水包油乳液中油脂氧化稳定性的研究进展

随着消费者对不饱和脂肪酸及其产品营养价值越来越重视,不饱和脂肪酸富集食品已经成为食品工业发展的趋势。水包油(oil-in-water,O/W)乳液是食品油脂最常见的存在形式,也是必需脂肪酸、脂溶性营养素和风味物质的有效载体。然而,富含不饱和脂肪酸的O/W乳液食品在加工和贮藏过程中极易氧化,引起风味恶化、营养损失,甚至形成威胁人类健康的有毒化合物。因此,如何提高乳液中油脂的氧化稳定性是食品工业中亟待解决的问题。然而,消费者对天然食品需求的提高,又限制了合成抗氧化剂和氢化等传统抗氧化方法的使用。本文综述了O/W乳液中油脂氧化的机制、影响因素和调控机制,重点概述了食品分散体中油-水界面的理化性质如何影响油脂氧化稳定性这一基础研究,为高稳定性乳液体系和新型功能食品的开发提供新思路和理论支持。     

Chemical profiles of heated perilla meal extracts and their antioxidant activities

Chemical profiles of aqueous or ethanolic extracts of 140, 170 and 200 °C-heated perilla meal were identified by GC-MS, and antioxidant properties of the extracts were observed via in vitro assays and in bulk oil or oil-in-water (O/W) emulsion. A total of 22 and 27 chemicals were found in aqueous and ethanolic extracts from non-heated samples, respectively. As the heating temperature increased to 200 °C, the carbohydrate and derivative contents decreased significantly (P < 0.05), whereas rosmarinic acid concentration decreased in both extracts. Ethanolic extracts possessed higher antioxidant activities than aqueous extracts based on the results of radical scavenging and ferric-reducing antioxidant power assays and the Rancimat assay, but there were no significant differences among samples (P > 0.05). In the case of O/W emulsions, aqueous extracts inhibited lipid oxidation more efficiently than ethanolic extracts at 50 °C. In particular, heat treatment decreased the antioxidant activities of ethanolic extracts and not aqueous extracts in the O/W emulsion system. Aqueous extracts are recommended in moisture-rich emulsion-based foods while ethanolic extracts are more suitable in a lipid-rich environment for enhancing oxidative stability.     

Effects of Green Tea Extract and α‐Tocopherol on the Lipid Oxidation Rate of Omega‐3 Oils,Incorporated into Table Spreads,Prepared using Multiple Emulsion Technology

Abstract: This study examined the effectiveness of fat and water soluble antioxidants on the oxidative stability of omega (ω)‐3 rich table spreads, produced using novel multiple emulsion technology. Table spreads were produced by dispersing an oil‐in‐water (O/W) emulsion (500 g/kg 85 camelina/15 fish oil blend) in a hardstock/rapeseed oil blend, using sodium caseinate and polyglycerol polyricinoleate as emulsifiers. The O/W and oil‐in‐water‐in‐oil (O/W/O) emulsions contained either a water soluble antioxidant (green tea extract [GTE]), an oil soluble antioxidant (α‐Tocopherol), or both. Spreads containing α‐Tocopherol had the highest lipid hydroperoxide values, whereas spreads containing GTE had the lowest (P < 0.05), during storage at 5 °C, while p‐Anisidine values did not differ significantly. Particle size was generally unaffected by antioxidant type (P < 0.05). Double emulsion (O/W/O) structures were clearly seen in confocal images of the spreads. By the end of storage, none of the spreads had significantly different G′ values. Firmness (Newtons) of all spreads generally increased during storage (P < 0.05). Practical Application: Lipid oxidation is a major problem in omega‐3 rich oils, and can cause off‐odors and off‐flavors. Double emulsion technology was used to produce omega‐3 enriched spreads (O/W/O emulsions), wherein the omega‐3 oil was incorporated into the inner oil phase, to protect it from lipid oxidation. Antioxidants were added to further protect the spreads by reducing lipid oxidation. Spreads produced had good oxidative stability and possessed functional (omega‐3 addition) properties.     

