Effect of different structural flaxseed lignans on the stability of flaxseed oil-in-water emulsion: An interfacial perspective

Conversion of α-linolenic acid into n-3 long-chain polyunsaturated fatty acids: bioavailability and dietary regulation

N-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs) are essential for physiological requirements and disease prevention throughout life but are not adequately consumed worldwide. Dietary supplementation with plant-derived α-linolenic acid (ALA) has the potential to rebalance the fatty acid profile and enhance health benefits but faces challenges such as high β-oxidation consumption, low hepatic conversion efficiency, and high oxidative susceptibility under stress. This review focuses on the metabolic fate and potential regulatory targets of ALA-containing lipids in vivo, specifically the pathway from the gastrointestinal tract to the lymph, blood circulation, and liver. We propose a hypothesis that positively regulates the conversion of ALA into n-3 LCPUFAs based on the model of "fast" or "slow" absorption, transport, and hepatic metabolic fate. Furthermore, the potential effects of dietary nutrients on the metabolic conversion of ALA into n-3 LCPUFAs are discussed. The conversion of ALA is differentially regulated by structured lipids, phospholipids, other lipids, carbohydrates, specific proteins, amino acids, polyphenols, vitamins, and minerals. Future research should focus on designing a steady-state and precise delivery system for ALA, coupled with specific nutrients or phytochemicals, to effectively improve its metabolic conversion and ultimately achieve synergistic regulation of nutrition and health effects.

Fabrication of the W1/O/W2 emulsions loaded with Torreya grandis protein hydrolysate/polysaccharide complexes in the internal water: Characterization and stability

In this study, the effect of Torreya grandis protein enzymatic hydrolysates (TGPH)/alginate dialdehyde (ADA) complexes in the internal aqueous phase on the physical stability of the water-in-oil-in-water (W1/O/W2) emulsions was studied. In the case of TGPH/ADA emulsions, the presence of ADA decreased the apparent viscosity of the emulsions and changed the flow behavior from shear thinning to Newtonian, leading to a decrease in volume-weighted average droplet diameter (D43) of the emulsions. Additionally, the emulsions at the TGPH/ADA ratios of 1:1 showed a lower turbiscan stability index (TSI) value, and smaller change in delta backscattering signal, compared to the emulsions. The enhanced pH stability and storage stability of the emulsions at the TGPH/ADA ratios of 1:1 was due to the formation of Schiff bases between TGPH and ADA. These results suggested that the covalent cross-linking of TGPH with ADA could significantly improve the stability of the emulsions, which provided an effective means for the development of new food-grade protein-polysaccharide complexes stabilized emulsions.

Effect of heat-treated flaxseed lignan macromolecules on the interfacial properties and physicochemical stability of α-linolenic acid-enriched O/W emulsions

Flaxseed lignan macromolecules (FLMs) are important polyphenols present in flaxseeds with interfacial adsorption behavior. However, FLMs are easily degraded during thermal treatment in emulsions, which further influences their interfacial properties and application. In this work, the interfacial properties of FLMs between oil and water were evaluated using compression isotherms and interfacial tension to investigate the regulation mechanism of FLMs and their heat-treated products on the stability of O/W emulsions. Furthermore, the improvement mechanism of FLM heat-treated products on the physicochemical stability of flaxseed oil emulsions was clarified. Studies showed that thermal degradation occurred on terminal phenolic acids in FLMs when treated under 100 and 150 °C (FLM-100 and FLM-150) without any decrease in antioxidant activity. FLM-100 and FLM-150 improved the physicochemical stability of sunflower lecithin (S90)-stabilized flaxseed oil emulsions and reduced the concentration of hydroperoxides and TBARS by 26.7% and 80% (p < 0.05), respectively, during storage. This was due to the high interfacial anchoring of FLM-100 and FLM-150, which further strengthened the interface of oil droplets and improved the interfacial antioxidant effect of FLMs. This implies that FLM-100 and FLM-150 could act as new efficient antioxidants for application in food emulsions.

Fatty Acid Release and Gastrointestinal Oxidation Status: Different Methods of Processing Flaxseed

Flaxseed has been recognized as a superfood worldwide due to its abundance of diverse functional phytochemicals and nutrients. Various studies have shown that flaxseed consumption is beneficial to human health, though methods of processing flaxseed may significantly affect the absorption and metabolism of its bioactive components. Hence, flaxseed was subjected to various processing methods including microwaving treatment, microwave-coupled dry milling, microwave-coupled wet milling, and high-pressure homogenization. In vitro digestion experiments were conducted to assess the impact of these processing techniques on the potential gastrointestinal fate of flaxseed oil. Even though more lipids were released by the flaxseed at the beginning of digestion after it was microwaved and dry-milled, the full digestion of flaxseed oil was still restricted in the intestine. In contrast, oil droplets were more evenly distributed in wet-milled flaxseed milk, and there was a greater release of fatty acids during simulated digestion (7.33 ± 0.21 μmol/mL). Interestingly, wet-milled flaxseed milk showed higher oxidative stability compared with flaxseed powder during digestion despite the larger specific surface area of its oil droplets. This study might provide insight into the choice of flaxseed processing technology for better nutrient delivery efficiency.

