Development of Trans-free Lipid Systems and their Use in Food Products

Jorge F Toro-Vazquez

• Publisher: Royal Society of Chemistry
• Year: 2022
• Print ISBN: 9781839162206
• eBook ISBN: 9781839166549
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biochemistry
• Index: Biological Sciences

The physical properties associated with the saturated and trans fats obtained through partial hydrogenation of vegetable oils (PHVOs) provide the solid fat content, melting and textural properties that consumers require in food products like butter, margarines, vegetable creams, spreads, and confectionary fats. However, saturated and trans fats increase low density lipoprotein, while trans fats also lower high-density lipoprotein serum levels. These indicators increase the risk of developing cardiovascular disease, type II diabetes, stroke, and have recently been associated with metabolic syndrome. Consequently, regulatory agencies worldwide have passed legislation restricting the addition of PHVOs and their derivatives ( i.e., shortenings) to food products. This has lead research groups worldwide to investigate different mechanisms to provide structural and physical properties to edible, healthy unsaturated oils. The overall objective is to achieve similar functional properties to those provided by PHVOs and shortenings to food products.

This book encompasses the work of leading researchers discussing, from a scientific and technological perspective, the latest and most innovative approaches to structure edible oils without the use of trans fats. Additionally, the authors discuss practical uses and technical limitations associated with the use of "structured edible oils" in different food systems. Appealing to researchers and professionals working in lipid science, food chemistry and fat metabolism, it fills the gap in the literature for a book in this fast-changing field.

CHAPTER 1

Concentrated O/W Emulsions Stabilized by Proteins: A Route to Texturize Vegetal Oils Without Using Trans or Saturated Fats

W. DRIDI^a, R. KAPEL,^b, S. ALBE-SLABI,^b AND F. LEAL-CALDERON^a

^a Université de Bordeaux, CNRS, Bordeaux INP, CBMN UMR 5248, 33600, Pessac, France

^b Laboratoire Réactions et Génie des Procédés, Université de Lorraine, CNRS, LRGP, 54000 Nancy, France
^*Email: [email protected]

1.1 Introduction

Public health and sustainable development objectives induce a pressing need for the substitution of saturated fats. Palm oil (PO) has been widely used owing to its advantageous features: texturizing ability linked to its solid-like behavior at room temperature, chemical stability, and high oil yield per hectare. The demand for PO has increased over recent decades, which has had profound consequences for the environment in terms of deforestation, land tenure, and community conflicts in countries where it is cultivated. This issue has led to the so-called “Roundtable on Sustainable Palm Oil” (RSPO) certification system, whose guidelines are sometimes considered insufficiently restrictive and are not always respected.

The interesting properties of PO are linked to its composition rich in saturated fatty acids (SFAs). Many countries are not PO producers but they produce vegetable oils from rapeseed or sunflower. One alternative to PO consists of submitting vegetable oils to hydrogenation. However, this process may induce the formation of trans double-bonds that have harmful effects on human health. In particular, they have a negative impact on the plasma lipoprotein profile as they increase the level of LDL (Low Density Lipoproteins, “bad cholesterol”) and lower the level of HDL (High Density Lipoproteins, “good cholesterol”). Studies show that a daily intake of trans-fatty acid chains (TFACs) larger than 2% of the total energy intake (TEA) significantly increases the prevalence of cardiovascular diseases, which represent the major proportion of non-communicable diseases (40%), ahead of cancer (27%).¹ The World Health Organization (WHO) recommends limiting consumption of SFAs to 10% and that of TFACs to 2% of the TEA. As a matter of fact, WHO already foresees complete elimination of industrial TFACs.²

In this context, food grade systems based on liquid vegetal oils and exhibiting the rheological properties of soft solids are highly sought after. To achieve this goal, two different strategies can be envisaged. The first one consists of introducing compounds which are partially insoluble in oil. Very often, this involves crystallizing triacyglycerides rich in saturated long chains and aggregating the microcrystals to form fractal structures.³ Other organogel-like systems consist of self-assemblies into long nanotubes that form a 3D entangled network.⁴ The second strategy consists of forming oil-in-water (O/W) concentrated emulsions. For instance, Patel et al.⁵ proposed an emulsion-templated approach for the preparation of oleogels by using a combination of a surface-active and a non-surface-active polysaccharide. The oleogels were prepared via a two-step process: (1) formulation of a concentrated O/W emulsion stabilized with a combination of cellulose derivatives and xanthan gum, and (2) selective evaporation of the continuous water phase to drive network formation. An analogous strategy will be considered in the present study, but using solely proteins to stabilize the emulsions. Our approach aims at conferring viscoelastic properties to liquid oils through the interfaces that oil droplets form with the aqueous phase. Texturizing will result from the emulsification of oil in water by vegetable proteins that adsorb at the oil/water interface, followed by droplet concentration through centrifugation or water evaporation.

At low volume fractions, emulsions comprise spherical droplets and behave like viscous fluids. Owing to droplet deformation, emulsions may be concentrated up to volume fractions much higher than the volume fraction corresponding to the close packing of a dispersion of hard spheres, ϕ*. For randomly monodisperse spheres, ϕ* ≈ 64 vol%. Above ϕ*, the droplets can no longer pack without deforming. Emulsions then become predominantly solid at low deformations and exhibit considerable yield stress. As stated by Princen⁶ and Mason et al.,⁷ the elasticity (solid-like behavior) of concentrated emulsions is due to droplets that have been compressed by the application of an external osmotic pressure, Π. Actually, emulsions minimize their free energy by reducing droplet repulsion at the expense of deforming the droplet interfaces at each contact (films become flat), which creates additional surface area. The osmotic pressure Π is the energy per unit volume required to deform the droplets up to a volume fraction ϕ. Additional excess surface area created by a perturbative strain or stress determines the elastic shear modulus, G′. Although Π and G′ represent different properties, they both depend on the degree of droplet deformation and therefore on ϕ.

