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

The aroma profiles of dried gonggans: Characterization of volatile compounds in oven-dried and freeze-dried gonggan

Dehydration is an effective method for the long-term storage and aroma retention of gonggan (Citrus sinensis Osb. 'Deqing Gonggan'), which is a Chinese variety of citrus, with unique and characteristic floral, fruity, and citrus flavors. However, the aroma profiles of gonggans prepared using oven- and freeze-drying, the most widely-used drying methods, remain unclear. In this study, a total of 911 volatile organic compounds (VOCs) were detected in dried gonggan. These were primarily composed of alcohols (7.69%), aldehydes (7.03%), esters (15.38%), ketones (7.58%), and terpenoids (23.19%). A total of 67 odorants contributed significantly to the overall aroma of dried gonggans, with the major odor qualities being detected as green, citrus, fruity, floral, and sweet. These were mainly attributed to the presence of aldehydes, esters, and terpenoids. Freeze-drying was more effective in maintaining the unique citrus and mandarin-like aromas attributed to compounds such as limonene, citrial, β-myrcene, β-pinene, and γ-terpinene. Moreover, (E,E)-2,4-decadienal had the highest relative odor activity value (rOAV) in freeze-dried gonggans, followed by (E)-2-nonenal, furaneol, (E, E)-2, 4-nonadienal, and E-2-undecenal. Oven-drying promoted the accumulation of terpenes such as octatriene, trans-β-ocimene, cyclohexanone, copaene, and ɑ-irone, imparting a soft aroma of flowers, fruits, and sweet. Increasing the temperature led to an increase in existing VOCs or the generation of new VOCs through phenylpropanoid, terpenoid, and fatty acid metabolism. The findings of this study offer insights into an optimized procedure for producing high-quality dried gonggans. These insights can be valuable for the fruit-drying industry, particularly for enhancing the quality of dried fruits.

Amino acid regulated citrus pectin-based emulsion stability mediated by pH

BACKGROUND

Citrus residuals are rich in nutrients like pectin, essential oil, and amino acids, which are wasted in the food industry. Moreover, citrus components often coexist with amino acids during emulsion preparation and application.

RESULTS

Adding glutamic or arginine after emulsification resulted in a stable emulsion compared with adding them before emulsification. Adding glycine before or after emulsification had no effect on the emulsion stability. Emulsion stability was improved by adding glutamic acid at pH 6. Ionic interaction and hydrogen bonding were the main forms of bonding. The rhamnogalacturonan II domain was the potential binding site for the amino acids.

CONCLUSIONS

The emulsions prepared by adding acidic amino acids or basic amino acids after emulsification were stable relative to those in which the amino acids were added before emulsification. However, the order in which neutral amino acids were added did not affect the emulsion stability after storage for 7 days. With an increase in the pH level, droplet size increased and emulsion stability decreased. All the results could be attributed to changes in the structure and properties of citrus pectin, as well as the interaction between citrus pectin and amino acids. This study may expand the application of citrus-derived emulsions in the food industry. © 2023 Society of Chemical Industry.

Preparation of lemon essential oil nanoemulsion and its effect on the microbial community of pork patties

The purpose of this study was to prepare an essential oil nanoemulsion and apply it to meat products to achieve antimicrobial effect. The nanoemulsion of lemon essential oil was produced by high power ultrasonication. The influences of ultrasonic power, ultrasonic time, and mass ratio of sodium caseinate to essential oil on the particle size were examined. The optimal conditions for preparing nanoemulsion were ultrasonic power 327 W, ultrasonic time 18 min, and sodium caseinate to essential oil mass ratio 4.23:1. Lower temperature was more conducive to the preservation of nanoemulsion. Compared to control and essential oil group, the nanoemulsion could decrease the total volatile basic nitrogen content and total bacterial colony in pork patties. When applied to pork patties, the nanoemulsion decreased the microbial diversity and inhibited the growth of a variety of microorganisms such as Bacillus, extending the storage time of pork patties. This study developed a novel and workable nanoemulsion for inhibiting bacteria of meat products.

Flavour encapsulation: A comparative analysis of relevant techniques, physiochemical characterisation, stability, and food applications

Flavour is an important component that impacts the quality and acceptability of new functional foods. However, most flavour substances are low molecular mass volatile compounds, and direct handling and control during processing and storage are made difficult due to susceptibility to evaporation, and poor stability in the presence of air, light, moisture and heat. Encapsulation in the form of micro and nano technology has been used to address this challenge, thereby promoting easier handling during processing and storage. Improved stability is achieved by trapping the active or core flavour substances in matrices that are referred to as wall or carrier materials. The latter serve as physical barriers that protect the flavour substances, and the interactions between carrier materials and flavour substances has been the focus of many studies. Moreover, recent evidence also suggests that enhanced bioavailability of flavour substances and their targeted delivery can be achieved by nanoencapsulation compared to microencapsulation due to smaller particle or droplet sizes. The objective of this paper is to review several relevant aspects of physical-mechanical and physicochemical techniques employed to stabilize flavour substances by encapsulation. A comparative analysis of the physiochemical characterization of encapsulates (particle size, surface morphology and rheology) and the main factors that impact the stability of encapsulated flavour substances will also be presented. Food applications as well as opportunities for future research are also highlighted.

