RECOVERABLE WORK VERSUS ASYMPTOTIC RELAXATION MODULUS IN AGAR,CARRAGEENAN AND GELLAN GELS1

Cylindrical specimens of agar, carrageenan and gellan gels (1&2%) were uniaxially compressed to various predetermined strain levels and then decompressed. In an independent set of tests, specimens of the same gels were compressed to the same strains and then allowed to relax. Both the percent recoverable work, calculated from the stress-strain relationships in the compression-decompression cycles and the magnitude of the asymptotic relaxation modulus, calculated from the normalized and linearized relaxation curves, decreased as the strain increased. In all three gels there was a linear correlation between the percent recoverable work and the magnitude of the asymptotic modulus at corresponding strains, a sign that both parameters are indicative of these gels’ degree of elasticity and the latter's strain dependency.     

Stability, solubility, mechanical and barrier properties of cassava starch - Carnauba wax edible coatings to preserve fresh-cut apples

This work aimed at evaluating edible coatings/films formulated with cassava starch, glycerol, carnauba wax and stearic acid, analyzing the stability of emulsion (creaming index and lipid particle size), the barrier properties of coatings applied in fresh-cut apples (respiration rate and water vapor resistance), the solubility and mechanical properties of films prepared with coating solutions. A central composite rotatable design 2³ was used to select optimized formulation. Independent variables used were: cassava starch concentration (2-4% w/w), glycerol content (1-3% w/w) and carnauba wax: stearic acid ratio (0.0:0.0-0.4:0.6% w/w). The creaming index and the lipid particle size of emulsified coatings were strongly affected by the carnauba wax: fatty acid ratio. Glycerol content was the variable that most influenced the respiration rate of coated apple slices, water vapor resistance of coatings and the elastic modulus of films. The water solubility was positively affected by the cassava starch and glycerol contents. Models and response surfaces were obtained for the respiration rate, water vapor resistance of coatings, elastic modulus and solubility of films. According to statistical analysis results, the optimized conditions corresponded to 3.0 g of cassava starch/100 g of coating solution, 1.5 g of glycerol/100 g of coating solution, 0.2:0.8 g of carnauba wax: stearic acid ratio/100 g of coating solution. The models obtained in the experimental design were predictive, which was evidenced by the relative deviations below 10% in validation procedure.     

RHEOLOGICAL BEHAVIOUR OF BUTTER AT SMALL DEFORMATIONS

Thirteen continuously churned commercial butter samples were evaluated for rheological properties at small deformations. The methods performed included dynamic experiments in shear and compression, stress relaxation in shear and static compression at 5–20C each. Linear viscoelastic behaviour was observed up to a critical strain of 0.001. The structure breakdown due to shear strains between 0.001 and 0.01 was found to be fully recoverable. No qualitative differences in the rheological behaviour were observed between the samples. Temperature-induced variations were mainly ascribed to changes in the solid fat content. Correlations between selected rheological measures in the linear viscoelastic region (i.e., complex modulus G* [Pa], relaxation modulus G(t) | _t ≃ 0[Pa], and modulus of deformability M_D[Pa]) were found to be causal and only slightly affected by the solid fat content.     

Injury and death of frozen Listeria monocytogenes as affected by glycerol and milk components

A cell suspension of Listeria monocytogenes strain Scott A in phosphate buffer solution alone or with added glycerol, milk fat, lactose, or casein was frozen and stored at -18 degrees C. At suitable intervals, samples of cell suspensions were thawed at 35 degrees C and plated on suitable media to distinguish between surviving injured and noninjured cells of L. monocytogenes. Glycerol (2 or 4%) protected L. monocytogenes from death and injury during frozen storage for up to 6 mo; however, when 2% glycerol was present, 30 min of frozen storage had to elapse after completion of freezing before protection against death was evident. During short-term (2 wk or less) frozen storage, lactose, milk fat, and casein, each at 2%, provided better protection to L. monocytogenes than did 2% glycerol. During long-term frozen storage, milk components, each at 2%, protected L. monocytogenes against death and injury, but less than that provided by glycerol. Protection by lactose and milk fat against death during frozen storage was observed during 4 wk and against injury during 5 mo and 4 wk of frozen storage, respectively. Protection by casein against death and injury occurred during frozen storage for up to 6 mo. Salts that simulate milk ultrafiltrate provided almost no protection to L. monocytogenes during freezing and frozen storage. Increasing the concentration of milk fat from 2 to 4% resulted in almost no change in death of L. monocytogenes, but in a decrease in injury only during the first 24 h of frozen storage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dynamic mechanical study of hair viscoelasticity and softness

