Non-enzymatic Browning Reactions Research Articles

Non-enzymatic browning in citrus juice: chemical markers, their detection and ways to improve product quality.

Citrus juices are widely consumed due to their nutritional benefits and variety of pharmacological properties. Non-enzymatic browning (NEB) is one of the most important chemical reactions responsible for quality and color changes during the heating or prolonged storage of citrus products. The present review covers various aspects of NEB in citrus juice viz. chemistry of NEB, identifiable markers of NEB, analytical methods to identify NEB markers and ways to improve the quality of citrus juice. 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) is one of the promising marker formed during browning process with number of analytical methods reported for its analysis; therefore it can be used as an indicator for NEB process. Amongst analytical methods reported, RP-HPLC is more sensitive and accurate method, which can be used as analytical tool. NEB can be prevented by removal of amino acids/ proteins (via ion exchange treatment) or by targeting NEB reactions (e.g. blockage of furfural/ HMF by sulphiting agent).

Influence of air drying temperature on kinetics, physicochemical properties, total phenolic content and ascorbic acid of pears

This study was conducted to evaluate quality and structural changes in parallelepipedic pieces of pears during convective drying at different air temperatures (30–70°C).Submitted to atmospheric O2 conditions, ascorbic acid deterioration demonstrated first-order kinetic behaviour and was found to depend on air temperature and pear moisture content. Loss of ascorbic acid content increased with increasing air temperature. Possible explanation could be the irreversible oxidative reaction occurring during drying. Phenol content degradation fitted a pseudo first-order reaction and was significantly influenced by air temperature.Variations in bulk density, shrinkage and porosity essentially depended on changes in moisture content. Porosity exhibited a nonlinear variation with respect to moisture content. Volume change showed, as expected, a linear variation with moisture content. Drying temperature significantly induced the increase of a* and b* colorimetric parameters due to non-enzymatic browning reaction, which turned the samples more reddish and yellow when the temperature rose.

An application of methylcellulose-whey protein films on Japanese persimmon

Enzymatic and non-enzymatic browning reactions, water loss, oxidation and microbial growth can cause decreases in the quality of fresh fruits. Packaging can be an effective way to control and prevent these undesirable changes. Edible films and coatings having low water vapor permeability (WVP) are used to extend the shelf life of these perishable foods. Use of the methylcellulose-whey protein (MCWP) based edible films which have low WVP may retard ripening and softening of fruits. In this study, Japanese persimmons (Diospyros kaki L.) were wrapped with MC-WP films and stored at 10 and 25°C. Changes in the weight and firmness of the fruits during storage were investigated. Wrapping had no effect on weight losses and firmness of the fruits stored at 10°C. On the other hand, wrapping had no significant effect on firmness but caused an increase in weight loss of the fruits stored at 25oC. The wrapped fruits showed higher weight loss than non-wrapped ones at 25°C after the 10 days. The appearance of wrapped fruits was better than non-wrapped ones at the end of storage, since mold growth on non-wrapped fruits was observed.

Meaty flavour compounds formation from the submerged liquid culture of Pleurotus ostreatus

Summary The capacity of oyster mushroom (Pleurotus ostreatus) mycelium to produce meaty flavour compounds in the presence of amino acids and sugars was studied. The submerged liquid culture of P. ostreatus mycelium along with base medium made of defatted soybean powder, sucrose, potassium phosphate, and magnesium sulphate was incubated for 3 days at 25 °C. Cysteine, glutamine, or methionine and fructose, galactose, ribose, or xylose were added to the base medium to study the effect of amino acids and sugars on meaty flavour formation by trained panelists. The flavour compounds were isolated and identified by GC–MS and GC retention time of authentic compounds. The base medium required P. ostreatus, cysteine, ribose, and heat treatment to produce meaty flavour. The sulphur containing heterocyclic compounds such as 2,5-diethylthiophene, 2-formyl-5-methylthiophene, 3-ethyl-2-formylthiophene, and dimethylformyl thiophene were responsible for meaty flavour. These compounds were formed by non-enzymatic browning reaction between ribose and cysteine during heat treatment.

