Influence of the Composition of Potatoes on Their Cooking Kinetics

A previous study of three potato varieties indicated that shear force measurement may be used to predict the behavior of certain potato properties during cooking. To verify this hypothesis and to confirm other previous findings, slices (6 mm thick, 30 mm in diameter) of 21 potato varieties were thermally treated in water at 100°C. Mathematical expressions were assessed, and coefficients were determined to describe the kinetic behavior of the varieties.     

Physico‐Chemical and Structural Characteristics of Vegetables Cooked Under Sous‐Vide,Cook‐Vide,and Conventional Boiling

In this paper, physico‐chemical and structural properties of cut and cooked purple‐flesh potato, green bean pods, and carrots have been studied. Three different cooking methods have been applied: traditional cooking (boiling water at 100 °C), cook‐vide (at 80 and 90 °C) and sous‐vide (at 80 °C and 90 °C). Similar firmness was obtained in potato applying the same cooking time using traditional cooking (100 °C), and cook‐vide and sous‐vide at 90 °C, while in green beans and carrots the application of the sous‐vide (90 °C) required longer cooking times than cook‐vide (90 °C) and traditional cooking (100 °C). Losses in anthocyanins (for purple‐flesh potatoes) and ascorbic acid (for green beans) were higher applying traditional cooking. β‐Carotene extraction increased in carrots with traditional cooking and cook‐vide (P < 0.05). Cryo‐SEM micrographs suggested higher swelling pressure of starch in potatoes cells cooked in contact with water, such as traditional cooking and cook‐vide. Traditional cooking was the most aggressive treatment in green beans because the secondary walls were reduced compared with sous‐vide and cook‐vide. Sous‐vide preserved organelles in the carrot cells, which could explain the lower extraction of β‐carotene compared with cook‐vide and traditional cooking. Sous‐vide cooking of purple‐flesh potato is recommended to maintain its high anthocyanin content. Traditional boiling could be recommended for carrots because increase β‐carotenes availability. For green beans, cook‐vide, and sous‐vide provided products with higher ascorbic acid content.     

PRECISE STUDY OF COOKED POTATO TEXTURE

Cylindrical specimens from potato tubers were cooked at constant temperatures (75, 80, 85, 90, 95C) in a special heating cell located on the table of an Universal Testing Machine and arranged in such a manner that a cooked specimen could be tested repeatedly in nondestructive compression test during the whole cooking process. The decrease of Young's modulus during cooking form the basis for the calculation of the Cooking Depression Coefficients and activation energies of the process. The whole cooking time could be divided into two parts for varieties 'Nicola' and 'Panda'. The first part represents a modulus decrease of at least 50% and can be well described by a first order kinetic equation. The second part is kinetically very complicated and represents only a 10–15% further decrease of the original modulus value. Temperature dependence of mean Cooking Depression Coefficients (CDC) for both parts of the cooking curve, as well as Cooking Time Limits (CTL—time limit between both parts) fit the Arrhenius model. Cooking differences between both tested varieties are briefly discussed.     

A study on degradation kinetics of ascorbic acid in drumstick (Moringa olifera) leaves during cooking

The kinetics of ascorbic acid degradation in drumstick (Moringa olifera) leaves as well as in pure ascorbic acid solutions at the initial concentrations present in drumstick leaves over a temperature range of 50–120 °C (isothermal temperature process) has been studied. The degradation kinetics of ascorbic acid was also evaluated in normal open‐pan cooking, pressure‐cooking and a newly developed and patented fuel‐efficient eco cooker (non‐isothermal heating process). The ascorbic acid degradation followed first‐order reaction kinetics where the rate constant increased with an increase in the temperature. The temperature dependence of degradation was adequately modelled by the Arrhenius equation. A mathematical model was developed using the isothermal kinetic parameters obtained to predict the losses of ascorbic acid from the time–temperature data of the non‐isothermal heating/processing method. The results obtained indicate the ascorbic acid degradation is of similar order of magnitude in all the methods of cooking. Copyright © 2005 Society of Chemical Industry     

A study on degradation kinetics of riboflavin in green gram whole (Vigna radiata L.)

