BETWEEN-SPECIES DIFFERENCES IN FRACTURABILITY LOSS: COMPARISON OF THE THERMAL BEHAVIOR OF PECTIC AND CELL WALL SUBSTANCES IN POTATO AND CHINESE WATERCHESTNUT1

This study was undertaken to determine how the mode of chemical changes taking place during the cooking of two chemically similar vegetables (potato and waterchestnut) might explain the tremendous between-species differences in cooked tissue fractura bility as determined by Instron Texture Profile Analysis. Although pectin breakdown and depolymerization by heat weakens the cell wall structure, loss of cell wall physical strength does not necessarily coincide with pectin depolymerization. Potato phosphate-soluble pectin (PSP) showed a more rapid rate of depolymerization than waterchestnut PSP as proven by both chemical and gel chromatographic studies. The unique composition (e.g., neutral sugar content) of the cell wall microstructure of a given vegetable species is the major determinant of the resistance of that plant tissue to fracturability loss during cooking. Based on GLC analyses of cell wall components, cell wall models have been proposed to illustrate the possible structural differences between potato and waterchestnut tissue. It appears that the cell wall character of edible plant tissue for a given species is determined genetically.     

Influence of cooking and microwave heating on microstructure and mechanical properties of transgenic potatoes

The transgenic potato clones of cultivar Irga with improved resistance to a necrotic strain of potato virus Y (PVY(N)) were subjected to heat treatment in order to determine their technological quality. The technological quality was determined on the basis of differences between mechanical properties of unmodified potato and transgenic clones during cooking and microwave heating. The compression test was applied in order to evaluate the mechanical resistance of raw, cooked and microwave-treated potatoes. Compression resistance was expressed by fracture stress F (kPa), fracture strain D (mm/mm), and Young modulus E (kPa). The differences in microstructure of potato tubers (unmodified and modified) were investigated using scanning electron microscopy (SEM). The observed differentiation in the mechanical properties of heat-treated potatoes was less connected with genetic modification but most of all with a kind of the process used. The heat processes caused a distinct decrease in mechanical resistance in all the examined tubers. However, the process of microwave heating resulted in more significant changes in mechanical properties of tubers than cooking. Deformation of parenchyma cells during cooking was directly connected with starch, gelatinisation and gel formation. Microwave heating affected significantly cellular water evaporation which resulted in intercellular failure, collapsing of cells, and limitation of starch gelatinisation.     

THE THERMAL FRACTURABILITY LOSS OF EDIBLE PLANT TISSUE: PATTERN AND WITHIN-SPECIES VARIATION1

The pattern of fracturability loss of 11 selected fruits and vegetables during thermal processing was studied. In general, the first-order kinetic model is adequate in describing such changes during heating of edible plant tissue before reaching equilibrium texture. However, textural changes are less predictable by the first-order kinetic model in tissues having thick cell walls (such as those derived from stems and roots) than in tissues having thin cell walls (such as those derived from fruits). For a given species (potato), the first-order model can be applied regardless of sample dimension, morphological origin of the sample, heating temperature, variety, prior storage conditions, maturity and minor agronomic variation.     

MODELLING THE MECHANICAL AND HISTOLOGICAL PROPERTIES OF CARROT TISSUE DURING COOKING IN RELATION TO TEXTURE AND CELL WALL CHANGES

A tensile test was used to measure four mechanical properties of carrot tissue cooked under various time-temperature conditions. A kinetic model describing the changes of these mechanical properties measured during cooking was developed. The histological properties of the rupture surfaces caused by the mechanical testing were investigated. The kinetic model was found capable of predicting the changes in the rupture mechanism of the cell walls. Determining the percentage of cell wall ruptures proved to be an accurate method to assess the textural state of carrot tissue during cooking as compared to the measurement of the mechanical properties.     

