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.     

Effect of superheated steam prefrying treatment on the quality of potato chips

Superheated steam drying (SSD) was used as a prefrying treatment prior to deep‐fat frying for potato slices. The effect of SSD at 130, 150 or 180 °C and steam velocity of 2.0 m s^?1 on the fat uptake, colour and texture of fried potato chips was evaluated; microstructure and degree of starch gelatinization were also evaluated to help explain the fat uptake results. SSD and frying yielded potato chips with the fat content from 0.263 ± 0.002 to 0.304 ± 0.002 kg kg^?1 (d.b.), while frying without SSD led to chips with the fat content as high as 0.359 ± 0.003 kg kg^?1 (d.b.). SSD did not promote starch gelatinization. Lower fat uptake was correlated to modified surface structure and lower moisture content of potato slices prior to frying. Frying with/without SSD pretreatment yielded potato chips of similar hardness, crispness and lightness. On the other hand, SSD significantly increased redness and yellowness of the fried chips.     

Optimization of the blanching process to reduce acrylamide in fried potatoes

A central composite design was used to study the effect of blanching time and temperature on the extraction of reducing sugars from potato strips and slices. After frying, the impact of both factors on the acrylamide content in French fries and potato crisps was evaluated. Acrylamide could be lowered more efficiently in potato crisps compared to French fries, due to a more pronounced extraction of sugars from potato slices upon blanching. In both products, blanching temperature was the main influencing factor for sugar extraction and subsequent acrylamide mitigation. Blanching at temperatures of about 70 °C for a short period of time (about 10 min) was more efficient compared to blanching at lower temperatures, which appeared more time-consuming. However, the extraction efficiency of reducing sugars was over 10% lower when the potato cuts were blanched in water which was previously used for blanching, leading to over 10% less reduction in the final acrylamide content.     

Microwave heating instead of blanching to produce low-fat French fries

Blanching pretreatment is necessary for preparing French fries, but it causes water consumption and nutrient outflow. This work was aimed to investigate the effects of microwave (MW) pretreatment instead of blanching on the quality of fries, evaluated via changes to microstructure and crust characteristics. First, MW pretreatment could inactivate polyphenol oxidase in fresh-cut potato strips to inhibit enzymatic browning. Subsequently, the fries after proper MW pretreatment (60 s) had a golden appearance and better texture. As compared with the blanching process, the oil content of the fries obtained by MW pretreatment was decreased sharply from 41.3% to 18.1%. The results of scanning electron microscopy showed that MW pretreatment significantly altered the crust and internal microstructure of fries. Specially, it was found that the MW pretreatment made the fries form a thicker “protective crust” (1.81 μm), which was crucial to prevent oil adsorption during the frying and improve texture.Industrial relevanceBlanching is a traditional thermal processing technique that was once widely used in French fries around the world. However, blanching has some drawbacks, such as slow heat conduction, long processing time, substantial loss of soluble nutrients, massive water wastage, and even increased oil content of the fries. Meanwhile, MW heating is known for its high efficiency. The fries obtained with proper MW pretreatment are of good quality, but the oil content is drastically reduced compared to conventional blanching pretreatment. So, the above findings may provide helpful information to guide effective strategies for applying MW heating instead of blanching in the preparation of fried potato foods.     

Kinetics of oil uptake during frying of potato slices:: Effect of pre-treatments

Oil uptake in fresh, blanched and, blanched and dried potato slices was studied during frying. Potato slices blanched in hot water (85 °C, 3.5 min) and potato slices blanched (85 °C, 3.5 min) and then dried until to a moisture content of ∼60 g/100 g (wet basis) were deep fried in sunflower oil at 120, 150 and 180 °C. A control treatment consisted of unblanched potato slices without the pre-drying treatment (fresh samples). It was studied applying two empirical kinetic models in order to fit the oil uptake during frying: (i) a first order model; (ii) a proposed model, with a linear time behavior for short times, while time independent for long times. Oil uptake was high even for short frying times at the different temperatures tested suggesting that oil wetting is an important mechanism of oil uptake during frying. For control slices, oil uptake increased approximately by 32% as the frying temperature decreased from 180 to 120 °C at moisture contents ?1 g water/g dry solid. No apparent effect of frying temperature in oil uptake was observed at moisture contents ?0.5 g water/g dry solid in fried slices previously blanched and dried. The two kinetic models studied fitted properly the values of oil uptake during frying, with similar correlation coefficient r².     

