Bojan Butinar

Chemical changes in extra virgin olive oils from Slovenian Istra after thermal treatment

Changes in the physico-chemical parameters of extra virgin olive oils after heating for 142h at 100°C with an air flow 10L/h were investigated. The experimental study was carried out on the two predominant olive cultivars in Slovenian Istra - cv. Istrska belica and cv. Leccino. The data obtained showed that oils from Istrska belica were more stable than those from Leccino. Peroxide values and spectrophotometric data showed higher amounts of oxidation products in oils from Leccino than in those from Istrska belica. After thermal treatment fatty acid composition was changed more in Leccino oils; particularly the amounts of polyunsaturated fatty acids dropped significantly, while α-tocopherol was completely depleted in all samples. The content of total biophenols decreased from 598mg/kg to 241mg/kg in Istrska belica oils and from 391mg/kg to 176mg/kg in Leccino oils. HPLC data showed that transformation of secoiridoid biophenols to the simple biophenols, tyrosol and hydroxytyrosol took place.

Monitoring of Quorum-Sensing Molecules during Minifermentation Studies in Wine Yeast

At high cell density or under low nutrient conditions, yeasts collectively adapt their metabolism by secreting aromatic alcohols in what is known as quorum sensing. However, the mechanisms and role of quorum sensing in yeast are poorly understood, and the methodology behind this process is not well established. This paper describes an effective approach to study quorum sensing in yeast fermentations. The separation, detection, and quantification of the putative quorum-sensing molecules 2-phenylethanol, tryptophol, and tyrosol have been optimized on a simple HPLC-based system. With the use of a phenyl HPLC column and a fluorescence detector, the sensitivity of the system was significantly increased. This allowed extraction and concentration procedures to be eliminated and the process to be scaled down to 2 mL minifermentations. Additionally, an innovative method for rapid viable-cell counting is presented. This study forms the basis for detailed studies in kinetics and regulation of quorum sensing in yeast fermentation.

Influence of Phenols Mass Fraction in Olive (Olea europaea L.) Paste on Volatile Compounds in Buža Cultivar Virgin Olive Oil

The influence of the phenolic content in olive paste of cv. Buža increased by the addition of an aqueous solution of phenolic extract of freeze-dried olive pulp (cv. Istarska bjelica) on the final products of the lipoxygenase pathway in oil was studied. Increases by 12, 38, and 56% for ripe fruits (maturity index = 4.0) and by 38% for unripe fruits (maturity index = 1.2) were examined. Phenols in the olive paste were determined according to the HPLC method, whereas volatiles in oil were determined according to SPME-GC-MS. A significant negative effect on Z-3-hexenal and E-2-hexen-1-ol (Tukeys test, p < 0.05) was found for ripe fruits (average decreases of 55 and 60%, respectively), but not for the unripe sample. Positive effects in both ripening levels were found for Z-3-hexenyl acetate (average increase of 68% for ripe and a double increase for unripe fruits) and total C5 compounds (average increase of 32% for ripe and an increase of 30% for unripe fruits).

Impact of weather conditions and drought stress on primary and secondary metabolites of olives from Slovenian Istra

Sugars, the primary metabolites of plants, play an important role in the process of olive ripening, as they provide energy for metabolic changes and serve as a source for the biosynthesis of fatty acids. Phenolic compounds, which are secondary metabolites, can be synthesized in plants as a reflection of stressful situations such as tissue damage and UV irradiation. The objective of this study was to assess the impact of different irrigation treatments (0, 15, 33, 40, and 100% crop evapotranspiration (ETc)) on primary metabolites (sugars, sugar alcohols) and secondary metabolites (phenolic compounds). In different phenological periods, the levels of oleuropein, sugars and sugar alcohols were determined in olives and leaf samples in the crop years 2014, 2015, and 2016. The levels of oleuropein in olive fruits and leaves were highest under the irrigation treatment of 40% ETc and decreased noticeably under the irrigation treatment of 100% ETc. The median levels of glucose were higher compared with the mannitol and fructose levels in olive fruits. Total determined sugars in olive fruits during maturation decreased. While significant correlations were found in olive fruits between determined sugars and sugar alcohols and different irrigation treatments, we did not observe any correlation between determined sugars and sugar alcohols in olive leaves and irrigation treatments. Our research confirmed the complexity of the content of oleuropein and sugars or sugar alcohols in the leaves and fruits of olive trees from Slovenian Istra, which depend on various factors, not just drought stress. Weaker and less obvious correlations between the studied compounds and drought stress might be a consequence of unusual rainfall in the studied crop years.

Genetic, Biochemical, Nutritional and Antimicrobial Characteristics of Pomegranate (Punica granatum L.) Grown in Istria

This study characterises the genetic variability of local pomegranate (Punica granatum L.) germplasm from the Slovenian and Croatian areas of Istria. The bioactive components and antioxidant and antimicrobial properties of ethanol and water extracts of different parts of pomegranate fruit were also determined, along with their preliminary nutritional characterisation. Twenty-six different genotypes identified with microsatellite analysis indicate the great diversity of pomegranate in Istria. The pomegranate fruit ethanol extracts represent rich sources of phenolic compounds (mean value of the mass fraction in exocarp and mesocarp expressed as gallic acid is 23 and 16 mg/g, respectively). The ethanol extracts of pomegranate exocarp and mesocarp showed the greatest antimicrobial activity against Candida albicans, Candida parapsilosis, Rhodotorula mucilaginosa, Exophiala dermatitidis and Staphylococcus aureus, and the same water extracts against S. aureus and Escherichia coli. To the best of our knowledge, this study represents the first report of the characterisation of pomegranate genetic resources from Istria at different levels, including the molecular, chemical, antimicrobial and nutritional properties.

Extra Virgin Olive Oil and Table Olives from Slovenian Istria

Olive oil production has a long tradition in Slovenian Istria, and extra virgin olive oil from the region with protected designation of origin (EDOOSI ZOP) is the first Slovenian agricultural product to be registered at the European level, while table olives from Slovenian Istria avail of a protected designation of origin at national level. EDOOSI ZOP has been produced from different olive varieties or from a single olive variety grown in the area of Slovenian Istria. The blended olive oil is characterised by a specially bitter and piquant taste resulting from the fact that it contains at least 30 % of ‘Istrska belica’ olives. In Slovenian Istria, table olives are usually processed using the traditional production technology that involves initial debittering in water for 10–20 days, which is replaced every 2 days, and fermentation in a brine solution. The table olives produced are lightly sour, bitter and salty and are characterised by a good separation between flesh and stone. The flesh of ‘Storta’ table olives, a variety that is very popular among consumers, easily detaches from the stone.