Salvador Valle-Guadarrama

Modeling temperature variations in a pilot plant thermophilic anaerobic digester

A model that predicts temperature changes in a pilot plant thermophilic anaerobic digester was developed based on fundamental thermodynamic laws. The methodology utilized two simulation strategies. In the first, model equations were solved through a searching routine based on a minimal square optimization criterion, from which the overall heat transfer coefficient values, for both biodigester and heat exchanger, were determined. In the second, the simulation was performed with variable values of these overall coefficients. The prediction with both strategies allowed reproducing experimental data within 5% of the temperature span permitted in the equipment by the system control, which validated the model. The temperature variation was affected by the heterogeneity of the feeding and extraction processes, by the heterogeneity of the digestate recirculation through the heating system and by the lack of a perfect mixing inside the biodigester tank. The use of variable overall heat transfer coefficients improved the temperature change prediction and reduced the effect of a non-ideal performance of the pilot plant modeled.

Betalains and phenolic compounds profiling and antioxidant capacity of pitaya (Stenocereus spp.) fruit from two species (S. Pruinosus and S. stellatus)

Pitaya fruits (Stenocereus spp.) contain betalains and phenolic compounds that have not been completely characterized. Fruits of two ecotypes of S. pruinosus, red-fleshed (SpR) and orange-fleshed (SpO), and two of S. stellatus, red-fleshed (SsR) and white-fleshed (SsW), were characterized in their betalains and phenolic compounds. The chromatographic profile of betalains was similar in SpR, SpO, and SsR, where indicaxanthin, gomphrenin I, phyllocacthin, and their isomers predominated. Betaxanthins content was higher than betacyanins and ranged from 17,706.7±1128.1 to 22,053.6±328.1µg/g dry sample. The identified phenolics mostly corresponded to hydroxycinnamoyl derivatives, flavonols and flavanones. The phenolics content was higher in S. stellatus than in S. pruinosus. The ecotype SsW, that had flesh without color, showed the highest concentration. The antioxidant capacity varied within 9.21±0.84 and 2.41±0.36μmolTrolox/g fresh sample, as determined by the ABTS assay. By its phytochemical composition, the fruits of pitaya can be a good source of antioxidant compounds.

Effect of microperforation and temperature on quality of modified atmosphere packaged huitlacoche (Ustilago maydis)

Huitlacoche (Ustilago maydis) is a food in the rural communities of some Latin American countries, but it is very perishable. For this reason, its postharvest quality was evaluated in refrigeration (3°C) and at ambient thermal conditions (20°C), with modified atmosphere packaging (MAP) implemented in low-density polyethylene bags of 27 × 28 cm, with 0, 2, 5, 10, and 20 microperforations (mp) of 15 μm. Batches of 150 g of huitlacoche galls with firmness of 5.6 N, pH of 4.8, lightness of 52.4, and hue angle of 87.0° were used. The product proved to be resistant to concentrations of O2 as low as 1.7 kPa. The adjustment of the number of orifices allowed the control of gas concentrations inside bags, and those with 5 mp permitted the best quality characteristics at 20 and 3°C, with weight loss rates of 0.42 and 0.02% d−1, lightness of 43.7 and 40.3, hue angle of 81.4° and 78.0°, respectively, and firmness of 3.4 N a both conditions. Change rates of quality attributes at 3°C were lesser than at 20°C, which proved that with refrigeration the shelf life was extended up to 30 days.

Purification and concentration of cheese whey proteins through aqueous two phase extraction

ABSTRACT Whey is a by-product of cheese manufacture and contains proteins that can be recovered, but lactose presence limits its use. Proteins can be separated with aqueous two-phase extraction (ATPE), thus the objective was to evaluate this strategy to recuperate proteins from whey attending lactose elimination. An ATPE system with (NH4)2SO4 and polyethylene glycol 4000 (PEG4000) was studied at 25°C. As PEG4000 diminished the volume ratio between phases diminished and a biphasic system was maintained in absence of the polymer. Minimum protein recovering and lactose elimination were 54.5% and 62.1% with mixtures having 25% PEG4000 and 12.1% (NH4)2SO4, but values were 93.0% and 72.3%, respectively, with 0.1% PEG4000 and 34.7% (NH4)2SO4. Therefore, whey incorporated with (NH4)2SO4 in concentration higher than 34% and without polyethylene glycol can be used in ATPE systems to maximize lactose elimination and protein recovering and to concentrate proteins up to 2.45 times through a non-energy strategy.