Two sensory reference materials

Prof. Alessandra Bendini, Dr. Diego Luis Garcia Gonzalez, Prof. Tullia Gallina Toschi

In the case of virgin olive oil, sensory assessment is a standard method and, according to International Olive Council (IOC) norms and other national and international regulations (EU Regulations, Codex Alimentarius), its application is mandatory for establishing possible quality grades (e.g. for EU: extra virgin, virgin, lampante) and for marketing the product. 

The laboratories that implement the analytical methods must demonstrate their proficiency in applying testing methods, following the procedures described by EU and IOC, with trials that ensure the validity of the results: this validation process should be carried out with Reference Materials (RMs). In fact, the use of RMs is mentioned as necessary for sensory analysis in current regulations (COI/T.28/; COI/T.20/Doc. no.14/Rev.5). 

The use of reference materials (RMs) for which definitive numerical values can be associated with different sensory attributes is of absolute necessity to calibrate the measurement process, help assessors in memorization of sensory stimuli, and compare their judgment with “assigned values” and thus improve their individual abilities. For these reasons, the RMs should be applied for continuous monitoring of panels over time as well as for intra-panel and inter-panel control studies. Moreover, the RMs could be very useful also for selection and training of new assessors recruited during numerous courses organized at national and international levels by different organizations and addressed at the specific formation of sensory panellists of virgin olive oils. 

For sensory analysis of VOOs, at present only RMs from natural matrices (authentic olive oils that are used as reference samples of sensory defects provided by IOC, samples from proficiency tests, or certified by at least three accredited sensory panels) are available for training of sensory panels; they are effective in resembling real samples, although they have some limitations in their use over time (e.g. limited availability, difficult to obtain, low homogeneity year by year).

RMs emulating the aromas of winey-vinegary and rancid defects have been formulated at specific dilutions by CSIC, using a collection of synthetic volatile compounds diluted in a flavorless refined olive oil at specific concentrations (Aparicio-Ruiz et al., 2020, Foods, 9(12), 1870), then UNIBO has coordinated their sensory evaluation inside the OLEUM consortium (six panels have been involved) as well as in the context of inter-lab validation just concluded (pre-trial and trial proper phases).

The main outcomes of the inter-lab validation were:

The evaluation of the representativeness of reference materials (RM1 and RM2), in terms of an assessment by the panellists of their ‘usefulness in resembling natural sensory defects of winey-vinegary and rancid’: the data received demonstrated that the RMs were valued as appropriate by a high proportion of end-users. 

The calculation of perceived intensities of the winey-vinegary and rancid defects (RM1 and RM2) because the definition of the intensity of each sensory RM is a fundamental information to permit its possible future use in training of assessors: the alignment among panels respect to the intensity of defect in each RM was reached.