Hot Air-assisted Radio Frequency Research Articles

Kinetic analysis and back propagation neural network model for shelf-life estimation of stabilized rice bran

To establish a general model for predicting shelf-life of stabilized rice bran, different samples with varying residual enzyme activity, water activity (aw), and packaging materials were used, and hot air assisted-radio frequency (HA-RF) heating was applied as stabilization method. Free fatty acids (FFA) were recorded during storage at different temperatures and kinetic analysis was conducted to compare the effects of different conditions on rice bran shelf-life. FFA content increased rapidly during storage, and higher aw and lipase (LA) activity corresponded to a higher FFA generation rate. Only the increase in FFA of samples with low LA activity (≤30 mg/g) and aw (≤0.3) conformed to Zero-order model, while that of other samples conformed to Fractional Conversion model. For the inhibitory effect of packaging materials on the generation of FFA, BOPP/Kraft-paper/PE > PA/PE > PET/PE > LDPE. A back propagation neural network (BPNN) model was also constructed to predict rice bran shelf-life, which employing LA activity, aw, packaging materials, and storage temperature as input parameters. The BPNN model trained by Levenberg–Marquardt achieved the best prediction performance, with coefficient of determination (R2) of 0.996 and root mean square error (RMSE) of 2.077. Rice bran packaged by BOPP/Kraft-paper/PE with LA activity of 20 mg/g and aw of 0.2 had the longest shelf-life of 147 d at 25 °C. This model is of great help in predicting the shelf-life of stabilized rice bran and guiding the development of rice bran stabilization process.

Influence of ultrasonic-assisted osmotic dehydration pretreatment on hot air-assisted radio frequency drying of bitter gourd

Bitter gourd is a versatile vegetable that brings health-promoting benefits to consumers. To maintain its high nutrition values and ensure year-round availability, proper post-harvest processes are essential for preserving its original properties. However, there is limited knowledge regarding how pretreatment methods impact the physicochemical properties of pretreated bitter gourd and the performance of subsequent hot air-assisted radio frequency drying (HARFD) process. In the present study, bitter gourd underwent osmotic dehydration (OD) and ultrasonic-assisted osmotic dehydration (UAOD) pretreatment with different ultrasound power levels (400, 800, and 1200 W). The physicochemical properties of the pretreated samples, such as mass transfer behavior, water migration status, dielectric loss factor, and others, were compared. The drying duration, energy consumption, and various quality attributes (e.g., color index, rehydration, nutritional compositions, antioxidant activity, etc.) of the HARFD dried products were also examined. The microstructure observations demonstrated that acoustic waves induced the structural changes and created microchannels. Additionally, physicochemical properties of the pretreated samples showed that OD and UAOD methods significantly facilitated water migration status and increased the dielectric loss factor. Compared to control and OD methods, three UAOD methods successfully reduced the drying duration by 7.9%–30.3% and total energy consumption by 5.8%–28.3% for the entire processing steps. Furthermore, UAOD methods improved the total phenolic content, total chlorophyll retention, DPPH and ABTS values of dried bitter gourds by 32.3%–36.7%, 12.6%–20.3%, 23.4%–31.6%, and 20.7%–26.3%, respectively, compared to the control methods. Overall, UAOD-400 W samples after drying exhibited improved quality characteristics, including reduced color difference, increased retention of bioactive compounds, higher rehydration ratio, and enhanced antioxidant capacity. This study underscores the effectiveness of UAOD application in improving both processing efficiency and quality of bitter gourds produced by HARFD.

