Liposomal Vitamin C Vs Ascorbyl Palmitate

Liposomal Vitamin C Vs Ascorbyl Palmitate

Ascorbyl Palmitate

Dispersed ascorbyl palmitate (AsP)-loaded liposomes into poloxamer hydrogel matrix (lipogel) showed good skin permeation characteristics as compared to control hydrogel containing Transcutol (which is known as a drug solubilizer).

From: Nanobiomaterials in Galenic Formulations and Cosmetics , 2016

What nanocrystals can offer to cosmetic and dermal formulations

Ranjita Shegokar , in Nanobiomaterials in Galenic Formulations and Cosmetics, 2016

4.4.1 Ascorbyl Palmitate

Ascorbyl palmitate is a highly bioavailable, fat-soluble form of ascorbic acid (vitamin C) and possesses all the properties of native water-soluble counterpart, that is vitamin C. It is a potent antioxidant in protecting lipids from peroxidation and is a free radical scavenger.

To enhance its chemical stability, ascorbyl palmitate was processed as a nanosuspension using an HPH (20 cycles at 1500   bar) technique using sodium dodecyl sulfate and polysorbate 80 as a stabilizer. Tween 80 was comparatively effective in producing uniform nanosuspensions (mean particle size of 365   nm) with improved active pharmaceutical ingredient (API) chemical stability. Further enhancement in drug stability can be achieved by lyophilization. Authors confirmed the stability of trehalose incorporated ascorbyl palmitate nanosuspensions (Teeranachaideekul et al., 2008). Recently, a combination technique (milling followed by HPH) is applied to produce smaller nanocrystals of ascorbyl palmitate using sugar-based nonionic surfactant decyl glucoside. Two different milling bead sizes were employed, namely 0.4–0.6 and 0.2   mm. The nanocrystals produced using larger bead dispersion of mean particle size of 442   nm and small bead size produced a dispersion of 286   nm. Further reduction in mean particle size down to 354   nm is observed only for the dispersions produced using larger beads after one cycle at 500   bar and 286   nm after one cycle at 1500   bar. The increased saturation solubility of ascorbyl palmitate can exhibit higher concentration gradient profile and faster dissolution of smaller crystals (Romero et al., 2013).

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Antioxidants

Anna Wypych , George Wypych , in Databook of Antioxidants, 2020

Ascorbyl palmitate

PARAMETER	UNIT	VALUE
GENERAL INFORMATION
Name	Ascorbyl palmitate
CAS #	-	137-66-6
EC number	-	205-305-4
Chemical name	[(2S)-2-[(2R)-4,5-dihydroxy-3-oxo-2-furyl]-2-hydroxy-ethyl] hexadecanoate
Synonym	6-O-palmitoylascorbic acid
Category	ascorbyl ester
Chemical formula	-	C22H38O7
Structural formula
Molecular mass	-	414.5
Product contents	assay >97%
Other properties	ascorbyl palmitate is the oil soluble form of Vitamin C also known as Vitamin C Ester
PHYSICAL PROPERTIES
State	-	solid, powder
Odor	-	citrus-like
Color	-	white to yellowish
Freezing point	°C	113-117
Solubility in solvents at 20°C	alcohol, animal oil, vegetable oil
HEALTH & SAFETY
Flash point	°C	177.78
Flash point method	-	TCC
LD50, oral, rat	mg kg−1	>25000
ECOLOGICAL PROPERTIES
Bioaccumulative and toxic (PBT) assessment	no components considered to be either persistent, bioaccumulative and toxic (PBT), or very persistent and very bioaccumulative (vPvB) at levels of 0.1% or higher
Partition coefficient	logKow	6.00 (est)
USE & PERFORMANCE
Manufacturer	TCI America, Spectrum Chemical Manufacturing Co., GC Chemicals Co.
Outstanding properties	antioxidant, ascorbyl palmitate is one of the most stable forms of vitamin C, oil soluble, and nonacid, it is much more stable than the water soluble form of vitamin C, L ascorbic acid
Recommended for products	food industry as a natural preservative for oils, vitamins and colors, cosmetics industry

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Natural Antioxidants in Cosmetics

Idha Kusumawati , Gunawan Indrayanto , in Studies in Natural Products Chemistry, 2013

Application of Antioxidants in Cosmetics

Antioxidants are responsible for the chain-breaking of radical scavengers and for inhibiting the oxidation reaction; by these mechanisms, antioxidants can prevent oxidative damage [56,57]. In cosmetic preparations, antioxidants have two functions, that is, as the active ingredients and as protectors of other ingredients against oxidation [38].

