Effects of parboiling and fluidized bed drying on the physicochemical properties of germinated brown rice

Changes in physicochemical properties of germinated brown rice (GBR) and parboiled germinated brown rice (PGBR) dried in a fluidized bed dryer at 110–150 °C were investigated. Results indicated that parboiling altered the properties of GBR owing to starch gelatinisation. The moisture content, yellowness, peak viscosity and hardness of PGBR increased, but internal fissured kernel, cooking time, water absorption and total solids loss decreased when compared to GBR. γ‐aminobutyric acid (GABA) content in GBR was 23.31 mg per 100 g and was reduced to 17.91 mg per 100 g in PGBR. The drying times required to reduce the moisture content of GBR and PGBR to 16% d.b. were 4.01–7.65 min and 5.11–9.50 min, respectively. Final moisture content, which is optimum to prevent internal fissures of dried GBR and PGBR, was 27–29% and 25–28% d.b., respectively. The same trend was observed in the physicochemical properties of GBR and PGBR when increasing drying temperature and time.     

Microwave and microwave-vacuum drying as alternatives to convective drying in barley malt processing

Barley malt is widely used in food and beverage industries. Although microwave drying can be an interesting alternative for stabilization, it has been traditionally processed by convective drying. This work studied the microwave and microwave-vacuum drying of barley malt, evaluating hydration, germination and drying. Both hydration and germination reduced the grain compression force, but without demonstrating a defined endpoint. The traditional convective drying (50–70 °C) took 540–840 min, while microwave reduced processing time in ~95%. Vacuum increased the drying rate and reduced the product temperature. Moisture profiles over processing were calculated based on the obtained effective diffusivity. The drying rate showed an intermediate moisture value when microwave radiation is optimum, which was associated with the best combination between absorption and conversion across the water molecules within the sample. The behavior parameter of Page Model suggested super-diffusion. In conclusion, microwave and microwave-vacuum technologies showed to be attractive alternatives for barley malt drying.     

Development of phase change material assisted evacuated tube solar dryer: Investigation of thermal profile,drying characteristics,and functional properties of pumpkin slices

The present work aimed to develop a phase change material-assisted evacuated tube solar dryer (PCM-ETSD) and experiments were performed with and without PCM for drying pumpkin slices. Thermal performance, drying characteristics, and quality attributes were analyzed with and without PCM at different airflow rates: 34.64 kg/h, 51.96 kg/h, and 69.28 kg/h. The average temperature elevation between the ambient and drying chamber was achieved at 29.62 °C to 36.33 °C and 25.64 °C to 28.93 °C without and with PCM-assisted drying respectively. PCM-ETSD extended the drying period by 2 h and maintained the temperature ranges from 50.78 °C to 61.29 °C after sunshine hours. The PCM-ETSD reduced the moisture content of pumpkin slices by 4–5% and 8% more as compared to without PCM and sun drying respectively. Drying rate and effective moisture diffusivity are enhanced with the increase of airflow rate in the drying process and higher without PCM-assisted drying followed by PCM and sun drying. The total phenolic content and total flavonoid content are higher in PCM-assisted drying and continuously decreased with the increases in airflow rate in both drying processes. Antioxidant activity and total carotenoid content are higher in PCM-assisted drying. FTIR analysis confirmed the presence of active functional groups and phenols in dried pumpkin. The inferior color changes were observed in PCM-assisted drying of pumpkin slices. The developed PCM-ETSD could be capable of drying other food commodities on a pilot scale after sunshine with retention of quality attributes.     

