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Deep fat fried food products have been considered as a vital dietary contributor to certain chronic diseases, including the risk of atherosclerosis, cancer and hypertension. Hence, many food industries are focusing on low fat fried products to attract consumers. In general, oil is absorbed during deep fat frying, and this century old process is used for preparing various kinds of fried food products such as potato chips, banana chips, savory snacks, etc. Vacuum frying, electric field frying and two-stage frying technologies have been developed as an alternatives to traditional frying. These two technologies are suitable for most fried products; however, they may not be suitable for sugar based fruits as they can lead to the formation of browning reactions, which are generally considered unacceptable. This review aims to cover recent work done in the area of vacuum frying and two-stage frying, including the role of pre-treatment and post-treatment novel methods. Additionally, emphasis has been given on recent innovations to improve the quality of vacuum and two-stage frying, particularly concerning the reduction of oil uptake in fried food products. [ABSTRACT FROM AUTHOR]

The purpose of this study was to optimize product yield and quality of the sweet potato chip manufacturing process in a pilot-scale industrial fryer using vacuum frying (VF) technology, response surface methodology (RSM), and artificial neural network (ANN) model. The variables, osmotic dehydration (OD) concentration, OD temperature, and VF temperature were designed to optimize the yield, oil content, and browning index (BI) of vacuum-fried sweet potato chips. Yield, oil content, and BI achieved optimal conditions for 52.46%, 10.65%, and 61.14 in RSM, and 53.52%, 11.58%, and 60.40 in ANN, respectively. Based on the statistical evaluation performance, the ANN model had a higher predictive performance than the RSM model. These findings highlight the high-quality pilot-scale manufacturing process along with a better statistical approach. Moreover, the optimized process can be used for the commercial production of vacuum-fried sweet potato chips. [ABSTRACT FROM AUTHOR]

Potato fries, a relatively an untapped food matrix for fortification, was fortified with iron using vacuum impregnation technique and impact of this fortification on quality attributes (structure, color, texture, flavor, acrylamide, sensory characteristics) of the product was assessed. Further, to reduce the dietary restraints of consumers for fried fries, fat reduction was achieved using vacuum frying. Ferrous ammonium sulphate hexahydrate was used as a fortificant to yield 3.15 mg iron from 30 g fries (RACC for snacks- Recommended Amount Customarily Consumed). Effect of iron fortificant level, blanching, vacuum and restoration time (independent variable) were evaluated on responses (iron impregnation level and firmness) of fries using box-behnken design of response surface methodology. Results showed that blanching time was the most significant variable affecting iron impregnation followed by iron concentration and vacuum time. Ferrous ammonium sulphate hexahydrate was found to be the most appropriate fortificant since reflecting the least colour and sensory changes in fries. A fortified raw potato fries when fried under vacuum, provided better retention of colour and reduced fat absorption (by 17.72%) with comparable crispiness (0.37 kg/sec vs 0.35 kg/sec), firmness (0.39 kg/sec vs 0.38 kg/sec), color (ΔE = 1.39) and sensory score (7.9 vs 8.1 on 9-point scale) with control fries. [ABSTRACT FROM AUTHOR]

Foods, rich in oil content, have been found to be a key dietary contributor of certain chronic diseases such as cardio-vascular diseases, hypertension, cancer, etc. Therefore, the market trends are shifting towards low-fat containing foods. Oil rich foods are generally fried products where oil is absorbed during frying process. Vacuum-frying has been identified as an alternative to traditional frying. It is also highly suitable for frying of sugar rich fruits which otherwise is not possible in traditional frying as it leads to browning of the end product making them unacceptable. This review is a compilation of recent research works done in the area of vacuum frying of fruits and vegetables and allied products and gives an insight to the physical and chemical changes occurring during vacuum frying of fruits and vegetables. The effects of pre-treatments, processing conditions as well as use of novel technologies in combination with vacuum frying on quality characteristics of products have also been discussed. Emphasis has also been given on future aspects of vacuum frying with respect to fruits and vegetables processing. [ABSTRACT FROM AUTHOR]

The study reveals effect of pre-treatments, i.e., partial drying (PD), partial drying + freezing (PDF) and freezing (F) on physico-chemical, structural and sensory quality of vacuum fried papaya chips (100 °C for 28 min at 13.33 kPa). Pre-treatments significantly (p < 0.05) influenced the quality parameters of vacuum fried papaya chips. Partial drying pre-treated sample showed significantly (p < 0.05) higher reduction in oil uptake, i.e., 19.61% (d.b.) besides retaining significantly (p < 0.05) higher total phenolics content (394.07 mg/100 g gallic acid equivalent) as compared to other samples. Ascorbic acid content was retained significantly (p < 0.05) high in untreated control samples (209.81 mg/100 g). Freezing pre-treatment was found better in retaining total flavonoids, total carotenoids and antioxidant activity. The SEM micrographs of papaya chips showed dense and shriveled structure due to partial drying pre-treatment, however, more porous structure was observed in freezing pre-treated sample as compared to control. Freezing pre-treated samples were also rated high on hedonic scale for their sensory parameters, i.e., colour, crispness, taste, mouth feel, appearance and overall acceptability, which were in agreement with instrumental CIE colour values, firmness and microstructural characteristics of samples. The percent moisture, fat, protein, total carbohydrate, and ash content of freezing pre-treated vacuum fried papaya chips was found to be 1.51 ± 0.13%, 23.68 ± 0.12%, 3.42 ± 0.14%, 67.64 ± 1.78% and 3.75 ± 0.08%, respectively. [ABSTRACT FROM AUTHOR]

