EFFECT OF PROTEIN HYDROLYSATE ON THE INSTRUMENTAL TEXTURE PROFILE OF GELATIN GELS

The texture of gels containing 2 to 8% of gelatin and 1 to 10% of alcalase protein hydrolysate obtained from poultry meat was examined using the instrumental texture profile analysis (TPA) method in compression and penetration mode. Response surface analysis modelled the effects of the two components of the gels on textural properties. In both tests the addition of hydrolysate decreased hardness and chewiness, and the effect was more pronounced for higher gelatin concentrations. The senses of changes in cohesiveness and springiness as measured in both tests employed here were not in agreement with each other owing to different consequences produced on the sample. In the case of compression, both parameters decreased with increased hydrolysate addition, whereas for penetration an increase in cohesiveness was observed as well as small changes in springiness. Hydrolysate produced a statistically significant negative linear and positive quadratic effect with regard to the majority of the studied texture parameters. This component interacted significantly with gelatin with regard to hardness, chewiness, and fracturability which led to a decrease in the first two and an increase in the last texture parameter. The weakening effect of the protein hydrolysate upon texture may be of great importance for the quality of gelatin gels.     

EFFECT OF THERMAL PROCESSING ON STRUCTURE AND RHEOLOGICAL PROPERTIES OF CARRAGEENAN/CAROB GUM GELS

Optical rotatory dispersion and rheological studies have been used to investigate changes in carrageenan and carob gels on thermal processing. A synergistic effect was observed on the gel strength of both unprocessed and heat processed carrageenan carob gels when compared to gels without carob, although a lower gel strength was measured after processing. The reduction in strength of gels on heat processing appears to be due mainly to the depolymerisation of the network chains while the crosslinks of the gel are largely unaffected.     

EFFECT OF SUCROSE ON THE MECHANICAL AND ACOUSTIC PROPERTIES OF FREEZE‐DRIED AGAR,K‐CARRAGEENAN AND GELLAN GELS1

Agar, K‐carrageenan and gellan gels (2%) with and without infused sucrose (5, 10 and 12.5%) were freeze dried and the mechanical and acoustic signatures of the resulting solid sponges recorded. For comparison, agar gels with 5 and 10% starch were also prepared and likewise tested. The presence of the sugar, or starch, in the dried gels increased their density in a manner that could not be predicted from the corresponding stoichiometric relations between the gum and additive indicating that the sugar, or starch, were not inert fillers. In general, the presence of the sucrose in the dried gel solid matrix increased the brittleness of the sponges. The effect could be quantified in terms of the increase in the mechanical signature's apparent fractal dimension (Richardson's and Kolmogorov's). The more brittle dried gels also had a “richer” acoustic signature whose apparent fractal dimension was determined with the “blanket” algorithm. Despite the irregular and jagged appearance of all the dry gels stress‐strain relationships, they could be described by the same kind of a three parameter empirical model originally derived for soft baked products and polymeric foams. Although the added sugar, or starch, stiffened the dehydrated gels the effect could not be quantified unambiguously because of the differences in the density and in the overall shape of the stress‐strain curve.     

STUDIES ON THE MOLECULAR BASIS OF WORT CLARIFICATION BY COPPER FINING AGENTS (KAPPA CARRAGEENAN)

A comparison of the fining and gelation behaviour of kappa carrageenan suggested that folding of the polymer into a helical conformation is an essential element in the mechanism of copper fining action. Factors which destabilise or prevent the formation of helices result in the reduction or removal of fining action. Finning trials with kappa, iota and lambda carrageenan suggested that fining performance decreased with increasing carrageenan sulphate content. Carrageenan mediated clarification of dialysed wort preparations exhibited a specific requirement for the presence of potassium Ions. The deterioration of fining action in worts at acidic pH was attributed to failure of helix formation rather than chemical changes in the structure of the carrageenan molecule.     

THE EFFECT OF MONOVALENT CATIONS AND ANIONS ON THE RHEOLOGICAL PROPERTIES OF KAPPA-CARRAGEENAN GELS1

The change in dynamic Young's modulus E' and in volume of 2% and 4% kappa-carrageenan gels induced by immersion in alkali metal salt solutions was observed for various kinds of salts, LiCl, NaCl, KCl, CsCl, LiBr, NaBr, KBr, CsBr, Nal, KI, Csl, and for various salt concentrations. E' of the gels increased rapidly up to 1 h after immersion, and then it increased more gradually. However, E' decreased after a certain immersion time when the concentration of the salt exceeded a certain value which depended on the kind of the salt. The volume of the gel immersed in salt solutions for 24 h decreased with increasing concentration of the salt except in the case of Nal where the gel swelled remarkably.     

