KINETICS of QUALITY CHANGE DURING COOKING and FRYING of POTATOES: PART II. COLOR

Color, as a quality attribute of cooked and fried potatoes, is affected by the extent and nature of heat during thermal processing. Improvement of color parameters has been made possible by the increase in knowledge of kinetics of color change. Analysis of kinetic data allows processors to minimize undesirable changes and optimize color retention. the objective of this study was to evaluate kinetics of color change during cooking and frying of potatoes. Potatoes were cut into cylinders (diameter × height: 20 mm × 20 mm for cooking and 10 mm × 20 mm for frying) and cooked in a temperature controlled water bath at 80–100C or fried in a commercial fryer at 160–190C for selected times. Color changes associated with cooked and fried potatoes were evaluated using a tristiumulus colorimeter in the L, a, b mode. For cooked potatoes, L and b values decreased while ΔE and a values increased with time at each cooking temperature. For fried potatoes, L value decreased while a, b and ΔE values increased as frying time increased. A modified first order model was used to characterize color change kinetics of both cooked and fried potatoes based on changes occurring between the initial and a maximum or minimum value. Temperature sensitivity of rate constants was adequately described by the Arrhenius and z‐value models.     

Determination of acrylamide content of food products in Korea

Acrylamide (AA) contents of commercial market‐purchased foods and of traditional home‐cooked Korean foods were investigated. The effect of cooking method on AA amount in potatoes was also studied. AA contents of roasted barley and corn ranged from 116 to 449 µg kg^?1 and of chips ranged from 12 to 3241 µg kg^?1, representing a very high variation in AA contents among tested samples. Lower levels of AA were found in wheat flour chips compared to potato chips. AA contents of ramen noodles were below 37 µg kg^?1, whether they contained potato starch or not. The AA contents of Korean home‐cooked oil fried foods increased in the following order: yakwa < whole deep‐fried sea tangle < ground and deep‐fried lotus root < ground and pan‐fried lotus root < French fries < ground and pan‐fried potato. Lotus root and garlic also had the potential to produce AA during cooking. Pre‐treatment such as grinding, boiling, freezing and thawing increased the AA formation in oil‐fried potato. Temperature was more influential than time on AA formation during deep‐oil frying. Removing water‐soluble fractions reduced AA content of cooked potatoes. Copyright © 2006 Society of Chemical Industry     

INSTITUTIONAL COOKERY OF RESTRUCTURED BEEF STEAKS

Restructured beef steaks were cooked under four institutional cooking methodologies: oven roasting, grill frying, deep fat frying and broiling. The samples were evaluated for fat and moisture contents, cooking loss and texture. Sensory panels evaluated the steaks for texture desirability, flavor desirability, appearance and overall palat-ability. Evaluations were repeated using breaded, restructured beef steaks cooked by the four institutional methods, with grilled unbreaded steaks included for comparison. Deep fat fried, breaded and unbreaded steaks were significantly lower in moisture and higher in fat than those cooked by any other methodology. No significant differences in juiciness, flavor desirability or overall palatability were found between the unbreaded broiled, oven roasted or grilled samples. Broiled and grilled steaks were preferred for texture in the unbreaded and breaded samples. The unbreaded, deep fat fried samples received the lowest scores for all sensory attributes. Breading significantly improved the juiciness, texture and overall palatability of the deep fat fried steaks. For both breaded and unbreaded samples, grill frying was the preferred method of preparation.     

THE CONTINUOUS WOK — A NEW UNIT OPERATION IN INDUSTRIAL FOOD PROCESSES

The preparation of fine cut vegetables and meat by stir‐frying is characterized by a short cooking time and high rates of heat and mass transfer, which makes scale‐up difficult. A new principle for carrying out an industrial, continuous stir‐frying process is studied at pilot plant scale. The ingredients are transported in a horizontal, open frying tube by a conveyor helix while being tossed by scrapers and stirring rods mounted on the helix. During the frying process the average product temperature stabilizes around 80C, despite the intense heating, and this may explain why the texture of stir‐fried vegetables is firmer than the texture of vegetables cooked in water. However, the heat inactivation of a model microorganism applied as a surface contaminant showed that the effective surface temperature was above 90C which ensures a safe process. Vigorous evaporation from the free surfaces of the turning pieces may cause this temperature gradient to be established by an evaporation cooling effect.     

