Transfer of phenolic compounds during olive oil extraction in relation to ripening stage of the fruit

The transfer of phenolic compounds of Olea europaea L. cv. Arbequina variety during olive oil extraction in relation to ripening stage was investigated. The parameters of oil extraction by the Abencor system are shown together with mass balances of the products and by products from the olive oil extraction in relation to olive paste. The phenolic compounds in olive paste, pomace, oil and wastewater were identified and measured by HPLC. Throughout the study, the concentrations of simple phenols, secoiridoids and flavonoids were higher in the olive paste and pomace phases than in oil and wastewater phases. High concentrations of 4‐(acetoxyethyl)‐1,2‐dihydroxybenzene (3,4‐DHPEA‐AC) and secoiridoid derivatives such as the dialdehydic form of elenolic acid linked to 3,4‐DHPEA (hydroxytyrosol) or p‐HPEA (tyrosol) (3,4‐DHPEA–EDA, p‐HPEA–EDA, where EDA is elenolic acid dialdehyde) and an isomer of oleuropein aglycone (3,4‐DHPEA–EA, where EA is elenolic acid aldehyde) were found in olive oil, together with lignan compounds. It was observed that 3,4‐DHPEA–EDA was the most abundant polyphenol present in the wastewater phase. This indicates that biotransformation occurred during olive extraction, especially in the crushing and malaxation operations, and reflects the possible chemical changes that lead to the formation of new compounds. Moreover, the distribution of compounds showed their affinities toward different phases. Copyright © 2005 Society of Chemical Industry     

Olive oil extractability index as a parameter for olive cultivar characterisation

Extractability, when applied to the olive oil extraction process is defined as the percentage of oil extracted from the total oil content of the fruit. In this work, extractability index (EI), a new parameter determined in a laboratory oil mill, has been studied for 24 olive (Olea europaea L) cultivars from the Olive Germplasm Bank Collection of Mengibar (Spain). In order to evaluate the genetic variability of this new parameter, the influence of cultivar and tree on EI variability has been analysed in olive fruits collected at the same ripening index. The results indicate that cultivar is the most important variation source. Thus olive oil extractability depends on extraction process variables and cultivar. Extractability index could be used together with pulp oil content (on a dry matter basis) as a parameter for olive cultivar characterisation and selection for breeding projects. Copyright © 2003 Society of Chemical Industry     

Modelling of virgin olive oil extraction using response surface methodology

Malaxation of the paste is the most important step for virgin olive oil extraction because it affects both oil yield and quality. In this work the influence of temperature and mixing time on oil yield, quality parameters and oil composition in photosynthetic pigments and total polyphenols is assessed by using Response Surface Methodology. Seven Picual‐variety olive samples from two consecutive seasons, with different maturity index, were used. Results show that temperature and malaxation time exert a positive influence in olive yield, with optimal values ranging from 20.1 to 32.2 °C and from 73.3 to 90 min. Oil quality decreased slightly as temperature and time of malaxation were increased. Top quality oils were obtained below 30 °C and shorter mixing time. The oil content in photosynthetic pigments increased with temperature and mixing time, while total polyphenols increased with temperature but decreased with mixing time.     

Influence of regulated deficit irrigation strategies applied to olive trees (Arbequina cultivar) on oil yield and oil composition during the fruit ripening period

This study evaluated the effect of regulated deficit irrigation (RDI) strategies applied to olive trees (Arbequina cv) during the fruit ripening and harvest periods on oil yield and oil composition. Fatty acid composition, pigments, colour, polyphenol content and stability of oils were evaluated. The results indicate that regulated deficit irrigation induces fruit ripening; at harvest, oil yield increased when water supply was decreased, probably as a consequence of lower water content in the olive. Acidic composition was not affected by irrigation treatments. Irrigation affected pigment content and oil colour primarily during the early stages of olive ripening. RDI increased polyphenol concentration and stability of oils at all picking dates, especially during the first stages of the ripening period, probably owing to water stress. © 2000 Society of Chemical Industry     

Respiratory rate of olive drupes during their ripening cycle and quality of oil extracted

During the ripening cycle of Frantoio and Leccino olive varieties, the respiration rate of drupes was measured, giving the respiratory curve of fruits. This curve, for both varieties, dropped to a minimum point towards the end of November (a few days earlier for the Leccino variety) followed by a rise up to a maximum. This phase of the ripening process of olives corresponds to the climacteric crisis of the fruits. In this period the oil extracted from drupes gave the best analytical characteristics and was rich in tocopherols, phenols and aromatic volatile substances, components closely related to the shelf-life and the organoleptic quality of the product. The climacteric phase of drupes therefore corresponds to the optimal ripening stage of fruits and the harvesting of olives should be carried out during this period, in order to obtain oils of elevated quality. The respiration rate of drupes is therefore proposed as a new ripening index for drupes. © 1998 SCI.     

