Impact of whey protein hydrolysates on the formation of 2,5-dimethylpyrazine in baked food products.

Peptides have been reported to serve as precursors in the generation of alkylpyrazines, key aroma compounds in heated foods. Most previous studies, concerned with the generation of pyrazines via the Maillard reaction, were conducted using model systems of varying complexities. However, the formation of pyrazines in real food systems has received less attention. The aim of this study was to investigate the impact of adding protein hydrolysates as precursors for the generation of alkylpyrazines in baked food products such as bread and cookies. Two whey protein hydrolysates, obtained using either trypsin or proteinase from Aspergillus melleus, were used in the presented study. 2,5-Dimethylpyrazine was produced in both food systems. Therefore, its formation was quantitatively monitored using a stable isotope dilution assay. Additionally, sensory evaluation was performed. Results demonstrated that the addition of the protein hydrolysates were effective in promoting the generation of 2,5-dimethylpyrazine and other aroma compounds in two well-known food products.

Cocoa-specific flavor components and their peptide precursors.

Essential precursors of the cocoa-specific roasting-flavor notes were formed during proteolysis of the cocoa vicilin-class(7S) globulin by a mixture of cocoa aspartic protease and carboxypeptidase. These could be partially purified by ligand-exchange chromatography. Many constituents of this peptide fraction were destroyed by post-treatment with pepsin, but the cocoa-specific flavor-precursor peptides were largely resistant against pepsin treatment. However, these peptides were not generated when the cocoa vicilin-class(7S) globulin was digested with a mixture of pepsin and carboxypeptidase. By nano-liquid chromatography mass spectrometry, the peptide composition of these peptide fractions were compared in order to identify the putative precursors of the cocoa-specific flavor components. These peptides were assigned to five regions of the cocoa vicilin-class(7S) globulin. Analyzing the roasting products of the different protein fractions by headspace solid-phase microextraction, followed by gas chromatography mass spectrometry, eight volatile compounds were detected, whose occurrence correlated with the sensory detection of cocoa-specific flavor notes.

Impact of different enzymatic hydrolysates of whey protein on the formation of pyrazines in Maillard model systems.

The generation of pyrazines in model systems containing enzymatically hydrolyzed whey protein under dry heating conditions was studied. Pyrazines are important Maillard flavor compounds. Hydrolysates, obtained with different peptidases (pepsine, chymosine, thermolysin and a non-specific peptidase from Aspergillus melleus), contained a varying peptide profile and free amino acid content. The impact of each hydrolysate on the generation of flavor volatiles was measured by HS-SPME-GC/MS. The presence of oligopeptides had an enhancing role on the generation of pyrazines while, in contrast, free amino acids contributed to a lesser extent in pyrazine formation, except in the hydrolysate using the non-specific peptidase because of its high free amino acid content. Typically, 2,5(6)-dimethylpyrazine was the most abundant pyrazine found, although in the chymotripsine hydrolysate also other pyrazines were dominant. The hydrolysate obtained from the non-specific peptidase contained a larger variety of pyrazines, including the typical Strecker aldehydes originating from specific amino acids. This study demonstrates that oligopeptides are important Maillard flavor precursors.

Assessing the influence of pod storage on sugar and free amino acid profiles and the implications on some Maillard reaction related flavor volatiles in Forastero cocoa beans.

The practice of pod storage (PS) has been applied in many cocoa producing countries, especially by Ghanaian farmers over the years. However, the study of PS has not received much attention, hence, until now, its potential impact on specific flavor precursor development and implications on the flavor of cocoa beans still remains uncovered. The study was therefore aimed at exploring this possibility through physico-chemical and flavor precursor analyses, carried out on equally fermented and dried pod stored (0, 3 and 7 days) Ghanaian cocoa beans. Flavor analysis was also conducted on equally roasted pod stored cocoa beans. Through visual assessment of the pods, pulp and beans, the compelling impact of PS on fermentation index (FI) and nib acidity could be demonstrated by the various biochemical and physical changes such as respiration, moisture reduction, and cellular degradation, occurring during the process. Whereas the entire reaction of sugar degradation may be deemed complex, a clear relationship between the FI, nib acidity and the glucose content was observed. Also, PS was found to increase with marginal increase in total reducing sugars (glucose and fructose). Although the concentration of free amino acids was directly proportional to the duration of PS, within the framework of this study, a significant difference (p < .05) was only observed in the case of extended duration (7 days). Overall, 7 PS seemed to have enhanced the formation of more volatiles. This was followed by 0 PS and finally 3 PS. Suggestively, these findings could provide some indications in explaining the typical flavor profiles of the Ghanaian cocoa beans, considering the fact that 87.8% of Ghanaian farmers adhere to this practice. Meanwhile, for the chocolate industry, the surging demand for cocoa/chocolate products exhibiting unique flavors, could be partly addressed by adopting PS as a tool for varietizing the flavor capacity of "bulk" cocoa through the expression or suppression of specific flavor precursors in the raw material on the farm level, which comes with almost no additional cost.

Influence of Free Amino Acids, Oligopeptides, and Polypeptides on the Formation of Pyrazines in Maillard Model Systems.

Pyrazines are specific Maillard reaction compounds known to contribute to the unique aroma of many products. Most studies concerning the generation of pyrazines in the Maillard reaction have focused on amino acids, while little information is available on the impact of peptides and proteins. The present study investigated the generation of pyrazines in model systems containing whey protein, hydrolyzed whey protein, amino acids, and glucose. The impact of thermal conditions, ratio of reagents, and water activity (a(w)) on pyrazine formation was measured by headspace solid-phase microextraction with gas chromatography/mass spectrometry (HS-SPME-GC/MS. The presence of oligopeptides from hydrolyzed whey protein contributed significantly to an increased amount of pyrazines, while in contrast free amino acids generated during protein hydrolysis contributed to a lesser extent. The generation of pyrazines was enhanced at low a(w) (0.33) and high temperatures (>120 °C). This study showed that the role of peptides in the generation of pyrazines in Maillard reaction systems has been dramatically underestimated.