The metabolite 3-deoxyglucosone (3-DG) is formed by carbohydrate caramelisation or the Maillard reaction. 3-DG is a precursor in the Strecker reaction forming beer ageing compounds, such as 2-methylbutanal or 3-methylbutanal. Although 3-DG is known as intermediate, recent studies have focused on 3-DG in beer. Foremost, the thermal load during wort boiling provides the best conditions for 3-DG formation and degradation, however, the reactivity of the dicarbonyl during the boiling process has not yet been explained. As a key intermediate, 3-deoxyglucosone could be a critical indicator for beer ageing stability. The 3-DG formation and reactivity during wort production depends on its precursor reactants (amino acids and glucose). The concentration in wort of these substances was varied using two malts with different malt modification along with two different mashing programmes. 3-Deoxyglucosone reactivity was observed by analysing dehydratisation to HMF (HPLC-UV), interconversion to 3-deoxygalactosone (3-DGal, HPLC-UV) and selected Strecker aldehydes (GC-SPME-MS). This study shows that wort boiling is the most important process in 3-DG formation as it contributes 47% of the final content compared with malting (28%) and mashing (25%). With degradation reactions, 3-DG is mainly interconverted to 3-DGal and, contrary to the literature, it could not be confirmed that enhanced 3-deoxyglucosone content affects Strecker reactions. The interconversion reaction during wort boiling determines the dicarbonyl potential of beer and influences the ageing stability.
Summary. The subject of this paper is an optimal control problem with ODE as well as PDE constraints. As it was inspired, on the one hand, by a recently investigated flight path optimization problem of a hypersonic aircraft and, on the other hand, by the so called "rocket car on a rail track"-problem from the pioneering days of ODE optimal control, we would like to call it "hypersonic rocket car problem". While it features essentially the same ODE-PDE coupling structure as the aircraft problem, the rocket car problem's level of complexity is significantly reduced. Due to this fact it is possible not just to obtain easily interpretable results but also a certain degree of insight into the structure of the adjoints. Therefore, the rocket car problem can be seen as a prototype of an ODE-PDE optimal control problem. The main objective of this paper is the derivation of first order necessary optimality conditions.
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