Gonzalo Velazquez

Effect of the addition order and amylose content on mechanical, barrier and structural properties of films made with starch and montmorillonite

This study considered the effect of amylose content (30% and 70%), montmorillonite (MMT) fraction (5 and 15%) and preparation method on mechanical and barrier properties of starch/clay nanocomposites prepared by casting. In Method 1, (30% w/w) glycerol was incorporated before starch gelatinization and MMT addition, while in Method 2 after gelatinization and MMT addition. Nanocomposites with higher amount of MMT showed the highest tensile strength and Youngs modulus for both preparation methods. Method 1 favored nanocomposite properties of films with less amylose content, meanwhile Method 2 favored nanocomposites properties with higher amylose content. Water vapor permeability did not decrease significantly in starch films with different amylose content with the two different preparation methods. X-ray diffraction of the starch films indicated intercalated structures. Higher melting temperature (Tm) was found for nanocomposites with Method 2, indicating more ordered structures. Films with 70% amylose content have higher Tm than films with 30% amylose.

Effect of equilibrium moisture content on barrier, mechanical and thermal properties of chitosan films

Water molecules modify the properties of biodegradable films obtained from hydrophilic materials. Most studies dealing with thermal, mechanical and barrier properties of hydrophilic films are carried out under one relative humidity (RH) condition. The objective of this work was to evaluate the effect of the moisture content on the thermal, mechanical and barrier properties of chitosan films under several RH conditions. Microclimates, obtained with saturated salt solutions were used for conditioning samples and the properties of the films were evaluated under each RH condition. Chitosan films absorbed up to 40% of moisture at the higher RH studied. The percentage of elongation and the water vapour permeability increased while tensile strength, Youngs modulus and glass transition temperature decreased, when the moisture content increased. The results suggest that the water molecules plasticized the polymer matrix, changing the properties when the films were in contact with high RH environments.

Effect of amylose content and nanoclay incorporation order in physicochemical properties of starch/montmorillonite composites

The effects of the amylose content and the preparation sequence in physicochemical properties of starch/montmorillonite (MMT) composites were studied in this work. Native (30%) and high amylose Hylon VII (70%) starches were considered for assessing the effects of amylose content. Glycerol and MMT were used as additives to evaluate the effects of the former as plasticizer and the latter as reinforcer. The glycerol was incorporated before (Method M1) and after (Method M2) the addition of MMT. FTIR studies indicated that water bonding was affected by amylose content. Sorption isotherms indicated that method M2 favoured water adsorption and method M1 reduced water adsorption due to competition for active sites for interaction. TGA showed that method M1 induced a higher degradation rate than method M2. Wettability analysis by contact angle measurements showed that plasticizer promoted the hydrophilicity of the film, whereas MMT promoted a hydrophobic surface for both cases of amylose content.

An improved quarantine method for mangoes against the Mexican fruit fly based on high-pressure processing combined with heat.

The Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae) is one of the most important insects infesting mangoes, citrus, and other fruits in Mexico and other Latin-American countries. Quarantine methods approved to destroy this insect decrease the shelf life of commodities. The objective of this study was to determine the effect of high-pressure processing using an initial temperature of 50 degrees C on the survivorship of eggs and larvae of the Mexican fruit fly. Eggs and larvae were pressurized at 25, 50, 75, 100, or 150 MPa for 0, 5, 10, or 20 min. The hatching ability of pressurized eggs of 1, 2, 3, and 4 days old and survivorship of the first, second, and third instars were registered. Further, the ability to pupate was studied in surviving third instars. The results showed that eggs were more resistant than larvae to the high-pressure processing. Treatments at 150 MPa at initial 50 degrees C for 10 min destroyed all eggs and larvae of A. ludens, indicating that this process might be useful as a quarantine method for infested mangoes or other fruits.

High hydrostatic pressure at low temperature as a quarantine treatment to improve the quality of fruits.