Effects of hot air-assisted radio frequency stabilization of brown millet and millet bran: Enzyme inactivation, microstructure, nutritional quality, and storage stability

Brown millet (BM) and millet bran (MB) are rich sources of nutrients, but their storage is affected by rapid rancidity deterioration, which primarily due to the activity of lipase (LA) and peroxidase (POD). High moisture content and water activity also have adverse effects on rancidity. In order to inactivate enzyme activities and extend storage stability of BM and MB, hot air-assisted radio frequency (HA-RF) heating was applied in this study. BM was treated at 95 °C and 105 °C while MB was heated to 105 °C and 115 °C with various holding times. The effects on enzyme inactivation, microstructure, nutritional quality, and storage stability of the samples were investigated. The results showed that HA-RF treatment effectively reduced LA and POD activities in both BM (<13%) and MB (<10%); Low-temperature (95 °C for BM and 105 °C for MB) HA-RF treatment caused less damage to the structure of the samples and maintained the structural integrity of most starch and proteins, although the treatment significantly (p < 0.05) reduced free phenolic and flavonoid contents of the samples; Low-temperature HA-RF treatment had less impacts on main nutrients of BM and MB when compared to the high-temperature treatment (105 °C for BM and 115 °C for MB). HA-RF stabilization effectively improved the storage stability, and slowed down the increase in fatty acid value (FAV) and malondialdehyde (MDA) content during storage.

Effect of microwave and hot air radiofrequency treatments on physicochemical and functional properties of foxtail millet flour and its protein isolate

The current study investigated the impact of microwave (MW) and hot-air assisted radiofrequency (HARF) technologies on physicochemical characteristics of foxtail millet (FM) flour. Besides, the physicochemical characteristics of foxtail millet protein (FMP) from MW and HARF treated FM flour were also evaluated. Residual relative lipase activity (LA) (10.86%) was least at 15% moisture (w.b.) for two passes-28 min treatment in HARF, while the MW heating showed lower LA at 786.80W power level for 6 min (0.27%) and 4 min (8.17%). Peak viscosities of MW and HARF treated FM flour exhibited a decreasing trend compared to untreated. An increase was observed in emulsifying, and oil/water absorption properties of MW and HARF treated FMP in comparison with the untreated sample, while it was vice versa with the foaming properties, and protein purity. This changes can be attributed to the decrease in relative crystallinity and modifications in the secondary structural elements (i.e., increase in β-turn, and decrease in α-helix, β-sheets), as confirmed by FTIR and XRD analyses performed.

Investigation of Physicochemical and Textural Properties of Brown Rice by Hot Air Assisted Radio Frequency Drying

Investigation of Physicochemical and Textural Properties of Brown Rice by Hot Air Assisted Radio Frequency Drying

Hot air-assisted radio frequency drying of grated potato (Solanum tuberosum L.): Drying behavior and the associated effect on characteristics of potato flour.

In this study, drying of grated potato in a hot air-assisted radio frequency system (HA-RF) and the associated effects on the final potato flour quality were studied. The drying behavior of the grated potatoes at different electrode distances (70-90mm) and sample thickness (2-4cm) was investigated. The safe drying (without burning tendency) of the maximum amount of sample (1000g) in a reasonable drying time was carried out at 80mm of electrode gap and 4cm of sample thickness. HA-RF drying kinetics were studied and compared with hot air (HA) and radio frequency (RF) (without hot air) drying methods. HA-RF drying increased drying rate and shortened drying time by about 58% and 70% compared to HA and RF drying, respectively. The properties of the final potato flour obtained after HA-RF drying were also compared with those produced by RF, HA, and freeze drying. The flour obtained by HA-RF was superior to RF and HA dried samples with better retention of cellular microstructure and color. The drying method significantly affected the functional properties, thermal characteristics, pasting properties, and other characteristics of potato flours. PRACTICAL APPLICATION: HA-RF as an alternative drying technology was used for the first time to produce potato flour. The functional, thermal, and structural properties of the HA-RF dried product were compared with those dried by HA, RF, and freeze drying. The results of this study ensured very useful information for the use of potato flour obtained by different drying methods in the development of products with specific functional and rheological properties.

Thermal Inactivation Kinetics and Radio Frequency Control of Aspergillus in Almond Kernels.

