The effect of mixing on the liquefaction and saccharification of cellulosic fibers.

The enzymatic hydrolysis of cellulosic material is a key step in the biochemical routes for production of renewable fuels and chemicals. This must be performed at high solids to be economically viable. High solids operations creates numerous processing challenges, most importantly the limitations due to mass transfer and poor mixing of enzymes in the cellulose suspensions. We use magnetic resonance imaging (MRI), a cylindrical penetrometer, and HPLC to demonstrate the importance of spatial homogeneity in the distribution of enzyme on the rates of liquefaction of the substrate and in the suspension mechanical strength. Our results show that the largest mechanical strength changes occur in a narrow interval of time during the initial stages of conversion. Differences in enzyme concentration distribution occurring at the centimeter-scale produced order of magnitude differences in liquefaction and saccharification rates, supporting the hypothesis that mixing quality has a major influence in both liquefaction and saccharification rates.

Yield stress of pretreated corn stover suspensions using magnetic resonance imaging.

Cellulose fibers in water form networks that give rise to an apparent yield stress, especially at high solids contents. Measuring the yield stress and correlating it with fiber concentration is important for the biomass and pulp industries. Understanding how the yield stress behaves at high solids concentrations is critical to optimize enzymatic hydrolysis of biomass in the production of biofuels. Rheological studies on pretreated corn stover and various pulp fibers have shown that yield stress values correlate with fiber mass concentration through a power-law relationship. We use magnetic resonance imaging (MRI) as an in-line rheometer to measure velocity profiles during pipe flow. If coupled with pressure drop measurements, these allow yield stress values to be determined. We compare our results with literature values and discuss the accuracy and precision of the rheo-MRI measurement, along with the effects of fiber characteristics on the power-law coefficients.

Oil migration in chocolate and almond product confectionery systems.

UNLABELLED: Oil migration from high oil content almond confections into adjacent chocolate causes changes in product quality. The objective of this study was to quantify the oil migration from almond products to dark chocolate. Magnetic resonance imaging (MRI) was used to monitor spatial and temporal changes of liquid lipid content. A multislice spin echo pulse (MSSE) sequence was used to acquire images with a 7.8-ms echo time and a 1000-ms repetition time using a 1.03T Aspect AI MRI spectrometer. Samples were prepared as a 2-layer model system of chocolate and almond confection. Six different almond products and 1 type of dark chocolate were used. Samples were stored at 20, 25, and 30°C for a time frame of several months. Rate and extent of migration were quantified by a kinetic expression based on the linear dependence of oil uptake by chocolate and the square root of the time. Samples showed distinctly different rate and extent of oil migration, as evidenced by quantitative differences in the kinetic rate constants and equilibrium uptake for the different sample types. This work will be helpful to design formulations for almond and almond-based products in confections. PRACTICAL APPLICATION: This work will be helpful to design formulations for almond use in confections.