José Caro-Corrales

ANALYSIS OF RANDOM VARIABILITY IN BISCUIT COOLING

Abstract The cooling of biscuits after baking can be considered as a random phenomenon. The Fourier field equation for transient heat transfer is used as the basis for the deterministic modelling of a single biscuit in a laboratory cooler. The Monte Carlo method is applied to the Fourier equation to predict the dispersion in biscuit surface temperature at the end of the cooling process. Theoretical solutions are also used to characterise the variability in biscuit temperature by considering biscuit cooling as a probabilistic thermal process. The mean and standard deviation in biscuit thermal properties, initial biscuit temperature and heat transfer coefficient are measured and are considered as the input random variables. The numerical output and theoretical solutions are compared with experimental results. Parameter studies are conducted with the probabilistic model to assess the influence of variability in thermal properties on final biscuit temperature variability and to suggest process improvement strategies.

Characterization and Optimization of Extrusion Cooking for the Manufacture of Third-Generation Snacks with Winter Squash (Cucurbita moschata D.) Flour

ABSTRACT The aim of this work was to study the effects of barrel temperature (BT, 93.5–140.5°C), feed moisture (FM, 21.3–34.7%), and winter squash flour content (SFC, 0.43–15.6%) on physicochemical properties of microwave-expanded third-generation snack foods obtained by extrusion. Physicochemical properties used for optimization were expansion index (EI), penetration force (PF), specific mechanical energy (SME), and total color difference (ΔE). Response surface methodology was used for the analysis of data. The highest values of EI and lowest values of PF were found at high BT and low FM. The lowest values of SME were obtained at high levels of FM throughout the range of BT and SFC, whereas the highest values of ΔE were obtained at high SFC and low FM. Increasing levels of SFC increased ΔE values, whereas EI and SME values decreased. The best processing conditions (EI > 6.0, PF < 9.5 N, SME < 172 kJ/kg, and ΔE < 18) were found in the range of BT, 122–141°C; FM, 24.7–29.5%; and SFC, 0–10.9%. Under optimal...

PROBABILISTIC ANALYSIS AND DESIGN OF THE INDUSTRIAL TIMBER DRYING PROCESS

ABSTRACT The distribution in the moisture content of dried planks is an important parameter for kiln operators. The evolution of variability in the moisture content of timber boards during a batch drying process is investigated. This random variability in moisture content arises from a distribution in plank initial moisture content and dispersion in plank drying rate. A simple deterministic model of timber drying is outlined. Theoretical probabilistic analysis is applied to this model to predict the mean and standard deviation in board moisture content as a function of time. The solution is assessed with representative industrial kiln drying data. The utility of the approach in suggesting strategies to promote uniformity in final moisture content is outlined using some design studies. These strategies include sorting of the timber by moisture content and adjusting the drying rate and equilibrium moisture content to reduce variability. It is also demonstrated that the probabilistic approach can yield a better estimation of kiln average moisture content.

Physicochemical Evaluation and Optimization of Enriched Expanded Pellets with Milk Protein Concentrate

ABSTRACT The objective of this work was to study the effect of addition of milk protein concentrate (MPC, 0–10%) and feed moisture (FM, 20–30%) in a blend of corn starch (CS, 80%) and quality protein maize (QPM, 20%) on different physicochemical characteristics of third-generation (3G) snack foods using extrusion technology. A laboratory single-extruder with a 3:1 compression ratio, a rectangular die, and a central composite nonroutable model with two variables were used. The physicochemical characteristics evaluated were expansion index (EI), bulk density (BD), penetration force (PF), and color parameters L*a*b*. EI decreased with the increase of MPC and FM, whereas BD and color parameters (a* and b*) increased; PF showed a minimum point (MPC = 5% and FM = 25%). EI, BD, and PF were selected for the optimization process in an area of superposition of 1.5–4.1% of MPC and 20.0–24.1% of FM. A validation of the optimal area was performed on samples with average values of 4.64 (±0.28) for EI, 141.02 (±7.29) kg...

Probabilistic Studies of the Thermal Processing of Discrete Solid Products

The evolution of variability in the centre temperature of discrete solid products during a batch thermal process is investigated. A simple deterministic model of transient heat transfer in a discrete solid body is outlined. Theoretical solutions based on functions of random variables are derived to characterize the output of such a thermal process where the rate constant is randomly distributed. The solutions are validated by being compared to experimentally measured temperature dispersion. The utility of the approach in improving the design of non-deterministic thermal processes is outlined.

Hot-Water Phytosanitary Treatment Against Ceratitis capitata (Diptera: Tephritidae) in ‘Ataulfo’ Mangoes

ABSTRACT We determined the thermal death rate constants and mortality curves for the eggs and different instars of Ceratitis capitata (Mediterranean fruit fly) (Wiedemann) submerged in isolation in water at 44, 46, and 48°C and submerged within fruits of Mangifera indica (mango) (L.) in water at 43.1, 44.1, 45.1, and 46.1°C. The first instar was the most tolerant to this treatment, with estimated times for achieving 99.9968% mortality of 103.28,92.73, and 92.49 min at temperatures of 43.1, 44.1, and 45.1°C, respectively. The results of the study indicate that ‘Ataulfo’ mangoes weighing <329 ±2.11 g and at risk immature Mediterranean fruit fly infestation should be immersed for 95 min at 46.1-47°C to ensure that the fruit pulp remains at this temperature for 10 min. An efficacy test was conducted that involved treating 730 mangoes, with an average weight of 326 ±2.11 g (mean ±SE) and infested with 84 ±1.15 first instars. In this test, none of the 61,720 larvae treated survived. The confirmatory test was performed using commercial equipment in which 1,112 infested mango fruit weighing an average of 329 ±2.11 g were treated. Each fruit was previously infested with an average of 59 ±0.61 first instars (=65,825 total larvae) of which none survived. The data collected on mango quality indicate that hot water immersion for 95 min at 46.1–47°C can produce a more uniform fruit-color and positively modify the pH (producing more palatable fruits), but can also produce a loss of firmness and weight (5%). Taking all factors into consideration, we conclude that this treatment is sufficient to meet quarantine restrictions against C. capitata while maintaining market quality at least for 15 d.

