Peroxyl and hydroxyl radical scavenging activity of some natural phenolic antioxidants

The autoxidation of linoleic acid dispersed in an aqueous media and the antioxidant effect of hydroxytyrosol, oleuropein, caffeic acid and tyrosol were studied. Linoleic acid autoxidation rate was estimated by the increase of conjugated diene level and by the decrease of linoleic acid content in the samples. The phenolic compounds exhibited an antioxidant activity which increased in the order: tyrosol < caffeic acid < oleuropein < hydroxytyrosol. The analysis of the hydroperoxide isomers pointed out that hydroxytyrosol, oleuropein and caffeic acid at a concentration of 10⁻⁴M inhibited the formation oftrans- trans isomers in the increasing order: caffeic acid < oleuropein < hydroxytyrosol. This inhibition could be related to the ability of phenolic compounds to scavenge peroxyl radical. Tyrosol did not inhibit the formation oftranstrans isomers. Phenolic compounds were degraded as a consequence of their antioxidant activity and their degradation rate was positively correlated to their antioxidant efficacy. These phenolic compounds, at a concentration of 6 × 10⁻³M, also scavenged hydroxyl radical, with an efficiency which increased in the order: tyrosol < hydroxytyrosol < oleuropein < caffeic acid. Polar substituents at the para position, such as in caffeic acid and oleuropein, were correlated with higher hydroxyl radical quenching ability.     

酚酸类化合物在化妆品中的研究进展

简单介绍了酚酸类化合物的来源和生物活性,综述了酚酸类化合物作为一种天然化合物,通过清除自由基、抑制炎症反应、抑菌、抑制酪氨酸酶活性、加速分解肌肤中的晚期糖化终末产物等途径起到的美白淡斑、抗衰老、抗炎、屏障修护等多重护肤功效,并介绍了酚酸类化合物的安全性问题,提出了酚酸类化合物生物利用度低、低水溶性等实际应用问题,采用生物基纳米颗粒负载酚酸类化合物可使部分实际应用问题得到改善。最后阐述了目前酚酸类化合物在化妆品行业应用中存在的问题,以期为酚酸类化合物在护肤领域的应用提供参考。     

酚酸类化合物的应用及改性研究新进展

综述了天然酚酸类化合物的性质及近年来对其改性的新进展。阐述了常用的化学方法改性的优缺点。重点介绍了生物技术方法对其改性的优越性及在生物改性过程中反应介质、水活度、生物催化剂选择上所面临的挑战。客观的评价了不同改性工艺的特点。提出了今后采用生物方法对天然酚酸类化合物进行改性的一些建议。     

酚酸结构对酚酸-g-聚甘露糖醛酸抗氧化性能的影响

以海藻酸钠水解产物聚甘露糖醛酸(PM)为原料,通过聚甘露糖醛酸-乙二胺(PM-EDA)中间体与酚酸接枝共聚,制备了8种PM的酚酸(PA)接枝共聚物酚酸-g-聚甘露糖醛酸(PA-g-PM),并探究了PA结构对8种PA-g-PM抗氧化活性的影响。在n_PM:n_EDA=1:1.5,PM与两种活化剂碳二亚胺(EDC)、N-羟基琥珀酰亚胺(NHS)的摩尔比1:2:1,活化0 h,pH 8.0条件下,反应24 h,获得最高取代度(17.27%)的PM-EDA。PM的PA-g-PM接枝率在4.171±0.16 ~ 8.880±0.32 mg GA/g之间。UV-vis、FT-IR、XRD表征证实酚酸已成功接枝到PM上获得PA-g-PM。相比PM,8种PA-g-PM的对DPPH的清除率和对铁的还原力均显著提升。PA-g-PM的抗氧化性能与其中的酚羟基个数呈正相关关系,对位酚羟基PA-g-PM的抗氧化性能优于邻位酚羟基PA-g-PM的抗氧化性能,PA-g-PM中的酚羟基被甲氧基取代其抗氧化性能减弱。以期本研究结果为海藻酸钠在食品、化妆品、医药等行业高值开发利用奠定理论基础。     

