Search

Increasing consumption of dietary fiber in food leads to many important health benefits: for example, reduction in blood cholesterol, reduced risk of diabetes, and improved laxation. Water soluble soybean polysaccharide (SSPS) is a dietary fiber extracted and refined from okara, a byproduct of soy manufacturing. It was incorporated into 3 categories of dairy-based products, thickened milkshake-style beverages, puddings, and low-fat ice cream, to the maximum amount without over-texturing the food. Rheological measurements and sensory tests were used to develop desirable SSPS-fortified products. From the rheological data, 4% SSPS-fortified dairy beverages and 4% SSPS -fortified puddings were in the range of commercial products. From sensory analyses, 4% SSPS-fortified dairy beverage with 0.015%kappa-carrageenan, 4% SSPS-fortified pudding with 0.1%kappa-carrageenan, and 2% SSPS-fortified low-fat ice cream gained the highest scores in consumer hedonic rating. Panelists also indicated their willingness to consume those products if they were available commercially. Practical Application: Since the dietary fiber intake of many people is below their suggested adequate intake values, strategies to successfully fortify foods with fiber may help alleviate this gap. We have developed 3 dairy products, a beverage, a pudding, and a low-fat ice cream, that have been fortified with soluble soybean polysaccharide at levels of 4%, 4%, and 2%, respectively. These products were within acceptable ranges of rheological parameters and other physical stability measurements and were judged to be acceptable by sensory analyses.

Aggregated particles of casein micelles and kappa-carrageenan were produced as a dried milk ingredient, then reconstituted and subjected to a heat treatment of 70 degrees C for 10 min. The reconstituted aggregates were found to be unstable when heated. Light scattering results showed that the aggregates dissociated partially into casein micelles. It was hypothesized that the removal of ions during ultrafiltration before spray-drying to produce the powdered ingredient significantly decreased stability upon reconstitution and heat treatment. When ions, either from whey permeate or calcium addition, were added to reconstituted aggregates, stability was greatly enhanced and the aggregates remained intact when subjected to heat. The effect of heat treatment on aggregates freshly produced with skim milk powder and kappa-carrageenan was also studied. These aggregates were found to be stable during heating due to the unchanged ionic environment. Therefore, incorporation of powdered aggregates of casein micelles and kappa-carrageenan into products would require the addition of whey permeate or calcium after reconstitution for stability during subsequent heating.

An in vitro digestion model mimicking the gastric phase of the human gastrointestinal tract coupled with SDS-PAGE and MALDI-TOF mass spectroscopy was employed to study the hydrolysis profiles of whey proteins in solution and adsorbed at the oil-water interface. The objective of this work was to understand the differences in hydrolysis behaviour of whey protein isolates once adsorbed at the interface, and comparisons were carried out with pure beta-lactoglobulin and alpha-lactalbumin fractions. In solution, while beta-lactoglobulin appeared to be resistant to enzymatic treatment, alpha-lactalbumin was fully degraded. Adsorption of both proteins at the oil-water interface affected their conformational structure and susceptibility to peptic hydrolysis. Adsorbed beta-lactoglobulin was hydrolyzed into small polypeptides and in contrast, the resistance of alpha-lactalbumin to pepsin increased upon adsorption at the interface. In addition, changes in the particle size distribution of the droplets during pepsin hydrolysis mainly depended on the original protein concentration. The results suggested that exchanges occur at the interface between adsorbed and non-adsorbed protein, that is to say that either some protein desorb from the interface and does not fully recover its structure in solution, or that hydrolysis of the protein at the interface induces further adsorption and hydrolysis of the protein in solution. These mechanisms have important implications in the digestibility of the proteins., (2010 Elsevier Inc. All rights reserved.)

Rheological and microstructural properties of rennet-induced milk gels containing different fat globules were studied. Recombined milks were prepared by mixing reconstituted low-heat skim milk powder and anhydrous milk fat emulsified with reconstituted skim milk powder (SMP), sodium caseinate (NaCas), whey protein isolate (WPI) or Tween 20. Final elastic modulus of the rennet gels containing WPI- or Tween 20-stabilized fat globules showed significantly lower values compared with those prepared with SMP-emulsified fat globules. SMP-stabilized fat globules interacted with the continuous casein network reinforcing the gel structure. Confocal micrographs supported the rheological data revealing that gels containing SMP-stabilized fat globules formed a tighter network relative to other treatments. Microscopy images also showed some degree of droplet flocculation in the case of gels containing WPI- or Tween 20-stabilized fat globules, and this was most likely the cause of the increase of elastic modulus of these systems. Contrary to reports for acid-induced casein gels, NaCas-stabilized fat globules hindered the formation of rennet gels. These results illustrate that rennet gel structure is affected by droplet-droplet and droplet-casein interactions, which in turn are determined by the composition of the oil-water interface as well as the ionic equilibrium in the reconstituted milk gels.

