Hot Air Puffing Kinetics for Soy-fortified Wheat-based Ready-to-Eat (RTE) Snacks

The soy-fortified wheat-based flat cold extrudate, after requisite steaming, was puffed in hot air using the high-temperature short-time (HTST) whirling-bed puffing system. The hot-air puffing was conducted at five different hot air temperatures, 200 to 240 °C at constant fluidizing air velocity of 3.95 m s⁻¹ for 50 s of puffing time. The initial moisture of sample was 0.4617 kg kg⁻¹ dm. The already existing 15 different thin layer-drying models were applied to determine the hot air puffing kinetics, based on puffing temperatures. It was found that the Page model could represent hot air puffing kinetics of the steamed flat cold extrudate within 99.3% accuracy. The effective diffusivity was found to be between 1.15623 × 10⁻⁹ and 2.58631 × 10⁻⁹ m² s⁻¹ for steamed flat cold extrudate in the temperature range of 200 to 240 °C. The activation energy for diffusion was found to be 2,341.824 kJ kg⁻¹. The optimum puffing conditions with respect to expansion ratio (ER) and sensory color score were found at puffing temperature of 220 °C and puffing time of 30 s. The variation in ER for the product was found to follow a linear relationship with moisture content of steamed flat cold extrudate during puffing. The Dincer Number for steamed flat cold extrudate puffed in fluidizing air at temperature 220 °C and 3.95 m s⁻¹ velocity was determined to be 276,223.8. This Dincer Number was used to predict the puffing time required to achieve predetermined moisture content of product. The prediction was found to be effective within 10% deviation from the values of experimental puffing time except during the initiation of puffing.     

Puffing Characteristics of Parboiled Milled Rice in a Domestic Convective–Microwave Oven and Process Optimization

Microwavable products are gaining worldwide acceptance as convenience foods, where hygiene can be maintained when processed in small quantities at the domestic level. One such ready to eat products are puffed or popped starchy grains like corn, rice, sorghum, etc. Owing to its high starch content, rice has high expandability, and the puffed rice produce thence has better digestibility. Considering these aspects, an attempt was made to produce puffed rice in a domestic convective–microwave oven. Puffing characteristics were studied for Gurjari variety of rice at 14 % (wb) moisture content for different preheating temperatures of the glass base plate (180, 200, and 220 °C), microwave power level (300, 600, and 900 W), and residence time (10–100 s), from which the range of residence time was selected for the optimization study. It was found that the puffing of rice was better at higher power level and preheating temperature of the base plate, and puffing started only after certain residence time. Further study was carried out to optimize the process parameters by using response surface methodology, for a Box–Behnken design at three levels for four parameters, i.e., moisture content (12, 14, and 16 % wb), preheating temperature of the base plate (180, 200, and 220 °C), microwave power level (300, 600, and 900 W), and residence time (50, 60, and 70 s). The optimized conditions were found to be 14 % (wb), 220 °C, 900 W, and 60 s. The second-order polynomial model was validated by conducting three trials at the optimized point and found to be agreeing with the predicted values.     

SPECIFIC HEAT of INDIAN UNLEAVENED FLAT BREAD (CHAPATI) AT VARIOUS STAGES of COOKING

A simple inexpensive calorimeter was built to measure specific heat of foods at various process temperatures. By using vegetable/mineral oil as the heating medium in place of water, specific heat at temperatures beyond 100°C can also be evaluated. Specific heat of whole wheat dough and Chapati (round disc prepared mostly from whole wheat flour dough) at various stages of cooking and puffing were determined. Based on the experimental data a linear equation (C = 2476.56 + 23.56M ? 3.79T_e) is proposed from the experimental data for specific heat of wheat flour, dough, cooked and puffed Chapati and for other food materials at moisture levels ranging from 0.1% to 80% and temperature ranges from 303° to 336° K.     

Effect of puffing conditions on physical properties and rehydration characteristic of instant rice product

The aim of this work was to study the effects of puffing conditions on the properties of instant rice and to obtain optimal processing condition for product with rehydration time within 5 min. Thai jasmine rice was soaked, cooked and dried at 80 °C in a tray dryer before being puffed at different moisture contents (15–20% wb), temperatures (200–220 °C) and time intervals (20–30 s). The rice puffed at higher moisture contents and puffing temperatures for longer time exhibited higher volume expansion ratios and shorter rehydration times. Presumably, case hardening of the grain surface occurred. Instant rice that can be rehydrated in 5 min with more acceptable hardness than the commercial instant rice was obtained. Regression models to predict the quality of instant rice were developed using response surface methodology.     

