François ; Béguin
email: beguin@cnrs-orleans.fr

Roman Mysyk

Vanesa Ruiz

Encarnacion Raymundo

Ricardo Santamaria

Crmd Cnrs

E Raymundo-Piñero

Capacitance Evolution of Electrochemical Capacitors with Tailored Nanoporous Electrodes in Pure and Dissolved Ionic Liquids

Keywords: Adsorption, Cyclic Voltammetry, Electrical Storage Systems, Electrochemical Power Sources, Electrode Activated carbon, ionic liquid, electrolyte, electrochemical capacitor, double-layer capacitance, ion sieving, pore size

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The increasing demand for highly effective energy storage devices has stimulated intensive research efforts on electric double-layer capacitors (EDLCs). In the energy/power spectrum, EDLCs are located between dielectric capacitors and batteries, having higher energy density than capacitors and higher power density than batteries [1,[START_REF] Conway | Electrochemical supercapacitors-scientific fundamentals and technological applications[END_REF]. Ongoing research on EDLCs is in particular connected with a growing interest in electric and hybrid vehicles [START_REF] Mastragostino | [END_REF] where EDLCs are used for providing the peak power required during acceleration.

EDLCs store charge by electrosorption of ions on an active surface, mainly by electrostatic forces without phase transformations in the electrode material. Owing to the high reversibility of electrosorption, EDLCs can withstand a large number of charge/discharge cycles without significant performance fading. Porous carbons have been extensively employed as electrode material for EDLCs due to their low cost, environmental friendliness and established electrode production technologies [4,5,[START_REF] Béguin | Carbons for Electrochemical Energy Storage and Conversion Systems[END_REF]).

Aqueous, non-aqueous and solid polymer electrolytes have mainly been investigated for EDLCs. Organic electrolytes, mostly solutions of tetra-ethylammonium tetra-fluoroborate and other tetra-alkylammonium salts in acetonitrile or propylene carbonate, are predominantly employed in industrial systems: they provide a higher working window (2.7 V) than the aqueous ones (about 1 V) and, correspondingly, a higher energy density.

Room temperature ionic liquids (RTILs), which are liquids exclusively made up of cations and anions, have been probed as electrolytes for EDLCs (see, e.g., [START_REF] Mastragostino | [END_REF][START_REF] Frackowiak | [END_REF]). RTILs have been favored because they should increase both the safety (non-volatile and non-flammable properties) and the working voltage window of a device.

Unfortunately, generally high viscosity and low electrolytic conductivity limit the high-power performance of the devices, especially at low temperature [START_REF] Frackowiak | [END_REF].

Studies on different RTILs showed that the 1-ethyl-3-methylimidazolium cation (EMI) possesses an exceptionally high ionic conductivity as compared with cations containing longer alkyl chains [8]. A variety of anions have been employed in pair with EMI for supercapacitor electrolytes, in particular, bis(trifluoromethylsulfonyl)imide, bis(perfluoroethylsulfonyl)imide, hexafluoroarsenate, hexafluorophosphate, and tetrafluoroborate [9,10].

A pure ionic liquid is also attractive as a convenient model electrolyte for studying the effects of ion size on capacitance [11,12]: the size of a bare ion can be assessed with greater precision as compared to that of a solvated ion in electrolytic solutions. In particular, it was established using a 1-ethyl-3-methylimidazolium-based ionic liquid that the maximum values of capacitance per unit surface area are achieved for carbons with an average pore size of 0.7 nm [12], corresponding closely to the cationic dimension of 0.76 nm. Earlier studies also evidenced a trend between the capacitance and the anion size of ILs dissolved in propylene carbonate, which was also attributed to the ion-sieving effect [13].

In this paper, we present an experimental study of the cation effect on the capacitive response by using a series of salts based on homologous 1-alkyl-3-methylimidazolium cations. We discuss the differences in performance of supercapacitors based on pure and dissolved ionic liquid together with the effect of electrode pore size distribution. We used electrodes from chemically activated carbons of different pore size distribution, which additionally allows assessing the possible effect of ion/pore size compatibility on capacitance.

Experimental

Preparation and characterization of electrode materials

Activated carbons were produced by chemical activation of mesophase pitch PR21 (Mitsubishi Gas Chemical Co.) with potassium hydroxide. Mixtures of KOH and pitch (KOH:pitch ratios of 1:1, 2:1) were ball-milled for 15 min at 350 rpm. They were then heat-treated in a muffle furnace under a nitrogen flow of 200 mL min -1 . The heating and cooling steps were carried out at a ramp of 2.5 °C min -1 with an intermediate 1 h isothermal step at 700°C. Potassium hydroxide was removed from the materials by consecutive treatments with diluted hydrochloric acid and water until neutral pH. The dry materials were ground in a mortar to a particle size less than 0.1 mm and further treated with hydrogen in a tubular furnace as follows: heating/cooling steps at 20 ºC min -1 to 700 ºC under a nitrogen flow of 280 mL min -1 , and a 1 h holding step at 700°C under a mixed nitrogen and hydrogen flow (280 mL min -1 for N 2 + 40 mL min -1 for H 2 ). The resulting nanoporous carbons are referred to as C1-1, C2-1, according to the KOH to pitch ratio in the precursor mixture.