Role of emulsifier layer,antioxidants and radical initiators in the oxidation of olive oil-in-water emulsions

Lipid oxidation in oil-in-water (O/W) emulsions is largely affected by the properties of the interfacial layer surrounding the oil droplets. In this work, the effect of the emulsifier layer structure, presence of both hydrophilic and lipophilic antioxidants and radical initiators on the development of lipid oxidation in olive oil-in-water emulsions was investigated. The olive oil-in-water emulsion is a suitable model of low fat food emulsions. The rationale of the work was to study the role of the interfacial layer when both the antioxidants and the radical initiators came from the two different emulsion compartments. Emulsions were prepared by using food grade emulsifiers of the Tween series (polyoxyethylene sorbitan esters) in the water phase and Span 80 (sorbitan monoleate) in the oil phase. The properties of the interfacial layer were changed by using Tween 20, Tween 60, Tween 80, which have different hydrophobic tails. These systems were oxidized by means of both hydrophilic (AAPH (2,2′-azobis,2-methyl-propanimidamide dihydrochloride), AIPH (2,2′-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride) and lipophilic (AMVN (2,2′-azobis(2,4-dimethylvaleronitrile)) radical initiators at 40 °C. A continuous fluorescent method based on the front face technique allowed us to follow directly the development of oxidation in the whole emulsion. The combination Tween 80/Span 80 produced an interfacial layer more resistant to radical attack. Moreover, a polar paradox was verified also for radical initiators, while the results suggest that the best way to protect emulsions is to use a combination of antioxidants in both phases, to promote a synergy and the regeneration of antioxidants mediated by the interfacial layer.     

Effects of different polarity of onion skin extracts on antioxidative properties and non-volatile profiles

Onion skins are agricultural by-products that contain high levels of antioxidants, including quercetin and protocatechuic acid. The solubility of extracts can affect their antioxidant capacity in food oil matrices. The antioxidative properties of onion skin extracts with different polarity were compared and the chemical profiles of the extracts were identified by GC-MS. Highly lipophilic, moderately hydrophilic and highly hydrophilic onion skin extracts (HLE, MHE and HHE, respectively) were prepared and their antioxidant properties were tested using in vitro assays and bulk oil or oil-in-water (O/W) emulsions. The most abundant phenolic compounds in the onion skin extracts were quercetin and protocatechuic acid. The lipophilicity levels of HLE, MHE and HHE were 0.674, 0.394 and −1.225, respectively. HLE showed higher antioxidant capacity in bulk oil and O/W emulsion matrices compared to MHE and HHE. The antioxidant capacity of HLE was higher in the O/W emulsion than in the bulk oil system. Therefore, highly lipophilic onion skin extracts can be used as effective natural antioxidants in oil matrices, especially O/W emulsions.     

Impact of iron encapsulation within the interior aqueous phase of water-in-oil-in-water emulsions on lipid oxidation

Iron (Fe³⁺) was encapsulated within the internal aqueous phase of water-in-oil-in-water (W/O/W) emulsions, and then the impact of this iron on the oxidative stability of fish oil droplets was examined. There was no significant change in lipid droplet diameter in the W/O/W emulsions during 7 days storage, suggesting that the emulsions were stable to lipid droplet flocculation and coalescence, and internal water diffusion/expulsion. The initial iron encapsulation (4 mg/100 g emulsion) within the internal aqueous phase of the water-in-oil (W/O) emulsions was high (>99.75%), although, a small amount leaked out over 7 days storage (≈10 μg/100 g emulsion). When W/O/W emulsions were mixed with fish oil droplets the thiobarbituric acid-reactive substances (TBARS) formed decreased (compared to fish oil droplets alone) by an amount that depended on iron concentration and location, i.e., no added iron < iron in external aqueous phase < iron in internal aqueous phase. These differences were attributed to the impact of W/O droplets on the concentration and location of iron and lipid oxidation reaction products within the system.     

