SELECTING DEFORMATION RATES IN TEXTURE TESTS *

Abstract . Since mastication involves high deformation rates (150cm min^?1), the arbitrarily selected slow deformation rates usually used in instrumental texture tests can lead to erroneous results and lack of correlation with sensory evaluation with respect to the order of sample ranking. Sophisticated instrumentation that is costly to operate is required to accurately simulate the deformation rates operating in the mouth. It is suggested that instrumental data obtained at slow rates could be evaluated in a more meaningful manner if series of similar samples were tested at increasing deformation rates and the plotted force/deformation curves extrapolated to 150cm min^?1. It is implied that recording systems would be more useful, if in addition to force, they sensed the rate of force change with deformation rate.     

Sulphur-coated urea as a fertiliser for potatoes

In a field experiment comparing sulphur-coated urea (SCU) and “Nitro-Chalk” at rates up to 400 kg N ha^?1, potato tuber yields were greater with “Nitro-Chalk” at rates up to 200 kg N ha^?1, but there was no consistent difference between forms of N at larger rates. The crop recovered more N from “Nitro-Chalk” at all rates except 350 kg N ha^?1. The largest measured yield was at 200 kg N ha^?1 with “Nitro-Chalk” and 250 kg N ha^?1 with SCU, and the optimum N rate inferred from split-line regressions of yield on N rate was also at a lower N rate with “Nitro-Chalk”. Yields of winter wheat following the potatoes increased significantly with the N rates given to the potatoes and, at rates above 200 kg N ha^?1, were larger where SCU had been used. SCU residues also lessened the response of the wheat to a spring top-dressing of new N slightly more than those of “Nitro-Chalk”. The sum of the apparent recoveries by the two crops of N given to the potatoes was greater from “Nitro-Chalk” at rates up to 200 kg N ha^?1. In the glasshouse, potato plants grown in 3 kg soil took 71 days to initiate tubers when given 2 g N as ammonium nitrate but this time was much decreased as increasing proportions of SCU were used. When 1 g N was given, the time was only 47 days with ammonium nitrate and the proportion of SCU had little effect. In the field, the number of tubers per plant by mid-June decreased with increasing N rate with “Nitro-Chalk” but not with SCU.     

A Computer Assisted Analysis of Some Theoretical Rate Effects in Mastication and in Deformation Testing of Foods

Simplified rheological models, with relaxation times comparable to those of solid foods, were used to simulate stress strain relationships at rates comparable to those in mastication and in common deformation tests (linear velocities on the order of 100 and 1 cm min^?1 respectively). The simulations included the regimes of constant deformation and strain rates and a sinusoidal deformation pattern. They demonstrated that the information in sensory perception and mechanical testing can be different in both kind and magnitude largely due to the rheological character of the food and its relaxation time and to a lesser extent, to the exact deformation regime.     

Textural Characterization of Cheeses Using Vane Rheometry and Torsion Analysis

ABSTRACT Vane rheometry was applied to textural characterization of cheeses and compared with torsion analysis. A Haake VT 550 viscotester was used for both vane and torsion tests at strain rates of 0.003 to 0.524 s^-1. Angular deformation and shear stress in the vane test increased with increasing low strain rate and was rate independent at higher rates. This shear rate dependency of stress and deformation varied with cheese types. Shear stresses from the vane method were lower than torsion shear stresses. Similar texture maps of cheeses were generated by plotting stress and strain or angular deformation values from the 2 testing methods. The findings indicate the vane technique can be used for rapid textural characterization of cheeses.     

Rupture Properties of Wheat Gluten in Simple Tension: The Role of Hydrogen Bonds

Gluten obtained from hard red winter wheat flour was freeze-dried and reconstituted wth deuterium oxide and aqueous solutions of urea to selectively alter the extent of hydrogen bonding. The rupture properties of the modified glutens were studied in simple tension at seven rates of strain covering three orders of magnitude (2.86 × 10^-2 to 28.6 min^-1). Tensile strength and rupture strain decreased steadily with the extent of hydrogen bonding disruption, i.e., with increase in urea concentration. For a given type of modified gluten, the strain at rupture was independent of the rate at which the material was deformed and the tensile strength increased with increasing deformation rate.     

