Multiscale structures of lipids in foods as parameters affecting fatty acid bioavailability and lipid metabolism

On a nutritional standpoint, lipids are now being studied beyond their energy content and fatty acid (FA) profiles. Dietary FA are building blocks of a huge diversity of more complex molecules such as triacylglycerols (TAG) and phospholipids (PL), themselves organised in supramolecular structures presenting different thermal behaviours. They are generally embedded in complex food matrixes. Recent reports have revealed that molecular and supramolecular structures of lipids and their liquid or solid state at the body temperature influence both the digestibility and metabolism of dietary FA. The aim of the present review is to highlight recent knowledge on the impact on FA digestion, absorption and metabolism of: (i) the intramolecular structure of TAG; (ii) the nature of the lipid molecules carrying FA; (iii) the supramolecular organization and physical state of lipids in native and formulated food products and (iv) the food matrix. Further work should be accomplished now to obtain a more reliable body of evidence and integrate these data in future dietary recommendations. Additionally, innovative lipid formulations in which the health beneficial effects of either native or recomposed structures of lipids will be taken into account can be foreseen.     

Bioimprinting strategies: From soft lithography to biomimetic sensors and beyond

Imprinting is a straightforward, yet a reliable technique to develop dynamic artificial recognition materials—so called as synthetic antibodies. Surface imprinting strategies such as soft lithography allow biological stereotyping of polymers and sol–gel phases to prepare extremely selective receptor layers, which can be combined with suitable transducer systems to develop high performance biomimetic sensors. This article presents an overview of the remarkable technical advancements in the field of surface bioimprinting with particular emphasis on surface imprinted bioanalyte detection systems and their applications in rapid bioanalysis and biotechnology. Herein, we discuss a variety of surface imprinting strategies including soft lithography, template immobilization, grafting, emulsion polymerization, and others along with their biomimetic sensor applications, merits and demerits. The pioneering research works on surface patterned biosensors are described with selected examples of detecting biological agents ranging from small biomolecules and proteins to living cells and microorganisms.     

Heterogeneous expression and emulsifying activity of class I hydrophobin from <Emphasis Type="Italic">Pholiota nameko</Emphasis>

Hydrophobins secreted by filamentous fungi self-assemble into an amphipathic film at hydrophilic/hydrophobic interfaces. This unique property suggests that the hydrophobins have a high potential for industrial applications. However, the assemblages of class I hydrophobins are highly insoluble, making such commercial applications difficult. To enhance the solubility of class I hydrophobins, we have attempted to express class I hydrophobin PNH1 from Pholiota nameko fused with glutathione S-transferase (GST) in Escherichia coli. The GST–PNH1 was effectively isolated from the soluble fraction of transformed E. coli, and subsequent analysis revealed that the purified GST–PNH1 had almost the same emulsifying activity as PNH1.     

Detection of radicals in single droplets of oil-in-water emulsions with the lipophilic fluorescent probe BODIPY665/676 and confocal laser scanning microscopy

Lipid oxidation is a widespread phenomenon in foods and other systems of biological origin. Detection methods for early stages of lipid oxidation are in demand to understand the progress of oxidation in space and time. The fluorescence spectrum of the nonpolar fluorescent probe BODIPY^665/676 changes upon reacting with peroxyl radicals originating from 2,2′-azobis(2,4-dimethyl)valeronitrile and tert-butoxyl radicals generated from di-tert-butylperoxide. The excitation wavelength of the main peak of BODIPY^665/676 was 675 nm in the fluorometer, and 670 nm under the microscope, and the optimum excitation wavelength for the secondary peak of BODIPY^665/676 was 580 nm. Advantages of using BODIPY^665/676 are fewer problems with autofluorescence and the possibility of combining several fluorescent probes that are excited and emitted at lower wavelengths. However, because of the spectrum of the probe, specific lasers and detectors are needed for optimal imaging under the microscope. Furthermore, BODIPY^665/676 is resistant to photobleaching at both excitation wavelengths, 670 and 580 nm. In diffusion studies, BODIPY^665/676 is highly lipophilic, remaining in the lipid phase and not diffusing into the aqueous phase or between lipid droplets.     

