Application of an electronic tongue for Tunisian olive oils’ classification according to olive cultivar or physicochemical parameters

Abstract

to their quality level (i.e., extra virgin, virgin or lampante olive oils) or autochthonous olive cultivar (i.e., cv Chétoui and cv Shali) was evaluated for the first time. Linear discrimination analysis coupled with the simulated annealing variable selection algorithm showed that the signal profiles of olive oils' hydroethanolic extracts allowed olive oils discrimination according to physicochemical quality level (classification model based on 25 signals enabling 84 ± 9% correct classifications for repeated K-fold cross-validation), and olive cultivar (classification model based on 20 signals with an average sensitivity of 94 ± 6% for repeated K-fold cross-validation), regardless of the geographical origin and olive variety or the olive quality, respectively. The results confirmed, for the first time, the potential discrimination of the electronic tongue, attributed to the observed quantitative response (sensitivities ranging from −66.6 to +57.7 mV/decade) of the E-tongue multi-sensors towards standard solutions of polar compounds (aldehydes, esters and alcohols) usually found in olive oils and that are related to their sensory positive attributes like green and fruity.

Perception of olive oils sensory defects using a potentiometric taste device

“…On the other hand, based on the experience of the research team, which used the same E-tongue device in several works, this type of potentiometric E-tongue could be used during at least one year period without requiring any replacement of the lipid polymeric sensor membranes, showing the storage stability of this type of sensor device. Furthermore, in previous works of the research team, it was verified that the lipid polymeric sensor membranes showed quantitative linear (sensitivities, mV/decade) response towards the decimal logarithm of the concentration of chemical standard solutions mimicking positive or negative sensory attributes usually perceived in olives or olive oils [22,24,25]. It should be emphasized that the sensing mechanism depends on the non-uniform hydrophilicity of the lipid membranes and on the ionic environment at the proximity of the membrane surface.…”

“…In each assay, 10.00 g of olive oil were mixed to 100 mL of hydro-ethanolic solution during 5-10 min under strong agitation, using a vortex stirrer (LBX V05 series, lbx instruments), with a constant speed of approximately 500 rpm. This process allowed the extraction of polar compounds, which are responsible for sensory attributes of olive oils [10,13,25,26]. The mixture was left at ambient temperature during 60 min, after which, 40.0 mL of the supernatant solution was carefully removed and immediately analyzed with the Etongue.…”

“…A similar electrochemical device was also used to classify table olives according to the sensory quality category based on the intensity of the defect predominantly perceived (DPP), to differentiate organoleptic negative attributes that may be perceived in table olives, using standard solutions and real samples as well as to quantify the intensity of the DPP in table olive and respective brine solutions as well as to evaluate table olives' gustatory attributes (e.g., acid, bitter and salty sensations) [22][23][24]. Furthermore, this type of E-tongue device showed quantitative responses towards polar compounds (aldehydes, esters and alcohols) usually found in olive oils and that are related to their sensory positive attributes (e.g., green and fruity) [25]. The Etongues successful performances may be attributed to the capacity of the lipid polymeric sensor membranes to promote interactions with polar taste substances via electrostatic or hydrophobic interactions, which are usually presented in the olive oils' alcoholic extracts [26,27].…”

A taste sensor device for unmasking admixing of rancid or winey-vinegary olive oil to extra virgin olive oil

“…The literature survey clearly point out the limited number of works reporting the successful use of E-noses (Oliveros et al, 2002;Jeleń, 2008, 2010;Lerma-García et al, 2010;Santonico et al, 2015) to detect olive oil adulteration with other vegetable oils or lower quality olive oils (possessing or not common sensory defects), as well as the scarce use of voltammetric E-tongues (Apetrei and Apetrei, 2014;Santonico et al, 2015). Recently, the use of a pontentiometric E-tongue device comprising cross-sensitivity lipid polymeric membranes, has demonstrated to be a practical and helpful taste sensor tool for olive oil analysis (Dias et al, 2014Veloso et al, 2016Veloso et al, , 2018Slim et al, 2017;Souayah et al, 2017). It was previously reported by Marx et al (2017b) and Slim et al (2017) the capability of this type of E-tongue to provide quantitative potentiometric responses towards aldehydes, alcohols and esters compounds that mimic positive olive oil sensory attributes namely, 4-hydroxy-3-methoxybenzaldehyde (vanilla sensation), hexyl acetate (sweet, green, grassy, fruity or apple sensations), (Z)-hex-3-en-1-ol (green leaves or banana sensations), (E)-hex-2-enal (green, almonds or apple sensations), (Z)-hex-3-enyl acetate (fruity or green leaves sensations), citric and tartaric acids (acid sensation), caffeine and quinine (bitter sensations) and sodium or potassium chloride (salty sensation).…”

“…Recently, the use of a pontentiometric E-tongue device comprising cross-sensitivity lipid polymeric membranes, has demonstrated to be a practical and helpful taste sensor tool for olive oil analysis (Dias et al, 2014Veloso et al, 2016Veloso et al, , 2018Slim et al, 2017;Souayah et al, 2017). It was previously reported by Marx et al (2017b) and Slim et al (2017) the capability of this type of E-tongue to provide quantitative potentiometric responses towards aldehydes, alcohols and esters compounds that mimic positive olive oil sensory attributes namely, 4-hydroxy-3-methoxybenzaldehyde (vanilla sensation), hexyl acetate (sweet, green, grassy, fruity or apple sensations), (Z)-hex-3-en-1-ol (green leaves or banana sensations), (E)-hex-2-enal (green, almonds or apple sensations), (Z)-hex-3-enyl acetate (fruity or green leaves sensations), citric and tartaric acids (acid sensation), caffeine and quinine (bitter sensations) and sodium or potassium chloride (salty sensation). On the other hand, for negative sensations, Marx et al (2017a) also described the quantitative responses towards n-butyric acid (butyric defect), 2-mercaptoethanol (putrid defect) and cyclohexanecarboxylic acid (zapateria defect).…”