A review from 1996 to 2021 of tuning methodologies and controller structures applied for an unstable/stable (bio)reactor with imperfect mixing and bypass.

This paper presents a critical review of tuning methodologies and controller structures applied to the Cholette bioreactor. This (bio)reactor has been studied extensively by the automatic control community from the point of view of controller structures and tuning methodologies, from controllers with a single structure to nonlinear controllers, and from the synthesis method to the frequency response. Therefore, new trends and opportunities of study have been detected with regard to their operating points, controller structures and tuning methodologies which could be addressed for this system.

Analysis of open-loop and L2∕D controlled closed-loop behavior of the Cholette's bioreactor under different operating conditions.

The scope of this paper is the analysis of open-loop and L2/D controlled closed-loop behavior of the Cholette's bioreactor under different operating conditions. The open-loop behavior is studied by means of the steady-state multiplicity areas formed by substrate feed concentration and substrate concentration in the output using the nonlinear model of the bioreactor. The stability of each steady-state inside areas is determined by a polynomial representation. The nonlinear dynamic and steady-state multiplicity areas of the Cholette's bioreactor are shown to depend on the operating conditions and concentration required. The closed-loop behavior is studied by the tuning of a set of Pareto-optimal L2/D linear controllers at a stable operating point. Numerical simulations and phase portraits are used to evaluate the control system. This paper could be a guide for theoretical and practical applications in the fields of biotechnology and automatic control.

Effect of repeated frying on the physical characteristics, the formation of acrylamide and oil uptake of tortilla chips subjected to pre-drying treatment.

Even though snacks such as tortilla chips are gaining popularity, the high intake of these products may cause problems related to their fat and acrylamide content. In consequence, this study is aimed at evaluating the effect of pre-fry drying on the absorption of oil, physicochemical characteristics and formation of acrylamide in corn tortilla chips fried in ten batches. Pre-drying was carried out at 40 °C, 50 °C and 60 °C and two air velocities (1.0 m/s2 year 1.5 m/s2). Frying conditions were selected from pre-tests where the physicochemical variables of frying oils (palm olein and avocado oil) were measured. Acrylamide content was measured by GC-MS analyses. The results revealed that the type of oil did not show a significant effect on the physicochemical variables studied. Pre-dried chips showed a decrease in the final oil content of 41-58% (depending on the type of oil used) when compared to two brands of commercial chips. All the detected acrylamide concentrations on the samples were below the detection limit (20 µg/kg). According to our results, avocado oil may also be an option for producing corn tortilla chips.

Risk assessment of exposure to mycotoxins (aflatoxins and fumonisins) through corn tortilla intake in Veracruz City (Mexico).

This study aimed to assess aflatoxin and fumonisin intake through corn tortilla consumption in Veracruz city. Between October 2013 and February 2015, a total of 120 corn tortilla samples (2 kg samples, 40 samples per year) were randomly collected. Aflatoxins and fumonisins were quantified by high performance liquid chromatography coupled with a fluorescence detector. A probability density function (PDF) was used for describing corn tortilla intake, body weight of the Veracruz city population, mycotoxin content of corn tortilla samples and estimated mycotoxin daily intake. The Monte Carlo method with 10,000 iterations was employed to assess the population exposure risk. The highest level of total aflatoxins (AFT) was 22.17 µg kg-1, and 526.6 µg kg-1 for fumonisins B1 plus B2, with 85% and 90% of contaminated samples respectively. Up to 69.7 % of the population was estimated to consume a higher aflatoxin dose than that recommended by the JECFA (1 ng kg-1 of body weight per day); it was found that the recommended dose was exceeded to a greater extent in the male population, due to higher consumption of corn. The risk of fumonisin intake was less than 5 % due to the low presence and levels of these toxins in corn tortillas. The results suggest that corn tortilla consumers are at dietary risk caused by AFT contamination; this information should be considered when taking action to protect public health.

Inactivation of the microbiota and effect on the quality attributes of pineapple juice using a continuous flow ultrasound-assisted supercritical carbon dioxide system.

Supercritical carbon dioxide inactivation technology represents a promising nonthermal processing method, as it causes minimum impact on the nutritional food properties. The aim of this study was to analyze the combined effect of supercritical carbon dioxide and high-power ultrasound on the inactivation of natural microbiota and the quality attributes of pineapple juice treated in a continuous flow system. Different juice residence times (3.06-4.6 min), at 100 bar and 31.5 ℃, were used. The results indicated that the microbiota inactivation was complete and the differences obtained in the quality attributes (2.2% for pH, 4.8% for °Brix, 2% for vitamin C) were minimal. During storage, microorganisms were not able to recover and the vitamin C decrease could be limited to 8.2% after four weeks. The results demonstrated that the supercritical carbon dioxide-high-power ultrasound technique could be an excellent alternative for the cold pasteurization of pineapple juice.