The kinetics of riboflavin degradation in green gram whole (Vigna radiata L.), as well as in pure riboflavin solutions, at initial concentrations present in green gram were studied over a temperature range of 50–120 °C (steady state temperature process). Riboflavin degradation followed first order kinetics, where the rate constant increased with an increase in the temperature. The temperature-dependence of degradation was adequately modelled by the Arrhenius equation. The degradation kinetics of riboflavin, in normal open pan cooking, pressure-cooking and a newly developed and patented fuel-efficient `Eco-cooker', were also studied (unsteady state heating process). A mathematical model, to predict the losses of riboflavin from the time–temperature data of the unsteady state heating/cooking process, has been developed using the steady state kinetic parameters obtained. The results indicate riboflavin degradation of a similar magnitude in all three modes of cooking used in the study.     

Immunochemical Quantification of Heat Denaturation of Bovine Meat Soluble Proteins

Immunoquantification of myoglobin, L-lactic dehydrogenases (LDH) M4 and H4, albumin, transferrin and immunoglobulin G (IgG) was performed after heat treatment of crude soluble sarcoplasmic protein extract over a range of 54–70°C for 30–780 min. Heat denaturation occurred in the following order: transfenin > IgG > LDH M4 > LDH H4 = myoglobin > albumin and could be described by first order reaction kinetics. The very low coefficient of variation (2–4%) of the single radial immunodiffusion technique resulted in a very weak calculated error (± 0.l–0.2°C) on temperature determination. Monitoring the concentration of LDH M4 appears appropriate for determining the minimum heating achieved in long-time, low-temperature cooking and albumin or myoglobin could be monitored for meat cooked at 69°C without holding time.     

Modeling the Kinetics of Cooking and Precooking Potatoes

This research investigated the kinetics of cooking potatoes over the temperature range in which starch gelatinizes. A back extrusion texture test was used to measure cookedness. By correlating the data with that of other researchers using different texture tests and potato varieties, we present a unified model of cooking which is first order, independent of variety, and applies to both cooking and gelatinization over the temperature range of 74°C to 100°C.     

A comparison of various rheological properties for modelling the kinetics of thermal softening of potato tissue (c.v. Monalisa) by water cooking and pressure steaming

The kinetics which can be used to describe thermal softening of potato tissue by water cooking and pressure steaming were established and the temperature dependence of rheological and textural properties, using six different instrumental objective methods as firmness indicators, was determined within the temperature range of 100–122 °C. In water cooking at 100 °C and in steaming at 100, 112 and 117 °C, the thermal softening was best expressed by one simple pseudo first-order kinetic mechanism, which was considered to be the response to the changes in the pectic material in the cell wall and interlamellar region. Tension energy was the best rheological property for establishing the kinetics of softening of potato by water cooking, whereas maximum shear force was the best method of representing the tissue softening by steaming, using first-order models. Steaming at 122 °C caused overcooking of the tissue, even for short times. At this high temperature, rheological parameters (compression, tension and creep compliance) and textural properties from Texture Profile Analysis (TPA) fitted second-order models. When second-order models were used, the Arrhenius equation was significant for chewiness, indicating that this textural property can be useful for detecting overcooking caused by prolonged pressure steaming in the experimental temperature range.     

Effect of cooking time and ingredients on the performance of different starches in white sauces

The effect of white sauce ingredients and increased cooking time at 90 °C on the degree of gelatinization of corn, waxy corn, rice, potato and modified waxy corn starches was studied. The changes in pasting properties, linear viscoelastic properties, and microstructure were determined. In all the native starches in water, a longer cooking time at 90 °C caused greater starch granule swelling and more leaching of solubilized starch polymers into the intergranular space. These effects were more noticeable in the waxy corn and potato starches. The potato starch was the most affected, with complete disruption of the starch granules after 300 s at 90 °C. The microstructural changes which transformed a system characterized by starch granules dispersed in a continuous phase (amylose/amylopectin matrix) into a system with an increase in the continuous phase and a decrease in starch granules were associated with a decrease in system viscoelasticity. The elastic moduli were higher in the sauce than in the starch in water system. However, with the exception of potato starch, the white sauce showed lower viscoelasticity than the starch in water system. The white sauce ingredients decreased the effect of cooking time on the starch gelatinization process, particularly in potato starch.     

