As a sample pretreatment, we took 0.1 g of the syrup into a test tube and added 2.5 mL of ultra- pure water, capped the test tube and manually shook it to dissolve the syrup. After making sure that the syrup was 0 5 10 15 min completely dissolved, 2.5 mL of acetonitrile was added. Sample : 1 mg/mL each in H2O/CH3CN = 1/1, 10 μL : Shodex HILICpak VG-50 4E Then, shook the tube again to mix the solutions and filtered Column Eluent : H2O/CH3CN = 20/80 the mixture with a 0.45-μm membrane filter. The obtained Flow rate : 1.0 mL/min solution was used for the analysis. Figure 7 shows the result Detector : RI Column temp.: 40 ºC of analyzing rare sugars in the syrup. By comparing the chromatograms of the syrup and the standards, the syrup Fig. 8. Optimization of LC conditions for ethyl α-D-glucoside analysis most likely contained D-psicose and D-allose. They were To examine its feasibility of analyzing the real samples, well separated from other saccharides. A peak was also we applied this method to analyze a commercial sake. We detected at L-glucose’s position, but as D-glucose also has prepared the sample as following. Take 1 mL of sake into a an identical retention time, its D or L configuration was not test tube and add 1 mL of acetonitrile. Cap the test tube identified in this analysis condition. and manually shook it to mix the solutions, and then filter

Sample: 5 μL the mixture with a 0.45-μm membrane filter. The obtained 1. L-Ribose 5. Fructose solution was used for the analysis. By comparing the 2. D-Psicose 6. D-Allose 3. Xylitol 7. Galactose chromatograms of the samples and the standards, 4. D-Tagatose 8. L-Glucose ethyl α-D-glucoside and glucose were found in the sake. Rare sugar syrup An unidentified peak was found after the ethyl α-D-glucoside peak. The LC/MS result showed that the unidentified compound was consisted of two components Standards having molecular weights of 138 and 252.

0 5 10 15 20 25 min Refer to Fig.6 for analytical conditions used.

Fig. 7. Analysis of rare sugar syrup

ShodexTM Technical Article No.010 Page 003 Technical Article No. 010

Sample: 10 μL 1. Ethyl α-D-Glucoside 2. Fructose Sake (A) 3. Glucose 4. Sucrose 5. Maltose

Sake (B)

Standards 0 5 10 15 min Refer to Fig.8 for analytical conditions used.

Fig. 9. Analysis of ethyl α-D-glucoside in sake

Conclusions This article demonstrated the effectiveness of Shodex™ HILICpak™ VG-50 4E with its HILIC mode for the analysis of various functional sugars in foods. The eluent typically used in HILIC mode is a mixture of water and acetonitrile. However, the use of a mixture containing water, acetonitrile, and methanol improved the separation efficiencies of the VG-50 4E for some applications. We also proved the effectiveness of the developed method for analyzing functional sugars in real food products.

Reference Shodex™ Technical Article No.3: LC/MS Analysis of Various Hydrophilic Compounds Using HILIC Mode and Alkaline Eluent. The article introduces an LC/MS analysis of nutritional components in a commercial energy drink using the HILICpak™ VG-50 2D column. The polymer-based packing materials allowed the use of alkaline eluent. The nutritional components included were saccharides, amino acids, caffeine, and water-soluble vitamins. All components were successfully and simultaneously analyzed using the method. Please read technical article No. 3 for details.

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Figures and descriptions in this article are provided to help you select appropriate columns. However they do not guarantee nor warrant the suitability for your applications. TA．NO．010．(2) 20 D．SEP．P

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