Research advances of in vivo biological fate of food bioactives delivered by colloidal systems

Food bioactives exhibit various health-promoting effects and are widely used in functional foods to maintain human health. After oral intake, bioactives undergo complex biological processes before reaching the target organs to exert their biological effects. However, several factors may reduce their bioavailability. Colloidal systems have attracted special attention due to their great potential to improve bioavailability and bioefficiency. Herein, we focus on the importance of in vivo studies of the biological fates of bioactives delivered by colloidal systems. Increasing evidence demonstrates that the construction, composition, and physicochemical properties of the delivery systems significantly influence the in vivo biological fates of bioactives. These results demonstrate the great potential to control the in vivo behavior of food bioactives by designing specific delivery systems. We also compare in vivo and in vitro models used for biological studies of the fate of food bioactives delivered by colloidal systems. Meanwhile, the significance of the gut microbiota, targeted delivery, and personalized nutrition should be carefully considered. This review provides new insight for further studies of food bioactives delivered by colloidal systems, as well as scientific guidance for the reasonable design of personalized nutrition.

Effect of Emulsion Particle Size on the Encapsulation Behavior and Oxidative Stability of Spray Microencapsulated Sweet Orange Oil (Citrus aurantium var. dulcis)

Three different feed emulsions of different particle sizes were mixed with a modified starch and maltodextrin and spray dried to make a large (LP), small (SP), and nano-size encapsulated powder (NP), respectively. Emulsion size, oil content, loading capacity (LC), encapsulation efficiency (EE), water content, aw, scanning electron microscopy (SEM), glass transition temperature (Tg), as well as d-limonene release characteristic and limonene oxide formation rate during 37 °C and various aw storage were determined. With the increase of the feed emulsion size, the reconstituted emulsion size of the LP tended to increase and change to a bimodal distribution. The surface oil content increased with the increasing size of the reconstituted emulsion, and the opposite was true for EE. The smaller the reconstituted emulsion size, the higher Tg during a low aw condition. The Tg of the LP, SP and NP were 62, 88, and 100 °C, respectively, and NP > SP > LP. The release and the oxidative rate of d-limonene was the lowest for the NP and then increased for the SP and LP. The release and oxidative rates increased with the elevation of aw and peaked at 0.33. The powder surface morphological structure was intact, the spray-dried powder was more stable, and microstructure changed from a glass state to a rubbery state during storage.

Impact of Storage Condition on Chemical Composition and Antifungal Activity of Pomelo Extract against Colletotrichum gloeosporioides and Anthracnose in Post-harvest Mango

Anthracnose caused by Colletotrichum leads to a tremendous post-harvest mango loss. While chemical fungicides are applied to control anthracnose, natural alternatives are preferred due to food safety and environmental concerns. Pomelo extract (PE) exhibits a broad spectrum of antimicrobial activities; however, its effect against anthracnose is unknown. Here we investigated the chemical profile of PE using GC-MS and the anti-anthracnose activity of PE using in vitro and in vivo assays. We also evaluated the impact of storage temperature (0°, 5°, 10°, 20°, -20°, and -80 °C) and light conditions on the composition and antifungal activity of PE. We found that PE inhibited C. gloeosporioides in vitro with an IC₅₀ of 3.2 mL L^-1. Applying chitosan-based coating incorporated with 20 mL L^-1 PE significantly suppressed anthracnose in post-harvest 'Keitt' mango. A storage temperature below 5 °C substantially preserved major compounds and the antifungal activity of PE after 6 m of storage. Finally, we showed that applying d-limonene, the key constituent of PE, inhibited C. gloeosporioides in vitro (IC₅₀: 10.9 mM) and suppressed anthracnose in vivo. In conclusion, we demonstrated that the application of PE and d-limonene are sustainable methods for anthracnose control in post-harvest crops and established the preservation protocol for PE.

