Effects of mild temperature conditions during dehydration procedures on saffron quality parameters

BACKGROUND: The dehydration procedure is responsible for saffron sensorial properties: colour, taste and aroma. Changes in the compounds responsible for these characteristics have been studied when dehydration processes at high and low temperature are employed. However, the evolution of these changes at mild temperatures is not available in the current bibliography. In this paper the effect of different mild conditions (18–20 °C for 24 h, 40–50 °C for 75 min and 55 °C for 75 min) applied to 45 saffron samples with the same origin was investigated. RESULTS: Crocetin esters, the compounds responsible for saffron colour, increased their content with no significant differences from other processes when high temperatures (55 °C) were used, thus producing a noticeable increment in saffron colouring capability. Similar behaviour was obtained for picrocrocin, the compound responsible for saffron taste, with higher average content at the highest temperature (55 °C) but without significant differences with the inferior conditions (40–50 °C). However, more volatile compounds were generated, especially safranal,at higher temperatures, e.g. 55 °C, during the dehydration procedure. CONCLUSIONS: The results found support the idea for employing mild to high temperatures during the dehydration process of saffron. Copyright © 2010 Society of Chemical Industry     

Prediction of Infinite Dilution Volatilities of Aroma Compounds in Water

ABSTRACT: The prediction of infinite dilution volatilities (Henry's law constants) of aroma compounds is examined. At 25 °C, the Bond Contribution model is recommended. At other temperatures where the Bond Contribution model cannot be used, the Kow-UNIFAC group contribution model, coupled with either experimental or predicted by the Antoine-Grain model vapor pressure values, provides estimates only of the volatilities with errors in the range of 20% to 40%. Finally, the effect of a cosolvent (ethanol) on the infinite dilution volatilities of some aroma compounds is examined.     

Hierarchical simulation approach to structure and dynamics of polymers

Many different theoretical and simulation techniques are available for studying the properties of polymer systems, over a wide range of length and time scales. Recent progress has seen a major improvement in the links between the different scales. Thus quantitative and rigorous connections between molecular structure and bulk properties for microstructurally complex materials could soon become a reality.     

M-dimensional Cayley-Hamilton theorem

The theorem states that every block square matrix satisfies its own m-D (m-dimensional, m⩾1) matrix characteristic polynomial. The exact statement and a simple proof of this theorem are given. The theorem refers to a matrix A subdivided into m blocks, and hence having dimension at least m. The conclusion is that every square matrix A with dimension M satisfies several m-D characteristic matrix polynomials with degrees N₁ . . ., N _m, such that N₁+ . . . +N_m ⩽M     

The effects of local structural relaxation on aluminum siting within H-ZSM-5

Semiempirical molecular orbital calculations have been performed to study aluminum siting in H-ZSM-5 zeolites. Local structural rearrangements upon substituting aluminum (with a charge compensating proton) for silicon are found to be important. The T12 site is found to be the most preferred site for aluminum substitution. However, the calculated energetics for substitution show that several tetrahedral sites are energetically comparable with regard to aluminum siting. Results pertaining to the electronic properties of the acidic site upon aluminum substitution at each of the twelve distinct tetrahedral sites are presented. The acidic center is found to be a rather soft species, with the HOMO-LUMO energy gap being roughly 8 eV.     

Computation of the stability margin of two-dimensional discretesystems

Two methods of computing the stability margin of two-dimensional discrete systems are presented. The first method uses the Schur-Cohn stability criterion, and the second method is based on results concerning the 1-D Lyapunov equation with complex coefficients. Several examples illustrate the applicability of the two methods     

Evidence of a role for plant proteases in the degradation of herbage proteins in the rumen of grazing cattle

Protein breakdown in the rumen is generally regarded as a two-stage process in which proteases produced by rumen microorganisms cleave plant protein into peptides and amino acids. However, many of the fiber-degrading cellulolytic species in the rumen are not in fact proteolytic, and the proteolytic activity of the entire rumen microbial population is only moderate when compared to the gastric and pancreatic secretions in the abomasum. Moreover, plant cell walls remain largely intact after initial chewing (particularly in cattle), presenting a physical barrier that must be breached prior to their effective colonization. The present study considers the hypothesis that the plant enzymes are at least partly responsible for herbage protein degradation in grazing ruminants. Ryegrass, red clover, white clover, and bird's-foot trefoil were incubated in the presence and absence of rumen microorganisms. The production of volatile fatty acids indicated the level of microbial activity, whereas the relative disappearance of the large subunit of ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco LSU) indicated proteolytic activity. In all incubations, the relative abundance of the Rubisco LSU decreased as the incubation progressed. When rumen microorganisms were absent, low molecular weight peptides (below 20 kDa) accumulated as the incubation progressed. This accumulation was not observed in the presence of rumen microorganisms. Therefore we suggest that the intrinsic plant proteases contribute to the initial stages of proteolysis of grazed herbage.