W emulsions: A rheological and physical study

Accepted Manuscript Cornstarch nanocrystals as a potential fat replacer in reduced fat O/W emulsions: A rheological and physical study Fatemeh Javidi, Seyed M.A. Razavi, Asad Mohammad Amini PII:

S0268-005X(18)31698-9

DOI:

https://doi.org/10.1016/j.foodhyd.2018.12.003

Reference:

FOOHYD 4807

To appear in:

Food Hydrocolloids

Received Date: 30 August 2018 Revised Date:

28 November 2018

Accepted Date: 3 December 2018

Please cite this article as: Javidi, F., Razavi, S.M.A., Mohammad Amini, A., Cornstarch nanocrystals as a potential fat replacer in reduced fat O/W emulsions: A rheological and physical study, Food Hydrocolloids (2019), doi: https://doi.org/10.1016/j.foodhyd.2018.12.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Cornstarch nanocrystals as a potential fat replacer in reduced fat O/W

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emulsions: A rheological and physical study

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Fatemeh Javidi a, Seyed M. A. Razavi a,∗∗, Asad Mohammad Amini b

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Food Hydrocolloids Research Center, Department of Food Science and Technology, Ferdowsi

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b

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University of Mashhad, PO Box: 91775-1163, Mashhad, Iran

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Department of Food Science and Technology, University of Kurdistan, PO Box: 66177-15175, Sanandaj, Iran

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Abstract

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The objective of this study was to evaluate cornstarch nanocrystals (CSNC) suspensions (10, 12

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and 14%) as a fat replacer in reduced fat emulsions (25% fat reduced: 25FR, 50% fat reduced:

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50FR and 75%fat reduced: 75FR). Atomic force microscopy (AFM) showed rounded edge

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platelet-like particles with size around 10-150 nm. Sulfate content and zeta potential of CSNC

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were 0.21% and -34.6 mV, respectively. Nanocrystals crystallinity (36.8%) was higher than the

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source starch (25.7%). Rheological and physical properties of reduced fat emulsions were

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compared to full-fat emulsion (control, 80% fat). All the emulsions indicated good homogeneity

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(PDI= 0.21-0.29). There was no significant difference between the Z-average of the control and

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some samples (25FR with 14% CSNC, 50FR with 12% CSNC and 75FR with 10-12% CSNC).

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The reduced fat emulsions showed higher absolute zeta potential values (33.2-39.4 mV) than

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control (31.9 mV), resulting from the negatively charged surface of CSNC. Although the full-fat

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emulsion revealed the highest whiteness index (99.27), no significant changes were observed at

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∗

Correspondent email: [email protected]

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the low levels of fat reduction and CSNC substitution. On the basis of dynamic rheological

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properties, the emulsions indicated a more solid like behavior as a result of fat reduction and

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CSNC addition, related to smaller droplet size and more negative charges. The reduced fat

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samples had more spreadability than the control. The results indicated a probable formation of

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nanocrystal network in the continuous phase, which trapped the oil droplets and prevented

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creaming after 6-month storage.

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Keywords: Emulsion; Fat replacer; Rheology; Stability; Starch nanocrystal.

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1. Introduction

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Food emulsions are comprised of two immiscible ingredients (oil and water), which should be

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stabilized by adding proper compounds to ensure product quality. In this regard, amphiphilic

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compounds (emulsifiers) are able to improve emulsion stability by forming a thin layer around

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the dispersed phase and hindering their aggregation. Conventionally, emulsions are classified as

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either oil dispersed in an aqueous phase (O/W), or water dispersed in oil (W/O). Oil in water

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emulsions are the most common emulsions in food products, such as mayonnaise. The oil

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content of traditional mayonnaise is about 70-80% (wt%); hence, it is considered as a high-fat

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food (McClements, 2002; Depree and Savage, 2001; Zhao et al., 2002; Chang and McClements,

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2014).

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On the other hand, it is believed that the amount of fat consumed is directly related to several

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chronic diseases, such as obesity, diabetes, cardiovascular diseases and cancer. Therefore, the

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food safety authorities have drawn attention to developing fat reduced products. However, as an

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important food ingredient, fat affects the overall properties of food emulsions such as

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appearance, flavor, mouthfeel, texture, and rheology (Taylor and Linforth, 1996; Chanamai and

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McClements, 2000; McClements, 2002; Derkach, 2009; Tadros, 2010). Thus, functional

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ingredients with less energy content than fat are commonly utilized to minimize the negative

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effects of fat reduction on emulsion quality. There are some published papers about the use of

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food hydrocolloids (such as starches, gums and proteins) in reduced fat emulsions (Bortnowska

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and Tokarczyk, 2009; Mun et al., 2009; Chung et al., 2013; Teklehaimanot et al., 2013;

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Bortnowska et al., 2014; Li et al., 2014; Roman et al., 2015). It should be stressed that the ability

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of hydrocolloids to replace some or all of fat-related characteristics depends on their molecular

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characteristics (e.g., molar mass, conformation, charge, hydrophobicity, and concentration) and

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their influence on bulk physicochemical properties (e.g., thickening, gelling, stability and light

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scattering). Modified starches are valuable natural ingredients in reduced fat foods because of

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their abundance, biocompatibility, biodegradability, and nontoxicity as well as their low cost.

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Additionally, these ingredients show specific functional properties obtained by different methods

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of modification (Thaiudom and Khantarat, 2011; Chung et al., 2013; Teklehaimanot et al., 2013;

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Román et al., 2015). With regard to reduced fat products, starch particle size plays an important

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role in forming stable systems. Small-granule starch about 2 µm in diameter, or similar in size to

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the lipid micelle can be used to mimic smooth texture and fat-like mouthfeel (Jane et al., 1992;

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Ma et al., 2006). A number of important changes occur with decreasing starch particle size to

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nanometer scale including specific surface area, total surface energy and an increase in available

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reactive sites. Chemical depolymerization (e.g., acid or enzymatic hydrolysis) is therefore one of

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the most common modifications of starches useful for replacing fat (Ma et al., 2006; Chaudhry et

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al., 2010; Wang et al., 2013; Dufresne, 2015; Kim et al., 2015). Also, esterification prevents or

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minimizes the association of amylopectin branches as a result of introducing hydrophobic,

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cationic, or anionic groups (Shresth and Halley, 2014). It is expected that starch nanocrystals

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produced by sulfuric acid hydrolysis may be a promising candidate for fat replacement in O/W

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emulsion, because it not only is an anionic nanosized material but also has the ability to increase

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the viscosity of aqueous dispersions (Kim et al., 2015). Although some researchers have assessed

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feasibility of micronized cornstarch as fat replacer in emulsion foods (Ma et al., 2006; Wang et

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al., 2013), and stabilizing potential of acid hydrolyzed starch nanocrystals in O/W emulsions (Li

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et al., 2012; Li et al., 2014), there has been no study on the application of cornstarch nanocrystals

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(CSNC) in fat-reduced emulsions. In this regard, the aim of the present study was to evaluate the

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effects of CSNC suspension at different concentrations (10, 12 and 14%) as fat replacer on

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rheological and physical properties of O/W model emulsions with 25, 50 and 75% fat reduction.

