The formation and subsequent chemical cross-linking of heteroaggregates from oppositely charged oil-in-water (O/W) emulsions were investigated. For this purpose, 10-30% (w/w) O/W emulsions (d(43) approximate to 0.5 -0.9 mu m) were prepared at pH 3 using whey protein isolate (WPI) as positively charged emulsifier and sugar beet pectin or Quillaja saponins as negatively charged ones. The oppositely charged emulsions were then combined at a weight ratio of 1: 1 and treated with 0, 50, 250, and 500 mM glutaraldehyde as model cross-linker. Particle sizes, zeta-potentials, confocal light scanning microscopic images, and the rheological behavior of the individual and combined emulsions were analyzed. Although FT-IR measurements indicated that glutaraldehyde was able to cross-link all emulsifiers used, combined emulsions stabilized by Quillaja saponins/whey protein isolate remained relatively unaffected from glutaraldehyde treatment as compared to those prepared with sugar beet pectin and whey protein isolate. When the latter pair was treated with 50-500 mM glutaraldehyde, aggregate sizes (delta(43)) significantly increased 1.6-to 10-fold for 10-30% (w/w) O/W emulsions. Furthermore, significantly higher yield stress values were observed when increasing oil content and glutaraldehyde concentration. Simultaneously, decreased phase angles were observed, also confirming the occurrence of a particulate gel after addition of the cross-linker. The presented study provides new insights into the "cross-linkability" of heteroaggregates by chemical and physical means. (C) 2016 Elsevier Ltd. All rights reserved.

Heteroaggregated oil-in-water (O/W) emulsions formed by targeted combination of oppositely charged emulsion droplets were proposed to be used for the modulation of physical properties of food systems, ideally achieving the formation of a particulate 3-dimensional network at comparably low-fat content. In this study, rheological properties of Quillaja saponins (QS), sugar beet pectin (SBP), and whey protein isolate (WPI) stabilized conventional and heteroaggregated O/W emulsions at oil contents of 10% to 60% (w/w) were investigated. Selected systems having an oil content of 30% (w/w) and different particle sizes (d43 ≤ 1.1 or ≥16.7 μm) were additionally subjected to chemical (genipin or glutaraldehyde) and thermal treatments, aiming to increase network stability. Subsequently, their rheological properties and stability were assessed. Yield stresses (τ0 ) of both conventional and heteroaggregated O/W emulsions were found to depend on emulsifier type, oil content, and initial droplet size. For conventional emulsions, high yield stresses were only observed for SBP-based emulsions (τ0 ,SBP approximately 157 Pa). Highest yield stresses of heteroaggregates were observed when using small droplets stabilized by SBP/WPI (approximately 15.4 Pa), being higher than those of QS/WPI (approximately 1.6 Pa). Subsequent treatments led to significant alterations in rheological properties for SBP/WPI systems, with yield stresses increasing 29-fold (glutaraldehyde) and 2-fold (thermal treatment) compared to untreated heteroaggregates, thereby surpassing yield stresses of similarly treated conventional SBP emulsions. Genipin-driven treatments proved to be ineffective. Results should be of interest to food manufacturers wishing to design viscoelastic food emulsion based systems at lower oil droplet contents.

The global consumption of sausages has increased immensely over the last few years, while bovine collagen has become scarce. Thus, collagen from alternative sources is being considered for application in the food industry. Therefore, chicken skin and bone collagen were characterized and compared with the bovine telopeptide-poor collagen aiming at the feasibility of producing pure, co-extruded chicken sausages. Hence, the chemical composition, microstructure and rheological properties of the different collagen samples were examined and SDS-PAGE, mass spectroscopy, and ζ-potential analysis were conducted.Weak bands in the SDS-PAGE gel indicated only partial maceration of chicken bone collagen, whereas chicken skin and telopeptide-poor collagen revealed distinct bands indicating collagen type I and III. This was also verified by mass spectroscopy. Large fragments were visible in optical microscopy for chicken bone collagen, whereas chicken skin collagen revealed a delicate network. Moreover, the highest dynamic consistency index, at 14146Pasn*, was determined for chicken bone collagen, followed by chicken skin and telopeptide-poor collagen at 606 and 320Pasn*, respectively. By contrast, the intrinsic viscosity was the highest for telopeptide-poor collagen (3.16–3.26L/g), whereas chicken bone collagen exhibited the lowest value at 0.13L/g, suggesting poor swelling behavior. Moreover, telopeptide-poor collagen featured the highest dynamic power law factor, suggesting the least crosslinks, serving a negative standard rather than an actual chicken collagen analog.Finally, chicken skin collagen displayed the most suitable source of collagen for the co-extrusion process compared to the well established bovine hide split collagen.

The formation and subsequent enzymatic and chemical cross-linking of heteroaggregates from oppositely charged oil-in-water (O/W) emulsions was investigated. For this purpose, 10% (w/w) oil-in-water emulsions (d43<1 μm) were prepared at pH 4 using a positively charged emulsifier (Nα-lauroyl-L-arginine ethyl ester (LAE), cold water fish gelatin, or whey protein isolate) or a negatively charged one (sugar beet pectin or Quillaja saponins). The oppositely charged emulsions were then combined at a volume ratio of 1:1 and treated with laccase or glutaraldehyde in order to further stabilize the electrostatically attached aggregates by covalently cross-linking the oppositely charged membranes. Emulsions and heteroaggregates were characterized by their rheological properties, their surface charge, particle size distribution, and microstructure using dynamic and static light scattering as well as confocal laser scanning microscopy. Prior to cross-linking, the emulsifiers' stabilization mechanism were found to greatly influence the formation of heteroaggregates. Laccase treatment (1.34 mU/mL) increased aggregate expansion by ca. 30% for the combined emulsions stabilized by Quillaja saponins/whey protein isolate, while combined Quillaja saponins/fish gelatin stabilized emulsions remained unaffected. When combined emulsions were treated with 50mM glutaraldehyde, aggregate size significantly increased 2- and 3-fold, respectively. Thus, our study provides novel insights into the enzymatic and chemical cross-linking of heteroaggregates composed of oppositely charged O/W emulsions.