Microwave assisted fluidized bed drying of nutmeg mace for essential oil enriched extracts: An assessment of drying kinetics,process optimization and quality

The drying mechanism of the myristicin enriched nutmeg mace has been optimized in a microwave assisted fluidization bed dryer (MWFBD) through multiple linear regression (MLR) and artificial neural network (ANN) modeling. The developed drying technique overcomes the non-uniformity heating problems in microwave heating and prolonged drying in fluidized bed drying. During the novel method of drying selected input variables were drying air temperature (DT) (40–50 °C) and microwave power (MP) (480–800 W) and output variables involving colour, oil yield, and myristicin quantity have been investigated by a continuous air velocity of 5.1 m/s. Six mathematical models about one to four conditions have fitted with an experimental design. Suitable enforcement of such models was evaluated through statistical measures. The coefficient of determination (R²) of MLR varied from 0.89 to 0.98, and the sum of squared error (SSE) varied within 6 × 10⁻³ to 158.18, while R² of ANN fluctuated from 0.82 to 0.95, and the mean squared error (MSE) varied between 0.006 and 0.1450, which shows MLR design performance superior than ANN design. The processing conditions of 48.24 °C DT and 637.431 W MP with a drying time of 1.3 h were identified as optimum conditions with a desirability value of 0.98 to obtain maximum oil yield (13.38%) and good colour (L* (20.83), a* (17.34), b* (8.62)) of nutmug mace. Moreover, no myristicin (5.92%) degradation was observed compared with the sun and convective drying. Among the tested models, page and logarithmic models gave a better prediction of moisture ratio.     

Development of infrared-assisted hybrid solar dryer for drying pineapple slices: Investigation of drying characteristics,mass transfer parameters,and quality attributes

The research aims to the development and performance evaluation of an infrared-assisted hybrid solar dryer (IR-HSD) for drying pineapple slices. The IR-HSD contains an evacuated tube solar collector, blower assembly, drying chamber, infrared heater, phase change material (PCM) chamber, etc. The study investigates and compares the thermal profiling, drying kinetics, mass transfer parameters and quality attributes of pineapple slices dried using different methods, such as direct drying, phase change material (PCM)-assisted drying, PCM + IR-assisted drying, and sun drying. The average temperatures achieved inside the drying chamber for direct drying and PCM-assisted drying were 60.16 °C and 57.29 °C, respectively, while the temperature reached 60 °C for PCM + IR assisted drying. The average drying rate in PCM + IR drying was higher than in direct and PCM-assisted drying methods. The best-fitting models were the Modified Page model for direct and PCM + IR-assisted drying and the Midilli-Kucuk model for PCM-assisted and sun drying. The higher effective moisture diffusivity for PCM + IR-assisted drying was 2.59 × 10⁻⁹ m²/s, followed by direct and PCM-assisted drying. Similarly, the convective mass transfer coefficient obtained was 1.085 × 10⁻⁷ m/s, 8.321 × 10⁻⁸ m/s, and 1.381 × 10⁻⁷ m/s for direct, PCM-assisted, and PCM + IR-assisted drying, respectively. The superior quality attributes such as total flavonoid content (TFC), total phenolic content (TPC), and antioxidant activity were observed in all drying approaches with retention of colour except open sun drying, which decreased significantly. FTIR spectroscopy analysis confirmed the presence of different bioactive, including aromatic compounds, phenols and hydrocarbon functional groups. The infrared-assisted hybrid solar drying of pineapple slices showed a better drying process and quality attributes.     

Water sorption and cooking time of red kidney beans (Phaseolus vulgaris L.): part I – Effect of freezing and drying conditions on water sorption and cooking time

Water sorption and cooking time of kidney beans were determined. The beans were manually harvested at 19.2 ± 0.1% moisture content and stored at ?20 and ?10 °C for about half a year. The beans were further dried at 30, 40 and 50 °C inside a thin‐layer drier for 7.5 h or under room conditions for 4 week. The freezing storage temperature before the beans were dried did not influence their cooking time and water sorption. The saturated kernel volumes decreased approximately 7% after drying. The beans decreased their sphericity during water sorption and had a larger swelling ratio in the thickness direction than in other directions. Lower initial moisture content, especially with a higher drying temperature, decreased water sorptivity and resulted in higher percentage of uncooked kernels if the beans were not soaked before cooking. However, there was no relationship between initial moisture content and uncooked percentage if the beans were soaked before cooking. High drying temperature resulted in hard‐to‐cook (HTC) phenomenon.     

