The optimization of vacuum frying to dehydrate carrot chips

The effects of pretreatment and processing conditions, such as frying temperature, absolute vacuum pressure and frying time; on the properties of fried carrot chips were studied. Statistical analysis with response surface regression showed that moisture content, fat content and breaking force of carrot chips were significantly (P < 0.05) correlated with frying temperature, vacuum absolute pressure and frying time. The optimum conditions were a vacuum frying temperature of 100–110 °C, a vacuum absolute pressure of 0.010–0.020 MPa and a frying time of 15 min.     

Effects of processing conditions on the quality of vacuum fried apple chips

The effects of pretreatment and processing conditions on the quality of vacuum fried apple chips were studied. As blanched apple slices were pretreated by immersing in fructose solution and freezing prior to vacuum frying, more uniform porosity was observed on the surface (or cross-section) of apple chips as examined by scanning electron microscopy (SEM). During vacuum frying, the moisture content and breaking force of apple chips decreased with increasing frying temperature and time while the oil content increased. The L values of fried apple chips decreased apparently with increasing frying temperature. However, when apple slices were fried at 100°C for up to 20 min, both a and b values increased rapidly. Statistical analysis with the central composite rotatable design showed that the moisture content, oil content, color, and breaking force of apple chips were significantly (P⩽0.05) correlated with concentration of immersing sugar solution, frying temperature and frying time. Based on surface responses and contour plots, optimum conditions were: vacuum frying temperature of 100–110°C, vacuum frying time of 20–25 min, and immersing fructose concentration of 30–40%.     

Effects of maltodextrin level,frying temperature and time on the moisture,oil and beta‐carotene contents of vacuum‐fried apricot slices

Response surface methodology was used to investigate the effects of frying temperature, time and maltodextrin (MD) levels on the moisture, oil and beta‐carotene contents of the vacuum‐fried apricot slices. Based on the results, the moisture content of vacuum‐fried apricot slices decreases with increasing frying temperature and frying time. Generally, the oil content of vacuum‐fried apricot slices decreases with decreasing frying temperature and frying time. The beta‐carotene content of vacuum‐fried apricot slices increases with increasing frying temperature. But the trend of increase in the beta‐carotene content of the product with frying temperature was higher at lower MD level. When processing vacuum‐fried apricot slices, a frying temperature of 100 °C, frying time of 72.5 min and an MD level of 70% must be used to achieve a product of acceptable moisture, oil and beta‐carotene contents.     

Effects of osmotic pretreatment and frying conditions on quality and storage stability of vacuum-fried pumpkin chips

The effects of osmotic (OP), ultrasound-assisted osmotic pretreatment (UAOP) and frying conditions on quality and storage stability of vacuum fried pumpkin chips were investigated. The pumpkin samples were pretreated in maltodextrin solution and subsequently fried at different temperatures (90–110 °C) and time periods (10–30 min). The results demonstrated that the moisture content, water activity, lightness, yellowness and carotenoid content of the fried chips decreased, while oil content, hardness and a* (dark brown colour) value increased with increasing frying temperature and time. UAOP reduced about 16.0% of oil absorption and enhanced approximately 70% of carotenoid retention in the fried chips. UAOP samples were also more stable during storage than the untreated ones, indicated by lower degradation kinetics constants of key quality parameters. The proposed pretreatment could be an effective method for food industries to develop vacuum fried pumpkin chips with improved quality and stability.     

Optimisation of vacuum frying of gold kiwifruit slices: application of response surface methodology

Response surface methodology was used to investigate the effects of the level of maltodextrin (MD), frying temperature and time on the moisture, colour and texture properties of the vacuum‐fried gold kiwifruit slices and to determine the optimised conditions for vacuum frying. The moisture content of vacuum‐fried gold kiwifruit slices decreased with increasing frying temperature and frying time. The colour change of the product increased with increasing frying temperature. The browning index of the product increased with increasing frying temperature and frying time. The breaking force of the product gave higher values when processed at middle range of frying temperature and MD level. When processing vacuum‐fried gold kiwifruit slices, there was a need to use frying temperatures of 72.0–76.3 °C, frying times of 35.0–65.0 min and an MD level of 40% to achieve products with acceptable moisture, colour and texture properties.     

