Rate-Controlling Mechanisms in the Photo-degradation of 5-Hydroxymethylfurfural

Rate-controlling mechanisms in the photo-degradation of 5-hydroxymethylfurfural (HMF) were studied applying kinetic and thermodynamic compensations. Aqueous solutions of HMF were prepared at a concentration of 100 mg L^?1 and at pH values of 3, 3.4, 4, and 5. The UV irradiation of samples was performed in an installation consisting of a black chamber containing the reactor and a mid-pressure mercury lamp with emission wavelengths between 250 and 740 nm. Every sample was irradiated at 12, 25, 35, and 45 °C for 120 min, analyzing their HMF content each 10 min. The photo-degradation data fitted well to zero-order kinetic model, and the constant values were used to study whether the kinetic and thermodynamic compensation could be applied. The isokinetic temperature was very similar for kinetic compensation (T_B?=?278.0 K) and thermodynamic compensation (T_B?=?277.8 K). Applying the Leffler’s criterion, the HMF photo-degradation was entropically controlled, probably as a consequence of hydrophobic interactions. In order to check the entropical control, two experiments were repeated at pH 3 but avoiding agitation. As the new obtained kinetic constants were highly different from the values previously obtained using agitation, it can be concluded that the HMF photo-degradation is an entropy-controlled process and can be speeded up by changing non-thermal parameters, like agitation.     

Effect of UV–Vis Photochemical Processing on Pear Juices from Six Different Varieties

The effect of ultraviolet irradiation on the activity of polyphenol oxidase and peroxidase in pear juices from six different varieties (Abate Fétel, Passa Crassana, Ercolini, Flor de Invierno, Blanquilla, and Conference) was investigated. The samples were irradiated for 120 min with a 400-W nominal power medium-pressure mercury lamp, emitting in a range between 250 and 740 nm. The temperature was kept at 25?±?1 °C with help of a refrigeration system consisting on a metallic coil fed with cold water. Polyphenol oxidase was inactivated in different rates, depending on each variety’s properties. Besides, as irradiation time increased, there was a general decrease in the absorbance spectrum, which means that some of the juice’s pigments could have been damaged. This decrease was especially significant between 400 and 450 nm. These changes were also observed by means of CIELab parameters. Vitamin C also decreased during the treatment. No variations in the pH, soluble solids, and sugar content were observed.     

Protective Effect of Melanoidins from Fructose–Glutamic Acid on Polyphenol Oxidase Inactivation by Ultraviolet–Visible Irradiation

Ultraviolet irradiation has been proved to be effective for inactivating polyphenol oxidase in some fruit derivatives. However, some compounds that may be found in these products, such as melanoidins, can protect the enzyme during the irradiation process. In this piece of work, the protective effect of melanoidins synthesized from fructose and glutamic acid on Agaricus bisporus polyphenol oxidase inactivation by ultraviolet–visible irradiation has been assessed. The polymers with molecular mass lower than 150 kDa had a greater protective effect than those molecules higher than 150 kDa. If the obtained melanoidins are not fractioned by their molecular mass, the protective effect that they exert is lower. It was found that the most effective radiation to inactivate this polyphenol oxidase is that between 260 and 310 nm.     

A comprehensive survey of image segmentation: clustering methods,performance parameters,and benchmark datasets

Multimedia Tools and Applications - Image segmentation is an essential phase of computer vision in which useful information is extracted from an image that can range from finding objects while...     

Effect of UV–Vis Irradiation on Enzymatic Activities and Physicochemical Properties of Four Grape Musts from Different Varieties

The influence of ultraviolet–visible irradiation on some quality attributes (pH, soluble solids content, color parameters, absorption spectrum, vitamin C, total acidity, total phenolics, formol index, and total and reducing sugars) and polyphenol oxidase, peroxidase, and pectinmethylesterase activities of fresh grape juices was investigated. Grape juice was made from two varieties of white grapes (Victoria and Dauphine) and two varieties of pink grapes (Emperor and Red Globe). Each juice was irradiated for 140 min with a high-pressure mercury lamp of 400 W that emits in a range between 250 and 740 nm. Polyphenol oxidase was not completely inactivated during irradiation, reducing only 80% of its initial activity in juices from white grapes and only 50% in those from pink grapes. On the contrary, peroxidase was completely inactivated. A slight or nonexistent variation was observed in most of the measured physicochemical parameters, showing high stability during irradiation. Only vitamin C and color had a significant variation, with an average decrease of 30% for vitamin C in all varieties and a more important variation of color parameters in the pink varieties than in the white ones.     

Discoloration Kinetics of Clarified Apple Juice Treated with Lewatit® S 4528 Adsorbent Resin During Processing

The present work studies the adsorption of colored compounds in apple juice with a Lewatit® resin S 4528. The sorption equilibrium through the adsorption isotherms for 20, 35, and 50 °C was studied. The absorbance at 420 nm was used to measure the concentration of colored compounds, which permits correlating the residual concentration with the adsorbed concentration, proving that the data matched reasonably well according to the Langmuir and Freundlich models. Also, the efficiency of the adsorption process was studied for different resin/juice mass ratios at different temperatures, from which it was observed that there was an improvement in efficiency as the resin content increased, while the increase in temperature was not so important in the process. The adsorption kinetics at 35 °C for different resin/juice mass ratios was also studied. The kinetic model developed by Ibarz was used, concluding that the data matched this model reasonably well. The adsorption kinetic constant was always higher than the desorption kinetic constant, which indicates that the adsorption stage predominates the desorption stage. The adsorption kinetic constant shows a decreasing tendency with the raise in the resin/juice ratio, and the desorption kinetic constant shows an increasing tendency. The variation of the CIELab color parameters (L*, a*, and b*) with the adsorption time was studied, obtaining results that match the kinetic adsorption model proposed.     

Enzymatic peeling and discoloration of Red Bartlett pears

In purees manufacturing from some fruits, problems related to undesirable colours that come from fruit skin may arise. In this article, the feasibility of using an enzyme preparation to reduce the colour of Red Bartlett pears to be used for industrial purees has been studied. Kinetic models that suitably describe changing colour parameters with treatment time have been tested, seeking for the optimum ones. It was found that the most appropriated processing conditions for Red Bartlett pears discoloration are as follows: 45 °C with an enzyme concentration of 5000 ppm and a time that does not exceed 200 min. Although this treatment constitutes a solution for the problem of skin colour, a high concentration of enzyme and high treatment times are required, which makes the process expensive from the economic standpoint.     

Nationwide Survey of 60Co Teletherapy Dosimetry

The National Bureau of Standards is performing a study of the ability of radiation-therapy departments to deliver prescribed absorbed doses of ⁶⁰Co gamma radiation to a water phantom. Batches of thermoluminescence dosimeters are mailed to participating therapy departments for irradiation under prescribed conditions. Upon return of the dosimeters, the participants’ computations are checked and the absorbed dose is evaluated from dosimeter response. The rugged dosimetry system was assembled mainly from commercial components adapted to the present requirements of relatively high flexibility of readout parameters and data-handling techniques, and of relatively high accuracy. The uncertainty in the dose interpretation inherent in the system is estimated to be about 4 percent.In order to illustrate the type of information that can be obtained from such a study, results of the first four mailings involving tests on 114 ⁶⁰Co gamma-ray beams are discussed. They show about 75 percent of the dose interpretations to be within 5 percent of the prescribed absorbed dose, and about 20 percent to be within 5 to 10 percent of this dose. Four dose interpretations showed discrepancies larger than 20 percent. Differences in the computations larger than 1 percent were observed in over one-half of the cases.