两株假单胞菌对烃的作用及其协同效应

研究了两株假单胞菌K80-A、K80-B对大港油田官69原油的作用效果。实验证明,能产生乳化因子和假溶因子的K80-B菌株对原油粘度的降低率为51.6％、凝固点降低2℃;而只产生表面活性剂的K80-A菌株对同一原油的作用效果分别为43.5％和3℃。当两菌株以等比例混合共同作用原油时,以上指标均有明显提高。说明两菌株具有协同效应。矿场试验证明了混合菌种的优势。     

Rheological Behavior of Food Emulsions Mixed with Saliva: Effect of Oil Content, Salivary Protein Content, and Saliva Type

In this paper, we studied the effect of saliva on the rheological properties of β-lactoglobulin- and lysozyme-stabilized emulsions, prepared at pH = 6.7 in relation to variation of emulsions- and saliva-related parameters. The effect of oil–volume fraction (2.5% w/w to 10% w/w), salivary protein concentration (0.1 to 0.8 mg ml⁻¹), and the use of both stimulated and unstimulated saliva was investigated. Viscosity and storage modulus were measured before (η _emul and G′_emul, respectively) and after addition of saliva (η _mix and G′_mix). To better estimate the changes due to saliva-induced flocculation of the emulsions, the ratios η _mix/η _emul, G′_mix/G′_emul were calculated. In addition, tan δ (=the ratio of the loss and storage moduli) was investigated to evaluate the viscoelastic behavior of the emulsion/saliva mixtures. Increasing the oil–volume fraction and salivary protein concentration resulted in an increase in η _mix/η _emul and G′_mix/G′_emul, while a decrease in tan δ of the emulsion/saliva mixtures is occurring. When compared with unstimulated saliva, mixing β-lactoglobulin-stabilized emulsions with stimulated saliva led to a reduction in η _mix/η _emul and G′_mix/G′_emul, and an augment of tan δ at all measured deformations. In case of lysozyme-stabilized emulsions, the use of stimulated saliva increased G′_mix/G′_emul for γ < 3 when compared to unstimulated saliva. The effect of stimulated saliva on the η _mix/η _emul and tan δ in this mixture is similar to that of unstimulated saliva. These results indicate that the influence of stimulated saliva on the rheological parameters of emulsion/saliva mixtures largely depends on the type of emulsions. To conclude, our findings demonstrate that the rheological behavior of emulsions upon mixing with saliva is greatly affected by both saliva and emulsion properties.     

Lipase-catalysed hydrolysis of short-chain substrates in solution and in emulsion: a kinetic study

We have studied the enzymatic hydrolysis of solutions and emulsions of vinyl propionate, vinyl butyrate and tripropionin by lipases of various origin and specificity. Kinetic studies of the hydrolysis of short-chain substrates by microbial triacylglycerol lipases from Rhizopus oryzae, Mucor miehei, Candida rugosa, Candida antarctica A and by (phospho)lipase from guinea-pig pancreas show that these lipolytic enzymes follow the Michaelis–Menten model. Surprisingly, the activity against solutions of tripropionin and vinyl esters ranges from 70% to 90% of that determined against emulsions. In contrast, a non-hyperbolic (sigmoidal) dependence of enzyme activity on ester concentration is found with human pancreatic lipase, triacylglycerol lipase from Humicola lanuginosa (Thermomyces lanuginosa) and partial acylglycerol lipase from Penicillium camembertii and the same substrates. In all cases, no abrupt jump in activity (interfacial activation) is observed at substrate concentration corresponding to the solubility limit of the esters. Maximal lipolytic activity is always obtained in the presence of emulsified ester. Despite progress in the understanding of structure–function of lipases, interpretation of the mode of action of lipases active against solutions of short-chain substrates remains difficult. Actually, it is not known whether these enzymes, which possess a lid structure, are in open or/and closed conformation in the bulk phase and whether the opening of the lid that gives access to the catalytic triad is triggered by interaction of the enzyme molecule with monomeric substrates or/and multimolecular aggregates (micelles) both present in the bulk phase. From the comparison of the behaviour of lipases used in this study which, in some cases, follow the Michaelis–Menten model and, in others, deviate from classical kinetics, it appears that the activity of classical lipases against soluble short-chain vinyl esters and tripropionin depends not only on specific interaction with single substrate molecules at the catalytic site of the enzyme but also on physico-chemical parameters related to the state of association of the substrate dispersed in the aqueous phase. It is assumed that the interaction of lipase with soluble multimolecular aggregates of tripropionin or short-chain vinyl esters or the formation of enzyme–substrate mixed micelles with ester bound to lipase, might represent a crucial step that triggers the structural transition to the open enzyme conformation by displacement of the lid.     

