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In recent years microorganisms have been engineered towards synthesizing interesting plant polyphenols such as flavonoids and stilbenes from glucose. Currently, the low endogenous supply of malonyl-CoA, indispensable for plant polyphenol synthesis, impedes high product titers. Usually, limited malonyl-CoA availability during plant polyphenol production is avoided by supplementing fatty acid synthesis-inhibiting antibiotics such as cerulenin, which are known to increase the intracellular malonyl-CoA pool as a side effect. Motivated by the goal of microbial polyphenol synthesis being independent of such expensive additives, we used rational metabolic engineering approaches to modulate regulation of fatty acid synthesis and flux into the tricarboxylic acid cycle (TCA cycle) in Corynebacterium glutamicum strains capable of flavonoid and stilbene synthesis. Initial experiments showed that sole overexpression of genes coding for the native malonyl-CoA-forming acetyl-CoA carboxylase is not sufficient for increasing polyphenol production in C. glutamicum. Hence, the intracellular acetyl-CoA availability was also increased by reducing the flux into the TCA cycle through reduction of citrate synthase activity. In defined cultivation medium, the constructed C.glutamicum strains accumulated 24 mg·L −1 (0.088 mM) naringenin or 112 mg·L −1 (0.49 mM) resveratrol from glucose without supplementation of phenylpropanoid precursor molecules or any inhibitors of fatty acid synthesis. K E Y W O R D Scitrate synthase, Corynebacterium glutamicum, malonyl-CoA, naringenin, polyphenols, resveratrol

The morphological forms and habits of crystals and agglomeration are important properties on crystallization processes. Online techniques for realtime measurement of these properties are mandatory for a better comprehension of crystal growth phenomenon. The present paper presents and describes a new online method to determine the complexity level of a crystal or a population of crystals during a crystallization process. An image analysis technique is combined with discriminant factorial analysis leading to results that allow the computation of the complexity of crystals through the parameter agglomeration degree of crystals. With this methodology, it has been possible to distinguish online and automatically among three different classes of crystals according to their complexity. It further describes the application of such methodology on the study of CaCl 2 , D-fructose, and D-glucose influence on the crystallization of sucrose, namely, on crystal size, morphology, and complexity. The effect of supersaturation, growth rate, and impurity concentration on the type, amount, and complexity level of the agglomerates was determined at different temperatures. The combination of image analysis and kinetic results allowed to understand better the crystallization phenomena in the presence and absence of impurities. The image analysis results suggest the possible application of this tool for process control, optimizing, by this way, laboratory and industrial crystallizers. ' INTRODUCTIONThe impurities effect on crystal growth has been investigated over the years. A great deal of interest in this field is well attested in Sangwal's work. 1 Originating from raw materials and sometimes from production processes, the impurities affect not only the manufacturing process but also the crystallization kinetics. Some impurities act on the properties of the solutions while others act on the crystals surface, changing their morphology or habit. This morphology change is an important property that affects not only the downstream processing and handling but also the end-use functional properties. Crystal habit is closely associated with filterability, flowability, and compaction behavior among other properties. A sudden change in crystal habit may suggest the appearance of a new polymorph or the presence of trace impurities. Agglomeration may lead to profound changes in final product quality, as well as entrapment of unacceptable levels of occluded solvent, causing difficulties in washing and drying. 2 On the other hand, the impurity affinity for a specific crystal surface can be useful for crystal morphology changes. The tailormade additives have obtained great importance on crystal growth. They interact in specific ways with selected faces of crystalline materials, thereby inhibiting the growth of preselected faces, and not changing or changing slightly the growth of the other faces. Consequently, a specific crystal morphology is obtained. The additive molecules can lower the growth rate either by physically blocking the layers or by ...

Industrial filamentous fungal fermentations are typically operated in fed-batch mode. Oxygen control represents an important operational challenge due to the varying biomass concentration. In this study, oxygen control is implemented by manipulating the substrate feed rate, i.e. the rate of oxygen consumption. It turns out that the setpoint for dissolved oxygen represents a trade-off since a low dissolved oxygen value favors productivity but can also induce oxygen limitation. This paper addresses the regulation of dissolved oxygen using a cascade control scheme that incorporates auxiliary measurements to improve the control performance. The computation of an appropriate setpoint profile for dissolved oxygen is solved via process optimization. For that purpose, an existing morphologically structured model is extended to include the effects of both low levels of oxygen on growth and medium rheological properties on oxygen transfer. Experimental results obtained at the industrial pilot-scale level confirm the efficiency of the proposed control strategy but also illustrate the shortcomings of the process model at hand for optimizing the dissolved oxygen setpoints.

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