A validated strategy to design efficient fermentation-industrial processes: agave spirit production.

An industrial process is profitable when its individual unit operations are efficient and thus, this work shows a guideline for designing efficient fermentation-industrial processes for agave distilled production based on a sequential approach of optimization, beginning in the laboratory and followed by the adjustment of the variable values using the evolutionary operation method for successful process scaling. The results at the laboratory showed that a starter inoculum containing a 5 × 106 cells/mL mixture of Kluyveromyces marxianus, Clavispora lusitaniae, and Kluyveromyces marxianus var. drosophilarum strains in a bioreactor containing agave syrup with 120 g/L fermented sugar, processed at a constant temperature of 33 °C and 1.0 VVM aeration for 1.6 h, led to a fermented product with a 4.18% (v/v) alcohol content after 72 h of processing time. The scale-up process results showed that the best operating conditions at the pilot-plant level were a temperature of 35 °C and aeration at 1.0 VVM for 1.2 h, which led to a fermented product with a 4.22% (v/v) total alcohol content after 72 h of processing time. These represent similar performance values for both production processes, but each one worked with their specific values of process variables, which demonstrates that each level of production had its own specific values for process variables. The volatile compound analysis shows that both distilled products contained a similar profile of volatile components that provide fruity and ethereal aromatic notes pleasant to the palate. Therefore, the process design for agave spirit production at the semi-industrial level was successfully achieved.

Design of a fermentation process for agave fructooligosaccharides production using endo-inulinases produced in situ by Saccharomyces paradoxus.

Saccharomyces paradoxus, a native microorganism of the aguamiel, was used successfully for endoinulinase synthesis for agave fructooligasaccharide (FOS) production. We optimized the fermentation parameters to maximize the enzyme synthesis, and we performed enzyme kinetics studies to achieve agave fructans hydrolysis. The results showed that under constant operating conditions (pH 7.7, 40 °C, 175 rpm of agitation, and 0.005 VVM of aeration) results in the production of an enzymatic extract with 49.57 mg/L. This enzymatic extract, when mixed with an agave fructans solution containing 37.8 g/L, allowed us to obtain products with 18% more FOS content the original concentration. The mass spectrum plot shows that the hydrolyzed product contains FOS with a degree of polymerization from 5 to 9 hexose units. These results are promising because they show FOS production from agave and confirm that importance of using native strains in the design of directed fermentation processes.

An experimental strategy validated to design cost-effective culture media based on response surface methodology.

For any fermentation process, the production cost depends on several factors, such as the genetics of the microorganism, the process condition, and the culture medium composition. In this work, a guideline for the design of cost-efficient culture media using a sequential approach based on response surface methodology is described. The procedure was applied to analyze and optimize a culture medium of registered trademark and a base culture medium obtained as a result of the screening analysis from different culture media used to grow the same strain according to the literature. During the experiments, the procedure quantitatively identified an appropriate array of micronutrients to obtain a significant yield and find a minimum number of culture medium ingredients without limiting the process efficiency. The resultant culture medium showed an efficiency that compares favorably with the registered trademark medium at a 95% lower cost as well as reduced the number of ingredients in the base culture medium by 60% without limiting the process efficiency. These results demonstrated that, aside from satisfying the qualitative requirements, an optimum quantity of each constituent is needed to obtain a cost-effective culture medium. Study process variables for optimized culture medium and scaling-up production for the optimal values are desirable.

Effect of two viscosity models on lethality estimation in sterilization of liquid canned foods.

A numerical study on 2D natural convection in cylindrical cavities during the sterilization of liquid foods was performed. The mathematical model was established on momentum and energy balances and predicts both the heating dynamics of the slowest heating zone (SHZ) and the lethal rate achieved in homogeneous liquid canned foods. Two sophistication levels were proposed in viscosity modelling: 1) considering average viscosity and 2) using an Arrhenius-type model to include the effect of temperature on viscosity. The remaining thermodynamic properties were kept constant. The governing equations were spatially discretized via orthogonal collocation (OC) with mesh size of 25 × 25. Computational simulations were performed using proximate and thermodynamic data for carrot-orange soup, broccoli-cheddar soup, tomato puree, and cream-style corn. Flow patterns, isothermals, heating dynamics of the SHZ, and the sterilization rate achieved for the cases studied were compared for both viscosity models. The dynamics of coldest point and the lethal rate F0 in all food fluids studied were approximately equal in both cases, although the second sophistication level is closer to physical behavior. The model accuracy was compared favorably with reported sterilization time for cream-style corn packed at 303 × 406 can size, predicting 66 min versus an experimental time of 68 min at retort temperature of 121.1 ℃.

