Lactose-free Dulce de leche: compositional characterization, browning and texture profile

Our objective was to elaborate lactose-free Dulce de leche (DL) and evaluate the influence of the hydrolysis of this sugar on the attributes of the products. Fluid milk used was divided into two portions and, in one of them, enzymatic hydrolysis of lactose was carried through. Next, the homogenization of milk was performed at 20 MPa. Four different treatments were studied. The final products were evaluated in relation to their composition and physico-chemical characteristics. The main results show that the homogenized lactose-free DL obtained a higher concentration of free 5-Hydroxymethylfurfural (HMF) (133.77 ± 3.42 μmol l−1). Consequently, browning was more intense due to Maillard Reaction. Texture parameters were higher (1611.00 ± 598.78 g hardness and 19.52 ± 2.46 g gumminess) when compared to the homogenized traditional product (28.45 ± 1.16 μmol l−1 free HMF, 437.17 ± 279.3 g hardness, and 406.20 ± 311.69 g gumminess). Lactose-free products are in high demand by consumers; however, the results of this work highlight the challenges to properly control the browning and the texture parameters of DL.

Arrested development – a comparative analysis of multilayer corona textures in metamorphic rocks

Coronas, including symplectites, are vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include P, T and aH2O during formation, continuous or non-continuous corona formation, reactant bulk compositions and extent of metasomatic exchange with the surrounding rock, relative diffusion rates for major components, and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P-T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P-T conditions during successive layer growth along the P-T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steady-state growth at constant P and T. Corona formation in pelitic and mafic bulk rock compositions requires dry, restitic bulk rock compositions. Since most melt is lost at or near peak conditions only a fraction of melt is retained in the restitic post-peak assemblage. Reduced melt volumes with cooling limit length-scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for kinetically-constrained corona growth are only commonly realised in mafic rocks, owing to their intrinsic anhydrous bulk composition, and in dry, restitic pelitic compositions that have lost melt in an earlier metamorphic event. Mafic and pelitic prograde coronas show similar ranges of thickness and vermicule size; prograde contact aureole coronas display similar thicknesses but slightly longer vermicule lengths compared to regional metamorphic coronas. Retrograde coronas in mafic rocks are significantly thinner than pelitic coronas and have smaller vermicule lengths, whereas retrograde pelitic coronas show similar parameters to their prograde counterparts. Reduced maximum corona thickness and smaller maximum vermicule size in retrograde mafic coronas compared to retrograde pelitic coronas attests to more restricted length-scales of diffusion in melt-poor, anhydrous, mafic bulk rock compositions. Increased maximum layer thickness and vermicule size in prograde mafic coronas compared to retrograde mafic coronas is due to greater length-scales of diffusion in more melt-rich bulk compositions with protracted reaction along the prograde path. Prograde pelitic coronas do not differ significantly from retrograde pelitic coronas with respect to microstructure, owing to the intrinsically more hydrous pelitic bulk compositions and capacity to generate diffusion-enhancing melt during decompression. Through the application of either quantitative physical diffusion modelling of coronas or phase equilibria modelling utilising calculated chemical potential gradients, it is possible to model the evolution of a corona through P-T-X space by continuous or non-continuous processes. Since corona modelling employing calculated chemical potential gradients assumes nothing about the sequence in which the layer forms and is directly constrained by phase compositional variation within a layer, it allows far more nuanced and robust understanding of corona evolution and its implications for the path of a rock in P-T-X space. Key words: corona, chemical potential gradient, diffusion, disequilibrium, metamorphism, mineral compositional zoning, reaction dynamics, reaction texture, symplectite.

Spectroscopic characteristics of humic acids originated in soils and lignite

The aim of our work was to characterise the stability, humification degree, and principal classes of fluorophores in humic acids isolated from different matrices. Soil humic acids were isolated from arable soils and grassland that differ in the texture and moisture regimes (e.g. aquic; udic; and ustic moisture regimes). Basic soil characteristics, such as total organic carbon content, humus fractionation, cation exchange capacity, soil reaction, texture, and optical indexes were determined. The international standard method for humic acids (HA) isolation was used. Lignite represents a valuable organic substrate, with mineral inclusion situated on the transformation route from phytomass to a dehydrated, dehydrogenated, and deoxidised carbon type complex and water. One of the most attractive ways of non-energetic exploitation of lignite is humic substances source exploitation. It is known that humic acids isolated from lignite show typical bands known from other HA soil samples due to aromatic and various C-O structures. Spectroscopic characterisation has been a topic of great interest, chemical species being analysed with respect to the overall spectral characteristics of the system. Therefore UV-VIS, FTIR, and synchronous fluorescence spectroscopy (SFS) were applied in our study. The elemental composition and ash content in HA samples were determined. HA preparations were more hydrated in hydromorphic soils (Fluvi-Eutric Gleysol and Gleyic Stagnosol). The highest carbon content was found in lignite HA (57.5 weight %). Generally, carbon content was decreasing in the following order: Lignite HA > Haplic Chernozem HA > Fluvi-Eutric Gleysol HA > Haplic Luvisol HA > Gleyic Stagnosol HA > Eutric Cambisol HA. FTIR spectroscopy showed that the aromatic indexes varied from 0.61 to 0.73. HA were divided into two groups according to the aromatic and aliphatic compounds in their molecules. The highest aromatic degree and stability was found in lignite HA and Haplic Chernozem HA. Humic acids isolated from grassland and hydric soils contained more aliphatic and newly formed compounds. Synchronous fluorescence scan spectra identified aliphatic compounds in grassy and hydric soils at lower wave lengths. At higher wave lengths, identical fluorophores were detected. We registered five main peaks at: 467/487, 481/501, 492/512, 450/470, 339/359 (at Δλ = 20 nm). The peaks positions corresponded to the fluorescence behaviour of Elliot soil HA standard. Only lignite HA revealed another fluorescence peak at 492/512 nm. The peaks positions complied with the fluorescence behaviour of Leonardite standard HA. The relationships between the fluorescence indexes, colour indexes, aromatic indexes, humification degree, and elemental composition were evaluated by correlation analysis.