Kinetics of thermal softening of potato tissue (cv. Monalisa) by water heating

The temperature dependence of rheological parameters as firmness indicators for potato tissue was determined within the temperature range 50-100 °C using four different objective methods. The rate of thermal softening of potato tissue by water treatment at 50 °C, 90 °C, and 100 °C was consistent with one pseudo first-order kinetic mechanism, while at 70 °C and 80 °C the rate of softening was consistent with two simultaneous pseudo first-order kinetic mechanisms. Kinetic theory was suitable to detect an increase of firmness through heating at 60 °C, mainly between 20 min and 40 min, presumably by pectinesterase activation. This study shows that two substrates S_a and S_b may be involved in providing firmness to potato tissue at 70 °C and 80 °C. For these temperatures, mechanism 1 is more probably due to gelatinization and light cooking, whereas mechanism 2 is more likely to represent the changes of the pectic substances in the cell wall and interlamellar region. At 90 °C and 100 °C the gelatinization process was fast and therefore the simple mechanism fitted presumably reflects the degree of solubilization of the pectic substances. At 50 °C and 60 °C there was practically no gelatinization, so that the simple mechanism fitted presumably represented incipient solubilization of pectic material. In water heating, gelatinization contributes less than the cell wall structure to potato tissue firmness on the basis of either kinetic parameters or microscopic observations. Maximum breaking compression force and modulus of rigidity were the most suitable rheological parameters for studying the softening of potato tissue in water heating.     

Kinetics of thermal softening of potato tissue heated by different methods

The kinetics of thermal softening of potato tissue heated by steaming, steaming+hot air and microwave exposure were evaluated using the rheological properties from four objective methods as firmness indicators. In the three heat treatments, the rate of thermal softening of tissue could be described by two simultaneous first-order kinetic mechanisms. Shear rheological properties were best for studying softening of the tissue with these methods on the basis of chemical kinetic theory. A comparison of kinetic parameters showed that steaming produced a greater degree of softening than the other two heating methods used. The firmness ratios for shear force showed that approximately 16% of the firmness of fresh potato is retained after steaming treatments as compared to 46% and 36%, respectively, for steaming+hot air and microwave. The loss of moisture of samples accounted for the increase in the firmness ratios, especially in steaming+hot air treatments, resulting in a potato with greater firmness but with a texture unacceptable to the consumer. Tension rheological properties and relaxed force detected the loss of moisture to a more significant degree and could therefore be considered very suitable for studying thermal treatments that involve the drying of tissues. With these heating methods, gelatinization contributes less than cell wall structure to potato tissue softening as determined either by kinetic parameters or by microscopic observations.     

Optimisation of freezing process with pressure steaming of potato tissues (cv Monalisa)

Response surface methodology (RSM) was used for determining optimum conditions of the freezing process on pectinesterase (PE) activity, rheological parameters and textural properties in potato tissues. In the process of production of frozen potatoes, the second step of the stepwise blanching prior to freezing was considered as a fixed factor and performed at 97 °C for 2 min as well as the freezing rate in the freezing step itself, which was carried out at −2 °C min⁻¹. The effects of variation in levels of temperature (57.93–72.07 °C) and time (15.86–44.14 min) in the first blanching step on the PE activity were studied using a central composite rotatable design. A Box–Behnken factorial design was used to investigate the effects of simultaneous variation of temperature (60–70 °C) and time (20–40 min) in the first blanching step and steaming temperature (112–122 °C) and time (1–3 min) on rheological parameters and textural properties. Blanching temperature was the independent variable that most influenced either enzymatic activity or rheological parameters. Stationary points showing maximum PE activity had critical temperature and time values of 64.22 °C and 29.37 min before freezing and 64.39 °C and 28.02 min after freezing and steaming of the tissues, and these values were very close to those obtained for some creep compliance parameters. Results show a high correlation between increases in PE activity and tissue firmness below optimum experimental freezing conditions, proving the role of the enzyme as one of the main contributors to the firmness which determines the textural quality of frozen potato tissues. © 1999 Society of Chemical Industry     

Textural and Gelatinization Characteristics of White,Cream, and Orange Fleshed Sweet Potato Tubers (Ipomoea Batatas L.)