Mechanisms of lipid oxidation in water-in-oil emulsions and oxidomics-guided discovery of targeted protective approaches

Lipid oxidation is an inevitable event during the processing, storage, and even consumption of lipid-containing food, which may cause adverse effects on both food quality and human health. Water-in-oil (W/O) food emulsions contain a high content of lipids and small water droplets, which renders them vulnerable to lipid oxidation. The present review provides comprehensive insights into the lipid oxidation of W/O food emulsions. The key influential factors of lipid oxidation in W/O food emulsions are presented systematically. To better interpret the specific mechanisms of lipid oxidation in W/O food emulsions, a comprehensive detection method, oxidative lipidomics (oxidomics), is proposed to identify novel markers, which not only tracks the chemical molecules but also considers the changes in supramolecular properties, sensory properties, and nutritional value. The microstructure of emulsions, components from both phases, emulsifiers, pH, temperature, and light should be taken into account to identify specific oxidation markers. A correlation of these novel oxidation markers with the shelf life, the organoleptic properties, and the nutritional value of W/O food emulsions should be applied to develop targeted protective approaches for limiting lipid oxidation. Accordingly, the processing parameters, the application of antioxidants and emulsifiers, as well as packing and storage conditions can be optimized to develop W/O emulsions with improved oxidative stability. This review may help in emphasizing the future research priorities of investigating the mechanisms of lipid oxidation in W/O emulsion by oxidomics, leading to practical solutions for the food industry to prevent oxidative rancidity in W/O food emulsions.     

Effect of proanthocyanidin-rich extracts from Chinese quince (Chaenomeles sinensis) fruit on the physical and oxidative stability of sunflower oil-in-water emulsions

To evaluate the effect of Chinese quince proanthocyanidins (PAs) on the physical and oxidative stability of sunflower oil-in-water (O/W) emulsions during storage, three proanthocyanidin (PA)-rich extracts, namely water extract (WE), ethanol extract (EE), and acetone extract (AE), were prepared. When added to O/W emulsions, all the three extracts inhibited the increase in droplet size and the absolute zeta-potential value during storage (55 °C, 24 days). All three extracts also exhibited superior antioxidative activity in the O/W emulsions. WE showed the highest efficacy in retarding lipid oxidation as proved by its lower conjugated dienes (8.18 ± 0.49 mmol L⁻¹) and thiobarbituric substances values (0.68 ± 0.0025 mg MDA L⁻¹), and such efficacy was similar to that of BHA at the same level. Lower molecular weight and degree of polymerisation have a positive effect on antioxidant activity of PA-rich extracts. According to these results, all three PA-rich extracts are potential natural antioxidants for improving the stability of food-grade emulsions.     

Lipid Oxidation in Oil‐in‐Water Emulsions: Involvement of the Interfacial Layer

More polyunsaturated fats in processed foods and fewer additives are a huge demand of public health agencies and consumers. Consequently, although foods have an enhanced tendency to oxidize, the usage of antioxidants, especially synthetic antioxidants, is restrained. An alternate solution is to better control the localization of reactants inside the food matrix to limit oxidation. This review establishes the state‐of‐the‐art on lipid oxidation in oil‐in‐water (O/W) emulsions, with an emphasis on the role of the interfacial region, a critical area in the system in that respect. We first provide a summary on the essential basic knowledge regarding (i) the structure of O/W emulsions and interfaces and (ii) the general mechanisms of lipid oxidation. Then, we discuss the factors involved in the development of lipid oxidation in O/W emulsions with a special focus on the role played by the interfacial region. The multiple effects that can be attributed to emulsifiers according to their chemical structure and their location, and the interrelationships between the parameters that define the physicochemistry and structure of emulsions are highlighted. This work sheds new light on the interpretation of reported results that are sometimes ambiguous or contradictory.     