Acrylamide reduction in potato chips by using commercial asparaginase in combination with conventional blanching

In this research acrylamide reduction in potato chips was investigated in relation to blanching and asparaginase immersion treatments before final frying. Potatoes slices (Verdi variety, diameter: 40 mm, thickness: 2.0 mm) were fried at 170 °C for 5 min (final moisture content of ∼2.0 g/100 g). Prior to frying, potato slices were treated in one of the following ways: (i) Rinsing in distilled water (control I); (ii) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min; (iii) Rinsing in distilled water plus immersion in an asparaginase solution (10000 ASNU/L) at 50 °C for 20 min; (iv) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min plus immersion in an asparaginase solution (10000 ASNU/L) at 50 °C for 20 min; (v) Rinsing in distilled water plus blanching in hot water at 85 °C for 3.5 min plus immersion in distilled water at 50 °C for 20 min (control II). Blanching in hot water (ii) was almost as effective as asparaginase potato immersion (iii) in order to diminish acrylamide formation in potato chips (acrylamide reduction was ∼17% of the initial acrylamide concentration). When potato slices were blanched before asparaginase immersion, the acrylamide content of the resultant potato chips was reduced considerably by almost 90%. We have demonstrated that blanching of potato slices plus asparaginase treatment is an effective combination for acrylamide mitigation during frying. It seems to be that blanching provokes changes in the microstructure of potato tissue leading to an easier and more effective diffusion of asparaginase.     

Effects of ultrasound pretreatments on the kinetics of moisture loss and oil uptake during deep fat frying of sweet potato (Ipomea batatas)

The possibility of ultrasound assisted pretreatments of sweet potato to lower the moisture content and oil uptake during deep fat frying and its effects on the mass transfer rate was investigated. Sweet potato samples prior to frying were immersed in distilled water with ultrasound (UD), osmotic dehydration without ultrasound (OD) and ultrasound assisted osmotic dehydration (UOD). Ultrasound probe having frequency of 28 kHz at 300 W maximum power and time of 30 min was used for the pretreatment. The control (without pretreatment) and the pretreated samples were fried using sunflower oil at temperature of 130, 150 and 170 °C for 2, 4, 6, 8 and 10 min. The first order kinetic model was used for the mass transfer rate for moisture loss and oil uptake. The lowest moisture content was found in fried samples pretreated in UOD and OD while the lowest oil uptake was obtained in fried samples pretreated in UD having 65.11 and 71.47% oil reduction at temperature of 150 and 170 °C, respectively, compared to the untreated sample. The k values of all pretreated samples were higher than that of the untreated at 150 and 170 °C. The highest activation energy for moisture loss was found in untreated samples while the lowest activation energy for oil uptake was found in samples pretreated in UOD. The results from this work proved that ultrasound is a good pretreatment that can be used to obtain a low moisture content and oil uptake during deep fat frying of sweet potato.Industrial relevanceUltrasound is a novel technology that is widely used in the food industries because of its numerous advantages over conventional methods. Its application in the frying of foods could also help in the reduction of oil uptake, thus making safe the consumption of fried foods. The information about frying kinetics could also help in the design and optimization of the process in the food industry.     

