Browsing by Author "Oueslati, Souheib"
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- Alterações dos parâmetros físico-químicos e sensoriais de azeite virgem extra durante o uso doméstico simulado ao longo de um mêsPublication . Rodrigues, Nuno; Oliveira, Letícia; Mendanha, Lorena; Sebti, Mohamed; Dias, L.G.; Oueslati, Souheib; Veloso, Ana C.A.; Pereira, J.A.; Peres, António M.O azeite tem características sensoriais e nutricionais únicas, o que torna altamente apreciado pelos consumidores. Neste trabalho estudaram-se as alterações da qualidade do azeite que podem ocorrer ao longo de um mês de consumo doméstico simulado.
- Alterações dos parâmetros físico-químicos e sensoriais de azeite virgem extra durante o uso doméstico simulado ao longo de um mêsPublication . Rodrigues, Nuno; Oliveira, Letícia; Mendanha, Lorena; Sebti, Mohamed; Dias, L.G.; Oueslati, Souheib; Veloso, Ana C.A.; Pereira, J.A.; Peres, António M.O azeite tem características sensoriais e nutricionais únicas, o que o torna altamente apreciado pelos consumidores
- Application of an electronic tongue for Tunisian olive oils’ classification according to olive cultivar or physicochemical parametersPublication . Slim, Souihli; Rodrigues, Nuno; Dias, L.G.; Veloso, Ana C.A.; Pereira, J.A.; Oueslati, Souheib; Peres, António M.Olive oil commercialization has a great impact on the economy of several countries, namely Tunisia, being prone to frauds. Therefore, it is important to establish analytical techniques to ensure labeling correctness concerning olive oil quality and olive cultivar. Traditional analytical techniques are quite expensive, time consuming and hardly applied in situ, considering the harsh environments of the olive industry. In this work, the feasibility of applying a potentiometric electronic tongue with cross-sensitivity lipid membranes to discriminate Tunisian olive oils according 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.
- Characterization of commercial Tunisian monovarietal olive oils produced from autochthonous olive cultivarsPublication . Slim, Souihli; Rodrigues, Nuno; Veloso, Ana C.A.; Dias, L.G.; Cruz, Rebeca; Casal, Susana; Oueslati, Souheib; Pereira, J.A.; Peres, António M.Tunisian commercial monovarietal olive oils, produced from two predominant autochthonous olive cultivars (cvs Chétoui and Oueslati) and another less investigated olive cultivar (cv Sahli) were studied. Chemical and sensory data have shown that most olive oils should be classified as lampante olive oil, pointing out the need of improving producing and/or storage conditions. Sahli olive oils showed the lowest total phenols content (157±48 mg/kg), oxidative stability (6.5±2.1 h), DPPH scavenging activity (68%±14) and monounsaturated fatty acids content (63.1%±3.1). These olive oils had the highest saturated and polyunsaturated fatty acids contents (19.9%±2.4 and 16.9%±1.4) as well as total tocopherols levels (222±49 mg/kg). Finally, the information of 12 selected parameters (total phenols, oxidative stability, nine fatty acids and γ-tocopherol), allowed establishing a linear discriminant model that correctly classified olive oils according to the olive cultivar with predictive rates of 90%±8. Heptadecenoic, behenic and eicosenoic acids were the three fatty acids identified as the most relevant chemical markers of Sahli olive oils.
- Classification of single-cultivar Tunisian olive oils according to the geographical origin using an electronic tonguePublication . Souayah, Fatma; Rodrigues, Nuno; Veloso, Ana C.A.; Dias, L.G.; Oueslati, Souheib; Pereira, J.A.; Peres, António M.The marketing of olive oil is focused to a greater extend on the distinction and characterization of products according to their geographical origins. Due to the great impact of geographic, agronomic and technological factors on the physicochemical quality of olive oils, it is important to be able to discriminate them according to their geographical origins in order to avoid or minimize the risk of frauds. In this work, it was intended to verify the capability of an electronic tongue to classify monovarietal Tunisian olive oils (cvs Chemlali or Sahli) according to geographical origins (i.e. Tunisian districts). For this purpose, chemometric tools were applied in order to establish linear discriminant models based on selected sub-sets of potentiometric signals profiles gathered with the electronic tongue. In this research, 30 samples belonging to the two above-mentioned varieties were analyzed by the electronic tongue additionally to legally required physicochemical analysis, which included the free acidity, the peroxide value and the coefficients of extinction K232, K270 and t::.K. These olive oil samples were grouped according to 3 regions for the Chemlali variety (i.e. Kairouan, Sidi Bouzid and Sfax- Center Tunisia) and 3 regions as well for the Sahli variety (i.e. Mahdia, Sousse and Kairouan - North and Center Tunisia). Preliminary results showed that it was possible to classify Tunisian olive oisl according to the geographical region with a minimum correct classification rate of 94% for cross-validation procedure. These findings pointed out the potential use of the electronic tongue as an efficient and low-cost analytical technique for classifying the Tunisian autochthonous monovarietal olive oils according to their geographical origin.
