Microwave-assisted Vacuum Frying Research Articles

Microwave-assisted vacuum frying of durian chips: Impact of ripening level on the drying rate, physio-chemical characteristics, and acceptability

The microwave assisted vacuum frying (MWVF) of Durian cv. Monthong was performed to investigate the effect of microwave power levels (400, 480, and 560 W) and ripening stages (1 Day, 2 Days, 3 Days, and 4 Days after harvesting) on the kinetics of the durian chips. The physio-chemical properties, the specific energy consumption (SEC) and product acceptability using sensory evaluation were also determined at 110 °C and absolute pressure of 8 kPa. At the higher microwave power, the frying time was reduced leading to a lower SEC. Moreover, it also resulted in decreasing oil absorption, decreasing shrinkage, and increasing porosity. In addition, more ripeness in durians led to longer frying time, increased oil uptake, but also produced a more porous structure and higher crispiness. Furthermore, using the 7-point hedonic scale test, the sensory evaluation revealed that the chips from the more ripened durian had the higher overall acceptability score.

Reduction of oil uptake with osmotic dehydration and coating pre-treatment in microwave-assisted vacuum fried potato chips

Microwave-assisted vacuum frying (MVF) was reported to improve the processing efficiency with the microwave heating method, while the oil uptake of products also needs to be reduced to enhance the overall quality. In this research, the effectiveness of osmotic dehydration and coating pre-treatment on reducing the oil absorption of MVF potato chips were evaluated with the verification of empirical models. Meanwhile, the effects of different pre-treatment on dielectric properties, moisture loss kinetics, texture, and color of MVF samples were analyzed. Results suggested that the oil uptake of MVF products was reduced by 16.6%–31.4% and 27.8% with osmotic dehydration pre-treatment in 1%–5% NaCl and 2.5% MSG solution, which is related to the enhanced moisture removal induced by the dielectric property improvement. The coating pre-treatment with 25% maltodextrin, 1.0% CMC-Na, and 1.5% chitosan had no negative effect on the dielectric properties and the moisture loss rate of samples during frying. While the oil absorption of MVF products was reduced by 53.5%, 36.8%, and 15.2% respectively due to the colloidal layer barrier formed by the coating pre-treatment. The empirical model provided better fits for the oil absorption process of MVF samples with osmotic dehydration pre-treatment, while it is not applicable to the coating pre-treatment. The hardness and color of MVF products was generally improved by the osmotic dehydration and coating pre-treatment. The osmotic dehydration and coating pre-treatment can be utilized as an alternative de-oiling method for MVF potato chips, but the law and mechanism of reducing the oil uptake are differs.

Water loss and partitioning of the oil fraction of mushroom chips using ultrasound-assisted vacuum frying

Sonication and microwave treatments for vacuum frying (VF) were studied to achieve the optimal frying conditions and improve the quality of fried products. Button mushrooms were used as a raw material. VF, microwave-assisted vacuum frying (MVF), ultrasound-assisted vacuum frying (UVF), and microwave combined with ultrasound VF (UMVF) techniques were used to produce the mushroom chips. Moisture content, oil partitioning coefficient (Kp), dielectric properties (DP), water activity (aw), and temperature distribution of chips were measured and compared among different frying methods. The UMVF increased the moisture evaporation rate and reduced the oil content of chips compared to other treatments. The Kp of UMVF was 0.069, whereas, for UVF, MVF, and VF, it was 0.041, 0.050, and 0.034, respectively, indicating that sonication could reduce oil penetration into the product. Odor profile analysis using an e-nose suggested that the sonicated chips had the most acceptable flavor parameters. The treatments did not significantly affect the aw, which ranged from 0.58-0.37. Whereas, the DP were enhanced. The UMVF process was shown to be a viable technology that could be used for frying to obtain high-quality products.