EFFECTS OF OHMIC PRETREATMENT ON OIL UPTAKE OF POTATO SLICES DURING FRYING AND SUBSEQUENT COOLING

The effect of ohmic pretreatment on the oil uptake of potato slices during frying and subsequent cooling was investigated. The treated potato slices were heated by either directly sandwiching the slices between two electrodes or by heating them in a 0.11% salt solution. The treatment was carried out using an alternating current field of 35.5 V/cm. Results of this study indicate that oil uptake during frying and subsequent cooling of potato slices was decreased by the ohmic pretreatment without involving a liquid medium (direct sandwiching). However, when the ohmic pretreatment was carried out in a liquid medium, the effect was not evident. This might be due to water absorption during the treatment, which increased initial moisture content as well as porosity of the treated samples.     

油炸马铃薯片中丙烯酰胺形成的影响因素的研究

丙烯酰胺是富含碳水化合物和氨基酸的食品经高温加热发生美拉德反应而产生的,但有关影响丙烯酰胺形成因素的研究却较少。探讨了油炸温度、原料中还原糖和氨基酸含量、鲜薯切片浸泡液的柠檬酸浓度、油炸前薯片的水分含量及抗氧化剂和油的使用时间对丙烯酰胺形成的影响。结果表明:原料中还原糖和氨基酸含量越高,产品中生成的丙烯酰胺就越多;油炸温度越高,产品中丙烯酰胺含量也相应越高;浸泡液柠檬酸浓度越大,产品中丙烯酰胺含量越低;而随着半成品中含水量的降低,产品中的丙烯酰胺含量也逐渐减少;在油中添加不同浓度的BHT和TBHQ以及采用使用时间不同的油,对加工出来的薯片之间丙烯酰胺含量没有显著的影响。     

Acrylamide in potato crisp—the effect of raw material and processing

Reducing sugars and free amino acids were analysed in slices from three potato cultivars before and after blanching (0-3 min). The potato crisps were deep fried at 185 °C for different times (3-8.5 min), and analysed for the concentration of acrylamide (AA) and moisture. Potato cultivar and the temperature during processing were important parameters for AA formation in potato crisps. The amount increased with an increase in the processing time. Blanching before deep-frying reduced the concentration of free asparagine and reducing sugar in the raw material. We found no effect of blanching as pretreatment on the concentration of AA in the potato crisps. Any relationship was not detected between the levels of asparagine in the different cultivars, before and after blanching, and the formation of AA in the crisp products. However, it was shown that the content of reducing sugars determined the level of AA after frying.     

Improvement of color and limpness of fried potatoes by in situ pectinesterase activation

 Low-temperature, long-time blanching (LT–LT blanching) was performed on potato strips prior to frying. Application of this treatment actived the pectinesterase enzyme in situ resulting in a decrease in the limpness of the fried potatoes; likewise, an improvement in color was obtained as the result of a decrease in reducing sugar content. LT–LT blanching at 65  °C for 45 min gave the greatest improvement in the color and limpness of french fries. Received: 1 December 1998     

Effects of potato strip size and pre-drying method on french fries quality

Potato strips of 8 mm × 8 mm and 10 mm × 10 mm after blanching were pre-dried using two methods: convective and vacuum-microwave (VM). A two-stage frying in rapeseed oil was applied to prepare French fries from pre-dried potato strips. The quality of French fries in terms of texture, oil content and color was analyzed based on the results from instrumental tests and sensory evaluation. Using vacuum-microwave instead of hot air resulted in substantial shortening of the potato strips’ pre-drying time and decreasing the fat content in French fries. Pre-drying of potato strips, particularly by VM method, improved color and increased maximum cutting force as well as maximum cutting work estimated for French fries. French fries prepared from potato strips of 10 mm × 10 mm exhibited lower lightness, higher fat content and higher cutting strength compared with those made from potato strips of 8 mm × 8 mm. Based on the sensory results, it was found that the best French fries were those from pre-dried potato strips of 8 mm × 8 mm, independently of the pre-drying method used, and the worse were those from potato strips of 10 mm × 10 mm pre-dried with the convective method. SEM images confirmed structural changes occurred in potato tissue during pre-drying and frying.     