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2. Materials and Methods

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2.1. Materials

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Cornstarch was supplied by Sigma (St. Louis, MO, USA). Sulfuric acid and Tween 80 were

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purchased from Merck (Darmstadt, Germany). Sunflower oil (Ladan Company, Tehran, Iran)

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was obtained from a local market and used without further purification. The deionized water was

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used in all experiments.

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2.2. Preparation of cornstarch nanocrystals

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Dispersions of cornstarch with 40% (wt%) concentration were prepared in 3.16 M sulfuric acid

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solution and stirred at a constant speed (250 rpm) at 40ᵒC for 5 days, according to Angellier et al.

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(2004). Then, the suspensions were washed successively with distilled water until neutrality. The

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final precipitate was dried using an air oven dryer at 25oC, milled to a fine powder and placed in

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air-tight containers before performing the experiments.

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2.3. Preparation of emulsions

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To obtain nanocrystal suspensions at selected concentrations (10, 12 and 14 wt% CSNC), the

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required amounts of the nanocrystal and deionized water were mixed and homogenized (Ultra

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Turrax T25D IKA, Germany) at 12000 rpm for 5 min. Full-fat emulsion regarded as control

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hereinafter included 80% oil, while 25FR, 50FR and 75FR emulsions were prepared with 25, 50

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and 75 wt% fat substitution based on a full-fat sample, respectively (Table 1). The emulsion

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samples were prepared in three steps; first, the CSNC suspension was taken into a glass beaker

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and mixed with Tween 80 (1%) and required amount of deionized water, and then stirred for 5

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min. In the second step, the proper amount of sunflower oil was added and stirred for another 10

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min to achieve a uniform mixture. In the third step, the mixture was homogenized at 12000 rpm

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for 5 min.

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2.4. X-ray diffraction (XRD)

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XRD pattern of CSNC was recorded using X-ray diffraction (XRD, GNR. Co, Explorer)

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operating at 40 kV and 30 mA with Cu Kα radiation (λ= 1.54ºA). The scans were performed in

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the diffraction angle (2θ) range of 4-40° at a step size of 0.04°. Relative crystallinity was

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calculated based on the method described by Mohammad Amini and Razavi (2016).

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2.5. Particle size and zeta potential measurements

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Mean particle size of nanocrystals and droplet size of emulsions were assessed at 25ᵒC using a

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Vasco-3 particle size analyzer (Cordouan Technologies, France) based on cumulants method and

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Stokes-Einstein equation. Also, the polydispersity index (PDI) was calculated by the following

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equation: PDI= (particle size standard deviation /mean particle size) ^2. According to

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microelectrophoresis technique, zeta potential of CSNC and emulsions were determined using a

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Zeta Compact zetameter (CAD Instruments, France) at 25ᵒC and pH 7.0 ± 0.1 on the basis of

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Smoluckowski equation. The samples were diluted prior to making particle size and zeta

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potential with distilled water using a dilution factor of 1:50 sample-to-water.

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2.6. CHNS elemental analysis

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The starch nanocrystal powder were loaded into a specific tube and sulfate content of

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nanocrystals

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Analyser systeme GmbH, Hanau, Germany). This equipment worked according to the principle

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of catalytic tube combustion in an oxygenated CO2 atmosphere and high temperatures which

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helium served as flushing and carrier gas. The desired elements (carbon, hydrogen, nitrogen, and

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sulfate) were determined with the help of specific adsorption columns and a thermal conductivity

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detector.

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an elemental analyzer (Vario EL III, Elementar

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was

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2.7. Atomic force microscopy (AFM)

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The AFM imaging was carried out by an Atomic Force Microscope (Ara Research Company,

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Iran). The CSNC samples were diluted with distilled water to 2.5µL mL-1, and then dripped onto

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a cleaved mica and air-dried before imaging. A silicone tip probe with tip curvature less than 10

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nm was used.

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2.8. Color assessment

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The color measurement of the emulsions was performed using a calibrated image processing

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system as follows. The samples were scanned using a Color Page HR6X Slim scanner (Genius,

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Taiwan) in RGB color space with 24bit color depth at 200 dpi optical resolution. The images

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were then cropped to 500 × 500 pixels and converted to CIELAB color space. The

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corresponding parameters (L*, a*, b*) were extracted using ImageJ software (National Institute

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of Health, USA), then whiteness index of the emulsions was calculated as:

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WI = 100 − [ 100 − L∗

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2.9. Rheological measurements

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Rheological experiments were performed on the emulsions using a Physica MCR 301 rheometer

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(Anton Paar, Austria) equipped with a parallel plate geometry (5 cm diameter, 0.1 mm gap size).

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The temperature was regulated at 25ᵒC and maintained precisely (±0.01◦C) during the

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experiments using a Peltier-plate system and a Physica circulating water-bath. To prevent sample

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evaporation, a hood accessory was used along with a thin layer of low viscosity silicone oil

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around the edges of the sample. A rest period of 5 min was given to the samples before each

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experiment.

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2.9.1. Stress sweep test

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Stress sweep test was carried out at the shear stress range of 0.01-100 Pa and constant frequency

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(1 Hz) to determine the linear viscoelastic region (LVE) and some rheological parameters

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including elastic modulus (G′LVE, Pa), viscous modulus (G″LVE, Pa), loss tangent (Tan δLVE), the

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limiting value of stress (τy or dynamic yield stress, Pa) at the LVE range, viscoelastic modulus at

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flow point (Gf: G′=G″, Pa), and the slope (s) of the loss tangent at the nonlinear viscoelastic (n-

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LVE) range (Tan δs(n-LVE)) which was considered as an indicator of spreadability index (SI).

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Spreadability corresponding to the rate of change in the elastic to viscous behavior, starts from

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the yield point.

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2.9.2. Frequency sweep test

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The frequency dependence was probed from frequencies of 0.01 to 10 Hz at constant amplitude

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(0.2 Pa). The viscoelastic properties of the samples as a function of frequency were characterized

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by the elastic modulus (G′, Pa), viscous modulus (G″, Pa), loss tangent (Tan δ) and complex

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viscosity (η*). The G' and G" were modeled as a power function using the following equations:

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×

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(2)

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Where n', n" (-), and K', K" (Pa.sn', Pa.sn'') are slopes and intercepts, respectively. Furthermore,

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the Bohlin’s parameters were assessed from the next equation:

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=

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∗

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(3)

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Where z (-) is coordination number and A (Pa.s1/z) is proportional coefficient (Bortnowska et al.,

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2014).