Sweet potato is an important food crop having nutritive value in terms of starch, carotein, and minerals. The acceptability and overall quality of the products depend on their textural and rheological attributes. Cooking quality of the tubers could be related to the textural, pasting, and gelatinization properties, which vary depending on the flesh color of the tubers. Also, being a promising ingredient in many of the traditional and industrial products, the physico-chemical and functional properties of sweet potato flour are very much important for their selection for developing various value added products. The textural, gelatinization, and pasting characteristics of white, cream, and orange fleshed sweet potato tubers were analyzed and their thermal softening behavior was modeled by linear regression and fractional conversion techniques. Significant variations were observed in the properties among different varieties (p < 0.05). Kinetics of texture degradation on cooking were explained by first-order and dual-mechanism first-order models and the latter was found to be more suitable. The first three principal components explained about 85% of the total variation in texture profile parameters, gelatinization, and pasting properties. Though there was no similarity in the textural properties of the raw tubers among the varieties of same flesh color group, the quality of the cooked tubers and flours of different varieties in the same group are similar as revealed by the multivariate analysis.     

Effect of Cultivars and Thermal Processing with Salt Solutions on the Textural Attributes (Hardness,Chewiness and Rate of Softening) of Potatoes (Solanum Tuberosum L.)

The change in textural attributes (hardness, chewiness and rate of softening) of three potato cultivars (Russet Burbank, Desiree and Sebago) was investigated. Uniform cylindrical samples (35-mm diameter and 3-mm thick) were prepared and exposed to different thermal processing regimes including; heating at 85°C, 95°C in water and steaming (100.2°C). The effect of salt on these textural attributes was also investigated using different salt concentrations (1.5%, 3% and 6% (w/w) NaCl). After thermal treatments the samples were subjected to texture profile analysis. The instrumental textural attributes were greatly affected by the cultivars and the thermal processing regimes. The change in textural attributes upon steaming was only marginally different compared to that at 95°C in water. Low concentrations of salt (1–3%) were found to accelerate the softening of the texture in these cultivars especially at lower temperatures. The textural attributes were modelled using a two-parameter reaction kinetics model. There was reasonable agreement by the model findings on the textural attributes prepared from all the thermal processing regimes and in presence and absence of (within average absolute error of 1.9–7%). Further, the model indicated that the order of reaction varied from 1.15–2.18 indicating that the changes in textural attributes in these thermal processing regimes followed higher reaction orders.     

Low-temperature steaming improves eating quality of whitefish

In this study, effects of different steaming conditions (temperature–time scales) on quality characteristics of cooked whitefish (Coregonus peled) were characterized to guide product development. Investigation of three cooking conditions, including 60°C (3–20 min) 80°C (1–12 min) and 100°C (1–6 min) indicated that properties including textural properties, cooking loss, color change, water holding capacity (WHC), and protein content were all significantly correlated to the cooking condition. It was observed that the color changes of fish meat, especially the brightness L* were strongly correlated to the relative extraction rate (RER) of myofibrillar proteins (MFPs), which could be considered as a marker for the doneness of the cooked whitefish. Our results indicated that during the steaming process, the water holding capacity of the fish continued to decline, and the cooking loss continued to increase. However, a sudden jump in cooking loss occurred when the fish sample became overcooked. To minimize cooking loss, a good control of the doneness hence is needed to avoid overcooking. Moreover, results of this study demonstrated that low-temperature steaming could better maintain the springiness and cohesiveness of the fish as the myofibrillar proteins experienced less sudden swelling and shrinkage. Hence, low temperature steaming should be the preferred method for whitefish processing to minimize the negative impact on fish sensory qualities.     

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.     