Nitrogen adsorption isotherms were recorded at -195.8°C for relative pressure (P/P 0 ) in the range of 10 -6 to 1, using an Autosorb-1 (Quantachrome) instrument. Preliminarily, the samples were outgassed for 12 h at 300°C. The values of DFT specific surface area are 1214 m 2 g -1 for carbon C1-1 and 2202 m 2 g -1 for carbon C2-1. The pore size distribution (PSD) obtained according to the quenched solid density functional theory (QSDFT) approach [14] is represented in Figure 1. The PSD is widened and shifted to larger pores as the KOH to pitch ratio in the precursor mixture increases. It is also remarkable that the carbon C1-1 does not contains pores over 1 nm. The PSD of the carbon 2-1 presents a main maximum at about 0.6 nm, and the pore size distribution extends up to 2 nm.

Electrolytes

The electrolytes were high purity (>99 %) imidazolium salts from Merck, 1-ethyl-3-methylimidazolium (EMI) trifluoromethanesulfonate (TFMS), 1-butyl-3-methylimidazolium (BMI) trifluoromethanesulfonate and 1-hexyl-3-methylimidazolium (HMI) trifluoromethanesulfonate. They were used either as pure ionic liquids or as the salts dissolved in acetonitrile (0.5 mol L -1 ). Experiments on pure ionic liquids (ILs) were conducted at 60°C as suggested in [11] to decrease the cell resistance. The conductivities of the ionic liquids at 25 0 C are 0.92 S m -1 for EMI TFMS, 0.37 S m -1 for BMI TFMS and 0.25 S m -1 for HMI TFMS.

Electrochemical characterization

The electrode mass was prepared as a mixture of activated carbon with polyvinylidene fluoride binder and conductivity additive (PUREBLACK ® , Superior Graphite, USA). Carbon electrodes were then formed as pellets (10-15 mg) from the electrode mass. Electrochemical tests were conducted on two-electrode cells (without reference electrode) using two identical carbon pellets, titanium current collectors, a porous membrane separator and a Teflon Swagelok ® airtight system. The assembling was carried out in a glove box under argon atmosphere with O 2 and H 2 O content less than 1 ppm. The electrochemical measurements (cyclic voltammetry and galvanostatic charge-discharge cycling) were performed using a VMP multichannel generator (Biologic, France).

The gravimetric capacitance was calculated per electrode from the formula:

C = 2I/(dV/dt)/m ( 1
)
where C is the gravimetric capacitance per electrode, (F g -1 ), I the current, (A), dV/dt is the sweep rate, (V s -1 ), m the mass of active material per electrode, (g).

3 Results and discussion The differences in capacitance for the carbons C1-1 and C2-1 can be clarified based on the analysis of pore size distribution and ions geometry. The maximum possible dimensions of ions can be estimated through direct measurement from software visualization models by probing different conformations and taking into account the van der Waals radii of the terminal atoms [12]. The longest possible dimension of the imidazolium cations (Figure 3) can be evaluated as 0.76 nm, 0.86 nm, 0.95 nm for EMI + , BMI + , HMI + , respectively, the two other dimensions being approximately equal to 0.43 nm and 0.37 nm for any of the cations. The largest possible dimension of the anion can be estimated to be about 0.7 nm, which is smaller than the largest dimension of any of the cations. Charge storage in a two-electrode cell is described by formula (2) for two capacitors in series:

1/C=1/C + + 1/C - ( 2
)
where C is the cell capacitance, C + and C -the respective capacitance values of the positive and negative electrodes. According to this formula, the overall capacitance C is mostly influenced by the lowest value between C + and C -. Literature data on electrosorption on non-porous glassy carbon and gold electrodes reveal that the EMI cation is adsorbed vertically on the electrode surface [15] in a potential range from -1.3 to +0.6 V vs. Ag/Ag + (as evidenced by FTIR on a gold electrode), whereas 1-butyl-3-methylimidazolium adopts a tilted position close to the vertical at positive potentials [16][17][18][19]. Because the cations are bulkier than the anion when entering the porosity almost perpendicularly to the pore walls, we can assume that C + > C -, and consequently the cell capacitance is essentially controlled by the negative electrode.

