Influence of Reducing Sugars and Amino Acids in the Color Development of Fried Potatoes

Color development during potato frying was studied. Increments of reducing sugars led to increase in color of fried potatoes. For L (luminosity) between 60–51, corresponding to a reducing sugar content of 120–140 mg %, an acceptable color was obtained. Both amino acids and reducing sugars participated in the color development of potato during frying, with the amount of reducing sugars being the limiting factor. Fructose yielded the highest browning followed by glucose. Sucrose addition caused practically no change in the final color of the fried potato. At low content of reducing sugars the reaction followed first-order kinetics, the activation energy, Ea, being equal to 31 Kcal mol^-1.     

Color changes and acrylamide formation in fried potato slices

The objective of this work was to study the kinetics of browning during deep-fat frying of blanched and unblanched potato chips by using the dynamic method and to find a relationship between browning development and acrylamide formation. 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 acrylamide content and final color were measured. Color changes were recorded at different sampling times during frying at the three mentioned temperatures using the chromatic redness parameter a¹. Experimental data of surface temperature, moisture content and color change in potato chips during frying were fit to empirical relationships, with correlation coefficients greater than 90%. A first-order rate equation was used to model the kinetics of color change. In all cases, the Arrhenius activation energy decreases alongside with decreasing chip moisture content. Blanching reduced acrylamide formation in potato chips in ∼64% (average value) in comparison with control chips at the three oil temperatures tested. For the two pre-treatments studied, average acrylamide content increased ∼58 times as the frying temperature increased from 120 to 180 °C. There was a linear correlation between acrylamide content of potato chips and their color represented by the redness component a¹ in the range of the temperatures studied.     

Kinetics of colour and texture changes in Gulabjamun balls during deep-fat frying

Gulabjamun, a popular Indian milk sweet, is prepared by deep-fat frying of balls of dough made of khoa, wheat flour and baking powder, and subsequent dipping in sugar syrup. Kinetics of colour and texture changes in gulabjamun balls were investigated with regard to frying temperature (120, 130, 140 °C). Crust colour was evaluated in terms of CIELAB parameters L*, a*, b*, and ΔE, and rheological properties in terms of hardness, stiffness and firmness. Frying-induced surface browning was reflected in a decreasing lightness value L* as well as the ratio of yellow hue index b* and red hue index a* and total colour expressed in terms of ΔE, L* following a zero-order change whereas the other parameters, a first-order change. Increase in the texture parameters hardness and firmness followed zero-order reaction kinetics whereas stiffness rise followed a first-order reaction. The temperature dependence of reaction constants could be explained by the Arrhenius equation. Activation energy was also obtained for both the colour and texture changes, which were in the range of 24.5-77.6 kJ/mol. High correlations between colour and texture parameters were observed and it was concluded that L* alone could be used to predict the firmness of deep-fat fried gulabjamun balls.     

Effect of Pretreatments and Air‐Frying,a Novel Technology,on Acrylamide Generation in Fried Potatoes

This paper investigated the effect of air‐frying technology, in combination with a pretreatment based of soaking the samples in different chemical agent solutions (citric acid, glycine, calcium lactate, sodium chloride, or nicotinic acid [vitamin B3]), on the generation of acrylamide in fried potatoes. The influence of reducing sugars on the development of surface's color was also analyzed. The experiments were conducted at 180 °C by means of air‐frying and deep‐oil‐frying, as a reference technology. Based on the evolution of color crust with frying time, it could be concluded that the rate of Maillard reaction decreased as the initial reducing sugars content increased in the raw material, and was also lower for deep‐oil‐frying than for air‐frying regardless of pretreatments applied. Air‐frying reduced acrylamide content by about 90% compared with conventional deep‐oil‐frying without being necessary the application of a pretreatment. However, deep‐oil fried potatoes pretreated with solutions of nicotinic acid, citric acid, glycine at 1%, and NaCl at 2% presented much lower acrylamide levels (up to 80% to 90% reduction) than nonpretreated samples.     