Textural Characterization and Kinetics of Potato Strips During Frying

ABSTRACT: A single puncture test (SPT) system was designed to determine textural changes in potato strips in situduring frying at 160, 175, and 190 °C. Puncture force changed drastically with time and depth in the strip during frying. Force-distance curves were expressed as representative textural parameters as CF (core force), RF (rupture force), and S (springiness). Normalized parameters CF* and S* for core force and springiness were used in modeling textural changes in the core during initial tissue softening and later crust development process, respectively. High frying temperatures accelerated the process, and the finished fried potato strip was a composite structure made of a hard crust and a soft core.     

A kinetic approach to textural changes of different banana genotypes (Musa sp.) cooked in boiling water in relation to starch gelatinization

A standardized textural test was developed for characterizing the banana pulp softening process during boiling. While a correlation was established between initial dry matter content and firmness, we observed large differences in cooking behavior between varieties and genotypes, with various softening rates and equilibrium retainable firmnesses. After 33-min cooking, some genotypes exhibited firmnesses 7 times higher than the softest. The biggest firmness losses relative to initial textures found after cooking were: FHIA 20 (20-fold) and FHIA 18 genotypes (40-fold) after 2 h, and Guineo (100-fold) after 98 min. The extent of starch gelatinization was investigated by differential scanning calorimetry and correlated to the amylographic maximum slope using rapid visco analyzer. Regardless of water uptake, the first 15-min cooking demonstrated a strong contribution by the gelatinization process to thermal softening. The firmness losses of 15 Colombian cultivated dessert and cooking banana varieties were evaluated using fractional conversion, and were best fitted by a first-order reaction (R² ? 0.98). Multiple regression was shown to be suitable for preliminary cooking time prediction using Musaceae flour amylographic properties. At 30-min cooking, firmness evaluation was shown to be sufficient for identifying genotypic behavior, and therefore for predicting consumer preferences.     

Effect of Cooking Method (Baking Compared with Frying) on Acrylamide Level of Potato Chips

ABSTRACT:  The effect of cooking method (baking compared with frying) on acrylamide level of potato chips was investigated in this study. Baking and frying experiments were conducted at 170, 180, and 190 °C using potato slices with a thickness of 1.4 mm. Raw potatoes were analyzed for reducing sugars and asparagine. Surface and internal temperatures of potato slices were monitored during the experiments to better explain the results. Fried and baked chips were analyzed for acrylamide content using an LC-MS method. The results showed that acrylamide level of potato chips prepared by frying increased with frying temperature (19.6 ng/g at 170 °C, 39 ng/g at 180 °C, and 95 ng/g at 190 °C). In baking, however, the highest acrylamide level was observed in potato chips prepared at 170 °C (47.8 ng/g at 170 °C, 19.3 ng/g at 180 °C, and 29.7 ng/g at 190 °C). The results showed that baking at 170 °C more than doubled the acrylamide amount that formed upon frying at the same temperature, whereas at 180 and 190 °C, the acrylamide levels of chips prepared by baking were lower than their fried counterparts.     

Firmness, seed wholeness and water uptake during the cooking of lentils (Lens culinaris cv. anicia) for 'sous vide' and catering preparations

The study aimed to optimize cooking conditions of lentils ( Lens culinaris cv. anicia ) for 'sous vide' processing and catering. the softening rate of lentil seeds during cooking in deionized water was consistent with two simultaneous first order mechanisms. the apparent activation energies of firmness breakdown and loss of integrity were 86.5 kJ mol⁻¹ and 271.3 kJ mol⁻¹, respectively. Wholeness of the lentils was better preserved when the cooking temperature did not exceed 90°C. the loss of firmness was a consequence of hydration of the seed since the regression coefficient between the logarithm of residual firmness and water uptake reached −0.93 regardless of cooking temperature and heating medium (steam or water). Thus, lentil seeds maintained their firmness and wholeness as required for 'sous vide' and catering if they were cooked below 90°C for up to 2 h. Higher temperature or longer cooking time resulted in loss of firmness and wholeness.     

