COLOR AND TEXTURE DEVELOPMENT OF POTATO CYLINDERS WITH LIQUID SMOKE DURING BAKING, FRYING AND MICROWAVING

The rate of color and texture development in partially fried before freezing potato cylinders processed by deep fat frying, microwaving and baking was determined. The effect of 0, 1, 3 or 5% wt/wt solution containing 30% liquid smoke was measured at intervals during thermal processing and the reaction order and rate determined. Also, five different wood and dextrose‐derived browning agents were compared at 1% wt/wt addition. The processing method had a significant effect on the reaction rates of color and texture development during processing. Microwaving was faster than frying, which was faster than baking. The addition of liquid smoke led to a significant increase in the rate of color production but had no statistically significant effect on texture. The addition of 1% liquid smoke increased the reaction rate by adding carbonyls, which limit the reaction rate in potatoes. Higher levels of liquid smoke did not change the reaction rate because the carbonyls were no longer limiting the reaction. The processing method and the addition of the browning agent had no effect on the reaction order which remained a pseudo zero‐order reaction. Thus, liquid smoke could be used to reduce processing times, potentially saving money and decreasing acrylamide formation.     

On the Possibility of Nonfat Frying using Molten Glucose

Fried products impose a health concerns due to considerable amount of oil they contain. Production of snack foods with minimal oil content and good management of oil during frying to minimize the production of toxic compounds continue to be challenging aims. This paper aims to investigate the possibility of producing a fat‐free food snack by replacing frying oil with a nonfat medium. Glucose was melted and its temperature was then brought to 185 °C and used to fry potato strips, to obtain a product referred here as glucose fries. The resulting product was compared with French fries prepared conventionally under conditions that resulted in similar final moisture content. The resulting products were also examined for crust formation, texture parameters, color development and glucose content. Stereo microscope images showed that similar crusts were formed in the glucose fries and French fries. Texture parameters were found to be similar for both products at 5 and 2 mm penetration depth. The maximum hardness at 2 mm penetration depth was also similar for both products, but different from cooked potato. The color development that characterized French fries was also observed in glucose fries. The glucose content in glucose fries was found to be twice the content of French fries, which is to be expected because glucose absorbed or adhered to the surface. In conclusion, glucose fries, with similar texture and color characteristics to that of French fries, can be prepared by using a nonfat frying medium.     

The influence of frying medium degradation on fat uptake and texture of French fries

The purpose of the present investigation was to study the influence of the degree of degradation of different kinds of oils used as a frying medium on fat uptake and texture of frozen pre‐fried French fries. As has been found, the degradation degree of the frying medium depends on the kind of oil and processing time. Liquid hydrogenated rapeseed oil exhibited the best thermo‐oxidative stability among the oils under investigation. The kind of oil influenced fat uptake and the texture of French fries. The lowest fat uptake was observed with French fries fried in solid oil. Some correlations between fat uptake and changes in fatty acid content were found in the frying medium during frying. Fat absorption increased with increasing unsaturated fatty acids and decreasing saturated fatty acid content. The texture of French fries fried in hydrogenated oils was harder than that exhibited by French fries fried in liquid rapeseed oil. The hardness of French fries fried in liquid oils decreased during frying while the hardness of French fries fried in solid oil increased. Some correlations between the texture of French fries and iodine value and fatty acids content of frying media were found. The hardness of French fries increased with increasing content of saturated fatty acids and decreasing unsaturated fatty acids and trans isomer fatty acid content. Copyright © 2005 Society of Chemical Industry     

THERMAL BROWNING OF TOMATO SOLIDS AS AFFECTED BY CONCENTRATION AND INHIBITORS

SUMMARY– The amount of brown color developed was always determined by reconstituting the sample to 5.6% total solids and measuring optical density (O.D.) of an acetone extract at 420 mμ. Tomato solids at concentrations of 5.6 to 98% were heated for 15 min at 95°C. The O.D. increased slowly with increasing concentration to about 50% solids. Thereafter, the O.D. increased rapidly to a peak at 95% and decreased to half this value at 98%. The effect of heating time at 55, 75 and 95°C and at 5.6 and 45% solids was studied. The browning rate was slight at the lower 2 temperatures relative to that at 95°C, and was much more rapid at the higher concentration than at single strength. Under each temperature and solids condition, the rate of browning was highest at the earlier times. The inhibition effects of pH and SO₂ were studied. Browning was at a minimum at pH 2.5. Browning could be further reduced at each pH by increasing levels of SO₂. The protective effect of acidification and SO₂ addition increased with increasing solids concentration.     

