Bongkosh Vardhanabhuti

Gelation properties of dispersions containing polymerized and native whey protein isolate

Whey protein polymers (WP-polymers) were prepared by heating whey protein isolate below the critical concentration for gelation at neutral pH and low salt conditions. The effects of WP-polymers and salt types (CaCl2 or NaCl) on rheological properties (large-strain and small-strain analysis), water holding properties, turbidity and microstructure of heat-induced whey protein isolate gels were investigated. Replacement of native whey protein isolate with WP-polymers increased fracture stress, fracture modulus, held water, and the translucency of gels. With both salt types, the addition of WP-polymers changed the gel structure from particulate to fine-stranded. However, the effect of WP-polymers on rheological properties was salt specific. Addition of 20‐100% WP-polymers in the presence of 10 mM CaCl2 caused a continued increase in fracture stress. In contrast, protein dispersions containing 30 mM NaCl did not form self-supporting gels when

Detection of Engineered Silver Nanoparticle Contamination in Pears

60% WP-polymers were added. Dispersions containing 200 mM NaCl formed self supporting gels at all levels of WP-polymer addition but fracture stresses for gels containing 20‐100% WP were similar. Dispersions containing 80% WP-polymers and 200 mM NaCl had lower gel points (time and temperature) than dispersions with 80% WP-polymers and 10 mM CaCl2. It appeared that CaCl2 was more effective in increasing gel fracture stress while NaCl was more effective in decreasing gelation time. Different gel properties may be prepared by altering the amount of WP-polymers and salt types. q 2001 Elsevier Science Ltd. All rights reserved.

Roles of charge interactions on astringency of whey proteins at low pH

Engineered nanomaterials such as silver nanoparticles (Ag NPs) have been increasingly used in agriculture owning to their antimicrobial and insecticidal properties. However, the contamination of Ag NPs in foods and water may pose a great risk to public health and the environment. In this study, the contamination of Ag NPs in pears was detected, characterized, and quantified by a combination of techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and inductively coupled plasma optical emission spectrometry (ICP-OES). Pear samples were treated with two different sizes (20 and 70 nm in diameter) of Ag NPs and stored for different times. Quantification results of Ag NPs in pear samples by ICP-OES demonstrate that there is a good linear relationship (R(2) = 0.983) between the spiked values and recovered values. Residual Ag NPs of both 20 and 70 nm were still detected in samples after 4-day treatment followed by rinsing with water. The penetration study reveals that 20 nm Ag NPs might penetrate the pear skin and pulp after 4-day treatment, while this phenomenon was not observed for 70 nm Ag NPs. These results demonstrate that a combination of techniques could provide accurate results for detection, characterization, and quantification of engineered nanoparticles in agricultural products.

Detection of aflatoxin M1 in milk by dynamic light scattering coupled with superparamagnetic beads and gold nanoprobes.

Whey proteins are a major ingredient in sports drink and functional beverages. At low pH, whey proteins are astringent, which may be undesirable in some applications. Understanding the astringency mechanism of whey proteins at low pH could lead to developing ways to minimize the astringency. This study compared the astringency of beta-lactoglobulin (beta-LG) at low pH with phosphate buffer controls having the same amount of phosphate and at similar pH. Results showed that beta-LG samples were more astringent than phosphate buffers, indicating that astringency was not caused by acid alone and that proteins contribute to astringency. When comparing among various whey protein isolates (WPI) and lactoferrin at pH 3.5, 4.5, and 7.0, lactoferrin was astringent at pH 7.0 where no acid was added. In contrast, astringency of all WPI decreased at pH 7.0. This can be explained by lactoferrin remaining positively charged at pH 7.0 and able to interact with negatively charged saliva proteins, whereas the negatively charged WPI would not interact. Charge interactions were further supported by beta-LG or lactoferrin and salivary proteins precipitating when mixed at conditions where beta-LG, lactoferrin, or saliva themselves did not precipitate. It can be concluded that interactions between positively charged whey proteins and salivary proteins play a role in astringency of proteins at low pH.

Designing Whey Protein–Polysaccharide Particles for Colloidal Stability

This study aimed to develop a rapid and sensitive method for detection of aflatoxin M1 (AFM) by dynamic light scattering (DLS) coupled with superparamagnetic beads and gold nanoprobes. The nanoprobes were synthesized by the conjugate of AFM and bovine serum albumin (AFM-BSA), BSA, and gold nanoparticles. Magnetic beads-based immunosorbent assay (MBISA) was used to measure the concentration of AFM by direct competition between AFM and nanoprobes. DLS was used to determine the concentration of unattached nanoprobes that was positively proportional to the concentration of AFM in the sample. TEM images prove that the as-prepared nanoprobes were able to attach on the magnetic beads through the antibody-antigen reaction. Compared to conventional ELISA, MBISA could effectively reduce the incubation time to 15 min in buffer solution and completely eliminate the color development step, thus simplifying the analysis of AFM. A linear relationship was observed between the inhibition values and the concentrations of AFM in both buffer solution (0-1000 ng·L(-1)) and spiked milk samples (0-400 ng·L(-1)). The limit of detection was found to be 37.7 ng·L(-1) for AFM in buffer solution and 27.5 ng·L(-1) in milk samples. These results demonstrate that DLS coupled with magnetic beads and gold nanoprobes is a rapid and effective method to detect AFM. This method could also be easily extended to rapid detection of other mycotoxins and biological species.

