INFLUENCE OF CELL SIZE AND CELL WALL VOLUME FRACTION ON FAILURE PROPERTIES OF POTATO AND CARROT TISSUE

This article presents the influence of cell size and cell wall volume fraction on the failure parameters of potato tuber and carrot tissue. Confocal scanning laser microscope was used for obtaining images of the cell structure of the tissues. The mean cell face area and the cell wall volume fraction obtained from the images was compared with work to failure, failure stress, failure strain and secant modulus obtained in a compression test of potato and carrot tissue at two strain rates. Bigger cells and less amount of cell wall material weakened the tissue, which was visible as a linear decrease in the parameters: work to failure, failure stress and failure strain. There were differences between potato and carrot in the secant modulus. For carrot, the secant modulus changed with microstructural parameters, whereas for potato, the secant modulus did not depend on these values. The strain rate decreases all the failure properties for potato. For carrot, only the work to failure was affected by the strain rate.     

TEXTURE AND COLOUR CHANGES IN MEAT DURING COOKING RELATED TO THERMAL DENATURATION OF MUSCLE PROTEINS1

Differential scanning calorimetry was used to select temperatures that diferentiated between thermal denaturation of the three major structural protein species in bovine muscle: myosin, collagen and actin. Samples of m. semimembranosus, m. semitendinosus and m. psoas major were heated to those different temperatures and evaluated sensorially. Three groups of sensory properties were needed to describe the main texture changes observed in the meat: 1. Firmness 2. Fiber cohesivity, bite-off force, residual bolus 3. Juiciness Firmness increased with thermal denaturation of the myofibrillar proteins (myosin; 40-60d?C and actin; 66-73d?C). Fiber cohesivity etc. decreased with collagen denaturation (56-62d?C). Reduction in juiciness was primarily associated with actin denaturation, while cooking loss increased over the whole temperature range. The property “total chewing work”, a composite of the first two texture groups mentioned, yielded like the judges' “total texture preference”, optimal texture in the 60-67d?C temperature region, implying denatured myosin and collagen but native actin. This meat was light pink-gray in colour, while the cooking juice released was dark red.     

THE EFFECT OF MARINATION AND COOKING ON THE MECHANICAL PROPERTIES OF INTRAMUSCULAR CONNECTIVE TISSUE

Effects of acid marination and cooking on the mechanical properties of intramuscular connective tissue and whole muscle were investigated. The transverse strength of cooked muscle was decreased by marinating and at all cooking temperatures between 40°C and 90°C. During marination the samples increased in cross-sectional area perpendicular to the direction of testing, and this increase was largely retained during cooking. A decrease in transverse strength brought about by marination could only be partly explained on the basis of this swelling thus diluting out the load-bearing connective tissue structures. Marinating also reduced the strength of isolated perimysia and produced a reversible increase in its initial stiffness, apparently due to straightening out of collagen fibers during swelling.
Real weakening of the load bearing components occurred only when the samples were subsequently cooked to above 60°C. Apparent weakening could be attributed to a dilution of the components due to swelling.     

CHANGES IN TEXTURE AND MICROSTRUCTURE OF PRESSURE-TREATED FISH MUSCLE TISSUE DURING CHILLED STORAGE

Activities of four endogenous enzymes (cathepsin C, collagenase, chymotrypsin- and trypsin-like enzymes), as well as firmness/strength and elasticity of pressurized fish tissues were monitored over 3 weeks of storage (4–7C). Results indicate that pressurization of fish muscle at 1,000 atm increased firmness whereas pressurization at 2,000 atm or 3,000 atm caused an opposite effect. Changes in tissue elasticity also showed similar trends with correlation between firmness and elasticity. During storage, pressure-inactivated enzymes were reactivated to various extents depending on level of pressurization. Scanning electron microscopy of the tissues revealed some morphological changes with pressurization. At 1,000 atm, there were no significant changes in the myofibers while pressurization at 2,000 atm and 3,000 atm resulted in breakdown of myofibers and connective tissue networks. The results indicate that pressurization may be used to enhance and maintain fresh seafood texture during storage.     

DYNAMIC MECHANICAL PROPERTIES OF THE APPLE CORTEX IN RELATION TO SAMPLE LOCATION AND RIPENING

Compressive complex moduli were determined for two cultivars of apples at two ripeness stages by subjecting cylindrical tissues from various locations within the apple to sinusoidal stress. The complex moduli varied within sampling regions and with regional sampling depths. They also varied with the degree of ripeness, but only at certain storage temperatures and in certain sampling regions of the fruit. The data analysis showed that the sinusoidally varying stress and strain test and the Magness Taylor pressure test did not measure the same mechanical properties and that apparently the complex modulus was influenced by changes in the cellular structure of the fruit tissues.     