Although soy proteins are often employed as functional ingredients in oil-water emulsions, very little is known about the aggregation state of the proteins in solution and whether any changes occur to soy protein dispersions during homogenization. The effect of dynamic high pressure homogenization on the aggregation state of the proteins was investigated using microdifferential scanning calorimetry and high performance size exclusion chromatography coupled with multiangle laser light scattering. Soy protein isolates as well as glycinin and beta-conglycinin fractions were prepared from defatted soy flakes and redispersed in 50 mM sodium phosphate buffer at pH 7.4. The dispersions were then subjected to homogenization at two different pressures, 26 and 65 MPa. The results demonstrated that dynamic high pressure homogenization causes changes in the supramolecular structure of the soy proteins. Both beta-conglycinin and glycinin samples had an increased temperature of denaturation after homogenization. The chromatographic elution profile showed a reduction in the aggregate concentration with homogenization pressure for beta-conglycinin and an increase in the size of the soluble aggregates for glycinin and soy protein isolate.

The rennet-induced aggregation of skim milk recombined with whey protein-stabilized emulsion droplets was studied using diffusing wave spectroscopy (DSW) and small deformation rheology. The effect of different volume fractions of casein micelles and fat globules was investigated by observing changes in turbidity (1/l*), apparent radius, elastic modulus and mean square displacement (MSD), in addition to confocal imaging of the gels. Skim milk containing different concentration of casein micelles showed comparable light-scattering profiles; a higher volume fraction of caseins led to the development of more elastic gels. By following the development of 1/l* in recombined milks, it was possible to describe the behaviour of the fat globules during the initial stages of rennet coagulation. Increasing the volume fraction of fat globules showed a significant increase in gel elasticity, caused by flocculation of the oil droplets. The presence of flocculated oil globules within the gel structure was confirmed by confocal microscopy observations. Moreover, a lower degree of kappa-casein hydrolysis was needed to initiate casein micelles aggregation in milk containing whey protein-stabilized oil droplets compared to skim milk. This study for the first time clearly describes the impact of a mixture of casein micelles and whey protein-stabilized fat globules on the pre-gelation stages of rennet coagulation, and further highlights the importance of the flocculation state of the emulsion droplets in affecting the structure formation of the gel.

Diffusing wave spectroscopy (DWS) was used to investigate the behavior of flaxseed gums when added to WPI-stabilized emulsions. The effect of different concentrations (0-0.33% (w/v)) of flaxseed gum, derived from two seed varieties, namely Emerson and McDuff, was studied at acidic and neutral pH. At pH 7.0 and low gum concentrations the dynamic and spatial characteristics of the system remained unchanged. While at gum concentrations from 0.075% to 0.20% a rapid phase separation was observed, at higher concentrations phase separation was retarded because of the increased background viscosity slowing down the mobility of the emulsion droplets. At pH 3.5, the difference in overall electrical charge between the gum (negative) and the protein on the emulsion surface (positive) led to electrostatic interactions. While at low concentration of flaxseed gum the general characteristics of the emulsions were not significantly different, at intermediate concentrations, bridging flocculation occurred. When sufficient flaxseed gum was present, the emulsion droplets mobility was arrested in a gel-like state. In spite of the compositional differences in the ratio of acidic and neutral fraction between the two polysaccharides extracted from different seed varieties, at both values of pH the behavior of the emulsions after addition of the polysaccharide was comparable.

