Correspondence/Rebuttal pubs.acs.org/JAFC
Comment on Addressing Analytical Requirements To Support Health Claims on “Olive Oil Polyphenols” (EC Regulation 432/212)
I
stress” is noteworthy.5 However, there is not an official method for the analysis of these substances in olive oil, and the one proposed by the International Olive Council (IOC) is under revision.6 In fact, the IOC is currently discussing several methods for analyzing the phenolic compounds in olive oils, and one of them is based on the hydrolysis of the secoiridoid substances. Consequently, it is of great importance to take into consideration the results reported in Table 1 and to conclude that protocol 2 by Romero and Brenes2 provides values equal to or higher than those given by protocol 2 by Mulinacci et al.,3 without the necessity of an extraction step of the polar fraction.
n a recent paper published in this Journal, Mastralexi et al.1 compared two methods for analyzing the total contents of hydroxytyrosol and tyrosol in olive oil. Both methods involve the hydrolysis of the derived bound forms of these compounds to their total free forms. The first method was studied by Mulinacci et al.2 (protocol 1), and it requires a previous extraction of the phenolic compounds from the oil and further hydrolysis with 1 M H2SO4 at 80 °C. The other method proposed by Romero and Brenes3 (protocol 2) implies direct hydrolysis with 2 M HCl at ambient temperature without a previous extraction step. Mastralexi et al.1 applied the two protocols to a series of extra virgin olive oils, and they concluded that the yields of both compounds, hydroxytyrosol and tyrosol, were much lower when using protocol 2 than protocol 1. They also tested the agitation speed as an important parameter for protocol 2,2 but they did not find it as critical. Surprisingly, they found the yields of total hydroxytyrosol and tyrosol to be >2−7 times higher with protocol 1 than with protocol 2. We have analyzed the total contents of hydroxytyrosol and tyrosol in four commercial extra virgin olive oils in triplicate using both protocols with the aim of verifying these differences. The results are shown in Table 1 and, as can be seen, the yields of both free phenols were not lower due to using protocol 2 rather than protocol 1. In contrast, our own data clearly show that protocol 2 gives rise to equal or higher yields than protocol 1 in most cases. It must be noted that protocol 1 requires an extraction step of the phenolic compounds prior to the acidic hydrolysis that sometimes is not exhaustive.4 We have no explanation for the contradictory results found by Mastralexi et al.1 except that the calculation of the concentration of hydroxytyrosol and tyrosol in oils was not correctly made. In fact, 2.5 g of oil is used with both protocols, but different dilutions are applied during the manipulation of the samples, and that factor must be taken into account. The beneficial effect that olive oil polyphenols exert on health is well-known, and the European Food Safety Authority (EFSA) has recently approved a health claim stating that “their contribution to the protection of blood lipids from oxidative
Concepción Romero Manuel Brenes*
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Food Biotecnology Department, Instituto de la Grasa (IG-CSIC), Avenida Padre Garcı ́a Tejero 4, 41012 Seville, Spain
AUTHOR INFORMATION
Corresponding Author
*(M.B.) E-mail:
[email protected]. Phone: + 34 954690850. Fax: + 34 954691262. Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Mastralexi, A.; Nenadis, N.; Tsimidou, M. Z. Addressing analytical requirements to support health claims on “olive oil polyphenols” (EC Regulation 432/2012). J. Agric. Food Chem. 2014, 62, 2459−2461. (2) Romero, C.; Brenes, M. Analysis of total contents of hydroxytyrosol and tyrosol in olive oils. J. Agric. Food Chem. 2012, 60, 9017−9022. (3) Mulinacci, N.; Giaccherini, C.; Ieri, F.; Innocenti, M.; Romani, A.; Vincieri, F. F. Evaluation of lignans and free and linked hydroxytyrosol and tyrosol in extra virgin olive oil after hydrolysis processes. J. Sci. Food Agric. 2006, 86, 757−764. (4) Brenes, M.; García, A.; García, P.; Garrido, A. Rapid and complete extraction of phenols from olive oil and determination by
Table 1. Total Hydroxytyrosol and Tyrosol Contents of Several Virgin Olive Oils According to Protocols 1 and 2 hydroxytyrosola (mg/kg) virgin olive oil A B C D
protocol 1 68.7 180.5 51.3 191.0
a a a a
± ± ± ±
2.2 0.3 0.8 1.1
tyrosola (mg/kg)
protocol 2 91.8 b 187.9 b 72.6 b 193.1 a
± ± ± ±
1.2 0.6 1.0 1.7
protocol 1 138.0 259.8 109.7 253.5
a a a a
± ± ± ±
2.6 0.7 2.3 1.4
protocol 2 153.1 b 258.4 a 141.8 b 251.8 a
± ± ± ±
0.6 2.8 4.9 4.9
a Data are the mean ± standard deviation (n = 3). Different letters in the same mean value row indicate significant differences according to Duncan’s multiple-range test (p < 0.05).
Received: June 18, 2014 Published: September 24, 2014 © 2014 American Chemical Society
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Journal of Agricultural and Food Chemistry
Correspondence/Rebuttal
means of a coulimetric electrode array detection. J. Agric. Food Chem. 2000, 48, 5178−5183. (5) International Olive Council (IOC). Determination of biophenols in olive oil by HPLC; COI/T.20/Doc. No. 29, November 2009. (6) European Community Council Regulation No. 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children’s development and health. Off. J. Eur. Communities L. 2012, 136, 1−40.
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