The values of gravimetric capacitance, C e , for microporous carbons can approximately be governed by the recently-developed formula for an electric wire-in-cylinder capacitor [20,21]:

C e =Aε r ε 0 /[bln(b/a 0 )] (3)
where ε r is relative dielectric constant of the electrolyte, ε 0 the permittivity of vacuum, A the interphasial surface area, b the micropore size, and a 0 the effective size of the counterions. Formula (3) was found to correctly describe the experimental capacitance values of various microporous carbons. The interphasial surface area can be adopted to be the accessible surface area, i.e. the surface area of pores larger than the largest cation dimension [22,23]. Therefore, it appears obvious that a tilted or vertical orientation of the cations with respect to the pore wall would result in different values of accessible surface area for the series of imidazolium cations, because of their differences in the largest dimension. Accordingly, this would give rise to dissimilar values of gravimetric capacitance, i.e. the shorter the alkyl chain, the higher the accessible surface area and, consequently, the higher the gravimetric capacitance.

In fact, the smaller capacitance evolution with C2-1 as compared to C1-1 when the length of the alky chain increases could be explained by the relationship between ion and pore sizes. Indeed, the pore size distribution of the carbon C1-1 does not extend over 1.2 nm, and a very small portion of pores is above ~ 1 nm. Therefore, cations with the largest dimension close to 1 nm, especially HMI and BMI, would have difficulties penetrating the porosity of such carbon if their largest side were close to perpendicular to pore walls (Figure 3). By contrast, for carbon C2-1, the accessible porosity extends up to 2 nm (Figure 1), so ion-sieving becomes less apparent than for carbon C1-1 due to less hindered access of larger cations to porosity. It is also likely that there is no strong effect of dielectric permittivity on the observed differences in capacitance since the same electrolyte should normally possess the same ε r value independently of the electrode material. Since capacitive responses vary strongly in the series of ionic liquids for carbon C1-1 only, such dissimilarity in capacitance evolution is most likely due to the effect of pore size distribution.

A recent study using ionic liquids with the chloride anion [24] and a non-porous glassy carbon electrode has shown the differential capacitance to follow the order HMI < BMI < EMI in ionic liquids, which is attributed to the denser double layer for smaller imidazolium cations (the shorter the alkyl chain length, the closer the approach to the electrode surface). For nanoporous electrodes, our study brings out a similar trend, but for the gravimetric capacitance data of two-electrode cells. Since this trend is much more spectacular for the carbon C1-1, it is heavily strengthened by the effect of pore size distribution of this carbon, which excludes the larger cations.

3.2 Comparison between pure and dissolved ionic liquids.

The most striking and unexpected result of our study is the capacitive behavior of the carbons C1-1 and C2-1 when using ILs solutions in acetonitrile (Figures 2B and2D). As distinct from the case of pure IL electrolytes, dissolved ILs exhibit little or no difference in capacitive response whatever the carbon used. In fact, for the C1-1 carbon (Figure 2B), the capacitance of the dissolved HMI-based system is only slightly smaller than that of the dissolved EMI or BMI-based ones; it is also noteworthy that the voltammograms for the EMI-and BMI-based electrolytes virtually overlap. Another important result is significantly lower capacitance values using pure ILs in comparison to their dissolved salts. However, this can be seen only for the carbon C1-1 (see Figure 4A for the pure or dissolved HMI solution) whose feature is a closer fit of pore and ion sizes. For the carbon C2-1, having from the respective systems using dissolved electrolyte even for the IL having the cation with the longest alkyl chain, i.e. HMI (Figure 4B). At the same time, the voltammograms with pure ILs are more resistive, which arises naturally from their higher resistivity in comparison to their respective solutions (Figure 4).

Hence, the ion-sieving effect is markedly distinguishable with pure ionic liquid electrolytes for the carbon C1-1, but disappears virtually when the same salts are used in dissolved state in a capacitor with the same carbon C1-1.

This suggests that, even for the carbon C1-1, virtually the same surface area A (see formula 2) is accessible for any of the three cations moving out of acetonitrile into the electrode pores, i.e. there is almost no difference in pore accessibility among the cations. This could plausibly arise due to non-rigid alkyl chains being freer to move in solution than in pure ILs. In other words, dissolved cations, especially BMI and HMI, could more readily adopt a geometry that provides no or little difference in cation size before penetrating the pores. As a result, the overall cation size could easily be minimized for the non-rigid cations to fit smaller pores. Thus, in the case of dissolved electrolytes, a larger part of specific surface area would become available for charge storage, which consequently enhances the gravimetric capacitance.

Lower capacitance values with pure ILs in comparison with their dissolved use were observed for phosphoniumbased salts [25], but this study did not focus on the effect of pore size distribution on capacitance, which prevents a detailed comparison with our work. On the other hand, the ion-sieving effect was demonstrated using a series of phosphonium-based ionic liquids [11], but the behavior of dissolved salts was not studied, which also precludes a deeper analysis in comparison with our data.

A distinctive feature of ion-selective electrosorption is a clear kinetic effect, which can be manifested by a stronger decrease in the charge storage rate when there is a good size fit between pores and ions [26][27][28]. In fact, Figure 5 shows that the capacitance values undergo a stronger enhancement at a lower scan rate for pure ILs than for dissolved electrolytes (compare the difference between the voltammograms at 0.2 mV/s and 1 mV/s in Figure 5A and B for the pure HMI-based IL and dissolved IL). It is an additional proof for the stronger ion-sieving effect in pure ionic liquid medium.

