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As an important research aspect in food industry, fried products possessing both low oil content and good appearance still poses a challenge. The processing parameters of vacuum fried shiitake mushroom slices were investigated using response surface methodology. Frying temperature, vacuum pressure and frying time were studied as independent variables due to their significant effects on the quality attributes. Temperature and vacuum pressure presented the opposite effects on the four responses, for instance, the enhancement of fracturability and sensory performance and the reduction of color difference and oil absorption were observed as the temperature decreasing and vacuum pressure increasing. However, frying time generally induced all the response values increased among the testing range but only fracturability decreased after 28 min. In the optimal vacuum frying condition of frying temperature 105 °C, vacuum pressure −0.085 MPa and frying time 27.3 min, the total oil content and sensory values were observed to be 33.54% higher and 18.78% lower than those in conventional frying condition. The reason was supposed to be stronger surface-related phenomenon due to faster moisture loss and the resistant structure formation as starch gelatinization in vacuum frying environment. It provided a feasible optimized vacuum frying process for low-oil content and comprehensive acceptability fried shiitake slices. • Independent variables showed significant effects on shiitake quality attributes. • Temperature and vacuum pressure presented opposite effects on the responses. • Mechanism of low oil in vacuum may relate with water loss and starch gelatinization. • Optimum frying conditions can produce a low-oil and more acceptable fried mushroom. [ABSTRACT FROM AUTHOR]

Abstract The effectiveness of hybrid frying based on vacuum frying with application of ultrasound (USVF) and combined ultrasound and microwave (USMVF) enhancement was presented in this study. The ultrasound revealed significantly the "vibration effect", and the combination of ultrasound and microwave had a synergistic effect on the energy efficiency and quality attributes of vacuum fried potato chips, shortening the frying time by 36.4%–54.5% and improving the effective moisture diffusivity by 60.5%–144.5% with the ultrasound power levels ranged 300 W–600 W. The USMVF process was found to consume about 34.9%–48.3% less energy compared to that in VF. The oil uptake of vacuum fried potato chips was reduced by 27.4%–32.3%, the texture (crispness) and the color was greatly improved, and the volume shrinkage and water activity were diminished by the combination of ultrasound and microwave. The moisture loss kinetics and quality parameters were also improved markedly when higher ultrasound power was used. The SEM revealed a more porous microstructure in USMVF samples. The vacuum frying technology that combines both ultrasound and microwave found to be much more effective technology in terms of energy efficiency and product quality. Industrial relevance In recent years, the fruit-vegetable crisp produced by vacuum frying (VF) has been widely concerned due to natural color, superior sensory and nutritional quality. However, there are certain defects in the application of VF technology, such as backward heating method, low efficiency especially with low-temperature frying, relatively high oil uptake in products and the quality attributes of fried products need to be improved. One of the recommended methods to overcome the limitation of low-temperature dehydration is to utilize the synergistic effect of different energy, which providing the energy by a combination of several mechanisms, such as vacuum frying with microwave radiation, or with ultrasounds, which leads to a significant improvement in energy efficiency and quality attributes of fried fruits and vegetables. Focused on these problems, this research investigated the effects of low-frequency ultrasound and the synergistic effect of ultrasound and microwave on the efficiency and quality of vacuum frying with potato chips as experimental material. The effect of variable hybrid drying conditions was analyzed with different power levels of ultrasound. The application of ultrasound showed improve the moisture loss rate and quality attributes of vacuum fried products as a non-thermal technology. The combination of ultrasound and microwave in vacuum frying system achieved better energy efficiency, lower oil uptake, crispier, better shaped and colored products compared to the VF produced samples. The storage stability and safety of vacuum fried products also improved by the combined ultrasound and microwave. Thereby, the experimental results will contribute to the development of modern vacuum frying technologies of fruits and vegetables, which reduced the oil uptake and retained their high quality, with reduced process time and lower power consumption at much lower frying temperature. Highlights • The combination of ultrasound and microwave in vacuum frying system was investigated. • The USMVF increased the moisture evaporation kinetics and effective moisture diffusivity. • The increase of ultrasound power had positive effect to the energy efficiency and product quality. • The oil uptake of samples was reduced and the chips became crispier in USMVF compared to the VF. [ABSTRACT FROM AUTHOR]

In this study, deep fat frying, microwave frying, air frying, and vacuum frying processes were used to mitigate acrylamide (AA) and hydroxymethylfurfural (HMF) formation during the frying of French fries. The highest reduction of AA and HMF range was found in vacuum frying (61.42–81.14%), followed by air frying (59.2–78.7%), as compared to deep fat frying and microwave frying. Both these method samples also showed significantly (p < 0.05) lower browning index (BI) and CIE a* values. Principal component analysis (PCA) was used to visualize the effects of the different frying methods on AA and HMF content. Vacuum frying and air frying were found to be alternative frying technologies to minimize AA and HMF content in French fries. • Effect of deep fat, air, vacuum, and microwave frying on the formation of AA. • Air frying and vacuum frying both methods showed less oil absorption. • The advanced frying method improved the taste, color, and texture of french fries. • Reducing sugar, asparagine & browning index is strongly correlated with AA and HMF. [ABSTRACT FROM AUTHOR]

