HEAT TRANSFER DURING FLUIDIZED BED PUFFING of RICE GRAINS

A pneumatic rice puffing machine was developed for increasing the production capacity of puffed rice for which a knowledge of the heat transfer process during puffing was required. the physical properties of the rice grains and other fluidization parameters, necessary for this study was experimentally determined. the surface heat transfer coefficient in case of hot air fluidized bed puffing was found to be 155.39 W/m²K. the calculated grain surface temperature for puffing was about 170°C and this did not vary significantly for experimental puffing air temperatures ranging from 200°C to 270°C. the air temperature ranging from 240°C to 270°C with corresponding exposure time of 9.7 s to 7s was found to be optimum for higher expansion ratio (8.5 to 10) and better color of the product. the temperature differentials between surface and center temperatures and between surface and average temperatures of the grains at the time of puffing were found to vary linearly with various puffing air temperatures and their ratios remained almost constant at 2.056.     

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.     

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.     

气流膨化过程中马铃薯方便粥水分变化动力学模型及品质变化分析

以双螺杆挤压微膨化工艺开发的马铃薯方便粥为原料,采用气流膨化技术处理马铃薯方便粥,通过测定干基水分含量、水分有效扩散系数、活化能以及色泽、膨化度、孔隙率和复水时间等研究膨化温度和气流速率对马铃薯方便粥水分及品质特性的影响,并建立气流膨化过程中马铃薯方便粥水分变化的动力学模型。结果表明：膨化温度和气流速率对马铃薯方便粥的水分变化均有明显影响。Page模型水分比预测值与实测值的拟合度较高,可以较好地预测马铃薯方便粥气流膨化过程中不同膨化温度、气流速率条件下的水分变化。水分有效扩散系数随着膨化温度、气流速率的升高均增大,气流膨化过程中马铃薯方便粥的活化能为18.96 kJ/mol。膨化时间、膨化温度和气流速率对马铃薯方便粥的亮度L*值、黄蓝度b*值、膨化度、孔隙率和复水时间均有明显影响。由相关性分析可知,气流膨化过程中马铃薯方便粥各品质特性指标间存在极显著相关性（P＜0.01）。本研究可为气流膨化过程中马铃薯方便粥水分实时监测及实现高品质气流膨化提供理论依据。     

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.     

Development of ready‐to‐eat rice starch‐based puffed products by coupling freeze‐drying and microwave

The rice starch mixtures with varying amylose contents (AC) of 0.12–19.00% weight were prepared by mixing waxy and nonwaxy rice starches. The 5% rice bran oil shortening was added in the starch paste. After gelatinisation, thin slabs of starch pastes were aged at 4 °C for 24 h. The aged slabs were dried by freeze‐drying to obtain 25% moisture content. A microwave oven set to 600 J s^?1 for 90 s was then used for puffing. The crucial factors affecting the snack purchase were texture and nutrition. The relative crystallinity and retrogradation enthalpy (?H_r) of freeze‐dried pellets increased with increasing the AC. From using a differential scanning calorimeter (DSC), endotherms of pellets were shown only when AC > 0.12%. An amylose–lipid complex was shown in pellets with AC ≥ 9.00%. Relationships between the AC and all puffed product properties were linear. Increasing AC provided greater hardness, fracturability, bulk density, but lower expansion ratio. From the sensory evaluation, the panellists preferred the puffed products with 9.00% AC. Increasing the AC gave higher crispness, hardness, brittleness, air cell opacity and density, but resulted in less puffiness. Thus, the microwave drying has the potential to puff a healthy expanded snack but giving the desirable properties depends on AC.     

Optimising pulsed microwave‐vacuum puffing for Shiitake mushroom (Lentinula edodes) caps and comparison of characteristics obtained using three puffing methods

Shiitake mushroom (Lentinula edodes) caps were puffed using pulsed microwave‐vacuum puffing (PMVP), microwave‐vacuum puffing (MVP) and microwave puffing (MP). The response surface method was used to optimise the process parameters for using PMVP to puff mushroom caps. The experiments were conducted using a central composite design to determine the visual appearance and initial moisture content (30–50%) of the mushroom caps. The initial moisture content and microwave power intensity showed highly significant linear relations with the expansion ratio and sensory evaluation. The optimal conditions for puffing mushroom caps were initial moisture content, microwave intensity, vacuum pressure and pulse ratio of 35%, 40 W g^?1, 77.5 ± 1.5 kPa and 1.35, which resulted in an optimal expansion ratio and sensory score of 163.2% and 6.83, respectively. The caps puffed using PMVP showed better textures, sensory scores and microstructures than those puffed using either MP or MVP.     