CHANGES IN PHYSICO-CHEMICAL, THERMAL, COOKING AND TEXTURAL PROPERTIES OF RICE DURING AGING

Studies were undertaken to investigate the effect of aging on the physico-chemical, thermal, cooking and textural properties of milled rice obtained from two rice cultivars (Basmati-370 and Sharbati). The physicochemical properties like amylose content, liquification number decreased while the free fatty acid content increased with aging. Basmati-370 milled rice had higher cooking time and elongation ratio which subsequently increased with aging in both the cultivars. Water uptake and gruel solids loss also decreased significantly with the aging of the milled rice from both the cultivars. Sharbati milled rice showed higher transition temperatures, enthalpy of gelatinization and peak height index than Basmati-370 rice cultivar when determined by Differential Scanning Calorimeter. All these thermal parameters decreased with the aging of milled rice from both the cultivars. Textural properties such as packability, hardness, cohesiveness, extrudability and chewiness of cooked rice were measured using Instron Universal Testing Machine by back extrusion test. Basmati-370 cooked rice had higher packability, hardness, cohesiveness, extrudability and chewiness value as compared to Sharbati cooked rice. The values for all textural parameters in both the cultivars increased during aging, however, the increases were greater in Basmati-370 rice.     

CHANGES IN COOKING AND TEXTURAL PROPERTIES OF SPAGHETTI COOKED WITH DIFFERENT LEVELS OF SALT IN THE COOKING WATER

The effect of cooking water on textural and cooking properties of spaghetti was examined using four different salt concentrations 0, 1, 2, 3 and 4% in the cooking water and two types of spaghetti. Brand A was normal durum wheat spaghetti and brand B was spaghetti enriched with bran. Regardless of the cooking water used, brand B was harder, less sticky than brand A and it absorbed less water. Brand A required less cooking time. As salt concentration increased cooking time and hardness scores increased. Adhesiveness values were highest at the early stages of cooking and declined as cooking time increased.     

RELATION OF RHEOLOGICAL PROPERTIES OF TESTA OF PISUM SATIVUM L. TO HISTOLOGICAL CHANGES*

The study was undertaken to determine histological distortions occurring in the pea testa (skin) as a result of various force applications. Multi-directional compression caused bending of macrosclereids and flattening of osteosclereids. Unidirectional pressure caused similar deformations plus eventual separation between cells; shearing caused bending, buckling and wedging of macrosclereids; bruising resulted in cracks between macrosclereids and buckling. The existence of a pentosan-cellulose complex in the basal and apical ends of the macrosclereids and in the end wall regions of the osteosclereids, as established by R. M. Reeve of the U.S.D. A., and the triangular arrangement of the osteosclereids might explain the ability of the macrosclereids to bend and buckle and of the osteosclereids to spread in the end wall regions. This in turn contributes to the resiliency and toughness of the testa in the face of varied physical forces.     

ULTRASTRUCTURAL AND TEXTURAL CHANGES IN PROCESSED CARROT TISSUE1

Processed carrot tissues were studied using a transmission electron microscope (TEM) and an Instron Universal Testing Instrument. Carrot slices were evaluated raw, after thermal processing and after freezing and thawing. Cell walls of carrot tissues, frozen and thawed, were intact and dense. The middle lamella lost pectic materials. Overall, frozen and thawed cells were not so closely pressed as those of raw tissues. In thermally processed carrots the cell wall and the middle lamella were less densely stained compared to raw or frozen-thawed carrots. Thermally processed carrots exhibited significantly smaller modulus of deformability and stiffness and toughness values than raw carrots. There were no significant differences between the modulus of deformability and stiffness values for frozen-thawed and thermally processed carrots. Toughness values were, however, significantly lower for the thermally processed in comparison with the frozen-thawed carrots. Instrumental texture measurements indicated that different areas of carrot tissue behave differently to thermal processing.     

MECHANICAL PROPERTIES AND TEXTURE OF STORED APPLES

Granny Smith, Delicious and Jonathan apples were placed in cool store immediately after harvest and were tested for ultimate tensile strength, fracture resistance and hysteresis of tensile specimens, and bruise resistance of whole apples under slow and impact compression over a period of 18 weeks. Sensory panel assessments of apple flesh texture were also made. Ultimate tensile strength and fracture resistance showed strong negative correlations with time for all varieties. Ultimate tensile strength decreased from 200–300 kPa at the beginning of the test period to 10 kPa at the end. Fracture resistance fell from 200–300 Jm⁻² to 10 Jm⁻² over the same time. The hysteresis ratio was unaffected by storage time but showed some effect of conditioning at 20° C for one week. Hysteresis ratios were between 0.1 and 0.2. Bruise resistance also remained fairly constant over the storage period for all varieties for both slow and impact compression. The explanation of this behaviour is the increase in the number of ruptured cells per unit volume of bruised tissue as storage time increases. Sensory panel assessment showed an inability to sense long term textural changes. There was, however, good correlation between panel assessment, ultimate tensile strength and fracture resistance for varietal effects and storage treatments. The tensile properties of apple tissue, namely, ultimate tensile strength and fracture resistance, provide a good measure of deterioration of apples during storage.     

CHANGES OF CELL WALL COMPONENTS AND PAL ACTIVITY IN FRESH-CUT BAMBOO SHOOTS DURING COLD STORAGE

Changes of cell wall components in relation to softening and lignifying of fresh-cut bamboo shoots (Phyllostachys heterocycla var. pubescens) was investigated. Increased activity of phenylalanine ammonia-lyase (PAL) was related to a rise of lignin content in the basal section but not in the middle and apical sections. PAL activity was also associated with an increase in phenolic content in the middle section, but not in the basal and apical sections. The softening process occurred mainly in the apical section, while lignification took place primarily in the basal section. In the middle section, both softening and lignification also occurred but to a lesser extent.