Mold infections in almonds are a safety issue during post-harvest, storage and consumption, leading to health problems for consumers and causing economic losses. The aim of this study was to isolate mold from infected almond kernels and identify it by whole genome sequence (WGS). Then, the more heat resistant mold was selected and the thermal inactivation kinetics of this mold influenced by temperature and water activity (aw) was developed. Hot air-assisted radio frequency (RF) heating was used to validate pasteurization efficacy based on the thermal inactivation kinetics of this target mold. The results showed that the two types of molds were Penicillium and Aspergillus identified by WGS. The selected Aspergillus had higher heat resistance than the Penicillium in the almond kernels. Inactivation data for the target Aspergillus fitted the Weibull model better than the first-order kinetic model. The population changes of the target Aspergillus under the given conditions could be predicted from Mafart’s modified Bigelow model. The RF treatment was effectively used for inactivating Aspergillus in almond kernels based on Mafart’s modified Bigelow model and the cumulative lethal time model.

Hot Air-Assisted Radio Frequency (HARF) Drying on Wild Bitter Gourd Extract.

Wild bitter gourd (Momordica charantia L. var. abbreviata S.) is a kind of Chinese herbal medicine and is also a vegetable and fruit that people eat daily. Wild bitter gourd has many bioactive components, such as saponin, polysaccharide, and protein, and the extract is used to adjust blood sugar in patients with diabetes. The objective of this study was to investigate simultaneous hot air-assisted radio frequency (HARF) drying and pasteurization for bitter gourd extract, and then to evaluate its effects on blood sugar of type II diabetic mice. The results showed that the solid–liquid ratio of the wild bitter gourd powder to water was 1:10 and it was extracted using focused ultrasonic extraction (FUE) for only 10 min with 70 °C water. Then, 1 kg of concentrated bitter gourd extract was mixed with soybean fiber powder at a ratio of 2:1.1. It was dried by HARF, and the temperature of the sample could reach above 80 °C in only 12 min to simultaneously reduce moisture content (wet basis) from 58% to 15% and achieve a pasteurization effect to significantly reduce the total bacterial and mold counts. Type II diabetic mice induced by nicotinamide and streptozocin (STZ) for two weeks and then were fed four-week feeds containing 5% RF-dried wild gourd extract did not raise fasting blood glucose. Therefore, the dried powder of wild bitter gourd extracts by HARF drying had a hypoglycemic effect.

Effects of hot air assisted radio frequency drying on heating uniformity, drying characteristics and quality of paddy

In order to solve the big challenge of cracking during paddy drying, this research revealed the application of hot air assisted radio frequency (HA-RF) drying technology on paddy grains based on its volumetric heating advantage. Drying characteristics and paddy quality were investigated at various combinations of air temperatures (50 °C, 55 °C and 60 °C), air velocities (0.5 m/s, 1.5 m/s and 2.5 m/s) and electrode gaps (100 mm, 110 mm and 120 mm). A comparison between the tempering-intermittent hot air (HA) drying was investigated to demonstrate the applicability of HA-RF drying on paddy grains. Increase in temperature and air velocity, while decrease in electrode gap resulted in increased average heating rate. The RF assistance significantly enhanced the drying rate of paddy grains and reduced drying duration and energy consumption by up to 62.5% and 42.9%, respectively, as compared to HA drying. A higher color and taste value, while a lower crack ratio (CR) without damage in starch granules of microstructure which caused formations of internal fissures were observed in HA-RF dried samples than HA dried ones. The findings of this study demonstrated that HA-RF drying is a good alternative of HA for industrial-scale drying of paddy grains.