Physical,chemical and nutritional characteristics of puffed quinoa

Puffed quinoa can be used as ready-to-eat breakfast food or as an ingredient in snack formulations. In this study, puffed quinoa products with and without starch–chitosan coating were developed by gun, extrusion and microwave puffing at different process conditions (pressure, power, moisture content and energy consumption). Size, bulk density, colour, expansion index, water absorption and solubility, microstructure, mechanical and thermal properties, chemical composition and in vitro digestibility of organic matter and proteins of popped quinoa were assessed. Optimal process conditions for gun puffing were maximum 1.31 MPa after 780 s, 500 r.p.m. and 180 s for extrusion puffing and 1200 W for 60 s applying microwave puffing at 18–20% moisture contents. Gun and extrusion puffing yielded high-quality popped quinoa with a biological availability of organic matter between 84–88% and 79–90% for proteins. Extrusion and gun puffing are the most promising processes to prepare quinoa snacks.     

Effect of different rehydration temperatures on the moisture,content of phenolic compounds,antioxidant capacity and textural properties of edible Irish brown seaweed

The effect of temperature (20, 40, 60, 80 and 100 °C) on the rehydration kinetics and phytochemical constituents of dried edible Irish brown seaweed, Himanthalia elongata, were studied. The moisture content of fresh and dried seaweed was 4.07 and 0.07 g water/g dry basis, representing a 98.1% reduction in water content. All rehydration moisture curves had a clear exponential tendency, and it was observed that the rehydration time decreased when temperature was increased. Although restoration of the product to its original moisture content was achieved, rehydration resulted in losses in phytochemical content. Moisture equilibrium was achieved fastest at 100 °C (40 min) with losses of 83.2 and 93% in the total phenol and total flavonoid contents, respectively. The moisture content was fitted to empirical kinetic models; Weibull, Peleg’s, first-order and exponential association. Activation energies of 4.03, 4.28 and 3.90 kJ/mol were obtained for the parameters of Peleg’s, first-order and exponential models, respectively.     

Changes in physicochemical characteristics of rice during storage at different temperatures

This study investigated the changes in the physicochemical properties of rice during storage at different temperatures. Milled rice stored at high temperatures showed higher fat acidity than rice stored at low temperatures. Although the moisture content of milled rice stored at 30 °C and 40 °C decreased below 15.5% (15.33% and 15.22%, respectively) after 1 month, adequate values were maintained with storage at 4 °C for 3 months (15.50%) and at 20 °C for 2 months (15.53%). Rice stored at low temperatures retained its white coloration, whereas low color retention values were obtained at higher storage temperatures. Peak viscosity increased during 4 months of storage and larger changes were found at higher storage temperatures. Breakdown decreased and setback increased with storage, regardless of storage temperatures. Storage at higher temperatures increased cohesiveness and hardness in compared with storage at lower temperatures. High temperatures also led to a decrease in adhesiveness with age. High temperatures (30 °C and 40 °C) significantly decreased all sensory values even after 1 month of storage. These results are similar to those obtained in an analysis of cooked rice texture. The results of this study indicate that storage temperature is an important factor affecting the physicochemical properties of rice. Short storage periods below room temperatures are recommended to maintain rice quality.     