Vacuum frying of fruits enables frying at lower temperatures compared to atmospheric frying, thereby improving quality attributes of the fried product, such as oil content, texture, retention of nutrients, and color. Producing high-quality vacuum-fried fruit is a challenge, especially because of the high initial water content of fruits that requires long frying times. Factors influencing vacuum-fried fruit quality attributes are the type of equipment, pre-treatments, processing conditions, fruit type, and fruit matrix. Pre-treatments such as hot air, osmotic drying, blanching, freezing, impregnation, anti-browning agents, and hydrocolloid application strongly influence the final quality attributes of the products. The vacuum-frying processing parameters, namely frying time, temperature, and vacuum pressure, have to be adjusted to the fruit characteristics. Tropical fruits have different matrix properties, including physical and chemical, which changed during ripening and influenced vacuum-fried tropical fruit quality. This paper reviews the state of the art of vacuum frying of fruit with a specific focus on the effect of fruit type and matrix on the quality attributes of the fried product. [ABSTRACT FROM AUTHOR]

Consumers like fried snacks, and taste, color, and texture are key aspects in their preference. However, during frying of foods some toxic compounds, such as furan and acrylamide, are produced. The objective of this work was to mitigate furan and acrylamide formation in potato chips, without affecting their main quality attributes, by using vacuum frying. To accomplish this purpose, potato slices were fried at atmospheric ( P 29.92 inHg) and vacuum conditions ( P 3.00 inHg), using equivalent thermal driving forces ( T − T = 50, 60, or 70 °C). Furan and acrylamide concentration, oil content, and texture of both atmospheric and vacuum-fried samples were determined. Vacuum-fried potato chips showed reductions of about 81, 58, and 28% of furan, acrylamide, and oil content, respectively, when compared to their atmospheric counterparts. Additionally, the texture was not affected ( p > 0.05) by changes in the pressure during frying. Results clearly showed that vacuum frying is an effective technology for furan and acrylamide mitigation in potato chips, since it reduces the content of both contaminants and preserves the quality attributes of fried snacks. [ABSTRACT FROM AUTHOR]

In the present work, the processing variables were optimized to retain betalain compound and their effect on quality attributes (oil content, breaking force and color) of fried beetroot chips. The beetroot slices were fried in lab scale vacuum fryer. Experimental design with temperature (86-153 °C), absolute pressure (1.3-9.7 kPa) and frying time (2.6-9.4 min) as independent variables which produced 20 different combinations, were studied using response surface methodology to study the effect of these variables on product responses. Multiple regression equations were obtained to describe the effects of each variable on product responses. Results predicted that optimum frying conditions namely temperature ranging from 101 to 110 °C, pressure ranging from 2.9 to 4.4 kPa and time 6.0 min required for preparing beetroot chips with oil content (Y) ≤ 15.7, breaking force (Y) ≤ 11.53, L* value (Y) ≥ 27.94, a* value (Y) ≤ 17.87, b* value (Y) ≥ 6.46, betalain content (Y) ≥ 13.05 (mg/l) and overall acceptability (Y) ≥ 7.5. Further results showed that traditionally fried beetroot chips contain 2.6 mg/l betalain, 19.68 N breaking force, 21.1 L*, 15.18 a*, 2.38 b*, overall acceptability 6.0 and 38.41 % oil content. [ABSTRACT FROM AUTHOR]

The objective of the research was to compare the effect of coating with sodium carboxymethyl cellulose, hot-air and vacuum microwave pre-drying on the physicochemical properties and sensory scores of vacuum-fried peas. The three pre-treatments prior to frying were shown to obviously reduce oil absorption in vacuum-fried peas. Among the three pre-treatments, coating with sodium carboxymethyl cellulose for peas produced the lowest oil content products (24.53 %), and the chlorophyll retention was 77.08 %. Vitamin C and breaking force for fried products with vacuum microwave pre-drying were 46.56 μg/100 g (db) and 8.64 N, which were significantly ( P ≤ 0.05) better than those of other treatments. However, fried peas treated by hot air pre-drying showed the highest breaking force and lowest chlorophyll retention. All the fried peas had water activity (A) values of less than 0.35, indicating that the products have a long shelf life. Sensory scores showed vacuum-fried peas treated by vacuum microwave pre-drying had the highest acceptability. [ABSTRACT FROM AUTHOR]