Relationship between oil uptake and moisture loss during frying of potato slices from c. v. Record U.K. tubers

The variations in moisture content and oil content of samples of 1.5-mm thick slices of potato (c.v. Record U.K.) were examined after various frying times at frying temperatures of 145, 165 and 185°C. The loss of moisture and the uptake of oil were found to be interrelated and both were linear functions of the square root of frying time. Within the temperature range examined, moisture loss and oil uptake were found to be independent of frying temperature. From the data and visual observations the mechanism of moisture loss and its influence on oil content in the final product were discussed. Suggestions are made for means of reducing the total oil content by modifications in the frying process.     

Effects of combined pulsed electric field and blanching pretreatment on the physiochemical properties of French fries

The aim of this work was to explore the effect of combining pulsed electric field (PEF) with blanching pretreatment on the physiochemical properties of French fries. The effects of PEF plus blanching pretreatment on the color parameters, texture, content and spatial distribution of moisture and oil, microstructure, colony count and acrylamide content of French fries were investigated. Results showed that the pretreated French fries were brighter (L value was 60.44) and golden yellow, with lower hardness (312.27 g), higher springiness (0.81) and higher chewiness (119.71). In addition, moisture and oil contents of the fries were reduced, with more uniform distributions. The cross-section microstructure of these French fries also showed near-complete gelatinization of starch particles, and the internal structure of fries was fluffy. Finally, French fries obtained by the combined pretreatment had an improved food safety profile, with a lower colony count (13 CFU/g) and acrylamide content (1533.75 ng/g).Industrial relevanceBlanching is a traditional thermal processing technology widely used in the field of fried potatoes. However, blanching has some disadvantages such as slow heat conduction, long processing time, substantial loss of soluble nutrients, and huge water wastage. PEF is an emerging technology in the 21st century that can maintain the original flavor, color, taste, and nutritional value of foods treated by it. The French fries obtained by combining PEF and blanching pretreatment were brighter and golden yellow, and were also softer, and more springy and chewy – an overall net improvement in aesthetic appeal and organoleptic profile. The above findings may provide useful information to guide effective strategies for the practical application of PEF combined with blanching in the preparation of fried potato foods.     

EVALUATION OF THE TEXTURE OF FRIED POTATOES

Texture of potatoes with different shapes (slices and strips) were evaluated after frying and in some cases after baking. Blanched and unblanched potato slices (Bintje variety) were fried at four oil temperatures: 160, 170, 180 and 190C until reaching a moisture content of ∼1.7%. A puncture test with three point support for the slices was applied to measure the texture of potato chips using the following parameters extracted from the force versus distance curves: maximum force of break (MFB) and deformation of break (DB). These two parameters were useful to follow the changes in texture of the fried slices with moisture content at different frying temperatures. Blanched and unblanched potato strips were partially fried at 160C and 190C for 60, 90 and 120 s. The par-fried potatoes were frozen at -20C for one day after which they were baked at 200C for 15 min. The texture of the baked potato strips was evaluated using a bending test with two support points. From the force versus distance curves, two parameters were extracted: maximum force of deformation (MFD) and maximum deformation (MD). Significant higher MFB and lower DB values (P > 0.1) for unblanched fried slices indicate that these are crispier than blanched chips for moisture contents lower than 4% (6.59 N and 0.62 mm vs 5.74 N and vs 0.75 mm for unblanched and blanched chips, respectively, average values for the four frying temperatures employed). There was no effect of the frying temperature and the pretreatment (blanching or unblanching) on the texture of the frozen par-fried potatoes after baking when compared at the same residual moisture content, but blanched potato strips lost moisture more slowly both in frying and in baking.     

