Unravelling caramelization and Maillard reactions in glucose and glucose + leucine model cakes: Formation and degradation kinetics of volatile markers extracted during baking.

A large number of volatile compounds are formed during the baking of foods by reactions such as caramelization and Maillard reactions. Elucidating the reaction mechanisms may be useful to predict and control food quality. Ten reaction volatile markers were extracted during baking of solid model cakes implemented with known amounts of precursors (glucose with or without leucine) and then quantified by Thermal desorption-Gas chromatography-Mass spectrometry. The kinetic data showed that the level of air convection in the oven had no significant influence on the reaction rates. In contrast, increasing baking temperatures had a nonlinear accelerating impact on the generation of newly formed volatile compounds with a bell-shaped kinetic curve found for most of the markers at 200 °C. The presence of leucine triggered the activation of the Maillard and Strecker routes with a specific and very rapid formation of 3-Methylbutanal and pyrazines. A dynamic model was developed, combining evaporation flow rate and kinetic formation and consumption of reaction markers. It can be used to describe, for two furanic compounds of different volatilities, the vapor concentrations in the oven from the concentrations measured in the model cakes.

Unravelling caramelization and Maillard reactions in glucose and glucose + leucine model cakes: Formation and degradation kinetics of precursors, α-dicarbonyl intermediates and furanic compounds during baking.

Understanding the mechanisms leading to the multitude of newly-formed compounds generated during the thermal processing of food is important for the reasoned construction of quality. Thanks to a solid food model with a structure and technological history comparable to that of a real sponge cake and containing only known amounts of precursors (glucose with or without leucine), an adapted reaction scheme unravelling Maillard and caramelization reactions was built and then compared to experimental kinetic data measured on numerous reaction markers (precursors, α-dicarbonyl intermediates and furanic compounds). For caramelization, this study showed that glucose mainly formed 1,2-enediol and then fructose rather than glucosone and glyoxal. 5-hydroxymethylfurfural started to form when there were sufficient quantities of fructose, and 3,4-dideoxyoglucosone was not generated until after this step. Furfural was mainly formed via 3-deoxyglucosone. The involvement of leucine tended to accelerate the breakdown of sugars as more degradation pathways (via enaminols) were added.

Potential of model cakes to study reaction kinetics through the dynamic on-line extraction of volatile markers and TD-GC-MS analysis.

This study presents a novel strategy for the dynamic analysis of volatile compounds extracted from baking vapors using a fit-for-purpose model cake. This model imitates a real sponge cake in terms of structure and processing but it is not reactive towards Maillard and caramelization reactions. When implemented with precursors (glucose (G) or glucose + leucine (G + L)), the reactions are activated and volatile markers can be monitored dynamically during baking. A method for the on-line sampling of vapors during baking using sorbent tubes coupled to thermal desorption (TD-GC-MS) has been developed and proven to be an appropriate and rapid technique to analyze a large number of volatile compounds within a broad range of physical and chemical characteristics. Volatile markers such as acetic acid, furfural, furfuryl alcohol and 5-hydroxymethylfurfual were identified using both models: glucose (G) and glucose + leucine (G + L) because they arise from both caramelization and the Maillard reaction. On the other hand, 3-methylbutanal and 2,5-dimethylpyrazine were only identified in the (G + L) model cake as they arise from the Strecker degradation pathway induced by the presence of leucine. Moreover, the relative abundance of all markers of reactions covers a broad range. On-line sampling coupled to TD-GC-MS enabled the collection of kinetic data on these markers throughout the baking operation and discrimination of the two formulas (G vs G + L) and two baking temperatures (170 °C and 200 °C) used. These results offer promise for the further use of this approach to study reaction kinetics in model cakes.

Kinetic study of furan and furfural generation during baking of cake models.

This study describes the kinetics of furan and furfural generation in a cake model, for the first time. These process-induced compounds impact safety and sensory aspects of baked products. Understanding their generation with regards to process dynamics will serve food quality design. However, the complexity of real products makes this task challenging. This work provides a novel approach to understand and model chemical reactivity by implementing an inert cake model (starch, water and cellulose), specifically designed for mimicking a sponge cake structure. The addition of reaction precursors (glucose and leucine) to follow Maillard and caramelization reactions, resulted in browning and generated considerable levels of furanic compounds (up to 17.61ng/g for furan and 38.99µg/g for furfural, dry basis). Multiresponse data modeling resulted in a kinetic model which adequately describes experimental concentrations and makes it possible to estimate the degradation of precursors and the behavior of two hypothetic intermediates.