Changes in quality and phenolic compounds of virgin olive oils during objectively described fruit maturation

The effect of fruit ripening on the quality of the oil extracted and on the changes in the amount of phenolic compounds was determined in two olive varieties (Olea europaea, cvs. Arbequina and Picual) in two crop seasons, characterized by showing the same mean temperature and different rainfalls. Maturation level was evaluated using six methods: Harvest date, ripening index (RI), fruit skin colour, fruit firmness, and amount of chlorophylls and carotenoids in the oil. Oil quality, evaluated using the parameters established to determine the quality level of virgin olive oils (acidity, K₂₃₂, K₂₇₀, peroxide index, and panel test), was not affected by fruit ripening or by the increase in rainfall of the season. However, the changes in oil stability and phenolic compounds in the oils extracted during fruit ripening strongly differed according to the variety, the maturity level of the fruit and the crop season tested. Fruit skin colour and firmness allowed a better discrimination at the initial maturity stages than the other methods tested.     

Chemical composition of virgin olive oils from Koroneiki cultivar grown in Tunisia with regard to fruit ripening and irrigation regimes

The impact of different irrigation regimes based on two ripeness index, on the quantity and quality of virgin olive oil from the introduced olive cultivar Olea europaea L. Koroneiki grown at a high‐density olive orchard in northern Tunisia, was assessed. Olive trees were subjected to three treatments (T1, T2 and T3) that received a seasonal water amount equivalent to 50%, 75% and 100% of the estimated local evaporative demand by a drip irrigation system and olives were collected in two different ripeness index. The olive oil content decreased when the water applied was increased but rose during ripening. The quality indexes and fatty acid composition were less affected by the irrigation schedule but most significantly by the maturity of olives. Moreover, phenol contents increased according to fruit ripening whereas no clear cut differences or consistent effects were observed by irrigation. α‐tocopherol decreased slightly in the oils as ripening progressed while insignificant differences between the irrigation treatments studied were obtained. Consequently, a restitution of 75% of crop evapotranspiration (ET_c.) was sufficient to achieve good minor compounds; however, higher water volumes (100% ET_c.) gave little additional α‐tocopherol and phenols increases.     

酶处理对初榨橄榄油品质及抗氧化活性的影响

将纤维素酶、果胶酶应用于橄榄油提取工艺,旨在生产具有较高总酚含量及较强抗氧化活性的高质量初榨橄榄油。随着果胶酶和纤维素酶添加量的提高,橄榄油的过氧化值及K₂₃₂均出现下降的趋势,油酸比例有一定程度提高,并在添加0.2%纤维素酶时油酸比例达到最高(65.85%)。结合主成分分析,确定了在油橄榄融合过程中添加0.5%纤维素酶得到的初榨橄榄油总酚含量和抗氧化活性最高。这是由于果胶酶和纤维素酶能有效降解橄榄细胞壁,减少亲水酚类物质与细胞壁多糖的络合,有助于橄榄果皮中的游离酚的释放,从而提高橄榄油中总酚含量及抗氧化活性。     

High Power Ultrasound: Impact on Olive Paste Temperature,Malaxation Time,Extraction Efficiency,and Characteristics of Extra Virgin Olive Oil

High power ultrasound (HPU) provides rapid heating of olive paste and disrupts cell walls, helping small oil droplets exit tissue and coalesce. This has been shown to improve oil yield and reduce malaxation time without affecting oil quality. Indirect and direct HPU at different treatment times were examined on Arbequina and Frantoio olive pastes. Olive pastes were mixed at four different malaxation times to evaluate extraction efficiency. Additionally, oil yield and different quality parameters were observed. HPU increased olive paste temperature from 20?±?0.5 to 25.5 °C, achieving the optimum kneading temperature of 29?±?1 °C in less mixing time. HPU significantly (P?<?0.05) improved oil yield by 1% for both varieties. There were no significant differences (P?>?0.05) in oil yield between 35 and 45 min malaxation time, suggesting the possibility to reduce malaxation by 10 min with HPU. No significant differences (P?>?0.05) were observed in any quality parameters observed, except peroxide value, which increased slightly. Significant increases (P?<?0.05) in total tocopherol and pigments with increasing HPU treatment time occurred, while a decrease in total polyphenol and oxidative stability index resulted after 8 min treatment. HPU influenced L, a, and b values causing the oil to become darker. Sensory results showed no differences between commercially available and HPU-treated samples. These results suggest the possibility of using HPU treatment to increase oil extraction capacity and yield without loss of product quality.     