Currently, the application of antioxidants in cosmetics is increasing; however, to obtain the desired activities, some strategies should be considered. The short life of ROS can be overcome by using antioxidants that have high reactivity and capacity. Antioxidants must not be transformed into their radicals such as ascorbyl- or tocopheryl radicals; this will trigger the chain reaction. Antioxidants should remain stable in the product; they must not react with the other ingredients and should be protected from oxygen radicals. The selection of antioxidants that can be used in cosmetics depends on their hydrophobic or lipophillic characteristics. Unfortunately, sometimes the selection of antioxidant(s) (by pharmaceutical industries) used in cosmetic products is not based on scientific judgment, but rather on their price.

Generally, antioxidant by nature are unstable, deeply colored, and susceptible to hydrolysis and photodegradation in the presence of oxygen; that is why it is very difficult to have good cosmetic formulations and to maintain their aesthetic validity and acceptability. Modifying the chemical structure of the antioxidant such as substitution wiht its esters (e.g., tocopheryl acetate, ascorbyl palmitate), or by shortening the lipophilic chain of CoQ10, may be able to improve its stability, but unfortunately, it reduces its activity.

For being active, a stable antioxidant is needed, but unfortunately, antioxidants are generally unstable compounds. This instability can cause many problems. In a cosmetic formulation, the concentration of antioxidants must be stable for achieving the desired activity. Their color should not change in the production processes and storage, so that their antioxidant activities remain constant and the product retains an aesthetic appearance. All this raises many problems in the formulation of cosmetic products [12,21,32]. That is why a valid method is needed for determining the antioxidant's capacity to evaluate its activity [32].

Application of the relatively new "lipid-based delivery system" technology could protect and maintain the stability of the antioxidants. This technology also has protective effects against skin dehydration. Lipid carriers can increase the skin penetration of the antioxidant, so its desired activity can be guaranteed. Various lipid carriers such as nanoparticle emulsion, various vesicular systems (liposomes, phytosomes, transfersomes, etosomes, niosomes, and nanotopes), and particulate systems (lipid microparticles and lipid nanoparticles) have been developed and are being used. The stability of ascorbyl palmitate and vitamins K and A in cosmetics can be enhanced by using lipid nanocarriers. Phytosomes of green tea and grape seed can improve their free radical scavenging and UV protection activity. Skin penetration of vitamin E acetate was increased by using Nanotop™. The antiaging effect of vitamin E acetate and CoQ10 was improved by the application of nanoemulsions [36,56–60].

We have now developed various lipid carrier systems, such as liposomes, phytosomes, and lipid nanoparticles for the natural antioxidants pycnogenol, quercetin, squalene, and p-metoxycinnamic acid, which will be used in UV-protector preparations. Figure 3 shows liposomes of quercetin, which were prepared in our laboratory; the liposomes were viewed by using SEM. These liposomes can increase the permeation of quercetin into human skin, so it will have the desired photoprotective activity [55]. This part of our work is still in progress.

Figure 3. SEM of the liposomes of quercetin (5000   ×).

Cited from Ref. [55].

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Functional Materials for Hair

C.M. Rocafort , in Cosmetic Science and Technology, 2017

21.17 Skin Care–Inspired Solutions: Antipollution/Reconstruction

Skin care–inspired commercial hair care products are also being introduced. We are observing antipollution claims expanding from skin care into hair care, with many new shampoo and conditioner product launches claiming to protect hair from external pollutants. Pollution is the third highest concern of Chinese women aged 20–49; ²⁸ and there is a growing consumer awareness of pollution effects in other global urbanized regions. Manufacturers are turning to a range of ingredients to provide preventative treatments to fight pollution's negative effects. Antioxidants are the most utilized solution for the free radicals generated by pollution and the other irritants of everyday life. Vitamin E, vitamin C (with the most common forms being ascorbic acid and ascorbyl palmitate), and green tea are the most popular. They are frequently used in combination in formulations. Plant extracts are especially popular. Some examples are moringa, white and green tea, acai berry, and Litchi chinensis pericarp extract; all of which claim to offer different functional benefits. The botanical peptides extracted from the seeds of the moringa tree were developed to prevent damage from pollution buildup and to keep hair clean by inhibiting the adhesion of particulate pollution to the hair shaft. ²³