Studies on Expanded Rice. Optimum Processing Conditions

Optimum conditions of parboiling, milling and puffing for making expanded rice were studied on a small laboratory scale. Optimum puffing was obtained by heating milled parboiled rice at a moisture content of 10.5–11% with 15 times its weight of fme sand at 250°C for 10–11 sec. Raw and mildly parboiled rice gave minimal expansion, which increased with increasing severity of parboiling up to a steam pressure of 1.5 kg/cm². However, rice parboiled by heating with sand (250°C, 2.5 min) expanded best. Starch retrogradation after parboiling reduced expansion, as did cracked and broken grains and insufficient milling of the rice. Addition of salt increased expansion. Expansion initially increased and then decreased with increasing age of paddy after harvest.     

Heat Transfer Coefficients on Cakes Baked in a Tunnel Type Industrial Oven

Using an h-monitor, surface heat flux and effective surface heat transfer coefficients were evaluated during baking of two cakes in a tunnel-type multi-zone industrial oven. An average 75–80% of total heat flux was counted as radiation heat. Air-mass temperature outside the boundary layer was determined from the experimental temperature profiles over the h-monitor top plate. In the range of baking temperatures (186–22 5°C), relative air velocities (0.02-0.437 m/s) and absolute humidities (0.0267–0.0428 kg H₂O/kg dry air) heat transfer coefficients were 20 to 48.0 W/m²K. A simple regression model was developed based on experimental data.     

Effect of drying air temperature and storage on industrial and chemical quality of rice grains

The drying air temperature and storage time can change the milling yield and chemical composition of rice grains. Therefore, the objective was to verify the industrial quality and chemical composition of rice grains, white and integral subgroups, in response to drying air temperature and storage time. For such, the rice grains were subjected to drying in a column dryer with a grain capacity of 1 m³, using 55 and 65 °C drying air temperatures. After, they were stored in PP Woven Bags under environmental conditions for 240 days. After drying and every 60 days the milling was performed, aiming to evaluate the industrial quality and chemical composition of the grains. The whole grains yield was negatively affected by the increase in drying air temperature for both subgroups. The increase in the drying air temperature led to a reduction in the lipid content and an increase in the ash content for grains of white subgroup. The storage time promoted an increase in the whole grains yield in the white subgroup when the grains were dried with the highest drying air temperature. The lipids and proteins contents decreased, while the fibers and ash contents increased during storage for the white subgroup grains. The chemical composition of grains from the brown subgroup did not change during storage, regardless of drying air temperature.     

Thin-layer Drying of Parboiled Rice at Elevated Temperatures

Experiments were conducted to dry thin layers of long-grain parboiled rice at air temperatures ranging from 38–158°C and relative humidities from 0.3–80%. A series solution of the diffusion equation, considering long-grain rice as infinite cylinder, was used to express the moisture ratio. During thin-layer drying experiments it was necessary to develop a computational method to determine the relative humidity of air above 100°C without the use of wet bulb temperature measurements. An empirical exponential expression for moisture ratio gave the best fit to the drying data at all conditions. Parboiled rice was found to have higher values of effective diffusivity than raw rice.     

Roasting of Navy Beans (Phaseolus vulgaris) by Particle-to-Particle Heat Transfer

A rotating chamber dry roaster using pre-heated ceramic beads as heat transfer media was used to roast navy beans. Processing conditions were: beads temperature, 240 and 270°C; bean-to-bead ratio, 1/10 and 1/15 and contact times of 1 and 2 min. Product temperatures achieved ranged from 92–125°C for the eight runs. Heat transfer coefficients varied from 3.6–23.4 W/(m²) (°C). Roasted products showed reduced water-soluble nitrogen content and gel forming capacity, increased water-holding capacity and cold paste viscosities, and no changes in available lysine and degree of starch damage. Residual trypsin inhibitor (TIA) and hemagglutinin activity varied from 92 to 22%, and 48 to 1%, respectively. A correlation was found to exist between nitrogen solubility index and TIA of products. Roasting caused fracture and separation of hulls, and facilitated their removal.     

Bacillus cereus emetic toxin production in cooked rice

Three mesophilic strains of Bacillus cereus known to produce emetic toxin were used to model germination, growth and emetic toxin production in boiled rice cultures at incubation temperatures ranging from 8°C to 30°C. Minimum temperatures for germination and growth in boiled rice were found to be 15°C for all strains. Toxin production at 15°C was found to be significantly greater (P<0·01; reciprocal toxin titre of 373±124) than at 20°C and 30°C (reciprocal toxin titres 112±37 and 123±41, respectively). Toxin production became detectable after 48 h incubation at 15°C, with a maximum titre reached by 96 h. At 20°C and 30°C, toxin production was detected at 24 h incubation, with a maximum titre reached by 72 h. Toxin production at 15°C was detectable at lower bacterial counts (6·2 log₁₀ cfu g⁻¹), than with incubation at 20°C and 30°C (>7·0 log₁₀ cfu g⁻¹). In this study, the lower temperature limit for germination and growth on solid laboratory medium was found to be 12°C for all strains, i.e. 3°C lower than that observed in boiled rice.     

