Using Native Plants of the Northeast of Mexico for Developing Active Antimicrobial Food Packaging Films

The development of active food packaging is addressed using polyolefins such as LDPE and PVOH, as well as biopolymers from flour (sorghum and corn) and by-products of the food industry. Bacteriocins (nisin, natamycin), plant extracts such as oregano and thyme, as well as native plants of the northeast region of Mexico (Larrea tridentata, Schinus molle, Cordia boissieri, Leucophyllum frutescens), and essential oils of oregano and thyme as antimicrobial agents have been studied. The effect exerted by the process of incorporation of the antimicrobial agent (casting, extrusion) on the barrier and mechanical properties of the package as well as the antimicrobial activity of the containers (broad spectrum or selective activity) has been observed and the establishment of methods for their traceability

Effets de l'ionisation sur les materiaux polymeres : application a l'etude des transferts de masse (permeabilite et migration)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Studying mixing in Non-Newtonian blue maize flour suspensions using color analysis

BACKGROUND: Non-Newtonian fluids occur in many relevant flow and mixing scenarios at the lab and industrial scale. The addition of acid or basic solutions to a non-Newtonian fluid is not an infrequent operation, particularly in Biotechnology applications where the pH of Non-Newtonian culture broths is usually regulated using this strategy.METHODOLOGY AND FINDINGS: We conducted mixing experiments in agitated vessels using Non-Newtonian blue maize flour suspensions. Acid or basic pulses were injected to reveal mixing patterns and flow structures and to follow their time evolution. No foreign pH indicator was used as blue maize flours naturally contain anthocyanins that act as a native, wide spectrum, pH indicator. We describe a novel method to quantitate mixedness and mixing evolution through Dynamic Color Analysis (DCA) in this system. Color readings corresponding to different times and locations within the mixing vessel were taken with a digital camera (or a colorimeter) and translated to the CIELab scale of colors. We use distances in the Lab space, a 3D color space, between a particular mixing state and the final mixing point to characterize segregation/mixing in the system.CONCLUSION AND RELEVANCE: Blue maize suspensions represent an adequate and flexible model to study mixing (and fluid mechanics in general) in Non-Newtonian suspensions using acid/base tracer injections. Simple strategies based on the evaluation of color distances in the CIELab space (or other scales such as HSB) can be adapted to characterize mixedness and mixing evolution in experiments using blue maize suspensions

Studying mixing in Non-Newtonian blue maize flour suspensions using color analysis.

BACKGROUND: Non-Newtonian fluids occur in many relevant flow and mixing scenarios at the lab and industrial scale. The addition of acid or basic solutions to a non-Newtonian fluid is not an infrequent operation, particularly in Biotechnology applications where the pH of Non-Newtonian culture broths is usually regulated using this strategy. METHODOLOGY AND FINDINGS: We conducted mixing experiments in agitated vessels using Non-Newtonian blue maize flour suspensions. Acid or basic pulses were injected to reveal mixing patterns and flow structures and to follow their time evolution. No foreign pH indicator was used as blue maize flours naturally contain anthocyanins that act as a native, wide spectrum, pH indicator. We describe a novel method to quantitate mixedness and mixing evolution through Dynamic Color Analysis (DCA) in this system. Color readings corresponding to different times and locations within the mixing vessel were taken with a digital camera (or a colorimeter) and translated to the CIELab scale of colors. We use distances in the Lab space, a 3D color space, between a particular mixing state and the final mixing point to characterize segregation/mixing in the system. CONCLUSION AND RELEVANCE: Blue maize suspensions represent an adequate and flexible model to study mixing (and fluid mechanics in general) in Non-Newtonian suspensions using acid/base tracer injections. Simple strategies based on the evaluation of color distances in the CIELab space (or other scales such as HSB) can be adapted to characterize mixedness and mixing evolution in experiments using blue maize suspensions

Different mixing states in a stirred tanks containing blue maize non-Newtonian flour suspensions.