Sequential‐combined solar energy assisted hot air and hot air‐assisted radio frequency drying to produce high‐quality dried whole apricots: An optimization study for process parameters

A solar energy assisted hot air (SAAD) and its sequential combination with hot air-assisted radio frequency drying (HARFD) system was used to dry whole apricots. Sequentially combined drying conditions (pre-drying temperature (50–70°C), pre-drying time (300–1,140 min), distance between electrodes (77–85 mm), and radio frequency drying time (270–690 min)) were investigated and optimized using the Box–Behnken design for minimum browning and surface color and optimum texture and moisture content. Under optimum conditions of 63.5°C pre-drying temperature, 895 min pre-drying time, 77 mm distance between radio frequency electrodes, and 385 min radio frequency drying time; the moisture content, amount of browning products, total color change, and hardness were 22.31% ± 2.82%, 0.69 ± 0.03 (A420/g dry weight), 37.65 ± 2.23, and 1,293.46 ± 61.96 N, respectively. Sequential combination of SAAD with HARFD system provided high-quality whole apricots while reducing the processing time. Novelty impact statement Sequentially combined solar energy assisted hot air and hot air-assisted radio frequency drying system was used for the first time to dry whole apricots and process parameters were optimized to produce high-quality products using response surface methodology. The results showed that the applied sequential drying technique is promising to produce commercially marketable apricots in a short time with acceptable quality characteristics. Consequently, the sequentially combined drying system could be an alternative technology in industry.

Hot air-assisted radio frequency drying of black carrot pomace: Kinetics and product quality

This research investigated the application of combined hot air and radio frequency drying technology on the drying efficiency and the quality of black carrot pomace (BCP). Electrode gap (8, 9 and 10 cm), thickness (2, 3 and 4 cm), weight (500, 750 and 1000 g) and compaction density (0.44, 0.66 and 0.88 g/cm3) were the parameters studied to determine the drying characteristics of the pomace by hot air-assisted radio frequency (HARF) drying system. Electrode gap of 8 cm and thickness of 2 cm, weight of 500 g and compaction density of 0.44 g/cm3 were identified as the ideal HARF drying conditions. HARF drying shortened the drying time by 39% compared to conventional hot air (HA) drying. Six different mathematical models were used for describing the drying characteristic of BCP. The effective moisture diffusivities were estimated by two approaches: the diffusion equation method and the method of slope for HARF drying and HA drying methods. HARF drying provided the dried products with better color, phenolic content, anthocyanin content and antioxidant capacity. Industrial relevanceBlack carrot pomace is an industrial waste left after the juice extraction from black carrot. The most common utilization way of this valuable by-product is to use it as animal feed. The reason behind this fact is the difficulties in drying of a high moisture bulk material in huge quantities produced in winter season. If it is not dried on time, it gets fermented and become useless for the separation of valuable components such as anthocyanin, pectin and fiber. So, a fast and efficient drying method and its characterization is essential for the utilization of this valuable by-product.

Radio frequency combined hot air (RF-HA) drying of tilapia (Oreochromis niloticus L.) fillets: Drying kinetics and quality analysis

Hot-air assisted radio frequency (RF-HA) heating was utilized for tilapia fillets drying to achieve rapid, uniform drying and improved sample physical properties. Effects of sample thickness (5, 8 and 10 mm) and with or without wrapping material (skin or gauze) were investigated under both HA and RF-HA drying treatments. The drying characteristics and quality parameters of tilapia fillets in hot air (HA) and RF-HA drying were then determined. Results show the drying rate of RF-HA drying is 1.1–1.4 times of that of HA drying for tilapia samples with different thicknesses. RF-HA dried samples are with higher rehydration rate and lower volume shrinkage rate, especially for fillets with larger thickness. The wrapped gauze did not show significant influence on the color of tilapia sample in RF-HA drying but improved the rehydration rate, while the samples with preserved fish skin resulted in a lower overall quality under both HA and RF-HA drying treatments. Page model and Henderson-Pabis models were suitable to be used describing the drying kinetics of RF-HA drying and HA drying tilapia, respectively.