Effect of baking conditions and storage with crust on the moisture profile,local textural properties and staling kinetics of pan bread

To investigate the impact of baking conditions on staling kinetics and mechanical properties, pan breads were baked at 180 °C/34 min and 220 °C/28.6 min using a ventilated oven and metallic moulds. After baking, bread slices were stored with and without crust at 15 °C in hermetic boxes for 9 days. This investigation provides a textural and physical analysis by examining the Young's modulus, crumb density and crust/crumb ratio during storage. In order to understand the relationship between firmness and moisture content, a moisture profile and a Young's modulus profile were determined during the storage of bread. To fit the staling, a first order model was used. It was found that the kinetics were faster for samples baked with a fast heating rate than for those baked with a slow heating rate. Moreover, the staling rate of bread stored with crust was faster than for bread without crust and the outer crust area staled more rapidly than the centre of the bread slice. These results suggest that the firming of the crumb is related to moisture distribution between the crumb and crust and to the impact of local baking conditions on local firmness.     

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.     

Phytosterols in frying oils: evaluation of their absorption in pre-fried potatoes and determination of their destruction kinetics after repeated deep and pan frying

The levels of β-sitosterol and total phytosterols were monitored in pre-fried potatoes during eight successive pan- and deep-frying sessions in five different commercial frying oils (virgin olive oil, sunflower oil, palm oil, cottonseed oil and vegetable shortening oil). The amount of these constituents that were transferred from the frying oils to the potatoes at the end of each frying session was determined prior and after frying by GC/FID. Except for the potato enrichment with phytosterols, the kinetics of the destruction of β-sitosterol and total phytosterols, mainly due to thermal oxidation of the oils, were evaluated for each of the five different types of oil. The experiments showed that in most cases the destruction of both β-sitosterols and total phytosterols followed first order kinetics with quite good correlation coefficients (R>0.92) and the reaction constant k was found to be at the range of 0.004 - 0.028 min^-1. Concerning the absorption of the two types of phytosterols in the fried potatoes during frying, they were found to be at the range (average) of 0.4-27% of their initial content in the oil at the beginning of each frying process (eight frying processes/session), depending on the type of oil and the constituent.     

The effect of kefir addition on microstructure parameters and physical properties of porous white bread

The effect of kefir concentration on the quality of porous white bread has been investigated. Quality evaluation was done using flatbed scanning (FBS) for measuring crumb porosity, instrumental texture profile analysis (TPA), crust and crumb color (L ^* a ^* b ^*), moisture, specific volume, and density determination techniques. The correlations between porosity, brightness, and firmness were also investigated. Long fermentation time of the sourdough changed significantly (p<0.05) the cell mean area (mm²), cell mean perimeter (mm), firmness (N), chewiness (N), light reflectance, and specific volume (ml/g). A strong correlation was found between microstructure of porous white bread, brightness (L), and firmness from TPA test. Kefir prolonged the shelf life of bread.     

Thermal Sensitivity of Some Plantain Micronutrients during Deep-Fat Frying

ABSTRACT:  The impact of deep-fat frying on the micronutrient content of plantain ( Musa AAB "barraganete") was evaluated during processing of plantain chips called "tostones." Water content, micronutrients (potassium, L-ascorbic acid, α-carotene, β-carotene) content, and the temperature within the food were quantified during the course of frying. A nonisothermal kinetics analysis of the 1st-order reaction (micronutrient degradation) induced by deep-fat frying, particularly in terms of the spatial distribution of temperature, was proposed. The kinetic parameters (pre-exponential factor k _0, activation energy E_a ) were identified by nonlinear optimization, minimizing the residual variance between the experimental and theoretical micronutrient content. Agreement between model and experimental values was checked. During 1st and 2nd frying, potassium was well retained while carotenoid contents decreased significantly. Moreover, L-ascorbic acid contents decreased significantly, just during 2nd frying. k ₀ was identified as well as E_a observed for L-ascorbic acid, α-carotene, and β-carotene as 68.4 to 71.5, 79.6 to 84.9, and 85.9 to 88.6 kJ/mol, respectively. β-carotene appeared to be more heat-resistant than α-carotene and L-ascorbic acid. The behavior of the nutritional markers appears to be the consequence of the thermal and hydric histories of the crust and of the heart of the plantain disk related to heat transfer during preparation of the "tostones."     

Dynamics of Changes in Viscoelastic Properties of a Tofu During Frying

The viscoelastic properties of a tofu were characterized using the stress relaxation test after deep-fat frying at 147–172°C for 0 to 5 minutes. The results were expressed with a model with two Maxwell elements and a residual spring in parallel. Each elastic modulus and relaxation time followed zero order reaction kinetics. The Arrhenius temperature dependency was applied for the modeling of reaction rate constant, k. The activation energies for the viscoelastic properties were 1.00 × 10⁵ ? 1.49 × 10⁵ J/mol. There was a good agreement between the measured and computed data (R² = 0.976 ? 0.988).     