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2.10. Microscopy

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Optical micrographs of the emulsions were captured by an Olympus BX 41 optical microscope

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fitted with a digital camera (Olympus, DP 12). The samples were placed directly in a cavity

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microscope slide and covered with a coverslip. Micrographs of the emulsions were taken at 1000

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× magnification.

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2.11. Emulsion stability to creaming

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Seven milliliters of freshly prepared emulsions were poured into glass tubes and tightly sealed to

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prevent evaporation, then stored at 4°C for a period of 6 months. The instability of emulsions due

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to creaming was monitored visually by measuring the serum layer separated over the storage

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period, as follows: !" #$ $%&' % =

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%ℎ ℎ &*ℎ% +, - $" .$/ × 100 %ℎ %+%$. ℎ &*ℎ% +, "!. &+'

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2.12. Statistical analysis

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Data were analyzed using a two-way analysis of variance (ANOVA) and a Fisher's LSD for a

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statistical significance (p≤0.05) using Minitab statistical software (version 18, Minitab Inc, State

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College, PA). All experiments were done at least in triplicate and the data were presented as

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mean of replications.

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3. Results and discussion

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3.1. Cornstarch nanocrystal characterization

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The AFM image of cornstarch nanocrystals (Fig. 1) showed particles with size around 10-150

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nm can be achieved in the shape of round edge platelet-like particles. This result was in 9

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accordance with other reports (LeCorre et al., 2010; Mohammad Amini and Razavi, 2016). The

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resulting nanocrystals appeared to be aptly described as the building blocks of crystalline

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lamellae of granule, because the diameter of amylopectin blocklets vary in the range of 20-500

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nm depending on the botanical origin of starch and location in granule; specifically in the range

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of 10-30 nm for normal cornstarch (Kim et al., 2012; Mohammad Amini and Razavi, 2016), as

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reported by Baker et al. (2001). In addition, the number average particle size of CSNC was 48

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nm as determined by dynamic light scattering (DLS) method. This observation was comparable

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to the results of Mohammad Amini and Razavi (2016), who produced cornstarch nanocrystals by

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sulfuric acid hydrolysis with ultrasound treatment. They used LSD method to evaluate the

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particle size and reported that the size of sample treated for 45 min in 3.16 M acid at 40°C was

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82.9 nm. In addition, the mean particle size of normal maize starch nanocrystals determined by

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transmission electron microscope (TEM) was 41 nm in another study (Kim et al., 2012).

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Based on the results, the sulfate content of CSNC was 0.21%, which was higher than the value

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reported by others (Angellier et al., 2004; Romdhane et al., 2015) for waxy maize starch

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nanocrystals. In the current study, the ratio of acid sulfuric to amylopectin content was more than

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that of the research investigated by Romdhane et al. (2015). It has been reported that more

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sulfate groups are created at surface of starch nanocrystals by using a higher concentration of

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acid sulfuric for hydrolysis (LeCorre et al., 2012). Our results may also be related to the

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hydrolysis conditions (time, temperature) different from those of another work (Angellier et al.,

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2004). LeCorre et al. (2012) also produced waxy maize starch nanocrystals under different

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conditions (different temperatures, acid concentrations, time, and starch concentrations) and

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stated that optimum sulfate content was in the range of 0.14-0.53% in which particles were better

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individualized. In addition, the surface charge of CSNC was -34.6 mV as determined by zeta

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potential, which was in accordance with the reported values (-18.4 to -31.9 mV) for cornstarch

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nanocrystals produced at similar conditions (Mohammad amini and Razavi, 2016). The results

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shown in Fig. 2 clearly indicated the typical A-type X-ray pattern with five characteristic peaks

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at 2θ of 15.0◦, 17.0◦, 18.0◦, 20.0◦ and 23.0◦. As it was expected, the height of these peaks

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increased as the amorphous parts were removed by acid hydrolysis. The calculated values of

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relative crystallinity were 25.7% and 36.8% for native cornstarch and CSNC, respectively. In

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accordance with the present results, cornstarch nanocrystals prepared by Mohammad Amini and

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Razavi (2016) under similar hydrolysis conditions (3.16 M acid, 15% starch concentration,

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40°C), showed a crystallinity of 36.6%.

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3.2. Droplet size of the emulsions

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Analysis by two- way ANOVA showed that there were no significant effects of fat replacement

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level, CSNC concentration and their interaction on the droplet size (p<0.05). According to the

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results of droplet size analysis (Table 2), fat reduction resulted in a decrease in the Z-average

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diameter of the droplets. It probably occurred because, on the one hand, water is necessary to

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provide a fluid environment in which starch molecules hydrate and form gel (Choi and Kerr,

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2003) and on the other hand, the presence of lipids in starch systems decreases water binding

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capacity of starch (Kaur et al., 2011; Quiroga Ledezma, 2018). Therefore, as fat content

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decreased, the ability of starch nanocrystals to bind water increased and consequently viscosity

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of the aqueous phase enhanced. The observation may also be attributed to the fact that there was

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more emulsifier (Tween 80) available to cover the oil-water interfaces and thus to protect the oil

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droplets from aggregation due to higher ratio of emulsifier (Tween 80): oil resulting from fat

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reduction. In addition, a higher concentration of CSNC contributed to the droplet size reduction

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owing to the higher viscosity of the continuous phase surrounding the oil droplets and restricting

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their mobility. Moving oil droplets toward each other and coming into close proximity can lead

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to the droplet aggregation and consequently larger droplets. In quiescent emulsions, droplet-

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droplet encounters and their collision frequency are mainly a result of their Brownian motion,

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which can be reduced by increasing the viscosity of the continuous phase (Mun et al., 2009;

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Depree and Savage, 2001; McClements, 2015). Thickening and gelling agents e.g. biopolymers

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are considered as texture modifiers that are commonly used in O/W emulsions to provide

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desirable textural and mouthfeel characteristics, to retard the droplet movement and to improve

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emulsion stability. These functions can be related to the highly extended molecular conformation

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of biopolymers in solution and their ability to associate with each other through intermolecular

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cross-links. In addition, electrostatic repulsion due to homo-charges results in the formation of

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the fully extended and interpenetrated chains and consequently intermolecular bonding which

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induces gelation (Chen et al., 2006; McClements, 2015). Therefore, in this study, more negative

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charges available by increasing CSNC concentration led to enhanced electrostatic repulsions and

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increased gel strength.

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Taking into account the above-mentioned mechanisms, only three reduced fat emulsions

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including higher fat content and lower nanocrystals (25FR and 50FR samples containing 10-12%

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and 10% CSNC, respectively) indicated larger droplet size than that of the control sample. There

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was also no significant difference between the Z-average of full fat emulsion and 75FR as well

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as 50FR with 12% CSNC and 25FR with 14% CSNC. In addition, the emulsions whose fat was

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replaced by 50% and 75% with 14% CSNC, had smaller average size than control (p<0.05).