Effect of Ultrasound-Assisted Osmotic Dehydration as a Pretreatment on Deep Fat Frying of Potatoes

The objective of this study was to investigate the possibility of using ultrasound-assisted osmotic dehydration (UAOD) as a pretreatment prior to frying and to study its effects on the quality of fried potatoes. The quality parameters, moisture content, oil uptake, color, texture, and microstructure of fried potatoes, were chosen. Quality of fried potatoes treated with UAOD was also compared with the ones treated with osmotic dehydration (OD). Potato slabs (40 × 40 × 7 mm) were pretreated with different osmotic solutions (15 % sodium chloride and 15 % sodium chloride/50 % sucrose solutions) at different temperatures (25, 45, and 65 °C) with and without ultrasonic waves for different treatment times. The pretreatment conditions which are OD for 90 min and UAOD for 30 min using 15 % sodium chloride/50 % sucrose solution were applied prior to frying at 170 °C for 2, 4, and 6 min. UAOD reduced the oil content of fried potatoes by 12.5 % (db) as compared to untreated fried potatoes at the end of frying. There was no significant difference between OD and UAOD in reduction of oil uptake in fried potatoes. However, UAOD was found to have the advantage of improving the color of French fries. In addition, it shortened the pretreatment time of OD by about 67 %. Cell structure of fried potato was damaged in the presence of pretreatments of OD and UAOD.     

Minimum Cooking Time for Potato Strip Frying

The maximum force for shearing was used as texture parameter for raw and cooked potato strips. The force was satisfactorily correlated with the cook value C (equivalent cooking time at 100°C) showing complete cooking for C ≥ 300 sec. Thermal histories measured at the center of strips fried under different oil temperatures suggested the heat and mass transfer mechanisms involved in the frying process and allowed the calculation of the minimum frying time to assure cooking at the strip center. This time was independent of the oil temperature and slightly dependent on the strip size.     

Mechanisms of Docosahexaenoic and Eicosapentaenoic Acid Loss from Pacific Saury and Comparison of Their Retention Rates after Various Cooking Methods

The docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents of Pacific saury (Cololabis saira), a fatty fish and staple of the Japanese diet, have been reported to decrease after cooking. This study compared the DHA and EPA contents remaining in saury after grilling, pan‐frying or deep‐frying to center temperatures of 75, 85, or 95 °C, and examined physical loss, lipid oxidation, and thermal degradation as mechanisms of DHA and EPA loss. Temperature changes inside the saury were monitored using thermocouples, while DHA and EPA contents, oxygen radical absorbance capacity, and measurements of lipid oxidation (that is, carbonyl value and thiobarbituric acid value) were determined chemically. Visualization of temperature distribution inside fish samples during cooking revealed large differences in heat transfer among cooking methods. True retention rates in grilled (DHA: 84 ± 15%; EPA: 87 ± 14%) and pan‐fried samples (DHA: 85 ± 16%; EPA: 77 ± 17%) were significantly higher than deep‐fried samples (DHA: 58 ± 17%; EPA: 51 ± 18%), but were not affected by final center temperatures despite differences in cooking times. Physical loss via cooking losses (grilling and pan‐frying) or migration into frying oil (deep‐frying) accounted for large quantities of DHA and EPA loss, while lipid oxidation and thermal degradation did not appear to be major mechanisms of loss. The antioxidant capacity of saury was not significantly affected by cooking treatments. The results of this study suggest that minimization of physical losses during cooking may increase DHA and EPA contents retained in cooked Pacific saury.     

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.     

Effects of different cooking methods on the formation of food mutagens in meat

Hamburgers and chicken fillets were cooked in convection ovens, deep‐fried or contact fried and analysed for mutagenic activity using the Ames test. For the three different convection ovens, the cooking parameters studied included the presence of steam, air velocity, air temperature and holding time. For deep‐frying and contact frying, the cooking parameters included cooking temperature and cooking time. In cooked hamburgers, mutagenic activity was only detected in those that had been deep‐fried. In chicken fillets, mutagenic activity was detected in samples prepared with all cooking methods, being highest in the deep‐fried samples. Factorial analysis indicated that heat transfer was the most important factor affecting mutagenic activity. High temperature and high air velocity in the convection ovens enhanced mutagenic activity. The presence of steam reduced the mutagenic activity, except when high temperature was used in combination with high air velocity. In chicken fillets, high mutagenic activity correlated to high weight loss during cooking. Pan‐fried chicken fillets were analysed using high performance liquid chromatography (HPLC) and the mutagenic/carcinogenic heterocyclic amines 2‐amino‐3,8‐dimethylimidazo[4,5‐f ]‐quinoxaline (MeIQx), 2‐amino‐1‐methyl‐6‐phenylimidazo‐[4,5‐b]‐pyridine (PhIP) and the co‐mutagenic heterocyclic amine Norharman (9H‐pyrido[3,4‐b]‐indole) were identified. The HPLC fractions were tested for mutagenic activity and, apart from the mutagenic fractions corresponding to MeIQx and PhIP, several mutagenic fractions were detected that did not correspond to known heterocyclic amines.     