CONVECTION HEAT TRANSFER COEFFICIENT FOR A RESTRUCTURED PORK/SOY HULL PRODUCT1

Heat transfer coefficients, h, (J/cm²°C min) were determined for a pork/soy hull mixture during heating in a convection oven (142°C) with and without control of the dew point. Data were acquired by heat processing 5 stacked layers of product (10 × 10 × 1 cm) so that heat was only conducted into the top surface. One experiment was designed to determine h when the second layer from the top reached one of 6 temperatures: 20, 32, 44, 56, 68 and 77°C, with no control of the dew point. the second experiment determined h for 60 min of heating for 5 dew point levels: 6, 21, 31, 40 and 50°C. Without the control of humidity, values for h ranged from 0.0170–0.0366 J/cm²°C min. the heat transfer coefficient increased with temperature and heat processing time. Product yield and surface area ratios decreased as h increased. When relative humidity was controlled, values for h ranged from 0.0167–0.0270 J/cm²°C min, decreasing for dew points above 31°C.     

Effects of Heat Transfer by Radiation and Convection on Browning of Cookies at Baking

The effects of modes of heat transfer (radiation or convection) on the baking color development of food were studied. An experimental baking oven that could be altered to two heat transfer modes was designed; the ratio of heat by radiative transfer to total heat transferred was about 30% or 70%. The glucose-glutamate solutions were heated at different air temperatures to measure the browning rates to calculate the activation energies. Cookies were baked at 200°C to measure the lightness of color on the surface and the surface temperature. It was clarified that the development of color depended on the temperature only.     

Thermal Properties of Beef Loaf Produced in Foodservice Systems

There is a lack of information on thermal and other properties of foods, especially food mixtures. Physical properties of beef loaf prepared following formula and procedures used in alternate foodservice systems were determined: heat capacity (0.88 cal/g°C uncooked, 0.91 heated to 60°C) moisture content (72.1% uncooked, 66.2% heated), thermal conductivity (0.40 w/cm°C uncooked, 0.47 heated), fat (17.6% uncooked, 13.0% heated) and density (1.00 g/cm³ uncooked and 0.70 heated). The surface heat transfer coefficient for a forced convection oven was also determined (62 w/ m²°C.) Times to heat beef loaves to specified ending temperatures in a forced convection oven at 163°C and 176°C were calculated. There was less than 1 min difference in calculated heating time required to reach the desired end temperature. The actual times to reach ending temperature show very good agreement with the calculated times.     

Investigating shrinkage and moisture diffusivity of melon seed in a microwave assisted thin layer fluidized bed dryer

This work aimed to investigate the drying behavior of melon seed during combined fluidized bed-microwave drying system. Three drying air temperatures (40, 55 and 70 °C), three microwave powers (270, 450 and 630 W) and three air velocities (0.8, 1.5 and 2.3 m/s) were tested. Five mathematical models were selected to fit the experimental data for drying kinetics, and the results revealed that the Aghbashloo et al. model exhibited, in all cases, the best performance in fitting the experimental data (R² varying from 0.99088 to 0.99998; χ² from 0.00000 to 0.00185 and RMSE from 0.02289 to 0.82316). Calculated values of moisture diffusivity for dried melon seed varied from a minimum of 6.51 × 10?10 to a maximum of 6.59 × 10?9 m²/s under the tested drying conditions. Moisture diffusivity values increased as air temperature and microwave power was increased. Shrinkage values were calculated and found to vary in the range from 46.99 to 15.09 %.     

Estimation of Heat and Mass Transfer Coefficients During Air-Freezing of Cucumber

Freezing of foods involves coupled heat and mass transfer. It is essential to optimally design the freezing equipment and maximise the efficiency of the freezing process. Therefore, it is necessary to estimate the heat and mass transfer coefficients. In this study, the surface heat and mass transfer coefficients were estimated employing the Hilbert equation as well as the corresponding thermal and diffusive boundary layers during freezing of unpeeled cucumber at low air temperatures (?10 to??18 and??25°C). The estimated mean heat transfer coefficients ranged from 10.99 W m^?2 K^?1 for 0.5 m s^?1 up to 40.07 W m^?2 K^?1 for 5.0 m s^?1. The respective mass transfer coefficients ranged from 8.98 up to 32.40 m s^?1. The estimated heat transfer coefficients were compared with the respective ones calculated from Dincer and Dincer and Cengeli during air-cooling (22 to 2°C) of unpeeled cucumbers of similar size as well as other agricultural cylindrical products.     

Determination of the optimum intermittent drying conditions for rough rice (Oryza sativa,L.)