This paper explores the possibility of combining moderate vacuum frying followed by post-frying high vacuum application during the oil drainage stage, with the aim to reduce oil content in potato chips. Potato slices were initially vacuum fried under two operating conditions (140 °C, 20 kPa and 162 °C, 50.67 kPa) until the moisture content reached 10 and 15 % (wet basis), prior to holding the samples in the head space under high vacuum level (1.33 kPa). This two-stage process was found to lower significantly the amount of oil taken up by potato chips by an amount as high as 48 %, compared to drainage at the same pressure as the frying pressure. Reducing the pressure value to 1.33 kPa reduced the water saturation temperature (11 °C), causing the product to continuously lose moisture during the course of drainage. Continuous release of water vapour prevented the occluded surface oil from penetrating into the product structure and released it from the surface of the product. When frying and drainage occurred at the same pressure, the temperature of the product fell below the water saturation temperature soon after it was lifted out of the oil, which resulted in the oil getting sucked into the product. Thus, lowering the pressure after frying to a value well below the frying pressure is a promising method to lower oil uptake by the product. [ABSTRACT FROM AUTHOR]

Vacuum frying has gained a significant strategic importance for future fried food manufacturing since, due to the low-temperature processing, significant benefits such as the improvement of fried product safety and quality can be obtained. So far, all studies have focused on agricultural products, such as potatoes, which are already structured by nature, but none of them has included fabricated products. This imposes a challenge since minimum conditions must be ensured to form structure during processing. The objective of this work was to understand the role of water boiling point ( T) and processing temperature ( T) in structure formation, oil absorption, and most important quality attributes of starch-based products during vacuum frying. Fabricated products were made of a reconstituted blend of gluten (12 % d.b.) and wheat starch (88 % d.b.) in order to accurately control ingredients proportion. Samples were fried varying the T from 38 to 71 °C while keeping a thermal driving force of 70 °C (i.e., T − T = 70 °C). Another set of samples was fried varying the thermal driving force from 37 to 70 °C while maintaining a T of 71 °C. Results showed that a higher T favored the capacity of the matrix to form structure due to starch gelatinization in the presence of water and temperature, reducing the oil content of the fried products. This was confirmed by scanning electron microphotographs. Results were consistent with textural measurements that showed a higher breaking force as the processing pressure increased (i.e., T), which was inversely related to oil absorption ( R = 0.92). In accordance, this study allows understanding the effect of vacuum level in structure development and oil absorption in vacuum-fried products when different food building blocks (gluten and wheat starch) are combined. [ABSTRACT FROM AUTHOR]

The effects of vacuum frying and atmospheric frying on the physicochemical properties and quality characteristics of the deep-fat-fried snacks were compared in manufacturing snacks using general, yellow-fleshed, and purple-fleshed sweet potatoes. Regarding the moisture and lipid content of snacks, vacuum-fried snacks showed about 50% lower values compared to atmospheric-fried snacks, while for the colors, vacuum-fried snacks showed higher L and b values and a slightly lower a value, with almost no difference in the texture, compared to atmospheric-fried snacks. The total carotenoid and anthocyanin contents of snacks were decreased greatly compared to fresh sweet potatoes, and was considerably higher in vacuum-fried snacks compared to atmospheric-fried snacks. For the sensory evaluation of snacks, the acceptability for color and flavor was higher in the vacuum-fried snacks, while the acceptability for texture was higher in atmospheric-fried snacks due to a higher degree of crispiness. In conclusion, it is considered that the vacuum frying in manufacturing sweet potato snacks, compared to the atmospheric frying, is the appropriate deep-fat frying method for modern people who take excessive fats and oils from foods and are highly interested in health and high quality products. [ABSTRACT FROM AUTHOR]

Vacuum frying is an alternative way to improve the quality of the fried food and could reduce the final oil uptake in the product. The product is heated at low pressure thus decreasing the boiling points of the frying oil and the water in the product. Moreover, the absence of air during vacuum frying may inhibit lipid oxidation and enzymatic browning, and therefore, the color and nutrients of samples can be largely preserved. Many food research projects involving snack food industries therefore attempt to understand oil uptake during the vacuum-frying process in order to control and reduce the fat content of fried products without deteriorating their desirable organoleptic characteristics. This article is an update of the state-of-the-art in vacuum-frying technology, showing the effect of pretreatments and frying conditions on quality characteristics of the products. Facts pertaining to equipment and operation conditions are included. On the other hand, mathematical models to describe oil uptake and water loss are also mentioned. The effect of this treatment on color, texture, and nutritional value of the final products is also discussed. [ABSTRACT FROM AUTHOR]