Jordi Pagán

Kinetic models for colour changes in pear puree during heating at relatively high temperatures

Abstract The effect of thermal treatments on 11° Brix pear puree were studied at temperatures from 80°C to 98°C. Changes in colour measured with colorimetric parameters (reflectance spectra, colour difference, L *, a * and b * parameters), and the variation in 5-hydroxymethylfurfural (HMF) and sugars (hexoses and sucrose) content were used to evaluate non-enzymatic browning. A kinetic model based on a two-stage mechanism was applied to the changes in colour difference and a *. A first order kinetic model was applied to L * changes, while absorbance at 420 nm (A 420 ) for liquid fractions was described using a zero order kinetic model. Thermally treated samples became more reddish and suffered a slight loss of yellow hues. The effect of temperature on kinetic constants was described by an Arrhenius type equation. The presence of pulp in the samples implied that the activation energy was lower than in clarified juices with the same soluble solids content.

Non-enzymatic browning in peach puree during heating

Non-enzymatic browning in peach puree (11 Brix) due to extended thermal treatment was investigated. Absorbance at 420 nm, colorimetric parameters (CIE L, a, b and E), content in sugars (fructose, glucose and sucrose) and hydroxymethylfurfural were used to estimate the extent of nonenzymatic browning during heating at high temperatures (80, 85, 90, 95 and 98C) for 480 min. Zero and first order kinetics were applied to describe evolution of relative absorbance at 420 nm. Relative luminosity and sucrose content follow a first order kinetic. Colour diAerence was successfully adjusted to a model including two stages: the first one includes the colour formation and it follows a kinetic of order zero and the second includes the colour destruction and it follows a first order kinetic model. Both first and autocatalytical models can describe HMF formation. Parameter b was significantly reduced with heating time, especially at higher temperatures, on the contrary parameter a increases during heating. The Arrhenius model described well the temperature dependence of the reaction rate constant for all the parameters considered. # 1999 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.

Extraction and characterization of pectin from stored peach pomace

Extraction of pectin from peach pomace stored for 10 months at 3°C and 95% RH was carried out at 60° and 80°C, in acidified solutions in the 1.20–2.53 pH range, for times varying between 10 and 80 min. The kinetics of extraction was studied and pectin yields from fresh and stored pomace under equivalent conditions of temperature, pH, and time were compared. The intrinsic viscosity and degree of esterification of selected pectin samples from stored pomace were analyzed and were also compared with the equivalent samples previously extracted from fresh pomace [Pagan, J., Ibarz, A., Llorca, M., & Coll, L. (1999). Quality of industrial pectin extracted from peach pomace at different pH and temperatures. Journal of the Science of Food and Agriculture, 79, 1038–1042]. Finally, a quality index for each sample was obtained to allow an analysis of the effect of storage on the quality of the extracted pectin.

Kinetic models of non-enzymatic browning in apple puree

The effects of thermal treatments on 11∞Brix apple puree were studied at temperatures from 80 to 98∞C. Colour changes (measured by reflectance spectroscopy, colour difference, L*, a* and b* and the evolution of 5-hydroxymethylfurfural (HMF) and sugars (hexoses and sucrose) were used to evaluate non-enzymatic browning. A kinetic model based on a two-stage mechanism was applied to the evolution of colour difference and a*. A first-order kinetic model was applied to L* evolution, while the evolution of absorbance at 420 nm (A420 ) of the liquid fraction was described using a zero-order kinetic model. Thermally treated samples became more reddish and suffered a slight loss of yellow hues. The effect of temperature on the kinetic constants was described by an Arrhenius-type equation. The presence of pulp in the samples led to activation energies for A 420 and sucrose which were lower than those found previously for clarified juices with the same soluble solids content. # 2000 Society of Chemical Industry

Melanoidins Formed by Maillard Reaction in Food and Their Biological Activity

This paper is a review of the recent studies on Maillard reaction products, the formation mechanism for these compounds and melanoidin structure, the undesirable consequences in food especially in fruit juice processing, the desirable effects and the biological properties related to the beneficial health. Melanoidins are compounds generated in the late stages of the Maillard reaction from reducing sugars and proteins or amino acids during food processing and preservation. Recently, the effects of melanoidins on human health and the chemical characterization of the beneficial components have gained a lot of attention, and their implications on several levels, sensory, nutritional, toxicological and technological were investigated. Food melanoidins have been reported to be anionic, coloured compounds, and some of their key chromophores have been elucidated. The antioxidant activity and other biological effects of melanoidins from real foods and model systems have been widely studied. Despite this, very few different melanoidin structures have actually been described, and specific health effects have yet to be linked with chemically distinct melanoidins. The variety of Maillard reaction products formed during the reaction, in conjunction with the difficulty in purifying and identifying them, makes a thorough analysis of melanoidins challenging.

