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

Pectin powder is degraded during storage and transport by demethoxylation and depolymerisation. The degradation mechanisms and especially the influence of pre-treatments on the degradation reactions are not completely understood. In this study, commercial citrus pectin was modified by either acidic or alkaline demethoxylation. The modified pectins, as well as the commercial pectin, were thermally degraded during four weeks of storage at 60 °C and 80% relative humidity. Demethoxylation and depolymerisation as well as colour alterations were examined during degradation, and the course of the reactions was monitored. It was found that the type of pre-treatment during modification determined the material properties and, thus, the water uptake of the modified pectin powders. The resulting water availability in the samples was crucial to the extent of demethoxylation and to the type and intensity of depolymerisation since some of these reactions competed for the water in the climate chamber. The pre-treatment also determined the content of neutral sugars and sodium ions of the modified pectins. High contents of these components limited the extent of degradation in different ways. A previously assumed third depolymerisation mechanism of pectins, beside backbone hydrolysis and β-elimination, was confirmed.DFG, 268547215, Strukturabhängige Abbaureaktionen von Pektinen und deren Auswirkungen auf nicht-enzymatische Bräunung und technologische Funktionalitä

Simplified Kinetics and Colour Formation in Sucrose Solutions Based on A-Dicarbonyl Compounds

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Colour formation in technical and model sucrose solutions was investigated resulting in a novel kinetic approach of MAILLARD reaction during thermal processing of sugar solutions. Presented results describe new aspects of the non-enzymatic browning reaction (MAILLARD reaction). Two temperature depending pathways of colour formation were found. Both reaction mechanisms are based on the formation of a-dicarbonyl compounds, the key intermediates of colour formation.Discussing temperature dependence of colour formation, a change on MAILLARD reaction mechanism takes place at 100.4 °C. Above this temperature the colour formation is strongly accelerated. Activation energy of the non-enzymatic browning energy for temperatures from 65 ° to 100.4 °C amounts 77 kJ/mol. In this temperature range, D-glucosone is the most important a-dicarbonyl compound for studied reaction systems. Above 100.4 °C, activation energy is equal to 112 kJ/mol and 3-deoxyosone is the dominant colour formation intermediate. Achieved results bridge the gap between the termination step of a MAILLARD reaction i.e. of colour formation (represented by its activation energy) and intermediates formation (reaction kinetics). In particular, a change of colour formation mechanism with reaction temperature was confirmed by specific formation of two a-dicarbonyl compounds, responsible for MAILLARD reaction in technical sugar solutions

Einfluss der Lebensmittelprozessierung auf die Bioverfügbarkeit von Kupfer: Untersuchungen zur zellulären Kupferaufnahme aus CuSO4 und Melanoidin-Cu-Komplexen

AbstractKupfer gilt als essentielles Spurenelement, da es als struktureller und katalytischer Cofaktor Bestandteil vieler lebenswichtiger Enzyme ist. Andererseits kann jedoch eine exzessive Zufuhr von Kupfer nachfolgend zu irreversiblen Gewebeschäden führen. Um pathophysiologische Erscheinungen zu vermeiden, muss deshalb sowohl die physiologische Kupferhomöostase als auch die Aufnahme von Kupfer aus der Nahrung streng reguliert werden. Obwohl Melanoidine als finale Produkte der thermischen Prozessierung von kohlenhydratreichen Lebensmitteln nachgewiesenermaßen über metallchelatisierende Eigenschaften verfügen, ist ihre Bedeutung für die Resorption von lebensnotwendigen Mineralien und Spurenelementen bisher nur unzureichend geklärt. In der vorliegenden Studie konnte gezeigt werden, dass lebensmittelrelevante Melanoidine über ein revertierbares Kupferbindungsvermögen verfügen. Hierbei konnte ein Zusammenhang zwischen der Menge aus den Maillard-Reaktionsprodukten (MRPs) freisetzbarer Kupferionen und der Hemmung des Cu-sensitiven Enzyms poly (ADP-Ribose) Polymerase 1 nachgewiesen werden. Die Aufnahme der Cu-Ionen aus Melanoidin-Cu Komplexen in humane HCT116-Kolonkarzinomzellen erfolgt im Vergleich zu der anorganischen Verbindung CuSO4 in gleichem Ausmaß, jedoch mit deutlich größerer Geschwindigkeit. Die durchgeführten Genexpressionsanalysen weisen zudem auf Unterschiede in der zellulären Bioverfügbarkeit der aufgenommenen Kupferionen hin. Diese Ergebnisse verdeutlichen, dass Melanoidine als Endprodukte der Maillard-Reaktion regulierend in den Prozess der Kupferaufnahme in intestinalen Zellen eingreifen und thermisch prozessierte Lebensmittel somit als wichtige Modulatoren der Kupferhomöostase angesehen werden müssen

Effect of Different Drying Methods on Nutrient Quality of the Yellow Mealworm (Tenebrio molitor L.)