Low temperature vacuum frying of edamame assisted by ultrasound and microwave: Effects on the kinetics of oil and product storage properties

Ultrasonic microwave-assisted vacuum frying (USMVF) process was investigated to achieve better process efficiency and shorten the frying time and improve the quality of fried edamame at lower frying temperature. Kinetics of oil uptake in vacuum frying (VF), microwave-assisted vacuum frying (MVF) and USMVF samples was investigated. It was studied applying an empirical kinetic model in order to fit the oil content during frying. The first order model fitted properly the values of oil uptake during VF, MVF, and USMVF. For all the studied conditions of the model, the specific rate increased with the application of microwave and ultrasound and frying temperature, however the equilibrium oil content decreased with the application of microwave and ultrasound and frying temperature. The USMVF samples are the least temperature sensitive with an activation energy of 15.92 kJ/mol, while for MVF and VF it was 18.80 kJ/mol and 20.76 kJ/mol. The changes in moisture content, oil content, water activity, and vitamin C and chlorophyll retention of USMVF edamame at selected storage temperatures (0, 10, and 25 °C) were studied during a storage period of 6-months. Vitamin C and chlorophyll content retention was 72% and 80%, at the storage temperature of 10 °C and, 54% and 73% at 25 °C respectively.

A hybrid vacuum frying process assisted by ultrasound and microwave to enhance the kinetics of moisture loss and quality of fried edamame

The characteristics of fried edamame were investigated in a newly designed vacuum frying assisted by ultrasound and microwave (USMVF) equipment to get better frying efficiency, shorten the frying time and improve the quality of fried edamame at low frying temperature in this work. Three frying temperatures (80, 90 and 100°C) were comparatively analyzed in USMVF, microwave-assisted vacuum frying (MVF) and vacuum frying (VF). The USMVF remarkably enhanced the moisture diffusivity and moisture loss than MVF and VF at each frying temperature (80, 90 and 100°C). The values of moisture diffusivity and activation energy were in between 2.014–3.823×10−9m2/s and 22.57–20.07kJ/mol, respectively. Ten distinct mathematical models were applied to explain the dehydration kinetics of fried edamame and the most suitable model found was Midilli model. The drying data (moisture ratio versus time) were successfully fitted to the Midilli model. The energy consumption in USMVF decreased, diminishing by 28–39% depending on the frying temperature used in this work. The oil content and water activity of fried edamame was also reduced in the USMVF compared to the samples treated with MVF and VF. The color and texture (crispness), chlorophyll and vitamin C of fried edamame were also significantly improved in the USMVF.

Co-influence of ultrasound and microwave in vacuum frying on the frying kinetics and nutrient retention properties of mushroom chips

The frying kinetics (moisture loss rate and oil uptake rate) of an innovatively designed ultrasound and microwave-assisted vacuum frying (UMVF) system was investigated and the possibility of UMVF for reducing the nutrient losses during frying were evaluated in this work. The white button mushroom was the tested sample in this study. The chips were fried into two frying temperatures (80 and 90 °C), three different frying processes, vacuum frying (VF), microwave vacuum frying (MVF), and UMVF at a fixed vacuum pressure (12 ± 1 kPa). The first-order kinetic model was used for the mass transfer (moisture loss and oil uptake). Concerning the fitting performances, the logarithmic model and Pedrischi model showed the best-fitted model for moisture loss rate and for oil uptake respectively. Combining ultrasound and microwave in VF, the calculated moisture diffusivity rate was increased from 1.599 × 10−10 to 2.769 × 10−10 m2/s and oil uptake rate was decreased from 0.0121 to 0.0059 s−1. Total oil content (TOC) of fried mushroom chips (FMC) was quantified into two segments, surface oil (SO), and structure oil (STO) at a different time interval during frying. STO had the highest fraction of TOC and results revealed that UMVF had significantly low level of STO, which means UMVF helped to reduce the oil absorption during frying. In order to consider the nutrient retention values, UMVF exhibited the highest nutrition retention values. The exponential spectra of LF-NMR clearly revealed the water–oil distribution of FMC.