A 75% reduction in herbicide use through integration with sorghum + sunflower extracts for weed management in wheat

BACKGROUND: To reduce herbicide use by 75%, integrated use of sorghum and sunflower extracts each at 18 L ha^?1 combined with 1/4^th (75% less) of label rates of four herbicides (mesosulfuron + idosulfuron, metribuzin, phenoxaprop‐p‐ethyl and isoproturon) were investigated for the management of wild oat and canary grass, the two pernicious weeds in wheat fields worldwide. RESULTS: The results revealed that sorghum + sunflower extracts combined with 1/4^th (75% less) of label rates of herbicides inhibited dry matter production of wild oat by up to 89% and canary grass by up to 92%. The wild oat and canary grass persistence index in sorghum + sunflower extracts combined with 1/4^th (75% less) of label rates of herbicides was either lower or equal to respective label rates of herbicides, except sorghum + sunflower extract + 1/4^th phenoxaprop‐p‐ethyl. Lower herbicide rates + water extracts also produced wheat grain yield statistically equal with label rates of respective herbicides. Two treatments having water extracts + lower herbicides rates were economical and sorghum + sunflower + 1/4^th mesosulfuron + idosulfuron produced the highest (4404%) marginal rate of return. CONCLUSION: Herbicides use can be reduced by 75% through integration with sorghum + sunflower extracts without compromising yield and net benefits for cost‐effective and eco‐friendly management of wild oat and canary grass in wheat. Copyright © 2010 Society of Chemical Industry     

Fermentation of tea in aqueous suspension

The fermentation of macerated tea leaf in aqueous suspension has been studied both manometrically and in a suitably controlled fermentation vessel. Oxygen consumption proceeded rapidly at a steady rate for an initial period, termed the primary fermentation, then decreased sharply as the availability of simple polyphenol substrates became rate limiting. Maximum reaction rates were observed at 20-35 mg ml^?1 total solids, as a result of substrate inhibition. At higher concentrations of solids reaction rates were also affected by diffusion effects within the leaf particles. At 50 mg ml^?1 total solids and 25°C the system approximated to Michaelis-Menton kinetics with K_m⁰² = 5 × 10^?5M and V_max corresponding to a primary fermentation time (PFT) of 10-15 min. The PFT corresponded with the attainment of maximum total colour and maximum level of theaflavins (TF) (often >30% of total colour). Beyond the PFT total colour remained constant, TFs decreased and non-dialysable pigments increased with time. At fixed levels of dissolved oxygen and solids concentration > 60 mg ml^?1 the proportion of TFs was inversely related to solids concentration. At 50 mg ml^?1 total solids TFs increased to ca 60% of total colour as the dissolved oxygen level was increased to 0.175 mM. As temperature was increased from 15-35°C the reaction rate increased, the proportion of TFs decreased slightly and thearubigins of intermediate molecular weight increased markedly.     

The effect of washing water parameters (pH, hardness and sodium pyrophosphate content) on the water-holding capacity and gelation characteristics of sardine (Sardina pilchardus) mince

In order to determine the effect of washing water parameters [pH, hardness and tetrasodium pyrophosphate (TSPP) content] on the water-holding capacity (WHC) and gelation properties of sardine (Sardina pilchardus) mince, two experiments designed by response surface methodology were carried out. The WHC of the mince was maximum when washed in the pH range of 6.5–7.0, with TSPP>1.7?g???l^-1, and CaCO₃ between 30 and 60?mg???l^-1. With the exception of breaking deformation and the folding test, where the highest values were obtained at 60?mg???l^-1 CaCO₃, the variation of water hardness did not induce any significant changes in the other rheological parameters. The use of relatively high concentrations of TSPP in the leaching water contributed to the achievement of high values of breaking deformation, though beyond 2.5?g???l^-1 a detrimental effect on breaking force was observed, and consequently also on gel strength.     

