RHEOLOGICAL CHARACTERISTICS OF SELECTED FOOD GUM MIXTURES IN SOLUTION2

The viscosity of pure and mixed dilute solutions of commercial alginate, carrageenan, guar gum, CMC and gelatin solutions at different mixing ratios were measured by a coaxial viscosimeter at different shear rates. The results are presented in the form of measured viscosity divided by the expected viscosity, if no interaction between the gums existed. This technique provides a clear demonstration of the existence of synergism or antagonism between the gums and helps in quantitatively assessing their extent.     

植物胶的特性及在食品工业中的应用

简要介绍了阿拉伯胶、魔芋胶、黄蓍胶、刺梧酮胶、罗望子胶、卡拉胶、瓜尔豆胶、刺槐豆胶和亚麻籽胶的特性及在食品工业中的应用,并指出亲水植物胶体作为优良的功能性配料和可溶性膳食纤维的良好来源,对其进行研究和应用开发,具有重要的实用价值。     

COMPARISON OF STEADY SHEAR RHEOLOGICAL PROPERTIES AND SMALL AMPLITUDE DYNAMIC VISCOELASTIC PROPERTIES OF FLUID FOOD MATERIALS

Small amplitude dynamic viscoelastic properties of apple butter, mustard, tub margarine, and mayonnaise are compared with their respective properties in steady shear flow in the range of shear rates and frequencies of 0.1-100 sec⁻¹ using a Rheometrics Mechanical Spectrometer. Comparison of dynamic and steady viscosities shows that dynamic viscosities (η*) are much larger than steady viscosities (η). Consequently the Cox-Merz rule is not obeyed. Moreover the obvious nonlinearity suggests that shift-factor type relationships are not obeyed either. The in-phase (η') component of the dynamic viscosity shows similar behavior when compared to the steady viscosity (η).
Comparison of G'/ω² and Ψ₁ also suggests that any of the results predicted by classical theories of viscoelasticity are not obeyed. G'/ω² is always much larger than Ψ₁ and the relationship between these two material functions is nonlinear.     

RESEARCH NOTE EFFECT OF SELECTED ADDITIVES ON THE FLOW PARAMETERS OF 1:1 MIXTURES OF CARRAGEENAN-GUAR AND CMC-LOCUST BEAN GUM

Flow parameters of 1:1 mixtures of carrageenan-guar and CMC-locust bean gum in the presence of common food ingredients, namely, sugar, salt and proteins, were determined by using a coaxial viscometer. The effect of additives on yield stress, and power law model constants varied depending on the type of ingredient and its concentration, and the nature of the gum. Although, it is interesting to see the flow behavior of gum blends together with the additives in concentrations that are common in food products, it is necessary to study an enormous number of combinations in order to analyze a multicomponent system quantitatively.     

VISCOELASTIC PROPERTIES OF TABLE MARGARINE PREPARED FROM LIPASE-CATALYZED TRANSESTERIFIED MIXTURES OF PALM STEARIN AND PALM KERNEL OLEIN

A controlled-stress rheometer was used to evaluate dynamic viscoelastic (VE) performance of an experimental table margarine prepared from a transesterified palm stearin (PS):palm kernel olein (PKO) mixture (40:60 ratio) using Rhizomucor miehei lipase as the biocatalyst. Comparison was made using a commercial table margarine made of palm oil and palm kernel oil. The experiments were carried out over a period of three months with the margarines kept at 20 and     

CHANGES OF SOME THERMAL AND PHYSICAL PROPERTIES IN MODEL SYSTEMS SIMULATING AN ALCOHOLIC FERMENTATION

Highly simplified model systems, simulating the fermentation of 25.00% sugar-water mixture into a 12.78% ethanol-water mixture, were considered in order to study their thermo-physical properties. Calorimetric data, viscosity and water activity determinations showed that important thermal and physical changes are associated with the steps of a fermentation process. Besides the increase in ethanol content, other concomitant changes are a strong increase in ethanol vapor pressure and a decrease in water activity and viscosity. DSC measurements of the models during scanning from -140C to 25C showed three peaks: peak 1 (exotherm) covered a temperature range from -110C to -80C and was attributed to the recrystallization of the ethanol monohydrate; peak 2 (endotherm), with peak temperature around -70C, was attributed to the melting of the alcoholic monohydrate; peak 3 (endotherm) in the higher temperature range from -30C to OC, was due to ice melting. The alcoholic monohydrate appeared only in the final simulated step of the fermentation, where only ethanol and water were present. The inhibitory effect of even small amounts of sugars on the formation of the monohydrate might be related to the increase in viscosity. This would confirm the formation of the ethanol hydrate as kinetically hindered, as it is reported in the literature.     