Effect of temperature on fatty acid composition in the Nile tilapia (Oreochromis niloticus): A temperature dependent nutritive lipid profile

In this study, the effects of temperature on the fatty acids profile and the effects of temperature on the degree of unsaturation of fatty acids of Oreochromis niloticus were investigated. The analysis was performed by gas chromatography. The study showed that there were large temperature variations (10.0–32.0°C) during the study period (January–December). The highest crude fat content was found in January (3380 mg/100 g) and the lowest in June (2050 mg/100 g). The fatty acids profile showed significantly different diversity (p < 0.05). Total saturated fatty acid (∑SFA) content ranged from 409.54 to 1297.61 mg/100 g, monounsaturated fatty acid (∑MUFA) from 207.68 to 665.81 mg/100 g, and polyunsaturated fatty acid (∑PUFA) from 175.12 to 972.23 mg/100 g. The ∑MUFA and ∑PUFA concentrations were highest in January and lowest in June, and the ∑SFA concentration was lowest in January and highest in June. EPA and DHA contents were highest in January (198.96 mg/100 g) and lowest in June (48.76 mg/100 g). The contents of omega-3 (653.17 mg/100 g) and omega-6 fatty acids (252.54 mg/100 g) were highest in January and lowest in June (ω-3; 106.43 and ω-6; 60.91 mg/100 g). It concluded that the degree of unsaturation of fatty acids increases with decreasing temperature. In this study, the nutritional quality of the FAs profile was assessed using lipid quality indices. The indices indicating dietary quality of lipids by their values: Atherogenic index (0.47), thrombogenic index (0.38), hypocholesterolemic to hypercholesterolemic (3.00), meat fat quality (6.78), ω6/ω3 ratio (0.39), PUFA/SFA (2.37), MUFA/SFA (1.62), PUFA/MUFA (1.46), and PUFA + MUFA/SFA (3.99). These values are within the recommended range, indicating that the lipid profile of O. niloticus has high nutritional quality, which can be further improved by harvesting the fish during the winter season. Due to the nutritional importance of O. niloticus, the culture of this species could have significant interest to the people of Karachi, especially the coastal communities. To promote the nutritional diet in local population, the government should support the aquaculture of Nile tilapia.     

Influence of cholesterol on the kinetics of lipid autoxidation and on the antioxidative properties of α‐tocopherol and quercetin

The autoxidation kinetics of triacylglycerols of sunflower oil (TGSO) in the presence of 10% cholesterol (Chol) at 80, 90 and 100 °C has been studied. The process was followed by monitoring the peroxide value and the formation of conjugated dienes. Cholesterol has been found to exhibit a prooxidative effect. During the oxidation of the mixture (TGSO/Chol), cholesterol peroxides were not registered. It is supposed that the initial amount of cholesterol peroxides formed decomposes to free radicals and that these radicals accelerate TGSO oxidation. A kinetic analysis of the antioxidative behavior of α‐tocopherol and quercetin (2.9 x 10^?4‐17.8 × 10^?4 M) in both TGSO and TGSO/Chol at 100 °C was performed. It was found that the effectiveness, strength, and activity of α‐tocopherol are greater in TGSO/Chol than in TGSO, while these parameters for quercetin are practically the same in both lipid systems. The differences in the mechanism of action of α‐tocopherol and quercetin are discussed.     