Simultaneous hot-air assisted radio frequency drying and disinfestation for in-shell walnuts using a two-stage strategy

To develop an efficient simultaneous drying and disinfesting treatment for in-shell walnuts, a 2.4 kW, 27.12 MHz 50 Ω radio frequency (RF) system and a two-stage strategy were applied to investigate the effects of electrode gap, heating rate, and transition temperature on drying characteristics, disinfesting efficacy, and product quality. Peroxide value (PV) and free fatty acid (FFA) of walnuts with different packages during accelerated storage were also evaluated. The electrode gap of 160 mm for one-stage drying was selected for further investigations since it can ensure a short processing time (210 min), 100% mortality of C. cephalonica larvae, and eligible PV (0.183 meq/kg) and FFA (0.128%). The two-stage strategy with the heating rate of 5 °C/min and transition temperature of 55 °C shortened the drying duration to 170 min by nearly 20%, improved the heating uniformity index from 0.075 to 0.064, and reduced crack ratio from 43.75 to 26.04% significantly (P < 0.05) as compared to one-stage treatment. PV and FFA of vacuum and normally packaged walnuts still met the industrial standard after the 20-d accelerated storage. Therefore, the developed two-stage simultaneous RF treatment is recommended for further industrial applications owing to the shortened processing time and improved product quality.

Heating of milk powders at low water activity to 95°C for 15 minutes using hot air-assisted radio frequency processing achieved pasteurization

Salmonella persistence in milk powders has caused several multistate foodborne disease outbreaks. Therefore, ways to deliver effective thermal treatment need to be identified and validated to ensure the microbial safety of milk powders. In this study, a process of hot air-assisted radio frequency (HARF) followed by holding at high temperatures in a convective oven was developed for pasteurization of milk powders. Heating times were compared between HARF and a convection oven for heating milk powders to a pasteurization temperature, and HARF has been shown to considerably reduce the come-up time. Whole milk powder (WMP) and nonfat dry milk (NFDM) were inoculated with a 5-serotype Salmonella cocktail and equilibrated to a water activity of 0.10 to simulate the worst case for the microbial challenge study. After heating the sample to 95°C using HARF, followed by 10 and 15 min of holding in the oven, more than 5 log reduction of Salmonella was achieved in WMP and NFDM. This study validated a HARF-assisted thermal process for pasteurization of milk powder based on previously collected microbial inactivation kinetics data and provides valuable insights to process developers to ensure microbial safety of milk powder. This HARF process may be implemented in the dairy industry to enhance the microbial safety of milk powders.

Challenges of dry hazelnut shell surface for radio frequency pasteurization of inshell hazelnuts

Thermal inactivation kinetics (D and z values) of Salmonella and Enterococcus faecium in fresh hazelnut shell and kernel were determined. Aluminum pouches containing either 1.5 g hazelnut shell powder or 2 g of ground kernel inoculated with either bacterium at their original water activities (aw-shell = 0.91 ± 0.01, aw-kernel = 0.93 ± 0.01) were isothermally treated in a thermal death time (TDT) sandwich at 55, 60, 65, 70 and 75 °C for determining D values. A single layer inshell hazelnuts with one inoculated nut located at the center (cold spot) of a tray was subjected to hot air assisted radio frequency (HARF) heating in a 6-kW 27.12-MHz RF system with hot air temperature at ~75 °C for 10, 15 and 20 min. The log-linear model fits survival data of both Salmonella and E. faecium in hazelnut shell and kernel well. The D-values of both bacteria in hazelnut kernel were higher than those in hazelnut shell. Higher D-values of E. faecium demonstrated that it is a suitable surrogate for Salmonella in both hazelnut shell and kernel. There was a large variation between calculated (based on F-value) and experimental log reductions of Salmonella. Only 1.0 ± 0.1 log reduction of Salmonella was achieved in inshell hazelnut after 20 min of HARF heating. Because the RF pasteurization is a simultaneous drying process, the F-value methodology could not give an accurate and reliable lethality prediction due to the increased thermal resistance of Salmonella caused by moisture loss. Around one log increase in Salmonella inactivation was achieved after spraying 0.1% buffered peptone water (BPW) on inshell hazelnuts for the same RF treatment condition. While the water activity of the ground shell was 0.91 ± 0.01, the water activity of top surface layer of the shell where bacteria were inoculated for the RF treatment was 0.17 ± 0.01 before RF treatment. This very dry shell surface was the major factor for the deviation of calculated F-value from the observed microbial reduction in this RF microbial study. The dry shell surface creates a challenge for thermal inactivation of pathogens on inshell hazelnuts and other nuts with a similar shell structure. An efficient pasteurization protocol for inshell hazelnuts needs to be developed and optimized by combining surface disinfectants/salt solution and RF process conditions to enhance microbial food safety and quality of hazelnuts. This study provides valuable information and direction to the hazelnut industry for improving safety and quality of hazelnuts.