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Similar results have been reported by Thaiudomaand and Khantarat (2011), who used sodium

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octenyl succinate starch (E1450) as a fat replacer and found, in comparison with full-fat

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mayonnaise, that the size of droplets of fat-reduced samples significantly decreased. It was

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explained by the fact that E1450 not only was able to form polymeric network and thus increase

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the viscosity of the continuous phase, but also had an amphiphilic character which probably

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enhanced the stabilizing effect of egg yolk on fat droplets.

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investigated the emulsions stabilized by chitin nanocrystals, and reported that an increase in

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nanocrystal concentration from 0.01% to 0.5% decreased the droplet size, whereas at higher

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concentrations (0.7-1.0%), a slight increase in droplet size was observed. The authors related the

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increased droplet size to the higher viscosity of continuous phase that may prevent movement of

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nanocrystals to oil-water interface during emulsification. In another work, an increase in droplet

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diameter of low fat emulsion was observed with raising pregelatinized waxy maize starch

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concentration. This result was connected to non-covalent interactions between starch molecules

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and surface active components, and different mechanisms of flocculation such as bridging or

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depletion (Bortnowska et al., 2014).

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The results of the polydispersity index (PDI) are presented in Table 2. It can be seen that all the

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emulsions had a relatively narrow size distribution (PDI= 0.21-0.29). In other words, fat

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reduction and CSNC addition had generally no significant effect on homogeneity (p>0.05).

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Similar observations were obtained by Li et al. (2012), who used waxy maize starch nanocrystals

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as a stabilizer in O/W emulsion and observed no statistically significant differences between PDI

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of the samples containing 0.02-6% nanocrystal. In contrast, Carstensen et al. (1992) stated that

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increasing the concentration of disperse phase (oil) from 10 to 20% increased the PDI of the

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emulsion from 0.095 to 0.163. Additionally, in this study, the full fat emulsion showed slightly

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more homogenity as compared to the reduced fat samples, which may be due to the effect of

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CSNC present in the continuous phase on the power density distribution during homogenization.

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Tzoumaki et al. (2011) also

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However, this effect was not significant, confirming the suitability of CSNC as a fat replacer in

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the studied system.

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3.2. Zeta potential of the emulsions

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Zeta potential expresses the electrical potential difference between the mobile dispersion

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medium and the stationary layer of fluid attached to the dispersed particle. It has been reported

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that this term can be related to emulsion stability so that samples with zeta potential >±30 mV

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are considered as stable system resisting to droplet aggregation (Silva et al., 2012).

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In this research, CSNC particles were isolated by sulfuric acid hydrolysis. So, it was expected

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that the obtained nanocrystals would be negatively charged owing to sulfate groups emerged at

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the surface of CSNC. The zeta potential of the emulsions was in the range of -31.9 mV to -39.4

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mV (Table 2), indicating that the repulsive forces exceeded the attractive forces and thus, all the

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emulsions were electrically stabilized. A two-way ANOVA yielded a significant effect of CSNC

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concentration on zeta potential values (p<0.05), but no significant effects of fat replacement level

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and the interaction of them. The absolute magnitude of the zeta potential of O/W

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emulsions increased after fat reduction and CSNC addition and reached a maximum value at

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14% starch nanocrystal (p<0.05), irrespective of the level of fat substitution. However, CSNC

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had no significant effect on the zeta-potential when its concentration was 10 and 12%. The

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particle size is one of the most important factors affecting the zeta potential. In general,

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decreasing particle size resulted in more surface area and consequently, higher surface charges.

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This effect was in accordance with the results of another study (Hedjazi and Razavi, 2018) in

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which cellulosic nanocrystals were made to stabilize the canthaxanthin in the Pickering

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emulsions. The values of zeta potential of all emulsions were negative owing to charged groups

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of –C-O-SO3- on nanocrystal particles. It was also observed that the cotton cellulose nanocrystals

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(CCN) had more ability to stabilize the emulsions than bacterial cellulose nanocrystals (BCN).

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The reasons behind this result were attributed to smaller particle size of CCN and stronger

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repulsive forces between the oil droplets. Wu and McClements (2015) also utilized xanthan gum

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(0-0.02%) to design reduced fat food emulsions including fat droplets (5%), starch (4%) and

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whey protein isolate (5%). The negatively charged xanthan gum showed ability to

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electrostatically cross-link oppositely charged fat droplets coated by protein leading to partial

327

charge neutralization, so that the addition of xanthan reduced the zeta potential of the emulsions.

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3.3. Color of the emulsions

330

Two-way ANOVA on whiteness index (WI) indicated significant effects of both independent

331

variables (p<0.05), but no significant effect of their interaction (fat replacement level × CSNC

332

concentration). As shown in Table 2, whiteness index of the emulsions decreased as fat

333

substitution and CSNC concentration increased. In other words, the control sample demonstrated

334

the highest WI, close to an ideal whiteness (WI = 100). Nonetheless, there are no significant

335

differences between the full fat emulsion and the samples with 25% and 50% fat replacement

336

and 10% and 12% CSNC) (p>0.05). The values of WI appeared to be more affected by the

337

substitution of 75% fat than other levels. This occurrence may arise from the strong tendency of

338

fat droplets to scatter light, so that lightness of an emulsion increases with increasing droplet

339

concentration. Additionally, the interactions of emulsion components with radiation in the visible

340

region of the electromagnetic spectrum (e.g., reflection, transmission, absorption, and scattering),

341

may influence the appearance of an emulsion (McClement and Demetriades, 1998). Moreover,

342

Pearson correlation test showed that WI was well correlated to L* (p<0.001), which is in good

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accordance with Bortnowska et al (2014). Paradiso et al. (2015) also found no significant

344

differences in the lightness values between emulsions including different fat content (21-38%).

345

At the same fat content, the whiteness indices decreased as the CSNC concentration increased

346

(p>0.05), resulting in different interactions of the components of the emulsion with each other

347

(e.g., surface active components covering oil droplets and CSNC molecules) and in consequence,

348

variations in color coordinates (Bortnowska et al., 2014; Bortnowska and Tokarczyk, 2009). A

349

similar result was obtained in another study in which the lightness of mayonnaise was

350

insignificantly reduced by increasing Konjac glucomannan (Li et al., 2014). In contrast,

351

Bortnowska and Tokarczyk (2009) observed that when the concentration of xanthan gum ranged

352

from 0 to 0.5 wt%, the whiteness of low fat mayonnaise containing modified maize starch

353

increased from 90.26 to 92.63.

