Dubravka Škevin

Glycemic index and phenolics of partially-baked frozen bread with sourdough

Different lactic acid bacteria starters were used to prepare sourdough to make partially-baked frozen wholemeal wheat bread. The sourdough was prepared with a pure culture of Lactobacillus plantarum or with commercial starters containing Lactobacillus brevis combined with Saccharomyces cerevisiae var. chevalieri (LV4), Lactobacillus fermentum (PL1), or Lactobacillus fermentum with phytase (PL3). We determined the acetic and lactic acid concentrations in sourdough, bread chemical composition, total phenolics content and glycemic index (GI) in vivo. Depending on the starter, the lactic to acetic acid ratio in the sourdough was significantly different. The GI of control bread without sourdough (70) was significantly higher than that of bread containing sourdough prepared with LV4 starter (50), PL1 starter (56) or PL3 starter (56), but not from bread with L. plantarum sourdough (60). The addition of 10% sourdough with a lower molar ratio of lactic to acetic acid ( ≤ 4) and higher total phenolics content is preferable for generating bread with medium and low GI.

Changes in 4-vinylsyringol and other phenolics during rapeseed oil refining

The aim of the present study was to examine changes in phenolic compounds during refining of rapeseed oil. In crude rapeseed oil, 4-vinylsyringol (canolol) is the dominant phenolic compound, accounting for 85% of total phenolics. Refining decreased the total amount of phenolic compounds by 90%. NMR and MS analyses of edible rapeseed oil phenolic extracts identified 4-vinylsyringol dimer as the dominant phenolic compound. This phenolic compound appears to form through acid-catalyzed dimerization-aromatic substitution of 4-vinylsyringol monomers. Analysis of rapeseed oils from different stages of the refining process suggest that 4-vinylsyringol dimer forms during the neutralization phase, when H3PO4 acts as a catalyst, or during bleaching, when acid-activated bleaching earth acts as the catalyst. Whether 4-vinylsyringol forms during one or the other phase appears to depend on the phospholipid content of the crude oil. These insights may be useful for designing rapeseed oil refining processes that maximize levels of 4-vinylsyringol dimer.

Chapter 4 – Lipids

This chapter describes lipids, their nutritional and functional properties as well as the impact of processing in their bioaccessibility. The effect of emerging (nonthermal) processing technologies (e.g., high-pressure processing, pulsed electric field, cold plasma (CP), ultrasound (US), irradiation, high-pressure homogenization) on lipids is emphasized. Lipids can be very easily oxidized during processing, and some of the nonthermal technologies (e.g., CP and US) are considered as advanced oxidation processes. Indeed, they are conducted near ambient temperature and are based on highly reactive radicals. Consequently, during modern food processing the stability of lipids has to be considered.

Tocopherols: Chemical Structure, Bioactivity, and Variability in Croatian Virgin Olive Oils

Virgin olive oil (VOO) represents a rich source of natural antioxidants, with tocopherols as the most effective group of lipophilic, phenolic antioxidants. αTocopherol represents more than 95% of the total tocopherols in virgin olive oil, and it possesses the highest biological activity among members of the vitamin E family. Content and composition of the tocopherols of virgin olive oil depend on several agronomic factors, as well as olive processing and oil storage conditions. In this chapter, the tocopherol homologue activity in virgin olive oil and the biological importance are discussed. Research work is reported on the tocopherol content and composition variability in virgin olive oils of the most widespread Croatian cultivar “Oblica” and Italian cultivar “Leccino.” Factors studied such as year, growing area and olive fruit ripening and their influence on the tocopherol content and composition of virgin olive oils are discussed. The effect of filtration of the oil and storage conditions on tocopherols are also examined.