Effects of Molecular Distillation on the Chemical Components, Cleaning, and Antibacterial Abilities of Four Different Citrus Oils

Essential oils (EOs) from citrus fruits are excellent aromatic resources that are used in food, cosmetics, perfume, and cleaning products. EOs extracted from four citrus varieties, sweet orange, grapefruit, mandarin, and lemon, were separated into two fractions by molecular distillation. The composition, physicochemical properties, cleaning ability, and antimicrobial activity of each EO were then systematically evaluated. The relationships between each of the aforementioned characteristics are also discussed. In keeping with the principle of “like dissolves like,” most citrus EOs show better cleaning ability than acetone and all tend to dissolve the fat-soluble pigment. The key components of citrus EOs are 1-Decanol, α-terpineol, geraniol, and linalool for the inhibition of Staphylococcus aureus, Escherichia coli, Candida albicans, and Vibrio parahaemolyticus, respectively. The findings of this study will be of significant importance for the effective utilization of citrus peel resources and in the development of future applications for citrus EOs.

Chemical Compounds Studied in This Article: (+)-α-Pinene (PubChem CID: 6654); β-Phellandrene (PubChem CID: 11142); 3-Carene (PubChem CID: 26049); β-Myrcene (PubChem CID: 31253); D-Limonene (PubChem CID: 440917); γ-Terpinene (PubChem CID: 7461); Octanal (PubChem CID: 454); Decanal (PubChem CID: 8175); Linalool (PubChem CID: 6549); 1-Octanol (PubChem CID: 957); β-Citral (PubChem CID: 643779); α-Terpineol (PubChem CID: 17100); Hedycaryol (PubChem CID: 5365392); α-Citral (PubChem CID: 638011); 1-Decanol (PubChem CID: 8174); Geraniol (PubChem CID: 637566).

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.

Stability of Emulsions and Nanoemulsions Stabilized with Biosurfactants, and their Antimicrobial Performance against Escherichia coli O157:H7 and Listeria monocytogenes

Two novel biosurfactants – surfactin and its variant fatty acyl glutamic acid (FA-glu) – were compared with two commercial emulsifiers – lecithin, and a mixture of Tween 80 and lauric „arginate (TLA) – for formation and stability of emulsions and nano„emulsions containing cinnamaldehyde (CM). The nano„emulsions’/emulsions’ antimicrobial performance against two common foodborne pathogens Escherichia coli O157:H7 and Listeria monocytogenes was also compared. Two emulsifier concentrations (0.5% w/w and 1% w/w) and two homogenizing pressures (62.05 MPa and 124.10 MPa) were compared for emulsions droplet stability during storage for 46 days at 4°C, 25°C, and 37°C. Surfactin, FA-glu, and TLA resulted in formation of nanoemulsions at both concentrations, but lecithin did not. Droplet sizes did not change significantly during 38 days at stored temperatures for surfactin- and TLA- stabilized nano„emulsions. However, FA-glu and lecithin stabilized emulsions coalesced after Day 13 at 37°C; also, FA-glu stabilized emulsion thickened on the 38th day at 4°C. The incorporation of CM in nanoemulsions or emulsions did not lower the minimum inhibitory concentration (MIC) for two bacteria tested in broths. However, the CM nanoemulsions and emulsions showed enhanced effects in inhibiting bacterial growths at concentrations lower than MICs compared to non-emulfied CM, with more inhibition from nanoemulsions.

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.

Characterization of physical properties and electronic sensory analyses of citrus oil-based nanoemulsions

Citrus oils and their emulsions have been widely used in food and beverage products due to their flavor, various beneficial health functions and relative high solubility for lipophilic bioactive components. However, the non-digestibility and instability has limited the application of emulsions made from a single type of citrus oil. In this study, common triacylglycerol oils (i.e. corn oil and MCT oil) and citrus oils (i.e. bergamot oil and sweet orange oil) were used in combination with different mixing ratios (triacylglycerol oil:citrus oil = 1:0, 9:1, 5:1, 3:1, 1:1 and 0:1) to produce various nanoemulsions (10% oil phase), and their physical and electronic sensory properties were systematically characterized. The results demonstrated that the mixed oil nanoemulsions were much more stable than pure citrus oil emulsions. Electronic nose, electronic eye and electronic tongue were shown to be able to provide informative evaluation of the electronic sensory of the emulsions. Data-fitting of these electronic sensory devices significantly improved the effective discrimination and accuracy of sensory evaluation of the emulsions. These results provided basis for using triacylglycerol oils and citrus oils in combination to produce nanoemulsions with superior physical and electronic sensory properties. Moreover, the electronic sensory evaluation method utilized in this study provided a useful approach for evaluation of emulsion-based food and beverage products.

Quillaja saponin-based hollow salt particles as solid carriers for enhancing sensory aroma with reduced sodium intake

QS-based hollow salt particles were developed that improve flavor performance with reduced sodium intake.