O. Koprivnjak, K. Brkić Bubola, U. Kosić: Sodium chloride compared to talc as processing aid has similar impact on volatile compounds but more favourable on ortho-diphenols in virgin olive oil, European Journal of Lipid Science and Technology 2016, 118 (2) 318–324. (Q2) Abstract: The possibility of improvement of olive paste extractability by addition of talc or NaCl (1%, 2% and 3% mass ratio in olive paste), or their combinations (“talc 1.5% + NaCl 1.5%”; “talc 1% + NaCl 2%”; “talc 2% + NaCl 1%”), was investigated on a laboratory scale. Volatiles in oil samples were determined by headspace solid-phase microextraction with GC-MS, while ortho-diphenols by solid phase extraction and UV-VIS spectrophotometer. Significantly higher extractability of oil (from 25 to 29% compared to control, P < 0.05) was obtained by 3% of talc or NaCl and their combinations in mass ratio 1:2 or 2:1. At 3% addition level, no significant decrease of C6 aldehydes was observed, while significant increase of C6 alcohols (talc or salt) as well as of C5 compounds and terpenes (salt) occurred. Mass ratio of ortho-diphenols in oil was not influenced by talc, while NaCl led to significantly higher values compared to control (by 10-15%, P < 0.05). Practical applications: The influence of processing aids on characteristics of virgin olive oil has mainly been evaluated through the standard chemical quality parameters, while limited information about desirable volatile compounds of thus obtained extra virgin olive oils has been published so far. The results of this research show that NaCl can be used not only as a tool for enhancing the extractability, but also as a means for improving the nutritional value of virgin olive oils from cultivars which generally show low levels of hydrophilic phenols.
V. Majetić Germek, O. Koprivnjak, B. Butinar, L. Pizzale, M. Bučar-Miklavčič, L. S. Conte: Phenols and Volatiles of Istarska bjelica and Leccino Virgin Olive Oils Produced with Talc, NaCl and KCl as Processing Aids, Journal of the American Oil Chemists' Society (2016) 93:1365–1372 (Q2) Abstract: The effect of processing aids (2.5 % of talc, NaCl or KCl) on oil extractability and the profile of phenolic and volatile compounds of Istarska bjelica and Leccino oils was studied. Talc significantly increased extractability in both cultivars, while salts increased extractability in Leccino cv. In the laboratory extracted oils, phenols were determined by a RP-HPLC–DAD method, whereas volatiles were determined by SPME/GC–MS. Talc addition significantly decreased hydroxytyrosol and increased ligstroside derivatives in produced oils, but did not affect the total phenol content. Among volatile compounds, only Z-2-penten-1-ol in Leccino and 1-pentene-3-one in Istarska bjelica oils significantly increased by talc addition. Salts improved transfer of most individual phenols into oil, particularly oleuropein derivatives, and increased C6 aldehydes and C5 volatiles in Leccino oils. NaCl exerted a stronger effect in increasing individual phenols and volatiles than KCl.
V. Majetić Germek, O. Koprivnjak, B. Butinar, L. Pizzale, M. Bučar-Miklavčič, L. S. Conte: Influence of malaxation time on phenols and volatile compounds of virgin olive oil obtained from phenol enriched olive paste (Buža cv.) Proceedings of the 8th International Congress of Food Technologists, Biotechnologists and Nutritionists, Opatija (Croatia), 21 - 24 October 2014, (J. Frece, ed.) p. 93-98. ISBN 978-953-99725-6-9 Abstract: Biochemical synthesis of virgin olive oil volatile substances during olive processing depends on activity of endogenous enzymes involved in the LOX pathway. Phenols present in olive paste could be one of the inhibitory factors, since it is known that phenolic compounds are able to bind and inhibit various enzymes. Olive paste of Buža cultivar, known to have low phenols content and a relatively high C6 volatiles mass ratio in oil, was fortified with phenolic extract from olive fruits during processing, in order to study the effect on volatile compounds in oil. Oil samples were obtained by a laboratory plant from olive pastes containing two levels of phenols content (real and increased by 20%). Phenols in oils were determined by RP HPLC with UV-DAD detection using tyrosol, apigenin and luteolin (calibration standards) and syringic acid (internal standard). Volatiles were analysed by SPME-GC-MS with 4-methyl-2-pentanol as an internal standard. The increase of total phenols mass ratio in olive paste by 20% has led to a much higher rise of phenols in oil samples (hydroxytyrosol 185%; oleuropein and ligstroside derivatives by 175% and 750%, respectively). Oils from fortified pastes had up to 10 times reduced values of Z-3-hexenal and 2 times of E-2-hexenal, E-2-hexen-1-ol and hexyl acetate. Other substances (hexanal, E-3-hexen-1-ol, Z-3-hexenyl acetate and C5 compounds) showed minor changes in relation to the increased phenols mass ratio in olive paste. A relatively low odour threshold value of Z-3-hexenal, E-2-hexenal and E-2-hexen-1-ol suggests that a radical decrease of their mass fraction in oil should have an evident negative impact on the perception of green odour notes. Results confirm the hypothesis of inhibitory effect of phenols compounds in olive paste on the biosynthesis of the most important volatile compounds of pleasant virgin olive oil aroma.