Effects of lipophilic and hydrophilic antioxidants in oil-in-water emulsions under chlorophyll photosensitization

Antioxidative or prooxidative properties of α-tocopherol, Trolox, ascorbic acid, and ascorbyl-palmitate at the concentration of 0.1 and 1.0 mM were determined in oil-in-water (O/W) emulsions under chlorophyll photosensitization. Headspace oxygen depletion, lipid hydroperoxides, and headspace volatile analyses were conducted to determine the oxidative stability of O/W emulsions. For 32 h visible light irradiation, depleted headspace oxygen content in O/W emulsions were in the order of samples containing Trolox, ascorbic acid, ascorbyl palmitate, α-tocopherol, without antioxidants under light, and samples in the dark, which implies that all the added compounds acted prooxidant. These prooxidative properties of added compounds can be observed in the results of lipid hydroperoxides and headspace volatiles. Samples containing ascorbic acid and ascorbyl palmitate retained higher chlorophyll content than those containing Trolox up to 16 h. Increases of concentration of Trolox, ascorbic acid, and ascorbyl palmitate from 0.1 to 1.0 mM increased the lipid oxidation products whereas α-tocopherol decreased the degree of lipid oxidation implying α-tocopherol may not share the same prooxidant mechanisms compared to other compounds in chlorophyll sensitized O/W emulsions.     

Improvement of the lipid oxidative stability of soybean oil-inwater emulsion by addition of daraesoon (shoot of <Emphasis Type="Italic">Actinidia arguta</Emphasis>) and samnamul (shoot of <Emphasis Type="Italic">Aruncus dioicus</Emphasis>) extract

The effect of 75% ethanol extract of daraesoon and samnamul (200 mg/kg) on the lipid oxidation of soybean oil-in-water (4:6, w/w) emulsion containing iron (5 mg/kg) in dark conditions at 25°C was studied by determining headspace oxygen and hydroperoxide contents. Polyphenol, carotenoid, and chlorophyll contents were also evaluated using spectrophotometry. The headspace oxygen contents were higher and hydroperoxide contents were lower (p<0.05) in the emulsions with added daraesoon and samnamul extracts compared with the control emulsion without the extract. The antioxidant activity of the daraesoon and samnamul extracts in the lipid oxidation of the emulsions was comparable to that of dibutylhydroxytoluene at 200mg/kg. Polyphenols, carotenoids, and chlorophylls were degraded during oxidation of the emulsions, possibly due to a role of the antioxidants. The results suggest that contribution to the improved lipid oxidative stability of the emulsion with added samnamul and daraesoon would be due to polyphenols and pigments, respectively.     

Antioxidant and emulsifying properties of potato protein hydrolysate in soybean oil-in-water emulsions

The efficacy of a previously developed antioxidative potato protein hydrolysate (PPH) for the stabilisation of oil droplets and inhibition of lipid oxidation in soybean oil-in-water (O/W) emulsions was investigated. Emulsions (10% lipid, pH 7.0) with PPH-coated oil droplets were less stable than those produced with Tween 20 (P < 0.05). However, the presence of PPH, whether added before or after homogenisation with Tween 20, retarded emulsion oxidation, showing reduced formation of peroxides up to 53.4% and malonaldehyde-equivalent substances up to 70.8% after 7-d storage at 37 °C (P < 0.05), when compared with PPH-free emulsions. In the emulsions stabilised by PPH + Tween 20, 8–15% of PPH was distributed at the interface. Adjustment of the pH from 3 to 7 markedly increased ζ-potential of such emulsions (P < 0.05). Inhibition of lipid oxidation by PPH in soybean O/W emulsions can be attributed to both chemical and physical (shielding) actions.     

Processing and storage effects on the oxidative stability of hemp (Cannabis sativa L.) oil‐in‐water emulsions

Hempseed oil was used to form oil‐in‐water emulsions, and the effect of heating, storage and light on the oxidative stability of the dispersed phase was investigated. Lipid oxidation rate increased following thermal processing and light exposure, whereas oxidation markers remained relatively unaffected during emulsions storage at 4 °C for 10 days. Induction times of the emulsions were reduced up to 26% and the concentration of thiobarbituric acid reactive substances increased up to 4.5‐fold, depending on the processing conditions. Selected berries as potential sources of natural antioxidants were screened for polyphenol and anthocyanin content in order to investigate their ability to retard lipid oxidation in comparison with a commercially available synthetic counterpart. Raspberry powder extract significantly improved the oxidative stability of hemp‐based emulsion compared with the control and was even more effective compared to a synthetic antioxidant when samples were subjected to heat treatment.     