COMPARISON OF MECHANICAL TESTS FOR EVALUATING TEXTURAL CHANGES IN POTATOES DURING THERMAL SOFTENING

The changes in the texture of cylindrical samples of potato tissues immersed in water at 60, 70, 80 and 90C for up to 80 min were monitored at each temperature in terms of tangent modulus of elasticity in axial and radial compression tests, and elasticity and viscosity parameters in creep and stress relaxation tests. The magnitude of all mechanical test parameters decreased with an increase in heating time and temperature. The creep and stress relaxation responses of individual potato samples were adequately represented by respective mechanical models (R²= 0.94 to 0.99). The mechanical test parameters followed apparent first-order degradation kinetics due to the effect of thermal softening, and the rate constant was used as an index of the sensitivity of a mechanical test. The radial compression test was relatively more sensitive than the axial test. Based on an overall comparison, the parameters from creep and stress relaxation tests were found to be the most sensitive in describing the textural changes during thermal softening of potatoes.     

The influence of processing and preservation on the retention of health-promoting compounds in broccoli

ABSTRACT:  In this work the effects of common household practices such as chilling, freezing, and cooking on vitamin C retention in broccoli (Marathon cv.), as well as their influence on the release of sulforaphane upon enzymatic hydrolysis of glucoraphanin by the endogenous enzyme myrosinase, were investigated. When chilled at 6 °C and 95% R.H. for 35 d, broccoli showed a vitamin C and sulforaphane loss of about 39% and 29%, respectively, while storage at –18 °C for 60 d resulted in similar losses, but mainly due to the blanching step. Boiling, steaming, microwaving, pressure-cooking, and the combined use of pressure and microwaves were the cooking methods investigated. Boiling and steaming caused significant vitamin C losses, 34% and 22%, respectively, while with the other treatments more than 90% retention was observed. Sulforaphane was no more detectable after boiling or steaming, while pressure/microwave cooking did not cause any significant loss. The quantitative distribution of these moieties in the florets and stems of fresh and chilled broccoli was also investigated.     

高压蒸煮软化罗非鱼鱼骨的研究

以罗非鱼鱼骨为实验对象,以pH、蒸煮压力、蒸煮时间以及料液比为研究因素,采用万能试验机测量鱼骨最大承受压力来评价其硬度,研究高压蒸煮软化工艺。通过单因素实验及正交实验表明:当pH为6.5、蒸煮压力为0.13MPa、时间为75min、料液比为1∶1时,对鱼骨的软化效果最好,此工艺下所得鱼骨硬度为33.0N。      

Losses of pectic substances during cooking and the effect of water hardness

Differences in the extent of loss of pectic substances from potato (Solanum tuberosum L.) after boiling, steaming and pressure cooking were investigated. Losses were found to be significantly greater (P< 0.001) after boiling than after pressure cooking or steaming. The pectic substance content (g 100 g^?1 dry matter) of potatoes (cv. Pentland Crown) was 2.98 for raw peeled tubers, 0.97 after boiling for 35 min, 1.22 after steaming for 35 min and 1.24 after pressure cooking at 103.4 kPa (15 psi) for 15 min. The roles of cooking time, cooking temperature and heat transfer medium are discussed. The effects of calcium sulphate (at levels typical of ‘hard’ and ‘soft’ water supplies) in the cooking water on losses of pectic substances from potato (Solanum tuberosum L.), carrot (Daucus carota L.), and swede (Brassica napus L. var. napobrassica Peterm.) after boiling and pressure cooking were also investigated. Water hardness did not influence losses during pressure cooking but samples boiled in hard water had decreased losses of pectic substances compared to those boiled in soft water. The increase in retention of pectic substances due to hard water was about 8 % for potatoes (cv. Pentland Dell), about 33 % for sliced carrots (cv. Berlicum, approved maintenance Perfecta) and about 23% for diced swedes (cv. Acme). The interaction of water hardness with cooking method was significant for potato (P< 0.05) and swede (P<0.001) and approaching significance (P=0.055) for carrot.     