Aroma characteristics of flaxseed milk via GC-MS-O and odor activity value calculation: Imparts and selection of different flaxseed varieties

Currently, the effect of varieties on the flavor and stability of flaxseed milk remains unknown. Therefore, this study was conducted to investigate the effects of different varieties on the stability, sensory, and aromas of flaxseed milk. 51 volatile compounds were identified in flaxseed milk using Stir Bar Sorptive Extraction-Gas Chromatography-Olfactometry-Mass Spectrometry (SBSE-GC-O-MS). Among them, 1-octen-3-ol, 2-methoxy-4-vinylphenol, and 2,3,5-trimethylpyrazine contributed higher relative odor active values (ROAV), resulted in the fruity, roasted, sweet, and cucumber in flaxseed milk. Isovaleraldehyde (green notes) was not detected in XHZM. However, other compounds such as 1-nonanol (floral), γ-nonanolactone and γ-octanoic lactone (coconut milk) had higher concentrations, causing a better sensory evaluation. Additionally, its stability was relatively good. The orthogonal partial least-squares regression (OPLS) model and VIP values showed that eight compounds were responsible for the sensory differences from different varietals. The study provided references to selection and understanding flavor composition basis of flaxseed milk.

Comparative Assessment of Lignan, Tocopherol, Tocotrienol and Carotenoids in 40 Selected Varieties of Flaxseed (Linum usitatissimum L.)

Multiple varieties of flaxseeds have been identified in the world, yet the relationship between these varieties, their agronomic traits, and their seeds' quality remains unclear. This study aimed to determine the level of lignan, vitamins and carotenoids in 40 selected flaxseed varieties, and the relationship between varieties, agronomic traits, and seed quality was investigated. In this study, notably, fiber flax variety No. 225 exhibited the highest lignan content among all tested seeds. Additionally, oil variety No. 167 demonstrated the highest level of α-tocotrienol (α-T3), β-tocopherol (β-T), γ-tocotrienol (γ-T3), and β-carotene (β-Car.). Conversely, intermediate flax variety No. 16 displayed the highest content of α-tocopherol (α-T), but lowest content of lutein (Lut.), zeaxanthin (Zea.), β-carotene (β-Car.), and total carotenoids (Total Car.). Furthermore, a correlation was observed between petal color with the lignan, while a strong correlation has been explored in seed yield, seed type, plant natural height, and fiber content in straw. Nevertheless, further investigation is required to elucidate the internal relationship between varieties with compositions.

Effect of Different Temperatures on the Storage Stability of Flaxseed Milk

In this study, the physical and oxidative stability of flaxseed milk without food additives at different temperatures (25 °C and 37 °C) was assessed. Over in 206 days in storage, the particle size, Turbiscan stability index (TSI), centrifugal sedimentation rate, and primary and secondary oxidation products of flaxseed milk increased, viscosity decreased, and the absolute value of the potential first decreased and then increased. These phenomena indicated a gradual decrease in the physical stability of flaxseed milk, accompanied by drastic oxidative changes. The antioxidant capacity of flaxseed milk was related to the location of the physical distribution of flaxseed lignin, which was more effective in the aqueous phase compared to the non-aqueous phase. Interestingly, after 171 days in storage at 37 °C, the particle size of flaxseed milk was approximately doubled (6.98 μm → 15.27 μm) and the absolute value of the potential reached its lowest point (-13.49 mV), when the content of primary oxidation products reached its maximum (8.29 mmol/kg oil). The results showed that temperature had a significant effect on the stability of flaxseed milk and that stability decreased with increasing temperature and shortened shelf life. This work provides a theoretical basis for elucidating the stabilization-destabilization mechanism of flaxseed milk.