Cellular,biological, and physicochemical basis for the hard‐to‐cook defect in legume seeds

This review integrates current knowledge on the hard‐to‐cook (HTC) defect in legume seeds, with emphasis on the cellular and biological changes during storage and soaking, and the physicochemical changes during heating. Several postulated mechanisms, including the pectin‐cation‐phytate model, cell lignification, pectin β‐eliminative degradation, and protein denaturation in relation to starch gelatinization, are discussed in the context of current evidence. Subsequently, a developmental model of legume hardening is presented. It is held that the HTC defect develops during aging and soaking and is exhibited through cooking. During the process, there are many events involved. Free radical formation, lipid peroxidation, acid formation, membrane deterioration, protein denaturation, and leakage are events associated with aging and soaking, whereas pectin decomposition and solubilization, protein coagulation, and starch gelatinization are events that occur during cooking. Cooked HTC seeds are characterized by limited cell separation and restricted starch gelatinization. These defective features result from a restriction in pectin decomposition and solubilization as well as the protein coagulation that prevails over starch gelatinization during heating. This multichannel mechanism points to the direct involvement of two amphoteric colloids, cell wall pectin and storage protein, both of which are sensitive to pH and/or ion composition. The model also indicates the indirect involvement of cell membranes and starch granules. Except for events that occur during aging and soaking, it is likely that heat‐related textural problems in other plant tissues may proceed via a mechanism similar to legume hardening.     

The potential of ohmic heating as an alternative to steam for heat processing shrimps

The potential application of Ohmic Heating as an alternative to the conventional steam cooking for shrimps is examined in this study. Defrosted unpeeled shrimps (Pandalus borealis) were cooked either in a steamer or ohmically up to a 72 °C core-temperature. The head, body and tail of steam-heated shrimps cooked at different rates whereas the OH treatment was more uniform and faster. The impact of shrimp size on heating rate was also evaluated, with an overall cooking time of 38 s and 59 s for steam-cooked small and large shrimps, respectively, while only 40 s where needed for OH regardless of shrimp size and measured anatomical location. No differences were found for cook loss and texture (WBSF and Kramer methods) between cooking methods. However, shrimp size seemed to determine the effect of OH on colour differences (ΔE), with greater differences observed in large vs. small shrimps, although overall ohmically-cooked shrimps showed less colour differences compared to those cooked conventionally with steam.Industrial relevanceTraditional heating processes such as boiling or steaming are used in industrial cooking of shrimps. However, the low rate of heat penetration to the thermal centre of shrimps leads to heterogeneous treatments resulting in overcooking which may reduce yield. Ohmic heating technology offers a potential alternative over conventional heat treatments as heat is generated volumetrically inside the food. This form of heat generation results in more uniform temperature distribution which leads to shorter processing times and potentially higher yields while still maintaining the colour and nutritional value of food. This paper hence exploits the potential of Ohmic heating technology as an alternative to conventional steam processing for the cooking of shrimps.     

CELLULARITY, MECHANICAL FAILURE, AND TEXTURAL PERCEPTION OF CORN MEAL EXTRUDATES

Relationships among cellular structure, fracturability, and sensory properties in porous, brittle extrudates were investigated. Corn-based extrudates intentionally processed to exhibit a range of physical structures were characterized in terms of cell size distribution, bulk density, mechanical strength, fracturability, and sensory attributes. These measurements show both mechanical strength, defined by average compressive stress during extended deformation, and fracturability, quantified by fractal and Fourier analyses of stress-strain functions, increasing with either decreasing mean cell size or increasing bulk density. Fracturability parameters or structural characteristics are furthermore correlated with sensory scores for crunchiness, crispness, hardness and perceived density. These results indicate that cellularity strongly influences the pattern of mechanical failure and that failure characteristics, such as fractal dimension or power spectrum of stress-strain functions, are reflective of sensory texture.     

Effect of microwave cooking on the microstructure and quality of meat in goat and lamb

Fat cell distribution in the structure of semimembranosus muscle of goat and lamb was studied. The effect of various heating methods including conventional, domestic and industrial microwave were investigated using fluorescent light microscopy. Frequency used for microwave heating was 2450 MHz with two wattages levels of 700 (domestic microwave) and 12000 (industrial microwave). All samples were heated to internal temperature of 70 °C. The roasted samples in conventional oven were compared with microwave cooking. Fat distribution was different in various heat treatments. The roasted samples had greater fat retention in semimembranosus muscle. Results showed that uneven distribution of fat in muscle system influenced fat loss during cooking. The fat cells in the interior of muscle were lost more slowly compared to the fat located near the surface of the muscle. The overall migration of fat globules during microwave cooking was higher than conventional cooking.     

