Influence of the malting conditions on the modification and variation in the physicochemical properties and volatile composition of barley (Hordeum vulgare L.), rye (Secale cereale L.), and quinoa (Chenopodium quinoa Willd.) malts

The traditional malted cereal used primarily for beverages is barley (Hordeum vulgare L.), while rye (Secale cereale L.) is mainly used in baked goods. In contrast, quinoa (Chenopodium quinoa Willd.) is a gluten-free pseudocereal, rich in starch and high-quality proteins, that can be used similarly to cereals. Their physicochemical properties and volatile compositions (e.g., aroma compounds) directly influence the finished food products. The sharp bitterness of unprocessed rye and the earthy aroma of native quinoa can interfere with the development and acceptance of food products. Malting is known to improve the processing and sensory properties of barley. A face-centered, central composite design was used to investigate the individual and interactive effects of three malting parameters (i.e., steep moisture (SM), germination temperature (T), and germination time (t)) on malt quality indicators (e.g., extract) and volatile formation (e.g., 3-methylbutanal) in rye and quinoa, and were compared to barley. The malt modification predictive models were then used to determine standard malting regimes for brewing quality malts. The malting parameters for the steeping and germination stages were: 43 %, 15 °C, and 6 d for barley; 45 %, 12 °C, and 8 d for rye; and 46 %, 16 °C, 6 d for quinoa. Malt modification and volatile formation were primarily associated with the interactive effect of germination temperature and time. Conversely, steep moisture had limited impact on malt modification but strongly regulated the formation of 34 known (pseudo)cereal volatile compounds. Principal component analysis (PCA) of the volatile data identified (pseudo)cereal specific volatile patterns. Aldehydes were characteristic in the cereal malts, particularly barley, whereas phenyl compounds and pyrazines were abundant in rye and quinoa malts, respectively. Controlling (pseudo)cereal modification and volatile development through the malting process could help deliver targeted sensory properties and improve the acceptance of malt-based food products.