真空油炸胡萝卜脆片基本特性的研究

真空油炸技术可用于生产高品质的果蔬脆片．主要研究了油炸温度和真空度对胡萝卜片水分质量分数、脂肪质量分数、色泽及质构的影响．试验表明：随着油炸温度和真空度的升高，其干燥和脂肪吸收速度相应提高，且两者呈一定的相关性．统计分析可知：油炸温度和真空度并不显著性影响脆片的白度（L）、红度（a）、黄度（b）值（P〉0．05）；对于脆片的破碎力而言，真空度具有显著性影响（P〈O．05），而油炸温度不具有显著性影响（P〉0．05）．     

Optimization of processing conditions for vacuum frying of high quality fried plantain chips using response surface methodology (RSM)

Optimization of processing conditions (temperature 122 to 136°C, vacuum pressure 9.91 to 19.91 cmHg, and frying time 3 to 9 min) during vacuum frying of plantain chips was investigated using a Box-Behnken experimental design with response surface methodology (RSM). Models for various responses were developed and optimized frying conditions using numerical solutions were established. Optimized vacuum fried samples were compared with atmospheric fried samples based on the concept of equivalent thermal driving force (ETDF). Frying parameters had significant (p<0.05) effects on the moisture content, texture, and color with a coefficient of determination (R ²) for quadratic model responses varying between 0.53 and 0.99. Optimum vacuum frying conditions for plantain chips were a frying temperature of 133°C, vacuum pressure of 9.91 cmHg, and frying time of 6 min based on desirability concepts. Vacuum fried plantain chips had more acceptable sensory properties, based on ETDF values, than atmospheric fried samples.     

Optimization of Blanching Conditions Prior to Deep Fat Frying of Yam Slices

The effect of low-temperature blanching and frying time at a frying temperature of 170°C on moisture and oil contents, breaking force and colour of yam chips was investigated using response surface methodology to establish the optimum blanching conditions and frying time. A central composite rotatable design was used to study the effects of variation in levels of blanching temperature (60–80°C), blanching time (1–5 min) and frying time (2–6 min) on quality attributes of yam chips. The effect of blanching temperature and frying time was more significant than the time of blanching on the quality attributes. The response variables were fitted to predictive models applying multiple linear regressions. Statistical analysis with response surface regression showed that moisture content, oil content, breaking force and L? (lightness) parameter were significantly (P < 0.05) correlated with blanching temperature and time and frying time. However, the regression equation showed a poor fit for a? and b? respectively. The optimum conditions were a blanching temperature of 70–75°C, blanching time of 4–5 min while frying for about 5 min.     

Combination of Moderate Vacuum Frying with High Vacuum Drainage—Relationship Between Process Conditions and Oil Uptake

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.     

真空油炸过程中干燥特性和产品品质变化的研究

研究了胡萝卜脆片真空油炸过程中干燥特性和产品品质的变化,结果表明:真空油炸过程属于传统的降速干燥过程,其水分和脂肪的变化符合一级反应动力学规律,利用非线性回归法求解得到了胡萝卜脆片水分和脂肪含量、干燥速率随油炸时间变化的方程;随着油炸时间的延长,胡萝卜脆片直径不断减小,厚度不断增加,油炸20min后,其直径和厚度皱缩度分别达到6%和4.5%;真空油炸胡萝卜脆片气孔数量不断增加,细胞结构变形程度增强。真空油炸过程中胡萝卜脆片脂肪主要分布于脆片的表面,冷却过程中脂肪逐渐向中心渗透,中心脂肪含量可达到60%。     

Effect of vacuum frying on main physicochemical and nutritional quality parameters of pineapple chips

BACKGROUND: Slices of MD‐2 pineapple hybrid were vacuum fried at 24 kPa according to a central composite experimental design that simultaneously varied frying time (6.3–7.7 min) and temperature (106.3–117.7 °C). Major physicochemical and nutritional quality factors were measured and modelled using a second‐order polynomial equation. RESULTS: Moisture content, water activity a_w, colour parameters L*, C* and H* and total vitamin C content decreased while total phenolic content and dehydroascorbic acid content increased with increasing frying time and temperature. Oil content, hardness and hydrophilic antioxidant capacity reached minimum values near the centre of the experimental field. By superimposing contour curves, it was determined that processing conditions of 6.9 min frying time and 112 °C frying temperature produced pineapple chips with a golden colour (L*≥ 60, C*≥ 50, H*≥ 80), an a_w of less than 0.29, a moisture content of about 4% and a hardness of less than 1.9 N, giving rise to a crispy texture. Oil content was about 20% (d.b) and residual total vitamin C content (～90 mg per 100 g wet basis (w.b.)) was high. Phenolic compound content was about 150 mg gallic acid equivalents per 100 g w.b. and antioxidant capacity was around 22 µmol Trolox equivalents g^?1 w.b. CONCLUSION: Vacuum frying is a dehydration process that produces healthy fruit snacks which partially preserve the fruit's original colour and nutritional compounds and have a high hydrophilic antioxidant capacity. Copyright © 2008 Society of Chemical Industry     