Vacuum fried carrot snacks were prepared using high pressure processing or freezing as pretreatment before the vacuum frying process. Physicochemical, organoleptic and antioxidant parameters were evaluated in order to determine the effect of pretreatment on the final product. The results showed that the use of high pressure and freezing pretreatments had significant effects on the final product. Both pretreatments caused cell modification, as observed from microstructural analysis. Pretreatment application helped in maintaining phenolic content and antioxidant capacity of the samples, effect which could be observed over storage. Freezing pretreatment increased crispness values of the samples, as compared to HPP-pretreated or control samples. On the other hand, freezing pretreatment also favoured oil absorption. The use of the proposed pretreatments (HPP or freezing) resulted in a feasible approach for improving the nutritional and organoleptic properties of vacuum-fried carrot snacks. Industrial relevance Vegetable consumption remains lower than the recommended intake by health authorities. One possible strategy to increase the consumption of vegetable is the development of snacks. Most of vegetable snacks in the market are made through drying. However, dried products are far from the textural, appearance and mouthfeel properties of deep-fried products. The use of vacuum frying is an option for the development of appealing and yet healthy vegetable snacks. Nevertheless, pre-treatments are required to provide adequate final texture. To this regard, most studies are focused on osmotic pre-treatments. This study demonstrated that freezing and HPP pretreatments can be successfully applied in order to obtain crispy carrot chips. Furthermore, the use of pretreatments helped to maintain phenolic content and antioxidant capacity of the snacks. [ABSTRACT FROM AUTHOR]

Demand for safe and nutritionally rich fried products is gaining a momentum among consumers, leading to the increased consumption of vacuum fried products. The impact of vacuum frying (VF)(110 °C, 40 kPa) on chemical composition of food, fatty acid profile, microstructure, oxidative stability and sensory attributes was assessed and differentiated with that of atmospheric frying(AF) (180 °C). The potato slices were fried in mustard and soyabean oil used repetitively for 25 h. The oil content of VF potato chips was lower (15.18%) than AF chips (18.98%), however water loss in AF chips was higher than VF chips by 1.63-fold. VF significantly prevented the PUFA degradation, minimizes transfatty acid (TFA) formation and maintain a low C18:2/C16:0 ratio as compared to AF. VF Chips fried in soyabean oil show an increase in TFA content from 2.15 to 2.63% and a decrease in PUFA from 51.57 to 45.16% as compared to AF chips where TFA content increased from 2.15 to 3.72% and PUFA shows a higher reduction from 51.57 to 37.69% at the end of 25 h of frying. This indicate that in AF, oil is safe for use upto 10 cycles of frying, while as in VF, the same oil can be used for upto 40 cycles of frying without quality deteoriation. Sensorial analysis revealed that VF chips retain a better colour, taste and flavour but were less crispy than that of AF chips. These findings validate the application of vacuum frying technology for the production of high-quality foods with lesser degradation of frying oil. Food manufacturers are now impelled by the health-conscious consumer base for the production of healthy food products. The toxic effect of foods fried in degraded oils on human health is now widely known and thus the production of safe fried foods is the need of hour globally. In this context, vacuum frying is the most feasible approach for the production of quality fried products retaining the natural colour, flavour, sensory and nutritional properties better than that of atmospheric frying. Vacuum frying causes the least degradation of fatty acid of the frying oil and the fried potatoes, producing healthy potato chips. Therefore, the oil used for vacuum frying have a greater shelf life and oxidative stability than atmospheric frying. However, the higher installation cost of vacuum fryer still limits its use in the street fried food market, where degradation of oil is more likely. Thus, for its widespread commercialisation in developing countries, steps should be taken both by government and manufacturing companies to reduce the installation costs. • Vacuum frying minimizes the PUFA degradation and minimize TFA formation compared with atmospheric frying. • Vacuum fried chips retained better nutritional parameters. • Vacuum fried chips show low oil content than atmospheric fried chips. • Oxidative stability of frying oils was higher in vacuum frying compared to atmospheric frying. • Vacuum frying technology produces high-quality foods with lesser degradation of frying oil. [ABSTRACT FROM AUTHOR]

