Preparation of Monodisperse Food-Grade Oleuropein-Loaded W/O/W Emulsions Using Microchannel Emulsification and Evaluation of Their Storage Stability

W/O/W emulsion is an emerging system in developing new functional and low-calorie food products. The aim of this study is to produce food-grade monodisperse water-in-oil-in-water (W/O/W) emulsions loaded with a hydrophilic bioactive oleuropein. W/O/W emulsions were prepared via high-pressure homogenization and subsequent microchannel (MC) emulsification. The internal aqueous phase was a 5-mM sodium phosphate buffer containing d(+)-glucose (5 wt.%) and oleuropein (0.1–0.7 wt.%). The oil phase consisted of soybean oil and tetraglycerin monolaurate condensed ricinoleic acid esters (TGCR; 3–8 wt.%). The external aqueous phase was a 5-mM sodium phosphate buffer containing d(+)-glucose (5 wt.%) and decaglycerol monolaurate (1 wt.%). Oleuropein-loaded submicron W/O emulsions with average droplet diameters as small as 0.15 μm and monomodal droplet size distributions were prepared by high-pressure homogenization when applying high TGCR concentrations of 5–8 wt.% and low oleuropein concentrations of 0.1–0.3 wt.%. Monodisperse oleuropein-loaded W/O/W emulsions with average W/O droplet diameters of around 27 μm and coefficients of variation of below 5 % were successfully prepared when using a silicon MC array plate with wide channels of 5-μm depth and 18-μm width. The monodisperse W/O/W emulsions prepared at high TGCR concentrations and low oleuropein concentrations were the most stable during 40 days of storage. The adsorption behavior of oleuropein at the internal aqueous–oil interface was relevant to W/O/W emulsions microstructure and stability. The results are believed to provide useful information for successfully preparing stable monodisperse W/O/W emulsions loaded with hydrophilic functional compounds. The surface activity of the loaded material seems to be a key parameter in optimizing the formulation of W/O/W food emulsion.     

Effect of protein oxidation on kinetics of droplets stability probed by microrheology in O/W and W/O emulsions of whey protein concentrate

Whey protein concentrate (WPC) was oxidized by peroxyl radicals derived from 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) and the kinetics of droplet stability in O/W and W/O emulsions stabilized by oxidized WPC were evaluated by studying the micro-rheology. Degrees of protein oxidation were indicated by carbonyl concentration and emulsion types were distinguished by fluorescence microscopy. Oxidation resulted in free sulfhydryl groups degradation and surface hydrophobicity decrease. Moderate protein oxidation promoted to form diminutive droplets, which aggregated quickly to gel-network structure and decreased the motion rate of droplets, leading to the increased elasticity and viscosity, which led to better stability. Over-oxidation underwent severe droplet aggregation and sediment with increased motion rate, which resulted in instability of emulsions. The W/O emulsions of oxidized WPC were more inclined to block the motion of droplets and form a stable structure with higher viscosity, compared with the O/W emulsions.     

A Novel Approach to Improving the Quality of Bittern-Solidified Tofu by W/O Controlled-Release Coagulant. 1: Preparation of W/O Bittern Coagulant and Its Controlled-Release Property

To explore the controlled-release capacity and potential application of water in oil (W/O) emulsions, W/O emulsions with bittern solution as the aqueous phase were prepared with polyglycerol polyricinoleate (PGPR) as the emulsifier. Several factors that influenced the preparation of W/O bittern coagulants were investigated. Optimized conditions were applied as follows: bittern solution/oil phase at 4:6 or 5:5 (w/w), processing temperature at 65 °C, emulsifier concentration higher than 0.6 wt% and high-pressure homogenization at 60 MPa; W/O emulsions that had a good particle size distribution, good rheological properties, good embedding ratio and high stability were prepared. The optimized W/O emulsions also exhibited the expected controlled-release ability, affected by the bath temperature, shear speed and emulsion characteristics. The preliminary results also showed that the application of W/O emulsions has the potential to improve tofu quality by delaying the solidification of soybean protein and creating a much smoother and finer gel structure.     