External and internal forces affect the quality of the hair. As stated earlier in this chapter, everything from excessive wind, salt air, chlorine, sun, high humidity, to pollution can have a negative impact on the health of hair. Avoiding exposure to harsh weather conditions and unhealthy foods, and an occasional break away from certain chemical hair treatments, as well as the use of properly formulated hair care products will help to protect it. Hair treatment masks have been introduced to address these needs and provide deep-conditioning benefits to hair. In Argentina, Unilever introduced Dove Heat Activated Reconstructor Treatment for hair. The regenerative treatment mask and heat activated serum together generate a gentle heat for a deep hair treatment. The product claims to help restore hair at the deepest layers and leave the hair strong and shiny. In the United States, Pureology introduced Strength Cure Restorative Masque for color-treated hair containing protein, amino acid, and lipid complexes to help strengthen and deeply condition hair that has been microscarred and color damaged. Proteins are very useful for conditioning and moisturizing the hair. The proven substantivity of cosmetic proteins to the hair is well correlated to the degree of damage of the hair. Proteins may act as a humectant and a "moisture reservoir" for dry hair, increasing the rate of moisture uptake from the air and decreasing the rate of moisture loss in arid conditions. ²⁹ Proteins have been shown to aid in repairing hair damage such as split ends and to provide protection from damage such as that which occurs during permanent waving. The effects of protein treatment are not merely surface phenomena, as the cosmetic proteins are shown to penetrate into the hair cortex.

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Microemulsions and Nano-emulsions for Cosmetic Applications

C. Solans , M.J. García-Celma , in Cosmetic Science and Technology, 2017

29.5 Microemulsion and Nano-emulsion Components

A variety of surfactants, cosurfactants, and oils have been proposed to obtain microemulsions and nano-emulsions for cosmetic use. Selection of components have to take into account skin sensitization and toxicity as well as the influence on formulation properties and stability. The favorable active delivery properties of microemulsions appear to be attributed mainly to the excellent solubility properties. However, the microemulsion components may also act as penetration enhancers depending on the oil/surfactant constituents, which involve a risk of inducing local irritancy. The correlation between microemulsion structure/composition and active delivery potential is not yet fully elucidated. However, a few studies have indicated that the internal structure of microemulsions should allow free diffusion of the drug to optimize cutaneous delivery from these vehicles. ⁵²

O/W microemulsions were reported as vehicles for the sunscreens 4-methylbenzilidene camphor or octyl methoxycinnamate. Some of the components of the microemulsions were soya lecithin, decyl polyglucose, cyclomethicone, menthol, allantoin, and stearyl methicone, which provided good skin feel, waterproof effect, nonstickiness, and easy spreadability. ⁵³ Microemulsion formulations not only improve product efficiency but also enhance stability of the active ingredients. For instance, the photostability to ultraviolet B irradiation of the whitening agents arbutin and kojic acid was higher in O/W microemulsions comprising lecithin and an alkyl glucoside as amphiphiles than in aqueous solutions. ⁵⁴

To formulate an optimal microemulsion for an active ingredient, the factors that influence the stability of the product have to be considered. The type of microemulsions contributes to the stability of the active ingredients. For example, ascorbyl palmitate was more stable in W/O than in O/W microemulsions because the cyclic ring of the active ingredient that was sensitive to oxidation if located in the water phase, was shielded in microemulsion droplets. In contrast to ascorbyl palmitate, sodium ascorbyl phosphate was stable in both types of microemulsions. The location of the actives in the microemulsion nanostructure significantly influenced their release profiles. ⁵⁵

