The irregular force-deformation relationships of commerical cheese balls and Zwiebacks at nine levels of water activity in the range 0.11-0+3 were recorded with a computer-interfaced Universal testing machine. They were characterized by two empirical stiffness parameters, the force at 10 and 20% deformation, and two jaggedness measures, the apparent fractal dimension of the normalized force-deformation curve and the mean magnitude of its power spectrum. The plots of all four parameters versus the water activity had a stable region followed by a substantial drop at a characteristic water activity level, of the kind expected when a material undergoes a glass transition. The phenomenon over the entire experimental water activity range, could be described by a model whose mathematical format is a slightly modified version of Fermi's distribution function that is P(a,) = PJ{ 1 + exp[(a, -uwcp)]/bp] + c, where P(a,)is any of the stiffness or jaggedness parameters, P, and c, constants whose sum is the magnitude of the parameter when the material is in the dry state (c, is the residual level after plasticization), awcp is a characteristic water activity level representing the region where the major textural changes take place, and b, a constant representing the steepness of the relationship at the transition region.

It is investigated whether the catalyst system Ag-In/SiO 2 can be applied in the selective hydrogenation of citral, with the aim of synthesizing the acyclic, allylic terpene alcohols geraniol/nerol with high selectivity and space-time yield. In addition, as liquid-phase hydrogenations are often also influenced by the choice of solvent, it is of interest to know how the solvent, in particular in terms of its polarity and hydrogen solubility, affects the activity and the selectivity of catalysts during hydrogenation of the a,b-unsaturated aldehyde citral. ProblemTerpenes are a low-cost class of compounds for the production of fragrances, flavors and pharmaceuticals, with terpenoid hydrocarbons (e.g., myrcene) being used less than terpene alcohols (e.g., geraniol, nerol, citronellol) and aldehydes (e.g., citral, citronellal). The compounds are often extracted from essential oils (e.g., lemon grass oil, citrus oil) by fractional distillation. Geraniol is the most frequently used terpenoid fragrance compound and, like its isomer nerol, applied in perfumes of roses and in citrus fragrances [1,2]. As an a,b-unsaturated aldehyde citral itself is an important educt for the synthesis of terpene alcohols and aldehydes because of its three functionalities (carbonyl group, conjugated C=C bond, isolated C=C bond) and thus, with the right choice of catalyst and reaction conditions, enables the synthesis of geraniol/ nerol, citronellal and/or citronellol by selective hydrogenation. Fig. 1 shows the reaction network of citral hydrogenation up to the completely hydrogenated reaction product 3,7-dimethyloctan-1-ol.In academia, citral hydrogenation is often used as a model reaction to study the influence of metal specificities, support materials and solvents on the intramolecular selectivitiy and product yield [3][4][5][6]. From a vulcano plot of the specific activity (turnover frequency) vs. the %-d character [7] of the metal used at 300 K and 0.1 MPa hydrogen pressure it follows, as expected, that Pd is the most active metal, whereas Ni, Co and Rh catalysts exhibit an activity which is about one to two orders of magnitude lower [6] (1) = 3,7-dimethyl-2-octenal, (2) = dihydrocitronellal, (3) = 3,7-dimethyl-2-octenol, (4) = 3,7-dimethyloctan-1-ol.

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