Saturated hydrocarbon content in olive fruits and crude olive pomace oils

Olive fruits contain an n-alkane series of saturated hydrocarbons mainly in the pulp. Lower amounts of a complex mixture of paraffins, unresolved by gas chromatography (UCM – unresolved complex mixture), have been found in cuticle, stone (woody shell and seed), olive leaves, and talc used as an aid to olive oil extraction. The amounts of both kinds of hydrocarbons are related to the olive cultivar and are transferred to oils in a proportion depending on the oil-obtaining process (centrifugation or solvent extraction). In olive oil obtained by centrifugation, only n-alkanes were detected. However, in olive oil extracted by second centrifugation, small amounts of UCM paraffins were detected together with the n-alkanes. Olive pomace oils showed a very variable content of both types of hydrocarbons according to the different obtaining process, such as double centrifugation, solvent extraction or centrifugation followed by solvent extraction. ‘White mineral oil’ used in oil extraction machinery is the source of the high concentrations of UCM paraffins found in some olive and olive pomace oils. In the case of second centrifugation olive oil, a maximum limit of 50 mg kg^?1 of UCM is suggested, whereas in the case of crude olive pomace oil, it amounts to 250 mg kg^?1 plus an additional minimum of 1.0 for the n-alkanes/UCM ratio.     

Composition and organoleptic characteristics of oil from Arbequina olive (Olea europaea L) trees under deficit irrigation

This study evaluated the effects of different regulated deficit irrigation (RDI) strategies applied to olive (Arbequina cultivar) trees on the qualitative and quantitative parameters of the resulting oil during the maximum evaporative demand period for three consecutive crop seasons. Quality indices, fatty acid composition, pigments, colour, α‐tocopherol and phenolic contents, bitter index, oxidative stability and organoleptic properties of the oil were determined. Irrigation did not affect those parameters used as criteria for classifying olive oil in its commercial grades. Only polyphenol and o‐diphenol contents and, consequently, the bitter index and oxidative stability were affected by the RDI strategy, with increasing values as the water applied decreased. Regulated deficit irrigation resulted in important savings in irrigation requirements without detriment to oil quality. © 2002 Society of Chemical Industry     

Effect of olive ripeness on chemical properties and phenolic composition of chétoui virgin olive oil

BACKGROUND: The aim of the present work was to investigate the influence of fruit ripening on oil quality in an attempt to establish an optimum harvesting time for Chétoui olives, the second main olive variety cultivated in Tunisia. RESULTS: Our results showed that many analytical parameters, i.e., peroxide value, UV absorbance at 232 and 270 nm, chlorophyll pigments, carotenoids and oleic acid contents decreased during ripening, whilst oil content and linolenic acid increased. Free acidity remained practically stable with a very slight rise at the highest maturity index. The trend of oxidative stability, total phenols and o‐diphenols, showed an increase at the early stages followed by a reduction at more advanced stages of maturity. The major phenolic compounds, such as hydroxytyrosol, ligstroside aglycon, elenolic acid, acetoxy‐pinoresinol and oleuropein aglycon, seemed to have the same behaviour. In the case of tyrosol, a strong decrease was observed directly related with the ripening progress. CONLUSION: On the basis of the evolution of the analytical parameters studied, the best stage of Chétoui olive fruits for oil processing seems to be at ripeness index higher than 2.0 and lower than 3.0. Copyright © 2009 Society of Chemical Industry     

AFLP molecular markers to identify virgin olive oils from single Italian cultivars

Olive oil traceability becomes instrumental to ensure the consumer’s protection, particularly for extra virgin olive oil, the quality of which is highly related to the cultivars employed. The aim of this investigation was to evaluate the possibility of identifying the cultivar used to obtain the derived olive oil by the analysis of amplified fragment length polymorphism (AFLP) markers. To this purpose, ten virgin olive oils were prepared in the laboratory from ten different very common Italian cultivars and were then analysed using six AFLP primer combinations. The technique was optimised for fragmented DNA of oil in order to enhance the intensity of the bands in the AFLP patterns. The obtained results indicated a percentage of polymorphism ranging from 16% for Pst-AGC/Mse-AGT to 43% for Pst-AGC/Mse-ACA. The diversity index was comprised between 90.2% for Pst-AGC/Mse-AGT and 95.2% for Pst-AGG/Mse-AGG. One of the six primer combination analysed, namely Pst-AGG/Mse-AGG, was able to distinguish all the olive oil examined, and a similarity tree of the samples was elaborated.     

