Nelly Ramírez-Corona

Essential Oils: Antimicrobial Activities, Extraction Methods, and Their Modeling

Worldwide there is a wide variety of plants and spices that have different uses according to the culture and traditions of each region. Essential oils are gaining interest from the academic and industrial communities since they have been associated with possible antimicrobial activity against a wide range of microorganisms. Essential oil extraction can be made by traditional or emergent methods; nowadays, mathematical models are being developed for these methods in order to design efficient industrial processes. Although the majority of the essential oils are classified as GRAS, their use in foods as preservatives is often limited due to flavor considerations, since effective antimicrobial doses may exceed sensory acceptable levels. The antimicrobial effect of each essential oil mainly depends on the quality and quantity of their components, which are affected by different factors such as the environmental conditions of the growing season of the plant as well as the extraction method. The most common methods used to evaluate the antimicrobial activity of essential oils in vitro are diffusion and dilution (direct contact) or vapor-phase (gaseous contact) methods. This review focuses on available methods for extraction of essential oils and their mathematical modeling, as well as their application as antimicrobial agents.

Description of Aspergillus flavus growth under the influence of different factors (water activity, incubation temperature, protein and fat concentration, pH, and cinnamon essential oil concentration) by kinetic, probability of growth, and time-to-detection models

A Box-Behnken design was used to determine the effect of protein concentration (0, 5, or 10g of casein/100g), fat (0, 3, or 6g of corn oil/100g), aw (0.900, 0.945, or 0.990), pH (3.5, 5.0, or 6.5), concentration of cinnamon essential oil (CEO, 0, 200, or 400μL/kg) and incubation temperature (15, 25, or 35°C) on the growth of Aspergillus flavus during 50days of incubation. Mold response under the evaluated conditions was modeled by the modified Gompertz equation, logistic regression, and time-to-detection model. The obtained polynomial regression models allow the significant coefficients (p<0.05) for linear, quadratic and interaction effects for the Gompertz equations parameters to be identified, which adequately described (R2>0.967) the studied mold responses. After 50days of incubation, every tested model system was classified according to the observed response as 1 (growth) or 0 (no growth), then a binary logistic regression was utilized to model A. flavus growth interface, allowing to predict the probability of mold growth under selected combinations of tested factors. The time-to-detection model was utilized to estimate the time at which A. flavus visible growth begins. Water activity, temperature, and CEO concentration were the most important factors affecting fungal growth. It was observed that there is a range of possible combinations that may induce growth, such that incubation conditions and the amount of essential oil necessary for fungal growth inhibition strongly depend on protein and fat concentrations as well as on the pH of studied model systems. The probabilistic model and the time-to-detection models constitute another option to determine appropriate storage/processing conditions and accurately predict the probability and/or the time at which A. flavus growth occurs.

Critical Support Systems to Enhance the Development and Assessment of 21st Century Expertise in Engineering Students

Our goal is to enhance the development of the broad range of so-called 21st century expertise in engineering students by designing critical support systems. Recently our Department generated new curricula for its undergraduate degrees in chemical, food and environmental engineering. These new “integrated and spiral” curricula (that started in fall 2012) include several departmental courses considered chemical, food, and environmental engineering “pillars”, which were revamped to enhance the development of 21st century expertise. “Pillar” courses were redesigned taking into account technological advances and recent research on human learning and cognitive processes that underlie expert performances. Using the Framework for 21st Century Learning, and guidelines from research on How People Learn we: defined the standards for chemical, environmental, and food engineering 21st century expertise; created formative and summative assessments to evaluate student attainment of it; designed instruction activities to promote this expertise; developed professional development opportunities for “pillar” course instructors; and generated corresponding learning environments to foster 21st century expertise in these courses. By means of Tablet PCs and associated technologies high-quality learning environments were created to promote an interactive classroom while integrating multiple formative assessments. Up to date “pillar” courses are improving student understanding of the engineering method, ability to solve practical problems and complete real-world projects while developing 21st century expertise. This chapter discusses results of implementation at selected “pillar” courses, particularly with regards to metacognitive awareness, critical and creative thinking while emphasizing the potential of Tablet PCs and associated technologies to facilitate cognition and learning.