Inhibition of lipid peroxidation by anthocyanins,anthocyanidins and their phenolic degradation products

Food components that delay or prevent biomolecule oxidation may be relevant in shelf life extension as well as disease prevention. Anthocyanins are a potentially important group of compounds, but they are prone to degradation both in vitro and in vivo, producing simple phenols. In this study, eight structurally related (poly)phenols [anthocyan(id)ins and phenolic acids] were examined for their ability to inhibit lipid oxidation at physiologically relevant concentrations (100–1000 nM) using the Cu²⁺‐mediated low‐density lipoprotein oxidation model. Interaction between each (poly)phenol and Cu²⁺ ions was also investigated. (Poly)phenols with an ortho‐dihydroxy group arrangement, i.e. cyanidin‐3‐glucoside, cyanidin and protocatechuic acid, were the most effective within their class, extending the lag phase to oxidation by 137, 255 and 402%, respectively (at 1000 nM). At the same concentration, trihydroxy‐substituted compounds (delphinidin and gallic acid) were of intermediate efficacy, extending the lag phase by 175 and 38%, respectively. Compounds with the 4'‐hydroxy‐3',5'‐methoxy arrangement (i.e. malvidin‐3‐glucoside and malvidin) were the least effective (3 and 58% extension, respectively), while syringic acid (4‐hydroxy‐3,5‐dihydroxy benzoic acid) was pro‐oxidant (lag phase shortened by 31%). (Poly)phenols with the ortho‐dihydroxy arrangement chelated Cu²⁺ ions, which in part explains their greater efficacy over the other (poly)phenols in this model oxidation system. However, differences in their hydrogen‐donating properties and their partitioning between lipid and hydrophilic phases are also relevant in explaining these structure‐activity relationships.     

Lipase-catalyzed transesterification of trilinolein or trilinolenin with selected phenolic acids

The enzymatic transesterification of selected phenolic acids with TAG, including trilinolein (TLA) and trillinolenin (TLNA), was investigated in an organic solvent medium. Maximal bioconversion of 66% was obtained with a dihydrocaffeic acid (DHCA) to TLA ratio of 1∶2 after 5 d of reaction. Similarly, the highest bioconversion of 62% was obtained with a DHCA to TLNA ratio of 1∶2, but after 12 d of reaction. However, a ratio of 1∶4 DHCA/TLA decreased the bioconversion to 53%. Transesterification reactions of ferulic acid with both TAG, using a ratio of 1∶2, resulted in low bioconversion of 16 and 14% with TLA and TLNA, respectively. The overall results indicated that bioconversion of phenolic MAG was higher than that of phenolic DAG. The structures of mono- and dilinoleyl dihydrocaffeate as well as those of mono- and dilinolenyl dihydrocaffeate were confirmed by LC-MS analyses. The phenolic lipids demonstrated moderate radical-scavenging activity.     

Effect of substitutents on the composition and dissociation behaviour of some four component phenolic copolymers

Some random four component phenolic copolymers have been prepared by condensing formaldehyde with p-chlorophenol, p-aminophenol, p-toluidine, and p-cresol. The compositions of the copolymers have been determined by electrometric titration in a non-aqueous solvent, and halogen estimation. Several samples of the copolymers have been obtained by changing the feed composition. Composition of the copolymer has been correlated with the reactivity of the four monomeric units. Hyperacidity of some of the functional groups in the copolymer chain is interpreted in terms of intramolecular hydrogen bonding.     

Effect of organic acids on the mechanical properties of phenolic resin composites

The effect of salicylic acid and its derivatives on the properties of phenolic resin composites was evaluated. The composites were reinforced with aluminum oxide particles in both solid and hollow forms. Differential scanning calorimetry studies have shown that the reaction rate of phenolic resin was accelerated by salicylic acid, but was not affected by the other compounds. Salicylic acid also reduced the flexural strengths of the phenolic resin composites. The strength was decreased by more than 30% in comparison to that with no acid added. In contrast, two derivatives of this acid—sodium salicylate and 4‐hydroxybenzoic acid—have minimal impact on the flexural strengths of the composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 642–647, 2000     

The role of amino acids in the autoxidation of milk fat

The effects of amino acids and their analogs on milk fat oxidation were examined under various conditions by measuring oxygen consumption and total unsaturated fatty acids. All the amino acids tested acted as antioxidants, characteristically extending the induction period (IP). Not only primary amino groups are responsible for the antioxidative activities of amino acids, but also the side-chain groups contribute, at least partially, to the protective effects of L-cysteine, L-tryptophan and L-tyrosine. In aqueous and HCL solutions, the antioxidative effects of L-alanine were significantly reduced. The freeze-dried L-lysine-HCL and L-alanine-HCL accelerated, while the corresponding control amino acids inhibited, milk fat oxidation.     