RHEOLOGICAL AND TEXTURAL CHARACTERISTICS OF RAW AND PAR-COOKED TAEWA (MAORI POTATOES) OF NEW ZEALAND

The quality characteristics of raw and par-cooked (partially cooked) tubers from four different Taewa cultivars were evaluated and compared with a modern potato cultivar (Nadine). Significant differences in dry matter, starch content, color and specific gravity were observed among the raw tubers from the different cultivars. Moemoe and Tutaekuri Taewa cultivars showed higher dry matter content (21.97 and 21.57%, respectively) whereas the lowest specific gravity of 1.057 was observed for Nadine. Par-cooked chef-ready tubers were prepared from each cultivar and evaluated for quality during 21 days of storage at 4C. Tutaekuri raw as well as par-cooked tubers had higher fracturability and hardness whereas Nadine par-cooked tubers had higher adhesiveness than other cultivars. Rheological parameters such as storage modulus ( G' ), loss modulus and loss tangent (tan δ ) were dependent on the dry matter and starch contents of the tubers. The highest peak G' values of 24,930 Pa and 19,700 Pa were observed for Tutaekuri and Moemoe potato cultivars, respectively.

PRACTICAL APPLICATIONS

Ready-to-microwave par-cooked tubers with a refrigerated shelf life of 21 days were developed without using any chemical preservatives. The rheology of the tuber tissue was studied using a dynamic rheometer for the first time. The technique allows the continuous monitoring of the changes occurring in the potato tissue during the heating and cooling cycles. Significant correlations between the textural characteristics of raw and cooked tubers and the dynamic rheological characteristics of fresh tubers were observed. The technique may be helpful in predicting the viscoelastic characteristics of raw potatoes and the changes in the texture of cooked tubers during refrigerated storage.     

CFD analysis of the convection flow in the pan during induction heating and gas range heating

One difference between induction heating (IH) and gas range heating (GRH) is that, because the heating location of the pan is different, the convection in the pan is different. In particular, in cooking situations in which solids are mixed with liquids, such as the boiling of soup containing solid foods, the natural convection flow in the pan may affect food quality. The convection in the pan during IH and GRH was analyzed by using computational fluid dynamics (CFD), and the temperature distribution and the flow velocity distribution in the pan were obtained. These results were then compared with the measurement results. In GRH, the heat flux at the wall of the pan was obtained by experiment, and it was used for the analysis as a boundary condition. In IH, the heat generation distribution obtained by electromagnetic field analysis was used for the analysis as the boundary condition. Differences in convection flow in the pan during IH and GRH were observed by CFD modeling especially at the initial stage of heating. The simulated convection in the pan showed the same tendency as the captured movement of the tracer particle using flow visualization.     

Microstructural and mechanical properties of camel longissimus dorsi muscle during roasting,braising and microwave heating

This study was conducted to investigate the effects of various heating methods, including roasting, braising and microwave heating, on mechanical properties and microstructure of longissimus dorsi (LD) muscle of the camel. Shear value and compression force increased during microwave heating more than roasting and braising. Results obtained from scanning electron microscopy (SEM) showed more damage from roasting than in either braising or microwave heating. Granulation and fragmentation were clear in muscle fibers after roasting. The perimysium membrane of connective tissue was damaged during braising, while roasting left the perimysium membrane largely intact. The mechanical properties and microstructure of muscle can be affected by changes in water content during cooking.     

Heat transfer during contact cooking of minced meat patties

Experimental results on heat transfer during heating of four types of minced meat patties by contact with hot plates are given. Experimental equipment, method of measurement and experimental values of heat flux from heating plate to heated product surface during 4 min contact cooking are described. Simultaneous measurements of product and heating plate temperatures as a function of time were used to determine the contact heat transfer coefficient between heating plate and product surface. The results show that the heat flux varied during the heating process. The magnitude of the heat flux as a function of time varies with the type of material heated and the heating plate temperature. The heat transfer coefficients measured were in the range 200 to 1200 W m^?2 K^?1, depending on product type, contact plate temperature, contact pressure and stage in the heat treatment.     

Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 °C and 37 °C, respectively. Pasting study indicated that rice samples stored at 37 °C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 °C, aged rice (stored at 37 °C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 °C caused a significant increase in the amount of cell wall remnants along the storage at 37 °C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties.     

Enzymatic changes in pectic polysaccharides related to the beneficial effect of soaking on bean cooking time

BACKGROUND: Cooking time decreases when beans are soaked first. However, the molecular basis of this decrease remains unclear. To determine the mechanisms involved, changes in both pectic polysaccharides and cell wall enzymes were monitored during soaking. Two cultivars and one breeding line were studied. RESULTS: Soaking increased the activity of the cell wall enzymes rhamnogalacturonase, galactanase and polygalacturonase. Their activity in the cell wall was detected as changes in chemical composition of pectic polysaccharides. Rhamnose content decreased but galactose and uronic acid contents increased in the polysaccharides of soaked beans. A decrease in the average molecular weight of the pectin fraction was induced during soaking. The decrease in rhamnose and the polygalacturonase activity were associated (r = 0.933, P = 0.01, and r = 0.725, P = 0.01, respectively) with shorter cooking time after soaking. CONCLUSION: Pectic cell wall enzymes are responsible for the changes in rhamnogalacturonan I and polygalacturonan induced during soaking and constitute the biochemical factors that give bean cell walls new polysaccharide arrangements. Rhamnogalacturonan I is dispersed throughout the entire cell wall and interacts with cellulose and hemicellulose fibres, resulting in a higher rate of pectic polysaccharide thermosolubility and, therefore, a shorter cooking time. Copyright © 2011 Society of Chemical Industry     

DIFFERENTIATION OF MYOFIBRILLAR AND CONNECTIVE TISSUE STRENGTH IN BEEF MUSCLES BY WARNER-BRATZLER SHEAR PARAMETERS

Heat induced changes in aged bovine m. longissimus dorsi (LD) and m. biceps femoris (BF) were studied by water bath cooking to 60, 70 or 80°C at slow (.12°C/min) and fast (.6°C/min) heating rates. Forcedeformation curves from the Warner-Bratzler (WB) shear device were used to evaluate specific changes in the myofibrillar (WB M-force) and connective tissue component (WB C-force) of tenderness. Other measurements include WB peak force value, cooking loss, collagen solubility and sensory evaluations. Differences due to muscle type were significant in all parameters except collagen solubility. Both WB M- and WB C-force were reduced by slow heating rate but for samples heated to 80°C, WB M-force was affected only by heating rate below 60°C while WB C-force was most influenced above 60°C. Effect of final temperature resulted in higher WB M-force from 60°C to 70°C, whereas WB C-force was most affected from 70°C to 80°C. On the contrary, WB peak force was less affected by final temperature. Due to concomitant and opposing changes in myofibrillar and connective tissue strength with increasing end point temperature, it is concluded that improvements in interpretations with regard to heat-induced changes and response of heat treatment in various muscles may be increased by measurement of WB M-force and WB C-force from shear force-deformation curves.     

Optimum Cooking Conditions for Shrimp and Atlantic Salmon

The quality and safety of a cooked food product depends on many variables, including the cooking method and time–temperature combinations employed. The overall heating profile of the food can be useful in predicting the quality changes and microbial inactivation occurring during cooking. Mathematical modeling can be used to attain the complex heating profile of a food product during cooking. Studies were performed to monitor the product heating profile during the baking and boiling of shrimp and the baking and pan‐frying of salmon. Product color, texture, moisture content, mass loss, and pressed juice were evaluated during the cooking processes as the products reached the internal temperature recommended by the FDA. Studies were also performed on the inactivation of Salmonella cocktails in shrimp and salmon. To effectively predict inactivation during cooking, the Bigelow, Fermi distribution, and Weibull distribution models were applied to the Salmonella thermal inactivation data. Minimum cooking temperatures necessary to destroy Salmonella in shrimp and salmon were determined. The heating profiles of the 2 products were modeled using the finite difference method. Temperature data directly from the modeled heating profiles were then used in the kinetic modeling of quality change and Salmonella inactivation during cooking. The optimum cooking times for a 3‐log reduction of Salmonella and maintaining 95% of quality attributes are 100, 233, 159, 378, 1132, and 399 s for boiling extra jumbo shrimp, baking extra jumbo shrimp, boiling colossal shrimp, baking colossal shrimp, baking Atlantic salmon, and pan frying Atlantic Salmon, respectively.     