IFSCC Magazine , 12 (2009) (2) 93–98
Dynamic mechanical analysis (DMA) has been widely used to investigate material properties such as thermal transitions and complex modulus of polymers. Until now, only a few articles have been published to discuss applications of DMA in studying human hair and evaluating hair care products due to difficulties in handling hair samples. In DMA, a complex modulus (E*), an elastic (storage) modulus (E') and an imaginary (loss) modulus (E') are determined which give a better characterization of viscoelastic properties of hair than regular tensile strength. A new DMA test methodology including a hair bundle preparation and sample clamping technique was developed and applied to study human hair samples. Effects of hair type (Caucasian vs. Asian), bleaching time, environmental relative humidity (RH), and cosmetic treatments on hair viscoelasticity and storage bending modulus/stiffness were investigated. Average complex modulus and Young's modulus of single hair fibers and storage bending modulus of hair bundles before and after cosmetic treatments at various relative humidity levels were determined. Subjective evaluations of hair soft feel by salon panelists were conducted and the results compared with those of objective measurements (changes in hair storage bending modulus).
Keywords: Dynamic mechanical analysis, hair, viscoelasticity, softness, quaternium-91
This paper was presented at the 25th IFSCC Congress 2008, Barcelona, Spain     

Influence of equibiaxial extensional strain on stress relaxation of glycerol plasticised wheat gluten

BACKGROUND: Glycerol plasticised wheat gluten shows advantages for non‐food applications such as biodegradable package films and bioplastics because of their abundant resources, low cost, good biodegradability and suitable mechanical and oxygen barrier properties. The intention of this study was to evaluate to the equibiaxial stress relaxation of 400 g kg^?1 glycerol plasticised gluten at different biaxial strains at room temperature for a better understanding of the processibility. RESULTS: The plasticised gluten shows significant stress relaxation and the spectra span over six decades of time at biaxial strains from 0.03 to 1.51. Plotting the instantaneous modulus against strain reveals strain softening and strain hardening at strains below and above 0.25, respectively. The relaxation modulus as a function of time can be fitted to the Kohlrausch–Williams–Watts equation. CONCLUSION: These results suggest that stress relaxation of plasticised gluten is highly dependent on strain level and biaxial deformation accelerates the network relaxation by widening the distribution of relaxation times. Copyright © 2008 Society of Chemical Industry     

Viscoelastic properties of reconstituted cassava dough

The influence of water (60–70%) and salt (1–2%) content on the viscoelastic properties of cassava dough, reconstituted from cooked flour, was studied using a controlled strain rheometer. Reconstituted cassava dough behaved as a solid-like material with the storage modulus (G') predominant over the loss modulus (G"). As the water content was increased, G' decreased and G" increased; but tan δ was practically independent of the water content. This behaviour suggested that water had plasticising effects, but probably did not change dough structure. The effect of salt content on the dynamic rheological properties of cassava dough was not significant, except for G" values at water contents close to 60%.     

Chitosan globules

We prepared chitosan globules to use as a structural unit or as a means of controlled ingredient release in food products. Globules were fabricated by coagulating drops of chitosan solutions (1–2% w/w chitosan in 3.8–5.6% w/w citric acid solution) in 1 N NaOH. The chitosan solutions, dropped from a 2.9 mm diameter tube, resulted in ellipsoidal globules with diameters of 3.7–5.1 mm and an opaque, whitish appearance similar to that of cooked white rice. The globules contained more than 98% water, about half of which could be squeezed out under compression.
The force-deformation test indicated an increase in the strength, elastic moduli, and relaxation time of fabricated globules when the chitosan concentration was higher in the casting solution. When the citric acid concentration was higher, elastic moduli generally increased, but the longest relaxation time decreased. The globules sustained up to approximately 0.8 linear strain without fracture. Stress relaxation tests showed that the viscoelastic properties of globules may be represented by a one-element Maxwell model with a relaxation time on the order of 1000 sec and an elastic modulus of 0.05–0.27 g/mm².     