Non-enzymatic browning and ascorbic acid degradation of orange juice subjected to electroreduction and electro-oxidation treatments

Orange juice was submitted to electroreduction and electro-oxidation treatments prior to pasteurization and compared to a control juice for oxido-reduction potential (ORP), dissolved oxygen and ascorbic acid contents. Evolution of non-enzymatic browning reactions and ascorbic acid degradation was evaluated at 4, 21 and 37 °C storage temperatures. Electroreduction treatment of the juice at 6 V (cell length of 1.58 cm) created a substantial reducing reservoir as ORP decreased from + 161 to −406 mV and it decreased dissolved oxygen by more than 90% of its initial content while the ascorbic acid content was not altered. In contrast, the electro-oxidation treatment raised the final ORP of the juice by 15 to 20 mV, increased substantially the dissolved oxygen content and decreased significantly the ascorbic acid retention. Electro-oxidation treatment resulted in an increase of non-enzymatic browning reactions during storage. Both the control and electroreduced juice showed very similar trends in ascorbic acid degradation over the 3 months storage period whereas the anions, cations and amino acids profiles of the juice remain unchanged. Contrary to the control and electroreduced juices, the electro-oxidation process decreased severely the orange flavor intensity and character being characterized as musty with sour-bitter aftertaste. The limitation of shelf life imposed on comestible beverage systems (juice, beer, milk, wine, etc.) is an important and common issue for food manufactures and consumers. The shelf life is shortened by the time-dependent development of off-flavors, browning, change of colors, and deterioration of nutrients, caused by the oxidative reactions of chemical and nutrient components in the food systems. Consequently, the food is becoming unattractive to consumers. The electrochemical technique by means of an electrochemical cell has the potential in inhibiting or accelerating these deterioration reactions through reduction or oxidation of organic and inorganic compounds inherent to the products, as well as effectively controlling the oxygen content in the products. This technique can be used as an alternative to the deliberate addition of chemical compounds (sulfite and others reducing substances) to inhibit the deterioration reactions (electroreduction) as well as to accelerate the aging process of the comestible products via accelerated oxidation process (electro-oxidation).

Formation of Flavor, Color, and Reducing Power during the Production Process of Dark Specialty Malts

Important features of dark specialty malt, such as color, flavor, and reducing power, are mainly formed due to nonenzymatic browning reactions during the kilning and roasting process. In this study, the influence of the duration and temperature of the roasting process on the formation of these malt characteristics was monitored. The results indicated that the development of caramel-like flavor components was highly influenced by the roasting temperature and moisture content of the malt kernels, and the formation of pyrazines strongly increased at 180°C. In addition, the evolution of malt characteristics such as color and reducing power was greatly influenced by the applied processing parameters. Finally, the results indicated flavor development was not coupled with color formation.

Storage stability of cauliflower soup powder: The effect of lipid oxidation and protein degradation reactions

Soups based on cauliflower soup powders, prepared by dry mixing of ingredients and rapeseed oil, showed a decrease in quality, as evaluated by a sensory panel, during the storage of the soup powder in the dark for up to 12weeks under mildly accelerated conditions of 40°C and 75% relative humidity. Antioxidant, shown to be effective in protecting the rapeseed bulk oil, used for the powder preparation, had no effect on storage stability of the soup powder. The freshly prepared soup powder had a relatively high concentration of free radicals, as measured by electron spin resonance spectroscopy, which decreased during storage, and most remarkably during the first two weeks of storage, with only marginal increase in lipid hydroperoxides as primary lipid oxidation products, and without any increase in secondary lipid oxidation products. Analyses of volatiles by SPME-GC–MS revealed a significant increase in concentrations of 2-methyl- and 3-methyl butanals, related to Maillard reactions, together with an increase in 2-acetylpyrrole concentration. The soup powders became more brown during storage, as indicated by a decreasing Hunter L-value, in accord with non-enzymatic browning reactions. A significant increase in the concentrations of dimethyl disulfide in soup powder headspace indicated free radical-initiated protein oxidation. Protein degradation, including Maillard reactions and protein oxidation, is concluded to be more important than lipid oxidation in determining the shelf-life of dry cauliflower soup powder.