Optimisation of a pilot‐scale spray drying process for probiotic yoghurt,using response surface methodology

The influence of drying air temperatures, drying air flow rate and feed flow rate on percentage survival rate (% SR) of starter and probiotic bacteria, moisture content, water activity and colour of probiotic yoghurt powder produced using a pilot‐scale spray dryer was investigated. Optimisation of spray drying conditions was achieved based on the desirability value. Results showed that inlet air temperature, drying air flow rate, feed flow rate and outlet air temperature of 150 °C, 478 m³/h, 2 L/h and 63.3 °C, respectively, were optimal conditions to produce powder that meets quality specifications and with a satisfactory% SR.     

Improvement of drying efficiency and quality attributes of blueberries using innovative far-infrared radiation heating assisted pulsed vacuum drying (FIR-PVD)

A new drying technology, far-infrared radiation heating assisted pulsed vacuum drying (FIR-PVD) was applied to process blueberries. Influences of drying temperature, vacuum pressure duration (VPD), and ambient pressure duration (APD) on drying characteristics and quality attributes of blueberries were investigated under FIR-PVD. Results showed that drying temperature, APD, and VPD had significant influence on drying time and quality attributes of dried blueberries expect for color and cohesiveness. Compared to hot air dried blueberries, FIR-PVD seriously damaged the cellular walls of blueberries during drying at 65 °C. The highest total phenolics (TP) and total monomeric anthocyanins (TMA) contents of dried blueberries were obtained at 65 °C with pulsed ratio of 15 min: 4 min and 15 min: 2 min, respectively. The FIR-PVD products obtained lower color difference, better mechanical properties and rehydration performance and maintained higher antioxidant capacity by shortening drying time, reducing exposure to oxygen, and modifying the microstructure compared to hot air drying.Industrial relevanceBlueberry is a popular function fruit around the world. With high moisture content and tender tissue, fresh blueberry is very susceptible to microbial infection even under low temperature storage conditions. Drying is a good alternative to extend the shelf life and increase the availability of fresh blueberries. However, the existence of waxy hydrophobic layer covered the surface of blueberries inhibits moisture diffusion during drying. Chemical dipping and thermal blanching pretreatments were usually used to reduce the influence of skin hydrophobicity and promote moisture diffusion. Nevertheless, the chemical additive residue leads to food safety risk and it's a big challenge to deal with the corrosive waste chemical solutions, while thermal blanching resulted a high loss of bioactive compounds. FIR-PVD is a recent developed emerging drying technology to process berries with waxy layer beyond pretreatments. Results indicated that FIR-PVD is a very promising technology for processing blueberries with the improvement of drying efficiency and quality attributes.     

Effect of combined microwave‐hot air drying and superheated steam drying on physical and chemical properties of rice

Jasmine rice (Oryza sativa L.) was subjected to two drying operations: combined microwave‐hot air drying (MHA) at initial power intensity of 3, 4 and 6 W g^?1 and superheated steam drying (SHS) at 300 °C and 400 °C. During drying, kinetic rate constants of SHS were significantly higher than those of MHA. Both drying operations could decrease enthalpy of starch gelatinisation from 9.28 J g^?1 to 1.64–6.17 J g^?1, increase gelatinisation extent to 33.51–82.33%, decrease crystallinity from 28.87% to 18.15–21.33%, improve scavenging ability of 1,1‐diphenyl‐2‐picrylhydrazyl, increase ferric reducing antioxidant power and increase hardness of cooked rice from 5.66 N to 5.83–6.55 N, depending on microwave power and drying medium temperature. However, taste profiles and liking scores were comparable to the regular brown rice. Therefore, MHA and SHS operations could be potentially used for reducing drying process and promoting antioxidant activity.     