Yellow mealworm (Tenebrio molitor L.) represents a sustainable source of proteins and fatty acids for feed and food. Industrial production of mealworms necessitates optimized processing techniques, where drying as the first postharvest procedure is of utmost importance for the quality of the final product. This study examines the nutritional quality of mealworm larvae processed by rack oven drying, vacuum drying or freeze drying, respectively. Proximate composition and fatty acid profile were comparable between the dried larvae. In contrast, larvae color impressions and volatile compound profiles were very much dependent on processing procedure. High-temperature rack oven drying caused pronounced darkening with rather low content of volatiles, pointing toward the progress of Maillard reaction. On the other hand, vacuum drying or freeze drying led to enrichment of volatile Maillard reaction and lipid oxidation intermediates, whose actual sensory relevance needs to be clarified in the future. Beyond sensory and visual importance drying intermediates have to be considered with regard to their metal ion chelating ability; in particular for essential trace elements such as Zn2+. This study found comparable total zinc contents for the differently dried mealworm samples. However, dried larvae, in particular after rack oven drying, had only low zinc accessibility, which was between 20% and 40%. Therefore, bioaccessibility rather than total zinc has to be considered when their contribution to meeting the nutritional requirements for zinc in humans and animals is evaluated.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli

Interaction of drought stress and UV-B radiation - impact on biomass production and flavonoid metabolism in lettuce (Lactuca sativa L.)

The response of plants to stress such as UV-radiation or drought highly depends on the species, cultivar, plant organ, developmental stage, and furthermore, is influenced by ecophysiological interactions. Drought stress as well as UV irradiation are the most adverse factors for plant growth and productivity. In the present study, the interactive effect of UV-B and drought stress on biomass, primary and secondary metabolites, and mediated enzyme activity of phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) was investigated in lettuce (Lactuca sativa L.). It was found that biomass production decreased in response to both stressors, while dry matter, total phenolic contents and the flavonol quercetin were not significantly affected by UV-B and drought stress, neither solely nor in combination. In contrast, anthocyanins and luteolin accumulated only in response to drought stress. However, the precursor amino acid proline as well as the activity of PAL increased under conditions of increased UV-B and water deficit. Thus, the present results deduce that both stressors acted either synergistically or to some extent antagonistically in terms of inducing plant protective mechanisms

Influence of the brewing method and acidity regulators on the antioxidant capacity of coffee brews

The antioxidant capacity of coffee brews prepared with different coffeemakers (filter, plunger, mocha, and espresso) was measured by colorimetric (total phenolic compounds and ABTS) and electron spin resonance (ESR) spectroscopy techniques (Fremy's salt and TEMPO). The mocha coffeemaker had the highest yield in coffee antioxidant extraction per gram of ground roasted coffee, but espresso coffee was richest in terms of antioxidant intake (per milliliter of coffee brew) followed by mocha, plunger, and filter. Both Folin-Ciocalteu (total phenolic compounds) and ABTS assays reacted with standard solutions of chlorogenic acids (CGA) and melanoidins (MO-Ala and MO-Gly). However, Fremy's salt was mainly scavenged by chlorogenic acids, whereas the stabilized radical TEMPO was effectively scavenged by melanoidins, but not by chlorogenic acids. Thus, ESR spectroscopy allows distinguishing between phenolic and nonphenolic antioxidants. Moreover, the addition of pH-regulator agents to coffee, such as sodium carbonate (75 ppm) and bicarbonate (75 ppm), to extend its shelf life, slightly increases the pH, modifying the antioxidant capacity in those coffee brews with the highest capacity (mocha and espresso)

Extraction of coffee antioxidants: impact of brewing time and method

The aim of this work was to study the extraction behavior of the main coffee antioxidants (caffeoylquinic acids, melanoidins and caffeine) and the antioxidant capacity, during brewing time in the most widely consumed coffee brew methods (filter and espresso) in coffee. Antioxidant capacity by colorimetric assays (Folin-Ciocalteau, ABTS and DPPH) and electron spin resonance spectroscopy techniques (Fremy's salt and TEMPO) were analyzed. In espresso coffee, more than 70% of the antioxidants (except dicaffeoylquinic acids, diCQA) of a coffee brew were extracted during the first 8s. In filter coffee, a U-shape antioxidants extraction profile was observed, starting later (after 75 s) in Vietnam coffee than in Guatemala one, probably due to different wettability. Other technological parameters, such as turbulences and a longer contact time between water and ground coffee in filter coffeemaker, increased extraction efficiency, mainly in less polar antioxidant compounds as diCQA. In conclusion, these technological factors should be considered to optimize coffee antioxidants extraction that can be used as ingredients for functional foods

Evaluation of spent coffee obtained from the most common coffeemakers as a source of hydrophilic bioactive compounds

The main hydrophilic antioxidant compounds (3-, 4-, and 5-monocaffeoylquinic and 3,4-, 3,5-, and 4,5-dicaffeoylquinic acids, caffeine, and browned compounds, including melanoidins) and the antioxidant capacity (Folin-Ciocalteu, ABTS, DPPH, Fremy's salt, and TEMPO) were evaluated in Arabica and Robusta spent coffee obtained from the preparation of coffee brews with the most common coffeemakers (filter, espresso, plunger, and mocha). All spent coffee grounds, with the exception of those from the mocha coffeemaker, had relevant amounts of total caffeoylquinic acids (6.22-13.24 mg/g of spent coffee), mainly dicaffeoylquinic acids (3.31-5.79 mg/g of spent coffee), which were 4-7-fold higher than in their respective coffee brews. Caffeine ranged from 3.59 to 8.09 mg/g of spent coffee. The antioxidant capacities of the aqueous spent coffee extracts were 46.0-102.3% (filter), 59.2-85.6% (espresso), and <42% (plunger) in comparison to their respective coffee brews. This study obtained spent coffee extracts with antioxidant properties that can be used as a good source of hydrophilic bioactive compounds