354

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3.4. Rheological characteristics of the emulsions

356

3.4.1. Stress sweep properties

357

The linear viscoelastic (LVE) region indicates the range in which G′ and G″ are almost

358

independent of stress amplitude. There is an equilibrium between the rates of structural

359

breakdown and rebuilding within the LVE domain. The applied stress in the linear viscoelastic

360

range for frequency sweep assessments was limited to 0.2 Pa. Two-way ANOVA test

361

demonstrated that there were significant effects of fat replacement level, CSNC concentration

362

and their interaction on the all rheological properties presented in Table 3, however,

363

0$'12

364

on the rheological data from stress sweep (Table 3), G′LVE was much higher than G″LVE for all

365

emulsions. The G′ value at the limit of LVE (G′LVE) insignificantly decreased as the fat content

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was significantly affected by fat replacement and CSNC levels (p<0.05). Based

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was reduced by 25% and 50% and replaced with 10% CSNC. Typically, it is expected that

367

emulsions with a greater fat content would show a higher G′ value because of close packing of

368

the droplets (Peressini et al., 1998; Chanamaie and McClements, 2000). However, this result was

369

not observed for the samples with 12 and 14% CSNC, which probably demonstrated that the

370

strong structures formed by added fat replacer were more effective than close-packed droplets,

371

because the CSNC particles were capable of forming hydrogen bonds with water molecules. The

372

properties of O/W emulsions are also influenced by interactions between the emulsifier adsorbed

373

to the surface of the droplets and the biopolymer molecules in the gel like network of the

374

continuous phase. So that, a strong interaction between them can enhance the gel strength (Tang

375

et al., 2012; McClements, 2015). In the current study, Tween 80 (polyoxyethylene sorbitan

376

mono-oleate) was used as an emulsifier. The hydrophilic groups of this ingredient are

377

polyoxyethylene groups, which are polymers of ethylene oxide. Therefore, the hydrogen bond

378

interactions between hydroxyl groups of starch and oxygen atoms of the ethylene oxide played

379

an important role in reinforcing the system structure.

380

In addition, the G′LVE and values of the O/W emulsion including 10% CSNC increased for 75%

381

level of fat replacement in comparison with full fat sample (p>0.05), because the interference

382

effects of oil droplets diminished which resulted in increased electrostatic repulsion of negatively

383

charged nanocrystal particles and enhanced function of CSNC to interact with water molecules.

384

Pearson's correlation displayed a significant positive relationship between

385

potential values; the correlation coefficient was 0.52 and the p-value was 0.028 (p<0.05). For

386

this reason, under the same CSNC concentration, the emulsions with lower fat content indicated

387

higher values of elastic and complex moduli. On the other hand, increasing CSNC concentration

388

also yielded an increase in G′LVE values, meaning a stronger network structure (Table 3).

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and zeta

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According to Steffe (1996), the elastic modulus of stronger gels can be linear in a wider range of

390

amplitude compared to weaker ones. As mentioned in 3.2 section, the droplet size also decreased

391

with CSNC concentration and it is assumed that the smaller particles provided more interaction

392

surface which further increased the G′LVE values (Pal, 1996; Thaiudomaand and Khantarat, 2011;

393

Li et al., 2014).

394

The limiting values of stress at the LVE region is considered of dynamic yield stress (78 ,

395

resulting in the first nonlinear changes in the structure. It is a good indicator of gel strength as

396

well as creaming stability. In other words, emulsions with higher yield stress may, therefore, be

397

more resistant to the gravitational forces than those with lower yield stress (Tzoumaki et al.,

398

2011). As seen in Table 3, fat reduction generally led to an increase in yield point value of the

399

samples including the same CSNC concentration, which was more prominent in 14CSNC

400

samples. So that, there were statistically significant differences in the values of this property

401

between 25FR, 50FR and 75FR emulsions with 14% nanocrystals (p<0.05). It may be attributed

402

to the high potential of cornstarch nanocrystals to strengthen the emulsion structure. In contrast,

403

other researchers studied different dressing formulations (10, 20 and 30% fat, and 0.4 and 0.5%

404

xanthan/guar gum mixture) and observed that the samples containing higher levels of fat and

405

gum had higher yield stress than the formulations with lower fat content and gum concentration

406

(Wendin and Hall, 2001). Although, 10-12% CSNC reduced fat emulsions generally possessed

407

lower 78 values compared to the control, yield stress increased with rising nanocrystal content to

408

14%. With regard to the higher content of CSNC as well as their smaller size, it can be assumed

409

that more hydrogen bond interactions of nanocrystal particles with both water molecules and

410

subunits of the emulsifier were formed. It should be remembered that the increase in nanocrystal

411

concentration enhanced electrostatic repulsion between charged CSNC which resulted in more

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active groups available to form gel and interact with water and in turn increased the energy

413

needed to weaken the structural strength. Similar results have been observed by Wu and

414

McClement (2015), who stated that different values of yield stress in the model emulsions

415

resulted from different microstructures of the samples due to containing variable amounts of

416

xanthan gum.

417

As a result of shear stress exceeding, the linear region for all samples was entirely left and G′ and

418

G˝ intercepted (G′=G˝). At this point, the viscoelastic moduli considerably diminished, therefore

419

the corresponding modulus (Gf) shows the system stiffness and transformation of viscoelastic to

420

elastoviscous behavior. Although, the Gf values of 25FR and 50FR samples as well as 70FR

421

emulsion including 10% CSNC were lower than that of control, there was no significant

422

difference between the Gf of full fat emulsion and some samples (25FR and 50FR with 10%

423

CSNC and 10-12% CSNC, respectively) (Table 3). In other words, this modulus increased with

424

fat reduction and CSNC addition due to a decrease in droplet size, so that 75FR emulsions with

425

12-14% CSNC showed significantly (p<0.05) more Gf value as compared to the control.

426

Spreadability is a crucial textural attribute of semisolid and elastoplastic biomaterial which could

427

be considered as an essential feature perceived by the consumers. It could be shown as index of

428

the ease with which a product spreads. There are many methods applied to measure spreadability

429

involving sensory analysis and rheological (large deformation and small deformation) methods.

430

The value of 0$'12

431

stress at the n-LVE range, could be related to spreadability index (SI) of a system, as higher

432

values of 0$'12

433

hydrocolloid microparticles e.g., modified starches can be useful to prepare spreadable reduced

434

fat emulsions (Moran et al., 1994; Oleyaei et al., 2018). The results presented in Table 3 show that

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3456

3456

, indicating the viscous/elastic components behavior changes with

reflect higher SI and thus, easier spreadability. It has been reported that

19

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0$'12

436

levels increased. The reason behind this observation may be explained by considering the very

437

small particle size of cornstarch nanocrystals which resulted in increasing the electrostatic

438

repulsion of CSNC particles, enhancing function of them to interact with water and consequently

439

forming the cream-like textured systems.