The effect of osmosis pretreatment on hot‐air drying and microwave drying characteristics of chili (Capsicum annuum L.) flesh

Chili flesh pretreated with or without osmotic dehydration (OD) was dried in the hot‐air drying (AD) oven at 50–80 °C or in the microwave drying (MD) oven at 60–180 W. Results showed that the samples osmotically treated in mixed solution (10% salt + 50% sucrose) had the best dehydration effect as compared with single salt or sugar solutions. During the drying process, osmotically treated samples had one falling‐rate period and their effective moisture diffusivities (D_eff) showed a rapidly linear increase with the decrease in moisture content, while directly drying samples showed a three‐phase falling‐rate period and their D_eff increased gradually at the initial period and then rapidly at the final period. When the moisture content decreased, the activation energy increased gradually; however, for AD after OD, it decreased. Among all the processes, MD at 60 W after OD presented the largest vitamin C retention rate and the best colour difference, needing less drying time.     

Optimisation of convective drying of carrots using selected processing and quality indicators

The effect of drying temperature (40–65 °C) and air rate (2–6 m s^?1) on the formation of Maillard reaction indicators and vitamins content of carrots dehydrated by convection has been investigated. The range of assayed processing conditions, based on a previous central composite face design (CCD), led to moderate changes in the studied parameters, even under the most severe conditions. In addition, the drying kinetic of the process was studied taking into account the experimental quantitation of shrinkage, which allowed the determination of a first drying period with a constant rate of water evaporation per unit of exchange surface. The slope of the first drying period, the moisture loss during the first hour of drying and the level of quality parameters (Maillard reaction indicators and vitamins) were correlated with processing conditions with high accuracy. For the prototype here used, the optima temperature and air rate to maximise the desirability function (0.77) were 46 °C and 4.9 m s^?1.     

微波-热风联合干燥对高水分稻谷加工品质及微生物量的影响

研究了不同微波有效功率下高水分稻谷的微波干燥特性,以及探讨了微波处理工艺对稻谷加工品质及微生物量的影响。结果表明,在较低的微波功率(485和927 W)下,处理初期稻谷温度迅速升高,水分下降缓慢,当温度达到65℃、含水量达到19. 7%左右时,稻谷升温速度减小,而水分下降速度加快。微波功率增加可显著提高稻谷的升温速度和降水速率,但高功率微波干燥稻谷易产生焦糊现象。采用有效功率927 W的微波条件,2 min可将稻谷加热至60℃,稻谷含水量从21. 58%降低至19. 96%。通过4 h缓苏处理后,稻谷表面细菌量下降3. 6 log CFU/m L,表面霉菌量下降3. 3 log CFU/m L,对稻谷内部霉菌可实现95%灭菌,稻谷的出糙率和整精米率无显著下降(P 0. 05),分别为83. 92%和68. 14%。与自然通风及热风处理稻谷至入仓偏高水分18. 34%相比,微波与热风联合处理只需20 min,其稻谷加工品质较高,杀菌效果也远远高于自然通风及热风处理。因此,适宜的微波处理在保障高水分稻谷加工品质的前提下,可显著缩短干燥时间,并获得高质量的杀菌效果,实现高水分稻谷快速安全入仓处置。     

Effects of drying conditions in hybrid dryer on the GABA rice properties

In this study, pre-germinated rough rice was dried under various conditions using a hybrid dryer that incorporated heat pump dryer with fluidized bed drying (FBD) system in order to compare with the single-stage drying by hot air dryer. The main objective was to investigate the effect of drying conditions on the cooking and physical properties, nutrients and sensorial qualities of GABA rice products. It appeared that the FBD at 100–140 °C led to noticeable increase of head rice yield. The germination process caused the decline of gelatinization enthalpy of brown rice flour, the change of pasting properties, the reduction of cooking time and escalation of the total phenolic content, antioxidant activity and GABA content. The FBD at higher temperature significantly raised the degree of starch gelatinization and caused longer cooking time, higher hardness and adhesiveness of cooked GABA rice. Three-stage drying comprising FBD at 60 °C for 10 min in the first stage followed by FBD at 100 °C in the second stage and then heat pump drying at 45 °C together with tempering step between drying stages was recommended due to its superior GABA rice product quality.     

