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.     

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%.     

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 carrot chips

The effects of pretreatment and vacuum frying conditions on the quality of fried carrot chips were studied. The moisture and oil contents of fried carrot chips were significantly (p < 0.05) reduced when blanched carrot slices were pretreated by immersion in fructose solution and freezing prior to vacuum frying. Furthermore, more uniform porosity was observed on the vertical cross‐section of carrot chips when examined by scanning electron microscopy. During vacuum frying, the moisture content, colour and breaking force of carrot chips decreased while the oil content increased with increasing frying temperature and time. However, there was no apparent change in Hunter ΔE with time when the frying temperature was below 100 °C and the frying time was below 25 min. Results of this study suggest that vacuum frying at moderate temperature (90–100 °C) for 20 min can produce carrot chips with lower moisture and oil contents as well as good colour and crispy texture. Copyright © 2005 Society of Chemical Industry     

低温真空油炸山药脆片的工艺研究

对比不同油炸方式制作山药片,探究低温真空油炸山药脆片的优点及最佳生产工艺。以感官评价、含油率为考核指标,采用单因素和响应面方法对工艺进行优化,并通过色差仪和扫描电镜做色度及微观结构的观察。试验表明真空低温油炸山药脆片在色泽及含油率明显低于普通油炸方法,其最佳加工工艺为切片厚度6 mm,汽蒸5 min,油炸温度为95℃,油炸时间5 min 40 s,脱油时间为3 min 43 s。     

Frying Oil Temperature: Impact on Physical and Structural Properties of French Fries During the Par and Finish Frying Processes

The physical, mechanical, and structural changes in French fries at different frying temperatures (170, 180, and 190 °C) during par and finish frying were investigated. The experimental frying process includes blanching, par frying, freezing, and finish frying at the point of consumption. Par frying temperature had a greater effect on moisture reduction than on processing time with the greatest moisture loss at 180 °C after 160 s. At 180 °C, fries had the highest total oil uptake (29.56 % wb). Frying caused a significant change in color with the greatest effect at 190 °C. Micro-CT scan images showed structural changes in French fries over the course of the frying process. Frying time increased the volume of the pores relative to the size of the crust, and this was positively correlated with the hardness and shear cutting force. Overall, within the range of frying conditions studied, the higher temperature (190 °C) resulted in the lowest amount of oil uptake and the crispiest texture.     

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.     

Technological evaluation of new cultivars for potato chips manufacturing

Potato tubers of cvs. Condor, Diamont, Baraka, Mondial and Draga were used to produce chips of 1.0 mm slice thickness using an industrial slicer. Half of the slices quantity was immediately blanched in water at 100°C for approximately 5 min. Frying was carried out at 165–170°C in cotton seed oil. Both cvs. Diamont and Condor were the best varieties in the nutritional composition, since they contained the highest content of total solids (24.2 and 22.8%), crude protein (10.9 and 10.2%), total free amino acids (270 and 246 μmol/g DM), ascorbic acid (1.5 and 1.4 mg/100 g DM) and digested protein (49.8 and 49.6% for pepsin enzyme as well as 76.0 and 78.3% for trypsin enzyme). In contrast, they contained the lowest level of reducing sugars i.e. 0.8 and 0.9%, respectively. The same both varieties produced the maximum final yield of chips from both unblanched and blanched slices (50.0 and 47.4% as well as 48.9 and 45.8%, respectively) with the lowest final oil content i.e. <42%. Slightly differences in the final moisture content of chips were noticed. Blanching before frying led to a decrease in the final oil content of chips produced from all potato varieties. Sensory evaluation of the produced chips revealed that the favourable chips with the best quality attributes i.e. lighter and uniform in colour, lower final oil content, natural odour, more crisp and better in taste can be produced by using slices from cvs. Condor and Diamont. Furthermore, blanching before frying reduced significantly the oil content of chips and improved both colour and texture (more crispness) of the produced chips.     

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.     