Influence of the malaxation time and olive ripening stage on oil quality and phenolic compounds of virgin olive oils

The main objective of this study was to evaluate the influence of the malaxation time (Mt) and ripening stage on oil quality and phenolic compounds of Hojiblanca and Picual virgin olive oils. In both varieties of oil, phenolic content and oxidative stability decreased as ripening progressed. The total level of tocopherols diminished by up to 40% as fruit ripened. The compositions of palmitic, stearic, lignoceric, oleic, linoleic and linolenic acids were significantly influenced by the ripening process. The present work shows that an increased Mt promoted the increase of free acidity (up to 13.3%) and tocopherols (up to 11.6%) and negatively affected the oxidative stability and the concentration of phenols. Further research is required to determine ripening stages and malaxation conditions for all olive oil varieties to achieve a satisfactory balance between the improvement of both oil yield and oil quality and composition.     

Towards a technological ripening index for olive oil fruits

BACKGROUND: The aim of this work was to study the evolution of sugar and oil contents in Frantoio cultivar olives during ripening in order to propose a technological ripening index for olive oil fruits. Olive fruits were picked at nine different farms once a week from the beginning of September to the beginning of December during three crop seasons. RESULTS: As a result of the biochemical phenomenon of oil formation in olive fruits, sugar concentration during ripening was shown to follow a sigmoidal decrease, which recurred periodically in different microclimates over years. This trend resulted to be the cause of an opposite sigmoidal increase in oil content. Experimental data for sugar and oil contents were also statistically related by significant linear relationships. In addition, it was observed that reaching a minimum environmental temperature of ⩽10 °C resulted in a definite minimum asymptotic value for sugars. CONCLUSION: Sugar concentration can be proposed as an accurate, reproducible index for technological ripening of olive oil fruits by the following prediction function: proper ripening degree of olives corresponds to achievement of a constant minimum value for sugar content and, consequently, a constant maximum value for oil content, associated with reduced risk of fermentation activities of olive paste. Copyright © 2009 Society of Chemical Industry     

Lipoxygenase: Optimization of Extraction and Evaluation of its Contribution to Virgin Olive Oil Aroma

The volatile compounds responsible for the pleasant aroma of virgin olive oil are mainly derived from products of the lipoxygenase pathway. Lipoxygenase activity was assessed in olive pulp extracts. An optimization of its extraction by a 2⁴ experimental design was performed. Four parameters considered as influencing the extraction were optimised using minimum and maximum levels. The polyvinylpolypyrrolidone quantity seemed to be the more influencing parameter, followed by ethylenediamine tetraacetic acid concentration, pH value, and dithiothreitol concentration. To establish whether the levels of lipoxygenase activity correspond to the enhancement of olive oil aroma, we investigated the addition of soybean lipoxygenase extracts during malaxation. Volatile profiles analysis showed that lipoxygenase had a potential effect on the production of green and fruity note of olive oil.     

Effect of growing location,malaxation duration and citric acid treatment on the quality of olive oil

BACKGROUND: The total phenolic compounds of olive oil exert antiradical activity at cellular level and can prevent cardiovascular disease, metabolic syndrome and cancer. Increased awareness of its health benefits has increased the consumption of olive oil around the world. An alternative processing technique effective in increasing the amount of oil extracted while maintaining the oil quality is needed to meet the rising global demand for olive oil. RESULTS: Addition of 0.3 g mL^?1 citric acid at 1:1000 (v/w) to olive paste followed by a 30 min malaxation period significantly increased the oil recovery, concentration of total phenolic compounds and antiradical activity by 46.23, 120.27 and 31.48% respectively. While there was no significant effect on the acidity, the peroxide value was significantly reduced by 63.85%. The organoleptic characteristics of the olive oil extracted with citric acid were also comparable to those of the control. CONCLUSION: Addition of 0.3 g mL^?1 citric acid (i.e. 30% w/v) at 1:1000 (v/w) to olive paste followed by a 30 min malaxation period in a Blixer^® 4.0 blender is the most promising extraction technique to improve the oil recovery, concentration of total phenolic compounds and antiradical activity of the extracted olive oil without compromising other quality parameters. © 2012 Society of Chemical Industry     

Horizontal centrifuge with screw conveyor (decanter): Optimization of oil/water levels and differential speed during olive oil extraction

Olive oil extraction using a horizontal centrifuge with a screw conveyor is an essential operation to reduce production costs. However, proper control of the plant is required to maintain a high level of extraction yield and olive oil quality. Rheological characteristics of the olive paste, which change in relation to water content, fruit variety, maturity level and seasonal temperature variations, greatly affect the efficiency of centrifugal extraction. If olive paste is fed to a decanter without automatic control, then non-optimal extraction is performed.