Vacuum frying as a route to produce novel snacks with desired quality attributes according to new health trends

Consumers look for products that contribute to their wellness and health, however, even health-conscious consumers are not willing to sacrifice organoleptic properties, and intense full-flavor snacks remain an important trend. The objective of this study was to examine most important quality parameters of vacuum (1.92 inHg) and atmospheric-fried carrot, potato, and apple slices to determine specific advantages of vacuum technology. Slices were fried using equivalent thermal driving forces, maintaining a constant difference between oil temperature and the boiling point of water at the working pressure (ΔT = 60 and 80 °C). This resulted in frying temperatures of 160 and 180 °C, and 98 and 118 °C, for atmospheric and vacuum frying, respectively. Vacuum-fried carrot and potato chips absorbed about 50% less oil than atmospheric-fried chips, whereas vacuum-fried apple chips reduced oil absorption by 25%. Total carotenoids and ascorbic acid (AA) were greatly preserved during vacuum frying. Carrot chips vacuum fried at 98 °C retained about 90% of total carotenoids, whereas potato and apple slices vacuum fried at 98 °C, preserved around 95% of their initial AA content. Interestingly, results showed that the antioxidant capacity of chips may be related to both the presence of natural antioxidants and brown pigments developed at elevated temperatures. PRACTICAL APPLICATION: A way to reduce detrimental effects of deep-fat frying is through operating-pressure reduction, the essence behind vacuum deep-fat frying. In this way, it is possible to remove product moisture at a low temperature in a low-oxygen environment. The objective of this research was to study the effect of oil temperature reduction when vacuum frying traditional (potatoes) and nontraditional products (carrots and apples) on most important quality attributes (vitamins, color, and oil uptake). Results are promising and show that vacuum frying can be an alternative to produce nutritious and novel snacks with desired quality attributes, since vitamins and color were greatly preserved and oil absorption could be substantially reduced.     

Quality changes of edible oils during vacuum and atmospheric frying of potato chips

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.Industrial relevanceFood 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.     

低温真空油炸薯片生产工艺及其贮藏条件的研究

对马铃薯片进行低温真空油炸生产工艺的基础性研究,分析薯片在贮藏过程中水分、脂肪和VC含量的变化,并探讨等温吸湿规律。通过单因素试验确定最优的油炸工艺参数为温度105℃,时间20min,真空度0.090MPa;离心脱油的最佳条件为脱油转速400～500r/min,时间5～7min,真空度0.090MPa。研究结果对低温真空油炸薯片技术具有很好的指导和促进作用,同时改善了现在油炸薯片的品质和提高了能源利用率。     

Effect of frying time on acrylamide content and quality aspects of French fries

The effect of frying time on quality and acrylamide (AA) content of French fried potatoes, obtained simulating home-cooking practices, was studied in order to investigate the optimal conditions to minimize the amount of produced toxicant together with the maintenance of good culinary quality. French fries were obtained from fresh potatoes using a domestic fryer with static basket; a 4:1 oil:product ratio and a fixed initial oil temperature of 180 °C were used. Several batches were fried at different times (3, 4, 5, 6, 7, 8, 9 min). During frying tests the oil, the sticks surface and core temperatures were measured by thermocouples. Analysis of water removal, oil uptake, colour, texture and AA content were carried out on fried final products. AA content increased exponentially increasing the frying time. In our working conditions after around 4 min of frying, when the temperature of potato surface and the oil bath reached, respectively, 120 and 140 °C, the increase of time became a key factor in terms of the quantity of AA and its formation rate. On the basis of colour, oil content and AA level the best culinary product was obtained after 5 min of frying.     

Physicochemical Properties Changes of Donuts During Vacuum Frying

Vacuum frying was explored to cook donuts and compared to the conventional atmospheric frying. A temperature of 190°C was used for atmospheric frying. Three vacuum levels (3, 6, and 9 kPa vacuum) with three temperature levels (150, 165, and 180°C) were used for vacuum frying. The effects of initial moisture content (IMC), vacuum level and frying temperature on physicochemical properties, such as moisture loss, oil absorption, and quality were investigated. The properties of fried donuts were significantly affected by IMC. Under vacuum frying, volume and total color changes were affected by frying temperature; and oil uptake was affected by vacuum and frying temperature. Frying temperature and vacuum were not directly related to the final moisture content (MC) of donuts. There was no relationship between MC and fat content of donuts. Donut texture was directly related to the vacuum and frying temperature.     