Changes in the color of white chocolate during storage: potential roles of lipid oxidation and non-enzymatic browning reactions

Three different samples of white chocolate were prepared: a sample with a synthetic antioxidant, another with casein peptides as natural antioxidant, and a third sample without any kind of antioxidant. Parameters associated with lipid oxidation and non-enzymatic browning were evaluated in the different samples of white chocolate during 10months storage at 20 and 28°C. Acidity, thiobarbituric acid reactive substances and peroxide values increased with the incubation time. Samples stored at 20°C often showed lower values for these parameters than those stored at 28°C, although the differences were not always significant. The values for water activity increased from 0.4 to 0.53-0.57 during the period of 10months. The color parameter a* was increased in samples stored at 28°C from month 5, and the parameter b* was lower in samples containing antioxidants from month 2. The addition of antioxidants did not significantly influence most the parameters studied, suggesting that the main parameters governing the alterations of white chocolate during its shelf-life was the storage temperature and increase in water activity.

Effects of non-enzymatic browning reaction intensity on in vitro ruminal protein degradation and intestinal protein digestion of soybean and cottonseed meals

The effects of non-enzymatic browning reactions on in vitro ruminal gas production and in vitro ruminal and intestinal crude protein (CP) digestibilities of soybean (SBM) and cottonseed (CSM) meals were investigated. Non-enzymatically browned SBM and CSM samples were prepared using two xylose levels (10 or 30g/kg dry matter), two heating lengths (30 or 60min) and two heating temperatures (120 or 150°C) for a total of one untreated (commercially solvent-extracted, Control) and eight treated samples for each protein source. The control SBM had higher (P<0.001) in vitro ruminal CP degradability values than the treated samples. Intestinal protein digestibility and total-tract CP digestibility of CSM and SBM were affected by the treatment (P<0.01). The results of the study indicate that not only ruminal CP degradability is reduced but also intestinal and total-tract CP digestibilities may be lowered depending on protein source and intensity of the non-enzymatic browning reaction.

APPLICATION OF A FUNCTIONAL MATHEMATICAL QUALITY INDEX TO ASPARAGINE, FREE SUGAR AND PHENOLIC ACID CONTENT OF 20 COMMERCIAL POTATO VARIETIES

ABSTRACTIn this article, we apply a functional mathematical index (FMI), introduced in a previous publication, to 20 commercial potato varieties. The index allows evaluation of nutritional, safety and processing “quality parameters” of different potato cultivars. The main goal of the index is to link the quality of the chemical composition with factors that may affect the growth, production, distribution and processing of potatoes and potato products for commercial use. The index has been used to assess FMI values of 20 commercial potato cultivars in terms of their content of asparagine and reducing sugars, which form heat‐induced potentially toxic acrylamide and of antioxidative phenolic compounds, which participate in nonenzymatic browning reactions and may exert beneficial effects after consumption.PRACTICAL APPLICATIONSThe index could be useful to a wide set of users, including consumers of potatoes as well as to potato producers and breeders, because it makes it possible to relate the index to the potato price and operate a more accurate choice for selection of so‐called “optimal potatoes.” Potato producers may find the index useful because it can help them detect the critical points throughout the whole food production chain in order to facilitate selection of high‐quality potatoes for sale to consumers. Potato breeders could apply the index to the development and selection of improved cultivars for commercial use.

CONTRIBUTION OF MELANOIDINS TO THE ANTIOXIDANT ACTIVITY OF PRUNES

ABSTRACT Prunes, obtained by drying certain cultivars of plums, have greater antioxidant activity than most other fruits and vegetables. Recent research has attributed only a minor part of this antioxidant activity to phenolic compounds, and it has been hypothesized that most of the antioxidant activity is caused by unknown or new products created during processing. In this study, the relationship between the antioxidant properties of prunes and their phenolic compound and brown products content has been investigated. The latter is a result of the nonenzymatic browning reaction. The results show that most of the antioxidant activity of fresh plums is caused by the polyphenolic fraction. The prunes, obtained by drying at 60 and 85C, despite the significant decrease in polyphenols, showed an increase in antioxidant activity. This was mostly because of the nonenzymatic browning reaction products, mostly low molecular weight compounds, whereas polyphenols contributed only to 23% of the total value. PRACTICAL APPLICATIONSResults of this research could have direct or indirect applications. First of all, results give evidence of the best drying conditions related to the nutritional profile of the prunes. Results related to the antioxidant activity of melanoidin compounds can, moreover, stimulate medical researcher to test if melanoidin extracts are really in vivo or ex vivo antioxidants, and in that case, producers of functional foods or food ingredients can be encouraged to try to isolate and characterize the compounds responsible for increased antioxidant activity.

