Sense and Sensitivity: The Role of Separation Science in Sensory Evaluation

Jun 06, 2014

Kate Mosford of The Column spoke to Giorgia Purcaro of the Department of Food Science at the University of Udine, Italy, and Chiara Cordero of the Department of Drug Science and Technology at the University of Turin, Italy, about the sensory evaluation of olive oil and the benefits of a comprehensive approach.

Q: Olive oil is classified by law according to both the chemical composition and the sensory evaluation. Is olive oil the only food product analyzed by sensory evaluation?


PHOTO CREDIT: URSULA ALTER/GETTY IMAGES
Giorgia Purcaro: Sensory evaluation of foods has been widely applied in industry to study consumer acceptance, which influences business decisions and guides product development to get closer to a benchmark product. In academia the correlation between sensory perception and chemical composition and texture has always been an important topic of study in food science. Sensory quality has been used as an additional requirement in several food certifications, such as PDO (product designation of origin). Sensory evaluation has never been used as a legal parameter to define any kind of food products before olive oil. Olive oil has been a very important product of the Mediterranean basin since ancient times, and it has always been recognized, from both a quality and a commercial viewpoint, as high value oil compared to other vegetables oils. It has therefore been subjected to frauds by the addition of oils of lower quality and price.

Since the first European Regulation citing olive oil, which was enacted in 1966 (Regulation no. 136/1966)1 and directed to market regulation on fats and oils within Europe, both chemical and sensory evaluations have been used for assessment of purity and quality of olive oil. Although the definitions of sensory quality were initially "blurry" ("perfect flavour", "good flavour", and "off-flavour"), they were elucidated in detail in the European Regulation no. 2568, which was enacted in 1991. In fact, this regulation introduced — along with a long list of chemical analyses with an accurate description of the analytical methods — a detailed explanation of the procedure to be performed in the training of panellists, how to carry out the panel session, and the attributes to be used to evaluate the sensory quality of olive oil.2

Q: What does the sensory evaluation involve and what are the drawbacks?

GP: Sensory evaluation is fundamental in classifying olive oil within the specific commercial class, namely extra virgin, virgin, and lampante olive oil [Reg. CEE 2568/91, Reg CE 796/02; Reg CE 640/08].2–4

For example, extra virgin olive (EVO) oil, apart from respecting all the required chemical parameters, has to present a fruity aroma and no defects (muddy, fusty, rancid, musty, vinegary, or metallic) that have originated during olive or oil storage. Described in detail by both the European Regulation CEE 2568/912 (and following modifications) and by several International Olive Oil Council (IOC) documents (COI/T.20/Doc. No 15/Rev. 6; COI/T.20/Doc. No 13; COI/T.20/Doc. No 4),5–7 the sensory analysis is based on the judgement of a panel of assessors, composed of a minimum of eight testers (generally 12) headed by a panel leader, who has to motivate the judges, process the data, interpret results, and draft the final report.

The sensory assessment (both tasting and smelling) is performed according to codified rules, in a specific tasting room, and using a specific vocabulary (COI/T.20/Doc. No 4).7 The panel has to be continuously trained and the performance constantly evaluated, usually using reference samples provided by the IOC, to verify the reliability of the results and harmonize the perception criteria. However, despite a rigid codification of all the aspects of sensory analysis, several drawbacks can be pinpointed: (a) Organization of a panel session is not easy since panellists are usually employed in other jobs; (b) each session is very tiring, consequently only a limited number of samples (maximum of six) can be analyzed for each session; (c) low reproducibility has been observed among different panels, mainly as a result of uneven training, which is related also to the difficult availability of reference standards — in particular when presenting only one defect at a time. Therefore, an objective sensory evaluation is costly and time-consuming.8