CO2 injection can be used to enhance plant growth and it was used in hydroponic lettuce cultivation. Anti-aphid mesh covered lettuce plants to retain CO2 and to prevent its dissipation into the surroundings. A spatial temporal study of CO2 concentration between lettuce leaves was carried out, showing the effects of fan air circulation driven by a fan. One and four CO2 injections per hour were applied to lettuce grown in PVC tubes inside tunnels. Gas concentration was 25 % higher with multiple injections when the mesh covered the lettuce plants. Multiple injections helped to optimize CO2 waste, and lettuce weight using the mesh increased 87 % with respect to control lettuce weight produced without mesh. Single injection increased lettuce weight by 35.5 % without mesh.

The complexity of the greenhouse crop production, together with the environmental variables interaction, has encouraged the development of various models to predict and simulate variables in order to manage the greenhouse in an efficient way. One of the models that has been used successfully in prediction is the Artificial Neural Networks (ANN). The purpose of this paper was to predict the greenhouse inside conditions based on the outside environmental conditions. A data set of 19,960 values was used from the experimental greenhouse naturally ventilated, without CO2 enrichment, at Humboldt University of Berlin, from August 16 to October 24, 2007 and include the external variables: solar radiation, air temperature, wind velocity, relative humidity, and carbon dioxide concentration, heat transfer by heating system and ventilation opening; and the internal variables: air temperature, relative humidity and CO2 concentration. A three layer artificial neural network was trained and tested and validated using back conjugate gradient back propagation algorithm with a hyperbolic tangent function and momentum algorithm. The predicted values obtained from the ANN model were close to the measured values. These results showed that ANN model learnt the behavior and interactions between all variables. The aid of the ANN model developed was the simultaneous prediction of temperature, relative humidity and CO2 concentration inside of the greenhouse, which will be helpful in checking the accuracy of sensor readings.

The mango production in Mexico is an economically important activity, nevertheless, an inadequate handling in the postharvest operations causes mechanical damages in the product changing its metabolism and accelerating the senescence. The knowledge of the mechanical properties of fruits is considered an important aspect in the design of packing materials and operations of handling postharvest. The mechanical properties of mango fruit under dynamic axial compression tests, weight loss, the ratio º Brix/acidity and color of fruits during ripening were evaluated. The results showed that the elastic limit of the tissue of the fruit was reached at a distance of 2.3 cm with a compression load of 1.95 kN and a deformation of 13.3%. The bioyeld point was located at 2.6 cm with a maximum compression load of 1.89 kN and a deformation of 22.9 %. The rigidity of the tissue shown by the value of the Young’s modulus corresponded with the required load to deform the fruit. The fruits put under mechanical compression reached a yellow reddish color and, besides, the development of a better flavor with respect to the intact fruits after 10 days of storage. These results showed that the compression stimulated the metabolism of ripening of fruits.

The purpose of this study was to develop a new alternative for the use of aged beans with clear pericarp by optimizing its nixtamalization process to obtain a flower (NBF) that could be used as a partial substitute of the main ingredient in the elaboration of highly consumed products in Mexico, such as tortillas. Two varieties of bean (Bayomex and Flor de mayo) were nixtamalized. Twelve traditional nixtamalization treatments were used, which were obtained from the combination of four cooking times (35, 40, 45 and 50 min), four resting times (12, 13, 14 and 15 h), and four lime concentrations (0.5, 1.0, 1.5 and 2.0 %). Results showed that the optimal conditions to obtain flower from nixtamalized bean were 35 min of cooking, 12 h of rest, and 2 % of lime concentration. The protein, lime and fiber contents varied between both varieties within the ranges of 17.02 - 25.5, 0.08 - 0.51 and 7.8 - 8.3 %, respectively. Tortillas made with HBF and nixtamalized corn flower in porcentual proportion of 10-90 and 20-80, respectively, had good nutritional and sensorial quality.