THERMO-RHEOLOGICAL PROPERTIES AND COOKING YIELD OF SAUSAGE-TYPE PRODUCTS AS AFFECTED BY LEVELS OF FAT AND ADDED-WATER1

Consumer interest in low fat foods has led meat processors to introduce low fat sausages with high added-water. The purpose of this study was to use dynamic thermo-rheological techniques to study the influence of fat and added water on sausage batters and cooking yields during heating. Twenty different sausage batters were formulated to 15–30% fat and 18–35% added water. Batters were heated in a thermal scanning rheometer from 20–80C in increments of IC/min. Rheograms of all batters showed a gradual decrease in storage modulus (G') as temperature increased from 20–59C. Significant changes in G' occurred in the range of 60–75C leading to the formation of rigid gel networks. Batters with levels of fat ≤ 24% and added water > 24% or levels of fat and added water ≥ 27% showed increased cooking yields. Rheological measurements suggested that levels of added water influenced the G' of batters during heating and that high levels of added water could be used in sausage formulations without adversely affecting product yield.     

An examination of factors affecting radio frequency heating of an encased meat emulsion

The potential of radiofrequency (RF) heating for rapid cooking of a cased comminuted meat emulsion (white pudding) to a pasteurisation temperature of 73°C was examined. Immersion of the product in water was essential in order to prevent thermal damage to the casings by electrical arcing effects during heating. Using a polyethylene heating cell with non-circulating water the applied RF power, primary electrode distance as well as the mineral content, temperature and volume of the surrounding water all influenced the efficiency of the RF heating. Under optimised conditions maximum/minimum temperature gradients (ΔT) across the products in excess of 15°C were observed. These could be reduced to around 6°C by heating the white puddings in a cell operating with recirculating hot water (80°C). Using an oven power output of 450W a 4.3-fold reduction in cooking time compared to conventional steam oven cooking could be achieved.     

Temperature Related Structural Changes in Wheat and Corn Starch Granules and Their Effects on Gels and Dry Foam

The effect of processing temperature on structural changes in wheat, corn, and high amylose corn starch granules was investigated and related to the mechanical properties of gels and microcellular foam (MCF). Scanning electron micrographs (SEM) showed that wheat starch granules form ghosts with thicker walls than dent corn granules. The granule wall was permeable to water and appeared to be at least partially permeable to the solubilized contents of the granule. The ghost walls became visibly porous after heating at 95ºC for 60 min and were completely solubilized by heating to 120ºC. High‐amylose corn starch (HACS) granules were completely dissolved by heating to 140ºC. Gels made with wheat starch had higher gel strength and dynamic modulus compared to dent corn starch gels. The density, compressive strength and modulus of MCF were lower in samples cooked for 60 min. The density of dent corn MCF was higher than that of wheat starch which may have accounted for higher compressive strength and modulus in the corn sample. MCF made from HACS had higher surface area and lower density, compressive strength, and modulus than the other starches tested. There were no significant differences in pore volume or surface area due to extended cooking times.     

DRYING AND NaF ALTER VIABILITY AND SOLUBLE PROTEINS OF GERMINATING WHEAT SEEDS

The effect of heat drying and NaF on the viability and soluble proteins of wheat seeds was analyzed. Protein content measurements and sodium dodecyl sulfate polyacrylamide gel electrophoresis were carried out on germ (plantlet) and endosperm during the first four days of germination. Results showed that the viability of both normal and heated seeds decreased exponentially with NaF concentration. The parameter most affected by both NaF and heating was plantlet size. Although some differences in the electrophoretic patterns corresponding to different treatments were found, results showed similar trends in most of them, and the main changes appeared between different days of germination. Additive effects of both NaF and heating were observed in some cases.