Intermittent drying was studied by tempering rough rice (Philippine Seed Board, PSB-RC 52 variety) in between during hot air drying. The study was performed using a three-level, three-factor fractional factorial design and aimed to determine the optimum combination of drying air temperature (X₁), air speed (X₂) and tempering time (X₃) that resulted in high milling recovery (MR), high head rice ratio (HRR), short drying time (DT), high grain hardness (H), high germination ratio (GR), high degree of whiteness (W) and low cracked grains ratio (CGR). Drying air temperatures used varied from 35°C to 55°C. Airspeed, on the other hand, significantly affected H only and tempering time affected DT at the 95% significance level. Optimum drying conditions of 45°C drying air temperature and a tempering time of 2 h were established for the intermittent drying of rough rice.     

Puffing of Rice Cakes as Influenced by Tempering and Heating Conditions

Puffed rice cakes were produced from long grain brown rice by a pressure-drop puffing method. Effects of raw rice tempering conditions (time and moisture level) and heating conditions (temperature and time) immediately before puffing on rice cake volume were investigated. In general, a lower moisture level (14% vs 16–20%) in raw rice and longer tempering time (5 hr vs 1–3 hr) resulted in higher specific volumes in rice cakes. Higher heating temperature (230°C vs 200–220°C) and 8 sec heating produced rice cakes with higher specific volumes. Darker cakes were obtained with the high temperature and long time combinations.     

STUDIES ON THE EFFECT OF GERMINATION TIME AND TEMPERATURE ON MALTING OF RICE

The effect of germination conditions on rice malt quality was studied by germinating rice for different periods of time up to 7 days over a range of temperatures (22° to 32°C). Germination time and temperature had a significant effect on rice malt diastatic power, cold and hot water extracts, total reducing sugars, and free alpha amino nitrogen. In general, diastatic power, cold water extract, hot water extract, total reducing sugars and free alpha amino nitrogen, all increased with germination time and temperature. Germination temperatures of 28°C and 30°C were good for the development of diastatic power, cold water extract, hot water extract, total reducing sugars and free alpha amino nitrogen. However germinating at 30°C gave maximum result. The mashing trials with rice malted for 6 days showed a slow and incomplete saccharification, slow filtration rate, and high total available extract in spent grains.     

加热卷烟逐口抽吸过程传热数值模型

为实现加热卷烟数字化设计及烟气调控,对加热卷烟抽吸过程的传热机理进行深入研究,建立了基于多孔介质的气流流动模型与气固两相局部热平衡传热模型,模拟了加热卷烟在抽吸过程中的温度分布,并通过温度检测实验验证了模型的准确性。结果表明:①两相局部热平衡传热模型能够模拟加热卷烟传热过程,卷烟各段出口温度的模拟值与实验值差异均在15 ℃以内;②模拟了加热卷烟内部的气流场和温度场,各段气流流速随着抽吸呈现周期性分布,抽吸时间内中空段气流流速最大且其外围基本不流动,抽吸周期内加热卷烟烟支温度呈现D型分布;③计算了烟支加热片与烟支外周在抽吸过程中的最大热通量和最小热通量,加热片在1个抽吸周期内大约释放39 J的热量;烟支外周在1个抽吸周期内大约散失33 J的热量。      

Critical evaluation of viscometrically determined pasting temperatures in barley malt

Modern varieties of malting barley allow mashing to proceed efficiently to enable saccharification and other biochemical processes. A prerequisite for starch hydrolysis is the disruption of starch granule structure by exceeding a grain specific pasting temperature. For grains, several viscometric methods based on the Rapid‐Visco‐Analyser were developed to determine variations in the pasting temperature reproducibly. Absolute pasting temperatures, as they are necessary to optimize the isothermal mashing process, cannot be determined owing to constructional and data evaluation related limitations. The aim of this research is to investigate and compensate for temperature deviations caused by standard data evaluation and lagging heat transfer from the heating unit into the sample. Accordingly, an improved determination of the pasting onset and a formula to compensate for temperature lags were developed. The optimized data leads to more accurate and reduced pasting temperatures compared with the standard method. The heat transfer was reproducibly quantified (Δϑ : 2.9–5.8°C) and integrated into a compensation formula (R ² = 0.99). It was found that the lag is strongly dependent on the actual sensor temperature but independent of the unpasted sample's initial viscosity. The results were applied on viscometric analyses (n  = 161) to calculate the intrinsic pasting temperatures of barley malt. The determined temperature range is considerably lower than anticipated (56.7–60.5°C). Winter barley exhibits significantly lower pasting temperatures. The outcome of this work can be used to improve the accuracy of prospective analysis and to correct already existing viscometric raw data. Copyright © 2017 The Institute of Brewing & Distilling