EFFECT OF HYDROCOLLOIDS ON APPARENT VISCOSITY AND SENSORY PROPERTIES OF SELECTED BEVERAGES1

The effects were studied of low concentrations of 5 selected hydrocolloids (xanthan, hydroxypropylcellulose, sodium alginate, and carboxymethylcellulose of low and medium viscosity types) on viscosity and sensory properties of 3 commercial beverages: tomato juice, orange drink and soluble coffee. Tomato juice and orange drink were tested at 0° and 22°C, while coffee was tested at 22° and 60°C by 11-14 highly trained judges. Apparent physical viscosity was determined with a Brookfield uiscometer. Due to precipitate formation, it was not possible to test sodium alginate in orange drink nor hydroxypropylcellulose in coffee at 60°C. Without exception, increasing the hydrocolloid concentration significantly depressed (P < 0.001) the flavor and aroma intensities of all beverages a t both test temperatures. Taste effects were specific for the gumlbeverage combinations. In general, gums depressed the sourness and saltiness of tomato juice, the sourness of orange drink and the bitterness of coffee. Both physical and oral viscosities increased with gum concentration and decreased with temperature. Positive synergism was displayed by gums in tomato juice and orange drink. Excellent correlations (r > 0.9) were obtained between sensory and physical viscosities.     

EFFECT OF INCORPORATION OF DEFATTED SOYFLOUR ON THE TEXTURE OF CHAPATIS

Incorporation of defatted soyflour in an all wheat flour for making chapatis has a significant effect on its nutritive profile and textural profile parameters. The protein content was increased from 11.9% to 19.8% at the 20% blending level. The textural parameters hardness, cohesiveness, springiness and chewiness were also affected by the addition of defatted soyflour both at zero and 24 h of storage. All the chapatis were acceptable when fresh but not after 24 h.     

EFFECT OF EMULSION DROPLETS ON THE RHEOLOGY OF WHEY PROTEIN ISOLATE GELS

The effects of droplet size and emulsifier type on the rheology of whey protein isolate (WPI) gels containing emulsion droplets was studied. Gels were prepared by dispersing droplets of corn oil (20 wt%, d₃₂= 0.7 – 4 μm) in a 10 wt% WPI solution (pH 7.0, 50 mM NaCl), and heating at 90C for 15 min. Gel strength was determined by measuring the stress of gels at 20% compression using an Instron Universal Testing Machine. Droplets stabilized by WPI increased the gel strength, those stabilized by non-ionic surfactants (Tween 20 and Triton X-100) decreased it slightly, and those stabilized by SDS decreased it drastically. Gel strength increased as the droplet size decreased for droplets stabilized by WPI, but was relatively insensitive to the size of droplets stabilized by the small molecule surfactants. These observations may be explained in terms of the interactions between the emulsifiers and the protein network. Droplets coated with emulsifiers which can be incorporated into the protein network reinforce the structure and so increase gel strength, whereas droplets coated with emulsifiers which cannot be incorporated into the protein network disrupt the three dimensional structure of the gel and decrease its strength.     

EFFECT OF FRICTION ON THE PERFORMANCE OF TEXTURE TEST CELLS*

The relationship was measured between the normal contact force and the force required to overcome friction between food samples and a surface simulating a typical texture test cell. Peas produced frictional behavior that combined the characteristics of dry friction and fluid flow. Friction coefficients for selected foods ranged from 0.04 to 0.52. Friction force was linearly related to the normal contact force and non-linearly to the area of contact between the sample and the surface, and the speed of the sample relative to the surface. This verifies the fact that, with empirical texture test devices, these test variables must be held constant. The estimated friction forces represented a significant amount of the total force required to operate a wire extrusion cell and a back extrusion cell. It was concluded that standardization of the test cell would be easier to achieve if the contact area between the sample and the cell surfaces was minimized and if low friction materials were used to construct the cells.     

EFFECT OF A KAPPA CARRAGEENAN/LOCUST BEAN GUM MIXTURE ON BIND AND COOKING LOSS IN HIGH MANNURONATE ALGINATE RESTRUCTURED BEEF

Raw and cooked bind properties, cooking loss and pH were evaluated when adding three levels (0%, 0.25%, 0.50%) of a kappa carrageenan and locust bean gum mixture (C/LBG) to finely and coarsely ground high mannuronate alginate restructured beef. Treatments included variable levels of the following dry additives: Alginate (0.50%-1.00%), calcium carbonate (0.10%-0.20%) and glucono-delta-lactone (GDL, 0%-0.80%). Raw breaking strength of finely ground formulations was increased by elevated alginate levels (P<0.05), but was not affected by C/LBG addition (P>0.05). The effect of alginate and C/LBG on cooked bind properties depended on whether finely or coarsely ground meat was used. Sensory evaluations of coarsely ground treatments suggest that sufficient raw and cooked bind was achieved using 0.50% alginate, 0.10% calcium carbonate and 0.60% GDL. Addition of 0.50% C/LBG and/or 0.75% alginate to coarsely ground formulations further reduced cooking loss (P<0.05) by relatively 13% and 17%, respectively. No interaction between C/LBG and alginate was found (P>0.05).     