In summary, our results show that the use of dissolved ionic liquids is beneficial in terms of gravimetric capacitance due to the likely effect of more flexible cations in solutions, which makes more porosity available to charge storage. We have demonstrated a clear ion-sieving effect in pure ionic liquids, in agreement to other related studies [11,12], but the most important and novel result is a strong difference in capacitive responses between pure and dissolved ionic liquids for ion-sieving carbons. We have also evidenced that the ion-sieving effect, clearly observable in pure ILs, is heavily mitigated for the same salts used in solution, most likely due to somewhat stronger geometrical flexibility of dissolved ions. Furthermore, for the electrode materials showing the ionsieving effect, the gravimetric capacitance values of dissolved salts are higher in comparison to pure ionic liquids. The dissimilarity of capacitance values between pure ionic liquids and dissolved salts in ion-sieving carbons highlights their respective advantages and disadvantages in terms of energy density: whereas purely ionic electrolytes can potentially provide a larger working voltage window, the corresponding dissolved salts can access smaller pores, mostly contributing to higher capacitance values. Thus, this finding should be of use in the optimization of prospective industrial systems using both pure ionic liquids and their respective solutions.

Conclusion

3. 1

 1 Figures 2A and 2C represent the cyclic voltammograms for carbons C1-1 and C2-1, respectively, using the pure ILs. The voltammograms for the carbon C1-1 (Figure2A) demonstrate a decrease in gravimetric capacitance as the cation's alkyl chain increases. For the carbon C2-1, there is a decrease only from EMI to BMI-based electrolyte, whereas the characteristics in BMI and HMI-based media are comparable.

  the carbon C1-1, the capacitance values with the IL-based systems are not quite different

Figure 1 .

 1 Figure 1. QSDFT pore size distribution of the nanoporous carbons C1-1 and C2-1.

Figure 2 .

 2 Figure 2. Cyclic voltammograms at 1 mV s -1 for the EDLCs using the carbons C1-1 (A, B) and C2-1 (C, D). The left-hand side graphs are for the pure ionic liquids, and the right-hand side ones for their solutions in acetonitrile. Numerals indicate: 1-EMI; 2-BMI; 3-HMI.

Figure 3 .

 3 Figure 3. Structure and size of 1-alkyl-3-methylimidazolium cations used in the ionic liquids. The thickness perpendicular to the ion plane direction is 0.37 nm.

Figure 4 .

 4 Figure 4. Comparison between cyclic voltammograms at 1 mV s -1 for the EDLCs using the HMI cation and the carbons C1-1 (A) and C2-1 (B). 1: pure IL; 2: 0.5 mol L -1 solution.

Figure 5 . 1 Figure 3

 513 Figure 5. Cyclic voltammograms for the EDLCs using the carbon C1-1 and the HMI-based pure (A) and dissolved (B) ionic liquid. 1: 1 mV s -1 ; 2: 0.2 mV s -1 .

  Figure 4


Dr Hendrik Jan Smit
email: hsmit@brookes.ac.uk

BSc Emma Keenan

Dr Eva M R Kovacs

Dr Sheila A Wiseman

Harry Petrus

Ferdinand Peters

Dr David J Mela

Peter Rogers

Dr Harry P F Peters

Prof J Peter

PhD Rogers

No efficacy of processed Fabuless™ (Olibra™) in suppressing appetite or food intake

Keywords: Fats, emulsions, energy intake, appetite, satiety response, food manufacture

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Fabuless™ (previously called Olibra™ and Reducal™) is a 42% fat emulsion formulated from palm oil and oat oil fractions, used as a food ingredient and claimed to reduce appetite and food intake. It is produced by Lipid Technology Provider (LTP, Sweden) and marketed for satiety benefits in food applications by DSM (The Netherlands). Initial published research, performed in one laboratory by the same research group, reported significant decreases in energy and macronutrient intakes 4-8h post-treatment when Fabuless™, compared to a control fat, was added to yoghurt [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF], and that these effects were dose-dependent [START_REF] Burns | Dose-response effects of a novel fat emulsion (Olibra TM ) on energy and macronutrient intakes up to 36 h post-consumption[END_REF]. However, no subsequent studies have replicated these initial results. Indeed, a later study by the same group failed to replicate these positive findings [START_REF] Logan | Investigation of the medium-term effects of Olibra™ fat emulsion on food intake in non-obese subjects[END_REF] after either acute or chronic (3-week) intakes. Similarly, in a different laboratory, [START_REF] Diepvens | Short-term effects of a novel fat emulsion on appetite and food intake[END_REF] did not find any overall effects of Fabuless™ on food intake. Because Fabuless™ is a complex structured emulsion, rather than a single chemical entity, it is possible that unspecified differences in the material or its handling could contribute toward inconsistencies in its reported efficacy.