Effects of chitosan and collagen containing α-tocopherol on the oxidative stability in bulk oil and oil-in-water emulsion

To provide efficient antioxidant capacities, proper carriers are needed to protect antioxidants against oxidative stress. Collagen mesh structure or chitosan gel was loaded with α-tocopherol and their effects were evaluated in bulk corn oil or oil-in-water (O/W) emulsion at 60 °C. Added collagen and chitosan enhanced oxidative stability in corn oil and O/W emulsions at 60 °C compared to corn oils without carriers or with addition of α-tocopherol (p < 0.05). Stability of α-tocopherol in corn oil loaded in collagen or chitosan was significantly enhanced compared to that in oils without carriers (p < 0.05). In O/W emulsions, α-tocopherol loaded collagen showed higher antioxidant properties than α-tocopherol loaded chitosan (p < 0.05). Collagen mesh structure and chitosan gel retarded the rates of lipid oxidation efficiently in both food matrices when α-tocopherol was not loaded. Collagen mesh structure and chitosan gel can be useful carriers for α-tocopherol in bulk oil or O/W emulsion.     

Effect of frozen storage on emulsifying properties of actomyosin from mantle and fins of squid (<Emphasis Type="Italic">Illex argentinus</Emphasis>)

The emulsifying properties of actomyosin (AM) of mantle and fins obtained periodically from frozen-stored squid were investigated. Oil in water (O/W) emulsions and their stability were studied by optical characterisation. Both emulsions showed that the initial backscattering (BS) decreased after 3 months of frozen storage. O/W emulsions formulated with AM of squid mantle showed certain stability during the first 20 min, and presented destabilisation during the remaining analysed time, reaching a 20% of BS, approximately. However, for emulsions formulated with AM of fins, the BS diminution was recorded between 30 and 45 min, indicating a higher stability as a function of time with respect to the mantle. The size distribution of emulsions prepared after short times of storage presented three droplet size populations. With increasing the time of frozen storage, the size distribution changed from trimodal to bimodal: the large population decreased until it disappeared and the population with medium size increased at long time of frozen storage. The emulsions formulated with AM of squid fins presented a similar behaviour than emulsions of mantle. QuickScan profiles allowed discriminating creaming and coalescence processes to both emulsions mainly at short time of frozen storage. The emulsion prepared with AM from squid fins was further flocculated than emulsion of mantle. Actomyosin from fin squid exhibits the best properties as emulsifier agents of O/W emulsions. These results suggest that a short frozen-storage period can favour the emulsifying properties of actomyosin obtained from squid mantle and fins. On the other hand, the structure of flocs would affect positively the stability of emulsions.     

Oxidation Stability of O/W Emulsion Prepared with Linolenic Acid Enriched Diacylglycerol

The sn‐1,3‐regiospecific Rhizomucor miehei lipase (Lipozyme RM IM) was employed to produce structured diacylglycerol (SL‐DAG), which contained 67.3 mol% DAG with 27.2 area% of C18:3. To investigate the oxidative stability of the SL‐DAG in emulsion form, 5% oil‐in‐water (O/W) emulsions were prepared with 200 and 400 ppm sinapic acid. It was shown that the hydroperoxide values of the control (without any antioxidant) was the highest (117.7 meq/L) on day 43 of storage and thereafter the value decreased. However, the emulsions with 200 and 400 ppm sinapic acid resulted in slow oxidation degree until day 64 of storage (30.3 and 7.3 meq/L, respectively). Aldehyde measurements for the 200 ppm sinapic acid emulsion (12.8 mmol/mol) and the 400 ppm sinapic acid emulsion (7.5 mmol/mol) also showed better oxidative stability than that for the 200 ppm catechin emulsion (27.4 mmol/mol) and the control (52.7 mmol/mol). Although the SL‐DAG in the emulsions contains high levels of polyunsaturated fatty acids, the degree of oxidation in the emulsions can be reduced when sinapic acid is used as an antioxidant.     