三种多羟基醇协同海藻酸钠处理对油炸薯条吸油量和品质的影响

为了减少油炸薯条吸油量,探讨不同浓度多羟基醇协同1%海藻酸钠溶液预处理薯条对油炸薯条脂肪含量的影响,利用不同浓度的多羟基醇(木糖醇、山梨醇及丙三醇)溶液协同1%海藻酸钠溶液预处理自制薯条与商业冷冻薯条,研究薯条吸油量、质构、色差的变化。结果表明:在自制薯条中,经木糖醇、山梨醇与丙三醇协同1%海藻酸钠溶液分别处理的薯条,与不做任何处理的油炸薯条相比,脂肪含量分别减少了20.45%(1%海+0.5%木)、53.00%(1%海+0.25%山)、48.72%(1%海+0.75%丙),而与仅仅涂抹1%的海藻酸钠溶液的油炸薯条相比,脂肪含量分别减少了18.35%(1%海+0.5%木)、51.75%(1%海+0.25%山)、47.37%(1%海+0.75%丙)。而商业冷冻薯条,与不做任何预处理的油炸鲜样和仅涂抹1%海藻酸钠溶液组相比,脂肪含量反而分别增加了12.29%和29.11%(1%海+1%木)。同时,木糖醇处理还能显著提高薯条L*(p<0.05)和咀嚼性(p<0.05)。木糖醇对自制薯条具有减油效果,且作用效果是山梨醇 > 丙三醇 > 木糖醇,三种多羟基醇能改善自制薯条的色差与质构。     

Vitamin C Retention of Potato Fries Blanched in Water

Vitamin C retention was determined microfluorometrically for French fries heated in water. Vitamin C retention for 1.3 cm (½ in.) water blanched French fries ranged from 83.2–54.1%. The French fry blanch times were 5, 10 and 15 min at 66°C, 77°C and 88°C. The apparent Ea was 4.0 Kcal/mole.     

Browning Potential of Liquid Smoke Solutions: Comparison of Two Methods

The color-forming potential of carbonyl compounds from liquid smoke solutions with selected amino acids was determined with a colori-metric procedure used in industry and compared with a color analysis on filter oaoer discs. The two methods provided different evaluations of formed colors. Of the carbonyls tested, glycolaldehyde, methyl-glyoxal and glyoxal showed significant browning potential, while formaldehyde and hydroxyacetone showed very little color formation. Measurement of browning potential of amino acids varied between the procedures. The disc assay procedure enabled better characterization of smoke colors produced.     

The influence of oil type and frying temperatures on the texture and oil content of French fries

The purpose of the present study was to determine the effects of the frying medium and temperatures on fat content and texture of French fries. The material taken for the study consisted of seven types of vegetable oil: refined sunflower, rape, soy, olive oil, palm, partially hydrogenated rape oil (modified oil I) and a blend of vegetable oils (modified oil II). The French fries prepared from Asterix potato variety were fried at oils heated to 150, 160, 170, 180 and 190 °C. The length of frying (12, 10, 8, 6.5 and 4.5 min, respectively) depended on oil temperature. Fat content and the texture of French fries were determined. The type of frying medium significantly affects the texture of French fries. Temperature influenced both the fat content and texture of product. The increase of frying temperature decreased fat uptake and hardness of French fries. French fries fried in rape oil exhibited the most delicate texture and the lowest oil absorption when compared with French fries fried in other types of oil under investigation. Copyright © 2005 Society of Chemical Industry     

Frying Oil Deterioration and Vitamin Loss During Foodservice Operation

Oxidation and vitamin E loss in four frying oils (two partially hydrogenated soybean oils, one with methyl silicone, the other with tertiary butyl hydroquinone, citric acid and dimethyl siloxane added; a semi-solid hydrogenated soybean and palm oil shortening with mono and diglycerides added; and 100% corn oil) were studied under experimental and ‘actual’ operational conditions. Vitamin E loss in the frying oil increased significantly with increasing fatty acid oxidation. Added antioxidants, vitamin E and hydrogenation of fat decreased the rate of vitamin E loss. No significant change in vitamin E of the French fries occurred during 4 days of commercial frying; a significant increase in French fry fat uptake improved the 40% reduction in vitamin E of the frying oil. Vitamin C in the French fries (a major source of the vitamin in fast food meals) decreased significantly as the vitamin E content of the oils was reduced.     