EFFECT OF CELL SIZE ON THE PERFORMANCE OF THE SHEAR-COMPRESSION TEXTURE TEST CELL

Shear compression cells were manufactured to have dimensions 0.75, 0.5 and 0.25% that of the standard cell and used to test a range of foods. Maximum force and energy increased nonlinearly with increasing cell size and sample weight. The results demonstrate that cells of various sizes are practical for testing foods.
Friction in the cell is dependent on alignment of the cell components in the test machine. To obtain comparable readings the cell body must be oriented in the machine the same way for every test.     

EFFECT OF DE-ESTERIFICATION ON THE RHEOLOGICAL PROPERTIES OF κ-CARRAGEENAN GELS

The effect of de-esterification on the rheological properties of κ-carrageenan gels was studied by stress relaxation and dynamic mechanical measurements. By means of de-esterification, the elastic modulus of κ-carrageenan gels increased. This was attributed to the increase of alternation of D-galactose and 3,6-anhydro-D-galactose, and then the stabilization of the double helical structure in the κ-carrageenan gels.     

采用质构仪分析氯化钙对牛肉品质的影响

CaCl2对牛肉的嫩化作用多通过感官评定,评定结果存在较多主客观影响因素.采用质构仪测定代替感官评价,测定经CaCl2处理后牛肉的食用物理特性--嫩度、硬度、弹性、胶性和咀嚼性等,可增加评定的合理性.用质构仪穿刺法和质地多面分析(TPA)试验法,对不同部位的牛肉注射不同浓度、不同量CaCl2后的品质进行分析.结果表明,使肉的综合品质较好的较优参数组合为A3、B2、C3,即牛条形腰肉注射5%的浓度为300 mmol/L的氯化钙溶液.其中牛肉的不同部位影响最大,氯化钙溶液的注射量次之,氯化钙溶液的浓度影响较小.     

EFFECT OF CARRAGEENAN ON PROCESSING AND QUALITY CHARACTERISTICS OF LOW-FAT FRANKFURTERS

Three types of carrageenan (K, I, K+I) × 4 levels (0, 0.25, 0.5 and 1.0%) were evaluated with a complete factorial design to characterize the effect of carrageenans on processing and quality characteristics of low-fat frankfurters (9% fat, 13% protein). l-Carrageenan at 0.5–1.0% level appeared to be more beneficial for the production of low-fat frankfurters. It reduced (P<0.05) the hardness of the skin and contributed to a softer (P<0.05) product and higher overall acceptability. Low-fat frankfurters (9% fat) manufactured with I-carrageenan (IC) or in combination with finely ground toasted bread (TB), isolated soy protein (ISP) and pork skin (PSK), were compared to high-fat (27% fat, 11% protein) and to low-fat (9% fat, 13% protein) control frankfurters prepared with 3.5% potato starch (PS), as well as with commercial frankfurters (25% fat, 11.6% protein, 4.5% starch). Frankfurters with IC had higher (P<0.05) moisture, softer (P<0.05) skin and the highest (P<0.05) separation of gelatin. However, textural properties and overall acceptability were similar (P>0.05) to commercial and high-fat control frankfurters. Addition of TB had no significant effect. Use of ISP and PSK improved (P<0.05) the water-binding capacity but negatively affected the overall acceptability of frankfurters.     

THE EFFECT OF SOME MEAT PROTEINS ON THE RHEOLOGICAL PROPERTIES OF PECTATE AND ALGINATE GELS

The viscosity of 1% sodium alginate and 1% sodium pectate solutions containing low levels of calcium chloride were investigated using cone and plate viscometers. The level of calcium required to initiate partial gelation was significantly lower for pectate compared with alginate. With increasing calcium chloride concentration the solutions became more pseudoplastic and eventually showed thixotropy.
One percent bovine serum albumin or 1% myoglobin was incorporated into the polysaccharide solutions together with sufficient calcium to cause incipient gelation in the absence of the protein. Myoglobin inhibited the formation of an alginate gel, the effect being greatest at a pH of about 6.3. Bovine serum albumin also inhibited alginate formation, the effect increasing with increasing pH. In contrast the addition of both myoglobin and bovine serum albumin caused gel formation in the presence of pectate below pH 6.0.
The results are discussed in terms of the protein/polysaccharide interactions and the polymer/ion interactions that can take place in these systems. The relevance of this work to the use of these polysaccharides as thickeners and gelling agents in canned meat products is considered.     

THE EFFECT OF DEMETHYLATION PROCEDURES ON THE QUALITY OF LOW-ESTER PECTINS USED IN DESSERT GELS

Water uptake at 80°C and starch-iodine blue value at 65°C, both expressed as percentage of the respective parameter at 96°C gave good inverse estimates of the gelatinization temperature of rice. The equilibrium moisture content on soaking in water was 28–29s in indica , and 30–31% in dwarf indica and japonica rice. Similarly the fraction of total amylose soluble in water (96° C) was around 50% in indica and japonica , but 35% in dwarf indica. Dwarf indica rice viscogram showed a rather high setback value. The blue value of the excess cooking water of rice gave no useful information. Varieties with less than 25% amylose gave C-type alkali reaction.