Gelling properties of lysine-amidated citrus pectins: The key role of pH in both amidation and gelation.

The amidation of pectin by amino acids has been widely applied due to its safety and excellent gelling properties. This study systematically examined the effects of pH on the gelling properties of lysine-amidated pectin during amidation and gelation. Pectin was amidated over the range of pH 4-10, and the amidated pectin obtained at pH 10 showed the highest degree of amidation (DA, 27.0 %) due to the de-esterification, electrostatic attraction, and the stretching state of pectin. Moreover, it also exhibited the best gelling properties due to its greater numbers of calcium-binding regions (carboxyl groups) and hydrogen bond donors (amide groups). During gelation, the gel strength of CP (Lys 10) at pH 3-10 first increased and then decreased, with the highest gel strength at pH 8, which was due to the deprotonation of carboxyl groups, protonation of amino groups, and ß-elimination. These results show that pH plays a key role in both amidation and gelation, with distinct mechanisms, and would provide a basis for the preparation of amidated pectins with excellent gelling properties. This will facilitate their application in the food industry.

Caseinate-reinforced pectin hydrogels: Efficient encapsulation, desirable release, and chemical stabilization of (-)-epigallocatechin.

(-)-Epigallocatechin (EGC) has good health benefits, but its chemical stability is low. Pectin hydrogels have potential for the encapsulation and delivery of EGC, but they are limited by porous networks and poor mechanical properties. In this study, protein (whey protein isolate and caseinate)-reinforced pectin hydrogel beads (HBPEC-WPI and HBPEC-CAS) were developed to overcome these limitations. The results showed that HBPEC-CAS was a superior delivery system for EGC. HBPEC-CAS had a compact network structure, mainly because of the hydrogen bonds that formed between caseinate and pectin. Moreover, the EGC encapsulation efficiency of HBPEC-CAS (2.4%) reached 92.23 %; HBPEC-CAS (2.4%) could also delay the release of EGC in an aqueous environment, while ensuring its sufficient release in a simulated gastrointestinal environment. Notably, EGC was chemically stabilized in HBPEC-CAS (2.4%) during a 6-day storage period at 37 °C through the inhibition of its epimerization, oxidation, dimerization, and trimerization. The numerous hydroxyl groups in EGC readily interacted with the exposed amino acid residues in caseinate and created more protective sites. This study developed a strategy for protein-reinforced pectin hydrogel development and approaches for the protection of tea polyphenols; the findings offer useful insights for the tea-based food and beverage industry.

Upper digestion fate of citrus pectin-stabilized emulsion: An interfacial behavior perspective.

Citrus pectin can serve as a naturally digestion-resistant emulsifier, although how it achieves this effect is still unknown. In this study, the upper digestion fate of an emulsion stabilized by different concentrations of citrus pectin, and changes in its interfacial properties during digestion, were investigated. Emulsions stabilized by high-concentration citrus pectin (3 %) were relatively stable during digestion and had a lower free fatty acid (FFA) release rate than emulsions stabilized by low-concentration citrus pectin (1 %). At the low concentration, the citrus pectin interface had a thin absorbing layer and was largely replaced by bile salts, while at high concentration the citrus pectin interface possessed a uniform and thick adsorbing layer that resisted the replacement of bile salts and enabled lipase adsorption. This study has improved our understanding of the digestion of emulsion from the interface and will be useful for designing emulsion-based functional foods that can achieve targeted release.

Effect of mesoscopic structure of citrus pectin on its emulsifying properties: Compactness is more important than size.

We previously explored citrus oil emulsion stabilized by citrus pectin. In this report, we characterized key parameters of the citrus pectin mesoscopic structure and their effect on emulsifying capacity, and explored the underlying mechanism by determining the interfacial properties, emulsifying ability, and micromorphology. To generate different mesoscopic structure, citrus pectins were hydrolyzed or regulated by pH and NaCl. Hydrolysis decreased the size of citrus pectin mesoscopic structure with constant compactness, leading to superior interfacial properties but inferior emulsifying ability. In contrast, pH and NaCl regulation decreased the mesoscopic structure size and increased the compactness, and pH- and NaCl-regulated citrus pectin formed a compact absorbed layer at the interface to resist droplet coalescence/flocculation during homogenization. Our results support the importance of compactness of the citrus pectin mesoscopic structure on emulsifying capacity. This study increased our understanding on the relationship between the mesoscopic structures of polysaccharide emulsifier and emulsifying ability.

Citrus Oil Emulsions Stabilized by Citrus Pectin: The Influence Mechanism of Citrus Variety and Acid Treatment.

Citrus pectin and citrus oil are the main functional components of citrus residuals in the processing industry. In this study, citrus oil emulsions were fabricated for the first time using four different citrus pectins (orange, mandarin, grapefruit, and commercial citrus pectins) as the emulsifier. The influence mechanism of citrus variety and acid treatment (pH 1, 2, 3, 4, 5, 6, and 7) on the emulsifying capacity of citrus pectins was systematically investigated by understanding the relationship between molecular structure, solution property, interfacial property, and emulsion property. The results suggest that citrus variety and acid treatment can significantly influence the emulsifying capacity in relation to the molecular structure and molecular state of citrus pectins. A smaller molecular size of citrus pectin and lower pH between 2 and 7 produced a reduction in aggregate size, which improved the interfacial capacity and emulsifying ability by promoting their distribution at the interface. Although hydrolyzed citrus pectins at pH 1 with a lower molecular size exhibited better interfacial capacity, citrus oil emulsions were unstable due to electrostatic attraction caused by partially positive charged citrus pectins. Fine stable citrus oil emulsion was prepared using mandarin pectin with a relative high methyl ester content and small molecular size at pH 2. Our results provide a scientific basis for the fabrication of citrus oil emulsion based on citrus pectin and facilitate the application of citrus residuals in the food industry.

Effects of Preheating and Storage Temperatures on Aroma Profile and Physical Properties of Citrus-Oil Emulsions.

Citrus oils are used as good carrier oil for emulsion fabrication due to their special flavor and various health-promoting functions. In this study, the effects of preheating temperature (30, 40, 50, 60, and 70 °C) and storage temperature (4, 25, and 37 °C) on aroma profiles and physical properties of three citrus-oil (i.e., mandarin, sweet orange, and bergamot oils) emulsions were systematically investigated for the first time. The results demonstrated the significant impact of temperature on aroma profile and physical properties. The abundance of d-limonene was found to be the main factor determining the aroma of the three citrus-oil emulsions at different preheating and storage temperatures, while ß-linalool and linalyl acetate were important for the aroma of bergamot oil emulsion. Preheating temperature showed a profound impact on the aroma of citrus-oil emulsions, and the aroma of different citrus oil emulsions showed different sensitivity to preheating temperature. Storage temperature was also able to alter the properties of citrus oil emulsions. The higher was the storage temperature, the more alteration of aroma and more instability of the emulsions there was, which could be attributed to the alteration of the oil components and the properties of emulsions. Among all three emulsions, bergamot-oil emulsion was the most stable and exhibited the most potent ability to preserve the aroma against high temperature. Our results would facilitate the application of citrus-oil emulsions in functional foods and beverages.