STRUCTURE AND SOLUBILITY OF COLLAGEN AND GLYCOSAMINOGLYCANS IN TWO BOVINE MUSCLES WITH DIFFERENT TEXTURAL PROPERTIES

Meat samples were collected from two bovine muscles , psoas major and semitendinosus, exhibiting different textural properties as measured by Warner Bratzler Shear Force. The structure and composition of the intramuscular connective tissue was compared by transmission electron microscopy, fibril diameter measurements, statistical analysis, collagen and glycosaminoglycan solubility studies in acetic acid and acetic acid added pepsin. The mean fibril diameter was significantly larger in the tougher muscle and the fibrils were tightly bundled into fibers. The tender muscle exhibited mainly randomly oriented fibrils with more space in between. The biochemical study confirmed the microscopy, showing a higher hexuronic acid/hydroxyproline ratio in the tender muscle, mainly in pepsin digested samples. The content of hydroxyproline after defatting in acetone was 30% higher in ST. No major differences were seen in the proportion of acid labile or stable cross-links in the collagen of the tough and tender muscle.     

FRACTURE PROPERTIES OF STARCH GELS AND THEIR RATE DEPENDENCY

Fracture properties of potato starch gels, consisting of swollen granules, were studied by bending, uniaxial compression, tension and cutting experiments at various strain rates. The effects of starch granule size and retrogradation were also investigated. Starch gels are very notch-sensitive. Fracture starts from inherent defects in the gel with a size comparable to that of the swollen granules. Fracture parameters like stress and strain at fracture and fracture energy depend on the rate of deformation, in contrast with the rate independent elastic behaviour observed at small deformations. This rate dependency can be different for the different parameters. A possible explanation for the rate dependent fracture is discussed. It implies that the granular structure of the gels is essential for fracture behaviour.     

RHEOLOGICAL PROPERTIES OF PROTEIN/STARCH MIXED GELS

The influence on the viscoelastic behaviour of the heat transition temperatures of starch and protein in gelatinous systems prepared from the two components was studied. Four different starches were combined with Bovine Serum Albumin (BSA) in several protein-to-starch ratios. Both the transition temperature and the rates of gelation of the components were critical for the behaviour of the complex systems. In those cases where the starch gel was formed before the protein gel, the storage and loss moduli of the complex system could be predicted by a simple addition of the moduli of the components at corresponding concentrations. When the gelation occurred in the reverse order, the gels were considerably stronger than predicted by the additivity model. When the starches were combined with gelatin, the complex gels were all weaker than predicted. The gelation of gelatin was very slow compared to that of the starches and the BSA, and it is likely that the weakness of these gels was due to the aggregation of the amylose molecules or some other part of the starch retrogradation process.     

EFFECT OF HEN EGG PRODUCTION AND PROTEIN COMPOSITION ON TEXTURAL PROPERTIES OF EGG ALBUMEN GELS

The effect of hen age, strain and dietary amino acid intake on the egg albumen gel textural properties was studied in two experiments by textural profile analysis (TPA) and uniaxial compression (UC) tests. In experiment 1, eggs from 4 different hen flocks were heat processed industrially. Egg rejection due to poor albumen gelling was correlated to hen age (r = 0.502), albumen dry matter (r =−0.632), gel hardness of 1^st compression (r =−0.765), and gel work of 1^st compression (r =−0.740) in TPA. In experiment 2 two hen strains, representing two levels of egg production, were fed diets with supplementation of L-lysine, methionine or both amino acids compared to a control diet. The lysine intake ranged from 818–1272 mg/hen/day and methionine intake from 377–575 mg/hen/day among hen groups, but without significant effect on the albumen gel texture parameters. The hen strains differed significantly in egg production (P<0.001), physical (P<0.001), chemical (P<0.05) and gel textural parameters of egg albumen (P<0.01). Hen age was essential, and correlated to the industrial egg rejection (r = 0.729), albumen dry matter (r =−0.902) and gel stress at fracture (r =−0.884). Albumen gels with high fracture stress values were found to contain a modified form of ovofransferrin.     