Modeling phase separation and droplet size of W/O emulsions with oregano essential oil as a function of its formulation and homogenization conditions

ABSTRACT Oregano essential oil emulsions (W/O) were prepared using different emulsifiers’ blend concentrations of Tween 80/Span 20, to study their phase separation during storage and to optimize the homogenization processing parameters by minimizing the droplet size of emulsions. Phase separation followed a second-order kinetic model, and relationships between the kinetic parameters and the blend concentrations of emulsifiers were established for determining the best emulsion formulations. The instability mechanism of emulsions demonstrated to be Ostwald ripening; therefore, by means of surface response methodology, mechanical homogenization parameters (11,700 rpm for 12 minutes at 1°C) were specified in order to minimize the droplet size of emulsions (1.02 ± 0.12 µm). GRAPHICAL ABSTRACT

Tablet PC Goal-Directed Practice Coupled with Real-Time Targeted Feedback Enhances Food Chemistry Learning

The How People Learn framework was utilized to redesign the courses Food Chemistry and Advanced Food Chemistry in order to improve undergraduate and graduate food chemistry teaching and learning by creating learning environments that promote an interactive classroom while integrating formative assessments into classroom practices by means of Tablet PCs and associated software. By means of InkSurvey and Classroom Presenter we were able to gauge student learning during goal-directed practice in real-time, provide instantaneous targeted feedback, and make immediate pedagogical adjustments as needed. Course redesign increased student participation and formative assessments while instructors utilized the information gained through real-time assessments to tailor instruction to meet student needs. In this chapter, quantitative and qualitative data will be shared, as well as insights and conclusions from our experiences that indicate the effectiveness of goal-directed practice coupled with real-time targeted feedback to enhance food chemistry learning.

Analysis of Student Perspectives on Using Tablet PCs in Junior and Senior Level Chemical Engineering Courses

The How People Learn framework was used to redesign one junior-level chemical engineering course entitled Kinetics and Homogeneous Reactor Design (seventh semester) as well as two senior-level courses, Catalysis and Heterogeneous Reactor Design (eighth semester) and Process Dynamics and Control (ninth semester). Our goal was to improve chemical engineering teaching and learning by creating high-quality learning environments that promote an interactive classroom while integrating formative assessments into classroom practices by means of Tablet PCs and associated technologies. In order to examine how students perceived the use of Tablet PCs and associated technologies, we conducted semi-structured interviews with students that had completed the course sequence. The analysis indicated a number of themes that consistently appeared within the interview sessions and were addressed by students from different viewpoints. Five overall themes emerged: student experience in using Tablet PCs, impact on learning, potential of Tablet PCs and associated technologies, formative assessments, as well as advantages and disadvantages of using the Tablet PC in studied classrooms. This paper reports upon the themes identified in the analysis of the results from the semi-structured interviews.

Analysis of Dynamic Behavior of a Thermally Coupled Distillation Column Implemented on a Process with Recycles

Abstract Nowadays, the installation and operation of systems with minimum energy and material consumption is a main objective in the industrial ambit; this goal can be achieved through the implementation of recycle streams to recover raw materials and the use of energy integration techniques to minimize utilities requirements. However, when a process is highly integrated, e.g. processes with recycle streams and energy integration or thermal couplings, systems can present control problems. Several studies for Reactor-Separation-Recycle (RSR) systems using separation systems with conventional distillation columns have been reported, but few works have focused on energy-integrated columns or thermally coupled distillation sequences. This work presents a comparison between the dynamic behavior of a thermally coupled distillation column with side rectifier implemented within a RSR system and that obtained with a conventional distillation sequence.