In this study, we explored pathways to obtain very viscous fluids and highly elastic pastes by exploiting the intrinsic properties of concentrated emulsions. We used as emulsion stabilizers proteins extracted from by-products of the oil industry, namely press-cakes. These by-products were selected because they are abundant and have a large protein content. It has been established that in emulsions at droplet volume fractions above ϕ*, both the elastic and viscous moduli (G′ and G″) increase as the droplet radius decreases.⁷ Conditions were thus adopted so as to minimize the droplet radius. Dilute emulsions of various average droplet diameters were first fabricated. We used high pressure homogenization coupled with the so-called limited coalescence process, at low protein content, to produce fine emulsions (average diameter <5 μm) with narrow size distributions.⁸ The initially dilute emulsions were concentrated by centrifugation and evaporation. The osmotic compressibility, Π, was measured for two average droplet sizes and variable volume fractions above the random close packing, ϕ*. The dimensionless osmotic compressibility Π(ϕ)/(γ/R), where R is the average droplet diameter and γ is the oil/water interfacial tension, was compared to that obtained in previous studies for equivalent surfactant-stabilized emulsions. Finally, we explored the possibility to fabricate redispersible dry-emulsion powders through a freeze-drying process.

1.2 Experimental

1.2.1 Materials

Rapeseed oil (density = 0.916 g cm⁻³ at 20 °C) was purchased from a local supermarket. All other reagents were from Aldrich. Hexadecane (density = 0.773 g cm⁻³ at 20 °C) was the oil phase in model systems. NaN₃ at a concentration of 0.01 mol L⁻¹ was incorporated in all aqueous phases to prevent bacterial growth. Bradford reagent was used for protein quantification. Sodium dodecyl sulfate (SDS) helped to deflocculate emulsions during droplet size measurements. Different saccharides were probed as wall materials to protect emulsions from coalescence during the lyophilization step: Lactose (C₁₂H₂₂O₁₁), mannitol (C₆H₁₄O₆), and trehalose (C₁₂H₂₂O₁₁).

1.2.2 Sunflower Protein Isolate

All emulsions were fabricated with a sunflower protein (SP) isolate obtained from an industrial sunflower press-cake, made up of about 30% proteins, the two main families of which are globulins and albumins. Isolates contain 40 to 90% of globulins and 10 to 30% of albumins, depending on the variety of sunflower.⁹ The remaining protein fractions are composed of prolamins, glutelins, and free polypeptide segments.

SP extraction was performed using a one liter reactor stirred at 400 rpm. The appropriate amount of cake and a 1 mol L⁻¹ NaCl aqueous phase were added in order to obtain a 1 : 9 w/w (solid/liquid) mixture. A solution at 1 mol L⁻¹ NaOH was used to adjust and maintain the pH at 7. The mixture was processed in the reactor at room temperature, for 30 min. Solid–liquid separation was carried out by centrifugation at 15 000 g (with g being the earth gravity constant), at room temperature for 30 min. The aqueous phase was filtered through pleated cellulose filters (Fisherbrand, France). During this step, sunflower albumins and globulins were extracted as well as other water-soluble compounds (free phenolics, oses, osides, amino acids, and free peptides). These compounds were removed by an ultrafiltration process. This process began with a diafiltration step on an Akta flux^® 6 ultrafiltration pilot (GE Healthcare, USA) coupled with a 3 kDa cut-off, 4800 cm² hollow fiber. First, the liquid extract was concentrated by a 4.2 volume reduction factor, and the retentate was washed with 6 diafiltration volumes (DV) of 0.5 mol L⁻¹ NaCl. Then, the pH was adjusted to 10 using a solution of 1 mol L⁻¹ NaOH, and the retentate was washed additionally with 4 DV of ultrapure water. The final retentate was collected and freeze-dried. The sunflower isolate was analyzed by the Kjeldahl method¹⁰ to determine its protein content. The obtained sample contained 91 wt% of proteins on a dry matter basis.

In order to determine the protein nature, the isolate was analyzed by high pressure liquid chromatography (HPLC, LC20 system from Shimadzu, Japan) and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE). To...

Table of contents

• Cover
• Title
• Copyright
• Contents
• Chapter 1 Concentrated O/W Emulsions Stabilized by Proteins: A Route to Texturize Vegetal Oils Without Using Trans or Saturated Fats
• Chapter 2 Alternative Oil Structuring Techniques: Oil Powders, Double Emulsions and Oil Foams
• Chapter 3 Use of High-intensity Ultrasound to Structure Edible Fats
• Chapter 4 Pulse and Oilseed Protein-based Oil Structuring for Baking Application
• Chapter 5 Physicochemical Properties and Polymorphic Behavior of Tropical Fats: Their Potential and Practical Use in Trans-free Food Systems
• Chapter 6 Edible Oleogels Produced with Fatty Alcohols: The Use of Policosanol as an Oleogelator
• Chapter 7 On the Applicability of the Oryzanol–Sitosterol Structuring System
• Chapter 8 Structuring Vegetable Oils with Monoglycerides and Monoglyceride–Lecithin or Monoglyceride–Ethylcellulose Mixtures
• Chapter 9 Functionality of Natural Waxes in Hybrid Fat Crystal Networks
• Chapter 10 Glycerolysis-structured Lipid Systems
• Chapter 11 Modulating the Rheology of Oleogels to Mimic the Functionality of Commercial Fats
• Chapter 12 Sensory Properties and Aromatics Profile of Edible Oleogels
• Subject Index