EFFECT OF HEAT TREATMENT ON THE QUALITY OF COOKED CARROTS

We investigated the effect of heat treatment on the quality of cooked carrots (texture, chemical, and sensory evaluation). Slices of three carrot varieties (Rubika, Kundulus, and Rothild) were cooked at 90–120°C for 2–70 min. Compressive failure stress and rupture work were a by a Zwick Universal Testing Machine. Textural softening could be expressed by an exponential equation of the type: S = A exp(-kt), where 6 = rupture stress, t = cooking time, and A and k are constants. Plotting k versus l/T (T = cooking temperature, °K) revealed an Arrhenius-type relationship with apparent activation energy of about 28, 27, and 22 Kcal/mole for Rubika, Rothild, and Kundulus varieties, respectively. Chemical analysis (dry matter and p-carotene) showed that the cooking process caused insignificant changes. Statistical analysis of the sensory assessments showed an overall significant preference for 3 mm slice thickness and 110°C cooking temperature.     

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.     

Effect of pulsed electric field,mild thermal pretreatment and calcium on texture changes of potato (Solanum tuberosum L.) during subsequent cooking

The effect of pulsed electric field (PEF) and/or mild thermal processing at 60 °C (T60) on the cooking behaviour of potato tissue in media with different Ca²⁺ concentrations (0–0.5%) was investigated. The rate constant for texture degradation during cooking seemed to decrease after the different pretreatments in the order Untreated > T60 > PEF > PEF-T60, but only a significant effect (α = 0.05) could be found in the case of the combination pretreatment in 0.5% Ca²⁺ medium. These texture changes were linked with changes in pectin degree of methylesterification (DM) and Ca²⁺ crosslinking obtained after the pretreatments. The mild thermal pretreatment has little effect on the pectin DM but promotes ionic crosslinking. Both the PEF and combination pretreatment reduce the pectin DM and increase ionic crosslinking significantly. An exponential correlation was found between the texture degradation rate constant and the pectin properties studied.     

AN APPLICATION OF IMAGE ANALYSIS FOR THE STUDY OF KINETICS OF HYDRATION OF MILLED RICE IN HOT WATER

Two dimensional image analysis was carried out on basmati rice to determine the hot water hydration kinetics. A miniature water bath (105 × 55 × 15 mm) was fabricated to process the rice grains under the CCD camera and on-line images were obtained at regular intervals of the hot water hydration process at four temperatures from 60 to 75°C. Two-dimensional projected area of rice grains was converted into swelling ratios for suitability of comparison of the swelling at different temperatures. The reaction rate constant and the activation energy for the hot water hydration were obtained from the swelling data. The activation energy was 38.213 kJ/mole and was comparable with other processes reported in the literature. The hydration data was further analysed to obtain a polynomial equation to correlate swelling ratios in terms of heating time and temperature. This study helps in obtaining the swelling parameter of rice during cooking to be used in the design of continuous cookers.     

Potato Tuber Dynamic Mechanical Analysis at Temperatures of Starch Gelatinization

Dynamic mechanical analysis (DMA) was applied to potato cortex tissue in temperature scans in range 30–90°C and constant air humidity of 90%. The obtained scans indicate peaks in both storage and loss module of elasticity (SM and LM, respectively) at temperatures higher than 70°C. The peaks follow starch gelatinization processes in tissue detected by DSC at lower temperatures. The peak characteristic temperatures were determined in replicated experiments for seven potato varieties. It was shown that increasing tissue density leads to higher characteristic temperatures. The peak characteristic values (for both SM and LM) were more variable and cultivar role for them was not proved. The role of the observed module peaks in the potato cooking process is discussed.     

