Tuning functionality of waxy starch/xanthan gum systems by varying processing conditions

Starches and food gums are combined very often in commercial foodstuffs like sauces, dressings and dairy desserts. The central aim of this PhD research was to better understand waxy starch/xanthan functionality in order to improve their performance in industrial applications. More specifically, the influence of varying processing conditions was investigated. General principles were presented that can assist in tuning the final properties of these systems. The flow behavior of the mixed pastes during pasting, but also after cooling, strongly depended on the specific type of waxy starch that was combined with the gum. These differences were attributed to variations in swelling power and more importantly, variations in degradation behavior of the granules. It was concluded that granule integrity is a prerequisite for optimal xanthan functionality. However, when fragile native waxy starches are pasted at temperatures just above the gelatinization onset temperature, granule disruption can be limited and a higher shear rate is even beneficial towards complete viscosity development. Furthermore, these mild heating steps yield starch pastes with an acceptable physicochemical stability. Nevertheless, the correct choice of processing temperature appears of utmost importance considering that an increase in breakdown renders the pastes highly unstable and a strong gelation is observed during longer storage periods. Xanthan gum has the ability to inhibit granule disruption during pasting, whereas guar gum appeared not to have this property. It was suggested that xanthan gum reduces the impact between the granules by the formation of a shear-induced anisotropic organization in the continuous phase. This strong molecular alignment, which is typical for extended molecules like xanthan gum, may guide the granules and induce a smooth flow, thus protecting them from breaking down. Hence, the rheological properties of native waxy starch systems can be tuned directly and indirectly (granule protection) by the incorporation of xanthan gum

Wounding triggers callus formation via dynamic hormonal and transcriptional changes

Wounding is a primary trigger of organ regeneration, but how wound stress reactivates cell proliferation and promotes cellular reprogramming remains elusive. In this study, we combined transcriptome analysis with quantitative hormonal analysis to investigate how wounding induces callus formation in Arabidopsis (Arabidopsis thaliana). Our time course RNA-seq analysis revealed that wounding induces dynamic transcriptional changes, starting from rapid stress responses followed by the activation of metabolic processes and protein synthesis and subsequent activation of cell cycle regulators. Gene ontology analyses further uncovered that wounding modifies the expression of hormone biosynthesis and response genes, and quantitative analysis of endogenous plant hormones revealed accumulation of cytokinin prior to callus formation. Mutants defective in cytokinin synthesis and signaling display reduced efficiency in callus formation, indicating that de novo synthesis of cytokinin is critical for wound-induced callus formation. We further demonstrate that type-B ARABIDOPSIS RESPONSE REGULATOR-mediated cytokinin signaling regulates the expression of CYCLIN D3;1 (CYCD3;1) and that mutations in CYCD3;1 and its homologs CYCD3;2 and 3 cause defects in callus formation. In addition to these hormone-mediated changes, our transcriptome data uncovered that wounding activates multiple developmental regulators, and we found novel roles of ETHYLENE RESPONSE FACTOR 115 and PLETHORA3 (PLT3), PLT5, and PLT7 in callus generation. All together, these results provide novel mechanistic insights into how wounding reactivates cell proliferation during callus formation

Degradation of MONOCULM 1 by APC/CTAD1 regulates rice tillering

A rice tiller is a specialized grain-bearing branch that contributes greatly to grain yield. The MONOCULM 1 (MOC1) gene is the first identified key regulator controlling rice tiller number; however, the underlying mechanism remains to be elucidated. Here we report a novel rice gene, Tillering and Dwarf 1 (TAD1), which encodes a co-activator of the anaphase-promoting complex (APC/C), a multi-subunit E3 ligase. Although the elucidation of co-activators and individual subunits of plant APC/C involved in regulating plant development have emerged recently, the understanding of whether and how this large cell-cycle machinery controls plant development is still very limited. Our study demonstrates that TAD1 interacts with MOC1, forms a complex with OsAPC10 and functions as a co-activator of APC/C to target MOC1 for degradation in a cell-cycle-dependent manner. Our findings uncovered a new mechanism underlying shoot branching and shed light on the understanding of how the cell-cycle machinery regulates plant architecture

Relating crystallization behavior of monoacylglycerols-diacylglycerol mixtures to the strength of their crystalline network in oil

Diacylglycerols (DAGs) are interesting oil structuring molecules as they are structurally similar to triacylgly-cerols (TAGs), but are metabolized differently which results in weight loss and improved blood cholesterol levels upon dietary replacement of TAGs with DAGs. Many commercial products consist of a mixture of mono-acylglycerols (MAGs) and DAGs, yet the effect of MAGs on the crystallization behavior of DAGs is still to be unraveled. Two types of commercial MAGs, one originating from hydrogenated palm stearin and one of hydrogenated rapeseed oil, were added in concentrations 1, 2 and 4% to 20% DAGs derived from hydrogenated soybean oil. Using differential scanning calorimetry, it was shown that the presence of MAGs delayed the onset of DAG crystallization. Rheological analysis revealed that MAGs also hindered crystal network development. Synchrotron X-ray diffraction analysis demonstrated that the addition of MAGs suppressed the formation of the A form and stimulated the development of the beta' form. Likely, MAGs mainly hindered the crystallization of 1,3-DAGs, which are responsible for the development of the beta form, and stimulated the crystallization of the 1,2-DAGs, which can crystallize in the alpha and beta' forms. The presence of two polymorphic forms resulted in a decrease of the crystal network strength, as was derived from oscillatory rheological measurements. This research implies a different effect of monoacylglycerols on both the nucleation and crystal growth of 1,2- and 1,3-DAG isomers. This insight is not only relevant for oleogelation research, but also for emulsifying agents which often contain blends of MAGs, 1,2-DAGs and 1,3-DAGs