Daily assessment of malting-induced changes in the volatile composition of barley (Hordeum vulgare L.), rye (Secale cereale L.), and quinoa (Chenopodium quinoa Willd.).

Barley (Hordeum vulgare L.) is the traditional malting cereal and is primarily used for beverages, whereas rye (Secale cereale L.) is mainly used in baked goods. Conversely, quinoa (Chenopodium quinoa Willd.) is a gluten-free pseudocereal, rich in starch and high-quality proteins, and can be used in a similar manner to cereals. The sharp bitterness of unprocessed rye and the earthy aroma of native quinoa interfere with the acceptance and development of food products. Malting of barley is known to improve its processing properties and enhance its sensory quality. Therefore, the effect of germination and kilning on malt quality (e.g., viscosity) as well as the volatile composition of barley, rye, and quinoa were monitored. Moreover, temporal changes on the volatile patterns of rye and quinoa at the different stages of malting were compared to barley. In total, 34 volatile compounds were quantified in the three (pseudo)cereals; the alcohol group dominated in all unprocessed samples, in particular, compounds contributing grassy notes (e.g., hexan-1-ol). These grassy compounds remained abundant during germination, whereas kilning promoted the formation of Maillard reaction volatiles associated with malty and roasted notes. The volatile profiles of kilned barley and quinoa were characterized by high concentrations of the malty Strecker aldehyde, 3-methylbutanal. In contrast, green, floral notes imparted by phenylacetaldehyde remained dominant in rye malt. Hierarchical cluster analysis of the volatile data discriminated the samples into the different stages of malting, confirmed the similarities in the volatile patterns of barley and rye, and indicated clear differences to the quinoa samples. PRACTICAL APPLICATION: In this study, the effect of germination and kilning on the chemical and volatile composition of barley, rye, and quinoa was examined. Temporal changes on the volatile patterns of rye and quinoa at different stages of malting were compared to barley. Understanding the differences among the (pseudo)cereals as well as the influence of processing on malt quality and aroma development can help find new food applications.

Comparative study of the impact of malting on the aroma profiles of barley (Hordeum vulgare L.) and rye (Secale cereale L.).

Barley (Hordeum vulgare L.) remains the traditional malted cereal used for beverages, whereas rye (Secale cereale L.) is mainly used in baked goods. To evaluate the potential of rye malt for beverage production, malt quality indicators and the volatile composition of different rye malts were compared to barley malt. Sensory assessment revealed that pleasant malty and caramel aromas were formed by malting. Subsequently, three complementary isolation techniques and gas chromatography-olfactometry/mass spectrometry (GC-O/MS) were used for volatile analysis. Instrumental analysis detected 50 and 56 odor active volatiles in barley and rye, respectively. In part two, storage and the impact of three malting parameters on volatile formation were examined. Similarities in the malt volatile patterns were detected but the perceived intensity and composition varied. In barley, characteristic malty volatiles were lost during storage and staling compounds were formed. Conversely, nutty pyrazines and caramel furanones remained dominant in rye malts even after storage.

Characterization of the aroma profile of quinoa (Chenopodium quinoa Willd.) and assessment of the impact of malting on the odor-active volatile composition.

BACKGROUND: Quinoa (Chenopodium quinoa Willd.) is a gluten-free pseudocereal, rich in starch and high-quality proteins. It can be used as a cereal. Recently, a variety of nontraditional food products were developed; however, the sharp bitterness and the earthy aroma of unprocessed quinoa interfered with the acceptance of these products. Malting of cereals is known to improve their processing properties and enhance their sensory quality. To evaluate the acceptance and potential of quinoa malt as a raw material for beverage production, malt quality indicators (e.g., soluble protein) and the aroma profiles of different quinoa malts were compared. RESULTS: Initial sensory assessment of quinoa in its native and malted state identified differences in their aroma profiles and revealed that pleasant nutty and caramel aromas were formed by malting. Subsequently, three complementary isolation techniques and gas chromatography-olfactometry/mass spectrometry (GC-O/MS) were used for volatile analysis. Instrumental analysis detected 34 and 62 odor-active regions in native quinoa and quinoa malt, respectively. In the second part, storage and the impact of three malting parameters on volatile formation were examined. By varying the malting parameters, seven additional odor-active malting byproducts were revealed. CONCLUSION: Three naturally occurring methoxypyrazines were identified as important contributors to the characteristic quinoa aroma. In all fresh quinoa malts a similar number of volatile compounds was perceived but their intensity and composition varied. Higher germination temperature promoted the formation of lipid oxidation products. Fatty smelling compounds and carboxylic acids, formed during storage, were classified as aging indicators of quinoa malt. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.