Steroidal glycoalkaloids in potato foods as affected by cooking methods

Potato and its products have become indispensable foods and snacks for most people. Steroidal glycoalkaloids (SGAs) occur in all tissues of the potato, and consuming potatoes with a high SGA content harms human health. Therefore, the effects of different cooking methods on the SGA content in potato foods were investigated in this study. The results indicated that adding food-grade acetic acid during the manufacturing process did not affect the SGA content in stir-fried shredded potatoes or fresh mashed potatoes. However, the SGA content in potato food after peeling was significantly lower than that in non-peeled food, and the volume ratio of potato skin to flesh decreased with the increase of the potato tuber volume. Therefore, potato breeders and farmers should make the most hard to increase the proportion of commodity potato via corresponding science and technology. In addition, frying significantly reduced the SGA content in potato chips. Further research indicated that SGAs degraded slowly at 150°C, while they degraded rapidly at 190°C within 30 min. The temperature of rapeseed oil in the frying process can be as high above 200°C. Thus, frying significantly decreased the SGA content in potato chips, which could be attributed to temperature. These results will provide a theoretical basis and practical guidance for potato breeding and cooking.     

Cell wall modifications during cooking of potatoes and sweet potatoes

Sweet potato (Ipomoea batatas L) tissue, when cooked at 70 °C to activate β‐amylase and break down starch, takes on a distinctive firm, brittle texture and does not show the cell separation that occurs in, for example, cooked potato (Solanum tuberosum L). Similar cooking conditions increase firmness in other plants by activating pectin methyl esterase which de‐esterifies pectic polysaccharides and protects them from thermal depolymerisation. We therefore isolated cell walls from both potatoes and sweet potatoes cooked at 70 °C and 100 °C and determined the remaining degree of methyl esterification of their pectins. Pectins from both species were demethylated to a similar extent at 70 °C and 100 °C. Since cooking sweet potato at 100 °C induced cell separation and softening, it is concluded that β‐amylase is rapidly inactivated at that temperature and swollen starch distends and separates the cells, whereas the firm texture obtained by cooking that species at 70 °C is not the result of pectin demethylation but is caused by the breakdown of starch to oligomers that can escape from the cell. © 2000 Society of Chemical Industry     

KINETICS of QUALITY CHANGE DURING COOKING and FRYING of POTATOES: PART I. TEXTURE

Kinetics of texture change during cooking and frying of potatoes were evaluated in this study. 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. the cooked samples were water cooled while the fried samples were air cooled immediately after the treatment. Test samples were then subjected to a single cycle compression test in a computer interfaced Universal Testing Machine and three textural properties (hardness, stiffness and firmness) were derived from the resulting force‐deformation curves. Texture parameters of cooked potatoes decreased with progress of cooking time and the rate of texture changes associated with each temperature was found to be consistent with two pseudo first‐order kinetic mechanisms, one more rapid than the other. Textural values of fried potatoes were found to increase with frying time and also followed a first order kinetic model. Temperature sensitivity of rate constants was adequately described by Arrhenius and z‐value models.     

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.     

Degradation kinetics of anthocyanins from purple sweet potato (Ipomoea batatas L.) as affected by ascorbic acid

Storage (4°C and 25°C, 28 days) and thermal (70°C–90°C, 6 h) stabilities of purple sweet potato anthocyanins (PSPAs) with varying concentrations of ascorbic acid (AA) were investigated in a model soft drink medium. For storage stability, the model drink was sterilized at 85°C for 15 min prior to storage. Zero-order kinetics and first-order kinetics were fitted for storage degradation at 4°C and 25°C, respectively. However, all data for thermal degradation fitted first-order kinetics. The temperature dependence on degradation was modeled after the Arrhenius equation. Storage degradation of PSPAs was increased by the presence of AA (40–360 mg/L). Retarded thermal degradation was be achieved by adding 120 mg/L of AA, while accelerated thermal degradation resulted from 360 mg/L of AA. Heat treatment did not markedly change the DPPH radical-scavenging activity of PSPAs.     

ROLE OF TUBER DENSITY IN POTATO SLOUGHING

A new CPEM method was developed and used to study the cooking curves of two potato varieties showing differences in texture and of one variety cultivated in four different regimes. The two main cooking curve stages (i.e., cooking and disintegration) can be described by simple linear equations, with density as an independent parameter. The parameters in the equation describing the cooking stage were reformulated to express directly the role of starch. The two new parameters obtained were weakly correlated and expressed separately cooking time sensitivity to starch content and the basic potato characteristic in relation to sloughing. Data obtained indicate only a minor role of starch content during the first part of cooking that is determined primarily by basic potato characteristics probably related to the cell wall properties. In the second stage of disintegration, starch content plays a more important role.