Dropping macadamia nuts‐in‐shell reduces kernel roasting quality

Macadamia nuts ('nuts-in-shell') are subjected to many impacts from dropping during postharvest handling, resulting in damage to the raw kernel. The effect of dropping on roasted kernel quality is unknown. Macadamia nuts-in-shell were dropped in various combinations of moisture content, number of drops and receiving surface in three experiments. After dropping, samples from each treatment and undropped controls were dry oven-roasted for 20 min at 130 °C, and kernels were assessed for colour, mottled colour and surface damage. Dropping nuts-in-shell onto a bed of nuts-in-shell at 3% moisture content or 20% moisture content increased the percentage of dark roasted kernels. Kernels from nuts dropped first at 20%, then 10% moisture content, onto a metal plate had increased mottled colour. Dropping nuts-in-shell at 3% moisture content onto nuts-in-shell significantly increased surface damage. Similarly, surface damage increased for kernels dropped onto a metal plate at 20%, then at 10% moisture content. Postharvest dropping of macadamia nuts-in-shell causes concealed cellular damage to kernels, the effects not evident until roasting. This damage provides the reagents needed for non-enzymatic browning reactions. Improvements in handling, such as reducing the number of drops and improving handling equipment, will reduce cellular damage and after-roast darkening.

Treatments to inhibit the browning reactions in model solutions of olive fruit extracts

Crude enzymatic and polyphenol extracts from olives were subjected to reaction at diverse buffered pH values. At pH values similar to those found in olive flesh (pH 5.0), the colour of the solution increased with reaction time and, simultaneously, a consumption of phenols and oxygen in the reaction medium was observed, especially under aerated conditions. In alkaline solutions (pH 12.4), a strong initial solution browning was noticed while the phenols from the extract reacted with the oxygen present in the solution and caused a significant decrease in the total phenols and oxygen concentrations. This darkening was due to the appearance of non-enzymatic browning reactions since, at this pH, the polyphenoloxidase is not active. Under acidic conditions (pH 3.0), and in solutions with ascorbic acid added (100 mM), the consumption of oxygen and total phenols was negligible, under both aerated and non-aerated conditions; as a result, no significant changes in the colour of the solutions were observed. So, low pH or ascorbic acid solutions may be useful to prevent browning in the bruised areas of hand- or mechanically-harvested table olives.

Effect of storage on nonenzymatic browning reactions in carob pekmez

SummaryCarob pekmez was stored at 5, 25, 35 and 45 °C for studying the reaction kinetics of nonenzymatic browning reactions. Hydroxymethylfurfural (HMF) formation, browning index (A420) and CIE (International Commission on Illumination) colour parameters were analysed to evaluate nonenzymatic browning reactions. HMF formation and A420 values increased linearly with the storage time and temperature and both followed zero‐order reaction. No fitting model was found for the changes in visual CIE parameters. The dependence of rate constant of nonenzymatic reactions on temperature was represented by an Arrhenius equation and the activation values were found as 114.87 kJ mol−1 and 86.62 kJ mol−1 for HMF formation and A420 values, respectively. The excellent linear correlations (r = 0.728–0.99) among colour parameters, browning index and HMF were found.

