The multivariate calibration methods—principal component regression (PCR) and partial least squares (PLSs)—were employed for the prediction of total phenol contents of four Prunella species. High performance liquid chromatography (HPLC) and spectrophotometric approaches were used to determine the total phenol content of the Prunella samples. Several preprocessing techniques such as smoothing, normalization, and column centering were employed to extract the chemically relevant information from the data after alignment with correlation optimized warping (COW). The importance of the preprocessing was investigated by calculating the root mean square error (RMSE) for the calibration set of the total phenol content of Prunella samples. The models developed based on the preprocessed data were able to predict the total phenol content with a precision comparable to that of the reference of the Folin-Ciocalteu method. PLS model seems preferable, because of its predictive and describing abilities and good interpretability of the contribution of compounds to the total phenol content. Multivariate calibration methods were constructed to model the total phenol content of the Prunella samples from the HPLC profiles and indicate peaks responsible for the total phenol content successfully. 1. Introduction Prunella, belongs to the family of Lamiaceae, seems to be a rich source of plant species contain high amounts of phenolic compounds and anthocyanins [1, 2]. The research on antioxidant compounds in the Lamiaceae family has been focused on phenolic diterpenes, flavonoids and phenolic acids [3–6]. Several studies have shown that Prunella species exhibit high antioxidant potentials, which are tightly connected with the total phenolic content [7, 8]. The antioxidant activity could be dependent on the extraction solvent, the hydrophilicity of compounds, the sample, and type of phenolic compounds, which means that different phenolic compounds react in different ways in antioxidant activity assays. The phenolic compounds prove the importance of antioxidant behaviour and contribute significantly to the total antioxidant activity of medicinal and aromatic samples [9, 10]. Total phenolic content of plants is an important parameter for their antioxidant properties. The Folin-Ciocalteu procedure of Singleton [11] has been used as a measure of total phenolics in natural products for many years. On the other hand, analytical techniques have been used to isolate, identify, and determine individual phenolic compounds by gas chromatography and mass spectrometry (GC-MS) [12, 13], high
References
[1]
J. Psotová, M. Kolá？, J. Sou？ek, Z. ？vagera, J. Vi？ar, and J. Ulrichová, “Biological activities of Prunella vulgaris extract,” Phytotherapy Research, vol. 17, no. 9, pp. 1082–1087, 2003.
[2]
J. Sendra, “Phytochemical studies on Prunella vulgaris and Prunella grandiflora-flavonoids and Phenolicarnoxylic acids,” Dissertations on Pharmacy, vol. 15, no. 4, pp. 483–489, 1963.
[3]
J. H. Chen and C. T. Ho, “Antioxidant activities of Caffeic acid and its related Hydroxycinnamic acid compounds,” Journal of Agricultural and Food Chemistry, vol. 45, no. 7, pp. 2374–2378, 1997.
[4]
M. E. Cuvelier, C. Berset, and H. Richard, “Antioxidant constituents in sage (Salvia officinalis),” Journal of Agricultural and Food Chemistry, vol. 42, no. 3, pp. 665–669, 1994.
[5]
M. P. K？hk？nen, A. I. Hopia, H. J. Vuorela et al., “Antioxidant activity of plant extracts containing phenolic compounds,” Journal of Agricultural and Food Chemistry, vol. 47, no. 10, pp. 3954–3962, 1999.
[6]
K. Schwarz and W. Ternes, “Antioxidative constituents of Rosmarinus officinalis and Salvia officinalis-II. Isolation of carnosic acid and formation of other phenolic diterpenes,” Zeitschrift für Lebensmittel-Untersuchung und -Forschung, vol. 195, no. 2, pp. 99–103, 1992.
[7]
M. G. L. Hertog, E. J. M. Feskens, P. C. H. Hollman, M. B. Katan, and D. Kromhout, “Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study,” The Lancet, vol. 342, no. 8878, pp. 1007–1011, 1993.