Pre-Drying Effect and Quality Change of Rough Rice under Hot Air-Assisted Radio Frequency Disinfestation Treatment

HighlightsHA-RF disinfestation treatment had better pre-drying effect of rough rice than that of HA treatmentHighest moisture loss (8.7%) was obtained for samples with highest IMC (39.6% d.b.)Initial moisture content (IMC) correlated negatively with milling quality of rough riceHA-RF can be used as a pre-drying method to partially reduce the moisture contentAbstract.Hot air-assisted radio frequency (HA-RF) is an environmentally friendly disinfestation method, which can completely control the insects and meanwhile maintain quality of rough rice. In this study, the pre-drying effect of HA-RF disinfestation treatment of rough rice with different initial moisture contents (IMCs) (16.7%, 24.8%, 34.7%, and 39.6% d.b.) was investigated along with associated quality change. HA-RF treatments had better pre-drying effect of rough rice with various IMCs than that of hot air (HA) treatment and larger electrode gap obtained lower moisture removal. IMCs of rough rice also influenced the moisture removal for HA-RF treatments, and the corresponding moisture loss were 4.3%, 5.3%, 6.1%, and 8.7% for the treated rough rice with IMC of 16.7%, 24.8%, 34.7%, and 39.6%, respectively. More quality loss was observed for the rough rice with higher IMC, especially for broken rate, fissure, and water uptake ratio. HA-RF treatment had no influences on total phenolic acids, protein, and fat contents, but amylose and vitamin E contents were affected. Non-milled rice treated by HA-RF had an obvious decrease in the lightness (L*) except for the samples with highest IMC (39.6%). RF disinfestation treatment can be used as a pre-drying method to partially reduce the moisture content (MC) of rough rice. Keywords: Disinfestation, Moisture content, Pre-drying, Quality, Rough rice.

Computational modelling of survival of Aspergillus flavus in peanut kernels during hot air-assisted radio frequency pasteurization

In recent years, radio frequency (RF) heating is getting popular as an alternative pasteurization method for agricultural commodities and low moisture foods. Computer simulation is an effective way to help understand RF interactions with food components and predict temperature distributions among food samples after RF treatments. In this study, a computer model based on Joule heating and thermal inactivation kinetic of A. flavus was established to predict both temperature distribution and microbial reduction among peanut kernels after RF processing. For the process validation, three 2-g peanut samples inoculated with 40 μL A. flavus were placed at three representative locations among 2.17 kg peanut kernels and subjected to various processing conditions in a 27.12 MHz, 6 kW RF heating unit together with hot air system. Results showed that the average difference of the sample temperature and microbial reduction between simulation and experiment was small with RMSE values of 0.009 °C and 0.012 °C, and 0.31 log CFU/g and 0.42 log CFU/g for peanut moisture contents of 7.56% and 12.02% w. b., respectively. Nonuniform RF heating resulted in the least lethality of A. flavus at the cold spot. The validated computer model was further used to estimate microbial reduction distributions at other target temperatures based on predicted temperature profiles. This computer model may help design the RF pasteurization protocols for peanut kernels without extensive experiments in food industry.