K. Brkić Bubola, O. Koprivnjak: poglavlje 3.1. Influence of Filtration on Composition of Olive Oils, u: Processing and Impact on Active Components in Food (ur. V. R. Preedy), Elsevier, Academic Press, London (2015) ISBN: 978-0-12-404699-3 Abstract: Immediately after extraction from olive fruits, virgin olive oil is a turbid juice with suspended particles of plant tissue and vegetable water droplets, which can deteriorate their quality by facilitating hydrolysis or oxidation of oil. Recently, filtration becomes a standard virgin olive oils production step with the aim of faster product finalisation and shelf life extension. Filtration of olive oil could influence changes on antioxidant compounds such as phenols, tocopherols and pigments as well as volatile substances responsible for pleasant virgin olive oil aroma. In this work, changes of these minor compounds and fatty acids in relation to different filtration systems applied to virgin olive oil are discussed. In addition, influences of several agronomic and technological factors on composition of active compounds of virgin olive oil are reviewed. Moreover, analytical techniques for determination of virgin olive oil active components are pointed out. Chapter points:
K. Brkić Bubola, O. Koprivnjak, B. Sladonja, I. Belobrajić: Influence of storage temperature on quality parameters, phenols and volatile compounds of Croatian virgin olive oils, Grasas y Aceites 2014, 65 (3) doi: http://dx.doi.org/10.3989/gya. (0017-3495) (Q2) Abstract: The influence of low storage temperature (+4 °C and −20 °C) and conventional storage room temperature on the quality parameters, phenolic contents and volatile profiles of Buža, Črna and Rosinjola monovarietal virgin olive oils after 12 months of storage was investigated in this study. Virgin olive oils stored at low temperatures maintained better quality parameters than oils stored at room temperature. A negligible decrease in the total phenols was detected after 12 months of storage at all investigated temperatures. The total volatile compounds, aldehydes, alcohols and esters in almost all stored samples were unchanged compared to fresh oils. Total ketones increased after storage, although at a lower temperature these changes were less notable. An increase in the oxidation indicators hexanal and hexanal/E-2-hexenal ratio was the lowest in oils stored at +4 °C. Storage at temperatures lower than room temperature could help to prolong the shelf-life of extra virgin olive oil by maintaining high quality parameters and preserving the fresh oil’s volatile profile.
O. Koprivnjak, A. Kriško, S. Valić, D. Carić, M. Krapac and D. Poljuha: Antioxidants, radical-scavenging and protein carbonylation inhibition capacity of six monocultivar virgin olive oils in Istria (Croatia), Acta Alimentaria 2016, 45 (3) 427–433.(Q3) Abstract: Six monocultivar virgin olive oils (VOOs) produced from five autochthonous (Buža, Buža Puntoža, Istarska Bjelica, Porečka Rosulja, and Rosinjola) and one referent cultivar (Leccino), were investigated. The mass fractions of ortho-diphenols (ORT) and tocopherols (TOC) were analysed by VIS spectroscopy and HPLC. The radical-scavenging capacity was evaluated by electron spin resonance spectroscopy (ESR) using galvinoxyl free radical and the DPPH test. Results revealed a high level of total TOC in VOOs of Buža Puntoža (243 mg kg–1) and Porečka Rosulja (325 mg kg–1). VOOs contained in 100 g from 79% (Istarska Bjelica) to 261% (Porečka Rosulja) of recommended daily allowance of α-tocopherol. The mass fraction of ORT in Istarska Bjelica and Rosinjola was >250 mg kg–1 (on average 30–40% higher in comparison to other studied cultivars). Istarska Bjelica and Porečka Rosulja showed the highest antioxidant capacity in both methods of measurement. The highest capacity to inhibit protein carbonylation (PC) in response to oxidative stress (54–56%) was displayed by Buža Puntoža, Leccino, and Buža. High level of positive linear correlation between ORT mass fraction and radical-scavenging capacity measured by DPPH test (r=0.768), as well as strong negative correlation between PC inhibition and mass fraction of ORT (r= –0.697), were observed.