[8]
J. L. Lamaison and C. Petitjean-Freytet, “Derives hydroxycinnamiques et flavonoides dans le genre Prunella (Lamiaceae): activites antioxydantes et interet chimiotaxonomique,” Plantes Medicinales et Phytotherapie, vol. 24, pp. 152–157, 1990.
[9]
M. V. Eberhardt, C. Y. Lee, and R. H. Liu, “Antioxidant activity of fresh apples,” Nature, vol. 405, no. 6789, pp. 903–904, 2000.
[10]
H. Wang, G. Cao, and R. L. Prior, “Total antioxidant capacity of fruits,” Journal of Agricultural and Food Chemistry, vol. 44, no. 3, pp. 701–705, 1996.
[11]
V. L. Singleton and J. A. Rossi, “Colorimetry of total phenolics with phosphomolybdic and phosphotungstic acid reagents,” American Journal of Enology and Viticulture, vol. 16, pp. 144–147, 1965.
[12]
Y. C. Fiamegos, C. G. Nanos, J. Vervoort, and C. D. Stalikas, “Analytical procedure for the in-vial derivatization–extraction of phenolic acids and flavonoids in methanolic and aqueous plant extracts followed by gas chromatography with mass-selective detection,” Journal of Chromatography A, vol. 1041, no. 1-2, pp. 11–18, 2004.
[13]
C. Proestos, D. Sereli, and M. Komaitis, “Determination of phenolic compounds in aromatic plants by RP-HPLC and GC-MS,” Food Chemistry, vol. 95, no. 1, pp. 44–52, 2006.
[14]
H. J. D. Dorman, O. Bachmayer, M. Kosar, and R. Hiltunen, “Antioxidant properties of aqueous extracts from selected Lamiaceae species grown in Turkey,” Journal of Agricultural and Food Chemistry, vol. 52, no. 4, pp. 762–770, 2004.
[15]
C. Türkben, E. Sariburun, C. Demir, and V. Uyla？er, “Effect of freezing and frozen storage on phenolic compounds of raspberry and blackberry cultivars,” Food Analytical Methods, vol. 3, no. 3, pp. 144–153, 2010.
[16]
G. R. Beecher, B. A. Warden, and H. Merken, “Analysis of tea polyphenols,” Proceedings of the Society for Experimental Biology and Medicine, vol. 220, no. 4, pp. 267–270, 1999.
[17]
S. ？ahin, C. Demir, and ？. Gü？er, “Simultaneous UV-vis spectrophotometric determination of disperse dyes in textile wastewater by partial least squares and principal component regression,” Dyes and Pigments, vol. 73, no. 3, pp. 368–376, 2007.
[18]
S. ？ahin, E. Sariburun, and C. Demir, “Net analyte signal-based simultaneous determination of dyes in environmental samples using moving window partial least squares regression with UV-vis spectroscopy,” Analytical Methods, vol. 1, no. 3, pp. 208–214, 2009.
[19]
Y. Z. Liang, P. Xie, and K. Chan, “Quality control of herbal medicines,” Journal of Chromatography B, vol. 812, no. 1-2, pp. 53–70, 2004.
[20]
H. F. M. Boelens, R. J. Dijkstra, P. H. C. Eilers, F. Fitzpatrick, and J. A. Westerhuis, “New background correction method for liquid chromatography with diode array detection, infrared spectroscopic detection and Raman spectroscopic detection,” Journal of Chromatography A, vol. 1057, no. 1-2, pp. 21–30, 2004.
[21]
P. H. C. Eilers, “A perfect smoother,” Analytical Chemistry, vol. 75, no. 14, pp. 3631–3636, 2003.
[22]
M. Daszykowski, Y. Vander Heyden, and B. Walczak, “Robust partial least squares model for prediction of green tea antioxidant capacity from chromatograms,” Journal of Chromatography A, vol. 1176, no. 1-2, pp. 12–18, 2007.
[23]
C. Christin, A. K. Smilde, H. C. J. Hoefsloot, F. Suits, R. Bischoff, and P. L. Horvatovich, “Optimized time alignment algorithm for LC-MS data: correlation optimized warping using component detection algorithm-selected mass chromatograms,” Analytical Chemistry, vol. 80, no. 18, pp. 7012–7021, 2008.