A differential scanning calorimetry study on the oxidation of C12-C18 saturated fatty acids and their esters

The autoxidation of lauric, myristic, palmitic, and stearic acids, their ethyl esters, and palmitic and stearic triglycerides was investigated by means of the isothermal and nonisothermal differential scanning calorimetry methods under oxygen flow. The activation energies of oxidation of all investigated compounds were similar (106.0–134.3 kJ/mol) and did not depend on length of the carbon chain. Kinetic parameters of start of the oxidation were similar for each investigated fatty acid and ester. Esterification of carboxyl group did not interfere with the reaction rate. The study showed good agreement between isothermal and nonisothermal data.     

Thermal stability of some flavonoids and phenolic acids in sheep tallow olein

In this study, the thermal stability of some phenolic antioxidants including flavonoids (quercetin and catechin) and phenolic acids (gallic acid, tannic acid, ellagic acid and caffeic acid) in tallow olein was investigated. Tallow olein fractionated from sheep tallow fat was used as a medium to study the antioxidant activity at 120, 140, 160 and 180°C. In order to extract tallow olein, a three‐stage fractionation method was performed on sheep tallow fat at the constant temperatures of 25, 15 and 5°C using acetone as a solvent. The results suggested that quercetin and ellagic acid had the highest thermal stability amongst others, while gallic acid and caffeic acid exhibited the least thermal stability. Practical applications: The sheep tallow fat has been primarily used in soap manufacturing and its application as an edible fat has been limited due to its high content of saturated fatty acids. Extraction of the liquid phase of tallow fat (tallow olein) by fractionation reduces its long‐chain saturated fatty acid content to an acceptable level for edible consumption. The fractionation process, as negatively affects the stability to autoxidation, should be followed by stabilisation with antioxidants. The recent interest in natural antioxidants encouraged the authors to investigate the thermal stability of phenolic antioxidants in tallow olein. It is necessary to determine the thermal stability of antioxidants to predict their appropriateness to be used in high‐temperature applications such as deep frying. Fractionation and stabilisation with appropriate antioxidants are the important steps to utilise tallow olein as an edible oil for different applications in salad formulations, cooking and frying.     

丁腈橡胶粉末对酚醛树脂性能的影响

研究了在酚醛树脂中添加丁腈橡胶粉末对粘合剂的流动性、固化速度、弯曲强度和洛氏硬度等性能的影响。发现添加丁腈粉末能使树脂的固化速度加快,流动性降低,试样弯曲强度和洛氏硬度降低。因此通过加入丁腈粉末可调整酚醛树脂类磨具的性能,使磨具具有一个较宽的固化温度范围。     

Effect of oil unsaturation and wax composition on stability,properties and food applicability of oleogels

Oleogelation is emerging as one of the most exigent oil structuring technique. The main objective of this study was to formulate and characterize rice bran/sunflower wax-based oleogels using eight refined food grade oils such as sunflower oil, mustard oil, soybean oil, sesame oil, groundnut oil, rice bran oil, palm oil, and coconut oil. Stability and properties of these oleogels with respect to oil unsaturation and wax composition were explored. Sunflower wax exhibited excellent gelation ability even at 1%–1.5% (w/v) concentration compared to rice bran wax (8%–10% w/v). As the oleogelator concentration increased, peak melting temperature also increased with increase in strength of oleogels as per rheological studies. X-ray diffraction and morphological studies revealed that oleogel microstructure has major influence of wax composition only. Sunflower wax oleogels unveiled rapid crystal formation with maximum oil binding capacity of 99.46% in highly unsaturated sunflower oil with maximum polyunsaturated fatty acid content. Further, the applicability of this wax based oleogels as solid fat substitute in marketed butter products was also scrutinized. The lowest value of solid fat content (SFC) in oleogel was 0.20% at 25°C, resembling closely with the marketed butter products. With increase in oil unsaturation, oleogels displayed remarkable reduction in SFC. Depending upon prerequisite, oleogel properties can be modulated by tuning wax type and oil unsaturation. In conclusion, this wax-based oleogel can be used as solid fat substitute in food products with extensive applications in other fields too.     