Nonionic surfactants used to form both micro- and nano-emulsions include polyoxyethylene surfactants or sugar esters such as sorbitan esters. Among ionic surfactants, the anionic sodium bis-2-ethylhexylsulphosuccinate has been widely used because of its ability to stabilize W/O microemulsions. As cationic surfactants, quaternary ammonium alkyl salts such as hexadecyltrimethyl-ammonium bromide, and didodecylammonium bromide have been largely investigated to form microemulsions. Due to their high biocompatibility, biodegradability, and safety, phospholipids are the main class of zwitterionic surfactants used to form colloidal systems based on nanodroplets for drug or cosmetic delivery. ⁵⁶ Generally, microemulsions need high concentrations of surfactant and cosurfactant to reduce the interfacial tension and increase the flexibility of the interfacial film, respectively. Therefore, the probability of skin irritation or toxicity is also high depending on the properties of the surfactant and/or cosurfactant. Consequently, the choice of components is challenging and, besides their ability to form microemulsions, the formulator should carefully take into account their biological and cosmetic acceptability. ⁵⁷ Here, there is a growing interest in using nonionic surfactants, which are reportedly less toxic and irritant than other types of surfactants. New raw materials have been developed to be used in microemulsion formulations in order to give the cosmetic products more efficiency with less toxicity. ⁴² Some examples of cosmetic acceptable excipients are pentyl rhamnoside and cetyl rhamnoside that could be used as biocompatible cosurfactants. ⁵⁸ Biologically mild surfactants, such as the mixtures of ethoxylated glycerides, PEG8 caprylic/capric glyceride, and poly(glyceryl-6-dioleate), could be used to obtain microemulsions. ⁵⁹ Sucrose esters are meant to be nontoxic surfactants obtained from a naturally occurring carbohydrate, with features of low skin sensitization and enhancing skin penetration, as well as with a high environmental compatibility. ⁶⁰ Sucrose esters and lecithin-based microemulsions showed excellent eudermic properties. ⁶¹ Polyoxyethylene/polyoxypropylene dimethyl ether, a random copolymer of ethylene oxide and propylene oxide, was developed to use for skin care due to its humectant property and can be used to form microemulsions with water, liquid paraffin, and POE(7). ⁶² Different oils have been used to obtain microemulsions and nano-emulsions for pharmaceutical and cosmetic use. The most widely used are medium-chain triglycerides and fatty esters (isopropyl myristate, isopropyl palmitate, ethyl or methyl esters of lauric, myristic, and oleic acid). ⁵⁶

The nanostructure of microemulsions has been reported to influence dermal compatibility. Skin irritation and phototoxicity potentials of several microemulsions were studied. All microemulsions comprised approximately the same percentage of surfactant mixture, but varying oil/water content and consequently the inner structure; being either droplet-like (O/W microemulsion, O/W microemulsion with carbomer, W/O microemulsion, and W/O microemulsion with white wax) or lamellar (gel-like microemulsion). The gel-like microemulsion was more irritant compared to other tested formulations and the results of the phototoxicity test again indicated the increased potential of gel-like microemulsion to cause adverse effects on skin. Then, when comparing microemulsions consisting of the same amount of identical surfactants but having different structures, the latter represent a crucial factor that determines their dermal toxicity. ⁶³

Preconcentrated microemulsions, also known as self-microemulsifying drug delivery systems, are mixtures consisting of drugs, oils, and surfactants. Upon dilution with aqueous media and accompanied by gentle agitation, the preconcentrate spontaneously forms clear isotropic solutions, or microemulsions. The combined use of surfactants in preconcentrate microemulsions showed the formation of microemulsions with small particle size, increased drug loading, and improved physical stability, with significant implications in the development of poorly water-soluble actives formulations. The effect of different surfactants, when used either alone or in combination, on microemulsion formation from preconcentrates was studied. Cremophor EL (polyoxyl 35 castor oil) and Tween 20 (polysorbate 20) were used as surfactants, and Capmul PG8 (propylene glycol monocaprylate) as oil. Both Tween 20 and Cremophor EL are nonionic and generally-recognized-as-safe excipients and are widely used in pharmaceutical preparations. With Tween 20 being more hydrophilic than Cremophor EL, this surfactant combination (1/1 ratio, w/w) was found to be effective in drug emulsification in a number of compounds. ⁶⁴

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VITAMINS | Fat-Soluble: Thin-Layer (Planar) Chromatography

W.E. Lambert , A.P. De Leenheer , in Encyclopedia of Separation Science, 2000

Vitamin E

Vitamin E is a collective term for tocopherols and tocotrienols, a series of potent antioxidants derived from 6-chromanol by substitution with a saturated (tocopherols) or partially unsaturated (tocotrienols) isoprenoid side chain and one to three methyl functions (Figure 3). The principal form is α-tocopherol (5,7,8-trimethyltocol) which in nature occurs in the 2R, 4′R, 8′R configuration. Tocol can be regarded as the unsubstituted parent molecule, while α-, β- and γ- and δ-tocopherol form a homologue series of tri-, di- and monosubstituted tocols, respectively. The dimethyltocols (β- and γ-tocopherol) are positional isomers.