Development of effective drying strategy with a combination of radio frequency (RF) and convective hot-air drying for inshell hazelnuts and enhancement of nut quality

Drying characteristics of combined radio frequency (RF) and hot-air (HA) were investigated for inshell hazelnuts (Corylus avellana L.), which have air-gap between kernel and shell (shell, kernel, and air-gap between them). Inshell hazelnuts were subjected to HA, HA followed by RF (HAFRF), RF followed by HA (RFHA), and HA assisted RF (HARF) drying (simultaneous process). Fiber optic sensors were used to monitor temperature profiles for both hazelnut kernels and shells at three representative locations (center, edge, and corner) in a tray in 6-kW 27.12-MHz RF system with or without HA (~75 °C). RF heating resulted in higher kernel temperature than shell and was effective to remove kernel moisture. When RF heating was applied during or before HA drying, energy efficiency, drying efficacy, and nut quality were enhanced. This study provided a better understanding of drying characteristics of combined RF and HA process and suggested efficient RF-implemented drying strategies for inshell hazelnuts.

Hot air-assisted radio frequency heating for stabilization of rice bran: Enzyme activity, phenolic content, antioxidant activity and microstructure

Stabilization treatment of rice bran (RB) for reducing enzyme activity and improving storability is a key step to develop its value-added utilization. Hot air-assisted radio frequency (HA-RF) heating was investigated as a stabilization method for RB, and associated quality attributes were evaluated and compared with samples subjected to extrusion stabilization. Results showed that two HA-RF stabilization treatments (low-temperature HA-RF: 100–105 °C, 15 min; high-temperature HA-RF: 110–115 °C, 6 min) reduced lipase and polyphenol oxidase activities to 20–30% of fresh RB. HA-RF stabilized RB was darker than that of fresh RB. HA-RF stabilization had no significant (p > 0.05) effect on protein, lipid, total tocotrienol and total tocopherol contents, and fatty acid composition, but reduced free phenolic content of RB. HA-RF stabilized RB also showed higher free flavonoid content, higher antioxidant ability, and less damage to the microstructure than extruded RB. This study provides useful information for making HA-RF heating as an industrial stabilization method for RB.

Hot Air-Assisted Radio Frequency Stabilizing Treatment Effects on Physicochemical Properties, Enzyme Activities and Nutritional Quality of Wheat Germ

Wheat germ (WG) is a nutritional milling byproduct of wheat with short shelf-life. This study investigated hot air-assisted radio frequency (HA-RF) stabilizing treatment of WG. Physicochemical properties, enzyme activities and nutritional quality of HA-RF stabilized WG were evaluated and compared with WG stabilized by fluidized bed heating. Results indicated HA-RF heating to 100 °C with 15-min holding at 100–105 °C or heating to 110 °C with 6-min holding at 110–115 °C reduced lipase activity to about 10%. HA-RF inactivation of lipase, peroxidase, polyphenol oxidase and lipoxygenase was more effective in WG with initial moisture content of 14.5% or 20.0%, but less effective in WG with moisture content of 10.0%. For oils extracted from HA-RF stabilized WG with moisture content of 14.5%, peroxide and acid values were stable after storing at 25 °C for 3 days. After both HA-RF and fluidized bed stabilizations, color of WG and WG oils became darker, lipid content increased and reducing sugar content decreased, while extraction oil yield and protein content had no significant change (p > 0.05). HA-RF heating had no influence on α-tocopherol content, but fluidized bed stabilization decreased it from 299.42 mg/kg to 236.73 mg/kg. HA-RF heating had no distinct effects on amino acid and fatty acid composition. This study indicated that HA-RF heating had great potential in WG stabilization.