Influence of Protein and Fat Contents of Ultrafiltered Milk on Rheological Properties of Gels Formed by Chymosin

Enzymatically induced gelation of milk and milk concentrated by ultrafiltration was studied with a curd firmness tester which measured transmission of oscillatory deformations through the product. Scott Blair's relationship between pseudo modulus of rigidity (G) and time after clotting (t), G = G∞ e^—_λ/t described the gelation of ultrafiltered retentates satisfactorily. Maximum gel firmness G∞, and _λ, which is the time to reach a firmness of G∞/e, were affected substantially by protein content. The effect of protein content on rates of firming of gels were evaluated at different stages of gel formation. At the onset of gelation, rates increased up to protein content 90 g kg^—1 but decreased at higher protein concentrations. At a later stage, this decrease disappeared and rates correlated with protein content. Those observations are discussed relative to effects of protein content on proteolytic and aggregation phases of milk clotting.Times from clotting to point of cutting curd were affected significantly by slight increases in protein above that in unconcentrated milk, but clotting times were not affected. Variations in fat content had inconsequential effects on test measures.     

Determination of kinetic parameters of pectolytic enzymes at low pectin concentrations by a simple method

A simple and sensitive method for determination of the pectolytic enzyme activity was improved for soluble and immobilized forms of the enzyme. During enzymatic hydrolyzation of pectin, samples were collected from substrate solution at certain time intervals. Pectin in the samples was precipitated by alcohol and then pectin concentration was determined by measuring the refractive index of a prepared aqueous solution of these precipitates. The validity of this technique was evaluated using the kinetic behavior of soluble and immobilized enzymes. The kinetics of free and Duolite A568-immobilized pectinase was investigated. Michaelis-Menten constants and maximal reaction rates were found as K _m=20.71 g l ^-1 and V _max=81.30 g l ^-1s ^-1 for free enzyme and K _m=1.02 g l ^-1 and V _max=0.035 g s ^-1 g ^-1 particles for immobilized pectinase at 20 °C.     

ESTIMATION OF THE RATE OF SHEAR ENCOUNTERED IN TOPICAL APPLICATION OF COSMETICS

Abstract The rates of shear encountered in topical application of cosmetic creams and lipstick were obtained by dividing the application velocities, at which the samples are being sheared, by the applied thicknesses of the layer. The application velocity was measured by means of a high-speed camera. Beauty artists, formulating chemists of cosmetics and women employees were used as the sensory panel. For topical application of creams in make-up, the maximum rates of shear were found to be between 10⁴ and 10⁵ S^-1, though the rate of shear differed from one kind of cream to another. The maximum rates of shear for lipstick in make-up were smaller than those for creams and were between 10³ and 10⁴ s^-1.     

Rheological characterisation of cake batters generated by planetary mixing: Elastic versus viscous effects

Studies of cake batter rheology have focused on viscous behaviour. We demonstrate that elastic effects dominate at the shear rates used in commercial mixers. The development of batter structure was investigated for two flour types using two bench-scale planetary mixers with known shear rate profiles (Kenwood-KM250, maximum 100 s⁻¹; Hobart-N50, 500 s⁻¹). These wet foams (air volume fraction 0.39-0.45) showed shear-thinning behaviour at low shear rates (0.1-10 s⁻¹), with apparent viscosity dependent on air volume fraction. Simple shear thinning behaviour ceased, for foams, above 10-20 s⁻¹: for slurries (air volume fraction, 0.11-0.15) the limit approached 100 s⁻¹. Elastic effects, predominantly arising from the bubble phase, therefore dominate cake batter behaviour at the shear rates experienced in commercial mixers. Filament thinning extensional rheometry confirmed the VE behaviour of batters. These results indicate that visco-elastic analyses are likely to be the most appropriate probe of microstructure in cake batters.     