Raman Spectroscopic Characterization of Structural Changes in Heated Whey Protein Isolate upon Soluble Complex Formation with Pectin at Near Neutral pH

Interactions between whey proteins and polysaccharides, in particular the formation of food-grade soluble complexes, are of interest because of potential functional and health benefits. A specific application that has not received much attention is the use of complexes for enhanced colloidal stability of protein sols, such as protein-containing beverages. In beverages, the primary goal is the formation of complexes that remain dispersed after thermal processing and extended storage. This review highlights recent progress in the area of forming whey protein-polysaccharide soluble complexes that would be appropriate for beverage applications. Research in this area indicates that soluble complexes can be formed and stabilized that are reasonably small in size and possess a large surface charge that would predict colloidal stability. Selection of specific proteins and polysaccharides can be tailored to desired conditions. The principal challenges involve overcoming restrictions on protein concentration and ensuring that protein remains bioavailable.

Role of protein concentration and protein-saliva interactions in the astringency of whey proteins at low pH.

The mechanism leading to an alteration of heat aggregation of whey protein isolate (WPI) in the presence of pectin was investigated by assessing structural changes of proteins using Raman spectroscopy. WPI solutions were heated without or with pectin at 0.015-0.2 pectin to WPI weight ratios and pH 6.0-6.4. In the absence of pectin, thermal denaturation resulted in a loss of α-helical structure and an increase in β-structure and random coils of protein. At pH 6.0 and 6.2, heat aggregation of WPI was suppressed when pectin (0.05-0.15 pectin to WPI ratios) was present as shown by a decrease in turbidity and particle size. Concomitantly, changes in the secondary structures were reduced, indicating the enhanced stability of protein structure by pectin. Raman results also revealed that α-helix and β-sheet are dominant structures in heated WPI--pectin soluble complexes, and hydrogen bonding between biopolymers increased. The effect of pectin was pH dependent, indicating the involvement of electrostatic interaction.

Formation of Elastic Whey Protein Gels at Low pH by Acid Equilibration

Whey protein beverages are adjusted to pH <4.5 to enhance clarity and stability, but this pH level is also associated with increased astringency. The goal of this investigation was to determine the effects of protein concentration on astringency and interactions between whey and salivary proteins. Whey protein beverages containing 0.25 to 13% (wt/wt) beta-lactoglobulin and 0.017% (wt/wt) sucralose at pH 2.6 to 4.2 were examined using descriptive sensory analysis. Controls were similar pH phosphate buffers at phosphate concentrations equivalent to the amount of phosphoric acid required to adjust the pH of the protein solution. Changes in astringency with protein concentration depended on pH. At pH 3.5, astringency significantly increased with protein concentration from 0.25 to 4% (wt/wt) and then remained constant from 4 to 13% (wt/wt). Conversely, at pH 2.6, astringency decreased with an increase in protein concentration [0.5-10% (wt/wt)]. This suggests a complex relationship that includes pH and buffering capacity of the beverages. Furthermore, saliva flow rates increased with increasing protein concentrations, showing that the physiological conditions in the mouth change with protein concentration. Maximum turbidity of whey protein-saliva mixtures was observed between pH 4.6 and 5.2. Both sensory evaluation and in vitro study of interactions between beta-LG and saliva indicate that astringency of whey proteins is a complex process determined by the extent of aggregation occurring in the mouth, which depends on the whey protein beverage pH and buffering capacity in addition to saliva flow rate.

Intragastric Gelation of Heated Soy Protein Isolate-Alginate Mixtures and Its Effect on Sucrose Release: Intragastric gelation of soy protein…

Whey protein gels have a weak/brittle texture when formed at pH <or= 4.5, yet this pH is required to produce a high-protein, shelf-stable product. We investigated if gels could be made under conditions that produced strong/elastic textural properties then adjusted to pH <or= 4.5 and maintain textural properties. Gels were initially formed at 15% w/w protein (pH 7.5). Equilibration in acid solutions caused gel swelling and lowered pH because of the diffusion of water and H(+) into the gels. The type and concentration of acid, and presence of other ions, in the equilibrating solutions influenced pH, swelling ratio, and fracture properties of the gels. Swelling of gels decreased fracture stress (because of decreased protein network density) but caused little change to fracture strain, thus maintaining a desirable strong/elastic fracture pattern. We have shown that whey protein isolate gels can be made at pH <or= 4.5 with a strong/elastic fracture pattern and the magnitude of this pattern can be altered by varying the acid type, acid concentration, pH of equilibrating solution, and equilibrating time.

Rheological properties and characterization of polymerized whey protein isolates.

The goal of our study was to investigate the effect of alginate on in vitro gastric digestion and sucrose release of soy protein isolate (SPI) in model beverages. Model beverages containing 5% w/w SPI, 0% to 0.20% w/w alginate, and 10% w/w sucrose were prepared by heating the mixtures at 85 °C for 30 min at pH 6.0 or 7.0. Characterizations of beverages included determination of zeta potential, particle size and rheological properties. Digestion patterns and sucrose release profiles were determined during 2 hr in vitro gastric digestion using SDS-PAGE and HPLC analysis, respectively. Increasing alginate concentration led to increased negative surface charge, particle size, as well as viscosity and pseudoplastic behavior; however, no phase separation was observed. SPI beverages formed intragastric gel during in vitro gastric digestion when the formulations contained alginate or at pH 6.0 without alginate. Formation of the intragastric gel led to delayed protein digestion and release of sucrose. Higher resistance to digestion and a slower sucrose release rate were exhibited at increased alginate concentration, and to a lesser extent, at pH 6.0. This suggests that electrostatic interaction between SPI and alginate that occurred when the beverages were under gastric condition could be responsible for the intragastric gelation. These results could potentially lead to the formulation of SPI beverages with functionality to lower postprandial glycemic response. PRACTICAL APPLICATION The results could be used to design beverages or semi solid food products with altered digestion properties and lowered or slower glucose release.