The modified atmospheres are conservation systems of horticultural products in fresh, which use polymeric films as package. Its main problem is the development of a fermentative metabolism, caused by a non-adequate film selection. The objective of the work was to analyze the modified atmosphere design process to achieve an adequate conservation in fresh of horticultural products after harvest. Fruits of husk tomato (Physalis ixocarpa Brot.) at consumption maturity were used as system to be studied. The respiratory activity of these fruits was characterized in terms of the Michaelis-Menten enzymatic theory. Mass balances were applied to the modified atmosphere non-steady state and steady state phases. It was found that the CO2 concentration that is installed inside the package and the thickness of the later are function of the O2 concentration that has to be installed, and that the installation time depends on the free volume inside the system.

Three low-fat Panela cheeses were prepared from milk (13.5 g fat⋅L-1 milk) added with the following hydrocolloids: low methoxyl pectin (QPE), whey protein concentrate (QCP), and microparticulated whey protein (QPM). Additionally a low-fat Panela cheese was prepared from milk (6.75 g fat⋅L-1) incorporated with 6.1 g of emulsified canola oil in water⋅L-1 (QEM), and a low-fat Panela cheese was made from homogenized milk (13.5 g fat⋅L-1 milk) (QHM). As controls, a low-fat cheese (QBG) (13.5 g fat⋅L-1 milk), and a full-fat cheese (QCG) (27 g fat⋅L-1 milk) were prepared. After 48 h of manufactured, the different cheese treatments were subjected to chemical composition analysis, instrumental texture determination (Texture Profile Analysis), sensory texture evaluation (by a trained panel of judges), and microstructural analysis (Scanning Electron Microscopy). The QPE, QPM, and QEM cheeses had a relaxed, porous and open protein matrix associated with low values of hardness, springiness, cohesiveness, and chewiness; while the QBG and QHM cheeses showed a compact and dense protein matrix related with high values of hardness, springiness and chewiness. The QCP cheese presented instrumental textural characteristics comparable to those of the QCG cheese even though its protein matrix was apparently more compact and smoother than the corresponding to this latter. In general terms, the sensory texture characteristics correlated well with the instrumental textural characteristics.

The demanded drawbar pull by a subsoiler fitted with wing and chisel tines was determined when the item-item distance varies of 80 to 160 cm. The obtained equations in both kinds of tine in the two soil textures can be used to assess the delivery power of the tractor engine to select it. The field experiment was carried up in two plots, having clay soil and clay loam soil textures. According to the accomplished measures, for the subsoiler with wing tinethe best item-item distance is 120 cm with a demanded drawbar pull of 26.20 kN on the clay soil and 27.58 kN on the clay loam soil. When the subsoiler is fitted with chisel tines, the required drawbar pull does not vary with the item-item distance varying, being the drawbar force of 20.37 kN on the clay soil and increased the 7 % on the clay loam soil.

The Mexican fruit fly (Anastrepha ludens L.) is a problem for fruit exportation because of the phytosanitary barriers established by importing countries. Irradiation is an alternative process for quarantine treatments against the Mexican fruit fly and constitutes a physical process that does not leave residues in foods. The effect of the irradiation absorbed dose and ripening periods on the quality of guava fruits and larvae survival was evaluated. Matured guava (Psidium guajava L.) fruits at physiological maturity were used. In a first experiment, guava fruits were infested with Mexican fruit fly eggs. Afterwards, the fruits were irradiated at 0, 150 and 300 Gy, and were put into an insectarium for 15 d at 27 °C and at 68 % relative humidity (RH) to allow larvae growth. The irradiation doses showed effect on larvae mortality. Larvae of irradiated fruits died before those of non irradiated fruits. In a second experiment, guava fruits were irradiated at 0, 150 and 300 Gy and stored at 10 ± 1 °C for 15 d at of 80 % RH. After this period the fruits were stored at 20 °C until ripening. Evaluations were done at 0, 3 and 6 d of ripening. Data showed that irradiation did not affected quality fruits except for firmness and weight loss. The ripening periods did not show significant differences for peel firmness, acidity and total soluble solids.