Explosion puffing of bananas

Banana slices were satisfactorily dehydrated by incorporating explosion puffing into the drying process. Water contents in the range 27–38%, steam temperatures of 152–160°C, internal pressures of 0.8–1.0 Kg cm^-2 and residence times of approximately 1 min were typical explosion puffing conditions. Initial and final drying were performed with hot air at a temperature of 70°C, velocity 3.6 m s^-1, and relative humidity 35%. The increase in porosity obtained by puffing clearly reduced the total drying time compared with conventional air dried (CAD) samples. A simple diffusional model was applied to calculate the effective diffusivities of water vapour during drying of samples with and without puffing treatment. Analytical tests for colour differences, bulk density, porosity, rehydration parameters, and scanning electron microscopy in both puffed and CAD banana samples were also performed.     

Effect of heating rate at different moisture contents on starch retrogradation and starch–water interactions during gelatinization

The objective of this research was to investigate the effect of heating rate at different moisture contents on starch retrogradation and gelatinization process. Starch retrogradation was not influenced by either moisture content (water/starch ratio of 0.7 or 2.0) or heating rate (5°C/min, 20°C/min, or 40°C/min). In order to further understand the effects of heating rate on starch–water interactions, starch suspensions at a water/starch ratio ranging from 0.7 to 3.0 were heated at 5, 15, or 25°C/min by using a DSC to different final temperatures and rescanned. The deconvoluted G and M1 endotherms and the corresponding additional unfrozen water (AUW) were determined. The results showed that the G and M1 endotherms merged at higher heating rates and at higher moisture contents as expected. A significant interaction was observed between moisture content and heating rate. The results suggest that the gelatinization process is governed by moisture content at the lower heating rate (5°C/min) and by heating rate at the higher heating rates (15 or 25°C/min). Results from the AUW data suggest that the M1 component of gelatinization dominated at moisture content below water/starch ratio of 1.5 and at 5°C/min heating rate. However, at moisture contents above water/starch ratio 1.0, an interaction was observed between moisture content and heating rate. The data suggest that at higher moisture content (>1.5 water/starch ratio) and at higher heating rate (≥15°C/min), there is still a kinetic limitation to the complete melting of the M1 endotherm.     

Rheological Behavior of Hot-Air-Puffed Amaranth Seeds

Force-deformation and force-relaxation experiments were performed on amaranth seeds puffed at 290, 330 and 370°C. Less force and energy was required to cause a given deformation in seeds processed at 290°C than in those puffed at 330 and 370°C. It was also observed that the forces and energies required to produce a given deformation did not differ significantly (p ≤ 0.05) for seeds puffed at 330 and 370°C. The three-element generalized Maxwell model and Peleg model were applied for modeling force relaxation of puffed amaranth seeds. It was found that the generalized Maxwell model predicted the experimental data better than the Peleg model. The elastic parameters and asymptotic residual force of the generalized Maxwell model were significantly affected by puffing temperature, showing an increase with its rise. Relaxation times were not significantly affected by the puffing temperature. It was concluded that a higher puffing temperature resulted in a more rigid material and less viscous behavior.     

Storage of hybrid rough rice – Consideration of microbial growth kinetics and prediction models

The objective of this study was to determine kinetics of mold growth on popularly grown hybrid long-grain rough rice during storage at conditions that simulate delayed drying and prolonged storage. Three long-grain hybrid rice cultivars, XL753 (2014) and CL XL745 (2014, 2015) and XL760 (2015) conditioned to four different moisture contents (MCs) (12.5%, 16.0%, 19.0%, and 21.0% wet basis) were stored in rough rice form at temperatures ranging from 10 °C to 40 °C for a period of 16 weeks. The study was repeated using rice from two consecutive crop seasons, 2014 and 2015. For all cultivars, a direct relationship between mold counts and rice MC was observed – whereas more complex trends were observed for the effect of temperature and the duration of storage on mold growth. Kinetic models including Baranyi, Weibull, Gompertz, Richard and Buchanan were successfully modified and fitted using non-linear regression and used to predict the mold counts (log₁₀ CFU/g) for varying conditions (correlations = 0.65–0.76). The study concluded that long-grain hybrid rough rice could be stored at low MC levels (≤17%) and moderate temperatures (≤27 °C) for up to 6 weeks without any change in the mold growth profile. However, storing rice at high MC (>17%) for more than 8 weeks, especially at higher (>27 °C) temperatures should be avoided due to the potential for high mold activity leading to loss of the grain quality.     