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.     

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.     

基于主成分分析法的熟化马铃薯品质评价

以‘紫花白’马铃薯为原料,研究汽蒸、水煮、微波、烘烤、Air-frying（无油）、Air-frying（加油）、油炸7 种熟化方式对其基本营养成分和核苷酸类鲜味物质、质构、色泽及感官品质的影响,并对其品质指标进行主成分分析。结果表明：汽蒸和微波可最大程度地降低马铃薯基本营养成分的损失;微波显著提升了马铃薯核苷酸类鲜味物质含量且含量最高;Air-frying（无油）显著影响马铃薯质构特性;Air-frying（加油）与油炸显著加深马铃薯色泽;水煮熟化后马铃薯感官评分最高;经主成分分析后,7 种熟化方式下马铃薯品质评价综合得分由大至小依次是：Air-frying（加油）＞微波＞油炸＞水煮＞烘烤＞汽蒸＞Air-frying（无油）。由此得出结论：汽蒸可作为马铃薯深加工前期熟化处理的较优选择;Air-frying（加油）可较好地保留其品质特性,微波可满足摄食低脂类食品消费者的需求。     

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.     

Process optimization and consumer acceptability of salted ground beef patties cooked and held hot in flavored marinade

Food safety is paramount for cooking hamburger. The center must reach 71 °C (or 68 °C for 15 s) to assure destruction of E. coli O157:H7 and other food pathogens. This is difficult to achieve during grilling or frying of thick burgers without overcooking the surface. Thus, the feasibility of partially or completely cooking frozen patties in liquid (93 °C water) together with hot holding in liquid was investigated. Initial studies demonstrated that compared to frying, liquid cooking decreased (P < 0.05) patty diameter (98 compared with 93 mm) and increased (P < 0.05) thickness (18.1 compared with 15.6 mm). Liquid cooked patties had greater weight loss (P < 0.05) immediately after cooking (29 compared with 21%), but reabsorbed moisture and were not different from fried patties after 1 h hot water holding (61 °C). Protein and fat content were not affected by cooking method. However, liquid cooked patties were rated lower (P < 0.05) than fried patties for appearance (5.7 compared with 7.5) and flavor (5.9 compared with 7.5). An 8-member focus group then evaluated methods to improve both appearance and flavor. Salted, grill-marked patties were preferred, and caramel coloring was needed in the marinade to obtain acceptable flavor and color during liquid cooking or hot holding. Patties with 0.75% salt that were grill-marked and then finish-cooked in hot marinade (0.75% salt, 0.3% caramel color) were rated acceptable (P < 0.05) by consumers for up to 4 h hot holding in marinade, with mean hedonic panel ratings > 7.0 (like moderately) for appearance, juiciness, flavor, and texture. PRACTICAL APPLICATION: Grill-marked and marinade-cooked ground beef patties reached a safe internal cooking temperature without overcooking the surface. Burgers cooked using this method maintained high consumer acceptability right after cooking and for up to 4 h of hot holding. Consumers and foodservice operations could use this method without specialized equipment, and instead use inexpensive and common equipment such as a soup pot or a restaurant steam table. Use of marinades (salt/caramel color or others) in this cooking and holding method provides a nearly endless culinary flavoring opportunity.     