In the studies that showed a significant inhibitory effect of Fabuless™ on food consumption [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF]2002), it is not clear exactly how the active ingredient was added to the test yoghurts, and the amount of processing (i.e., significant mixing or heating) involved. The physical structure of the Fabuless™ emulsion is thought to be critical for its putative functionality within the gastrointestinal tract and it is not clear to what extent normal food processing may affect efficacy. It is therefore also not clear if research carried out under one set of processing conditions can support claims where this ingredient may undergo a different set of conditions (or for that matter, potential changes during product shelf life). Commercial food manufacturing processes, which guarantee food safety, expose ingredients to shear stress (through mixing and homogenisation) and raised temperatures (through pasteurisation etc). The goal of the study presented here was to assess the feasibility of Fabuless™ as a hunger control ingredient in yoghurt-based meal replacement beverages, and to establish the impact of specific production processes on its ability to reduce appetite and food intake.

Materials/Methods

Study Design

Twenty-four healthy volunteers were recruited for the study from the Bristol University campus and its surrounding area through an existing participant database, and through posters displayed in various Departments of Bristol University. Exclusion criteria were: currently dieting to lose weight; getting up and/or having breakfast after 9 A.M. regularly; skipping breakfast, lunch or dinner regularly; self-defined 'picky' eater; simultaneous involvement in other intervention studies, smoker, taking any prescription medication; pregnancy or breastfeeding. In order to minimise expectancy effects, the exact objectives of the study were concealed and the study was therefore presented as investigating 'Effects of a new yoghurt product on mood and hunger'. In addition, subjects were excluded if they scored high for cognitive restraint according to the Dutch Eating Behaviour Questionnaire (DEBQ; van Strien et al., 1986a). The exact exclusion criteria used were (van Strien, personal communication, updated from: van Strien et al., 1986b):

-men with BMI < 27 and DEBQ-restraint score > 2.37; -men with BMI ≥ 27 and DEBQ-restraint score > 3.04; -women with BMI < 26 and DEBQ-restraint score > 3.24; -women with BMI ≥ 26 and DEBQ-restraint score > 3.41.

The study protocol was approved by the relevant Human Research Ethics Committee at the University of Bristol, and participants provided written informed consent at the end of the practice/familiarisation visit. At the very end of the study, they received a full written debriefing including an explanation of the purpose of the study.

Participants were assigned to the three conditions according to a balanced randomised placebocontrolled, double-blind, cross-over design. The study was conducted over two periods of two weeks; however, due to the limited shelf life of the test product, participants 1-12 were tested in week 1-2 and participants 13-24 were tested in week 3-4. The design of the study balanced treatments within these cohorts.

Before testing commenced, subjects attended an introduction/familiarisation session in the laboratory, where they practiced the main visual-analogue scale (VAS) questionnaire of the study (see below) several times, and completed the DEBQ. Height and weight were measured and they were given a 'Drink, Activity & Evening Snack Diary' for additional data collection, with extensive instructions.

Subsequently, participants returned for their three testing days after fasting from 20:00h the previous evening. On test days, participants consumed their treatment (breakfast as meal replacement drink) at 9:00h, their ad lib lunch at 13:00h and their ad lib dinner at 17:00h. Before each ad lib meal, they were reminded to "eat until you feel comfortably full -no more and no less".

The meals selected were intended to be of average liking (not disliked so participants would eat much less than normal and possibly compensate with larger snacks in the evenings; and not overly liked so participants would eat much more than normal). This was explained, as was the food they would receive and they were asked to consider not taking part if they felt the meals were not moderately liked. Additionally, they were asked to keep an activity and drinks diary on the first testing day, which they had to follow as closely as possible on each of the subsequent testing days with the explicitly explained aim of keeping all testing days as identical as possible and thereby keep inter-day variability to an absolute minimum. Exercise was not allowed on a testing day until later that evening, nor were additional evening meals. Participants were asked not to eat anything else during the testing day until the evenings of the testing days, when snacks and alcoholic drinks were allowed, although these were recorded using the same diary. Also, participants were instructed to bring some light reading material to entertain themselves during in-laboratory waiting times, and magazines were also available. Each participant occupied an individual testing booth where distraction was kept to a minimum: they were visually separated; talking amongst participants was prohibited; and mobile phones were handed to the experimenter to avoid any further distractions.

Participants were allowed to leave when all present had finished eating their test meal, although for lunch and dinner, subjects could leave only after the first post-meal questionnaires (30 minutes after the start of the meal; see below) were completed.

At baseline and every 30 minutes post-treatment until after dinner, VAS questionnaires were filled out using a pre-programmed Palm Zire™ 21 handheld Personal Digital Assistant (PDA). VAS questionnaires recorded appetite and mood related feelings (see below). Five of these questionnaires were followed by a 4-point 'physical symptoms' questionnaire, including one immediately premeal, one at 11:00h and one at 15:00h. Additionally, a palatability questionnaire was completed for each of the treatments.