Phenolic compounds in aqueous, saponin-rich soapbark tree (Quillaja saponaria Molina) extracts were qualitatively and quantitatively characterized by HPLC-PDA-MS(n) and NMR spectroscopy. (+)-Piscidic acid represented the major constituent (75-87% (w/w) of total phenolics) in all examined extracts (n = 4), ranging from 22.1 ± 0.1 to 34.0 ± 0.2 mg/g of dry matter (DM). Derivatives of p-coumaric acid were present at concentrations from 2.2 to 9.3 mg/g of DM (8.1-20.4% of total phenolics), whereas other phenolic constituents such as glucosyringic acid and vanillic acid derivatives accounted for less than 7% of total phenolics. Generally, all Quillaja extracts showed a highly similar but unique pattern, potentially being useful to authenticate Quillaja extracts in foods, cosmetics, and pharmaceutical formulations. Furthermore, the desired antioxidant activity as well as undesired browning reactions in the final product might also be explained by these phenolic compounds, which were identified for the first time in Q. saponaria extracts.

The phenolic composition of freshly prepared aqueous extracts of the inner bark of Quillaja saponaria Molina was compared to that of commercially available Quillaja extracts, which are currently used as emulsifiers in foods and cosmetics. Major phenolics in both extracts were (+)-piscidic acid and several p-coumaroyl sucrose esters. Among the latter, two new compounds were isolated and characterized: α-l-rhap-(1→4)-α-l-rhap-(1→3)-(4-O-(E)-p-coumaroyl)-α-d-glup-(1→2)-(3-O-(E)-p-coumaroyl)-β-d-fruf (quillajaside A) and β-d-apif-(1→4)-α-l-rhap-(1→4)-α-l-rhap-(1→3)-(4-O-(E)-p-coumaroyl)-α-d-glup-(1→2)-(3-O-(E)-p-coumaroyl)-β-d-fruf (quillajaside B). In addition, a putative biosynthetic pathway of at least 20 structurally related p-coumaroyl sucrose esters was tentatively identified. Besides their antioxidant activity and their potential function as substrate for enzymatic browning reactions, the new compounds are highly characteristic for both the inner bark of Q. saponaria and commercial extracts derived therefrom. Consequently, they might serve as authenticity markers for the detection of Quillaja extracts in food and cosmetic formulations.

The pH-dependent formation and stability of food-grade heteroaggregates from oppositely charged oil-in-water (O/W) emulsions was investigated. After screening suitable emulsifiers, 10% (w/w) oil in-water emulsions (d32≈1 μm) were prepared at pH 3-7 using a positively charged emulsifier (Na-lauroyl-l-arginine ethyl ester; LAE) and four negatively charged ones (citric esters of mono- and diglycerides, soy lecithin, sugar beet pectin, and Quillaja saponin). The oppositely charged emulsions were then combined at constant pH values at a volume flow rate ratio of 1:1. Emulsions and heteroaggregates were characterized by their surface charge, particle size distribution and microstructure using dynamic and static light scattering as well as confocal laser scanning microscopy. The emulsifier type was found to greatly influence the type of heteroaggregates formed, as well as the pH value, specifically in combined LAE/Quillaja saponin emulsions. Larger aggregates particularly were formed with increasing pH values (2.71±1.21 to 46.53±4.30 μm from pH 3 to 7, respectively), while LAE/pectin aggregates appeared not to be affected by pH over the full pH range investigated (3.80±2.89 to 3.94±2.78 μm from pH 3 to 7, respectively). Our study thus provides valuable first insights into the mechanism of the formation of food-grade heteroaggregates for later use in food systems.

The structurally related carotenoids β-carotene, γ-carotene, lycopene, rubixanthin, and β-cryptoxanthin differ in their terminal end groups and the presence or absence of a hydroxyl function. In this study, emulsions containing these carotenoids were subjected to an in vitro digestion to compare bioaccessibilities and antioxidant activities of the resulting micellar fractions. The bioaccessibility of lycopene and β-carotene was 28.6±0.1% and 35.7±0.3% respectively, γ-carotene bioaccessibility was between these values (32.7±0.2%), while the bioaccessibility of rubixanthin (21.8%) and β-cryptoxanthin (28.8%) was significantly lower. The antioxidant activity of the corresponding micellized carotenoid fractions ranked as follows: rubixanthin≥lycopene>β-cryptoxanthin>γ-carotene>β-carotene for both the TEAC and FRAP assays. A similar trend was observed for the hexane-dissolved carotenoids. A negative linear correlation between bioaccessibility and FRAP (R2=0.7395) and TEAC (R2=0.9125) values was established. The presence of both open ψ-end groups and hydroxyl functions led to higher antioxidant activities as compared to the unsubstituted β-end group, presumably resulting in decreased stability during digestion and, thus, lowered bioaccessibility.