Analysis of volatile organic compounds in crumb and crust of different baked and toasted gluten‐free breads by direct PTR‐ToF‐MS and fast‐GC‐PTR‐ToF‐MS

Abstract

Proton transfer reaction (PTR)‐time of fight (ToF)‐mass spectrometry (MS) has been recently employed as a quick, easy, and sensitive alternative to gas chromatography MS for the analysis of volatile compounds in food. In the present work, PTR‐ToF‐MS was applied to the characterization of the volatile profiles of the baked and toasted crumbs and crusts of 5 gluten‐free breads elaborated with quinoa, teff, and rice flours as well as corn and wheat starches and wheat bread as a control samples. Two hundred fifty‐nine peaks (m/z) were detected, 86 peaks were tentatively identified, and 56 volatile compounds were selected as important contributors to bread aroma. Fast gas chromatography PTR‐ToF‐MS analyses were performed with 42 standards to identify them in the baked crumbs and crusts, 18 of them being present in all the samples. From the baked samples, it was concluded that quinoa crust was the 1 with higher volatile compound in high abundance, characterized by volatile compounds from fermentation, lipid oxidation, 2‐acetyl‐1‐pyrroline, and diethyl‐pyrazines, while wheat crust was characterized by the highest content in furan derivatives. The toasting time led to crust samples with an increased content in all the volatile compounds: Quinoa crust was now characterized by the highest content in all the pyrazines and furan derivatives, while starches were distinguished by the highest abundance in 2‐acetyl‐1‐pyrroline and diethyl‐pyrazines. Neither the baked crumbs nor the toasted crumbs presented the highest content in none of the volatile compounds. Therefore, it was concluded that quinoa flour can be a suitable alternative for the elaboration of baked and toasted breads due to the high content of pleasant volatile compounds from fermentation, the key volatile in crust 2‐acetyl‐1‐pyrroline (baked sample), as well as pleasant pyrazines and toasted‐like furan derivatives (baked and toasted samples); however, the off‐flavor volatile compounds from lipid oxidation as well as the bitter saponins present in quinoa bread should be taken into account.

Real-Time Monitoring of Volatile Compounds Losses in the Oven during Baking and Toasting of Gluten-Free Bread Doughs: A PTR-MS Evidence

“…Thereby, the detection of these compounds started around 20 min and they were released in much higher ratios than Maillard compounds from groups 7 and 8, also following the curve shape of an exponential growth. This is in accordance with previous analyses of furans in bread crusts by PTR-ToF-MS [ 15 ], where furans were in much higher concentration than pyrazines since furans have a double source of generation. Therefore, despite being released in a bigger amount to the headspace, a great part of furans also remains in the crumb.…”

“…This origin is in accordance with the evaporation from dough to crumb reported for 3-methyl-1-butanol, 2-methyl-1-butanol, and 2,3-butanedione in corn starch bread [ 19 ], as they have been demonstrated to be highly released to the oven during our PTR-ToF-MS measurements of baking. In spite of being released in great amounts to the oven, volatile compounds from fermentation have been reported to be the main compounds in breads crumbs analysed by PTR-ToF-MS [ 15 ], since the temperatures that are reached in the crumb during baking are not enough for a relevant generation of other types of volatile compounds.…”

“…The splitting between these groups is based on the stage of baking that their volatile compounds, mainly in the case of starch breads, are detected in the headspace of the oven. The higher release to the oven in starch breads could be attributed to their higher moisture loss as compared to cereal breads (as it was explained for group 1), as well as to their possible higher generation during baking considering their reported higher amount in the final crust of wheat starch breads that were prepared with a similar formula, in spite of their lighter colour compared to cereal breads [ 15 ]. Thus, volatiles are from group 7 (early Maillard origin, Figure 1 G, 2,3-diethylpyrazine) if they started to be visibly released in starch breads after 30 min.…”

“…PTR-ToF-MS is a direct-injection mass spectrometric technique that is based on the proton transfer reaction from hydronium ions (H 3 O + ) to those compounds with larger proton affinities than water, mainly producing protonated molecular ions MH + , but also smaller fragments, e.g., from the dehydration-protonation of tertiary alcohols, aldehydes, acids, and esters [ 8 ]. PTR-ToF-MS has already been successfully applied to the characterisation of volatile compounds in baked wheat bread for the evaluation of its freshness [ 9 ], the effect of bakery yeasts and flours in wheat doughs and baked breads [ 4 , 10 , 11 ], the retronasal aromas released from the nose-air of consumers during the oral processing of wheat breads [ 12 , 13 , 14 ], and even for the aroma of baked and toasted crumbs and crusts of gluten-free breads as final products [ 15 ]. However, PTR-ToF-MS has never been applied to the on-line monitoring of the vapours released into the oven from the bread dough during baking, which certainly would contribute to the understanding of the aroma intensity of the final product.…”

From Microbial Ecology to Innovative Applications in Food Quality Improvements: the Case of Sourdough as a Model Matrix

“…Lipids, also present in raw material or added in the form of fats or oils in order to improve dough handling and crumb appearance, can be oxidized and converted into aldehydes which are also involved in the formation of aroma profile [59][60][61].…”