Involvement of bovine lactoferrin metal saturation, sialic acid and protein fragments in the inhibition of rotavirus infection.

Although the antiviral activity of lactoferrin is one of the major biological functions of this iron binding protein, the mechanism of action is still under debate. We have investigated the role of metal binding, of sialic acid and of tryptic fragments of bovine lactoferrin (bLf) in the activity towards rotavirus (intestinal pathogen naked virus) infecting enterocyte-like cells. The antiviral activity of bLf fully saturated with manganese or zinc was slightly decreased compared to that observed for apo- or iron-saturated bLf. The antiviral activity of differently metal-saturated bLf towards rotavirus was exerted during and after the virus attachment step. The removal of sialic acid enhanced the anti-rotavirus activity of bLf. Among all the peptidic fragments obtained by tryptic digestion of bLf and characterised by advanced mass spectrometric methodologies, a large fragment (86-258) and a small peptide (324-329: YLTTLK) were able to inhibit rotavirus even if at lower extent than undigested bLf.

Involvement of bovine lactoferrin moieties in the inhibition of herpes simplex virus type 1 infection.

Bovine lactoferrin (BLf) is an iron binding protein folded in two lobes, N- and C-lobes. In this study we have reported the inhibitory activity towards herpes simplex virus type 1 (HSV-1) in vitro infection of BLf tryptic digested N- and C-lobes in comparison with the whole protein. The N-lobe and C-lobe exerted an anti-herpesvirus activity 50- and 10-fold lower than native BLf, respectively. In order to assess the phase of viral replication affected, lactoferrin-derived lobes were added to the cells at different non cytotoxic concentrations, during the whole cycle of viral infection or during viral attachment step, demonstrating that both lobes interfered with the early phases of infection. Among the BLf tryptic digested fragments, two negatively-charged small peptides deriving from N-lobe, previously shown effective towards HSV-1, have been further studied. We assessed that the net negative charge of these peptides was not responsible for the antiviral activity since their activity was not modified when the aspartic and glutamic acidic residues of these peptides were replaced with asparagine and glutamine, respectively. The experiments here reported confirm a pivotal role of N-lobe in inhibiting viral infection. However, the residual inhibiting activity of C-lobe and the similar efficacy shown by negatively or positively charged peptides strongly support the idea that the antiviral activity of bovine lactoferrin cannot be fully explained simply on the basis of competition between the protein and viral recognition sites for binding to glycosaminoglycans.

Modern mass spectrometric methodologies in monitoring milk quality.

Structural modifications induced by industrial treatments on milk proteins have been investigated using a new analytical protocol based on mass spectrometric procedures (electrospray and matrix assisted laser desorption ionization mass spectrometry) providing a direct correlation between the severity of the treatment and the damages observed. The application of this procedure to the analysis of whey proteins from milk samples submitted to different thermal processes confirmed that under these conditions protein modification is essentially due to the nonenzymatic glycation of amino groups by lactose (Maillard reaction). A detailed structural investigation of the modification sites, carried out by the mass mapping strategy, revealed the occurrence of preferentially lactosylated sites in both alpha-lactalbumin and beta-lactoglobulin.

Bovine lactoferrin peptidic fragments involved in inhibition of herpes simplex virus type 1 infection.

Bovine lactoferrin (BLf) prevents the infection of some enveloped and naked viruses. To identify BLf sequences responsible for the antiviral activity, we tested 31 HPLC fractions, derived from tryptic digestion of BLf, toward herpes simplex virus type 1 (HSV-1). Only a few HPLC purified fragments were active against HSV-1, even if at lower extent than the native undigested BLf. Two large fragments, one corresponding to the C-lobe (amino acid sequence 345-689) and the other corresponding to a large portion of the N-lobe (1-280), were inhibitors of HSV-1 infection, while a smaller part of the N-lobe (86-258) was ineffective. Among the low-molecular-weight fragments, only two small peptides, which coeluted in a single chromatographic peak, were effective towards HSV-1. These peptides, both present in the N-lobe, were identified as peptides 222-230 (ADRDQYELL) and 264-269 (EDLIWK). The same peptides, chemically synthesised, were able to inhibit HSV-1 infection only when they were assayed in association.