Design of multiloop PI controllers based on quadratic optimal approach.

The LQR methodology is extended to produce multiloop PI controllers in this study. With this method, a multivariable P controller is first obtained and then diagonalized using an iterative procedure. The resulting controller is further complemented with the integral action in a similar process. The proposed tuning process explores different values of the control weight matrix to balance the output error and control signal in both stages, and is refined through additional indices related with the error to reference tracking, disturbance rejection and the associated control use. In addition, the diagonalization procedure is generalized to obtain multiloop versions of existing multivariable PI controllers. The developed theory was applied to the design of multiloop controllers for a distillation column as well as the diagonalization of existing controllers for a nonlinear CSTR. The tuning procedure allowed the synthesis of multiloop PI controllers with performance indices comparable to those reported by other authors. Furthermore, diagonalized controllers exhibited a similar operation as the original multivariable ones.

Statistical analysis of corn consumption for improved mycotoxin exposure estimates for the population of Veracruz City, Mexico.

Corn consumption was evaluated in the population of Veracruz City, Mexico, through two different dietary intake questionnaires. The selection of 300 sampling locations was completely random. The population was segregated into gender and age categories. A daily consumption questionnaire was used to determine the consumption of corn tortillas and a frequency questionnaire to determine the consumption of other corn products. A book of photographs was used to adjust criteria on the size of the portions of corn products and a probability distribution was built of the weight and content of corn for tortillas. Probability density functions (PDFs) were used to describe the consumption of each corn product. Men and those between 14 and 65 years old have the highest consumption of tortillas. Tortillas, antojitos, tacos and chilaquiles are the products that provide the largest amount of corn to the Veracruz people's diet. Even though these products are nixtamalisated, there is evidence that after a thermo-alkaline process some contaminants such as mycotoxins (like aflatoxin, which is a mutagenic, teratogenic and carcinogenic toxin) could be present in high concentrations. These results highlight the need to characterise the consumption of one of the main foods included in dietary staple in Mexico as a first step for a probabilistic risk assessment.

Brewery wastewater treatment using anaerobic inverse fluidized bed reactors.

Two anaerobic inverse fluidized bed reactors were utilized to evaluate organic matter removal from brewery wastewater, applying different OLR and testing two support materials. Hydrodynamic tests varying liquid flow and solid concentration were developed on the supports in order to establish operational conditions. A batch colonization stage was applied using 25% active volume of extendosphere and triturated polyethylene as support materials. The reactors were subsequently operated continuously with stepwise increments in organic loading rate until limiting conditions was reached. For the supports studied, IFBR technology was suitable for organic matter removal present in brewery wastewater with COD removal efficiencies greater than 90%. The reactor with triturated polyethylene support showed an excellent COD removal with OLR values up to 10 g COD/Ld, whereas the reactor with extendosphere support had an excellent hydrodynamic and biologic behavior working with OLR values up to 70 g COD/Ld.

Simultaneous removal of carbon and nitrogen in an anaerobic inverse fluidized bed reactor.

The evaluation of simultaneous removal of carbon and nitrogen in an anaerobic inverse fluidized bed reactor is described. Continuous and batch experiments were used, with synthetic wastewater and glucose as the carbon source with two different nitrate concentrations of 100 and 250 mg N-NO3/L. The evolution of substrates and the concentrations of intermediary products in the gas phase were followed. Results indicate that the use of the biofilm in the inverse fluidized bed reactor allows the expression of denitrification and methanization activities simultaneously without physical or time separation. The removal of nitrogen with both the feeding of 100 and 250 mgN-NO3/L was higher than 90%, while the removal of carbon was 65% on average for the feeding with 100 mgN-NO3/L and 70% on average for the feeding with 250 mg N-NO3/L. This carbon degradation is equivalent to that obtained during the operation of the reactor in the period previous to the nitrate feeding. It was found that by using high values of the COD/N ratio, the dissimilative reduction of nitrates is favoured. Denitrification and anaerobic digestion occurs simultaneously under low values of COD/N.

Effect of physical factors on the production of bacteriocin from Pediococcus acidilactici ITV 26.

The effect of pH, temperature and agitation on growth and bacteriocin production by Pediococcus acidilactici ITV 126 was investigated. Experiments were made in flasks containing MRS medium at 30 to 40 degrees C, pH 5 to 7 and agitation 0 to 200 rpm. Factor levels were arranged in a 2(3) factorial design with central and axial points. Anova and Tukey paired comparison tests showed that a temperature of 35 degrees C favored bacteriocin production, whereas 40 degrees C was best for cell growth. A statistical interaction of temperature and agitation was observed affecting microbial growth. pH 5 favored both cell growth and bacteriocin production.