<p>(A) In a tank stirred by an eccentrically located inclined disc impeller, a subsurface acid injection was efficiently dispersed to achieve homogeneity. (B) Severe top segregation is evident following a subsurface base injection in a concentrically agitated system. The inadequate selection of the point of addition of a concentrated basic injection can lead to the creation of (C) stagnant zones where alkaline conditions prevail, causing high viscosity conditions and (D) further obstructing effective mixing.</p

Following mixing through color changes in blue-maize suspensions.

<p>(A) In blue maize suspension, the color varies significantly as a function of pH due to the presence of native anthocyanins that act as a natural wide spectrum pH indicator. (B) The evolution of mixing of a blue maize flour suspension in a stirred tank was followed by addition of a basic injection into an initially acidic condition. Frontal photographic images were taken at different time points of the mixing process. Each image was divided into sixteen sections (U1 to L4) and the color in the CIE<i>Lab</i> scale was determined by image analysis at each of the center points (indicated by blue circles). (C) Samples corresponding to different tank locations and times of agitation were dispensed in 6-well culture plates for color analysis using digital photography or colorimetric readings with a portable colorimeter. Reproducibility of the color readings among different plates can be validated by including a color standard in each plate (in this case, a circular plastic object of uniform color). (D) The experimental error associated with lighting heterogeneity at different well positions was estimated by placing the same sample in different wells.</p

Proposed set of values for K and n for the Ostwald-de Waele power-law equation [η = K (γ)^n–1] to model the rheology of blue maize suspensions at different pH values.

<p>K and n were calculated from linear regressions of the type ln η = ln K+(n–1) ln (γ).</p><p>Proposed set of values for K and n for the Ostwald-de Waele power-law equation [η = K (γ)^n–1] to model the rheology of blue maize suspensions at different pH values.</p

Blue maize flour suspensions exhibit different rheological behavior at different pH values.

<p>(A) Plot of apparent viscosity versus shear rate (in the range from 250 to 1500 s⁻¹) for blue maize suspensions prepared at different pH values. Gray dotted lines correspond to power-law fits to experimental data based on the Ostwald-de Waele model [η = K (γ)^n–1] using the parameter values reported in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112954#pone-0112954-t001" target="_blank">Table 1</a>. (B) Plot of apparent viscosity versus shear rate (in the range from 250 to 1500 s⁻¹) for blue maize suspensions prepared at different pH values. (C) Log-log version of the plot of apparent viscosity versus shear rate (in the range from 250 to 1500 s⁻¹) for blue maize suspensions prepared at different pH values. Straight dotted lines have been used to connect the experimental data points.</p

Evaluation of mixing progression using distances between colors.

<p>(A) Evolution of the distance in color, based on the CIE<i>Lab</i> color space, with respect to the final mixing state (D_i,j) at different tank locations for the experiment in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112954#pone-0112954-g005" target="_blank">Figure 5:</a> at U2 (▪); at A2 (▴); B2 (◊); L2 (□). The average distance with respect to the final point, considering all sampling points, at different agitation times is also presented (•). Lines indicate polynomial fits to data. (B) Time evolution of the standard deviation of all the D_i,j values (corresponding to the same time point); a direct indicator of the degree of heterogeneity in the mixing conditions within the vessel. Lines indicate polynomial fits to data.</p

Quantitation of mixing through the concept of distances between mixedness states in the <i>Lab</i> color space.

<p>(A) Evolution of the average distance (D_i,j) with respect to an ideal mixing state condition for five different sampling locations defined within the tank volume (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112954#pone-0112954-g002" target="_blank">Figure 2</a>): 7U (•); 1U (▪); 12M (▴); 5U (○); and 3L (♦). The average distance with respect to the final point is marked with black circles (•); a second order polynomial fitting is shown (solid curve). (B) Evolution of the standard deviation from an initially segregated condition to a homogeneous final state (•). A second order polynomial fitting is shown (solid curve).</p