3456

became steeper (higher spreadability) as fat reduction and CSNC concentration

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440

3.4.2. Frequency sweep properties

442

A two-way ANOVA on the frequency sweep properties indicated in Table 4, except 0$'1

443

and η∗ , yielded a significant effects of fat replacement, CSNC concentration and their

444

interaction. Fig. 3 shows the mechanical spectra of the emulsions. In all samples, the elastic

445

modulus (G′) was much higher than the viscous modulus (G˝) throughout the frequency range

446

and the crossover between moduli did not occur. No frequency dependence of G′ and G˝ was

447

also observed for the reduced fat emulsions, indicating the strong gel behavior. While owing to a

448

slight frequency dependency of the viscous modulus, the full fat sample had a weaker structure.

449

Generally speaking, mayonnaises with greater fat content show higher values of G′ (Ma and

450

Barbosa-Canovas, 1995; Li et al., 2014; Román et al., 2015). Although, in this study, it was

451

thought that the functionality of CSNC might be constrained by the fat droplets, so fat reduction

452

increased the interactions among structural components of the emulsions and hence increased the

453

G′ values of samples with the same CSNC concentration (Fig. 3). For the three levels of fat

454

substitution, G′ and G˝ values increased with increasing CSNC content, accompanied by

455

increasing the difference between G′ and G˝ curves. According to Li et al. (2014), this

456

observation may arise from more aggregation of CSNC and formation of a stronger inter-droplet

457

network improving the creaming stability.

9:

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", η∗ and 0$'1 at a constant frequency of 1 Hz for all the

458

Table 4 shows the values in ,

459

emulsions. The

460

comparison with the full fat sample (p<0.05). Whereas, decreasing fat and increasing CSNC

461

significantly ascended the

462

consequence stronger network structure. This observation agreed with the results obtained from

463

stress sweep test (Table 3). In addition,

464

function of fat and fat replacer contents. Loss factor, 0$'1 = "⁄ ′ , is a dimensionless factor

465

that denotes whether elastic (<1) or viscous (>1) properties predominate in the emulsion (Ma and

466

Barbosa-Canovas, 1995). It has been reported that Tan δ greater than 0.1 is typical of dressings

467

and mayonnaises (Li et al., 2014). The 0$' 1

468

were significantly lower than that of the full fat one (0.15), showing more solid like behavior at

469

higher level of fat substitution and starch nanocrystals. Therefore, the results obtained through

470

shear stress sweep test were proved (Fig. 3). Román et al. (2015) observed mayonnaise with

471

lower fat content had lower loss tangent. They also stated the smaller the particle size, the lower

472

the loss factor, which is in accordance with our results (Table 4). In addition, the functionalities

473

of cornstarch and chitin nanocrystals have recently been evaluated as a stabilizer in O/W

474

emulsions in other works (Tzoumaki et al., 2011; Li et al., 2014), where Tan δ declined with

475

nanocrystals concentration. Regarding the slope of complex viscosity (η*s), a similar conclusion

476

could be reached. From data in Table 4, it can be understood that the η*s data of the reduced fat

477

emulsions were in the range of 0.98 to 1, signifying the solid-like behavior for all the samples

478

(Zaidel et al., 2013). However, for full-fat emulsion, the lower value of the η*s (0.95) indicated a

479

more liquid structure in this system.

of 25FR and 50FR emulsions including 10% CSNC decreased in

reflecting the enhanced CSNC–water interactions and in

˶ 9: and

η∗ 9: illustrated similar trend with

9: ,

as a

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9: values

values of the reduced fat samples (0.030-0.072)

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480

Regarding the models fitted, two-way ANOVA test showed that there were statistically

481

significant effects of fat replacement level and CSNC concentration on all the parameters. Also,

482

the effect of their interaction was significant on K', A and z values (p<0.05). Power law

483

relationship (Eqns. 1 and 2) was used to assess the frequency dependence of the

484

moduli. As seen in Table 5, all the emulsions displayed strong gel like behavior because the

485

slopes (' =0.07-0.14 and ' "=0.08-0.21) were close to those of a true gel (' and '" = 0) and much

486

lower than those of a Maxwellian system (' =2 and ' "=1) (Razavi et al., 2017). The ' and

487

'" values decreased as fat substitution and CSNC concentration increased, which showed a

488

decline in frequency dependency of the emulsions. The K' magnitudes were always much higher

489

than the K" magnitudes and both of them enhanced with fat substitution and CSNC addition

490

(Table 5), which related to an increase in stiffness of the emulsion systems due to the formation

491

of stronger inter-droplet networks. Concerning the effect of starch concentration, a similar trend

492

in power law parameters of model low fat emulsions has been observed by Bortnowska et al.

493

(2014).

494

Bohlin's theory of flow (Eqn. 3), as a cooperative phenomenon is capable of giving information

495

on the link between the emulsion structure and macroscopic properties. In this regard, emulsions

496

can be modeled as a network of rheological units interacting to establish the system structure.

497

The number and the strength of conceivable interactions are specified by the coordination

498

number (z) and the proportional coefficient (A), respectively. It was stated that emulsion stability

499

depends on Bohlin's parameters, so that low magnitudes of A and z show a tendency of dispersed

500

phase to droplet-droplet coalescence while undergoing mechanical stress (Peressini et al., 1998).

501

For the O/W emulsions studied, 25FR and 50FR samples with 10% CSNC were the most similar

502

to the control. However, the other fat reduced emulsions had significantly (p<0.05) higher values

"

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and

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of Bohlin's parameters as compared to the full fat sample (Table 5), which confirmed the

504

stabilizing ability of the cornstarch nanocrystals. A similar result was obtained in another woke

505

in which the A and z values of model low fat emulsions were ascended by increasing

506

pregelatinized waxy maize starch (Bortnowska et al., 2014). Additionally, Román et al. (2015)

507

evaluated the potential of mixtures of extruded flour and water (1:3, 1:3.5 and 1:4 ratios) as fat

508

replacers in O/W emulsion. Considering the values of A parameter, the samples with 1:3 ratio

509

were more stable than full fat emulsion showing an increasing trend with fat substitution,

510

whereas inverse results was observed for 50% and 70% fat substitution. It was also reported that

511

decreasing fat content increased z value for all the ratios of flour-water.

512

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3.5. Microstructure of the emulsions

514

Fig. 4 illustrates the photomicrographs of some reduced fat emulsions (25FR-10CSNC, 75FR-

515

10CSNC and 75FR-14CSNC). As can be seen, the samples with lower fat content and higher

516

CSNC concentration had smaller particle size. Moreover, it was obvious that the CSNC particles

517

have the ability to form inter-droplet network, which could prevent the oil droplets from moving

518

and resulted in decreased droplet size as well as strengthened structure. These observations were

519

in good agreement with the results obtained by DLS experiments and rheological measurements

520

(Tables 2-5).