Dielectric properties of carrots affected by ultrasound treatment in water and oil medium simulated systems

The ultrasound treatment of vegetables can damage their tissue structure and release water and soluble solids altering the dielectric properties of the material. Changes in the dielectric properties will influence the microwave processing of ultrasound pretreated material. In order to investigate the effect of ultrasound pretreatment on dielectric properties, carrots were ultrasonicated in simulated water and oil systems. Microwave heating and microwave-assisted vacuum frying of carrot slices were also completed to explore the relation between dielectric properties of microwave pretreated samples and microwave absorption.Ultrasound of carrots in water simulated system showed that ε′ and ε″ of carrots tended to decrease with the increase of ultrasonic power (from 480 W to 640 W) and time (from 10 min to 30 min). Ultrasound treatment of carrots in salt solutions increased ε′ and ε″ of carrots. The combined pretreatment of microwave blanching with ultrasound in salt solutions increased ε″ (from 19.72 to 29.90). Conversely, in oil simulated system, the ε′ and ε″ of carrots also decreased as the ultrasonication power and time increased. Besides, the dielectric properties decreased as the temperature of oil medium increased from 35 °C to 75 °C. With improved dielectric properties, the dehydration rate during frying of carrot increased due to the enhanced microwave absorption. Therefore, the combined pretreatment of microwave blanching with ultrasound in salt solutions largely improved the dielectric properties of carrots, and reducing the required time of microwave vacuum frying.

Effect of low‐temperature vacuum frying assisted by microwave on the property of fish fillets (Aristichthys nobilis)

AbstractThis study investigated the effect of microwave‐assisted vacuum frying (MVF) on the processing of bighead carp fish fillets (Aristichthys nobilis, FF) at low temperature (90 ± 2°C) and at the same vacuum degree (0.085 ± 0.002 MPa). FF were fried with vacuum frying (VF) and MVF methods at different power levels (800, 900, and 1,000 W). Parameters were used to evaluate the effect of various VF conditions on the processing of fried FF, including moisture content, oil content, color parameters (L*, a*, b*, ΔE*), texture (hardness), also scanning electron microscopy and sensory evaluation of fried FF were carried out in our study. The application of MVF significantly increased the water evaporation rate. Oil content of the fried FF reduced significantly at lower power levels (800 and 900 W), producing with more well‐distributed pores, thinner fiber interval and more desirable outlooks. Higher microwave power (1,000 W) during MVF resulted in faster moisture removal, brighter the products. Results of this study indicated that MVF is an alternative frying method for the fried FF to maintain good quality.Practical applicationsMicrowave‐assisted vacuum frying (MVF) can significantly reduce the oil content in the fish fillets on the premise of ensuring the good appearance and texture of the products, compared with the traditional frying at normal atmospheric pressure and vacuum condition. It could be applied to other aquatic products and meat products in further study. With deepening of research on microwave technology and the development of microwave instruments, MVF technology will have wide application and development prospects.

Ultrasonically enhanced low-temperature microwave-assisted vacuum frying of edamame: Effects on dehydration kinetics and improved quality attributes

Using ultrasound (US) at microwave-assisted vacuum Frying (MVF) program was investigated to acquire better process efficacy and bodily high-quality attributes of fried edamame. Different power degrees of US (0, 150, 300, 600 W) and temperature (80, 90, and 100 °C) were utilized in a constant microwave power and frequency of 1000 W and 28 kHz during ultrasound and microwave-assisted vacuum frying (USMVF) process. Ten different mathematical models were employed to describe dehydration kinetics of the fried edamame, and nonlinear regression analysis was used to determine model parameters. Concerning fitting performance, the most suitable model was the two-term model. Drying kinetics, effective moisture diffusivity (De), activation energy (Ea), and physical properties of fried samples were evaluated in this newly designed USMVF equipment using different ultrasound power to the studied temperature range. By increasing the US power level, the calculated De increased from 1.947 × 10−9 to 4.742 × 10−9 m2/s. The results have revealed that the Ea of this fried edamame decreased significantly with increasing the US power level. The USMVF process at every frying temperature increased the drying kinetics and De when compared to the non-USMVF process. The USMVF samples always gave lower oil content and water activity in contrast to the non-USMVF samples. The color and texture properties of fried edamame were significantly improved and higher the US power level in the USMVF produced a better progress. Vitamin C and chlorophyll retention of fried edamame was highest in US600MVF process.