[24]
D. Clifford, G. Stone, I. Montoliu et al., “Alignment using variable penalty dynamic time warping,” Analytical Chemistry, vol. 81, no. 3, pp. 1000–1007, 2009.
[25]
T. Skov, F. Van Den Berg, G. Tomasi, and R. Bro, “Automated alignment of chromatographic data,” Journal of Chemometrics, vol. 20, no. 11-12, pp. 484–497, 2006.
[26]
G. Tomasi, F. Van Den Berg, and C. Andersson, “Correlation optimized warping and dynamic time warping as preprocessing methods for chromatographic data,” Journal of Chemometrics, vol. 18, no. 5, pp. 231–241, 2004.
[27]
N. P. V. Nielsen, J. M. Carstensen, and J. Smedsgaard, “Aligning of single and multiple wavelength chromatographic profiles for chemometric data analysis using correlation optimised warping,” Journal of Chromatography A, vol. 805, no. 1-2, pp. 17–35, 1998.
[28]
N. Nguyen Hoai, B. Dejaegher, C. Tistaert et al., “Development of HPLC fingerprints for Mallotus species extracts and evaluation of the peaks responsible for their antioxidant activity,” Journal of Pharmaceutical and Biomedical Analysis, vol. 50, no. 5, pp. 753–763, 2009.
[29]
C. Tistaert, B. Dejaegher, N. Nguyen Hoai et al., “Potential antioxidant compounds in Mallotus species fingerprints. Part I: indication, using linear multivariate calibration techniques,” Analytica Chimica Acta, vol. 649, no. 1, pp. 24–32, 2009.
[30]
A. M. Van Nederkassel, M. Daszykowski, D. L. Massart, and Y. Vander Heyden, “Prediction of total green tea antioxidant capacity from chromatograms by multivariate modeling,” Journal of Chromatography A, vol. 1096, no. 1-2, pp. 177–186, 2005.
[31]
S. ？ahin, C. Demir, and H. Malyer, “Determination of phenolic compounds in Prunella L. by liquid chromatography-diode array detection,” Journal of Pharmaceutical and Biomedical Analysis, vol. 55, no. 5, pp. 1227–1230, 2011.
[32]
K. Gü？lü, M. Altun, M. ？zyürek, S. E. Karademir, and R. Apak, “Antioxidant capacity of fresh, sun- and sulphited-dried Malatya apricot (Prunus armeniaca) assayed by CUPRAC, ABTS/TEAC and folin methods,” International Journal of Food Science and Technology, vol. 41, no. 1, pp. 76–85, 2006.
[33]
J. Vial, H. No？airi, P. Sassiat et al., “Combination of dynamic time warping and multivariate analysis for the comparison of comprehensive two-dimensional gas chromatograms. Application to plant extracts,” Journal of Chromatography A, vol. 1216, no. 14, pp. 2866–2872, 2009.
[34]
R. G. Brereton, Chemometrics Data Analysis for the Laboratory and Chemical Plant, John Wiley & Sons, Chichester, UK, 2003.
[35]
H. B. Li, C. C. Wong, K. W. Cheng, and F. Chen, “Antioxidant properties in vitro and total phenolic contents in methanol extracts from medicinal plants,” Food Science and Technology, vol. 41, no. 3, pp. 385–390, 2008.
[36]
Y. Cai, Q. Luo, M. Sun, and H. Corke, “Antioxidant activity and phenolic compounds of 112 traditional Chinese medicinal plants associated with anticancer,” Life Sciences, vol. 74, no. 17, pp. 2157–2184, 2004.
[37]
H. Y. Cheung and Q. F. Zhang, “Enhanced analysis of triterpenes, flavonoids and phenolic compounds in Prunella vulgaris L. by capillary zone electrophoresis with the addition of running buffer modifiers,” Journal of Chromatography A, vol. 1213, no. 2, pp. 231–238, 2008.