A non-invasive technique, diffusing wave spectroscopy (DWS), and traditional dynamic light scattering (DLS) were used to study the interactions of high methoxyl pectin (HMP) with sodium caseinate-stabilized emulsion droplets. At pH 6.8, the droplet size measured by DLS did not change as a function of HMP concentration (up to 0.3%). However, the droplet diameter measured by DWS kept relatively constant up to 0.07% HMP after which it showed drastic increases. The turbidity parameter 1/l* decreased with HMP concentration and levelled off at 0.07% HMP, indicating that the system underwent reorganization and reached equilibrium at 0.07% HMP. During acidification at pH 5.4, right before the pH of aggregation of control emulsions, all emulsions containing 0.05-0.2% HMP showed an increase of 1/l*. This increase indicated the interaction of HMP with sodium caseinate at the interface. Emulsions containing 0.05 and 0.1% HMP also showed destabilization, and the pH of destabilization depended on the concentration of HMP. Sufficient amounts of HMP (0.2%) stabilized the caseinate-coated oil droplets, and the mean square displacement slope was close to 1 throughout, indicating free diffusion of emulsion droplets.

The effect of sodium caprate (a fatty acid salt) on the formation of beta-lactoglobulin A gels was studied at constant temperature (30 or 35 degrees C) using ultrasonic spectroscopy. During incubation at these temperatures, ultrasonic attenuation increased with the addition of sodium caprate, and reached a plateau after 5-7 h of incubation. Comparing beta-lactoglobulin A with and without sodium caprate, a decrease in net ultrasonic velocity was observed. These results suggested that aggregation occurred during incubation with sodium caprate, and the sample showed an increase in compressibility. Transmission electron microscopy with negative staining showed the formation of filamentous aggregates of beta-lactoglobulin A at around 3-4.5 h of incubation with sodium caprate. These results demonstrated that sodium caprate induced the formation of structures with unique gel properties compared to those formed by heating beta-lactoglobulin in the presence of NaCl alone.

The effect of heating on the physicochemical properties of emulsions prepared with soybean soluble polysaccharide (SSPS) was investigated. The emulsions were stable after heating at 90 degrees C for up to 30 min. Heating at different pH values or in the presence of CaCl2 (<10 mM) did not affect the stability; however, at higher concentrations of calcium ions, the emulsion particle size increased. Two fractions, a high molecular weight (HMF) and a low molecular weight (LMF) fraction, were separated from the crude SSPS preparation by gel fitration. Emulsions prepared with SSPS/HMF (MW = 310-420 kDa) showed little change in size with heating, while the protein impurities of the SSPS/LMF fraction formed aggregates by heating at pH 7. Analysis of the heat-induced aggregation of the two fractions of SSPS suggested that the changes in SSPS functionality with heating can be attributed to the protein impurities (LMF) present in the SSPS.

The aggregation behavior during heating of a solution containing soy protein and whey protein isolate (WPI) was studied using rheology, confocal microscopy, gel filtration, and electrophoresis. Soy/WPI mixtures formed gels at 6% total protein concentration with a high elastic modulus (G') and no apparent phase separation. The ratio of soy to WPI was fundamental in determining the type of network formed. Systems containing a high soy to WPI ratio (>70% soy protein) showed a different evolution of the elastic modulus during heat treatment, with two apparent stages of network development. Whey proteins formed disulfide bridges with soy proteins during heating, and at low ratios of soy/WPI, the aggregates seemed to be predominantly formed by 7S, the basic subunits of 11S and beta-lactoglobulin. Size exclusion chromatography indicated the presence of high molecular weight soluble complexes in mixtures containing high soy/WPI ratios. Results presented are the first evidence of interactions between soy proteins and whey proteins and show the potential for the creation of a new group of functional ingredients.

The effects of the emulsifiers lecithin, Tween 20, whey protein isolate, mono-/diacylglycerols, and sucrose fatty acid ester on oxidation stability of a model oil-in-water emulsion prepared with enzymatically synthesized menhaden oil-caprylic acid structured lipid were evaluated. Oxidation was monitored by measuring lipid hydroperoxides, thiobarbituric acid reactive substances, and the ratio of combined docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) contents to palmitic acid in the emulsion. After high-pressure homogenization, all emulsions, except those prepared with lecithin, had similar droplet size distributions. All structured lipid emulsions, except for the lecithin-stabilized emulsions, were stable to creaming over the 48-day period studied. Emulsifier type and concentration affected oxidation rate, with 0.25% emulsifier concentration generally having a higher oxidation rate than 1% emulsifier concentration. Overall, oxidation did not progress significantly enough in 48 days of storage to affect DHA and EPA levels in the emulsion.