Figure 3. Structure of tocopherols.

All vitamin E derivatives have strong reducing properties, with α-tocopherol being the most biologically active homologue. By scavenging free radicals and other oxidative species, α-tocopherol is known to protect membrane lipids from peroxidation. Other functions described for vitamin E remain more controversial. In the absence of air, vitamin E derivatives are quite stable to heat and alkali. However, in the presence of air they are rapidly oxidized by alkali and metal ions. Vitamin E derivatives absorb light in the UV region (λ_max 292–295   nm; ε 3530   L mol⁻¹ cm⁻¹) and they are natively fluorescent (λ_ex 205 and 295   nm; λ_em 330   nm).

Chromatographic Conditions

For TLC separation of vitamin E derivatives, silica gel plates have been widely used. Within the group of tocopherols migration is correlated with the degree of ring methylation. However, for the separation of β- from γ-tocopherol (two dimethyl tocols), often two-dimensional TLC is necessary with an eluent based on petroleum ether and diisopropyl ether for the second TLC run (Table 3).

Table 3. TLC conditions for vitamin E-related compounds ^a

Compounds	Mobile phase	Visualization	Comments
α-Tocopherol in rat liver	1D: Benzene–ethanol (99:1, v/v)	20   h at 110–120°C
	2D: Hexane–ethanol (9:1, v/v)
α-, γ-, δ-Tocopherol in feeds, oils	Petr.ether–diethyl ether–acetic acid (90:10:1, v/v)	0.004% 2,7-dichlorofluorescein	β-Tocopherol and γ-tocopherol co-migrate
α-Tocopherol in pig organs	1D: Benzene–ethanol (99:1, v/v)	Ethanolic bathophenan-throline-FeCl3
	2D: Hexane–ethanol (9:1, v/v)
α-, β-, δ-Tocopherol and α-Tocopherol3 in algal lipids	Hexane–isopropylether (85:15, v/v)	15   min at 100°C 10% copper(II) sulfate phosphoric acid 10   min at 190°C	β-Tocopherol and γ-tocopherol co-migrate
α-, β-, γ-, δ-Tocopherol and (tocopherol3)	1D: Chloroform		γ-Tocopherol and β-tocopherol3 co-migrate
α-, β-, γ-, δ tocopherol3 in cereals and plant oils	2D: Hexane–isopropylether (80:20, v/v)

a

All separations were done on silica plates.

Resolution of the naturally occurring tocopherols and tocotrienols also requires two-dimensional TLC. The separation between β-tocotrienol and γ-tocopherol, in particular, remains an analytical challenge. Both capillary GC and HPLC have now replaced TLC approaches, but the solvents used in HPLC often rely on solvent systems applied in earlier TLC separations.

Traditionally, TLC on silica gel or on alumina has also played an important role in the clean-up of extracts of biological materials for the spectrophotometric analysis of tocopherols/tocotrienols in the presence of a large excess of interfering lipids. The whole procedure, however, often included saponification, extraction, column chromatography and two successive TLC runs before the final spectrophotometric measurement.

Both silica gel and alumina lend themselves to separation of tocopherols from their decomposition products (α-tocopherylquinone, α-tocopherylhydroquinone) from other fat-soluble vitamins or from other lipophilic antioxidants such as butylated hydroxytoluene, butylated hydroxyanisole, ethoxyquin, gallate esters and ascorbyl palmitate.

More recently, reversed-phase chromatographic conditions have been evaluated for the separation of α-, β-, γ- and δ-tocopherol. Kieselguhr G plates impregnated with a 10% solution of paraffin oil in benzene and eluted with methanol–water (9:1, by volume) offer the best separation. Of the four tocopherols considered, the difference between the R _F values of β- and γ-tocopherol was small.

Alternatively, reversed-phase C ₁₈ plates have also been applied to the separation of α-tocopherol from other antioxidants or from the other tocopherols. A new and interesting trend consists of the separation of d and l enantiomers of tocopherol on chiral plates (Stationary phase, chiral plate solvent: propanol–water–methanol (8.5:1.0:0.5 by volume) activated by heating at 100°C for 15   min). Because of the different biological activities of both enantiomers, this type of separation should be further investigated.