响应面法优化低脂甘薯脆片加工工艺

以红心甘薯为原料,优化低脂甘薯片生产过程中漂烫、热风干燥、油炸等关键工艺参数,以产品含油率和色差(L*值和b*值)为评价指标,并通过响应面优化确定最优的低脂甘薯片生产工艺。结果表明,较优漂烫工艺条件为:漂烫温度70 ℃,漂烫时间7 min;较优的热风干燥工艺条件为:热风干燥温度70 ℃,热风干燥时间40 min;最优油炸工艺条件为:预油炸温度149 ℃,预油炸时间98 s,二次油炸温度190 ℃,在该条件下测定含油率的平均值达(17.1±0.2)%。该工艺条件下制得的甘薯脆片含油率低于同类产品,外观亮黄,无焦糊现象。     

The Effect of Methylcellulose,Temperature, and Microwave Pretreatment on Kinetic of Mass Transfer During Deep Fat Frying of Chicken Nuggets

The aim of this study was to determine the effect of microwave pretreatment, usage of methylcellulose, oil temperature, and frying time on mass transfer during deep fat frying of chicken nuggets. Methylcellulose was used in batter and as a coating on product. Microwave with two power densities namely 3.7 and 7.4 W/g was used for reduction of initial moisture content of samples before frying. Frying was performed at three temperatures (150 °C, 170 °C, and 190 °C) and five intervals (0.5, 1, 2, 3, and 4 min) in the sunflower oil. The least oil content was observed when MC was used as a coating layer on non-precooked samples fried at 190 °C. Oil absorption of samples with MC in batter was partially higher compared to control samples. This could be attributed to the rheology of batters. The first-order kinetic model was fitted to moisture and oil content. For determining the correlation between temperature and moisture diffusivity, Arrhenius equation was used. The constant rate for moisture and oil transfer was in the range of 2.2–5 and 0.023–2.67 s^?1, respectively. Effective moisture diffusivity values were between 1.43?×?10^?8 and 3.24?×?10^?8 m²/s. Activation energy ranged between 0.71 and 1.71 kJ/mol.     

The effect of low-temperature blanching on the quality of fresh and frozen/thawed mashed potatoes

The effect of low‐temperature blanching (LTB) prior to cooking on colour, textural, firmness and oscillatory parameters, sensory attributes and overall acceptability of either fresh or frozen/thawed mashed potatoes was studied using response surface methodology (RSM) to establish the optimum temperature and time for blanching in both types of mashed potatoes. A central composite rotatable design was used to study the effects of variation in levels of blanching temperature (57.93–72.07 °C) and time (15.86–44.14 min) on the quality parameters. Stationary points showing maximum thickening had critical temperatures (approximately 67–69 °C) and times (approximately 26–30 min) in the ranges of temperature and time used for each independent variable for both fresh and frozen/thawed mashed potato. Results showed a high correlation between structural reinforcement and overall acceptability under optimum experimental blanching conditions. This demonstrates the potential of this experimental approach in terms of tailoring physical properties to predetermined levels in order to meet consumer preferences in mashed potatoes, and of altering the changes that occur after freezing and thawing.     

Grading of Potato Chips According to Their Sensory Quality Determined by Color

Potato chips were classified in quality categories according to their color after frying at oil temperatures (120, 140, 160, and 180 ± 1 °C) and undergoing some pre-treatments (control or unblanching, blanching, and blanching plus drying). For each oil temperature, six time intervals were considered since the beginning of the frying process until the corresponding time at which potato slices reached a moisture content of 2%. In order to define quality categories according to the surface color, we worked with 79 frequent consumers of potato chips who classified the color scores of the potato chip photographs located in a standard color chart in the following categories: (1) desirable color, (2) still acceptable color and (3) nondesirable color. A sensory panel was formed with 12 judges who were selected according to simple tests of color ordering. This sensory panel evaluated the samples processed at different oil temperatures, frying times, and pre-treatments based on the standard color chart previously mentioned. For each measured point, the score from the color standard chart indicated for more than 50% of the panel members was selected. Finally, time-temperature modeling was achieved in order to get potato chip with the best color surface for the three pre-treatments tested.     