Thermophysical Properties of Pulp and Rind of Papaya Cv. Maradol

Thermophysical properties of pulp and rind of papaya (Carica papaya L., cv. Maradol) were measured at 20, 30, 40, 50, and 60°C and modeled as a function of temperature. Thermal conductivity, specific heat capacity, and apparent density were measured using the line heat-source probe, differential scanning calorimetry, and the liquid displacement method. For pulp, the values of thermal conductivity, specific heat and apparent density ranged from 0.668 to 0.755 W/m K, from 3019 to 3732 J/kg K, and from 991 to 1036 kg/m3, respectively. The corresponding values for rind of papaya ranged from 0.651 to 0.714 W/m K from 2756 to 3282 J/kg K and from 1019 to 1043 kg/m3. Although thermal conductivity and apparent density of pulp and rind of papaya were significantly (p < 0.05) dependent on temperature, specific heat capacity and thermal diffusivity of pulp and rind of papaya were not affected by temperature in the measurement range.

Histopathological Changes in Third-Instar and Adult Anastrepha ludens (Diptera: Tephritidae) After in vitro Heat Treatment

ABSTRACT. The Mexican fruit fly, Anastrepha ludens Loew (Diptera: Tephritidae), is one of the most harmful pests of mango causing direct damage by oviposition on the fruit pulp. Mango for export is subjected to hydrothermal treatment as a quarantine method for the control of this pest, but exposure to heat for long periods of time reduces considerably the quality and shelf-life of treated fruit. The aim of this work was to study morphological changes of third-instar larvae and adults of A. ludens after in vitro exposure to high temperature at sublethal times. A heating block system was used to expose larvae at 46.1°C for 19.6 and 12.9 min, producing 94.6 and 70% mortality, respectively. Treated larvae were processed for optical microscopy. A fraction of surviving treated larvae was separated into containers with artificial diet to allow development into adults. Adult sexual organs were dissected and processed for transmission electron microscopy analysis. Results showed that 94.6% of the treated larvae died at 46.1°C for 19.6 min and none of the surviving larvae eclosed to adulthood, as they developed as malformed puparia. For the in vitro treatment at 46.1°C during 12.9 min, 70% of the treated larvae died and only 3.75% reached the adult stage, but ultrastructural damage in the male testes and in the female ovaries was observed. Additionally, 11.1% of the adult flies from the in vitro treatment also showed wing malformation and were incapable of flying. The analysis showed that surviving flies were unable to reproduce.

Impingement Cooking of Meat Products: Effect of Variability on Final Temperature

Heat transfer coefficient (HTC) for chicken fillets and beef burgers were determined at a number of product-to-tube distances in an impingement air unit. The coefficient varied from < 100 W/m2 K to over 200 W/m2 K depending on the input parameter settings. The level of variation in the coefficient between adjacent product items in the oven has been quantified as ±20 W/m 2 K. Models of sheat transfer for both food products have been developed. Parameter of the models indicated that depending on the product, either dimensional variation in the product or dispersion in the HTC between products can make the dominant contribution to dispersion in final product temperature.

Controlled Low-Temperature Vacuum Dehydration and Tunnel Drying: A Comparative Study

Controlled low-temperature vacuum dehydration (CLTVD) and tunnel drying (TD) processes were applied to mashed potatoes and the quality of the dried products was compared for both processes. Slabs of different thickness (0.26, 0.52 and 0.78 mm) were prepared. CLTVD was carried out at a low temperature avoiding freezing the product, at absolute pressure of 0.67, 1.00 and 1.33 kPa. For the TD experiments air temperatures were 40, 50 and 60° C. CLTVD and TD processes were compared using engineering and quality parameters (bulk density, water adsorption and total color difference). During the constant-rate drying period 40 to 70% of moisture was removed. The best quality product was generated at 0.26 mm, 0.67 kPa for CLTVD and 0.26 mm, 40° C for TD. For these treatments, the flux of mass was 7.8 3 1025 and 3.3 3 1024 kg m22s21 for CLTVD and TD, respectively. The mass transfer coefficient was 6.2 3 1026 kg m22s21 ΔY21 for CLTVD and 3.6 3 1022 kg m22s21 ΔY21 for TD. The falling-rate drying period was divided into three sub-periods. The effective diffusivity coefficient ranged from 1.1 3 10211 to 4.8 3 10211 m2/s and from 4.2 3 10211 to 9.6 3 10211 m2/s for CLTVD and TD, respectively. A change in water transport mechanism was achieved and both processes were controlled by mass transfer; internal and external mass transfer resistances were higher for CLTVD than for TD. CLTVD yields a product with lower shrinkage and a color closer to the white standard than the products obtained by TD. CLTVD may be considered as a potential alternative for drying of temperature-sensitive materials.