Detection

The commonest mode of detecting tocopherols and tocotrienols on TLC plates is based on quenching the fluorescence of supports impregnated with a fluorescent indicator. Alternatively, tocopherols and tocotrienols can be visualized by nonspecific procedures such as charring preceded by spraying with sulfuric acid, perchloric acid, nitric acid or 10% copper(II) sulfate in 8% phosphoric acid. More specific visualization procedures are based on the reducing properties of the vitamin E-related compounds. In this way, ferric ions are reduced to ferrous ions which react with α, α′-dipyridine or bathophenanthroline to form a red-coloured complex (Emmerie–Engel reaction). Phosphomolybdic acid and a 20% antimony pentachloride solution in chloroform both produce characteristic colour reactions allowing β-tocopherol to be distinguished from γ-tocopherol, or all four tocopherols from each other. Quantification of vitamin E-related compounds after TLC separation can be performed either off-plate or on-plate. Off-plate methods include scraping the areas of interest from the plate and eluting the compounds with an organic solvent, followed either by a colorimetric measurement or by GC determination. On-plate quantification is based on densitometry of the coloured spots obtained with chromogenic spray reagents, on the native UV absorbance or on the native fluorescence properties of the compounds of interest.

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Food Additives: Liquid Chromatography☆

A. Kumar , L.R. Gowda , in Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, 2014

Antioxidants

During storage, oils and fats undergo various reactions that reduce their nutritive value and also produce volatile compounds, to give unpleasant smells and tastes; the phenomenon is referred to as rancidity. In many cases the presence of antioxidants can inhibit the onset of rancidity. Synthetic antioxidants permitted to be added to food are: BHA – 1(or 3)-(t-butyl)-4-hydroxy anisole, PG – Propyl gallate, Ethyl gallate (EG), Octyl gallate (OG), dodecylgallate (DG), Ascorbyl palmitate, TBHQ – t-Butyl hydroquinone, NDGA – Nor dihydroguaiaretic acid, and, BHT – Butylated hydroxytoluene is allowed in a few countries.

Satisfactory and complete extraction of antioxidants from a food matrix into various organic solvents is not always easy because of co-extraction of interfering substances. Antioxidants such as BHA, BHT, TBHQ and Ionox-100 are susceptible to losses due to evaporation and utmost care needs to be exercised during concentration under vacuum. NDGA, PG, OG and DG are relatively polar nonvolatile compounds and their recovery is usually satisfactory. HPLC produces good separation between chemically similar compounds in mixtures to be analysed and enables the determination of up to 15 different antioxidants in one single run.

The general analysis protocols for antioxidants in foods comprise extraction in solvents and determination by reversed phase HPLC. The best solvents for extracting antioxidants from fats are acetonitrile and water-alcohol mixtures. The fat is usually dissolved in hexane or petroleum ether and the antioxidant is then extracted into the polar solvent. Literature indicates the use of a variety of chromatographic procedures with UV detection at 280   nm as most commonly used. Mobile phases are acetonitrile, acetic acid, methanol and water.

A HPLC method for the simultaneous determination of phenolic antioxidants in vegetable oils, lard and shortening has been reported. It was concluded that nine antioxidants, viz, BHA, TBHQ, IONOX-100 and THBP, PG, OG, DH and NDGA in vegetable oils, lards and shortening could be separated by gradient elution with water–acetonitrile plus 5% acetic acid as mobile phase. The recoveries ranged from 96% to 103%. A rapid and specific HPLC method for analysis of TBHQ in vegetable oils is also documented. A HPLC method was investigated with amperometric detection to analyse BHA, BHT and TBHQ in edible oils. The antioxidants were well separated, identified and quantified with high sensitivity. Recoveries ranged from 98% to 101%.

The use of RP-HPLC to quantitatively determine five antioxidants – BHA, BHT, PG, OG and DG – in fats has been described. HPLC enables the determination of the full range of antioxidants from polar compounds to the non-polar substances in a single chromatogram using gradient elution. Sensitive detection wavelengths are at 280   nm for UV and at 315   nm for fluorescence emission measurements.