Effects of foam-mat drying temperature on physico-chemical and microstructural properties of shrimp powder

This study was carried out to investigate the impact of different drying air temperatures (45, 60, 75, and 90 °C) on the physico-chemical and microstructural properties of foam-mat-dried shrimp powder. Physico-chemical properties such as moisture content, water activity, solubility, water binding capacity (WBC), and color of the powder were determined. The experimental results showed that as the temperature increased, the moisture content, water activity, and WBC of the samples decreased. However, their solubility increased significantly (p < 0.05). Furthermore, the total color difference (ΔE) increased by increasing temperature, yet decreased at 90 °C. The SEM images indicated as the drying temperature increased, the mat structure porosity increased, too, especially at 90 °C.Industrial RelevanceThe demand for ready-to-eat (RTE) and/or ready-to-cook (RTC) meals is gradually growing because they are easy to prepare. The dried shrimp powder can be used for producing formulated seafood and other food products such as soups, sauce, snacks, etc. to increase the protein content and improve the nutritional value of them. Fish and shrimp soup mixes and snacks are examples of dried RTE products. They are popular in Asian countries, due to easy transportation, quality, stability, and long shelf life.     

Effect of heat-moisture treatment for utilization of germinated brown rice in wheat noodle

Effect of heat-moisture treatment of germinated brown rice (GBR) on the texture and cooking quality of the noodles containing mixtures of wheat and GBR flours was investigated. With the increase in GBR content, hardness and tensile strength of the composite noodles decreased and cooking loss and water absorption increased. Pasting viscosity of the flour mixtures was significantly decreased by increasing the amount of GBR. Heat-moisture treatment of GBR (17 or 20 g/100 g moisture at 100 °C for 4 h), however, apparently increased the pasting viscosity and improved the texture and cooking quality of the composite noodles. The mixture of wheat and a treated GBR (1:1 weight ratio) showed a pasting viscosity similar to pure wheat flour. The noodle containing the heat-moisture treated GBR flours showed the lower cooking loss, and higher hardness and tensile strength than the noodle containing untreated counterparts. Among the treated GBR flours tested, the GBR treated at 100 °C for 4 h at a moisture level of 17 g/100 g was the most acceptable in terms of cooking quality and textural property, close to those of the noodle of pure wheat flour. Substitution with the heat-moisture treated GBR, however, made the noodle darker because of thermal discoloration of GBR.     

Hot air drying of tea flowers: effect of experimental temperatures on drying kinetics,bioactive compounds and quality attributes

The drying process is important for the quality and value of tea flower products. In the present work, the effects of different hot air drying (HAD) temperatures from 60 to 120 °C on drying kinetics, bioactive compounds (catechins, flavonol glycosides and triterpenoid saponins) and quality attributes (volatile compounds, colours and antioxidant properties) of tea flowers were systematically evaluated. The results showed that higher drying temperature resulted in a shorter drying time but with greater loss of bioactive compounds and quality attributes. Flowers subjected to HAD at 60 °C showed the highest bioactive contents and quality attributes of all HAD samples and the quality of HAD 60 °C samples were close to that of freeze-dried samples. Taking account of the production efficiency and energy consumption, the tea flowers dried at 60 °C for 180 min was preferred. These findings provide a guide for the processing of tea flowers with the aim of improving the overall quality of the product.     