- Classification of single-cultivar Tunisian olive oils according to the geographical origin using an electronic tonguePublication . Souayah, Fatma; Rodrigues, Nuno; Veloso, Ana C.A.; Dias, L.G.; Oueslati, Souheib; Pereira, J.A.; Peres, António M.Developing analytical techniques for EVOO authentication is a challenging task. Moreover, if a specific meteorological or geographical factor affects different geographical regions similarly, olive oils' geographical discrimination may be a hard task. Improved classification of olive oils may be achieved by combining electrochemical fingerprints with multivariate statistical techniques. In this work, we used an electronic tongue, comprising 40 lipid membrane sensors, to extract suitable potentiometric fingerprints of Tunisian monovarietal olive oils that could be used in combination with linear discriminant analysis to classify olive oils according to the geographical origin.
- Discrimination of olive oil by cultivar, geographical origin and quality using potentiometric electronic tongue fingerprintsPublication . Souayah, Fatma; Rodrigues, Nuno; Veloso, Ana C.A.; Dias, L.G.; Pereira, J.A.; Oueslati, Souheib; Peres, António M.Legal regulations are set for protecting claims regarding olive oil geographical denomination. When meteorological or agroecological factors similarly affect different regions, the origin identification is a challenging task. This study demonstrated the use of a potentiometric electronic tongue coupled with linear discriminant analysis to discriminate the geographical origin of monovarietal Tunisian olive oil produced from local cv Chemlali (Kairouan, Sidi Bouzid or Sfax regions) and cv Sahli (Kairouan, Mahdia or Sousse regions). The potentiometric fingerprints of 12 or eight lipid sensors (for Chemlali and Sahli, respectively), selected using a simulated annealing meta-heuristic algorithm, allowed the correct prediction (repeated K-fold cross-validation) of the geographic production region with sensitivities of 92 ± 7% (Chemlali) and 97 ± 8% (Sahli). It was also confirmed the electronic tongue capability to classify Tunisian olive oil according to olive cultivar or quality grade. The results indicated the possible use of potentiometric fingerprints as a promising innovative strategy for olive oil analysis allowing assessing geographical origin, olive cultivar and quality grade, which are key factors determining olive oil price and consumers’ preference.
