Stability and radical-scavenging activity of heated olive oil and other vegetable oilsThe effect of heating at 180 7C on the antioxidant activity of virgin olive oil (VOO), refined olive oil (ROO) and other vegetable oil samples (sunflower, soybean, cottonseed oils, and a commercial blend specially produced for frying) was determined by measuring the radical-scavenging activity (RSA) toward 1,1-diphenyl-2-picrylhydrazyl radical (DPPH . ). The RSA of the soluble (polar) and insoluble (non-polar) in methanol/ water fractions of olive oil samples was also measured. The stability of heated oils was assessed by determining their total polar compound (TPC) content. VOO was the most thermostable oil. Total polar phenol content and the RSA of VOO heated for 2.5 h decreased by up to 70 and 78%, respectively, of their initial values; an up to 84% reduction in RSA of VOO polar and non-polar fractions also occurred. Similar changes were observed in the RSA of ROO and its non-polar fraction after 2.5 h of heating. The other oils retained their RSA to a relatively high extent (up to 40%) after 10 h of heating, but in the meantime they reached the rejection point (25-27% TPC). The results demonstrate that VOO has a remarkable thermal stability, but when a healthful effect is expected from the presence of phenolic compounds, heating has to be restricted as much as possible.
Effect of Greek sage and summer savory extracts on vegetable oil thermal stabilityThe effect of ethanol and acetone extracts obtained from Greek sage (Salvia fruticosa) and summer savory (Satureja hortensis L.) on the thermal stability of vegetable oils heated at frying temperature (180 7C) was studied. Virgin olive oil (VOO), refined olive oil (ROO), sunflower oil (SO), and a commercial oil blend suitable for frying (BL), enriched with each extract obtained from the two plant materials at a concentration of 3 g/kg oil, were heated at 180 7C for 10 h. Changes during heating were assessed by quantification of total polar materials and determination of p-anisidine values. The acetone extract obtained from Greek sage showed a better inhibitory effect against thermal oxidation of heated refined oils (BL, ROO, SO) than the respective ethanol extract, although the latter was found to have a relatively higher total phenol content. Both summer savory extracts effectively retarded the thermal oxidation reactions during oil heating, showing a more pronounced effect than the Greek sage acetone extract. The activity of the acetone extract obtained from summer savory was stronger (SO, BL) or similar (ROO, VOO) to that of the summer savory ethanol extract, although the latter was found to have a higher total phenol content.
In November 2019, a severe outbreak of fruit rot was observed in olive orchards in Crete, southern Greece. Symptoms appeared primarily on fruits and stalks, resembling those caused by anthracnose. Typical symptoms were fruit rot, shrinkage and mummification, associated commonly with stalk discoloration and fruit drop. Disease incidence was estimated up to 100% in some cases and an unprecedented increase in olive oil acidity reaching up to 8% (percentage of oleic acid) in severely affected olive groves was recorded. Thirty-two olive groves were then surveyed, and samples of fruit, stalk, leaf and shoot were collected. Visual, stereoscopic and microscopic observations revealed several fungi belonging to the genera Alternaria, Botryosphaeria, Capnodium, Colletotrichum, Fusarium and Pseudocercospora. Fungal infection in fruits was commonly associated with concomitant infestation by the olive fruit fly Bactrocera oleae along with increased air temperature and relative humidity conditions that prevailed in October-November 2019. Twenty representative fungal strains isolated from symptomatic fruits and stalks were characterized by morphological, physiological and molecular analyses. By rDNA-ITS region and EF1-α gene sequencing analysis, these isolates were identified as Alternaria spp., A. infectoria, Botryosphaeria dothidea, Colletotrichum boninense sensu lato, Fusarium lateritium, F. solani species complex and Stemphylium amaranthi. Pathogenicity tests on punctured fruits revealed that all isolates were pathogenic; however F. solani isolates along with B. dothidea were the most virulent and wounds were necessary for efficient fungal infection. Moreover, as little as 10 spores of F. solani were sufficient of causing significant infection in punctured fruits. Fusarium solani was also capable of infecting olive fruits in the presence of B. oleae, with no additional wounding, in artificial inoculation experiments. Moreover, it was capable of colonizing and affecting olive blossoms. Further analyses in olive oil extracted from fruits artificially inoculated with F. solani indicated a significant increase in oil acidity, K232, K270 and peroxide value, whereas total phenols content was significantly decreased. To the best of our knowledge, this is the first report of Fusarium solani associated with olive fruit rot and olive oil degradation worldwide.
1.2.4. Ταχεία εκτίμηση του βαθμού αλλοίωσης ελαίων που έχουν υποστεί έντονη θέρμανση με εφαρμογή ειδικών δοκιμών……………………… 1.3. ΕΚΤΙΜΗΣΗ ΤΗΣ ΑΝΤΙΟΞΕΙΔΩΤΙΚΗΣ ΙΚΑΝΟΤΗΤΑΣ ΤΩΝ ΕΛΑΙΩΝ ΚΑΤΑ ΤΗ ΘΕΡΜΑΝΣΗ ΣΕ ΥΨΗΛΕΣ ΘΕΡΜΟΚΡΑΣΙΕΣ………………..
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