Amperometric detection, which is both sensitive and specific, has been used. Determination of BHA and BHT in chewing gums after extraction in hexane and with a second extraction into dimethyl sulfoxide has been reported. The resulting extract was acidified with hydrochloric acid and separated on a μ-Bondapak C-18 column with a mobile phase of acetonitrile–water (55:45, v/v). Antioxidants and antimicrobials (Parabens) have been analysed in a variety of commercial products, such as cereals, snacks and shortenings using amperometric detection. The typical linear range is from 10^{−   11} to 10^{−   6} mole of injected analyte.

Seven antioxidants have been determined using a linear gradient from 30% solution B (acetonitrile–acetic acid 95:5, v/v) in solution A (water–acetic acid 95:5, v/v) to 100% solution B over 10 minutes with detection at 280   nm. Fifteen antioxidants have been measured in dried foods as well as fats and oils. The antioxidants were separated by isocratic elution with fluorescence and UV detection. Recoveries ranged from 80% to 106.7%.

The antioxidants diphenylamine and ethoxyquin were estimated using methanol −   0.01   M ammonium acetate (60:30, v/v) with fluorescence and UV detection. This method has been used successfully for the separation of fungicide residues and antioxidants in fresh fruits. BHA, BHT, PG, OG, DG and TBHQ in corn oil, cottonseed oil and beef fat have been determined. A procedure for the determination of antioxidants in vegetable oils without prior extraction did not resolve BHT from neutral lipids and suffered from interference due to co-eluting materials. PG, trihydroxybutyrophenone, TBHQ, BHA, BHT, NDGA and 3, 5-di-tert-butyl-4-hydroxy-methyl-phenol have been determined in fats, oils and dry foods. Antioxidants in dried foods such as potato flakes, dry coffee, whiteners and dessert topping mixes were isolated after rehydration and extraction in acetonitrile and subsequent separation on a C-18 column. The overall recoveries ranged from 64.3% to 103.6%. The method is highly accurate and hence was adopted as an official method (AOAC).

Tocopherols in vegetable oils have been separated by both reversed-phase and normal-phase LC. A method using a Radial PAK cartridge has been used for analysing individual tocopherols in eleven samples of lupine oil. The results showed the presence of γ-tocopherol (42–69   mg/100   g oil), and δ-tocopherol in traces (0.1–0.7   mg/100   g oil). This method is superior to GC in which up to 30% tocopherol losses occur during pretreatment of the sample. The simultaneous determination of α-tocopheryl acetate, tocopherols and tocotrienols in food involving extraction in hexane, separation on Lichrosorb Si-60 with hexane–di-isopropyl ether (93:3) as mobile phase and fluorescence detection at 290, 330   nm, has been reported. Recoveries are 95–100% with a detection limit of ≤   20   ng.

Most methods for the analysis of antioxidants use C₁₈ columns with detection at 280   nm. However, electrochemical or fluorimetric detection or simultaneous detection by two or more techniques has also been used. Mobile phases are usually composed of aqueous acid (acetic/phosphoric acid), buffers or salts together with methanol or acetonitrile. In many cases results are improved by gradient elution.

A method using a C-18 column for α-tocopheryl acetate and tocopherols has been described which allows separation of nine synthetic phenolic antioxidants along with natural antioxidants. Gradient elution is with water-acetonitrile-methanol-isopropanol. This method not only allows simultaneous detection of antioxidants and triglycerides but is also useful in studying inhibition effects of antioxidants in oil.

BHA, BHT, TBHQ, NDGA and gallates have been resolved and quantitatively determined on a Lichrosorb RP-18 column with gradient elution using acetonitrile–water–phosphoric acid and detection at 280   nm. Fluorimetric detection can also be used. The analysis of BHA, BHT, TBHQ and gallates in carrot juice, powdered milk, appetizers and cake using electrochemical detection has also been reported. It was suggested that as many as twelve antioxidants could be detected by a single isocratic HPLC analysis. The quantitation of BHA, BHT, TBHQ, NDGA, gallates and other antioxidants in foods using Supelcosil LC-18 column with acetic acid–water–acetonitrile as mobile phase and UV detector at 280   nm has also been documented.

Table 2 shows details of major liquid chromatographic methods for the analysis of antioxidants in foods and food products.