Evaluation of Antioxidant or Prooxidant Properties of Selected Amino Acids Using In Vitro Assays and in Oil‐in‐Water Emulsions Under Riboflavin Sensitization

The antioxidant properties of selected amino acids were tested using in vitro assays and oil‐in‐water (O/W) emulsions under riboflavin (RF) photosensitization. Headspace oxygen content, lipid hydroperoxides, and conjugated dienes were determined for the degree of oxidation. Riboflavin photosensitization was adapted as the oxidation driving force. In vitro assays showed that cysteine had the highest antioxidant properties followed by tryptophan and tyrosine. However, in O/W emulsions under RF photosensitization, tyrosine inhibited lipid oxidation whereas tryptophan acted as a prooxidant. Tryptophan accelerated the rates of oxidation in O/W emulsion without RF. The antioxidant properties of amino acids differed depending on the antioxidant determination methods, oxidation driving forces, and food matrices.     

Free-radical scavenging and antioxidative activities of some polysaccharides in emulsions

The antioxidant activity in linoleate emulsion systems, radical scavenging activity and inhibition of autoxidation in sunflower oil-in-water emulsions were studied in the presence of polysaccharide produced by Rhizobium meliloti (RPS), xanthan, curdlan, and carboxymethylcellulose (CMC) and compared to tertiary butylhydroxyquinone (TBHQ). The antioxidant activity in the linoleate emulsion was improved with increasing pH from 3 to 9 and concentration of polysaccharide from 20 to 60 mg/100 g emulsion, while it decreased with increase in storage temperature between 30 and 90 °C. The antioxidant activity of xanthan, curdlan, and RPS at concentration of 40 mg/100 g emulsion was equal to that of TBHQ at 20 mg/100 g emulsion. RPS showed the highest thermal stability and the lowest linoleic oxidation values compared to TBHQ, xanthan, and curdlan at 90 °C. The antioxidant activity of xanthan, curdlan, and RPS in linoleate emulsions at pH 3 and 5 was in the first order with significant (P<0.05) values compared to emulsion, prepared using TBHQ.Curdlan and RPS were effective in radical scavenging being 60-90% at pH values ranging between 3 and 7. They showed an ability to inhibit lipid oxidation in sunflower oil emulsions during holding time for 50 h at 60 °C. In general, the polysaccharides RPS and curdlan can be used as food additives having many functions as stabilizers, radical scavengers, and antioxidants in emulsified foods such as mayonnaise, salad dressings, and cake products.     

Dispersion Stability of O/W Emulsions with Different Oil Contents Under Various Freezing and Thawing Conditions

Freezing and thawing of oil‐in‐water (O/W) emulsion‐type foods bring about oil–water separation and deterioration; hence, the effects of freezing and thawing conditions on the destabilization of O/W emulsions were examined. The freezing rate and thawing temperature hardly affected the stability of the O/W emulsion. O/W emulsions having different oil fractions were stored at temperatures ranging from –30 to –20 °C and then thawed. The stability after thawing depended on the storage temperature, irrespective of the oil fraction of the emulsion. A good correlation was found between the time at which the stability began to decrease and the time taken for the oil to crystalize. These results indicated that the dominant cause for the destabilization of the O/W emulsion during freezing and thawing is the crystallization of the oil phase and that the effects of the freezing and thawing rates on the stability are insignificant.     

Effects of chlorophyll photosensitisation on the oxidative stability in oil-in-water emulsions

Effects of chlorophyll photosensitisation on the oxidative stability of oil-in-water (O/W) emulsions were determined by analysing headspace oxygen content, lipid hydroperoxides, and headspace volatiles. The roles of transition metals and singlet oxygen were tested by adding ethylenediaminetetraacetic acid (EDTA) and sodium azide, respectively. Emulsions with chlorophylls and visible light irradiation had significantly high lipid hydroperoxides and headspace volatiles and low headspace oxygen content (p < 0.05) after 32 h while samples without light irradiation did not show any significant changes (p > 0.05). Sodium azide did not show clear antioxidant capacities in O/W emulsion systems rather showed prooxidant properties at some concentration. Addition of EDTA, a metal chelator, accelerated the rates of lipid oxidation in a concentration dependent manner. EDTA may enhance the stability of chlorophylls in O/W emulsions and the resulting higher chlorophyll concentrations may generate more singlet oxygen thus accelerating the rates of lipid oxidation.