Influence of coagulant level on proteolysis and functionality of mozzarella cheeses made using direct acidification

Nonfat (0% fat), reduced-fat (11% fat), and control (19% fat) mozzarella cheeses were made using direct acidification to test the influence of three levels (0.25X, 1X, and 4X) of coagulant concentration on proteolysis, meltability and rheological properties of cheeses during 60 d of storage at 5 degrees C. Changes in meltability, level of intact alpha(s1)-casein and beta-casein (by capillary electrophoresis), 12.5% TCA-soluble nitrogen, and complex modulus were measured. There were differences in rate of proteolysis and functional properties as a function of fat content of the cheese, but some of these differences could be attributed to differences in moisture contents of the cheeses. As fat level decreased, the percent moisture-in-nonfat-substance of the cheeses also decreased. Cheeses with the lower fat contents (and consequently the lowest moisture-in-nonfat-substance content) had slower rates of proteolysis. Fat content influenced the complex modulus of the cheese, with the biggest effect occurring when fat content was reduced from 11 to 0%. Coagulant level had only a small effect on initial modulus. Cheeses became softer during storage, and the decrease in modulus was influenced by the level of coagulant. At 0.25X, there was very little decrease in modulus after 60 d, while at 1X and 4X coagulant levels the softening of the cheese was more evident. The influence of coagulant level and fat content on cheese melting was similar to their effects on complex modulus. In general, higher fat contents promoted more melting and so did higher coagulant levels. Melting increased during storage although very little change was observed in the nonfat cheese.     

Glass Transition, Water, and Glycerol Effects on Sucrose Inversion in Pullulan-Sucrose Systems

ABSTRACT: Glass transition, water, and glycerol effects on sucrose inversion were investigated in pullulan-sucrose systems. Pullulan-sucrose (2:1), PS was dissolved into distilled water. Pullulan-sucrose-invertase, PSI, and pullulan-sucrose-invertase-glycerol, PSIG, were prepared by adding tiny amounts of invertase and glycerol, respectively, to similar PS blends. Samples were freeze-dried, further dehydrated over P₂O₅, and their physical properties were determined using water sorption isotherms and DSC. The amount of glucose formed by sucrose hydrolysis in samples stored at various RH was monitored. Water and glycerol plasticized the systems. DSC thermograms indicated complex phase behavior in PSI and PSIG depending on water content. Glycerol increased sucrose hydrolysis at 0.538 a_w, and favours it even at very moderate a_w.     

Mechanical and water vapor barrier properties of tapioca starch/decolorized hsian-tsao leaf gum films in the presence of plasticizer

The objectives of this research were to examine the mechanical and water vapor barrier properties of the starch/decolorized hsian-tsao leaf gum (dHG) films as a function of dHG and glycerol concentration. Edible film-forming solutions were prepared by mixing tapioca starch with dHG at different starch/dHG ratios to make a total solid content of 2%. In total, 15–40% glycerol was then added based on the dry film matter. Starch/dHG films were obtained by casting. It was found that the puncture strength, tensile strength, and modulus as well as the inverse of relaxation coefficient of starch/dHG films pronouncedly increased with increasing dHG, accompanied with a decreasing tendency in puncture deformation and tensile strain at break. Such results implied that starch interacted with dHG synergistically, resulting in the formation of a new network to improve the mechanical properties of tapioca starch/dHG films. Mechanical strengths of starch/dHG films decreased and water vapor permeability (WVP) at 75% RH increased with increasing glycerol concentration. However, the plasticizing effect of glycerol became less significant at high dHG concentration, particularly for the puncture deformation and tensile strain at break of the films. Water sorption isotherm results indicated that significant water sorption would only occur at high water activity (about 0.75), and generally became more pronounced with increasing glycerol and dHG concentration, but to a lesser extent for the latter. Dynamic mechanical analysis revealed that the major glass transition of starch/dHG films occurred at about −50 °C.     