热风联合真空微波膨化鸭胸肉工艺优化

以鸭胸肉为对象,优化真空微波膨化鸭胸肉的最佳工艺条件。采用单因素试验考察膨化前水分含量、微波强度、微波时间和真空度对膨化鸭胸肉体积收缩率、复水比、感官评分的影响,利用响应面试验优化热风联合真空微波膨化鸭胸肉的工艺条件。结果表明:膨化前水分含量、微波强度、微波时间和真空度对膨化鸭胸肉的品质均有一定影响。在固定真空度为0.08 MPa条件下,各因素对膨化鸭胸肉体积收缩率和感官评分的影响程度大小顺序均为微波强度微波时间膨化前水分含量,通过等高线叠加法确定最佳膨化鸭胸肉加工工艺参数范围:膨化前水分含量为59%~63%,微波强度为20.5~24.7 W/g,微波时间为6.1~6.6 min。在此条件下,膨化鸭胸肉的体积收缩率可低于34%,感官评分在4.75以上,研究结果可为鸭肉膨化食品工业化生产提供理论参考。     

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.     

Effects of pre-heating temperature and formulation on porosity,moisture content,and fat content of fried batters

The effect of pre-heating temperatures on moisture and fat contents, and porosity of fried batters was studied. Batter pre-heated at 60 °C showed higher moisture content, lower fat content and lower porosity than non-pre-heated batter and batters pre-heated at 70 and 80 °C. Moisture content, fat content, and porosity at 4 min frying for batters with different pre-heating treatments ranged from 35.08 to 39.37, 3.92 to 5.16, and 13.14 to 45.31 %, respectively. Because of significant reduction in fat content, 60 °C pre-heating temperature was chosen to study the effect of batter formulations on moisture and fat contents, and porosity. Different wheat to rice flour ratios were prepared, and then each batter was pre-heated at 60 °C. Batters with higher wheat flour content showed higher moisture content, and lower fat content and porosity than batters with higher rice flour.     

Effect of Osmotic Dehydration and Air Drying on Physicochemical Properties of Dried Kiwifruit and Modeling of Dehydration Process Using Neural Network and Genetic Algorithm

In this study, effect of osmotic dehydration and hot air-drying conditions on shrinkage, rehydration capacity, and moisture content of dried kiwifruit was investigated and artificial neural network and genetic algorithm were applied as an intelligent modeling system to predict these physicochemical properties. Kiwifruit slices were immersed in osmotic solutions (30%, 40%, 50%, and 60%) at different temperatures (20, 40, and 60 °C) and were dried at 60, 70, and 80 °C for 5, 6, and 7 h. The results showed that increasing drying time and temperature caused an increase in shrinkage, while rehydration capacity and moisture content were decreased. Neural network model with one hidden layer, four inputs (operating conditions) was developed to predict three outputs (shrinkage, rehydration capacity as a well as moisture content) and genetic algorithm was used to optimize network structure and learning parameters. Artificial neural network models were then tested against an independent dataset and results showed the ability of optimized intelligent model to estimate shrinkage, rehydration capacity, and moisture content with high correlation coefficients (0.94, 0.93, and 0.96, respectively). Moreover, sensitivity analysis indicated that the most sensitive input variable toward such predictions was drying time.     

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.     

The effects of heat–moisture treatment of rice grains before parboiling on viscosity profile and physicochemical properties

The effects of heat–moisture treatment (HMT) (120 °C for 10, 30 and 60 min) on paddy rice grains before parboiling, on head rice yield (HRY), pasting and thermal properties, and colour and cooking characteristics of parboiled rice were studied. The results indicated that the HMT performed intensifies the changes in grains after parboiling, impacting pasting and thermal properties, which results in rice kernels with yellowish colouration and greater cooking time. HMT increased the temperatures of gelatinisation, with increasing HMT time from 10 to 60 min and reduced the gelatinisation enthalpy. HMT also affected the pasting properties of rice flours, reducing setback and viscosity and increased their stability to heat and mechanical agitation. The HMT performed in rice grains before the parboiling process with 60 min of the treatment decreased the HRY and increased the level of metabolic defects only in the treatment with 60 min.