ANALYZING THE BROWNING OF APPLE JUICE BY FLUORESCENCE SPECTROSCOPY

Apple juice was produced from Malus × domestica 'Pinova', stored at 20°C for 4 d or heated at 80°C for 10 min and stored at the same conditions, in order to obtain both enzymatic browning and non-enzymatic browning reactions. Fluorescence spectroscopy as well as colour readings were carried out to monitor the quality changes of apple juice during storage. A standard set-up for colour readings with a colorimeter using an optical geometry for transmittance readings was applied. The fluorescence spectra were recorded with adapted parameters. Fluorescence excitation was set at 250, 266, 355 and 408 nm, and emission at 280-899 nm resulting in an excitation-emission-matrix (EEM) of 1240x4 for each sample. The sign test pointed out an enhanced sensitivity of EEM in comparison to the L * , a * , and b * values. Fluorescence EEMs were used to classify processed apple juice with different extent of browning. For classifying fresh and stored juice, as well as for differentiating fresh juice from heated-stored juice, the classification correctness was always over 90%.

Effect of Air Temperature on Drying Kinetics, Vitamin C, Antioxidant Activity, Total Phenolic Content, Non-enzymatic Browning and Firmness of Blueberries Variety O´Neil

Effect of air temperature on drying kinetics, vitamin C, antioxidant capacity, total phenolic content (TPC), colour due to non-enzymatic browning (NEB) and firmness during drying of blueberries was studied. Drying curves were satisfactorily simulated with the Weibull model at 50, 60, 70, 80 and 90°C. The scale parameter (β) decreased as air temperature increased and an activation energy value of 57.85 kJ mol−1 was found. Important losses of vitamin C were reported during drying for all the working temperatures (p < 0.05). Although TPC decreased as air-drying temperature increased (p < 0.05) in comparison to its initial value, the dehydration at high temperatures (e.g., 90°C) presented high values for these antioxidant components. Discoloration due to NEB reaction was observed at all the working temperatures showing a maximum value at 90°C (p < 0.05). The radical scavenging activity showed higher antioxidant activity at high temperatures (80 and 90°C) than at low temperatures (50, 60 and 70°C) (p < 0.05). A tissue firmness reduction was observed with increasing temperature (p < 0.05).

Browning of Freeze-Dried Probiotic Bacteria Cultures in Relation to Loss of Viability during Storage

Freeze-dried cultures of Lactobacillus acidophilus (La-5) showed visible brown discoloration even after a short storage at relatively mild conditions (a(w) = 0.22 and 30 degrees C), and the browning processes were found to coincide with bacteria inactivation. It was demonstrated, by using high-pressure treatment for obtaining bacteria samples with different ratios of live/dead bacteria, that death of bacteria is not a prerequisite for the browning processes. Furthermore, it was shown that hydroxymethylfurfural (HMF) (or condensation products of HMF) introduces accelerated viability loss when HMF is added to the freeze-drying medium. Discoloration of bacteria cultures containing only sucrose/maltodextrin or lactose/maltodextrin in the freeze-drying matrices is suggested to be related to various types of nonenzymatic browning reactions, including carbonyl-protein (or carbonyl-DNA) interactions and carbohydrate condensation/polymerization (without involvement of proteins), the latter proceeding at low a(w) following hydrolysis of the peptidoglycan layer in the bacteria cell wall. More than one single type of browning reaction is accordingly concluded to be related to bacteria death, and the loss of viability in freeze-dried bacteria seems to be influenced by oxidation reactions, browning reactions, and the physical instability of the bacteria membrane/cell wall.