CONSIDERATIONS OF A GENERAL RHEOLOGICAL MODEL FOR THE MECHANICAL BEHAVIOR OF VISCOELASTIC SOLID FOOD MATERIALS*

A model describing the rheological behavior patterns of solid foods is suggested and discussed. It consists of a parallel array of a generalized Maxwell body in which the Maxwell elements have been modified by incorporation of two fracture elements. The model enables the anticipation of response patterns of real food materials under various force—deformation histories without becoming inconsistent. It also predicts the viscoelastic phenomena of materials after their failure and does not exclude the elastic deformation stage. The effects of experimental conditions, differences between various types of foods, as well as variations and changes in the same food can be expressed or explained in terms of model components and their relative distribution. The application of the model is demonstrated with a small number of representative elements.     

EFFECT OF SUGAR AND GUMS ON THE PASTING PROPERTIES OF CASSAVA STARCH

Pasting properties of cassava starch solutions were prepared with different types of sugars (glucose, sucrose and fructose) at different levels as 10.71, 19.35, 32.43% and gums (gum acacia, guar gum and gum tragacanth) at 0.1, 0.2, 0.3, 0.4% levels, respectively, were analyzed using the Rapid Visco Analyzer. The pasting temperature increased with increase in the sugar concentration in cassava starch–water system and the maximum 78.27C at 32.43% sucrose solution. The peak viscosity (PV) and breakdown viscosity (BD) decreased with increase in the sugar concentration. Hot paste viscosity and cold paste viscosity decreased progressively with increase in sugar concentration in fructose and glucose solution. The PV and BD increased with increase in guar gum concentration and was maximum 5,704 and 3,773 mPa·s at 0.4% concentration, respectively.

PRACTICAL APPLICATIONS

Cassava starch performs most of the functions where maize, rice and wheat starch are currently used. In food industry, cassava starch is used in extruded snacks for improved expansion, as a thickener in foods, in processed baby foods as a filler material and bonding agent in biscuit and confectionary, textile, pharmaceutical, paper and cosmetic industries. Cassava starch can be converted to maltotriose, maltose, and glucose as well as to other modified sugars and organic acids. Starch from cassava can be used to make gelatin capsules. Starches and gums are often used together in food systems to provide texture, control moisture, water mobility, improve overall product quality and stability, reduce cost and facilitate processing. Cassava starch, due to its high swelling power, is reported to yield better quality instant noodles.     

A COMPARISON OF THE VISCOELASTIC PROPERTIES OF CONVENTIONAL AND MAILLARD PROTEIN GELS

The properties of gels prepared by heating solutions of bovine serum albumin (BSA) for 30 min at 121C in the presence and absence of glucono-delta-lactone (GDL gels) and xylose (Maillard gels) were compared. During formation the pH of the Maillard and GDL gels decreased to 4.9 whereas the pH of the gels formed in the absence of GDL or xylose remained near neutral. Maillard gels show much less syneresis compared with the GDL gels and contained nondisulphide covalent crosslinks as evidenced by very low protein solubilities in mixtures of sodium dodecyl sulphate and β-mercaptoethanol. Both the GDL and Maillard gels could be formed at much lower protein concentrations than the neutral conventional gels. The stress relaxation of the gels in compression was measured and the response analyzed using Peleg's equation. The parameters in this equation were not strongly dependent on protein concentration or degree of deformation. The neutral pH gels were far more elastic than the low pH gels, but despite the difference in crosslinking mechanisms the viscoelastic behaviour of the Maillard and GDL gels was similar. However, the break strength and asymptotic residual modulus of the Maillard gels were higher. It is suggested that the stress relaxation occurs in weaker, noncovalently linked regions of the gel, whereas the nondisulphide covalent crosslinks in the Maillard gels reinforce strong regions already containing disulphide linkages.     