A schematic representation of the various activities can be found below in Figure 1.

INSERT FIGURE 1 HERE

Test Foods

Breakfast (Treatment) The three treatment yogurt-based meal replacement drinks or 'test drinks' (325ml each) contained either 12.5g Fabuless™ (5g fat; added during manufacture, thus 'processed'); 12.5g Fabuless™ (5g fat; added at the end of manufacture, thus 'unprocessed') or 5g control fat (milk fat +corn oil). Additions of Fabuless™ at or below 12.5g has been reported to substantially reduce food intake in the original efficacy studies [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF]2002). In the "processed" condition Fabuless was mixed with all other ingredients at the start of the production process. Subsequent processing steps involved pre-heating to 72°C, homogenisation at 65°C, pasteurisation at 92°C for 5 minutes, cooling to 42°C for 5 hours, pH adjustment to 4.6 and final homogenisation with fruit-based ingredients. In the "unprocessed" condition, Fabuless was added after this final step with minimal mixing, then manually filled into aseptic containers for storage at <8°C. The product description of the test drinks was "A fresh raspberry yoghurt beverage containing vitamins and minerals, with sugars and sweeteners", and contained the following ingredients: Live yoghurt (milk, whey, milk protein); raspberry puree; sucrose; glucose; oligofructose (fibre); vegetable oils; minerals; vitamins; stabiliser (pectin); sweeteners (aspartame, acesulfame K); flavouring; colour (carmine). They were stored at max 8°C to ensure a shelf-life of 14 days. Serving size for all three treatments were 325ml (336g). Energy content was identical, and macronutrient composition was virtually identical between treatments. Fabuless™ containing test drinks (both processed and unprocessed): 266kcal, 15.2g protein (23% of delivered energy), 5.7g fat (19% of delivered energy) and 38g carbohydrate per serving; Control test drinks: 268kcal, 15.4g protein (23% of delivered energy), 5.8g fat (19% of delivered energy) and 39g carbohydrate per serving. The test drinks were manufactured by International Food Network Ltd, Reading, UK.

Lunch This ad lib meal consisted of: 1) A large plate of standardised cheese sandwiches made of 10 slices of bread with 5 slices of medium strength Cheddar cheese (24g each). Sandwiches were cut to the size of the cheese slice. Each slice of bread was buttered with 3.0g of margarine, and sandwiches were divided into four equal smaller triangles before serving; 2) A smaller plate containing one pack (200g) of 'custard creams' biscuits; 3) A clear jug containing 1 litre of noncarbonated water. Total energy content of the meal served was 10531 kJ.

Dinner This ad lib meal consisted of: 1) A large plate containing around 1000g bacon & leek pasta bake, prepared immediately before serving in a microwave oven according to food manufacturer's guidelines; 2) A bowl containing 450g strawberry yoghurt; 3) A clear jug containing 1 litre of noncarbonated water. Total energy content of the meal served was 8844 kJ.

Measures

The measures taken for statistical analysis were:

1)

Energy intake (kJ) at lunch, dinner, and lunch and dinner combined;

2)

Food intake (g) at lunch, dinner, and lunch and dinner combined;

3) Appetite and mood related feelings (100-point VAS), measuring 'Full', 'Hungry', 'Appetite for a snack', 'Thirsty', 'Satiated', 'How much you could eat', 'Energetic' and 'Drained'; 4) Physical symptoms experienced in the past hour (4-point scale, labelled 'not at all', 'mild', 'moderate' and 'severe');

5)

Pleasantness ratings for various sensory aspects of the yoghurt-based meal replacement drink (100mm paper VAS).

Appetite, mood and physical symptom ratings were recorded electronically on a Palm Zire™ PDA.

Statistical Analysis

Statistical analysis was carried out using SAS 8.0. As there were negligible differences between ANOVA and ANCOVA outcomes, estimated means adjusted for baseline differences were not calculated, and overall treatment effects for the VAS and food intake data were eventually analysed using ANOVA with subject, treatment and period as factors. P-values <0.05 were considered statistically significant. Next, 'active' treatments were compared against control using Fisher's Least Significant Difference (LSD) test as reported in the results section. The comparisons (1-tailed t-tests) were corrected for multiple comparisons by using a pooled error term. Frequencies of physical symptoms were compared between treatments using χ 2 .

RESULTS

Participant Characteristics

Twenty-four participants (16F, 8M) were recruited into the study, with an average age of 23.3 years (± 5.3; range 18-43), mean Body Mass Index (BMI) of 22.4 kg/m 2 (± 3.8; range 18.1-37.0) and DEBQ-restraint scores of 2.1 (± 0.6; range 1.2-3.2). Age did not differ significantly between the two sexes, though females showed a predictable trend for higher scores on BMI and dietary restraint (DEBQ restraint scale) compared to males. Baseline characteristics are presented below in Table 1.