The Impact of Blanching and High-Pressure Pretreatments on Oil Uptake of Fried Potato Slices

The effect of high-pressure (HP) pretreatment on oil uptake of potato slices is examined in this paper. Potato slices were treated either by HP or thermal blanching, or a combination of thermal blanching followed by HP prior to frying. The effect of HP on starch gelatinization and potato microstructure was assessed by differential scanning calorimeter and environmental scanning electron microscope (ESEM), respectively. After treatments, the slices were fried in sunflower oil at 185 °C for a predetermined time. Frying time was either kept constant (4 min) or varied according to the time needed to reach a desired moisture content of ≈2%. The high pressure applied in this study was found not to be sufficient to cause a significant degree of starch gelatinization. Analysis of the ESEM images showed that blanching had a limited effect on cell wall integrity. HP pretreatment was found to increase the oil uptake marginally. When frying for a fixed time, the highest total oil content was found in slices treated at 200 MPa for 5 min. The oil content was found to increase significantly (p < 0.05) to 41.23 ± 1.82 compared to 29.03 ± 0.21 in the control slices. The same effect of pressure on oil content was found when the time of frying varied. On the other hand, HP pretreatment was found to decrease the frying time required to achieve a given moisture content. Thus, high-pressure pretreatment may be used to reduce the frying time, but not oil uptake.     

Osmotic pre-treatment effect on fat intake reduction and eating quality of deep-fried plantain

The relationship between compositional changes during frying and an osmotic dehydration step before frying is described, including and explanation of their effects on eating quality of plantain chips. Three solutions were used to soak plantain slices (glucose, salt (NaCl) and glucose + salt) prior to deep-frying (170 °C). The temperature, moisture and fat changes during the frying were monitored, and the quality attributes and physicochemical properties were also determined. The osmotic pre-treatments had significant effects on most parameters of plantain chips. In general, treatments decreased oil intake, moisture content, and total volume and also reduced frying time, while the colour, rancidity, crispiness and sensory evaluation increased after 5 min of frying. However, a negative effect on high temperature induced colour development was observed for some of the treatments. Rancidity induction times were significantly higher for pre-treated samples, which is probably related to lower oil content, shorter frying times and lower water content.     

响应面法优化真空油炸-热风联合干燥桃脆片工艺

以真空油炸温度、分阶段干燥的水分转换点、后期热风干燥阶段温度为影响因素,以桃脆片含油率为评价指标进行响应面优化分析,得出联合干燥最佳工艺参数为切片厚度2mm、漂烫3min、真空油炸温度87.1℃、水分转换点15.9%、热风干燥温度65.5℃。根据实际操作条件,调整最佳联合干燥工艺为切片厚度2mm、漂烫3min、真空油炸温度87℃、分阶段干燥的水分转换点16%、热风干燥温度66℃。验证实验表明,最佳工艺条件下测得联合干燥桃脆片的含油率为12.5%,与理论预测值的误差为5.9%。     

Optimisation of processing variables in the preparation of sweet potato chips using response surface methodology

Models capable of predicting the product quality of sweet potato chips have been developed using response surface methodology and used to determine the optimum processing conditions. Moisture loss, oil uptake, crispness (measured using a bending-snapping test in the TA.XT2 Texture Analyser), and sensory attributes such as colour, flavour, and texture were used to assess the product quality in the preparation of sweet potato chips. The optimum conditions which were attained for maximum moisture loss (11.65% on wet basis), minimum oil uptake (2.57%), crispness (794.37 g), colour score (7), flavour score (7) and texture score (7) were: frying temperature, 174.7 °C; salt concentration, 0.45%; citric acid concentration, 0.37%; potassium metabisulphite concentration, 0.65%; and frying time, 26 s.     

Reproducible Texture Analysis of Potato Chips

An Instron punch test with three point support of a potato chip was developed, and factors affecting the results were evaluated. Individual potato chips were fried in palm oil in a forced circulation glass container, and their moisture content and texture were determined. Sample handling parameters contributing most to variability of moisture and texture were the cutting device, and position of the sample within the tuber. For oil temperatures 140 and 180°C, and two potato specific gravities, moisture and texture changes were studied during frying. Maximum force of break was in the 2–4% moisture region. Individual chips showed highly variable room temperature adsorption/desorption.     

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.