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522

3.6. Emulsion stability to creaming

523

Creaming is a reversible process in which the emulsion droplets separate from the continuous

524

phase and tend to migrate towards the top or the bottom, depending upon the density difference

525

between the continuous and disperse phases. This phenomenon does not appear to be a problem

23

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in the emulsions containing high-fat content (about 80%). It is because that oil droplets within

527

these systems are packed closely so that they encounter great resistance towards migration.

528

Therefore, in reduced fat systems, it is necessary to add some thickening agents to the aqueous

529

phase in order to increase its viscosity and slow down droplets mobility (Hennock et al., 1984;

530

Mun et al., 2009; Depree and Savage, 2001).

531

In this study, all the samples were stable with regard to creaming over the 6-month period, in that

532

no serum layer was observed in the bottom. This proves that the starch nanocrystals are able to

533

stabilize the reduced fat emulsions as well as full fat sample. Based on the rheological properties,

534

aggregated CSNC particles formed the gel-like network (inter-droplets interactions), which traps

535

the oil droplets and prevent creaming. It is notable that the electrostatic repulsion between CSNC

536

particles contributed to the stability of reduced fat emulsions and the particle size of all the

537

emulsions also were small enough to resist upward migration. Hennock et al. (1984) studied the

538

influence of 1% xanthan gum on stability of oil in water emulsions (20-70% fat). It was observed

539

that adding the hydrocolloid resulted in lowering of surface tension, reducing the droplet size and

540

forming liquid crystalline lamellae in the water phase. The degree of creaming at the end of 24 hr

541

also decreased with increasing oil content. The effect of chitosan (0.25-1%) on physical stability

542

of emulsions has been investigated by Calero et al. (2013). The sample containing the highest

543

chitosan concentration showed a remarkable stability to creaming after 15 days of storage at 20

544

ºC. The ability of chitin nanocrystals to stabilize o/w emulsions has also been demonstrated. In

545

this regard, Tzoumaki et al. (2011) found that increasing nanocrystal concentration led to

546

improved emulsion stability, so that no creaming was observed for the sample containing 1%

547

chitin nanocrystals after 6 month of storage.

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549

4. Conclusion

550

The present study showed that the rheological and physical properties of reduced O/W model

552

emulsions were affected by fat content and cornstarch nanocrystals (CSNC) concentration. The

553

results revealed that, in general, decreasing fat and increasing CSNC levels decreased droplet

554

size and increased zeta potential values which probably resulted in more hydrogen bond

555

interactions between CSNC particles and both water molecules and subunits of the emulsifier,

556

and in consequence, stronger inter-droplet networks, confirmed by the optical micrographs and

557

the rheological characteristics of the emulsions. Regarding the values of loss tangent, all the

558

reduced fat samples showed more solid-like behavior as compared to the full-fat one. However,

559

no creaming was observed for all the emulsions after 6-month storage. Additionally, there was

560

no significant difference between whiteness index of the control and some reduced fat samples

561

(25FR and 50FR with 10% and 12% CSNC). In comparison, the 50FR and 75FR emulsions

562

containing, 12% and 10% CSNC, respectively, were most similar to the control sample. To sum

563

up, the results of this study introduced CSNC as a very useful fat replacer/stabilizer for an O/W

564

model emulsion and considering its biodegradability, it can be a promising functional additive

565

for the food industry that deals with people’s health.

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Acknowledgment

568

This project was funded by the Iran Nanotechnology Initiative Council (INIC), Iran and the

569

Ferdowsi University of Mashhad, Iran. The financial support is gratefully acknowledged.

570 571

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EP

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Table 1. Formulations of the full fat (control) and reduced fat O/W emulsions. Ingredients (wt, %) Oil

Water

CSNC suspension

Tween 80

Control

80

19

-

1

10CSNC

60

19

20

12CSNC

60

19

20

14CSNC

60

19

20

10CSNC

40

19

12CSNC

40

19

14CSNC

40

25FR

20

12CSNC

20

14CSNC

20

1 1

1

40

1

19

40

1

19

60

1

19

60

1

19

60

1

AC C

EP

TE D

10CSNC

1

40

M AN U

75FR

SC

50FR

RI PT

Sample

33

ACCEPTED MANUSCRIPT

Table 2. Particle size, zeta potential and color characteristics of full fat and reduced fat O/W emulsions Sample

Z-average

PDI

Zeta potential

(nm)

WI

(mV) 0.21±0.01b

-31.9±1.1a

10CSNC

419±8a

0.23±0.05ab

-33.2±1.6ab

12CSNC

327±7c

0.26±0.01ab

-34.7±1.2ab

14CSNC

246±7d

0.24±0.06ab

-36.7±1.3b

10CSNC

367±11b

0.28±0.05ab

-35.3±0.8ab

12CSNC

251±5d

0.23±0.01ab

-36.2±1.5ab

92.51±0.9ab

14CSNC

171±7e

0.27±0.03ab

-38.0±1.1b

89.55±0.8b

10CSNC

277±12d

0.22±0.01ab

-36.3±0.9ab

89.94±0.3b

12CSNC

243±3d

0.29±0.01a

-36.1±2.1ab

86.99±0.6b

14CSNC

169±7e

0.23±0.02ab

-39.4±1.5b

84.91±0.2b

M AN U

50FR

92.98±0.7ab 91.44±0.6b

93.65±0.4ab

EP

Mean values followed by the same superscripts in each column are not significantly different (p>0.05).

AC C

a-e

TE D

75FR

94.53±0.3ab

SC

25FR

99.27±0.1a

RI PT

251±4d

Control

34

ACCEPTED MANUSCRIPT

Table 3. Elastic modulus (

456 ),

viscous modulus (

LVE region, viscoelastic modulus at flow point ( region (0$'12

3456

˶ 456 )

@)

and dynamic yield stress (78 ) in the

and slope of the loss tangent at n-LVE

) for full fat and reduced fat O/W emulsions at , = 1 Hz and T= 25 ºC.

Samples

CDEF GH

C˶DEF GH

IJ GH

CK GH

Control

132±4de

17.69±1.2b

1.27±0.08d

20.3±1.3bc

1.36±0.1d

10CSNC

119±4de

7.26±0.7de

0.16±0.03e

9.1±0.6d

1.34±0.2d

12CSNC

139±6d

8.06±0.3d

0.20±0.04e

11.5±1.0d

2.09±0.1c

14CSNC

211±3c

10.34±0.6cd

3.16±0.03c

15.6±1.3cd

2.15±0.1c

10CSNC

81±9e

4.78±0.2e

0.56±0.1de

8.7±0.8d

2.45±0.3bc

12CSNC

142±10d

6.96±0.8de

0.72±0.1de

13.5±1.5cd

2.41±0.3bc

14CSNC

203±11c

10.15±1.0cd

4.29±0.2b

16.8±1.9c

2.93±0.2b

10CSNC

178±4cd

9.08±0.7d

1.21±0.3d

11.0±1.2d

2.68±0.2bc

12CSNC

270±6b

12.69±0.9c

2.24±0.1c

22.8±1.8b

2.96±0.1b

14CSNC

549±3a

24.16±1.5a

7.45±0.7a

30.1±2.6a

3.71±0.2a

RI PT

N3DEF

EP

Mean values followed by the same superscripts in each column are not significantly different (p>0.05).