Comparative study of the product components of lipid oxidation in aqueous and organic systems

Ethyl esters and phosphatidylcholines (PCs) of polyunsaturated fatty acids (PUFAs) were oxidized in organic solvents, aqueous emulsions, and liposomes in the presence of a radical inducer. Oxidation products and the positional distribution of monohydroperoxide (MHP) were determined by gas chromatography-mass spectrometry (GC-MS) analysis. The total amount of the oxidation products, of PUFA ethyl esters and PCs in organic solvents, increased with an increase in the number of bis-allylic positions. However, the opposite results were obtained in an aqueous emulsion and liposomes. The distribution pattern of MHPs obtained from oxidation of the linolate and alpha-linolenate showed little difference between a chloroform solution and an aqueous emulsion or liposomes. However, there were differences between these systems with the arachidonate, the icosapentaenoate, and docosahexaenoate. These results may be due to the different rate of hydrogen abstraction from bis-allylic positions in the fatty acid moieties, and/or 1,3-cyclization of hydroperoxides in the systems.     

Dynamic changes in size distribution of emulsion droplets during ethyl acetate-based microencapsulation process

This study investigated the dynamic effect of the emulsification process on emulsion droplet size in manufacturing microspheres using ethyl acetate as an organic solvent. A dispersed phase consisting of poly(lactide-co-glycolide) and ethyl acetate was emulsified in a poly(vinyl alcohol) aqueous solution for a predetermined time ranging from 2 to 9, 16, 23, 30, 40, 50, or 60 minutes. Ethyl acetate was then quickly extracted to transform emulsion droplets into solidified microspheres, and their size distribution was determined. This experimental design allowed quantification of the size distribution of emulsion droplets over the course of emulsification. When emulsification time was extended from 2 to 60 minutes, the emulsion droplets decreased in size from 98.1 to 50.3 microm and their surface area increased from 0.07 to 0.29 m2/g. Overall, prolonging emulsification time up to 60 minutes resulted in the progressive evolution of smaller emulsion droplets (1-60 microm) and the simultaneous disappearance of larger ones (> 81 microm). Increases in the total number of microspheres and their surface area were caused mainly by continuous fragmentation of emulsion droplets before ethyl acetate extraction. The increase in the smaller microsphere population might also be due in part to shrinkage of microspheres. These results show that the onset of ethyl acetate extraction influenced the kinetics of the breakup and formation of emulsion droplets, thereby affecting to a great extent the size distribution of microspheres.     

Gum cordia effectively enhances foliage adhesion of neem oil and increases its efficacy against aphids (Homoptera: Aphididae)

The efficiency of pesticides is greatly affected by their ability to adhere and retain on foliage surface. Neem oil, though a very well-known source of many biologically active pesticidal compounds, is very sensitive to environmental parameters, such as UV light. Also, due to volatilization, it is lost in environment and hence fail to reach target and show activity. In this study we attempted to stabilize neem oil emulsion and increase its retention on foliage surface by adding varying concentration of gum cordia. Gum cordia is an anionic polysaccharide derived from Cordia myxa fruits with strong adhesion and emulsification properties. The lethal concentration (LC₅₀) of the final formulations were also determined against aphid species Myzus persicae and Schizaphis graminum. Adhesion was found to be dependent on the concentration of gum cordia as well as type of crop. Increasing gum cordia in neem oil formulations resulted in increase in adhesion of the spray on the leaf surfaces and up to 6 times higher adhesion was observed with 0.5% gum cordia on mustard leaf compared to control. The LC₅₀ decreased with increasing gum cordia concentration. The LC₅₀ values of neem oil sprayed on mustard, spinach, and wheat leaves with 0.5% gum cordia were 0.205, 0.715, and 2.074% respectively while for neem oil control spray (with no gum cordia) LC₅₀ values were 1.833, 2.112, and 4.992% respectively for the above tested leaves. Presence of greater than 0.125% gum cordia in neem formulations provided the barrier against UV irradiation.