Fresh cut ‘Tommy Atkins’ mango pre-treated with citric acid and coated with cassava (Manihot esculenta Crantz) starch or sodium alginate

This work aimed to evaluate quality parameters of ‘Tommy Atkins’ mango slices pre-treated with citric acid and cassava starch or sodium alginate edible coatings, with or without glycerol. Samples only treated with citric acid were also evaluated. Mango slices dipped in sanitising solution were used as control. Colour parameters, mechanical properties, weight loss and respiration rate were analysed during 15 days at 5 °C. Cassava starch coating, with or without glycerol, provided higher stress at failure and lightness values than control sample throughout storage (p ≤ 0.05). The citric acid promoted colour preservation, but increased significantly samples weight loss during storage. Sodium alginate coatings did not maintain quality characteristics, showing stress at failure and lightness values lower than control after 15 days. All coatings reduced respiration rate, but citric acid dipping and cassava starch coating without glycerol treatments were more effective, reaching values around 41% lower, when compared to control sample.

Industrial Relevance

Fresh-cut mangoes are appreciated world-wide for its exotic flavour and nutritional composition. However, their shelf life is limited by changes in colour, texture, appearance and microbial growth. The edible coatings act as gas and water vapour barrier, extending the storage time of fresh-cut fruit and vegetables. Thus, cassava starch and alginate are alternatives to preserve minimally processed mangoes, maintaining the quality parameters of fresh fruit. This work is useful for the minimal processing industry in order to increase shelf life of fresh-cut mangoes, which can be considered an alternative to fast food and other ready-to-eat products, attending the demand for healthy and convenient foodstuffs.     

氧化羟丙基木薯淀粉的流变特性

利用DHR-1流变仪,研究了氧化羟丙基木薯淀粉的静态流变和动态流变特性。结果表明,氧化羟丙基木薯淀粉糊为假塑性流体（n＜1）,符合Herschel-Bulkley模型（R2＞0.98）。随着羧基含量和羟丙基摩尔取代度（molar substitution,MS）的增大,稠度系数k减小,非牛顿性减弱,趋近于牛顿流体。在整个振幅范围（1×10－4～1 rad）,主要表现为黏性特性;随着振幅增加,样品的弹性模量（G’）和黏性模量（G”）变化不明显;随着羧基含量和羟丙基摩尔取代度（molar substitution,MS）的增大,G’和G”降低,损耗角正切（tanδ＝G”/G’）增加。在频率范围（0.1～12.5 rad）内,随着频率增加,样品的G’和G”增加,tanδ变化不明显;随着羧基含量和MS的增大,G’和G”降低,tanδ增加。     

淀粉成膜性和疏水性对表面施胶包装纸的影响

本文研究了添加甘油对疏水改性木薯淀粉膜力学性能及阻隔性能的影响,甘油的添加降低了疏水改性淀粉膜的玻璃转化温度、储能模量及水蒸气透过量.当温度低于临界温度上限时,疏水改性淀粉将会出现固态及液态两种形式.热的淀粉溶液中加入适量的甘油可以抑制淀粉微粒的沉淀.与羟丙基淀粉相比,疏水改性淀粉中添加不同量的甘油并涂覆干基材表面,对基材的阻隔性、水蒸气透过量、接触角及可勃吸水值均有一定影响.从表面施胶基材的可勃吸水值和水蒸气透过量的变化上可以看出,淀粉的成膜性对基材的性能有非常重要的影响.良好的成膜性可以改善基材的阻气、阻湿性,而对基材表面润湿性的影响不大.随着甘油含量的逐渐增加,基材的水蒸气透过量不断减少;但仍无法得到较好的阻湿性能.本文中所用的疏水改性淀粉具有较好的氧气阻隔性能和接触角,因此,表面施胶后的基材具有较好的疏水特性.同时在实验条件下研究了淀粉沉淀对基材性能的影响,利用淀粉沉淀对基材表面进行施胶后即使淀粉成膜性较差,也可以得到较低的水蒸气透过量和较高的接触角.通过增加疏水改性淀粉中甘油的含量,表面施胶基材的可勃吸水值可以得到显著改善.     