Table 2. Liquid chromatographic methods for the analysis of antioxidants in foods and food products

Food products	Antioxidant analysed	Analytical details
		Stationary phase/column	Mobile phase	Detection system
Potato flakes	BHA, BHT	C-18	Reversed phase gradient elution by acetonitrile with 5% acetic acid and 5% acetic acid in water	UV, 280   nm
Coffee whiteners	TBHQ, BHA	C-18	Reversed phase gradient elution by acetonitrile with 5% acetic acid and 5% acetic acid in water	UV, 280   nm
Dessert topping PG, DG, OG mixes		C-18	Reversed phase gradient elution by acetonitrile with 5% acetic acid and 5% acetic acid in water	UV, 280   nm
Cheese, snacks, cake mix	BHA, BHT, TBHQ, PG, OD, DG	C-18	Reversed phase gradient elution by acetonitrile with 5% acetic acid and 5% acetic acid in water	UV, 280   nm
Oils, lards, shortenings	BHA, BHT, TBHQ, THBP, Ionox-100, NDGA	C-18	Reversed phase gradient elution. Water-acetonitrile with 5% acetic acid	UV, 280   nm
Instant cereals, snacks, gelatin desserts, hydrogenated fats	BHA, TBHQ, PG, NDGA and Parabens	μ-Bondapak C-18	Methanol −   0.1   M ammonium acetate (or 0.01   M phosphate) buffer (1:1, v/v)	Amperometric detection

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The Why, Where, Who, How, and What of the vesicular delivery systems

Bhupinder Kapoor , ... Mukta Gupta , in Advances in Colloid and Interface Science, 2019

2.7 Aspasomes

Aspasomes are prepared by using ascorbyl palmitate (instead of phospholipids), cholesterol and negatively charged dicetyl phosphate. The inherent antioxidant activity of ascorbyl palmitate makes aspasomes a preferential drug delivery system in pathologies accruing from reactive oxygen species. Aspasomes were reported to enhance the transdermal delivery of azidothymidine. Antioxidant property of the vesicles combined with a potential to ferry the drugs across the skin make them a promising drug carrier for transdermal drug delivery. A recent study by Han, S., 2018, focused at the atomic level structure of these novel carriers and supported the assumption that water is excluded from the bilayer interior [ 48]. In a novel application, aspasomes prepared from ascorbyl palmitate encapsulating magnesium ascorbyl phosphate were found to be effective against melasma in a clinical study [49].

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https://www.sciencedirect.com/science/article/pii/S0001868619301277

Industrial applications of immobilized enzymes—A review

Alessandra Basso , Simona Serban , in Molecular Catalysis, 2019

3.5 Lipase CalB for vitamin C esters

L-Ascorbic acid (vitamin C) is the major water-soluble natural antioxidant. Acting as a free radical scavenger, L-ascorbic acid and its derivatives react with oxygen, thus removing it in a closed system. Also, esters of L-ascorbic acid with long-chain fatty acids (E-304) are employed as antioxidants in foods rich in lipids due to their solubility in fats compared to Vitamin C, which is insoluble in oils [48].

Ascorbyl palmitate and stearate are currently produced by reacting ascorbic acid with sulphuric acid followed by re-esterification with the corresponding fatty acid, and subsequently purified by re-crystallization. This chemical process has some disadvantages such as the use of strong acids, the low yields due to non-regioselective reactions and the need for tedious product isolation [ 49]. The biocatalytic methods described below employ the immobilized lipase B from Candida antarctica (CalB) as biocatalyst and free fatty acids or activated esters such as acyl donors (Fig. 8) [50].

Fig. 8. Manufacture of vitamin C fatty acid ester by transesterification catalyzed by immobilized CalB.

The biocatalytic conversion can achieve levels of approx. 95% conversion depending on the operating temperature, the efficiency of the side product (water) removal, and the length of the fatty acid.

Although enzymatic synthesis offers some advantages compared with the current chemical processes, such as lower reaction temperatures, purer product and reduced downstream processing, most of the production of ascorbyl esters is still performed by chemical synthesis, so this biocatalyzed process is still in its initial development stage. This is due to the long reaction time required by the enzymatic process and the high costs of the immobilized enzymes compared to the chemical catalysts.

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https://www.sciencedirect.com/science/article/pii/S2468823119304560

Liposomal Vitamin C Vs Ascorbyl Palmitate

Source: https://www.sciencedirect.com/topics/chemical-engineering/ascorbyl-palmitate