Effects of ultrasound pretreatments on the quality of fried sweet potato (Ipomea batatas) chips during microwave‐assisted vacuum frying

AbstractThe research was focused on the quality of sweet potato chips fried by microwave‐assisted vacuum frying (MVF) pretreated by ultrasound. Fresh sweet potato slices were pretreated at two different ultrasonic conditions: (1) ultrasound power of 150, 300, and 450 W for 20 min and (2) ultrasound power of 300 W for 10, 20, and 30 min. The pretreated samples were then fried by MVF. The dielectric properties, drying time, moisture content, oil uptake, texture, color, and microstructure profiles of the fried sweet potato chips were measured to determine the effects of ultrasound pretreatments on the quality of the fried sweet potato slices. This study found that the dielectric properties of the fresh sweet potato slices was significantly (p < .05) changed by ultrasound pretreatments. The moisture content and oil uptake of the fried sweet potato chips was reduced constantly by increasing the ultrasound pretreatments power and prolonging the processing time. The stronger ultrasound power and the longer processing time resulted into a crispier texture property of the fried sweet potato chips. However, the strong ultrasound power level and the prolonged processing time also caused the negative effect on the color preservation and cell integrity of fried samples. In conclusion, a proper ultrasound power level and time have to be selected to produce fried sweet potato chips with less oil uptake, crisper texture, and better appearance.Practical applicationsUltrasound pretreatments have great potential to improve the quality of fried food products. Ultrasound pretreatment before frying is a novel method for fabricating food products with healthier attributes, better appearance, more natural color and less frying time. The research found that, ultrasound pretreatments with proper ultrasound power level and processing time can produce higher quality products and shorten frying time.

Effect of ultrasound and microwave assisted vacuum frying on mushroom (Agaricus bisporus) chips quality

The effect of ultrasound on frying rate and product quality of fried mushroom chips (FMC) was investigated using microwave assisted vacuum frying (MVF). To determine the effectiveness of ultrasound during frying at different microwave power levels (800, 900 and 1000 W) and different frying temperature (80, 85 and 90 ℃), quality parameters (moisture loss rate, oil uptake rate, texture, color and microstructure) of the FMC obtained from vacuum frying (VF), MVF and ultrasound assisted microwave vacuum frying (UMVF) were analyzed and compared. It was found that UMVF accounts for the highest moisture loss rate with the increase of microwave power and frying temperature. Considering the oil uptake rate, UMVF could reduce oil content by 16–20% compared to VF and MVF. UMVF chips also had better texture and the most acceptable color characteristics among the frying techniques studied. The optimum condition of 1000 W and 90 ℃ achieved a higher moisture evaporation rate and lower oil content. Microstructure observations showed that the surface structures of UMVF fried samples were the smoothest and also showed less distorted cells. Based on the parameters evaluated, UMVF mushroom chips had the best-fried matrices as well as accelerated frying rate, lower oil uptake, improved texture and color.

Synergistic effects of ultrasound and microwave on the pumpkin slices qualities during ultrasound‐assisted microwave vacuum frying