常压煎炸和真空煎炸对中国对虾品质的影响

探究常压煎炸和真空煎炸对中国对虾理化性质和感官品质的影响。测定了不同煎炸温度下两种煎炸方式对中国对虾的水分含量、含油量、色泽、虾青素含量和感官品质的影响。结果表明：随着煎炸温度的升高,两种煎炸方式下中国对虾的水分含量均降低,含油量均增加,但真空煎炸下中国对虾的变化幅度较低;两种煎炸方式下中国对虾的虾青素含量均随着煎炸温度的升高呈现先增加后减少的趋势;相同热驱动力下,真空煎炸的中国对虾的色泽、虾青素含量和感官品质均优于常压煎炸的。相比于常压煎炸,真空煎炸的中国对虾品质更佳。     

Effects of variety and stage of fruit ripeness on the physicochemical and sensory characteristics of deep‐fat‐fried banana chips

The quality of banana chips prepared from two different varieties of banana, Pisang Abu and Pisang Nangka, at the ‘green’ and ‘trace of yellow’ stages of ripeness was studied. The fruits were peeled, sliced to a thickness of 2 mm and deep‐fat fried in refined, bleached and deodorised (RBD) palm olein at 180 ± 5 °C for 3 min. The quality parameters determined for fresh bananas were total soluble solids, pH, acidity, carbohydrate, sugar content, fat, protein, moisture content, ash, fibre, colour and fruit firmness. The results showed that Abu had a higher carbohydrate content than Nangka at both stages of ripeness before frying. No sucrose was detected in Nangka. The quality parameters determined after deep‐fat frying were moisture content, water activity, oil absorption, crispness and sensory evaluation. The moisture content and water activity of Abu chips were lower than those of Nangka chips. The texture of chips prepared from Abu at stage ‘green’ showed more crispness than the other three samples. Sensory evaluation showed that chips prepared from Abu at both stages of ripeness presented better colour, flavour, odour, texture and overall acceptability than those prepared from Nangka. Based on the matrix of correlation coefficients, fresh bananas with higher fruit firmness and carbohydrate content gave banana chips with higher crispness and oil absorption. © 2001 Society of Chemical Industry     

DEEP-FAT FRYING OF YAM SLICES: OPTIMIZATION OF PROCESSING CONDITIONS USING RESPONSE SURFACE METHODOLOGY

The deep-fat frying of yam slices was investigated with the aim of optimizing the processing conditions. During frying, frying temperature, initial dry matter and frying time have a significant effect on moisture loss and oil uptake. Response surface methodology central composite rotatable design was used to study the effects of the independent variables on quality attributes of yam chips. Breaking force, oil content, moisture content and color parameters were determined. Statistical analysis with response surface regression showed that breaking force, oil and moisture contents and color parameters ( L* and a* ) were significantly ( P <  0.05) correlated with frying temperature, initial dry matter and frying time. The optimum conditions were a frying temperature of 175–180C, using tubers of initial dry matter of 0.179–0.214 kg/kg with a frying time of 4–5 min. It was suggested that the regression equation can be used to estimate the dependent variables for fried yam chips except b* (yellowness) parameter.

PRACTICAL APPLICATIONS

It is expected that the optimized processing conditions highlighted in this work will be useful in obtaining fried yam chips of acceptable quality attributes. This optimized condition would be a good prospect for commercialization in small-scale industries.     

Quality changes in chicken nuggets fried in oils with different degrees of hydrogenatation

Quality changes in chicken nuggets fried in different mixtures of hydrogenated and non-hydrogenated canola oils were studied. Colour, texture, oil and moisture contents of the chicken nugget samples fried at 190 °C for 30, 60, 90, 120, 180, 240 and 300 s were investigated. The proportions of hydrogenated to non-hydrogenated frying oils used in the study were 0%, 20%, 40%, 60%, 80% and 100%.Results indicate that increase in frying time resulted in decreased product lightness (L*) whereas redness (a*) and yellowness (b*) increased. The maximum load to puncture increased with increasing frying time. In addition, oil content increased slowly with frying time, and moisture content decreased as expected. Both frying times and oil types have significant effects on the quality parameters investigated. First-order kinetic equation was used to describe colour changes as well as oil and moisture contents of the samples. Oil and moisture contents had negative correlation relationship. With increasing degree of oil hydrogenation, the surface colour of the fried chicken nuggets samples were lighter, texture increased, oil and moisture contents decreased.