The subject: Plant-based products that are praised as vegan or vegetarian substitutes for animal products must meet high expectations in terms of mouthfeel and flavor. Ideally, the sensory impres-sions should be as similar as possible to those of the original. Getting even remotely close to that goal is no easy feat, not least given the multitude of flavor-intense compounds found in plants that affect the overall aroma. In the product development and supplier selection phase, sensory evaluation of the plant-based protein is essential. Sensory needs to be accompanied by instrumental analysis in order to control the process and enable corrections when off flavors are encountered.  

First steps: In order to identify the main sensory active compounds that form meat or fish aroma and to determine unwanted interferences, GERSTEL scientists identified key aroma substances in both plant-based tuna substitute and in real canned tuna [1]. The method chosen by Kfoury et al. was Sen-sory Directed Analysis (SDA) [2]. 

SDA relies on human olfactory detection in combination with gas chromatography (GC) and mass spectrometry (MS) to find the determining aroma compounds food matrices. Simultaneous olfactory (O) and MS detection (GC-MS/O) enables the analyst to determine sensorily significant fractions and to identify individual sensory relevant analytes in the same analysis run. As a result, SDA can be used to identify compounds that form desirable flavors in foods.

Analytical details: Kfoury et al. used solvent-free dynamic headspace (GERSTEL-DHS) to extract the analytes from the matrix; all sample preparation steps including sample introduction and analysis were carried out automatically (GERSTEL MultiPurpose Sampler, MPS). The subsequent separation was performed by GC-MS, more precisely by 1D/2D GC-MS. The GC (Agilent Technologies GC 8890) was equipped with an LTM module (Low Thermal Mass) and two columns of different polarity (LTM 1: DB-5MS UI [Agilent] 30 m x 2.25 mm x 0.25 µm; LTM 2: DB- WAX [Agilent] 30m x 0.25mm x 0.25µm). A heart cut  was performed to separate co-eluting peaks on the 2nd column. Column switching is valve-less and fully software controlled. The analytes were determined by using an Agilent 5977B MSD and the system configured for simultaneous olfactory detection in the GERSTEL Olfactory Detection Port (ODP 4). 

The proof of the pudding: The combination of olfactory detection (O) of individual sensory active compounds with 1D/2D GC-MS enables efficient and accurate determination of the dominant desira-ble natural aromas and flavors. To find out whether such aroma compounds could be determined with their DHS-1D/2D-GC-MSD/O system and whether this could be replicated in food products, Kfoury et al. acquired and analyzed real samples.  
Canned tuna and two plant-based counterparts were analyzed. In the GERSTEL DHS, using nitrogen carrier gas, volatile analytes were continuously purged from the headspace above the sample and concentrated on a sorbent (Tenax TA). The Tenax-filled glass tube was subsequently placed in a Ther-mal Extractor (GERSTEL-TE), a nitrogen carrier gas flow was applied and combined aroma compounds were thermally desorbed for a combined olfactory assessment at the TE gas outlet. The scientists de-termined that the sensory impression of the combined extracted aroma compounds was similar to that of the freshly unpacked food sample in all cases. Kfoury et al. characterized the olfactory impres-sions of real tuna as fishy, brothy and meaty. The scientists describe the olfactory impression of the first plant-based tuna as bean-like and vegetable, while the second was characterized by attributes such as cereal, vegetable and algae-like.

Conclusion: The DHS-TE sensory test was successful and was taken as proof that a representative odor profile can be obtained using DHS. Overall, the SDA methodology enables the analyst to identify im-portant sensory active compounds in tuna samples.  Using DHS provides representative sample ex-tracts for analysis and 1D/2D GC-O/MS resolved co-eluting compounds. The presented approach makes it possible to identify sensory active compounds in a variety of sample types. Manufacturers of plant-based meat substitutes are thus able to replicate the product taste and to work towards con-sumer acceptance and appreciation in product development.

[1] Kfoury et al., Identification of Key Sensory-Active Flavor Compounds in Plant-Based Tuna Fish using Sensory Directed Analysis, GERSTEL AppNote 243
[2] Ray Marsili (Editor), Sensory-Directed Flavor Analysis (Food Science and Technology) 1. Auflage (2006)