INSERT TABLE 1 HERE

Pleasantness and mood ratings, and physical symptoms

No differences in overall product pleasantness (taste, aroma, flavour), mood or adverse physical symptoms were observed between treatments (Ps>0.1).

Appetite and satiety ratings

No treatment effects were found for any appetite measures over various time periods using Area-Under-Curve (AUC) data (Ps>0.5). Additionally, sporadic effects at individual time points, usually immediately pre-meal, are not confirmed by other, related measures (see Figure 2).

INSERT FIGURE 2 HERE

Food and energy intake

Results for food intake at lunch and dinner are shown in Table 2 Lunch Both energy intake (kJ) and food intake (g) at lunch were not significantly affected by either of the Fabuless™ test drinks when compared to control (Ps>0.2).

Dinner

Energy intake at dinner was significantly lower (pasta alone: t(42)=2.79; P=0.004; dinner total: t(42)=2.46; P=0.009) following the unprocessed Fabuless™ test drink compared to control, but not following processed Fabuless™ vs. control (Ps>0.1).

Accordingly, food intake at dinner was also reduced by the unprocessed Fabuless™ test drink compared to control [t(42)=211; P=0.021]. In contrast, neither energy or food intake at dinner were reduced by the processed Fabuless™ test drink compared to control (P=0.2). The results were similar for total (lunch + dinner) energy intake.

INSERT TABLE 2 HERE

DISCUSSION

The present study found that processing of Fabuless™ in a yogurt beverage eliminated the modest, but statistically significant effects on food intake observed when the ingredient was added at the end of manufacture. The significant effects of the unprocessed ingredient were found at eight hours after treatment consumption (dinner), and generally speaking not at four hours post-treatment (lunch).

An ingredient that reliably leads to significant and meaningful reductions in energy intake could be highly beneficial in a weight management context and therefore highly desirable to consumers who want to achieve an ideal weight. Fabuless™ is marketed as such an ingredient based on data obtained from an initial series of studies reported by [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF]2002), which suggested that Fabuless™ could reduce 24h energy intake by up to an impressive 30%. However, subsequent studies by the same and other groups [START_REF] Logan | Investigation of the medium-term effects of Olibra™ fat emulsion on food intake in non-obese subjects[END_REF][START_REF] Diepvens | Short-term effects of a novel fat emulsion on appetite and food intake[END_REF] have not replicated these initial results, and the nature of the ingredient (a structured emulsion) suggests it could be sensitive to common processes used in food production.

The sample size and sensitivity of measures in the current study were appropriate for this type of study design [START_REF] Flint | Reproducibility, power and validity of visual analogue scales in assessment of appetite sensations in single test meal studies[END_REF]; [START_REF] Gregersen | Reproducibility and power of ad libitum energy intake assessed by repeated single meals[END_REF]. However, the magnitude of food intake effects for unprocessed Fabuless™ seen here (~10% energy intake reduction compared to control) was much less than in the [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF]2002) studies (average = 23% reduction). The reasons for this difference are not entirely clear. However, compared to other studies, the magnitude of effect reported by Burns et al. is unusually large, especially considering that anorectic drugs have achieved similar magnitudes of effect. For example, [START_REF] Rogers | Effect of anorexic drugs on food intake and the micro-strucure of eating in human subjects[END_REF] found that fenfluramine reduced food intake by 26%, whilst [START_REF] Rolls | Sibutramine reduces food intake in non-dieting women with obesity[END_REF] showed a maximum energy intake reductive effect of 26%, but only after a 14-day sibutramine course.

Our findings may partially replicate results from [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF]2002) for the unprocessed Fabuless™ used here, but show that thermal and shear processing eliminates the functionality of this food ingredient. Indeed, high-shear mixing and homogenising may destabilise emulsified structures by means of coalescence or flocculation of the dispersed phase, whilst subsequent pasteurising may provide and additional destabilising risk through protein denaturisation [START_REF] Mcclements | Food emulsions: principles, practice and techniques[END_REF]. Note that it is unclear exactly what type or level of processing and storage of Fabuless™ was applied in the 'Burns' trials. Commercial products containing Fabuless™ will typically be exposed to the same or other basic food manufacturing processes as used in the 'processed' treatments in our study. Nevertheless, micrographic images of the products used in this trial (not shown here) indicate a finer dispersion of the lipid fraction in Fabuless™ after processing. However, we are not aware of any structural assessment of Fabuless™ that definitively predicts integrity of its functional efficacy. Without such a test, it is difficult to predict when functionality is retained, other than by empirical clinical testing. Therefore, evidence for the effectiveness of Fabuless™ is only relevant where there is explicit evidence that functionality (and not just a particular structure) is retained in products when processed, stored and prepared as relevant to the market product. While it is certainly possible that different or milder processes may have less effects on efficacy, the effects and limits of process-sensitivity need to be shown.