Droplet characterization and stability of soybean oil/palm kernel olein O/W emulsions with the presence of selected polysaccharides

Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water (O/W) emulsions as affected by the presence of xanthan gum (XG), carboxymethyl cellulose (CMC), guar gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The dispersed phase (40%) of the emulsions was based on soybean oil/palm kernel olein blend (70:30) that partially crystallized during extended storage at 5 °C. In freshly prepared emulsions, the presence of XG, CMC, GG and LBG had significantly decreased the droplet mean diameters. XG, LBG, GG and CMC emulsions exhibited a shear-thinning behavior but AG emulsion exhibited a Bingham plastic behavior and control (without gum) emulsion almost exhibited a Newtonian behavior. Both control and AG emulsions exhibited a severe phase separation after storage (30 days, 5 °C). The microstructure of stored XG emulsion showed the presence of partially coalesced droplets, explaining a large increase in its droplet mean diameters. Increases in droplet mean diameters and decreases in flow properties found for stored GG and LBG emulsions were attributed to droplet coalescence. Nevertheless, the occurrence of droplet coalescence in these emulsions was considered to be small as no free oil could be separated under centrifugation force. Increases in flow properties and excellent stability towards phase separation found for stored CMC emulsion suggested that CMC could retard partial coalescence. Thus, the results support the ability of CMC, GG and LBG in reducing partial coalescence either by providing a sufficiently thick continuous phase or by acting as a protective coating for oil droplets.     

米糠蛋白O/W及W/O/W乳液制备及界面稳定性

为对比不同米糠蛋白质量浓度下O/W及W/O/W乳液的稳定性,以米糠蛋白作为基料,采用双乳化法制备O/W及W/O/W乳液,考察不同米糠蛋白质量浓度下乳液的微观形态和稳定性并探究其界面稳定机理。结果表明：W/O/W乳液的贮存稳定性显著优于O/W乳液;与相同蛋白含量的O/W乳液相比,W/O/W乳液的黏度显著提高;当米糠蛋白质量浓度为0.4 g/100 mL时,W/O/W乳液的稳定性较O/W乳液提高了1 倍以上;乳液内部包裹更多的W/O液滴,W/O/W乳液的粒径较大;而此时静电斥力也较大,起到稳定乳液的目的。同时,米糠蛋白质量浓度不小于0.4 g/100 mL时,O/W及W/O/W乳液中蛋白质的吸附率较高,达到78%以上。本研究为天然米糠蛋白质在食品级乳液中的开发提供参考,为粮食副产物的综合利用提供了新思路。     

Release rate profiles of magnesium from multiple W/O/W emulsions

Water-in-oil-in-water (W/O/W) emulsions were formulated based on rapeseed oil, olive oil, olein and miglyol. Polyglycerol polyricinoleate and sodium caseinate were used as lipophilic and hydrophilic emulsifiers, respectively. Magnesium was encapsulated in the inner aqueous droplets. Emulsion stability was assayed through particle sizing and magnesium release at two storage temperatures (4 and 25 °C) over 1 month. Irrespective of the oil nature, both the primary W/O and W/O/W emulsions were quite stable regarding the size parameters, with 10-μm fat globules and 1-μm internal water droplets. Magnesium leakage from W/O/W emulsions was influenced by the oil type used in the formulation: the higher leakage values were obtained for the oils characterized by the lower viscosity and the higher proportion of saturated fatty acids. Magnesium release was not due to droplet–globule coalescence but rather to diffusion and/or permeation mechanisms with a characteristic rate that varied over time. In addition, W/O/W emulsions were resistant to various thermal treatments that mimicked that used in pasteurization processes. Finally, when W/O/W emulsions were placed in the presence of pancreatic lipase, the emulsion triglycerides were hydrolysed by the enzyme. These results indicated a possible use of W/O/W emulsions loaded with magnesium ions in food applications.     

Effects of flavonoids on physical and oxidative stability of soybean oil O/W emulsions

Flavonoids have attracted attention due to pharmacological and antioxidative activities. The effects of flavonoids on the physical and oxidative stabilities of lecithin emulsified soybean oil-in-water (O/W) emulsions were investigated at 25°C during 29 days of storage. Addition of 100 ppm hesperidin, hesperitin, rutin, or quercetin improved the physical stability of O/W emulsions but did not change particle size values, compared to a control with no flavonoids during storage. Quercetin showed the highest antioxidant activity for inhibition of lipid oxidation based on lowered lipid hydroperoxide formation and 2-thiobarbituric acid reactive substances values in emulsions, followed by rutin, hesperitin, and hesperidin. Hesperidin and hesperitin did not affect antioxidative activities in O/W emulsions under metal ion-catalyzed conditions. Addition of hesperidin, hesperitin, rutin, and quercetin to soybean oil O/W emulsions improved the physical and oxidative stability of emulsions lacking added metal ions.     

