Relevance of two-dimensional gas chromatography and high resolution olfactometry for the parallel determination of heat-induced toxicants and odorants in cooked food

Highlights

• An ASE-GC × GC–TOF/MS multiresidue method was set up for PAH analysis in food.

• GC–MS/8O enabled a robust determination of odour zones.

• Heart-cutting GC–GC–MS/O resolved the remaining coelutions of key odorants.

• PAHs and odour-active compounds were investigated in cooked meat.

Abstract

The assessment of the dual impact of heating treatments on food safety and aroma is a major issue for the food sector. The aim of the present study was to demonstrate the relevance of multidimensional GC techniques, olfactometry and mass spectrometry for the parallel determination of process-induced toxicants and odorants in food starting with cooked meat as a food model. PAHs were analyzed by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry after extraction by accelerated solvent extraction (ASE-GC × GC–TOF/MS). Odour-active compounds were determined by dynamic headspace–GC hyphenated with eightbooth olfactometry and mass spectrometry (DH–GC–MS/8O) and DH-heart-cutting multidimensional GC hyphenated with olfactometry and mass spectrometry (DH–GC–GC–MS/O). For PAH determination, the GC × GC conditions consisted of a combination of a primary non-polar BPX-5 column and a secondary polar BPX-50 column, and a modulation period of 5 s. In terms of linearity (R² ranging from 0.985 to 0.997), recovery rate (84–111%) and limit of detection (5–65 ng/kg of cooked meat), the ASE-GC × GC–TOF/MS method was found consistent with the multiresidue determination of 16 PAHs including benzo[a]pyrene in cooked meat. For aroma compounds, DH–GC–MS/8O and DH–GC–MS/O revealed 53 major meat odour-active compounds. A customized heart-cutting GC–GC–MS/O enabled the coeluting odour zones with high odour-activity to be resolved and revealed 15 additional odour-active compounds. Finally, these developments of multidimensional approaches were used to investigate the balance between 16 PAHs and 68 odour-active compounds generated with different cooking techniques.

Introduction

Cooking has both positive and negative impacts on food quality. While cooking is necessary to develop the desirable flavours in food, besides making it digestible as well as destroying harmful organisms, the oxidation and pyrolysis of fats, especially at frying temperatures, can give rise to compounds that decompose creating undesirable flavours and various process-induced toxicants, including polycyclic aromatic hydrocarbons (PAHs). Nowadays, there is an increasing demand to limit the negative influence of cooking, with a specific emphasis on heat-induced toxicants such as PAHs, while preserving sensory properties of processed food, focusing on odour-active compounds. It is therefore necessary to develop analytical tools for the parallel investigation of process-induced toxicants and odorants generated during food cooking.

More than 100 PAHs have been characterized in nature as genotoxic carcinogens and biological mutagens [1]. PAH-induced carcinogenesis may result when a PAH-DNA adduct is formed on a critical site for the regulation of cell differentiation or growth. Interactions of various PAHs have been shown to produce both synergistic and antagonistic effects in mutagenicity tests in vitro [2]. For non-smokers and non-occupationally exposed populations, dietary intake has been identified as the principal route of human exposure to PAHs [3]. Efforts have thus been made to limit their formation in food through understanding the influence of various food processes including cooking. Therefore, food control authorities including the United States Environmental Protection Agency (US EPA) [4] and the European Food Safety Authority (EFSA) [5] have started monitoring the priority PAHs and seeking advanced methodology related to their detection in food [6]. Recently, methods using comprehensive two-dimensional gas chromatography (GC × GC) have been reported to improve the chromatographic resolution for PAH determination in food [7], [8], [9]. The high resolution of GC × GC allows for separation of the target compounds from matrix interferences and may enable the resolution of most coelutions reputed to persist in one-dimensional GC [10], even if the recent development of congener-specific GC-columns for PAH analysis might also offer promising alternatives [11], [12]. The time-of-flight mass spectrometry (TOF/MS) detector has been largely used to detect narrow peaks obtained from fast separation in the second chromatographic dimension making it easier to identify additional relevant compounds [10], [13].

Cooking is also responsible for the development of food aroma [14], [15]. For the screening of key odorants in food products, gas chromatography olfactometry (GC-O) coupled with mass spectrometry (MS) is commonly applied involving one or more human assessors or sniffers [16]. However, most of the reported techniques are unable to provide precise quantitative evaluation due to the wide variability of individual responses, variability between experimental sequences, as well as coelutions making it difficult to identify odour-active compounds. Pollien et al. [17] have demonstrated that a panel of at least eight sniffers was required to obtain a robust and reproducible aromagram. To overcome this drawback, a computerized multibooth GC–MS/8O system was developed to obtain an aromagram from a panel of eight sniffers for simultaneous detection of compounds using a single run [18]. Despite using high resolution GC, the 1D-separation achieved with the GC–MS/8O system is not always sufficient to resolve all the coeluted odour zones. One of the most popular options to elucidate these complex odour zones is to re-separate them with a second GC column hyphenated to olfactometry. The importance of multidimensional separation (MDGC) techniques, including heart-cutting GC–GC–MS/O providing an improved capacity to resolve the constituents of a sample, was recently reviewed by Marriott et al. [19].

This paper is aimed at assessing the relevance of multidimensional GC techniques hyphenated to MS and olfactometry for the parallel investigation of process-induced toxicants and odorants generated during food cooking starting with meat as a food model. In a first step, a multiresidue method based on ASE-GC × GC–TOF/MS was developed in order to investigate 16 targeted PAHs in cooked meat matrices. In a second step, the main odour-active compounds of the same matrices were determined by high resolution olfactometry. This approach consists in refining the detailed aromagrams provided by GC–MS/8O with the high resolution of a customized heart-cutting GC–GC–MS/O. Finally, these analytical developments were used to investigate the parallel generation of PAHs and odour-active compounds for various domestic cooking conditions.