NONLINEAR VISCOELASTIC MODEL CONTAINING A YIELD ELEMENT FOR MODELING A FOOD MATERIAL1

A series-parallel model is introduced in which a yield element is incorporated in the parallel branch. Before the yield stress is reached, the stress-strain behavior is determined by the series branch to exhibit the linear uiscoelasticity of the material. When the yield stress is reached, the stress in the model which was sustained by the yield element is suddenly transferred to the spring and dashpot in parallel. As a consequence, a stress rate discontinuity was created. It is this feature which makes possible the simulation of the yield behavior of the food material. Data from Instron tests on American cheese are used to illustrate the model.     

CHARACTERIZATION OF AGGLOMERATION PROCESS AS A FUNCTION OF MOISTURE CONTENT USING A MODEL FOOD POWDER

A model food‐powder system using rice flour of different moisture contents (11 to 22%) was used to study rheological behavior by employing a powder rheometer to obtain maximum force, energy for compression and decompression. The latter parameters were sensitive at moisture contents of ≥18%. The compacted mass, obtained using a rotary punch‐tableting machine, was subjected to compression testing to determine the maximum force and firmness of the compressed tablets. These two parameters increased markedly above the 17% moisture content. A significant (P ≤ 0.01) relationship between energy for compression for powder and firmness of compacted mass indicated that an adequate integrity of the product could be achieved when a powder requires high energy for compression but low energy for decompression. A modified version of the Hausner ratio, often used to characterize the extent of compactness, was proposed that included a correction factor for loss of moisture during compaction.     

EFFECTS OF ADDED WEIGHTING AGENT AND XANTHAN GUM ON STABILITY AND RHEOLOGICAL PROPERTIES OF BEVERAGE CLOUD EMULSIONS FORMULATED USING MODIFIED STARCH

Stability of beverage emulsion is measured by the rate at which the emulsion creams, flocculates or coalesces, and is generally dependent on rheology of water phase, difference in specific gravities of the two phases and droplet size/distribution of the emulsion. The effects of weighting agents (sucrose acetate isobutyrate and brominated vegetable oil) and xanthan gum on modified starch‐based emulsions were evaluated in this study. Emulsion was formed by addition of 9% coconut oil, in the presence or absence of weighting agents, into the water phase containing modified starch at 10, 12 or 14% without or with the addition of 0.3% xanthan gum. Stabilities of emulsions were evaluated both in the concentrated form used for storage and dilute form used in beverages. The addition of xanthan gum into the water phase decreased the flow behavior index (n) from 0.88 down to 0.31 and increased elastic modulus (G′) over 20 times at elevated frequency (ω = 50 rad/s) and elevated the stability of the emulsion. The xanthan gum‐added emulsion had smaller particle size and demonstrated 14 and 5 times slower phase separation compared to the emulsions without or with the addition of weighting agents, respectively. When the elastic modulus was larger than the viscous modulus (G′ > G″), the emulsions demonstrated greater stability. In dilute beverage solutions, creaming was observed in the absence of xanthan gum.     

RHEOLOGICAL CHARACTERIZATION OF A MODEL FOOD SUSPENSION CONTAINING DISCS USING THREE DIFFERENT GEOMETRIES

The objective of this study was to characterize the flow behavior of a solid-liquid food model which imitates Mexican sauces. The model food suspension consisted of seeds suspended in a shear-thinning fluid (Avicel and Xanthan gum). The effects of size and particle concentration were investigated using a traditional disc geometry in wide gap (spindle), and a ribbon adapted to a rotational viscometer. The effect of particle size was evaluated in a tube viscometer. Power-law parameters and apparent viscosity were estimated in the shear range of each viscometer. The experimental apparent viscosity showed good agreement with predictions obtained using a theoretical expression of relative viscosity for uniform spheres. In all the viscometers investigated, shear-thinning behavior of the suspension was observed, as the aqueous phase, due to low interactions among particles. The ribbon geometry appears to be the best option for flow characterization of food suspensions containing coarse disc shaped particles.