Characterisation of osmotically dehydrated papaya with further hot air drying and microwave vacuum drying

Papaya was subjected to osmotic dehydration (OD) prior to hot air drying (HA; 70 °C) and microwave vacuum drying (MVD; 3.75 W g^?1 and 13.3 kPa). An increase in immersion time in a sucrose solution [65/100 g (w/w)] at 40 ± 2 °C from 0 to 4 h decreased moisture content from 7.5802 to 1.2215 kg water kg dry solid^?1. During HA and MVD, effective moisture diffusivity was in the range 7.09 × 10^?8 to 9.13 × 10^?8 m² s^?1 and 2.85 × 10^?6 to 3.50 × 10^?6 m² s^?1, respectively, depending on immersion time. The hue angle of HA samples was 0.83–0.91, whereas that of MVD samples was 48.55–50.32. Both drying methods decreased springiness. Porosity was clearly observed in MVD samples. Rehydration rate was enhanced by increased immersion time and MVD (P ≤ 0.05). From preference mapping, MVD samples were more preferable than HA samples. Moreover, MVD samples with 1–3 h OD were more preferable than those with 4 h OD.     

Effect of vacuum‐drying,hot air‐drying and freeze‐drying on polyphenols and antioxidant capacity of lemon (Citrus limon) pomace aqueous extracts

The aim of this study was to investigate the effect of freeze‐drying, hot air‐drying and vacuum‐drying at 70, 90 and 110 °C, on dried lemon pomace polyphenols and antioxidant capacity. The total phenolic content and antioxidant capacity were higher in lemon pomace dried by hot air or under vacuum than those dried by freeze‐drying and increased as the temperature increased. The highest total flavonoid content was recorded in the pomace dried under vacuum at 70 and 90 °C. Lemon pomace dried by freeze‐drying had the highest neohesperidin content, whereas pomace dried under vacuum at 70 °C had the highest rutin and p‐coumaric acid content. The highest gallic acid content was recorded in the pomace dried by hot air at 110 °C. The results of this study indicate that drying technique should be carefully selected according to the bioactive compounds aimed to be extracted.     

Microwave drying of pine and spruce

Drying rates and power densities are determined for pine-and sprucewood when dried from green to 8% moisture content by microwave power. The process is controlled by measurements of internal wood temperature, internal vapour pressure and rate of moisture evaporation. Microwave power densities ranged from 25 to 78 kW/m³, microwave energy consumption from 365 to 760 kWh/m³. Internal wood temperatures up to 140 °C were used. Internal vapour pressure in the wood could rise to about 20 kPa without checking. Maximal drying rates of 0.20 to 0.45% moisture content per minute are possible to obtain when drying above fiber saturation (fsp). Below fsp the feasible drying rates ranged from 0.10 to 0.20% moisture content per minute. Spruce dried approximately 1.6 times faster than pine. No conditioning of the wood was necessary since the wood was free of stresses. The wood was free of checks but colour changes occured in the interior of some specimens.     

Moisture diffusivity of rough rice under infrared radiation drying

To design efficient infrared (IR) dryers for rough rice, it is important to understand the drying behavior of rough rice under IR heating. The objective of this study was to determine the moisture diffusivity of rough rice under IR heating followed by cooling. The effects of initial moisture content, rice temperature, drying bed thickness, tempering, and cooling methods on moisture diffusivity and moisture diffusivity coefficient were investigated. Samples of freshly harvested medium grain rice (M202 variety) with initial moisture content (MC) of 25.8, 31.2 and 33.8 g moisture/100 g dry solid were used. They were dried with IR radiation intensity of 5348 W/m², for six exposure times, 15, 30, 40, 60, 90 and 120 s. The tested drying bed thicknesses were single-layer, 5 mm and 10 mm. The unsteady diffusion equation based on Fick’s law and slope methods were used to describe moisture diffusivity. The results indicated that rough rice moisture diffusivities under IR heating and cooling were significantly affected by rice temperature and tempering treatment, respectively. High heating rate and moisture diffusivity were achieved with IR heating. It took only 60, 90 and 120 s to achieve about 60 °C rice temperature with corresponding moisture diffusivities of 4.8 × 10⁻⁹, 3.6 × 10 ⁻⁹ and 3.4 × 10⁻⁹ m²/s during heating for drying bed thicknesses of a single layer, 5 mm and 10 mm, respectively. The moisture diffusivity coefficients during heating and cooling of IR dried rice with tempering were much higher than those of convective drying, which reflected the high drying rate of the IR drying method.