- Effect of different packaging materials on the shelf-life of chestnut (Castanea sativa Miller) during short-time storagePublication . Askri, Firas; Pereira, Ermelinda; Correia, Paula; Lema, Filipe; Martins, Fátima; Oueslati, Souheib; Droga, Rui; Ramalhosa, ElsaChestnuts are a perishable product that loses weight and spoils quickly. Therefore, it is essential to find methods to reduce economic losses. This study aimed to evaluate the effect of four different packaging materials - polyethene packaging" POLY", polyethene packaging with holes "PH", Modified Atmosphere Packaging "MAP", Vacuum bags "VAC-bags" and unpackaged chestnuts "control" - on the shelf-life of chestnuts stored at room temperature during 0, 2, 4 and 6 weeks. Several parameters such as colour, texture, moisture content, water activity, titratable acidity, total soluble solids, starch, amylose, aerobic mesophiles, and moulds and yeasts were determined. The results showed that the colour, texture, moisture content, water activity, titratable acidity and total soluble solids were little affected by the type of bags used. The starch ranged from 35.2 to 50.4% dry matter (d.m.) without a specific trend, and amylose expressed on the starch basis (25.7 to 45.0%) suggested no remarkable starch functionality changes. On the contrary, significant differences were observed between bags in weight loss, reducing sugars and microbial counts. The VAC-, MAP-, and POLY-bags showed percentages of weight loss lower than 2%, while the control and PH-bags had values equal to 13.2 and 9.2%, respectively. The highest values of reducing sugars were observed in POLY- and PH-bags, followed by the control, suggesting partial hydrolysis of the starch. Furthermore, VAC- and MAP-bags' application caused a considerable decrease in aerobic mesophiles, moulds and yeasts growth compared to the control during two and four weeks of storag
- Effect of using microperforated bags on the storage of chestnut (Castanea sativa Mill) for six monthsPublication . Askri, Firas; Pereira, Ermelinda; Correia, Paula; Lema, Filipe; Martins, Fátima; Oueslati, Souheib; Droga, Rui; Ramalhosa, ElsaChestnuts are very consumed worldwide; however, it is a perishable product that loses weight and spoils quickly. So, it is crucial to find methods to reduce economic losses. Thus, the purpose of the present work was to study the effect of using microperforated bags (MP-bags) in long-storage of chestnuts in refrigerated industrial chambers for 1, 2, 3 and 6 months. The weight loss, colour, texture, water activity (aw), moisture content, titratable acidity (TA), total soluble solids (TSS), reducing sugars, starch, amylose, and microbiological analysis were determined. No significant differences were noted in the colour of the chestnut kernel between the MP-bags and the control (unpackaged chestnuts) in most situations. After six months, the weight loss was much lower in MP-bags (1.9%) than in control (23%), and a significant difference in moisture content was observed between both conditions (55.2 and 42.7%, respectively). After six months, TA and TSS varied between packages, while the starch did not. The packaging type and storage time significantly influenced the reducing sugars. The highest values were observed in control. Some variability, without a definite trend in the MP-bags, was observed along the storage period. In control, the contents of reducing sugars increased from 0.09 to 2.06 g glucose/100 g d.m.. No significant differences in aerobic mesophilic and moulds and yeasts were observed for the control and MP-bags at the end of storage. MP-bags demonstrated to be a promising solution for extending the shelf-life of chestnuts by preserving the nutritional quality of the fruits.
- Electrochemical taste sensor for unmasking extra-virgin olive oils adulterated with rancid or winey-vinegary olive oilsPublication . Veloso, Ana C.A.; Harzalli, Ussama; Rodrigues, Nuno; Dias, L.G.; Oueslati, Souheib; Pereira, J.A.; Peres, António M.Olive oils may be commercially classified, in a decrease order of quality and economic value, as extra-virgin (EVOO), virgin (VOO) or lampante (LOO) olive oils, being quite prone to frauds. Thus legal protection regulations have been approved by the European Union Commission [1,2], being required the fulfilment of several physicochemical and sensory thresholds [3,4]. Unfortunately, the mixture of expensive olive oils with low quality oils aiming fraudulent economic revenue is still a common practice difficult to detect. In this work, a potentiometric electronic tongue (E-tongue) was used to detect adulteration of an EVOO with different added levels (2.5%, 5%, 10%, 20% and 40%; v/v) of an LOO with an intense sensory defect (rancid or wineyvinegary). Previously, similar electrochemical devices, also comprising lipid polymeric sensor membranes, showed to be able to give qualitative and/or quantitative responses towards basic taste sensations (acid, bitter, salty, sweet, and umami), positive sensory attributes (bitter, fruity, green and pungency) or defects (e.g., butyric, musty, putrid, winey-vinegary and zapateria) [5-8]. The E-tongue coupled with linear discriminant technique (based on the signal profiles of 19 or 20 E-tongue sensors, chosen using a simulated annealing meta-heuristic variable selection algorithm, for rancid and wineyvinegary adulterations, respectively) allowed to semi-quantitatively distinguish olive oils with different adulteration levels (repeated K-fold crossvalidation predictive correct classifications of 84±10% and 94±8% for rancid and winey-vinegary adulterations, respectively). The preliminary results showed the practical potential of the E-tongue as a taste device for the successful detection of EVOOs adulterated with LOO containing organoleptic defects.