K. Brkić Bubola, M. Lukić, I. Mofardin, A. Butumović, O. Koprivnjak: Filtered vs. Naturally Sedimented and Decanted Virgin Olive Oil during storage: Effect on Quality and Composition, LWT - Food Science and Technology 84 (2017) 370-377. (Q1) Abstract: The aim of this study was to compare quality changes and compositional characteristics (fatty acids, total phenols, sensory profile) during 12 months storage of Buza and Istarska bjelica cv. virgin olive oils clarified by filtration at an industrial scale (filter press equipped with cellulose filters) and those clarified by natural sedimentation and decantation, as well as the influence of filtration of virgin olive oils on sterols and triterpene dialcohols composition. There were no significant differences in hydrolytic deterioration and sensory scores during the whole storage period between filtered and naturally sedimented oil samples. After 6 months, natural sedimentation was more favorable as regards delaying of oxidative deterioration, while filtration provided a more stable sensory profile. As regards total phenols the impact of the clarifying procedure was dependent on cultivar and fruit ripeness degree and it was more emphasized than the impact of storage. Filtration slightly affected the fatty acids composition, but natural sedimentation and decantation had no effect on it. Nevertheless, filtration did not compromise the confirmation of virgin olive oil authenticity according to the fatty acid composition, as well as according to sterols and triterpene dialcohols. Highlights:
• Filtration vs. natural sedimentation and decantation of virgin olive oil (VOO).
• Filtration cause higher oxidation of VOO than sedimentation and decantation.
• Sensory profile of filtered VOO is more stable during storage than decanted VOO.
• Filtration affects the fatty acids composition, but decantation has no effect on it.
• Filtration does not compromise the VOO authenticity confirmation.
I. Lukić, M. Žanetić, M. Jukić Špika, M. Lukić, O. Koprivnjak, K. Brkić Bubola: Complex interactive effects of ripening degree, malaxation duration and temperature on Oblica cv. virgin olive oil phenols, volatiles and sensory quality, Food Chemistry 2017, Volume 232, 610-620. (Q1) Abstract: The interactive effects of ripening degree, malaxation duration and temperature on Oblica cv. (Olea europaea L.) virgin olive oil phenols, volatiles, and sensory quality were investigated. Olives were picked at three ripening degrees with International Olive Council indices of 0.68, 2.48 and 4.10, and processed by malaxation at 22 and 30 °C, and at both temperatures for 30 and 60 min. Ripening exhibited the strongest effect, and malaxation duration the weakest. Phenols were generally found to decrease during ripening; however 3,4-DHPEA-EDA and p-HPEA-EDA increased. Similar behaviour was observed for (E)-2-hexenal. Higher malaxation temperature induced an increase in particular important phenols and C6 alcohols, while C6 aldehydes mostly decreased. Interactions between the factors were established, mostly between ripening degree and malaxation temperature: the effect of the latter was most pronounced for ripe olives, especially for 3,4-DHPEA-EDA, p-HPEA-EDA and C6 volatiles. Sensory attributes were generally in agreement with the chemical composition. Highlights:
• Interactive effects of ripening and malaxation on olive oil quality were studied.
• Ripening degree exhibited the strongest effect, and malaxation duration the weakest.
• Ripening degree and malaxation temperature interacted most strongly.
• The effect of malaxation temperature was the strongest for ripe olives.
|Valerija Majetić Germekfirstname.lastname@example.org|
|dr. sc. Urška Kosićemail@example.com|
|dr. sc. Karolina Brkić Bubolafirstname.lastname@example.org|
|izv. prof. dr. sc. Dubravka Škevinemail@example.com|
|prof. dr. sc. Lanfranco Contefirstname.lastname@example.org|
|Milena Bučar Miklavčič||Milena.Miklavcic@guest.arnes.si|