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.     

Effect of Freezing on Textural Kinetics in Snacks During Frying

Kinetics of texture development during frying of snacks subjected to different initial conditions such as frozen, frozen–thawed, and unfrozen was investigated. The temperature dependency of the changes in the form of reaction constants was explained by Arrhenius equation. The increase in hardness and decrease in cohesiveness followed first-order reaction kinetics (R ² = 0.94–0.99) in all the samples. Frozen samples showed induction (phase I) and development/degradation (phase II) periods for textural parameters during frying. The activation energies for hardness were 33.81, 25.63, 19.09, and 20.13 kJ/mole for frozen (phase I and II), frozen–thawed, and unfrozen samples, respectively with the R ² = 0.96–0.99. Frozen samples showed high activation energies for textural parameters during frying as compared to the frozen–thawed and unfrozen samples. The increase in chewiness was found to follow the kinetics of zero-order reaction for all the samples. Temperature and time were found to have a significant effect (P < 0.01) on the changes in textural profile during frying.     

Kinetics of Color Change of Grape Juice Generated using Linearly Increasing Temperature

Kinetics of the color change of grape juice was studied using linearly increasing temperature for heating Noble grape juice in a stainless steel reactor. The juice was heated from 60^o to 95^oC in 9 hr. Kinetic parameters for the color change were determined using Hunter L, a, b-values, chroma values, and Total Color Difference (TCD) values. The reaction of the color change of grape juice measured by L- and a-values, and Chroma value followed first order kinetics with activation energies of 114.75, 131.80, and 121.21 kJ/mol and frequency factors of 1.30 × 10¹², 8.95 × 10¹⁴ and 1.93 × 10¹³ sec^?1, respectively. However, the reaction measured by TCD followed zero order kinetics with the activation energy and the frequency factor of 92.81 kJ/mol and 4.80 × 10¹⁰ mol/l/sec, respectively.     

Effect of frying variables on French fry properties

This work focuses on the effect of frying variables (repeated frying, potato‐to‐oil ratio, potato distribution in the fryer, oil type and potato variety) on French fry properties (water content, oil content, crust thickness and shrinkage). Furthermore, the rate of change in French fry properties during a frying batch is investigated. The temperature was acquired in several positions within the oil and the potato. It was found that when repeated frying was conducted up to regulation limits for frying oil use, the examined French fry properties were not significantly affected. On the contrary, the potato‐to‐oil ratio, potato distribution and potato variety significantly affected the water content of French fries. The most significant changes occurred during the first 1–2 min of a frying batch. According to the temperature measurements, the crust‐core front continued to advance after this first frying period. However, there was no observable crust thickness increase; this was attributed to crust shrinkage.     

Evaporation front compared with crust thickness in potato deep-fat frying

The various theoretical approaches that have been proposed for modeling heat and mass transport during deep-fat frying of potatoes provide a rather ambiguous view of the relation between the propagation of the evaporation front inside the food and the evolution of crust thickness. This can be partly attributed to the unavailability of detailed experimental information concerning the temperature field inside the developing crust to validate the models. The objective of the present work is to experimentally study the relation between crust thickness evolution and evaporation front propagation and how this varies with frying conditions. To achieve this goal, a special device has been constructed that permits (1) only 1 side of a potato stick to be exposed to hot oil, and (2) accurate and stable placement of miniature thermocouples in prescribed positions under but very close to the potato surface. Temperature recordings inside the developing crust allowed identification of different heating regimes during frying and a rough estimation of the evaporation front propagation. In addition, crust thickness was determined at intermittent time intervals by 2 independent methods (1) microphotography and (2) a micrometer. Comparison of the evaporation front propagation with crust thickness evolution indicates an interrelationship roughly up to the end of the boiling regime (bubble-end point). After this moment, the propagation of the evaporation front is faster than the evolution of crust thickness. PRACTICAL APPLICATION: Understanding the role of parameters that determine crust formation is of paramount importance since crust characteristics such as thickness and texture dictate the sensory perception of fried foods. This study aims to quantify the relationship between such parameters (that is, crust evolution and the propagation of the evaporation front inside the food) and to examine how frying conditions (oil temperature and frying duration) affect it. In addition, the present findings may be of particular value to deterministic modeling efforts on the coupled heat and mass transfer phenomena during deep-fat frying.     