Three interval thixotropy test (3ITT) in food applications: A novel technique to determine structural regeneration of mayonnaise under different shear conditions

In this study, three interval thixotropy test (3ITT) technique was firstly used to determine the effect of instant shear stress or shear rate along with different shear time and temperature values on the deformation and regeneration ability of a food material with respect to applied force during handling, processing, transportation etc. This test technique should be very important in food industry in terms of products like mayonnaise. 3ITT could be used for this aim in order to determine structural deformation and regeneration of food materials. In the present study, mayonnaise was instantly deformed with high levels of shear stress (5, 75, 150 and 200 Pa) or shear rate (100, 500 and 1000 s^− 1) for different time periods (20, 40 and 60 s) at different temperature levels (10, 25 and 40 °C). 3ITT results demonstrated that all shear rate/stress levels at different temperatures and shear times resulted in a remarkable deformation in mayonnaise samples, as revealed by increasing deformation percentage (D_r) values. This increase was also the case in values of time required for the recovery (R_time) values; however, under the highest shear conditions (1000 s^− 1 or 200 Pa), no regeneration was observed. Shear rate deformation resulted in higher D_r values than did shear stress deformation, indicating that deformation by shear rate was higher than that by shear stress. As a result, 3ITT was an effective test to apply instant shear stress/shear rate deformation on mayonnaise and collect data on deformation and structural regeneration kinetics, which suggests an effective tool to simulate and analyze effects of real pumping and instant stirring processes during production and handling steps of food materials.     

Influence of post-harvest treatments with fludioxonil and soy lecithin co-application in controlling blue and grey mould and fludioxonil residues in Coscia pears

The residue levels of fludioxonil (FLU) were determined in Coscia pear following a 1-, 2- or 4-min dip in an aqueous mixture of FLU containing 300 or 100 mg l^?1 (active ingredient, a.i.) at 20 and 50°C, respectively, with or without 2% soy lecithin. The efficacy of heat treatment with water and FLU mixtures was investigated on artificially inoculated pears for the control of post-harvest decay caused by blue (Penicillium expansum Link) and grey (Botrytis cinerea Pers. ex Fr.) mould. Treatment with 300 mg l^?1 FLU at 20°C increased residues significantly when treatment time rose from 1 to 2 min; no further increase was recorded when dip time raised from 2 to 4 min. FLU residue rates were unaffected by treatment time when 300 mg l^?1 a.i. was applied in combination with lecithin at 20°C. While treatment with 100 mg l^?1 a.i. at 50°C for 1 and 2 min resulted in similar residue levels, significantly higher residues were detected when dip time increased from 1 to 4 min. Co-application of lecithin significantly decreased FLU residues with respect to fruit treated with FLU alone. Treatments with FLU at 20 or 50°C effectively controlled decay over 10 days of incubation. While co-application of lecithin did not affect the efficacy of FLU at 300 mg l^?1and 20°C, treatment efficacy decreased when lecithin was applied in combination with 100 mg l^?1 FLU and 50°C for 4 min and to a greater extent when dip time was 1–2 min.     

Composition,structure, rheological properties,and sensory texture of processed cheese analogues

Processed cheese analogues were made with different fat and moisture in nonfat solids (MNFS) contents and used to study relationships between composition, microscopic structure, rheological properties and sensory texture. Fat contents ranged from 58 to 230 g kg^?1 and MNFS from 487.6 to 603.3 g kg^?1. Regressions showed that those rheological parameters measured by uniaxial compression at large deformations and moderately high rates were best explained by linear combinations of MNFS, protein and fat. The moisture in the protein network acted as a plasticiser lowering the rheological parameters. Fat alone had little direct effect on the rheological characteristics under these conditions but at small deformations and low deformation rates it formed elastic inclusions that contributed to the properties. Examination of fracture surfaces in the SEM suggested that, during fracture, fat was squeezed out and acted as a lubricant. Maximum stress and work to maximum stress measured at moderately high deformation rates related best to the sensory results and described fracture of the cheeses. From the regressions, for 95% confidence limits, sensory analysis could theoretically measure changes within the range of composition tested of <0.1% in MNFS or fat. Of the rheological parameters only work to maximum stress was as sensitive. However, interaction between these compositional factors reduced the sensitivity in practice.     