Application of high hydrostatic pressure has been proposed as an alternative quarantine process for the Mexican fruit fly, Anastrepha ludens Loew (Diptera: Tephritidae), one of the most important insects infesting mangoes, citrus fruits, and other fruits in Mexico and other Latin American countries. The present study was performed to determine the effect of high pressure treatments at 0 degrees C on the survivorship of eggs and larvae of this pest. The effect of time and pressure level at near-freezing temperatures on the egg hatch and survival of larvae is discussed. Eggs and larvae were pressurized at 25, 50, 75, 100, or 150 MPa for 0, 5, 10, or 20 min at 0 degrees C. Hatch was recorded for 1-, 2-, 3-, and 4-day-old pressurized eggs. For pressurized larvae (first, second, and third instars), percentage of survival was registered. Further, third instars were studied for their ability to pupate and develop to adulthood. The results showed that eggs had higher resistance than larvae to pressure. Larvae were not able to resist pressure treatments at 75 MPa for 20 min at 0 degrees C. Treatments at 150 MPa for 20 min at 0 degrees C were needed to destroy all eggs and larvae of A. ludens, indicating that this process might be useful as a quarantine method for infested fruits. However, more studies involving combination of high hydrostatic pressure at low temperature with precooling treatments are needed in order to decrease the pressure level to avoid fruit damage.

Effect of Input Data Variability on Estimations of the Equivalent Constant Temperature Time for Microbial Inactivation by HTST and Retort Thermal Processing

UNLABELLED Consumer demand for food safety and quality improvements, combined with new regulations, requires determining the processors confidence level that processes lowering safety risks while retaining quality will meet consumer expectations and regulatory requirements. Monte Carlo calculation procedures incorporate input data variability to obtain the statistical distribution of the output of prediction models. This advantage was used to analyze the survival risk of Mycobacterium avium subspecies paratuberculosis (M. paratuberculosis) and Clostridium botulinum spores in high-temperature short-time (HTST) milk and canned mushrooms, respectively. The results showed an estimated 68.4% probability that the 15 sec HTST process would not achieve at least 5 decimal reductions in M. paratuberculosis counts. Although estimates of the raw milk load of this pathogen are not available to estimate the probability of finding it in pasteurized milk, the wide range of the estimated decimal reductions, reflecting the variability of the experimental data available, should be a concern to dairy processors. Knowledge of the C. botulinum initial load and decimal thermal time variability was used to estimate an 8.5 min thermal process time at 110 °C for canned mushrooms reducing the risk to 10⁻⁹ spores/container with a 95% confidence. This value was substantially higher than the one estimated using average values (6.0 min) with an unacceptable 68.6% probability of missing the desired processing objective. Finally, the benefit of reducing the variability in initial load and decimal thermal time was confirmed, achieving a 26.3% reduction in processing time when standard deviation values were lowered by 90%. PRACTICAL APPLICATION In spite of novel technologies, commercialized or under development, thermal processing continues to be the most reliable and cost-effective alternative to deliver safe foods. However, the severity of the process should be assessed to avoid under- and over-processing and determine opportunities for improvement. This should include a systematic approach to consider variability in the parameters for the models used by food process engineers when designing a thermal process. The Monte Carlo procedure here presented is a tool to facilitate this task for the determination of process time at a constant lethal temperature.

Influence of high pressure processing and alkaline treatment on sugarcane bagasse hydrolysis

High pressure processing (HPP) is an emerging technology for food preservation, however its application in pretreatment of lignocellulosic biomass has not been studied; therefore, the objective of this work was to evaluate the effect of HPP in combination with sodium hydroxide on the enzymatic hydrolysis of sugarcane raw and prehydrolyzed bagasse. The results indicated that high pressure treatments alone or combined with sodium hydroxide had a little effect on the lignocellulosic fraction of sugarcane bagasse, however in prehydrolyzed bagasse, removal of the major hemicellulose was observed. Also, changes in the microstructure and crystallinity of sugarcane bagasse were observed at 450 MPa as the modification of the cellulose fiber improved the porosity, increasing the susceptibility of bagasse to cellulases, obtaining a glucose concentration of 25.91 g/L with NaOH (6% treatment). These results are important because the application of HPP on lignocellulosic materials could be used to get fermentable sugars for production of food additives.