AbstractThe aim of this study was to investigate the effect of the ultrasound‐assisted microwave vacuum frying (USMVF) technology on the quality parameters of pumpkin slices. Pumpkin slices fried for 15 min by different frying methods, such as USMVF, microwave‐assisted vacuum frying (MVF), and vacuum frying (VF), were compared in terms of parameters such as moisture content, oil content, color, texture, and microstructure. During the frying process, the effect of microwave powers (600 W, 800 W, and 1,000 W) and ultrasound powers (0 W, 300 W, and 600 W) was evaluated and compared with the conventional VF. The results showed that the application of ultrasound lowered the moisture content significantly (p < .05) in comparison to MVF and VF samples. The application of ultrasound also positively affected the oil content (low oil absorption) and texture (better crispness) of USMVF samples. Cellular structure of pumpkin chips was also preserved well when ultrasound‐assisted frying process. Color was not significantly influenced by applying ultrasound. In summary, the microwave and ultrasound applied in the VF process showed a synergistic effect in promoting the quality parameters of pumpkin chips.Practical applicationsThe results showed that the application of ultrasound lowered the moisture content significantly in comparison to microwave‐assisted vacuum frying and vacuum frying (VF) samples. The application of ultrasound also positively affected the oil content (lower oil absorption) and texture (better crispness) of ultrasound‐assisted microwave vacuum frying (USMVF) samples. Microstructure of pumpkin chips was also preserved well when ultrasound‐assisted frying process. Color was not significantly influenced by applying ultrasound. In summary, the microwave and ultrasound applied in the VF showed a synergistic effect in promoting quality parameters of pumpkin chips.

Enhancement of water removing and the quality of fried purple-fleshed sweet potato in the vacuum frying by combined power ultrasound and microwave technology

The combination of ultrasound and microwave in vacuum frying system was investigated to achieve higher drying efficiency and quality attributes of fried products. Purple-fleshed potato were used as test specimen and different power levels of microwave (0 W, 600 W, 800 W) and ultrasound (0 W, 300 W, 600 W) during vacuum frying. Drying kinetics, dielectric properties, moisture state variation and quality attributes of fried samples were measured in a vacuum frying (VF), and an innovatively designed ultrasound and microwave assisted vacuum frying (USMVF) equipment. The USMVF process markedly increased the moisture evaporation rate and effective moisture diffusivity compared to VF process. The oil uptake was reduced by about 16–34%, the water activity and the shrinkage was lowered, the texture (crispness) and the color of fried samples were greatly improved. The higher ultrasound and microwave power level in USMVF made a greater improvement. The total anthocyanin levels and retention of fried purple-fleshed potato chips was the highest (123.52 mg/100 g solids and 79.51% retention, respectively) among all treatments in US600M800VF process. The SEM analysis revealed a more porous and disruption microstructure in USMVF sample.

Ultrasonic microwave-assisted vacuum frying technique as a novel frying method for potato chips at low frying temperature

The ultrasonic microwave-assisted vacuum frying (USMVF) was properly designed and tested as a novel frying technique for potato chips at low frying temperature in this work. The USMVF was carried out by the combination of ultrasound and microwave in the vacuum frying to shorten the frying time and improve the quality of products. Two frying temperatures (90°C and 100°C) were comparatively analyzed both in USMVF and microwave-assisted vacuum frying (MVF). Based on the analysis of drying kinetics and quality assessment, the USMVF markedly increased the moisture evaporation kinetics and effective moisture diffusivity, reducing 20–28% of the drying time compared with the MVF, especially at lower frying temperature. The oil uptake of fried potato chips was reduced in the USMVF with low frying temperature. The texture properties (crispness) and color of fried potato chips were greatly improved by the combination of ultrasound in MVF. The energy consumption in USMVF was also decreased compared to that in MVF, decreasing 20.4–24.7% depending on the frying temperature in this test. A more porous microstructure in USMVF samples was observed by SEM and helped to explain the effects of ultrasound. The drying data (moisture ratio versus time) were successfully fitted to the Logarithmic model.