VOLATILE COMPOUNDS AND SENSORY CHARACTERISTICS OF FRYING FATS

Oxidation-derived volatiles in French fries were evaluated relative to sensory characteristics of the fries and of the frying oils (low linolenic acid soybean oil, LLA; creamy partially hydrogenated soybean oil, CPH; liquid low linolenic acid hydrogenated soybean oil, LLH; and liquid partially hydrogenated soybean oil, LPH) in which they were fried. Hexanal concentration in French fries increased as oil use time increased for all fats; LLA and CPH produced higher hexanal concentrations in French fries after 10 and 15 days of oil use than did LPH and LLH. Hexanal concentration was negatively correlated with overall odor quality of French fries and positively correlated with grassy, rancid, painty, and chemical odor. Buttery, sweet, and French fry odor decreased and grassy, rancid, painty, and acrolein odor increased as oil use time increased.     

Producing lower-calorie deep fat fried French fries using infrared dry-blanching as pretreatment

The main objectives of this work were to study the suitability of using infrared (IR) heating as a dry-blanching pretreatment prior to frying and to investigate its potential to reduce the oil uptake in French fry production. It was observed that by using IR heat complete inactivation of polyphenol oxidase enzyme could be achieved in 3 min with 4.7% moisture loss for 9 mm French fries. Following IR dry-blanching, the samples were fried at 146, 160, and 174 °C for 1, 3, 5, and 7 min. At the end of 7 min frying, compared to unblanched samples, dry-blanched samples had 37.5%, 32% and 30% less total oil at the frying temperatures of 146, 160 and 174 °C, respectively. The final moisture contents of unblanched and dry-blanched samples were between 50% and 60% after 7 min frying. The L*a*b* colour values of both unblanched and dry-blanched samples decreased initially and then increased as the frying progressed. The sensory evaluation revealed that panelists mostly favored the IR dry-blanched French fries in terms of taste, texture, colour and appearance.     

A Comparative Study of the Characteristics of French Fries Produced by Deep Fat Frying and Air Frying

Air frying is being projected as an alternative to deep fat frying for producing snacks such as French fries. In air frying, the raw potato sections are essentially heated in hot air containing fine oil droplets, which dehydrates the potato and attempts to impart the characteristics of traditionally produced French fries, but with a substantially lower level of fat absorbed in the product. The aim of this research is to compare: (1) the process dynamics of air frying with conventional deep fat frying under otherwise similar operating conditions, and (2) the products formed by the 2 processes in terms of color, texture, microstructure, calorimetric properties, and sensory characteristics. Although, air frying produced products with a substantially lower fat content but with similar moisture contents and color characteristics, it required much longer processing times, typically 21 min in relation to 9 min in the case of deep fat frying. The slower evolution of temperature also resulted in lower rates of moisture loss and color development reactions. Differential scanning calorimetry (DSC) studies revealed that the extent of starch gelatinization was also lower in the case of air fried product. In addition, the 2 types of frying also resulted in products having significantly different texture and sensory characteristics.     

NONUNIFORM BROWNING OR "MOTTLING" IN FRENCH FRY PRODUCTS ASSOCIATED WITH A HETEROGENEOUS DISTRIBUTION OF REDUCING SUGARS

An attempt was made to relate compositional factors to the unpredictable defect of "mottling", or nonuniform browning, which develops during the finish-frying step for French fry products prepared from stored potato tubers. Potato (Russet Burbank) strip samples originating from fresh tissue and tissue processed up to the point immediately prior to finish frying, were prepared from stored tubers. Fresh and processed tissue areas that were prone to mottling had significantly (P < 0.01 to 0.05) greater levels of total sugar, glucose and fructose than did areas that were lighter in color and provided the background coloration. Glucose oxidase/peroxidase staining of surfaces of commercial French fries also showed the association of a heterogeneous distribution of glucose and the incidence of mottling. Enrichments in total and reducing sugar levels in tissue prone to mottling were modest (40–60% greater) compared to tissue along the same potato tissue strips that provided background coloration.     