EFFECT OF STRAIN LEVEL AND STORAGE TIME ON THE RECOVERABLE WORK OF COMPRESSED BREAD CRUMB 1

Cylindrical specimens of bread crumbs were subjected to a compression-decompression cycle using a computer interfaced Universal Testing Machine during 11 days of storage at ambient temperature. The strain (% deformation) was set at various levels in the range of 20–80%. The overall work per unit volume, calculated from the area under the stress-strain curve, increased exponentially with the imposed strain while the percent recoverable work, calculated from the area under the decompression curve, decreased exponentially with the strain. The loss of elasticity that accompanies bread aging was clearly manifested in the percent recoverable work, irrespective of the imposed strain. It declined in a manner that could be described by a power law or an exponential decay model at the same degree of fit as judged by statistical criteria.     

Apple Peel-Based Edible Film Development Using a High-Pressure Homogenization

ABSTRACT:  Biopolymer films were developed from apple peels of apple process co-products and their physical properties were determined. Apple peel-based films with glycerol (23%, 33%, and 44%[w/w, dry basis]) were prepared using high-pressure homogenization (HPH) at different levels of pressure (138, 172, and 207 MPa). An evaluation of the rheological properties (elastic modulus [ G '], viscous modulus [ G "], and viscosity) of the film-forming solutions was performed. For the apple peel films, the water sorption isotherms, the kinetics of water absorption, the water vapor permeability (WVP), the oxygen permeability (OP), and the tensile properties were determined. The  G ' and viscosity of the film-forming solutions decreased significantly with increasing processing pressure ( P  < 0.05). However, no difference was observed in  G " values at different homogenization pressures ( P  > 0.05). The viscosity decreased from 644 to 468 kPa·s as the pressure increased from 138 to 207 MPa at 90 °C. The monolayer water content of the apple peel films decreased with increasing content of glycerol from 23% to 33%. Further increase in glycerol content did not change the monolayer water content. The water diffusion coefficient of the films was highest at the intermediate level of glycerol content. The barrier properties (WVP and OP) of the films increased with increasing level of glycerol, while processing pressure did not influence the gas barrier properties. The films prepared at 207 MPa were less stiff and strong, but more stretchable than those prepared at 138 and 172 MPa.     

鲍鱼预熟制及低温贮藏中的脂质氧化特性

为探究鲍鱼在不同预处理和贮藏条件下的品质变化,研究不同预熟制工艺和低温贮藏条件对其腹足脂质变化的影响。通过水蒸气蒸馏法、气相色谱-质谱联用仪检测硫代巴比妥酸反应物(thiobarbituric acid reactive substances,TBARS)值和脂肪酸组成。结果表明,新鲜鲍鱼样品的TBARS值为1.01 mg/kg,经4℃贮藏4 d、-18℃贮藏35 d、-80℃贮藏35 d后分别为4.12、4.31、3.40 mg/kg。而经80℃加热2 h预熟制处理鲍鱼的TBARS值为1.90 mg/kg,其在4℃贮藏4 d、-18℃贮藏35 d、-80℃贮藏35 d后分别为1.91、1.86、1.91 mg/kg,在贮藏过程中无明显变化。经预熟制处理的鲍鱼在-18℃冻藏21 d后的二十碳五烯酸和二十二碳五烯酸含量分别为9.78%和5.32%,明显高于直接冻藏(分别为8.76%和5.01%)的鲍鱼。因此,认为新鲜鲍鱼的脂质氧化主要发生在冻藏阶段,而预熟制工艺可以有效延缓冻藏过程中脂质氧化的发生。     