香菇脆片真空油炸过程中传质规律

真空油炸过程中传质现象对真空油炸果蔬脆片的品质和安全控制极为重要。研究了油炸温度（80、90、100℃）、真空度（0.075、0.085、0.095 MPa）、预处理方式（漂烫,漂烫+浸渍+涂膜）对香菇脆片真空油炸过程中水分扩散和油脂吸收的影响,结果表明:香菇脆片的含水率随油炸时间的增加而逐渐降低,采用Pabis经验模型能较好模拟香菇脆片真空油炸过程中的水分变化;利用菲克定律建立模型,得到香菇真空油炸的水分有效扩散系数为2.47×10-9~7.70×10-9 m2/s,并且随着油炸温度和真空度的升高而增大;采用浸渍和涂膜处理降低了水分有效扩散系数。香菇片的油脂含量随着油炸时间的增加而逐渐升高,一段时间后达到稳定值;浸渍和涂膜处理降低了真空油炸香菇脆片的含油率。Pabis经验模型能够较好的模拟真空油炸香菇脆片的油脂含量变化,油炸温度和真空度对香菇脆片的平衡含油率（Y_max）影响不大,油脂吸收系数（K_Y）随着油炸温度和真空度的升高而增加。     

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 blanching on the mechanical and rehydration properties of dried potato slices

 Short-time blanched (2 min, 90  °C), long-time blanched (30 min, 90  °C) and non-blanched potato slices were dried in a convective air drier and their mechanical and rehydration properties were compared. Blanching increased the flexibility and strength of dried potato slices, although the effects of short and long blanching were not significantly different. Unblanched potato slices did not have larger rehydration ratios than blanched ones. After rehydration for 30 min, samples from all treatments had higher strength and flexibility than cooked potatoes. Received: 2 November 1998 / Revised version: 15 February 1999     

Oil uptake and texture development in fried potato slices

The objective of this work was to study oil absorption and the kinetics of texture development of fried potato slices during frying. Prior to frying, potato slices were blanched in hot water at 85 °C for 3.5 min. Unblanched slices were used as the control. Control and blanched potato slices (Panda variety, diameter: 37 mm, width: 2.2 mm) were fried at 120, 150 and 180 °C until reaching moisture contents of 1.8% (total basis) and their texture and oil content were measured periodically. Oil uptake was higher in 15% for blanched samples than for control samples after 20 s of frying. Besides, the higher the frying temperature, the lower the oil absorption in control samples. Textural changes in fried potato slices were followed by the parameter maximum force (MF) extracted from the force vs. distance curves corresponding to different sampling times. Normalized maximum force (MF*) was used in modeling textural changes in the potato slices during frying in both the initial tissue softening process and the later crust development process. Higher temperatures accelerated these processes; however neither the temperature nor the pre-treatment had a significant effect (P > 0.05) over the final texture of the fried potato chips.     

Deep Frying Performance of Enzymatically Synthesized Palm-Based Medium- and Long-Chain Triacylglycerols (MLCT) Oil Blends

The main aim of this work was to assess the frying strength of the enzymatically synthesized palm-based medium- and long-chain triacylglycerols (MLCT) oil with the aid of different antioxidants under deep-frying conditions. Palm-based MLCT oil in the presence of synthetic or natural antioxidants showed significantly better (P < 0.05) thermal resistance and oxidative strength than refined, bleached, and deodorized (RBD) palm olein throughout the five consecutive days of frying. Rancimat induction period, free fatty acid content, anisidine value, E^\text1% _1\textcm E^{{\text{1\% }}} _{1{\text{cm}}} at 232 and 268 nm, color, percentage of oil uptake, and viscosity measurement can be used as oil quality parameters to indicate the degree of oil deterioration under continuous stressed frying conditions. No significant changes (P > 0.05) in the saturated/unsaturated fatty acids ratio across frying periods indicated good oxidative stability of the palm-based MLCT oil. Due to the polarity of medium- and long-chain triacylglycerols in palm-based MLCT oil, total polar compounds determination may not be a suitable oil quality measures. Sensory evaluation of fried chips showed no significant differences (P > 0.05) between chips fried in RBD palm olein and palm-based MLCT oil over the 3-month storage period.