Fish Oil Microcapsules from O/W Emulsions Produced by Premix Membrane Emulsification

Fish oil microcapsules were prepared by combining a low-energy emulsification method (premix membrane emulsification) with spray drying. Oil-in-water (O/W) emulsions were prepared using a two-step emulsification method that used a rotor–stator homogenizer followed by membrane emulsification. The influence of the emulsification method (mechanical stirring or membrane emulsification), the emulsification conditions (membrane and emulsifier type), and the amount of wall material on the physicochemical characteristics of the microcapsules was studied. The results show that the emulsification method and the type and amount of emulsifier and wall material affect the final amount of encapsulated oil. Microcapsules produced by membrane emulsification and stabilized with 2 % Tween-20 or 10 % whey protein presented the highest values (higher than 50 %) of oil encapsulation efficiency (OEE). It has been found that the OEE increases when decreasing the droplet size of the emulsions as well as with the increase of the amount of wall material employed during drying. Morphology analysis showed that the microcapsules obtained from O/W emulsions produced by premix membrane emulsification were rounder in shape, without visible cracks on the surface and no vacuoles on the inside. Oxidation stability tests performed on some selected samples indicate that the microcapsules with higher stability are the ones produced with a higher amount of wall material and have less surface oil.     

Optimizing microencapsulation of peanut sprout extract by response surface methodology

This study was carried out to optimize conditions for peanut sprout extract microencapsulation by response surface methodology (RSM). The coating materials of microencapsulation were medium-chain triacylglycerol (MCT) for primary emulsion, and whey protein concentrates (WPC), maltodextrin (MD) and gum Arabic (AG) for secondary emulsion. The yield of microencapsulation of peanut sprout extract was investigated with respect to four variables (ratio of core and coating materials, concentration of primary emulsifier, ratio of W/O emulsion and secondary coating materials and concentration of secondary emulsifier) in RSM. The optimal conditions for microencapsulation of peanut sprout extract were 1:2 as the ratio of core material to coating material, 1.25% (w/v) of primary emulsifier concentration, 1:1.23 as W/O emulsion to secondary coating material, 1.21% (w/v) as secondary emulsifier concentration and 30% (w/w) as WPC concentration for spray drying. In conclusion, the microencapsulation of peanut sprout extract under the optimized conditions by RSM ensures the smaller size (3–7 μm) of microcapsules with the highest yield reaching to 98.74%.     

Formulation and Stability Characterization of Rutin-Loaded Oil-in-Water Emulsions

In this work, formulation and characterization of oil-in-water (O/W) emulsions loaded with rutin were successfully overhead. We investigated the effect of homogenization pressure on the mean droplet size, droplet size distribution, physical stability, and rutin retention of these emulsions. O/W emulsions with a mean droplet size (d _3,2) of about 150 nm and a span of nearly the unit were formulated by microfluidization at the homogenization pressure 20–150 MPa. The O/W emulsion droplets loaded with rutin were physically stable in terms of variations of d _3,2 and span during 30 days of storage in the dark condition at 4 and 25 °C. The creaming velocity was characterized using centrifugal method showing a relative good shelf life. HPLC analysis demonstrated that 71–85% of initial rutin was retained in the fresh O/W emulsions and declined to 22–35% (w/w) for 30-day storage at 25 °C. Antioxidant activity assays confirmed that rutin-loaded emulsion participated in the antioxidant activity after encapsulation similarly to pure rutin. These results indicate that O/W emulsion systems can function as potential delivery systems to enhance bioavailability to encapsulate liposoluble antioxidant rutin for potential applications in the food industry.     

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.     