Resistance of Mexican Fruit Fly to Quarantine Treatments of High Hydrostatic Pressure Combined with Heat

High-pressure processing (HPP) has been proposed as an alternative quarantine method against the Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae), which is one of the most important pests infesting mangoes, citrus, and other fruits in Mexico and other Latin-American countries. However, processing conditions used to destroy eggs and larvae also affect the shelf life of fruits. The objective of this study was to assess the biological viability of A. ludens eggs treated with HPP, establishing whether undestroyed eggs were able to develop larvae, pupae, and adults capable of reproduction. Eggs of 1, 2, 3, and 4 days old were pressurized at 50, 75, or 100 MPa for 0, 5, 10, or 20 min. The hatching ability of pressurized eggs; survivorship of third instars, pupae, and adults emerged; and their capability to produce viable eggs were examined. The results showed that the hatching capacity of eggs and the larval development were affected negatively by the treatment duration and level of pressure. Treatments with 100 MPa for 20 min inhibited the hatching capacity of eggs of 2, 3, or 4 days old by 100%, but the inhibition was of 99.8% for 1-day-old eggs. Most of the eggs that survived the treatments were able to produce adults that can reproduce. The percent of hatching of eggs of A. ludens oviposited for adults obtained from pressurized 1-day-old eggs treated with 100 MPa for 20 min was 64.81%. Thus, more efforts must be addressed to destroy eggs and larvae during HPP because surviving organisms can reach adult stage and reproduce.

Resistance of Mexican Fruit Fly to Quarantine Treatments of High-Pressure Processing Combined with Cold

Mexican fruit fly Anastrepha ludens Loew (Diptera: Tephritidae) is one of the most important insects infesting fruits. Although high pressure has been proposed as an alternative quarantine process for this pest, conditions applied to destroy eggs and larvae can also damage the fruits. The objective of this study was to assess the biological viability of A. ludens eggs treated by high-pressure processing at 0°C, establishing whether nondestroyed eggs and larvae preserved their ability to develop and reproduce. One-, 2-, 3-, and 4-day-old eggs were pressurized at 50, 70, or 90 MPa for 0, 3, 6, or 9 min. The hatching ability of pressurized eggs and their capacity to develop larvae, pupae, and reproductive adults were evaluated. The ability of pressurized larvae to pupate was also registered. The results showed that most of the eggs that resisted the treatments were able to produce adults with capability to reproduce a new generation of A. ludens flies. Larvae were less resistant than eggs. All larvae were killed at 90 MPa for 9 min. The pressure induced the expression of heat shock proteins (HSP) in second- and third-instar larvae. The HSP showed a baroprotective effect in A. ludens larvae. These results are relevant to the industry because they show that eggs of insects infesting fruits treated by high-pressure processing were able to pupate after treatments. This indicates that efforts must be addressed to destroy all eggs because most of the surviving organisms could reach an adult stage and reproduce.

The effect of relative humidity on tensile strength and water vapor permeability in chitosan, fish gelatin and transglutaminase edible films

Composite films of chitosan, fish gelatin and microbial transglutaminase (MTgase) were developed. Films were produced by the casting method and dried at room temperature for 30 h, conditioned for 7 days at 30 °C at a relative humidity (RH) from 11 to 90%, and characterized. Chitosan:fish gelatin films in different proportions (100:0, 75:25, 50:50) with MTgase, were subjected to tensile properties and water vapor transmission (WVT) testing. The results showed that tensile strength decreased with an increase in RH and with an increase in gelatin content. Percent of elongation also increased with increasing RH and gelatin concentration. Water vapor transmission showed an increase proportional to an increase in RH with the presence of gelatin being unfavorable for reducing WVT. Results in this work allowed studying the effect of relative humidity on tensile and water vapor properties of chitosan and fish gelatin films.