Analysis of dehydration kinetics, status of water and oil distribution of microwave-assisted vacuum frying potato chips combined with NMR and confocal laser scanning microscopy

In this study, the dehydration kinetics, status of water and oil distribution of microwave-assisted vacuum frying (MVF) potato chips were analyzed combining with NMR and confocal laser scanning microscopy (CLSM). Results showed that the MVF markedly increased the moisture evaporation kinetics and effective moisture diffusivity compared to vacuum frying (VF). The higher microwave power level (1000W) used achieved higher moisture evaporation rate and higher effective moisture diffusivity, The Logarithmic model exhibited the best fit for the obtained data of MR versus frying time in the MVF. The NMR analysis showed the free water in the samples firstly evaporate and the linkage between water and structure of materials becomes tighter with the frying time. The total oil content, surface and structural oil content were all significantly lower in MVF samples than that in VF samples. The CLSM analysis confirmed that less oil adhere to the surface and less oil trapped in the structure in MVF slices. The surface morphology showed that there were less ruptured and damaged cells in MVF samples and helped to explain the reduction of oil content.

Low oil content potato chips produced by infrared vacuum pre-drying and microwave-assisted vacuum frying

ABSTRACTThe effects of vacuum infrared radiation (VIR) pre-drying on the microwave-assisted vacuum frying (MVF) potato chips were investigated to study its possibility of decreasing the oil content of fried potato chips. The moisture evaporation, oil content, texture, color, surface temperature, shrinkage, and sensory analysis of fried products were evaluated. Results showed that the VIR pre-drying significantly reduced the oil content in MVF products, a decrease from 22.38 to 13.49 g oil/100 g dry solid. The application of VIR pre-drying accelerated the dehydration rate, and increased the mechanical breaking force measured with a texture analyzer with 20–30 min pre-drying. The VIR pre-drying resulted in an increase in the total color change and the shrinkage of MVF potato chips. The sensory analysis showed that the proper duration of VIR pre-drying would achieve a higher consumers’ acceptance. Comparing with the current industrial applications, vacuum frying, and atmospheric deep-fat frying, the combined VIR and MVF technology would be an alternative frying method for producing healthier fried products with less oil content and high quality.

Effect of low temperature on the microwave-assisted vacuum frying of potato chips

ABSTRACTThe objective of this study was to investigate the effect of low temperature on the microwave-assisted vacuum frying of potato chips. A newly built, in-house, microwave-assisted frying machine was developed and used in this study. The effect of low temperature on the microwave-assisted vacuum frying of potato chips was investigated via comparing sample properties prepared with frying temperatures of 90°C, 95°C, and 100°C. The experience was taken at the same vacuum degree in every frying process. Parameters of included moisture content, oil content, color parameters (lightness, redness, and yellowness), and textures (hardness, crispness) were used to evaluate the effect of different frying temperatures on the microwave-assisted vacuum frying of potato chips. Results showed that with lower temperature in microwave-assisted frying, the rate of moisture evaporation of potato chips was slowed down and the time of the ending of frying was prolonged from 10 min with a frying temperature of 100°C to 14 min with 90°C and 12 min with 95°C. Meanwhile, the oil content in fried potato chips was increased with lower temperature in microwave-assisted vacuum frying. The breaking force of final products are not significantly (p > 0.05) affected in different frying temperatures of microwave-assisted vacuum frying. Also, the frying temperature of 100°C in microwave-assisted vacuum frying had better preservation of natural color than the lower frying temperature with prolonged frying time. Results showed that the temperature is one of the main factors that affect the quality of microwave-assisted vacuum frying of potato chips and the producer could find suitable temperature conditions according to experience.

Effect of Microwave-Assisted Vacuum Frying on the Quality of Potato Chips

We investigated the applicability of microwave-assisted vacuum frying in producing potato chips. Three microwave power levels (600, 800, 1000 W) were used for frying times of up to 360 s. The moisture loss and oil uptake histories were measured as a function of the microwave power levels. The textural crispness (breaking force) and color parameters (lightness, redness, and yellowness) were also measured as a function of microwave power levels and frying time. The application of microwave-assisted vacuum frying significantly increased the moisture evaporation and oil uptake rates in potato chips. At the same time, the amount of oil uptake was similar to that in vacuum-fried chips not assisted by microwave. The chips produced using microwave-assisted vacuum frying were crispier (lower breaking force), visually appealing, and could be produced in a shorter time.