A Kinetic Study of Furan Formation in Wheat Flour‐Based Model Systems during Frying

Furan is a possible human carcinogen, which is formed in worldwide highly consumed fried starchy foods. In order to elucidate the mechanisms responsible for its occurrence in this food category and propose techniques for its mitigation, the kinetics of furan formation, oil absorption, lipid oxidation, and color change were studied in wheat flour‐based model systems during frying at 160, 170, 180, and 190 °C up to 13 min and data were fitted to mathematical models. Additionally, an Arrhenius‐type dependency with temperature was evaluated for all studied responses. More drastic frying conditions increased significantly (P ≤ 0.05) the furan content of fried samples. Furan formation followed a sigmoid trend with frying time only for frying temperature of 190 °C (RMS_190°C: 7.6%). At lower temperatures, furan generation did not reach the asymptotic concentration level. Color change, lipid oxidation, and oil absorption increased with frying temperature and followed asymptotic relationships with frying time. For all evaluated temperatures, color change (RMS: 4.4% to 12.5%) and polar compound generation (RMS: 2.6% to 7.4%) presented good fit to a first‐order kinetic model. Oil absorption was successfully fit to a mass balance‐based model (RMS: 10.0% to 19.8%). Under the experimental conditions studied, only color change (E_A: 15.47 kJ/mol), lipid oxidation (E_A: 6.67 kJ/mol), and oil absorption (E_A: 76.98 kJ/mol) presented good fit (RMS: 0.7% to 6.3%) to an Arrhenius‐type equation. Based on our results, the keeping of frying temperature below 180 °C and the reduction of the frying time would contribute to reduce not only the final furan occurrence in fried foods but also their oil content.     

Kinetics of quality changes during food frying

This paper deals with kinetics of quality changes during food frying. The quality parameters of interests include color, texture, viscoelastic properties, volume/density, and nutraceuticals (Omega 3 fatty acids). The kinetic theory and determination methodology under isothermal/non-isothermal conditions are also reviewed. This paper presents the reported reaction rate constant, order of reaction, and activation energy for specific quality changes including phenomenological observations and important speculations. The changes of color, textural, and viscoelastic properties generally followed a first order reaction. In some studies, activation energy analysis could have been improved by applying corresponding system temperatures for the quality change reactions of interest. The kinetic information on volume/density changes and thermal degradation of nutraceutical is still limited to experimental observations of the changes.     

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.     

Oil Absorption During Frying of Frozen Parfried Potatoes

A tracer method was used to assess the uptake of oil by commercial frozen parfried potatoes fried (180 °C, 150 s) in colza oil (CO) involving a short post-frying immersion in hot coconut fat (CF). CO and CF were determined directly in the crust by differential scanning calorimetry (crystallization temperature and enthalpy −42.7 °C/50 J/g and 10 °C/71 J/g, respectively). Oil uptake by the crust during frying in CO or CF was similar (average 25.3%). Potato samples transferred immediately after frying in CO to the CF bath had most of the CO absorbed replaced by CF after a 10 s post-frying, meaning that CO was readily accessible in the crust structure. Samples fried in CO and cooled for up to 60 s before transfer to hot CF showed only partial replacement of CO. Oil wetting the surface of the sample at the end of frying was estimated as 70 to 80% of the total oil uptake. Formation of the crust (frying time > 1 min) was required for oil to migrate into intercellular spaces that are dynamically formed during frying and thus accessible to CF and solvents.     

QUALITY COMPARISON OF FRENCH FRY STYLE POTATOES PRODUCED BY OVEN HEATING, IMMERSION FRYING AND CONTROLLED DYNAMIC RADIANT HEATING

The effect of finish heating method (oven heating, immersion frying and controlled dynamic radiant (CDR) heating) on mechanical properties, color and sensory properties of par‐fried French fries was evaluated. Peak breaking force was highest for CDR‐heated French fries. An equivalent b value (yellowness) for the crust of immersion‐fried and CDR‐heated French fries was found by using color analysis. Sensory evaluation indicated overall acceptability of CDR‐heated French fries equivalent to immersion fried‐French fried potatoes. Finish heating of par‐fried French fries using CDR heating showed promise to produce a reduced‐fat fried product, as well as an alternative process to traditional immersion finish frying.