Development and application of soy‐protein films to reduce fat intake in deep‐fried foods

A soy protein film coating was developed and evaluated to reduce fat transfer in deep‐fried foods during frying. Soy protein isolate solutions (10% SPI) with 0.05% gellan gum as plasticizer cooled after being held at 80 °C for 20 min provided suitable films. There was a significant fat reduction (55.12 (±6.03)%db) between fried uncoated and coated discs of doughnut mix. The same films were used on potato fries. Some panellists observed a slight difference between the coated and uncoated fries but many preferred the coated fries over the uncoated ones. Penetration test on potato fries showed no significant difference between the texture of coated (SPI with gellan gum) and the uncoated fried samples. A solution of 10% SPI with 0.05% gellan gum is recommended for coating foods to reduce fat intake during deep‐fat frying. © 2000 Society of Chemical Industry     

不同热加工方式熟化对克氏原螯虾理化性质和风味的影响

通过电子鼻和电子舌及气相色谱-质谱等技术分析油炸（90、120、150、180 s）、空气炸（5、10、15、20 min）和沸水煮（150 s）熟化后克氏原螯虾虾肉中的风味差异。结合不同热加工方式熟化虾肉后理化指标（基础成分、质构、色度、硫代巴比妥酸反应物值）的测定结果,综合评价虾肉品质的变化。结果表明：电子鼻、电子舌能够很好地区分不同热加工方式熟化的虾肉,且随着热加工时间的延长,在主成分分析图中区域划分越明显;在新鲜虾肉和沸水煮虾肉内分别检测出8、16种风味物质,在油炸虾肉内检测出18、18、16、19种风味物质,而在空气炸虾肉内检测出19、20、20、16种风味物质,空气炸虾肉中吡嗪类化合物含量显著高于其他2种热加工方式;随着热加工时间的延长,虾肉内水分含量均逐渐降低,油炸和空气炸虾肉内脂肪含量和硬度逐渐上升,而弹性呈先上升后降低的趋势;不同热加工方式熟化虾肉的品质不一,结合感官鉴定结果,综合分析空气炸15 min的虾肉品质最佳。     

Effect of method of cooking on identification of heat processed beef using polymerase chain reaction (PCR) technique

Effects of various cooking methods including boiling, roasting, pressure cooking, and pan frying on species determination of beef by PCR was studied. The meat was cooked by boiling at 97.5°C for 140, 200 or 230min, by roasting at 200°C for 80, 120, or 150min or by autoclaving at 120°C for 30, 60, or 90min. The beef sample was pan fried until the meat was acceptable for sensory attributes (45min, meat temperature 115°C, fat temp 173°C) and further cooked until unacceptable. DNA was extracted from samples taken after cooking and a 271bp fragment of the mitochondrial DNA was amplified by PCR. The results indicated that with the exception of pan frying for 80min, beef was determined in all meat samples including the broth and sauce of the roasted meat.     

KINETICS OF ACRYLAMIDE FORMATION DURING TRADITIONAL AND VACUUM FRYING OF POTATO CHIPS

Acrylamide is considered a carcinogen in animals and a possible carcinogen in humans. It has been found in starch‐rich foods cooked at high temperatures. Vacuum frying (10 Torr) was investigated as a possible alternative to reduce acrylamide formation in potato chips. The cultivar Atlantic was used to determine the kinetics of acrylamide formation during traditional and vacuum frying at different temperatures. There was a 94% decrease in acrylamide content when potatoes were fried to the same final moisture content (1.5% ± 0.3% w.b.) under vacuum compared to those fried under atmospheric conditions. Acrylamide accumulation under vacuum frying was modeled using first‐order kinetics (during traditional frying, the logistic kinetic model was used). The behavior of the kinetics of acrylamide content in potato chips fried under the two processes was different mainly because of the different temperatures used. During traditional frying, higher temperatures are used (150 to 180C) and acrylamide after some time is produced but starts degrading, producing a constant level of acrylamide content at longer times. During vacuum frying (10 Torr), acrylamide increased exponentially (but at lower levels) for all frying times.     

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     

Transfer of heat and moisture during microwave baking of potatoes

Microwave baking of potatoes comprised two phases. In the first phase the internal temperature of the potatoes rose to approximately 100 °C with little loss of water vapour. The uniformity of internal heating during this phase was assessed by identifying gelatinised starch. Starch gelatinisation began near the outer surface after 1.5 min of cooking and was complete by 2.5 min. During the second cooking phase the thermal energy absorbed was used to evaporate water. When immersion in boiling water was substituted for this second phase of microwave cooking, it took significantly longer for the internal texture to soften adequately for the potatoes to be considered cooked. This suggests that microwave cooking influences texture independently of the thermal profile of the cooking process. Damage by escaping steam is suggested as a mechanism. © 2002 Society of Chemical Industry