Abstract: Starch gelatinization is a critical micro-scale phenomenon occurring during frying, which gets particular relevance during vacuum frying, where minimum conditions need to be fulfilled to get the required structure. The objective of this research was to understand the effect of water accessibility, temperature and vacuum level, in starch microstructural changes during heating in water and oil, in situ and in real time, using vacuum hot-stage microscopy. Potato starch was heated in water or in a pre-gelatinized corn starch solution, at different pressures (atmospheric, 6.5kPa, 30kPa). Also, a gluten–starch matrix immersed in oil was followed under the microscope. An increase in the heating rate as well as water inaccessibility increased the on-set gelatinization temperature. Under high vacuum no changes were observed, whereas under low vacuum, partial gelatinization occurred. Overall, this microstructural approach may help in explaining the high oil absorption of vacuum-fried formulated starchy products reported in previous studies. Industrial relevance: Vacuum frying is a novel and promising technique that allows obtaining fried products with a low amount of oil, making them healthier than atmospheric fried ones. So far most of the studies have focused on agricultural products, such as potatoes, which are already structured by nature, without focusing on fabricated/restructured products. This imposes a challenge since minimum conditions must be ensured to form structure during processing in this product category. In fact, vacuum fried restructured products have shown to increase their oil content compared to their atmospheric counterpart, probably due to lack of structure formation during processing. From this perspective, the understanding of the main microstructural changes of starch in formulated products during processing under atmospheric or vacuum conditions is of interest. Since, most of the structural changes occur at the micro-scale, process miniaturization using vacuum hot-stage microscopy seems to be a good approach. In accordance, the objective of this research was to understand the effect of water availability, temperature and vacuum level, in starch microstructural changes during heating in water and oil, in situ and in real time. Potato starch was heated in excess of water or in a pre-gelatinized corn starch solution, at different pressures. Also, a gluten–starch matrix immersed in oil was followed under the microscope. We found that an increase in the heating rate as well as water unavailability increased the on-set gelatinization temperature, which is a key process to reduce oil absorption. Further, under high vacuum no changes were observed, whereas under low vacuum, partial gelatinization occurred. The lower degree of gelatinization determined in vacuum-fried matrices compared to atmospheric fried ones, may explain the high oil absorption of formulated starchy products reported in previous studies, as a consequence of deficient structure development. The understanding of these properties could help the food industry to produce healthier low-fat formulated snacks. [Copyright &y& Elsevier]

Abstract: Vacuum frying was tested as an alternative technique to develop low oil content fried gilthead sea bream fillets. Three oil temperatures for vacuum frying (90, 100, and 110°C) were considered. For each temperature the times investigated were 1, 2, 3, 4, 5, 6, 8 and 10min. To compare the effect of vacuum frying to atmospheric frying on the characteristics of gilthead sea bream fillets and frying rate, treatment at 165°C was considered. The effect of oil temperature and pressure conditions on the drying process and oil absorption of sea bream fillets was investigated. Other product attributes such as shrinkage and colour were analyzed. Atmospheric frying (165°C) produces a greater decrease in the mass of the fillets than vacuum frying treatment. Compared with atmospheric frying, oil content of vacuum-fried fish fillets was lower. After ten minutes of treatment the values obtained for vacuum frying were 0.14±0.01goil/gdry solid, 0.18±0.02goil/gdry solid and 0.12±0.01goil/gdry solid for 90°C, 100°C and 110°C respectively and 0.27±0.01goil/gdry solid for traditional frying at 165°C. Atmospheric frying was the treatment that produced the greatest shrinkage in the fillets reaching values of 36.8% with respect to the fresh sample after ten minutes of treatment. For vacuum treatments shrinkage values ranged between 23.7% and 33.0% at 100°C and 110°C respectively after 10min of frying. According to the results, the vacuum treated samples became lighter, less greener and more yellow. Industrial relevance: Healthy products are a tendency in the international market. Vacuum frying offers some advantages that can include: the preservation of natural colour and flavours of the products due to low temperature and low oxygen content during the process (better than with conventional deep fat frying), and has less adverse effects on oil quality. The use of this technology on fish products can improve the problems of market saturation at the present time for some species like gilthead sea bream (Sparus aurata). [Copyright &y& Elsevier]

Moisture content plays a pivotal role in the kinetic modelling of the quality attributes during thermal processing of foods. Vacuum frying of mango chips, was chosen to demonstrate the applicability of this novel modelling approach that links a dynamic moisture model to models for changes in fat content, texture, and color. Results show that moisture loss is best described by an exponential model with an Ea of 40.0 ± 4.2 and 27.2 ± 2.3 kJ mol−1 for unripe and ripe mango respectively. The dynamic moisture content was linked to the fat content by a Gompertz model, and to the hardness by an exponential model. By using thermodynamic principles, the moisture model predicts the dynamic local product temperature that can be linked to the reaction rates of the consecutive color change reaction models. The integration of these models is a powerful tool in product and process optimization to produce high quality vacuum fried fruit products. Food moisture content changes during many thermal processing techniques but it also plays a pivotal role in changes of the quality attributes of foods. Quality change models were developed that integrate changes in the moisture content with changes in quality attributes. These models can be applied to produce a minimal fat content and low moisture content while getting a desired color change and/or to produce a specific texture characteristics. Moisture dependent models for quality changes are powerful tools for optimizing many other products and process. • The dynamic moisture content during drying influences other food quality attributes. • A model connecting moisture loss to other key quality parameters was developed. • Fat content and texture are directly related to the changes in moisture content. • Color changes depend on temperature, which is determined by the dynamic moisture. • Modelling of other processes with dynamic moisture changes is discussed. [ABSTRACT FROM AUTHOR]