INFLUENCE OF FLAVORING ON THE VISCOELASTIC PROPERTIES OF STARCH GELS DURING GELATION AND LONG-TIME RETROGRADATION

The effect of three different aroma compounds on the texture of starch dispersions during gelation and retrogradation was studied. Oscillatory measurements were used to follow gelation and to check the structure of the starch dispersions after retrogradation up to 28 days. Rheological tests did not indicate any effect of the presence of any of the aroma compounds on the mechanism of gelation. During long‐time retrogradation, some added aroma compound did. We assume that this is a consequence of the ability of aroma compounds to form a complex or to show another type of interaction with starch molecules like entrapment in the amorphous regions of starch. Linalool is known to form complexes with amylase, but did not induce texture modifications, probably because, in our experiments, the added amount of this compound was too low. Isoamyl acetate, which according to literature interacts with amylopectin, exhibited a weak effect after 3 or 4 weeks, depending on the amount added. Octanal also increased gel stiffness after 3 weeks. This phenomenon is consistent with the observation that this aroma compound can form complexes with starch as demonstrated by X‐ray diffraction in this study.     

TEXTURAL QUALITIES AND MOLECULAR STRUCTURE OF STARCH PRODUCTS

This review deals with the physical properties of starch important in foods and with some of the factors which influence those properties. The major topics discussed are the molecular structure of the starch grain, the interaction of starch with water and with other compounds, the rheology of starch and starch products, and textural problems of starch in some representative foods.     

MECHANICAL PROPERTIES OF FISH AND BEEF GELS PREPARED WITH AND WITHOUT WASHING AND SODIUM CHLORIDE

Excellent gels, as measured by fold test, were prepared from three species of fish without first washing the minced tissue. Dependent on species (red hake, cod, or winter flounder), excellent to adequate gels, as determined by the fold test, could be prepared from fish muscle without NaCl provided that the minced tissue was washed prior to gel formation. Postrigor beef formed inadequate gels while excellent to good gels could be produced from prerigor beef although salt was a requirement. The concentration of contractile proteins in fish gels was estimated and they did not appear to be a major factor determining gel quality. Soluble muscle protein did not appear to interfere with gel formation either. Percent expressible moisture, percent recovery, and modulus of deformability did not relate well to fold test scores.     

INSTRUMENTAL AND SENSORY TEXTURAL PROPERTIES OF FURA

ABSTRACT

A uniaxial compression test and sensory textural analysis was conducted of fura samples made from millet flour. Significant differences (p<0.05) existed among the samples for hardness (the force to compress the sample between molar teeth), cohesiveness (extent to which sample falls apart during chewing) and gumminess (denseness and cohesion persisting during mastication). Correlations between sensory and instrumental tests revealed that a significant relationship exists between modulus of deformability and cohesiveness (r=?0.93, p<0.05); gradient and springiness (r=?0.90, p<0.05); deformation at failure and chewiness (r=0.98, p<0.05); energy per unit mass and gumminess (r=?0.95, p<0.05). A fura quality scale was established based on the peak force; soft and poor quality fura have a peak force of <19 kN; acceptable fura has a peak force of 19–24 kN; a firm and good quality fura, 24–25 kN; very hard and very poor quality fura have a peak force of >25 kN.     

TEXTURAL PROPERTIES AND COLOR CHARACTERISTICS OF RESTRUCTURED BEEF STEAKS WITH SELECTED BINDERS AND NOMEAT ADJUNCTS

Restructured steaks were evaluated using subjective and objective texture and color analyses. Treatments included: intact muscle, restructured steaks with no additives, salt/sodium tripolyphosphate (NaCl/STP), calcium alginate, crude myosin extract (CME) with 0.1% Nad and 0.4% STP [low salt & phosphate (LSP)], CME with 1.0 NaCl and 0.4% STP [high salt & phosphate (HSP)], surimi LSP and surimi HSP. Restructured steaks made from CME (HSP) or surimi (HSP) exhibited superior (P < 0.05) sensory textural evaluation, tensile strength values, cooking loss properties, color and color stability (subjective and objective) when compared to other restructured steaks except CME (LSP) and NaCl/STP (in some parameters). Restructured steaks made with CME or surimi in combination with 1% NaCl and 0.4% STP improved or maintained textural properties as well as color and color stability of restructured steaks.     