Effects of Physical Aging on Thermal and Mechanical Properties of Glassy Normal Corn Starch

Physical aging of glassy corn starch and its effect on the physical properties of compressed starch bars were investigated by using differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA), and Instron texturometer. Amorphous corn starch samples were prepared by drying a starch paste, followed by compressing the dried powders to bar‐type specimens under heat (100°C, 1.38×10⁷ Pa). These bars were then aged at 25°C for up to 22 days, after which thermal and mechanical characteristics were determined. There were progressive increases in glass transition temperature and relaxation enthalpy during the aging, which reached limiting values as structural equilibrium of the amorphous matrix was approached. The peak temperature of the relaxation endotherm (DSC thermogram) changed with time in a trend similar to the relaxation enthalpy. The storage modulus (DMTA) increased with aging time, but the peak intensity of tan δ decreased. The breaking strength (Instron texturometer) increased gradually with time of aging and reached a maximum. It has been demonstrated the relaxation kinetics for glassy amorphous corn starch can be characterized by both thermal and mechanical properties, such as relaxation enthalpy, storage modulus, and breaking strength.     

THE EFFECTS of PLASTICIZERS ON CRYSTALLINITY, PERMEABILITY, and MECHANICAL PROPERTIES of METHYLCELLULOSE FILMS

The effects of plasticizers (polyethylene glycols [PEG] 400, 1,450, 8,000 and 20,000, glycerol [G] and propylene glycol [PG]), 30% dry basis, on the physical properties of methylcellulose (MC) films were investigated. With the exception of PG, plasticizers with low molecular weights (G and PEG 400) caused the largest increase in the d₁₀₁ spacing of the crystal lattice. All plasticizers significantly (α= 0.05) increased oxygen (O₂P) and water vapor permeabilities (WVP) of the films as compared to that of unplasticized MC, with PEG 400 having the greatest effect on O₂P and G having the greatest effect on WVP. With the exception of PG, all plasticizers decreased the tensile strength of MC films, with PEG 400 causing the largest decrease. With the exception of PG and PEG 400, all plasticizers increased percent elongation values of MC films, with PEG 1,450 having the greatest effect. Glycerol and PEG were the most effective plasticizers for MC. the higher molecular weight plasticizers do provide some plasticizing properties and may be more suitable for applications that require a lower permeability to water vapor than can be achieved with glycerol.     

Microbial, physical and sensory properties of yogurt supplemented with lentil flour

In this study, skim milk (9.5% w/v solid content) was supplemented with 1-3% (w/v) lentil flour or skim milk powder, inoculated with a yogurt culture, fermented and stored at 4 °C. Acid production during the fermentation, microbial growth, physical properties (pH, syneresis, and color), rheological properties (dynamic oscillation temperature sweep test at 4-50 °C), during 28 days of refrigerated storage and also sensory properties (flavor, mouth feel, overall acceptance and color) after production, were studied. Milk supplementation with 1-3% lentil flour enhanced acid production during fermentation, but the microbial population (CFU) of both S. thermophilus and L. delbrueckii subsp. bulgaricus were in the same range in all lentil flour and skim milk powder supplemented yogurts. The average pH of samples decreased from 4.5 to 4.1 after 28 days storage. Syneresis in 1-2% lentil flour supplemented yogurts was significantly higher than all other samples; however, greater lentil supplementation (3%) resulted in the lowest syneresis during the 28 days storage. With respect to color, “a” and “L” values did not significantly differ in all samples and remained constant after 28 days whereas “b” value increased as a result of lentil supplementation. Yogurt with 3% lentil flour showed higher storage (G') and loss (G?) moduli in comparison with samples supplemented with 1-3% skim milk powder and the non-supplemented control yogurt. Storage modulus (G') was higher than loss modulus (G?) in all samples and at all temperatures between 4 and 50 °C and they showed a hysteresis loop over this temperature range when the samples were heated and cooled. 1-2% lentil flour supplemented yogurt showed comparable sensory properties in comparison with 1-2% skim milk powder supplemented yogurt and the control sample.