A strategy to design efficient fermentation processes for traditional beverages production: prickly pear wine.

This paper describes a methodology to establish an optimal process design for prickly pear wine production that preserves the peculiar and unique traits of traditional products, generating at the same time, technical information for appropriate design of both bioreactor and overall process. The strategy includes alcoholic fermentation optimization by the mixed native culture composed by Pichia fermentans and Saccharomyces cerevisiae, followed by malolactic fermentation optimization by Oenococcus oeni. The optimization criteria were based on multiple output functions: alcohol content, volatile compounds profile, organic acids profile, and compound contents related to color, which were analyzed by spectroscopy-chromatography methods and sensory analysis. The results showed that the mixed culture inoculated into a bioreactor containing prickly pear juice with 20 °Bx of fermentable sugars concentration, processed at a constant temperature of 20 °C for 240 h, leads to a fermented product with 9.93% (v/v) total alcohol content, and significant abundance of volatile compounds, which provide fruity and ethereal aromatic notes, complemented by a lively but not unpleasant acidity. This young wine was further subjected to malolactic fermentation at constant temperature (16 °C) for 192 h, decreasing malic acid, and balancing volatile compounds contents, thus resulting in a product with better aroma and flavor perception, and a velvety feeling of long aftertaste. Repeated assays showed that the process is stable, predictable, controllable, and reproducible. These results were used for process design and spreadsheet construction in order to simulate the process, and properly select and size the equipment required for such process.

Kinetic study of the thermal hydrolysis of Agave salmiana for mezcal production.

The kinetics of the thermal hydrolysis of the fructans of Agave salmiana were determined during the cooking step of mezcal production in a pilot autoclave. Thermal hydrolysis was achieved at different temperatures and cooking times, ranging from 96 to 116 °C and from 20 to 80 h. A simple kinetic model of the depolymerization of fructans to monomers and other reducing sugars and of the degradation of reducing sugars to furans [principally 5-(hydroxymethyl)furfural, HMF] was developed. From this model, the rate constants of the reactions were calculated, as well as the pre-exponential factors and activation energies of the Arrhenius equation. The model was found to fit the experimental data well. The tradeoff between a maximum fructan hydrolysis and a critical furan concentration in allowing for the best ethanol yield during fermentation was investigated. The results indicated that the thermal hydrolysis of agave was optimal, from the point of view of ethanol yield in the ensuing fermentation, in the temperature range of 106-116 °C and the cooking range time of 6-14 h. The optimal conditions corresponded to a fructan hydrolysis of 80%, producing syrups with furan and reducing sugar concentrations of 1 ± 0.1 and 110 ± 10 g/L, respectively.

Microbial ecology studies of spontaneous fermentation: starter culture selection for prickly pear wine production.

A procedure for designing starter cultures for fermentation is illustrated for prickly pear wine production. The illustration includes kinetic studies on inoculated and spontaneous fermentation, microorganism identification studies based on molecular biology tools, and microbial ecology studies, which led to the selection of strains that are capable of synthesizing alcohol and desirable volatile compounds. Results show that a mixed starter inoculum containing Pichia fermentans and Saccharomyces cerevisiae leads to a fermented product that contains 8.37% alcohol (v/v). The gas chromatography and mass spectrometry (GC-MS) analysis shows the presence of 9 major volatile compounds (Isobutanol, Isopentanol, Ethyl acetate, Isoamyl acetate, Ethyl octanoate, Ethyl decanoate, Ethyl 9-decanoate, ß-Phenylethyl acetate, and Phenylethyl alcohol) that have ethereal, fruity, aromatic notes that are considered to be essential for a fine wine flavor. These compounds harmonically synergize with the alcohol to produce a fermented product with a unique flavor and taste. Several assays using the mixed culture show that the process is stable, predictable, controllable, and reproducible. Moreover, the results show that a mixed culture leads to a broader range of aromatic products than that produced by a single, pure culture. Therefore, we conclude that combinations of Saccharomyces strains and non-Saccharomyces strains can be used to obtain high-quality fermented beverages from prickly pear juice.