The fate of flaxseed-lignans after oral administration: A comprehensive review on its bioavailability, pharmacokinetics, and food design strategies for optimal application

Lignans are one of the most important and abundant phytochemicals found in flaxseed-diets. These have shown to possess several health-benefits, including anticancer, antioxidant, neuroprotective, cardioprotective, and estrogenic-properties etc. The potential of lignans health-promoting effects are circumscribed due to their poor-bioavailability resulting from their bound structure. Recent studies have demonstrated that various food design strategies can enhance the release of bound-lignans from agro-industrial residues, resulting in a higher bioaccessibility and bioavailability. This review focuses primarily on the bioavailability of flaxseed lignans, key factors affecting it and their pharmacokinetics, different strategies to improve the contents of lignans, their release and delivery. Present study will help to deepen our understanding of the applications of lignans and their dietary-supplements in the prevention and treatment of diseases. Several absorption issues of lignans have been observed such as impaired-bioavailability and variability in pharmacokinetics and pharmacodynamics. Therefore, the development of novel strategies for optimizing lignan bioavailability is critical to ensure its successful application, such as the delivery of lignans to biological targets via "targeted designs." In addition, some detailed examination is required to identify and understand the basis of variation in lignans bioavailability caused by interactions with the gastrointestinal system.

Fabrication and Characterization of Botanical-Based Double-Layered Emulsion: Protection of DHA and Astaxanthin Based on Interface Remodeling

Both DHA and astaxanthin, with multiple conjugated double bonds, are considered as health-promoting molecules. However, their utilizations into food systems are restricted due to their poor water solubility and high oxidizability, plus their certain off-smell. In this study, the interactions between perilla protein isolate (PPI) and flaxseed gum (FG) were firstly investigated using multiple spectroscopies, suggesting that hydrophobic, electrostatic force and hydrogen bonds played important roles. Additionally, double-layer emulsion was constructed by layer-by-layer deposition technology and exhibited preferable effects on masking the fishy smell of algae oil. Calcium ions also showed an improving effect on the elasticity modulus of O/W emulsions and was managed to significantly protect the stability of co-delivered astaxanthin and DHA, without additional antioxidants during storage for 21 days. The vegan system produced in this study may, therefore, be suitable for effective delivery of both ω-3 fatty acid and carotenoids for their further incorporation into food systems, such as plant-based yoghourt, etc.

Exploration of suitable in vitro simulated digestion model for lipid oxidation of flaxseed oil emulsion during digestion

BACKGROUND

The INFOGEST model is a standardized general in vitro digestion study, but it cannot accurately simulate the fatty acid release process of lipids in the stomach and small intestine. In this study, the internationally universal INFOGEST 2019 was used as the basic model and flaxseed oil emulsion was used as the research object. In various improvement models, the effect of fatty acid release rate on the oxidation stability of flaxseed oil was assessed by adding rabbit stomach extract and changing the order of bile salts addition.

RESULTS

With the presence of rabbit gastric extract, flaxseed oil emulsion flocculation and coalescence in stomach were reduced, and the absolute value of ζ-potential increased. Moreover, the release rate of fatty acids in the small intestine increased by 12.14%. The amount of lipid oxidation product (i.e. hexanal) in the gastric and intestinal phases increased by 0.08 ppb. In addition, the fatty acid release rate in the small intestine phase increased by 5.85% and the hexanal content increased by 0.011 ppb in the digestion model of adding bile salts before adjusting the pH in the small intestine phase compared with the model of adjusting the pH first and then adding bile salts.

CONCLUSION

The results obtained from this study will contribute to finding the most suitable static digestion model for simulating digestion and oxidation of lipid during lipid gastrointestinal digestion. © 2022 Society of Chemical Industry.

NMR Analysis of Lipid Oxidation in Flaxseed Oil-in-Water Emulsions

The formation of linolenic (Ln) and linoleic (L) acyl oxidation products during storage of flaxseed oil (FO)-in-water emulsions was monitored using proton nuclear magnetic resonance (¹H NMR) spectroscopy, as well as chemical analytical methods and gas chromatography. Emulsions containing 10% FO and 1% Tween 60 were prepared by homogenization and then stored at 37 °C in the dark for 21 days under accelerated oxidation conditions (500 μmol ferrous sulfate). The induction time of the emulsions, after which rapid lipid oxidation was first observed, was 5-7 days, as shown by increases in peroxide values and hydroperoxide concentrations determined by NMR spectroscopy. Analysis of the hexanal and propanal concentrations during storage by HS-SPME-GC indicated that the oxidation of Ln and L acyls in the emulsions occurred simultaneously. The oxidation products originating from the Ln and L acyls were monitored using ¹H NMR spectroscopy throughout the oxidation process. These results also showed that the Ln and L acyls oxidized simultaneously, and isomers of hydroperoxy-cyclic hydroperoxides (HCPs), Z,E-conjugated dienic hydroperoxides (ZECDHPs), and E,E-conjugated dienic hydroperoxides (EECDHPs) were the major primary oxidation products. Aldehydes were observed after 7 days, which was taken to be the start of the propagation stage, with the formation of a significant amount of oxygenated α, β-unsaturated aldehydes (OαβUAs). Based on the concentrations of hydroperoxides originating from the Ln and L acyls, our results suggested that the loss rate of L acyls was parallel to that of Ln acyls. This result was consistent with Ln acyls adopting a tighter packing at the oil-water interface in the emulsions than L acyls. This hypothesis was supported by the NMR relaxation time data. A good correlation between the isomer concentrations of ZECDHPs and HCPs in Ln acyls and between ZECDHPs and EECDHPs in L acyls was shown, with the mole ratios between them being 1.2 and 1.1, respectively. Droplet size and microstructure analyses showed that droplet aggregation occurred from 11 days onwards, which was attributed to polar oxidation products located at the oil droplet surfaces promoting coalescence. Zeta-potential measurements indicated that the droplets became more negative during storage, which was attributed to the accumulation of anionic reaction products at the droplet surfaces.