Measurement techniques for steady shear viscosity of Mozzarella-type cheeses at high shear rates and high temperature

While measuring steady shear viscosity of Mozzarella-type cheeses in a rotational rheometer at 70 °C, three main difficulties were encountered; wall slip, structural failure during measurement and viscoelastic time dependent effects. Serrated plates were the most successful surface modification at eliminating wall slip. However, even with serrated plates shear banding occurred at higher shear rates. Because of the viscoelastic nature of the cheeses, a time dependent viscous response occurred at shear rates <1 s⁻¹, requiring longer times to attain steady shear conditions. Prolonged continuous shearing altered the structure of the molten cheeses. The effects of structural change were greatly reduced by minimising the total accumulated strain exerted on the sample during flow curve determination. These techniques enabled successful measurement of steady shear viscosity of molten Mozzarella-type cheeses at 70 °C at shear rates up to 250 s⁻¹.     

Conversion of natural cellulosic substrates into fermentable sugar by recombinant fungi strains

 The use of intergeneric recombinant fungi strains for the degradation of natural cellulosic substrates gave rise to various degrees of hydrolysis rates. Pretreating crude cellulose with alkaline or dilute acidic catalysts and heating removed the lignocellulosic fraction that is not attacked by microbial cellulase system, resulting in higher activity values and hydrolysis rates than when untreated substrates were used. Pretreated wheat straw was the best substrate, giving higher hydrolysis rates expressed as glucose ml^–1 min^–1 by recombinant strain 5–3-1 that exeeded other fungi strains investigated.     

Respiratory parameters of onion bulbs (Allium cepa) during storage. Effects of ionising radiation and temperature

The O₂ and CO₂ respiration rates of untreated and irradiated onion bulbs (Allium cepa) at 0.15 and 0.30 kGy were measured at 4, 10 and 20 °C. The O₂ respiration rate increased for 24 h after treatment from 0.19 mmole kg⁻¹ h⁻¹ at 20 °C for control samples up to 0.26 and 0.39 mmole kg⁻¹ h⁻¹ for 0.15 and 0.3 kGy irradiated onions respectively. Respiratory quotient (RQ) increased with temperature. The Q₁₀ of the respiration of the control samples (1.61) was lower than that of any other plant tissue, but it increased with storage duration and irradiation dose. The respiration rate of control onions increased steadily over 25 weeks of storage at 4 °C, while that of the irradiated samples decreased during the same period after a peak observed after irradiation treatment. The apparent K_m for the Menten–Michaelis equation was determined on a new respirometer and averaged 1.6 kPa at 10 °C and 6.3 kPa at 20 °C. However, at this higher temperature (20 °C) apparent K_m varied with O₂ partial pressure, proving that the respiration of onion bulbs does not follow a Menten–Michaelis‐like process. The Fermentative Index (FI) of onions was measured under anoxic conditions as CO₂ production rates in mmole kg⁻¹ h⁻¹ at 4, 10 and 20 °C. © 2000 Society of Chemical Industry     

Conversion of natural cellulosic substrates into fermentable sugar by recombinant fungi strains

 The use of intergeneric recombinant fungi strains for the degradation of natural cellulosic substrates gave rise to various degrees of hydrolysis rates. Pretreating crude cellulose with alkaline or dilute acidic catalysts and heating removed the lignocellulosic fraction that is not attacked by microbial cellulase system, resulting in higher activity values and hydrolysis rates than when untreated substrates were used. Pretreated wheat straw was the best substrate, giving higher hydrolysis rates expressed as glucose ml^–1 min^–1 by recombinant strain 5–3-1 that exeeded other fungi strains investigated. Received: 23 January 1998