Growth of Bacillus cereus on Oil-blanched Potato Strips for "Home-style" French Fries

Fresh cut, oil blanched strips from whole potatoes stored at 7 or 13 °C were inoculated with approximately 3 or 5 log CFU/g Bacillus cereus and incubated at 21 or 26.7 °C for up to 9 h to model handling of "home-style" French fries. Whole potato storage at 13 °C and incubation at 26.7 °C resulted in faster growth than 7 or 21 °C. Frying (2 to 3.5 min at 185 °C) inactivated up to 5.1 log B. cereus spores. Oil blanched potato strips for "home-style" French fries should be stored at £ 21 °C or finish fried or discarded within 3 to 4 h.     

Prevention of Discoloration in Retorted Whole Egg

Prevention of the green-grey discoloration of liquid whole eggs cooked at high temperatures was studied. Disodium ethylenediaminetetraacetic acid (NaZEDTA) was used to prevent the discoloration in whole egg adjusted to pH 8.5. Liquid egg samples in flexible packages were subjected to retort conditions (121°C, for 20 min) and evaluated for off-color development. Discoloration was more severe at higher temperatures and longer cooking times; however, the use of 0.015% NazEDTA was effective in preventing green-grey color development.     

Changes of polysaccharide content and texture of potato during French fries production

The purpose of the present study was to determine the changes in non-starch polysaccharide and lignin contents of potato during French fries production and also the relationship between the texture of the finished product and half-products, as a result of processing at each stage under investigation. The samples for laboratory studies were taken from potato tubers, strips and French fries collected from nine locations of a technological line. The greatest changes in non-starch polysaccharide content and texture of potatoes resulted from blanching and frying. The texture of French fries was mainly affected by pectin and cellulose. The texture of French fries can be predicted from the measurements of the texture of potato strips after blanching.     

Effects of Processing Conditions on Qualities of Rice Fries

ABSTRACT Two rice flour mixtures, 2 extruding temperatures, and 2 insert sizes were used to develop rice fries. The extruded material was cut into pieces 7 to 8‐cm long, prefried in rice oil at 180°C for 20 s, and kept frozen until final frying for another 70 s. The rice fries were evaluated 5 min and 10 min after final frying for their lipid, moisture, and instrumental texture characteristics. Extruding temperature, rice cultivar, and insert size were significantly related to fat content, moisture, hardness, and fracturability values. A mixture consisting of 80:20 (waxy:long‐grain), and extruded at 70 °C using a 6 mm insert, 5 min after frying, gave a texture profile analysis value for hardness, cohesive‐ness, and gumminess values comparable to commercial potato French fries. The rice fries made by the process also had less than 50% fat than potato fries.     

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.     

Quality of French Fried Potatoes as Affected by Surface Freezing and Specific Gravity of Raw Potatoes

Russett Burbank potatoes were stored at 7.2°C for 9 months and processed into French fries. Some of the potato strips were subjected to partial freezing at – 20°C for 25 min before water blanching for surface leaching. The samples treated by partial (surface) freezing generally absorbed more oil during par-flying but less oil during finish-frying compared to the untreated samples (control). French fries made from partially frozen potato strips contained less reducing sugar and ascorbic acid and were lighter in color than the control. Darker fries were produced from potatoes of lower specific gravity because of the higher reducing sugar content. The surface freezing treatment was an effective means of decreasing oil absorption and improving color of French fries.     

Structural changes and shrinkage of potato during frying

Summary Light microscopy was used to study changes in cell size, blister formation and crust evolution during potato frying. Frying experiments with both French fries and crisps of different thickness (1–5 mm) were performed at temperatures of 140 and 180 °C. Thickness, volume and density changes were also measured. The formation of crust in French fries starts after the potato surface reached approximately 103 °C, and then the crust thickness increased linearly with the square root of frying time, this increase being faster at 180 °C. The potato volume decreased during frying, although in the late stages the volume may increase because of oil uptake and cell separation caused by entrapped water vapour. Shrinkage was adequately described by the Weibull model with a residual value, with shrinkage rate increasing with temperature and decreasing with potato thickness. The residual volume was not affected by temperature (65% for French fries and 59–30 for crisps, depending on thickness). Volume appeared to decrease mainly as the result of water loss, except for very low water content, and thus potato density changes were very small.