Comparative Composition Structure and Selected Techno-Functional Elucidation of Flaxseed Protein Fractions

This study aimed to comparatively elucidate the composition structure and techno-functionality of flaxseed protein isolate (FPI), globulin (FG), and albumin (FA) fractions. The results showed that FA possessed smaller particle dimensions and superior protein solubility compared to that of FG (p < 0.05) due to the lower molecular weight and hydrophobicity. FA and FG manifested lamellar structure and nearly spherical morphology, respectively, whereas FPI exhibited small lamellar strip structure packed by the blurring spheres. The Far-UV CD, FTIR spectrum, and intrinsic fluorescence confirmed more flexible conformation of FA than that of FG, followed by FPI. The preferential retention of free phenolic acids was observed for FA, leading to excellent antioxidant activities compared with that of FG in FPI (p < 0.05). FA contributed to the foaming properties of FPI, relying on the earlier interfacial adsorption and higher viscoelastic properties. FA displayed favorable emulsifying capacity but inferior stability due to the limited interfacial adsorption and deformation, as well as loose/porous interface. By comparison, an interlayer anchoring but no direct interface coating was observed for lipid droplets constructed by FG, thereby leading to preferable emulsion stability. However, FPI produced lipid droplets with dense interface owing to the effective migration of FA and FG from bulk phase, concomitant with the easy flocculation and coalescence. Thus, the techno-functionality of flaxseed protein could be tailed by modulating the retention of albumin fraction and specific phenolic acids.

Review on the Regulation of Plant Polyphenols on the Stability of Polyunsaturated-Fatty-Acid-Enriched Emulsions: Partitioning Kinetic and Interfacial Engineering

The plant polyphenols are normally presented as natural functional antioxidants, which also possess the potential ability to improve the physicochemical stability of polyunsaturated fatty acid (PUFA)-enriched emulsions by interface engineering. This review discussed the potential effects of polyphenols on the stability of PUFA-enriched emulsions from the perspective of the molecular thermodynamic antioxidative analysis, the kinetic of interfacial partitioning, and the covalent and non-covalent interactions with emulsifiers. Recently, research studies have proven that the interfacial structure of emulsions can be concurrently optimized via promoting interfacial partitioning of polyphenols and further increasing interfacial thickness and strength. Moreover, the applied limitations of polyphenols in PUFA-enriched emulsions were summarized, and then some valuable and constructive viewpoints were put forward in this review to provide guidance for the use of polyphenols in constructing PUFA-enriched emulsions.

Effects of tocopherols on the stability of flaxseed oil-in-water emulsions stabilized by different emulsifiers: Interfacial partitioning and interaction

The potential effects of tocopherols (100 μM in emulsions) on the physicochemical stability of whey protein isolate (WPI), soy lecithin (SL), or Tween 20 (TW) stabilized flaxseed oil (FO)-in-water emulsions were investigated. During the storage (18 days at 55 ℃), the particle size, microstructure, and multiple light scattering results showed WPI-stabilized emulsions exhibited better physical stability when tocopherols were added hydroperoxides and TBARS concentration in TW-stabilized emulsions were higher than those of SL or WPI, which were suppressed differently by tocopherols. Among homologues, δ-tocopherol was more effective in inhibiting lipid oxidation than α-tocopherol, which was related to the higher interface partitioning. Moreover, the increased interfacial tension indicated tocopherols, especially δ-tocopherol, were adsorbed on the interface and interacted with WPI or SL via hydrophobic or electrostatic interactions determined by isothermal titration calorimetry. Our results suggest tocopherols are more applicable in WPI emulsion systems to achieve steady-state delivery of ALA.