Quality of industrial pectin extracted from peach pomace at different pH and temperatures

Two molecular characteristics of pectin related to good gelling properties of the polysaccharide are degree of esterification (DE) and length of molecular chain. Industrial pectin from peach pomace was extracted at different pH and temperatures. DE, acetyl content, intrinsic viscosity and molecular weight of the samples were analysed, and the effect of the extraction conditions on these parameters were studied. On the basis that high DE and intrinsic viscosity indicate good gelling pectin or good quality of pectin has chains with low acetyl content, all extracted samples were compared using a multicriteria method in order to find the best extraction conditions.

Toxic effect of melanoidins from glucose–asparagine on trypsin activity

In this work the effect of the presence of the melanoidins from glucose-asparagine on the enzymatic activity of trypsin is studied. It was observed that an excess of N alpha-benzoyl-L-arginine ethyl ester (BAEE) has an inhibiting effect on this enzyme activity. The maximum reaction rate was obtained for a 0.06 mN substrate concentration. It is also observed that the presence of melanoidin inhibits the enzymatic activity of trypsin. This inhibition can be described as a linear mixed type where the inhibition constant alpha K(i) of the substrate-inhibitor complex is higher than the inhibition constant K(i) of the complex enzyme-inhibitor with a alpha value of 1.88.

Albedo hydrolysis modelling and digestion with reused effluents in the enzymatic peeling process of grapefruits

BACKGROUND Until now, the optimisation of enzymatic peeling of grapefruit in the reactor has been obtained as the result of the semi-qualitative effects of enzyme activity. This work is an attempt to obtain quantified data. The reuse of enzymes to reduce costs in this process is unprecedented in the literature and is the aim of the present work. RESULTS The optimal conditions determined for the maximum albedo degradation were a temperature of 40.6 °C and a time of 13.1 min in an enzymatic concentration of 0.067 mL enzymatic preparation per gram of peel in each litre of citrate buffer solution. The decrease in relative enzymatic activities in reused effluents was determined, as was the increase in activity when the enzymes were purified. These increases were 15.5% for polygalacturonase and 15.4% for cellulase activity. CONCLUSION Optimal temperature, time and the ratio between peel mass and the enzymatic preparation volume were the best conditions for obtaining good peeling efficiency. The effluents from the enzymatic peeling process of the grapefruit still contain appreciable enzymatic activity after the digestion process. Thus, reusing these effluents while maintaining peeling efficacy and a subsequent recovery of the active enzymes by ultra-filtration of the effluents is the way to improve the efficiency of the process.

Kinetics of Peach Clarified Juice Discoloration Process with an Adsorbent Resin

This paper deals with the effects of adsorbent resin upon kinetic process of peach juice adsorption de-coloration at different temperatures ranged from 10 °C to 50 °C. The adsorption equilibrium was quantified by means of adsorption isotherms in the range from 10 °C to 50 °C. Absorbance data at 420 nm were used to plot all the isotherms, which correlated reasonable well with the Freundlich and Langmuir isotherms. Also, the efficiency of the adsorption process was studied for different resin/juice ratios at different temperatures, from which it was observed that there was a notable improvement in efficiency as the resin content increased, while the increase in temperature was not so important in the process. The adsorption kinetics was also studied at 30 °C, for relationships of 1, 2, and 3 g resin/100g juice. A kinetic adsorption— desorption model in two simultaneous steps was proposed, where the adsorption step is considered as zero order and the desorption step as first order. This allows a global expression to be obtained that fits the experimental data appropriately to this kinetic type equation. The initial adsorption rate depended on the resin/juice relationship in such a way that the higher its value, the lower this relationship was. It was also shown that the equilibrium constant showed a similar tendency, its value being superior to the unit, which indicates that the retention stage over the resin prevails over the colored product desorption stage.

Kinetics of color development of melanoidins formed from fructose/amino acid model systems

The formation of soluble melanoidins from a single combination of sugar (fructose) and amino acid model systems were evaluated kinetically. The selected amino acids, commonly found in apple juice and highly reactive in the Maillard reaction, were asparagine, aspartic acid, and glutamic acid. The effect of these reagents and the treatment at different temperatures (50 ℃, 85 ℃, and 100 ℃) during 96 h on the color intensity of the melanoidin formed was measured by absorbance at different wavelengths (280, 325, 405, and 420 nm). The absorbance of the melanoidin formed from all model systems was located on the wavelength of 405 nm, that is, the area of the visible spectrum close to the UV region. The color of the melanoidins was directly measured using the CIELAB color space system. A first-order kinetic model was applied to the evolution of the ΔE* (color difference) and L* (lightness) of the color. The fructose/aspartic acid model system values of a * (redness) and b * (yellowness) were found in the brown-red zone. Therefore, the color development of the melanoidins was influenced by the type of amino acid and temperature. Especially, it is thought that the a * and b * values can be used to explain the differences among the amino acids in the color development of melanoidins.