Owen J. McCarthy

Rheology of whey protein concentrate solutions as a function of concentration, temperature, pH and salt concentration

Rheological properties of whey protein concentrate (WPG) solutions were studied in steady shear, using a Bohlin VOR Rheometer, as a function of concentration, temperature, shear rate, shearing time, pH, salt type, salt concentration and solution age. At 22 °C and pH 7, the WPC solutions exhibited Newtonian behaviour up to a concentration of 10% total solids, pseudoplastic behaviour between 10 and 30% and time-dependent shear thinning at 35% and above. The apparent viscosity of solutions at 22 °C and pH 7 was linearly related to concentration up to 8%. The effect of temperature on apparent viscosity in the range 5–60 °C was closely described by the Arrhenius equation. The viscosities of WPC solutions were independent of solution age in the pH range 4–8 at all concentrations up to and including 20%, the precise pH range narrowing as concentration increased. At pH values above or below this range apparent viscosity became dependent on both pH and solution age, the age effect becoming more marked at higher WPC concentrations. Apparent viscosity at pH 7 increased markedly with both CaCl 2 concentration and solution age at concentrations above 0·6 M-CaCl 2 , the age effect in this case increasing with CaCl 2 concentration. In contrast, NaCl concentrations of up to 0·8 M-NaCl had little effect on apparent viscosity. The rheological behaviour of WPC solutions changed from time-independent to time-dependent shear thinning at high concentration, at extreme pH values, at high CaCl 2 concentration (after ageing) and on heating to above ∼ 60 °C. This change is considered to be caused by the formation of structure in solutions; a 40% solution (at 22 °C and pH 6·75) exhibited classic thixotropic behaviour in a step–shear rate experiment.

Potato Starch and Its Modification

Publisher Summary This chapter provides information on important physicochemical and functional characteristics of native potato starch in comparison with some cereal starches. It also discusses various modification techniques being used to modify potato starch, with an emphasis on the post-modification changes in its morphological, physico-chemical, rheological, and thermal behavior. The various factors that influence potato starch modification are also discussed. Progress in understanding the high value of chemically modified starches has encouraged the starch industry to produce modified starches using different modification reagents and starch sources. Some factors such as starch composition, concentration and type of reagent, and reaction conditions may affect the reactivity of starch during chemical modifications such as acetylation, hydroxypropylation, and cross-linking. The heterogeneity of the granule population within a single starch source may also affect the extent of modification. The changes observed in the morphological, physico-chemical, pasting/rheological, and gelatinization and retrogradation (thermal) properties of the starches after modification may provide a crucial basis for understanding the efficiency of the starch modification process at industrial scale.

Oscillatory rheological study of the gelation mechanism of whey protein concentrate solutions: effects of physicochemical variables on gel formation

The thermal gelation of a commercially available whey protein concentrate was studied by oscillatory rheometry using a Bohlin rheometer. Gelation time increased with decreasing protein concentration with a critical protein concentration (at infinite gelation time) of 6·6%. The effect of temperature in the range 65–90 °C on gelation time was described by an Arrhenius equation with an activation energy of 154 kJ/mol. Gelation time was a minimum at pH 4–6, the isoelectric region of the whey proteins. Small additions of NaCl or CaCl 2 dramatically decreased gelation time. Higher protein concentrations always produced higher storage modulus ( G′ ) values after any heating time. Loss modulus ( G″ ) v. time curves exhibited maxima at relatively short times for protein concentrations of 30 and 35%. G′ values for 10% protein concentration increased with temperature for heating times up to 59·5 min. G′ values at 59·5 min for 25% protein concentration were higher at 78 °C than at either 85 or 90 °C. The results are discussed in terms of current theories for biopolymer gelation.

Behavior of Protein in the Presence of Calcium during Heating of Whey Protein Concentrate Solutions

The effect of added CaCl(2) on heat-induced changes in whey protein (WP) solutions prepared from whey protein isolate (WP1), acid whey protein concentrate (WP2), and cheese whey protein concentrate (WP3) was investigated. The loss of native-like, proteins, aggregation, and gel firmness of WP were maximum at certain levels of added CaCl(2). These levels were different for different WP products. The effect of added CaCl(2) on these changes appeared to be related to the initial calcium concentrations of these solutions. The higher the calcium content of the product, the less available sites for added CaCl(2) to bind. It was considered that addition of CaCl(2) changed the types of protein interactions that formed the protein aggregates during heating. Added calcium caused dramatic decreases in fracture stress of WP gels due to the formation of large protein aggregates.

A classification of food properties

Abstract Proper classification and terminology comprise an essential basis for avoiding confusion or imprecision. Classification will assist in recording available data, setting up a global database and developing predictive relationships. In this paper, an attempt to develop a well‐accepted classification of and terminology for food properties is made. The proposed four classes of food properties are: physical and physico‐chemical properties, kinetic properties, sensory properties, and health properties.

Chapter 8 – Potato Starch and Its Modification

Food- and industrial-grade modified potato starches have improved functional properties compared to the native potato starches. In this chapter, the effects of some common physical and chemical modifications, such as heat/moisture treatment, acetylation, hydroxypropylation, and cross-linking, on the physicochemical, morphological, thermal, and rheological characteristics of potato starch are discussed. The distinguishing factors that affect the efficiency of modification are the starch source, amylose-to-amylopectin ratio, molecular structure, presence and type of catalyst, morphology and size of granules, reaction time, and type and concentration of the modifying reagent. The extent of alteration in the starch properties reflects the resistance or the susceptibility of a starch toward various modifications. Modified potato starches with desirable properties and degree of substitution can be prepared by critically selecting a suitable modifying agent, suitable reaction conditions, and a native starch source. The challenges in the field of starch modification include the development and use of modification methods that are friendly to the environment and safe for the consumer. The nutritional and toxicological aspects of modified starches are also discussed.