AC C

a-e

TE D

75FR

M AN U

50FR

SC

25FR

LMNOP

35

ACCEPTED MANUSCRIPT

Table 4. Elastic modulus ( ′), viscous modulus ( " , loss tangent 0$'1 and complex viscosity (η∗ ) at , = 1 Hz, and slope of complex viscosity (η∗2 ) for full fat and reduced fat O/W emulsions at 7 = 0.2 Pa and T= 25 ºC. CT UV GH

C˶T UV GH

LMNOT UV

η∗T UV GH. W

η∗P

Control

128±4g

20.0±0.4e

0.150±0.013a

20.4±0.6f

0.95±±0.04b

10CSNC

61±6h

4.1±0.8d

0.070±0.019b

9.7±1.0g

0.98±0.01ab

12CSNC

140±5ef

10.2±0.5b

0.072±0.017b

22.3±0.8ef

1.00±0.01a

14CSNC

195±8d

9.3±0.2b

0.048±0.012b

31.1±1.3d

0.99±0.02a

10CSNC

58±5h

3.4±0.5de

0.060±0.001b

9.2±0.8g

1.00±0.01a

12CSNC

162±10e

9.2±0.6b

14CSNC

263±8c

13.0±0.6a

10CSNC

136±6fg

6.1±0.5c

12CSNC

321±11b

12.6±0.7a

14CSNC

484±7a

13.7±1.0a

25.8±1.6e

1.00±0.02a

0.050±0.021b

41.9±1.3c

1.00±0.01a

0.046±0.003b

21.7±1.0f

0.98±0.01ab

0.040±0.014b

51.1±1.8b

1.00±0.00a

0.030±0.005b

77.1±1.1a

1.00±0.01a

EP

Mean values followed by the same superscripts in each column are not significantly different (p>0.05).

AC C

a-h

0.053±0.018b

TE D

75FR

M AN U

50FR

SC

25FR

RI PT

Samples

36

ACCEPTED MANUSCRIPT

Table 5. Frequency dependence of the elastic and viscous moduli and Bohlin's parameters for full fat and reduced fat O/W emulsions at 7 = 0.2 Pa and T= 25 ºC. N

C =X × Y ' −

Pa

C" = X" × Y \

'" −

"

N"

C∗ = Z × Y

RI PT

Samples

T

[

^ −

\

115±2g

6.7±0.7e

0.95

0.98

85±1h

5.7±0.3e

0.94

0.98

131±3f

9.0±0.8cd

0.96

12.3±1.3b

0.98

180±5d

11.2±0.8bc

0.98

6.0±0.5e

0.96

86±1h

6.1±0.2e

0.95

12.6±0.4b

0.94

145±6e

8.8±0.7d

0.95

\

Pa

]$.

0.14±0.02a

114±2g

0.95

0.21±0.03a

13.7±1.1b

10CSNC

0.13±0.01ab

84±1h

0.94

0.16±0.01b

6.0±0.1e

12CSNC

0.11±0.02ab

130±4f

0.98

0.13±0.02bc

10.2±0.7c

14CSNC

0.09±0.01d

177±4d

0.97

0.11±0.01cd

10CSNC

0.12±0.02ab

85±1h

0.95

0.14±0.01bc

12CSNC

0.11±0.01ab

145±8e

0.95

0.13±0.01bc

14CSNC

0.08±0.01b

253±3c

0.99

0.10±0.01cd

13.7±0.1b

0.96

255±2c

12.5±0.4b

0.99

10CSNC

0.10±0.01b

127±4f

0.96

0.12±0.02c

7.0±0.2d

0.99

128±2f

10.2±0.9c

0.98

12CSNC

0.09±0.01

b

b

0.97

b

bc

0.95

0.07±0.01

b

a

0.97

a-h

a

454±6

0.96 0.98

0.10±0.02

cd

0.08±0.01

AC C

14CSNC

290±2

EP

75FR

TE D

50FR

M AN U

25FR

d

0.99

SC

Control

13.1±0.2

b

15.3±0.6

a

0.96

Mean values followed by the same superscripts in each column are not significantly different (p>0.05).

37

290±3

457±6

a

11.3±0.8

14.2±1.3

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

300 nm

AC C

EP

TE D

Fig. 1. AFM image of cornstarch nanocrystals.

38

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

(CSNC).

AC C

EP

Fig. 2. Illustrations of the X-ray pattern of native cornstarch and cornstarch nanocrystals

39

ACCEPTED MANUSCRIPT

a

RI PT

1000

G', G" (Pa)

100

M AN U

SC

10

1 0.1

1

10

100

Angular Frequency (rad/s)

EP

100

G', G" (Pa)

b

TE D

1000

AC C

10

1

0.1

1

10

Angular Frequency (rad/s)

40

100

ACCEPTED MANUSCRIPT

c 1000

G', G" (Pa)

RI PT

100

SC

10

1 1

10

100

M AN U

0.1

Angular Frequency (rad/s)

Fig. 3. Frequency sweep dependency of elastic modulus (G′) and viscous modulus (G˝) of samples. a) full fat and 25% fat reduced emulsions; b) full fat and 50% fat reduced emulsions; c)

TE D

full fat and 75% fat reduced emulsions. G′ (filled symbols) and G˝ (open symbols) of full fat

AC C

EP

(diamond), 10CSNC (circle), 12CSNC (triangle) and 14CSNC (square) samples.

41

ACCEPTED MANUSCRIPT

C

B

M AN U

SC

RI PT

A

1 µm

1 µm

1 µm

AC C

EP

TE D

Fig. 4. The optical micrographs of the reduced fat emulsions. A: 25FR-10CSNC, B: 75FR10CSNC, C: 75FR-14CSNC.

42

ACCEPTED MANUSCRIPT

Research highlights

Reducing fat and adding CSNC led to smaller droplet size and more zeta potential.

RI PT

The ability of CSNC to strengthen the structure was affirmed by rheological data. All reduced fat emulsions showed more solid-like behavior than full fat sample. No creaming was observed for all studied emulsions after 6-month storage.

AC C

EP

TE D

M AN U

SC

Higher spreadability was obtained as fat reduction and CSNC levels increased.