The importance of the guava lies in the economical contribution for some regions in Mexico. The fruits are harvested in areas which have a certain type of conditions in Mexico, similar to those of Zacatecas, Aguascalientes and Michoacán. Several problems related to mechanical damage, such as those that happen during harvesting, transporting and storage appear during the commercialization. The objective of this paper was to determinate the relation between the mechanical damage and the guava fruits physiological activity. Fruits of the Calvillo (Cv1) and Criolla (Cv2) varieties were exposed to compression at horizontal (p1) and vertically (p2) positions. Three axial compression distances were valuated: elastic limit (d1), bioyield point (d2) and rupture point (d3). The production of ethylene and CO2 were measured and they were was found to be significant due to the fact that the production of these gases increased as the compression load increased, which was more noticeable by the second day of applied force of compression. The Cv2d1p2 treatment supported the highest compression load. The percentage of deformity was also measured, finding a higher rate of eformation in the Cv2p2 treatment with values of up to 43%. In the case of Young module, values of 0.37 MPa for the Cv2 fruits and 0.32 MPa for the Cv1 fruits were reported. Variables were measured during the four days, finding weight loss of up to 13 %.

In this work, an analysis of land use change was done under two scenarios, 1990 and 2005, to evaluate its effects in Huehuetán watershed runoff by using the same historical storm of the hurricane Stan and the HEC-HMS software; this watershed is located in Chiapas, Mexico. The land use change was made with satellite images interpretation and overlay cartographic operation in the GIS software, ArcView GIS 3.2; the satellite image for 1990 year was LANDSAT TM while 2005 year was SPOT 5. With GeoHMS, an extension for Arc View, was delimitated 25 subbasins and calculated hydrologic parameters to build HMS models, which were constructed in the HEC-HMS 2.2.2 software under synthetic SCS unit hydrograph and with a historical storm during hurricane STAN in October 2005 year. The results show that there were not significant differences in runoff between the two scenarios. In 1990 the flow was 2,566.4 m3·s-1 and 2005 year the flow was 2,544.0 m3·s-1. The runoff decreased 0.87 % in the period of analysis. The results obtained are an expression of good condition of natural resources conservation in the watershed.

For developing the pull force, the tractive elements from the tractor generate slippage due to the adhesion between the tire and the soil. When the tractor moves straight forward, the pull forces and slippages do not change in the rear tires in the 4x2 scheme, neither the rear nor front tires in the 4x4 scheme. As the tractor makes a turn, these parameters change up to generate an instability torque, so that the engine has to develop a torque to overcome it and the driver has to keep forcibly the turn of the tractor toward the indicated side. In this work, were developed the equations to determine the tires pull force and slippage, according to turning radius for tractors having engaged the differential (4x2) and connected the front axle (4x4), considering the sum of the tires slippages, which corresponds to the total pull force developed by the tractor. The results indicated that while the tractor made a turn, as the turning radius decreased, the tire pull force and slip increased in the inner tire (4x2) and rear tire (4x4) and decreased in the outer tire (4x2) and front tire (4x4). For each total pull force needed, there was a limit condition to disengage the differential (4x2) and disconnect the front axle (4x4).

A drying solar tunnel was built with an auxiliary desiccant air recirculation system based on silica gel to adsorb moisture. Onion was cut in slices and dried inside the solar tunnel. Based on empirical data previously obtained, every fifteen minutes per hour, heat regeneration was applied to the auxiliary desiccant system to eliminate the moisture from the silica. Temperature and relative humidity were monitored during the process and drying data were compared with those of a drier that operated without the auxiliary desiccation system. In practical operation without considering initial conditions, the equipment with desiccant system dried the onion slices in 11.1 hours meanwhile the solar tunnel without the auxiliary system required 16.3 hours. A RGB (red green blue) color analysis was carried out for both drying treatments and a better quality was achieved on onions dried with the air-desiccant strategy, as the time exposed to high temperatures under low water quantity was reduced. Onion oxidation was evident when the blue value felt bellow below 100.