Protein-stabilized emulsions containing beta-carotene produced by premix membrane emulsification

Protein-stabilized O/W emulsions containing beta-carotene were produced by premix membrane emulsification (ME) using polymeric microfiltration membranes. Bovine serum albumin (BSA) and a whey protein concentrate (WPC) were used as protein emulsifiers while a nonionic small-molecule surfactant, Tween 20, was used both as a control and co-emulsifier. Membrane fouling caused by WPC reduced more significantly transmembrane flux than that by BSA. Mixtures of WPC or BSA with Tween 20 reduced protein membrane fouling and, simultaneously, decreased the mean droplet size. WPC/Tween 20 mixtures enable to produce emulsions with low polydispersion (span < 1) but with a significant membrane fouling while BSA/Tween 20 mixtures led to higher transmembrane fluxes although polydisperse emulsions (span = 7). During storage at 22 and 35 °C, the chemical degradation rate of emulsions with WPC/Tween 20 was slower than those with BSA/Tween 20 whereas Tween 20-stabilized emulsions led to the highest rate of beta-carotene reduction during storage at 35 °C.     

Evaluation of Folic Acid Nano-encapsulation by Double Emulsions

In this study, optimization of spray drying for double emulsions containing pectin-whey protein concentrate (WPC) was investigated for nano-encapsulation of folic acid. Five independent variables including pectin and WPC content, dispersed phase content, pH, surfactant type of Span, and polyglycerol polyricinoleate (PGPR) were considered along with encapsulation efficiency (EE) as the main response. The experiment design was performed by a Taguchi approach. Final double emulsions were formulations containing an internal nano/micro-emulsion composed of a water in oil (W/O) system with folic acid present in the water phase, re-emulsified within an aqueous phase of pectin-WPC complexes. The average of folic acid EE was approximately 88.3 % in a range of 82.3 to 95.0 %. The main effect analysis with a Taguchi technique revealed that the dispersed phase content of double emulsions was the most important factor affecting EE (36 %) and surfactant had the minimum influence (5 %). Also, it was revealed that the most important interaction between independent variables in terms of EE was between WPC and dispersed phase content while pectin-pH had the lowest interaction. Finally, optimum conditions were determined as 1.0 % pectin, 4.0 % WPC, and 15 % dispersed phase, pH = 6, with a PGPR nano-emulsion which resulted in 99.0 % EE of folic acid.     

A Novel Approach to Improving the Quality of Bittern-Solidified Tofu by W/O Controlled-Release Coagulant. 2: Using the Improved Coagulant in Tofu Processing and Product Evaluation

To improve the quality and yield of traditional firm tofu prepared with bittern as coagulant, water-in-oil (W/O) emulsions with bittern solution as the aqueous phase, where the ratio of the bittern solution to the oil phase was 1:1.5 or 1:1 (w/w), and an emulsifier at a concentration of 0.8 or 1.0 wt.% were prepared. The parameters water content, water-holding capacity, yield, texture, and microstructure of the tofu were tested. The results indicated that the bittern W/O emulsions provided satisfactory controlled-release application potential. The use of the W/O emulsions significantly improved tofu’s water content, and the product remained moist for at least 24 h. Moreover, emulsified bittern increased the yield and made the gel network more homogenous and compact compared with the control. As expected, emulsions with an emulsifier concentration of 1.0 wt.% showed slightly better controlled-release capacity than those with 0.8 wt.%.     

阿拉伯树胶-肌原纤维蛋白共建乳状液体系的物理稳定性

研究不同质量分数阿拉伯树胶(arabic gum,AG)对肌原纤维蛋白(myofibrillar protein,MP)为乳化剂的乳化体系稳定性的影响。结果显示,乳化活性和乳化稳定性随着AG质量分数的增加呈先增加后降低的变化趋势。AG质量分数为0.3%时,MP-AG共建乳状液体系表现出最高的物理稳定性,显著地增加了ζ-电势,降低了粒径大小,表现出最低的乳析指数(P0.05)。激光共聚焦显微镜(confocal laser scanning microscopy,CLSM)观察结果表明,与单独以MP为乳化剂的样品相比,添加0.3%AG的乳状液样品液滴颗粒最小,这与粒径大小和分布的结果相一致。通过CLSM进一步观察MP在界面上的吸附行为,结果表明,与未添加AG的乳状液样品相比,添加0.3%AG的MP-AG共建乳状液体系所形成的界面膜更加坚固和致密。总之,AG可以促进蛋白质在油水界面上的吸附作用,提高MP乳化的水包油型乳状液的物理稳定性。     

Determination of Antifungal Effect of Edible Coatings Containing Williopsis saturnus var. saturnus Against Yeast and Mold Growth on Kashar Cheese