Composition of phenolic acids in sea buckthorn (<Emphasis Type="Italic">Hippophae rhamnoides</Emphasis> L.) berries

The composition of phenolic acids in several varieties of sea buckthorn berries was determined by GC and MS. In six cultivars the total content of phenolic acids ranged from 3570±282 to 4439±405 mg per kg of berries, on a dry basis. Seventeen phenolic acids were tentatively identified in the berries. Salicylic acid was the principal phenolic acid in sea buckthorn berries, accounting for 55 to 74.3% of the total phenolic acids present. The phenolic acids liberated from esters and glycosidic bonds were the major fractions of phenolic acids in the berries, whereas free phenolic acids constituted only up to 2.3% of total phenolic acids present.     

Extracts of phenolic compounds from seeds of three wild grapevines-comparison of their antioxidant activities and the content of phenolic compounds

Phenolic compounds were extracted from three wild grapevine species: Vitis californica, V. riparia and V. amurensis seeds using 80% methanol or 80% acetone. The total content of phenolic compounds was determined utilizing the Folin-Ciocalteu’s phenol reagent while the content of tannins was assayed with the vanillin and BSA precipitation methods. Additionally, the DPPH free radical scavenging activity and the reduction power of the extracts were measured. The RP-HPLC method was applied to identify the phenolic compounds in the extracts, such as phenolic acids and catechins. The seeds contained large amounts of tannins, catechins and gallic acid and observable quantities of p-coumaric acid. The total content of phenolic compounds and tannins was similar in the extracts from V. californica and V. riparia seeds. However, the total content of total phenolic compounds and tannins in the extracts from V. californica and V. riperia seeds were about two-fold higher than that in the extracts from V. amurensis seeds. Extracts from seeds of the American species (V. californica and V. riparia) contained similarly high concentrations of tannins, whereas extracts from seeds of V. amurensis had approximately half that amount of these compounds. The content of catechin and epicatechin was similar in all extracts. The highest DPPH^• anti-radical scavenging activity was observed in the acetonic and methanolic extracts of V. californica and V. riparia seeds— while the acetonic extract from the V. californica seeds was the strongest reducing agent.     

Antioxidant activity of Magnolol, honokiol, and related phenolic compounds

The antioxidant activity of 10 Japanese and Chinese crude drugs (Kampo drugs) was determined in vitro. Extract of Magnolia cortex, which had the highest antioxidant activity, contained phenolic compounds magnolol and honokiol. However, inhibitory effects of these compounds on lipid oxidation were weaker than that of α-tocopherol as measured by thiobarbituric acid assay. The structure-activity relationship of phenolic compounds showed that antioxidant activities were in the order 4-allyl-2,6-dimethoxyphenol ≥ p,p′-biphenol > eugenol > 2-allyl-6-methylphenol > honokiol > magnolol > caffeic acid > p-ethylphenol > guaiacol. As expected, these results showed that an electron donor and/or bulky groups at the ortho- or para-position of the phenol were required for inhibition of lipid oxidation. Electron spin resonance spin trapping experiments showed that phenol compounds with an allyl substituent on their aromatic rings directly scavenged superoxide (O ₂ ⁻ ), and that only eugenol trapped hydroxyl radicals. These findings suggest that phenolic compounds that contain allyl groups may be effective antioxidants because of the scavenging ability of O ₂ ⁻ or hydroxyl radical, whereas other phenols, without an allyl moiety such as α-tocopherol, may play a role in the termination of free radical chain reactions.