One remarkable aspect of the study presented in this paper is the general lack of effects on selfreported appetite and satiety measures. Methodologically, the VAS measures were sound as clear effects were found in a subsequent work using the same participants, measures and instructions (not related to the current hypothesis and/or Fabuless™; data not published). Note, however, that [START_REF] Burns | Dose-response effects of a novel fat emulsion (Olibra TM ) on energy and macronutrient intakes up to 36 h post-consumption[END_REF] also reported no effects of Fabuless™ on appetite related ratings, regardless of test conditions.

The proposed mechanism in support of the claims for Fabuless™ has been termed the 'ileal brake', where fat when presented to the distal ileum elicits a strong satiety response (e.g., [START_REF] Lin | Fat absorption is not complete by midgut but is dependent on load of fat[END_REF], an inhibition of upper gastrointestinal functions elicited mainly by the release of GLP-1 in response to the presence of unabsorbed nutrients in the ileum (e.g., [START_REF] Delgado-Aros | Effect of GLP-1 on gastric volume, emptying, maximum volume ingested, and postprandial symptoms in humans[END_REF][START_REF] Brubaker | Prolonged gastrointestinal transit in a patient with a glucagon-like peptide (GLP)-1-and -2-producing neuroendocrine tumor[END_REF][START_REF] Näslund | GLP-1 slows solid gastric emptying and inhibits insulin, glucagon, and PYY release in humans[END_REF][START_REF] Giralt | Glucagonlike peptide-1 (GLP-1) participation in ileal brake induced by intraluminal peptones in rat[END_REF]. Even the infusion of 3g fat into the ileum delayed small intestinal transit (Symersky et al., 2004[START_REF] Maljaars | Ileal brake: A sensible food target for appetite control A review[END_REF]. Although it is unclear how much undigested fat of the 5g fat in the Fabuless™ conditions reaches the ileum, it is unlikely to be more than 3g. Moreover, Fabuless™ is generally added in amounts less than 5g per daily intake equivalent. Finally, although fat is the most commonly researched macronutrient in this respect, also undigested carbohydrates and proteins can induce the ileal brake mechanism [START_REF] Maljaars | Ileal brake: A sensible food target for appetite control A review[END_REF], and the mechanism underlying the ileal brake effect is yet to be established [START_REF] Maljaars | Ileal brake: A sensible food target for appetite control A review[END_REF]. Note also that there is currently no direct evidence in support of the proposed 'targeted delivery' mechanism in Fabuless™ (i.e., how the emulsion passes through the stomach into the ileum without being affected). Although a recent report by Haenni et al. (2009) claims that Fabuless™ leads to a 45 min longer oro-caecal transit time (OCTT), this seems incongruent with the fact that the only significant effects observed in our study were at 8 hours post-ingestion. In addition, Haenni et al. (2009) used an unconventional method of calculating OCTT (using group mean plasma marker values instead of individual marker appearance times; e.g., [START_REF] Staniforth | Comparison of Orocecal Transit Times Assessed by the Lactulose Breath Hydrogen and the Sulfasalazine-Sulfapyridine Methods[END_REF] and [START_REF] Peh | Indirect gastrointestinal transit monitoring and absorption of theophylline[END_REF]), which may have exaggerated individual outlier responses.

In summary, the results of this study show a modest, statistically significant effect only of unprocessed Fabuless™ on food and energy intake, while no significant effects were observed when the active ingredient was added prior to homogenisation and pasteurisation. These findings replicate to some extent the earlier demonstrations of inhibitory effects of Fabuless™ on food and energy intake [START_REF] Burns | Short-term effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-obese subjects[END_REF][START_REF] Burns | The effects of yoghurt containing a novel fat emulsion on energy and macronutrient intakes in non-overweight, overweight and obese subjects[END_REF]2002), although the magnitude of effects were much smaller here, and perhaps more realistic. Moreover, no effects of Fabuless™ on appetite related ratings were found. Given the clear loss of efficacy when Fabuless™ is subjected to normal food processing, functionality after actual processing and storage conditions must be empirically confirmed for any product making claims based on this ingredient.

FIGURE 1 -

 1 FIGURE 1 -Typical testing day schedule

Table 1

 1 Subject characteristics at baseline : BMI -Body Mass Index; DEBQ -Dutch Eating Behavior Questionnaire. Mean ± s.d.; † indicates a marginally significant difference between men and women: 0.1>P>0.05.

		Overall (N=24)	Males (n=8)	Females (n=16)
	Age (years)	23.3 (±5.3)	21.4 (±2.8)	24.2 (±6.1)
	BMI (kg/m2)	22.4 (±3.8) †	24.3 (±5.3)	21.5 (±2.4)
	DEBQ-restraint	2.1 (±0.6) †	1.8 (±0.6)	2.3 (±0.6)

Abbreviations

Acknowledgements

This work was funded by Unilever R&D, Vlaardingen, The Netherlands.

Conflict of Interest