d-Galacturonic Acid as a Highly Reactive Compound in Nonenzymatic Browning. 1. Formation of Browning Active Degradation Products

Abstract

Thermal treatment of an aqueous solution of D-galacturonic acid at pH 3, 5, and 8 led to rapid browning of the solution and to the formation of carbocyclic compounds such as reductic acid (2,3-dihydroxy-2-cyclopenten-1-one), DHCP (4,5-dihydroxy-2-cyclopenten-1-one), and furan-2-carbaldehyde, as degradation products in weak acidic solution. Studies on their formation revealed 2-ketoglutaraldehyde as their common key intermediate. Norfuraneol (4-hydroxy-5-methyl-3-(2H)-furanone) is a typical alkaline degradation product and formed after isomerization. Further model studies revealed reductic acid as an important and more browning active compound than furan-2-carbaldehyde, which led to a red color of the model solution. This red-brown color is also characteristic of thermally treated uronic acid solutions.

Thermal degradation of citrus pectin in low-moisture environment - Influence of acidic and alkaline pre-treatment

“…Several groups tested the influence of external factors such as temperature and pH and of internal parameters such as degree of methoxylation (DM) and of ions (for instance Bornik & Kroh, 2013;Diaz, Anthon, & Barrett, 2007;Fraeye et al, 2007;Krall & McFeeters, 1998;Renard & Thibault, 1996;Axelos & Branger, 1993;Sajjaanantakul, Van Buren, & Downing, 1993;Kravtchenko, Arnould, Voragen, & Pilnik, 1992;Voragen, Schols, & Pilnik, 1988;Thibault, 1983;Van Buren, 1979;Keijbets & Pilnik, 1974;BeMiller & Kumari, 1972). Most works did, however, not consider a possible influence of pectin pre-treatments or of different production details on the thermal degradation reactions.…”

New Frontiers in the Catalytic Synthesis of Levulinic Acid: From Sugars to Raw and Waste Biomass as Starting Feedstock

“…Examples of important chemicals from LA and their potential applications are showed in Figure 5. Such valuable chemicals include γ-valerolactone, levulinate esters and also angelica lactone, ketals, diphenolic acid and δ-amino The overall process involves three steps: (i) an acid-catalyzed hydrolysis of hemicellulose polymer and dehydration of the C5 sugars to furfural [38,39]; (ii) the hydrogenation of furfural to furfuryl alcohol; (iii) the acid-catalyzed hydrolysis of furfuryl alcohol to the desired LA [18,40]. Yields in LA are in the range 83-93 mol % [23].…”

Production of uronic acids by hydrothermolysis of pectin as a model substance for plant biomass waste

“…The presence of lactic acid, formic acid, and furfurals in the WS fraction indicates the co-occurrence of unwanted side reactions along with the depolymerization of HMP -chain fragmentation and degradation of low molecular weight primary reaction products [36]. Further increase in HMP hydrothermolysis temperature, especially above 160°C resulted in a decrease in the yield of uronic acids, which were readily decomposed under hydrothermal conditions [37][38][39][40][41][42]. The degradation of uronic acids was accompanied by secondary transformations of components present in the reaction mixture, leading, among others, to the progressive increase of furfurals content (Figure 3).…”

“…The specific mechanism of hydrothermal decomposition of uronic acids is challenging to study. Depending on the used reaction conditions, they can be degraded into a massive number of compounds, which may be obtained via different reaction pathways [37][38][39][40][41][42].…”

“…In the literature [38,41,42] there was described mechanism of galacturonic acid degradation under hydrothermal conditions which are probably based on its decarboxylation. Bornik and Kroh [41] and Wegener et al [42] under slightly acidic to alkaline conditions, identified two processes leading to two detected intermediate products: decarboxylation to L-arabinose and eliminative decarboxylation to unsaturated 4-deoxy-L-arabinose. These compounds were further converted to carbocyclic products such as reductic acid by ring opening followed by dehydration and cyclization.…”