不同烹调方式对蔬菜植物化学物及V_C的影响

目的:研究不同家庭烹调方法对紫薯、西兰花和青辣椒中的花色苷、硫苷、辣椒素和V C的影响。方法:三种蔬菜经过微波、蒸制、焯制和油炒等烹调后,以pH示差法测定花色苷,以高效液相色谱法测定硫苷和辣椒素,以2,6-二氯靛酚滴定法测定V C。结果:保存V C效果:蒸制>微波蒸制,焯制>油炒>微波煮制;保存花色苷效果:蒸制>微波蒸制,且蒸制使花色苷增加;保存总硫苷效果:油炒>焯制>微波煮制;保存辣椒素效果:微波煮制>焯制>油炒。结论:若控制烹调时间不过长,蒸制是最适宜保存蔬菜植物化学物及维生素的烹调方法。      

不同处理方式对紫甘薯全粉面品质的改良效果

本研究通过考察紫甘薯全粉面蒸煮损失率、微观结构、流变学特性及抗性淀粉含量的变化,探讨加工过程中蒸制、老化和冷冻等处理条件对紫甘薯全粉面品质的影响。结果表明,经蒸制、老化或冷冻处理后,挤压制备紫甘薯全粉面的蒸煮损失率、抗性淀粉含量、微观结构及流变学特性均发生了变化。在老化时间为2~4h时,紫甘薯全粉面中抗性淀粉含量从3.01%增加至4.02%,老化时间的进一步延长则对抗性淀粉含量无显著影响;在蒸制时间为3~5 min范围内,抗性淀粉含量由3.41%增加至4.82%,而在5min~11min范围内则从4.82%降至2.40%。处理方式对紫甘薯全粉面表面微观结构变化影响显著,适宜的蒸制、老化或冷冻处理可以改善紫甘薯全粉面的微观结构,但处理时间过长反而导致其结构被破坏。未经处理的紫甘薯全粉面其储能模量和损耗模量得值均明显高于经过不同处理的紫甘薯全粉面,且其储能模量均明显高于损耗模量,弹性模量占主导地位。因此,适宜的蒸制、老化和冷冻等处理可以有效改善紫甘薯全粉面的整体品质。     

Effect of pretreatment of hydrostatic pressure on physicochemical properties of tilapia muscle protein gels induced by setting

ABSTRACT:  Tilapia meat pastes were subjected to pretreatments of hydrostatic pressure (50 to 300 MPa/4 °C/60 min) followed by setting (50 °C/60 min) with or without subsequent cooking (90 °C/20 min) to investigate the changes of rheological properties, gel-forming ability, whiteness, and protein solubility of gels. The gel by setting only as the control was elastic, rigid, and mainly constituted by covalent bonds. The gel by pretreatments of 50 MPa was similar to the control. A 100-MPa pretreatment induced a viscous and soft gel with mainly noncovalent bonds. The 200-MPa pretreatment produced a gel with strongest breaking force and strain compared with all the treatments in this study; moreover, the gel was mainly constituted by hydrogen bonds. A gel induced by a 300-MPa pretreatment was the most viscous. Via subsequent cooking (90 °C/20 min), all the gels became more rigid and elastic except that induced by a 100-MPa pretreatment.     

Modeling the Spaghetti Hydration Kinetics During Cooking and Overcooking

ABSTRACT: A mathematical model to predict the hydration kinetics of spaghetti during cooking and overcooking is presented. The phenomena involved during the hydration process, such as starch crystalline domains melting kinetics, water diffusion, macromolecular matrix relaxation kinetics, and "residual deformation" release kinetics, were separately described. To validate the developed model, water sorption tests on commercially available spaghetti strands were run at 100 °C. In particular, the weight, diameter, and length of spaghetti strands were monitored over a period of 200 min. The fitting and predictive ability of the model was successfully tested, corroborating the validity of the approach used to derive the model.     

Water desorption isotherms of two varieties of sweet potato

Water desorption isotherms were determined for New Zealand sweet potato at 25, 40 and 55°C, and for Philippines sweet potato at 28°C. The isotherms were sigmoid in shape and of type II according to the BET classification. The data were fitted to eight two-parameter equations reported in the literature. The effect of water activity, a_w, and temperature, T °C, on the equilibrium moisture content, M _e g water/100g dry solids, was best described for New Zealand sweet potato by: Me = 20.51 T-^0.204 (a_w/(1-a_w)0.39 for a_w= 0.06–0.81