The role of peptides and proteins in melanoidin formation

High-molecular-weight (HMW) coloured compounds called melanoidins are widely distributed, particularly in foods. It has been proposed that they originate through the Maillard reaction, a non-enzymatic browning reaction, due to the interaction between protein or peptide amino groups and carbohydrates. The melanoidin structure is not definitively known, and they have been generally defined as HMW nitrogen-containing brown polymers.In order to gain information on the nature of melanoidins, a simple in vitro model was chosen to investigate the products of the reactions between sugars and peptide/proteins. This approach would elucidate whether melanoidin formation is due to the binding of different sugar units to a peptide/protein or vice versa. With this aim, the reactivity of two different peptides, EPK177 and physalaemin, and a low-molecular-weight (LMW) protein, lysozyme, was tested towards different saccharides (glucose, maltotriose (MT), maltopentaose and dextran 1000) in aqueous solutions at different temperatures. The incubation mixtures were analysed at different reaction times by MALDI/MS. Furthermore, in order to verify the possible role of sugar pyrolysis products in melanoidin formation, the products arising from the thermal treatment at 200 degrees C of MT were incubated with lysozyme, and the reaction products were analysed by the same MS approach.The obtained results allowed the establishment of some general views: melanoidins cannot simply originate by reactions of sugar moieties with proteins. In fact, the reaction easily occurs, but it does not lead to any coloured product, as melanoidins have been described to be; melanoidins cannot originate from the thermal degradation products of glycated proteins. In fact, the thermal treatment of glycated lysozyme leads to a severe degradation of the protein with the formation of LMW species, far from the view of melanoidins as HMW compounds; experimental evidence has been gained on the melanoidin formation through reaction of intact protein with the pyrolysis products of MT. This hypothesis has been supported either from MALDI measurements or from spectroscopic data that show an absorption band in the range 300-600 nm, typical of melanoidins.

Glycotoxins: a possible threat to health?

AGEs are produced by a nonenzymatic glycation process called the Maillard reaction which involves the condensation of a reducing sugar or an aldehydic group and a protein amino group, with the formation of a series of reactive intermediates leading to stable, irreversible, seldom fluorescent, compounds known as advanced glycation end-products (AGEs). The reaction occurs both in food during heating and in animal and human tissues. During the heating of food containing sugars, lipids and proteins, nonenzymatic protein browning reaction occurs, resulting in the formation of a large series of compounds, which include the melanoidins and other AGEs. Accumulation of AGEs in the cells and in the extracellular matrix in animals is also observed; it is age-dependent, is related to cell or tissue turnover and is species-specific. These processes are accelerated in chronic diseases in which the production of pathogenetic AGEs and their accumulation rate are increased. The two research fields, the Maillard reaction in food chemistry and the glycation cascade in medicine, ran in parallel independently for a long time, but recently a new scientific society (the International Maillard Reaction Society, IMARS) has opened the way for an exciting fusion of knowledge. Pioneering studies resulted in concerns about the non-negligible bioavailability of dietary AGEs and related plasma concentrations in humans, and there are now claims that dietary AGEs may be toxic because of their bioreactivity in different chronic diseases. This has been confirmed by several studies in animals and in humans (AGEs-restricted diets resulted in a reduction of serum and tissue AGEs, related AGE receptors, inflammatory cells, and proatherosclerotic factors) and by in vitro studies on cells in culture. In view of the emerging evidence of a pathogenetic role of glycotoxins, an assessment of the benefits of a shift to a specific nutritional approach (the Mediterranean diet being the healthiest in terms of the low amount of AGEs and high amount of antioxidants) and an innovative therapeutic approach, aimed at directly breaking AGEs molecules or reversing their impaired gut absorption to favour their renal or faecal excretion, may be warranted. At any rate, a new scientific field is open for an interdisciplinary debate (involving chemists, geriatricians, and specialists in metabolic disorders, diabetes, and diet) paving the way for possible, remarkable clinical progress.

Influence of a Rare Sugar, d-Psicose, on the Physicochemical and Functional Properties of an Aerated Food System Containing Egg Albumen

d-Psicose (Psi) might be an ideal sucrose (Suc) substitute for food products due to its sweet taste, easy processing, and functional properties (noncaloric and low glycemic response). In the present study, the effects of Psi on foaming properties of egg white (EW) protein and the quality of butter cookies were analyzed to find a better use of Psi in aerated food systems. The results showed that Psi could improve the foaming properties of EW protein with increasing whipping time in comparison to Suc and d-fructose (Fru). The addition of Psi to butter cookies, as partial replacement of Suc, had no influence on the cook loss while significantly contributing to a color change of the cookie crust through a nonenzymatic browning reaction. Furthermore, Psi-containing cookies possessed the highest antioxidant capacity in all tested cookies using two assays of radical scavenging activity and ferric reducing power. It was found that there was a close correlation between the crust color and the antioxidant activity of the cookie. The results suggest that the addition of Psi enhanced the browning reaction during cookie processing and, consequently, produced a strong antioxidant activity.