EFFECT OF ADDED SALT ON TEXTURAL PROPERTIES OF HEAT-INDUCED GELS MADE FROM GUM–PROTEIN MIXTURES

Large deformation rheological tests were employed to determine the textural differences in heat‐induced gel systems. Three different large deformation rheological methods (viscosity index and apparent elasticity, texture profile analysis (TPA) and torsional fracture) were employed to study the dependence of the ion type on the textural properties of heat‐induced mixed protein–gum gels. Protein–gum mixed solutions were prepared with bovine serum albumin (BSA) or egg white albumin (EWA) (20% w/v) with κ‐carrageenan (KCG), gellan (GLN) or xanthan gums (XNT) (0.5% w/v) at 0.1 M sodium chloride (NaCl), potassium chloride (KCl) or no added salt. Despite inherent differences in protein type, the main effect on the textural properties evaluated was for the kind of salt added, since potassium ions, with a strong influence on KCG and GLN gelation, affected the parameters related to the structure or hardness of the samples. There was no significant effect on parameters associated with sample ductility or elasticity. GLN formed stronger gels than KCG, whereas XNT did not perform as well in gel formation since it does not contribute to protein matrix formation. The results indicated that potassium may be substituted for sodium ions at low ionic strengths in foods where the incorporation of KCG or GLN helps to improve texture and related features.     

FLOW CURVES, STRESS RELAXATION AND CREEP MEASUREMENTS OF STARCH GELS

Flow curves, stress relaxation, and creep compliance were measured for various types of corn starch gel that underwent different degrees of modification. The four starches were native corn starch, medium hydroxypropylated distarch phosphate, highly hydroxypropylated distarch phosphate, and distarch phosphate. All the starches exhibited pseudo-yield stress behavior at low shear rates and shear-thinning at higher shear rates. Stress relaxation data at different strains indicated strain-softening phenomenon for all starches. Higher degrees of cross-linking decreased the half relaxation time due to the addition of rigid filler into the matrix. Increasing the concentration increased the relaxation modulus for all starches. Creep compliance and recovery measurements were conducted over the range of 3.2 Pa-320 Pa. In the linear viscoelastic region, the compliance data were not dependent on the magnitude of stress applied. As concentration increases, higher stress magnitude leads to nonlinear behavior. The creep compliance data were fitted into the Ninomiya and Ferry relation from dynamic viscoelastic data and the Maxwell-Voigt model. Ninomiya and Ferry overpredicted the relaxation data while the Maxwell-Voigt model fitted the data reasonably well.     

SENSORY AND INSTRUMENTAL EVALUATION OF TEXTURE OF COOKED AND RAW MILLED RICES WITH SIMILAR STARCH PROPERTIES

Three pairs of milled rices with similar starch properties (low gelatinization temperature waxy, and low gelatinization temperature low amylose, and intermediate gelatinization temperature intermediate amylose) were assessed for cooked rice properties by two industry taste panels and for raw and cooked rice properties by 30-member Filipino consumer panels. Only slight differences in texture within pairs were noted by the two industry taste panels who had not been trained to assess boiled raw rice or waxy rice. The Filipino consumer panel gave significantly higher ranked scores for one low-amylose variety in both raw and cooked forms. Malagkit Sungsong suman sa antala was ranked higher than modern waxy rices. Instrumental methods for translucency and whiteness of raw rice and Instron hardness and stickiness of cooked rice were not able to detect differences perceived by the Filipino consumer panels.     

MEASUREMENT OF TEXTURAL PROPERTIES OF FOODS WITH A CONSTANT SPEED CONE PENETROMETER

Abstract A constant speed cone penetrometer was used to measure textural properties of a variety of foods. Apparent viscosity and yield value were calculated from the recorded relationships of penetrating force and depth. Good agreement was found between yield values determined by this method and those obtained with a constant weight cone penetrometer.