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Malheiro, Ricardo

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  • Olive oil stability under deep-frying conditions
    Publication . Casal, Susana; Malheiro, Ricardo; Sendas, A.; Oliveira, Beatriz; Pereira, J.A.
    The suitability of different commercial olive oil categories for domestic frying was investigated. Oil samples were taken every 3 h of frying and evaluated for free acidity, peroxide and p-anisidine values, specific extinction coefficients, oxidative stability, fatty acids, vitamin E, b-carotene and total phenols, until the total polar compounds achieved the maximum legal value (25%). All olive oils were fried during more time than the commercial vegetable oil blend taken for comparison (from 24 to 27 h, against 15 h). The extra-virgin Protected Designation of Origin (PDO) olive oil was characterized by reduced levels of oxidation and hydrolysis, and superior amounts of minor antioxidant compounds. The ‘‘olive oil” commercial category behaves similarly, but ‘‘Cobrançosa” olive oils performance was slightly worse, and clearly different between years, highlighting the importance of blending different cultivars. The vegetable oil, despite containing significantly higher amounts of vitamin E, was highly susceptible to oxidation under frying conditions when compared to all olive oils. The results also show that the chemical composition of olive oils, particularly the amount of natural antioxidants, are important parameters in their predictive behavior along the frying process, but mostly that olive oil is clearly resistant to frying conditions, independently to the commercial category chosen.
  • Effect of olive leaves addition during the extraction process of overmature fruits on olive oil quality
    Publication . Malheiro, Ricardo; Casal, Susana; Teixeira, Hélder; Bento, Albino; Pereira, J.A.
    The harvest period is one of the most important factors influencing olive oil quality. This period is extended for several months and the late-extracted olive oils are characterized by quality loss and reduced resistance to oxidation. The aim of this work was to verify the effect of olive leaves addition during the oil extraction process in the olive oils quality and composition. In two consecutive years (2009 and 2010), different olive leaves amounts (1%, 2.5%, 5% and 10% w/w) were added during the extraction process of cv. Cobrançosa olive fruits, collected in the late season. Standard quality parameters, oxidative stability, fatty acids profile, tocopherols, chlorophylls, and carotenoids contents were evaluated. Olive leaves addition induces a slight increase in acidity, peroxide value, K232, and K270 without compromising olive oils classification, but the resistance to oxidation was significantly improved. Vitamin E increased nearly 30% with 10% of leaves added mainly due to the considerable increase in α-tocopherol. A similar effect was observed in the contents of chlorophylls (chlorophyll a and pheophytin a) and carotenoids (lutein and β-carotene), that attributed a more intense greener pigmentation and enhanced nutritional attributes. Significant correlations were observed for several parameters with the amounts of leaves added. Moreover, leaves addition modified the characteristics and composition of the olive oils in a way that was possible to discriminate and to classify each group.
  • Can tea extracts protect extra virgin olive oil from oxidation during microwave heating?
    Publication . Malheiro, Ricardo; Casal, Susana; Lamas, Hugo; Bento, Albino; Pereira, J.A.
    Olive oil is a key ingredient in worldwide cuisine. Microwave cooking is also increasingly used as a timesaving technology but it induces severe changes in the lipids, such as hydrolysis and oxidative reactions that lead to quality and nutritional losses. In this sense, the present work intends to verify the potential increased olive oil stability under microwave cooking induced by white and green tea aqueous extracts, rich in antioxidants. Quality parameters (free acidity, peroxide value, K232, K270 and ΔK), composition (fatty acids profile, tocopherols and total phenols content), antioxidant activity and oxidative stability were studied during different microwave heating exposure times (0, 1, 3, 5 and 10 min). Until the first 3 min of heating the tea extracts protect olive oil from the oxidative process. However, with higher heating periods the extracts were pro-oxidants, mainly green tea extracts. Globally, and independently from the addition of tea extracts, the olive oils suffered drastic changes in their quality and composition. PUFA content decreased with exposure time as well as antioxidant activity, total phenols and total vitamin E content, and oxidative stability, with higher losses in the olive oils with green tea extracts. Positive correlations were established between the quality parameters and the increasing heating time, and negative correlations with the composition and bioactive and stability indexes.
  • Improvement of sensorial and volatile profiles of olive oil by addition of olive leaves
    Publication . Malheiro, Ricardo; Rodrigues, Nuno; Bissaro, Camila Andressa; Leimann, Fernanda Vitória; Casal, Susana; Ramalhosa, Elsa; Pereira, J.A.
    The changes caused by the addition of olive leaves (0, 5, and 10%) during the extraction of olive oil and malaxation time (20, 30, and 30 min) in the volatile profile and sensory attributes of olive oil from cv. Cobrançosa were studied. To investigate such transformations, a central composite designs from the Response Surface Methodology (RSM) was used, retrieving 13 runs combining leaf percentages and malaxation times. Each run was extracted in triplicate (39 olive oils overall). Sensory attributes were improved to leaves addition, mainly green and fruitiness attributes in olfactory and gustatory-olfactory sensations, but high malaxation times ( > 30 min) reduced pungent and bitter notes. Leaves addition increased the amounts of total volatiles, particularly the GLV's (green leaves volatiles) (E)-2-hexenal, (Z)-3-hexenal, and (Z)-3-hexenyl acetate, directly correlated with the improved sensory attributes. RSM models a showed positive linear effect with leaves addition, but a negative effect with malaxation time. These results suggest the use of olive leaves as effective odorants for the olive mill industry, while enabling the reduction of malaxation times and by-product amounts. Practical applications: The results obtained clearly open new lines of research to use olive leaves, a sub-product of olive oil extraction, in a valuable way. Olive leaves can be used as natural sources of odorants for olive oils. Furthermore, their use during the extraction of olive oils from overmature olives may also lead to an improvement of the volatile fraction and provide enhanced sensory properties to the consumers, thus conferring an added value to these oils. Another important practical application is the extraction process. In our work, we advise to optimize both the percentage of leaves and the malaxation time as much as possible, as they facilitate both sensory and volatile fractions of the extracted olive oils. Sensory attributes are improved to leaves addition, mainly green and fruitiness attributes in olfactory 17 and gustatory-olfactory sensations, but high malaxation times ( > 30 min) reduced pungent and bitter 18 notes. Leaves addition increase the amounts of total volatiles, particularly the GLV's (green leaves 19 volatiles) (E)-2-hexenal, (Z)-3-hexenal, and (Z)-3-hexenyl acetate, directly cor related with the improved 20 sensory attributes. RSM models a show positive linear effect with leaves addition, but a negative effect 21 with malaxation time. These results suggest the use of olive leaves as effective odorants for the olive mill 22 industry, while enabling the reduction of malaxation times and by-product amounts.