A. Ibarz

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.

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.

Effect of Pectinase Immobilization in a Polymeric Membrane on Ultrafiltration of Fluid Foods

The aim of this research was to obtain an enzymatic membrane reactor for use to clarify a model system and apple juice with a 12% soluble solid content and 1 mg/mL of pectin by water-soluble pectinolytic enzymes which were immobilized on polysulfone membranes. These membranes were synthesized in the laboratory by immersion precipitation (phase inversion) from polysulfone with and without active carbon. To ensure the cut-off separation of the membrane in the ultrafiltration process a commercial flat membrane with an 8-kDa molecular weight cut-off was used. The influence of different parameters (viscosity, density, reducing sugars, color, pH, and presence of pectin) on the initial sample and the volumetric permeate flux was also evaluated. The obtained membranes were characterized physically using a scanning electron microscopy SEM and analyses were performed with IFME® software. The results indicated that immobilization of the enzyme in the membrane allowed an interaction between the recirculating sample and the membrane, the one obtained with activated carbon and immobilized enzymes showed higher degradation of pectin, improving the performance of the volumetric permeate flux.