One of the most important problems of Kashar cheese producers is mold and yeast spoilage during storage. Williopsis saturnus var. saturnus killer yeast has been reported to have an antagonistic effect on mold and yeast reproduction. In this study, the antifungal effect of a whey protein concentrate (WPC) coating containing W. saturnus was investigated in Kashar cheese. WPC with or without W. saturnus (7 log CFU/g) or W. saturnus without coating was applied on the surface of Kashar cheese samples and stored at 4 °C for 56 days. Microbiological, chemical, physical and sensory properties of cheese samples were assessed. After 56 days of storage, the numbers of lactic acid bacteria were not affected by WPC containing W. saturnus; however, the population of W. saturnus increased by 1 log CFU/g. Application of W. saturnus reduced the growth of other yeasts and molds (P < 0.05). Chemical, physical and sensory properties of all coated cheeses remained unchanged. In a conclusion, use of WPC coatings containing W. saturnus can potentially minimize mold and yeast spoilage of cheese during storage.     

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.     

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.     

基于三种多糖与酪蛋白复配制备W/O/W型乳液及其包封红景天苷效果的研究

为提高红景天苷稳定性及口服吸收效果,本研究以红景天苷为内水相,含聚甘油蓖麻醇酯的菜籽油为油相,分别采用葡聚糖、壳聚糖和大豆多糖混合酪蛋白作为外水相,制备W/O/W型多重乳液。研究了不同浓度的三种多糖对多重乳液的微观结构、粒径、电位、贮藏稳定性、乳化性、包埋率、载药量和体外消化过程的影响。结果显示,相比于酪蛋白对照组、壳聚糖-酪蛋白组和大豆多糖-酪蛋白组,葡聚糖-酪蛋白W/O/W型多重乳液稳定性最好。高浓度的葡聚糖能够明显提升葡聚糖-酪蛋白多重乳液的贮藏稳定性,当葡聚糖添加量为1.2%时,多重乳液平均粒径最小,可达623.03±5.21 nm（P<0.05）;电位绝对值最高（P<0.05）,平均电位为?37.3±0.46 mV;对酪蛋白乳化性质提升最大（P<0.05）;对红景天苷的包埋率最高（P<0.05）,可达92.8%,载药量为162.89±4.21 μg/g。模拟消化研究发现葡聚糖-酪蛋白多重乳液不仅能有效地保护红景天苷,还能够靶向地在模拟肠道内传递和释放,葡聚糖添加量为1.2%的葡聚糖-酪蛋白负载体系的稳定性和控释效果最佳。该研究结果可为红景天苷在食品和医药中的应用提供理论支撑。     

Impact of Milk Protein Type on the Viability and Storage Stability of Microencapsulated Lactobacillus acidophilus NCIMB 701748 Using Spray Drying

Three different milk proteins — skim milk powder (SMP), sodium caseinate (SC) and whey protein concentrate (WPC) — were tested for their ability to stabilize microencapsulated L. acidophilus produced using spray drying. Maltodextrin (MD) was used as the primary wall material in all samples, milk protein as the secondary wall material (7:3 MD/milk protein ratio) and the simple sugars, d-glucose and trehalose were used as tertiary wall materials (8:2:2 MD/protein/sugar ratio) combinations of all wall materials were tested for their ability to enhance the microbial and techno-functional stability of microencapsulated powders. Of the optional secondary wall materials, WPC improved L. acidophilus viability, up to 70 % during drying; SMP enhanced stability by up to 59 % and SC up to 6 %. Lactose and whey protein content enhanced thermoprotection; this is possibly due to their ability to depress the glass transition and melting temperatures and to release antioxidants. The resultant L. acidophilus powders were stored for 90 days at 4 °C, 25 °C and 35 °C and the loss of viability calculated. The highest survival rates were obtained at 4 °C, inactivation rates for storage were dependent on the carrier wall material and the SMP/d-glucose powders had the lowest inactivation rates (0.013 day^?1) whilst the highest was observed for the control containing only MD (0.041 day^?1) and the SC-based system (0.030 day^?1). Further increase in storage temperature (25 °C and 35 °C) was accompanied by increase of the inactivation rates of L. acidophilus that followed Arrhenius kinetics. In general, SMP-based formulations exhibited the highest temperature dependency whilst WPC the lowest. d-Glucose addition improved the storage stability of the probiotic powders although it was accompanied by an increase of the residual moisture, water activity and hygroscopicity, and a reduction of the glass transition temperature in the tested systems.