A method for reducing the oil content of snacks by increasing spreadability

Field of the Invention

The invention relates to a method of enhancing the spreadability of cooking oil on snack surfaces. In particular, the invention relates to a method for enhancing the spreadability of an edible oil on the surface of a baked or fried comestible product such as a biscuit, cracker, potato crisp, chips etc.

Background to the Invention

Snacks occupy a notable position among food items and possess wide diversity in terms of their formulation, processing method and varieties. Biscuits, cookies and crackers are produced from wheat flour, sugar, fat and leavening agent, along with other minor ingredients. The ingredients are mixed together to obtain the dough, sheeted to optimal thickness, cut to a desired shape and baked. It is common practice in many biscuit production processes to apply vegetable oil to the freshly baked biscuits. Potato chips or crisps are commonly fried in vegetable oils.

Oil is either applied by spraying or by using a device similar to an enrober, in which case the snack pass through a flowing curtain of oil. Oil spraying is often accomplished using pressurised nozzles, spinning discs or electrostatic charge. The oil present on the surface improves the palatability and imparts an aesthetic appearance.

Oils used as surface coatings for savoury snacks are best if they have limited absorption into the product and remain on the surface as a glossy film. A thicker oil film on the surface is undesirable and leads to diffused reflectance. Furthermore, excess fat or oil on the surface has a tendency to set and cause adhesion between touching products when packed in stacks. This adhesion may result in damage to the thin surface of the product as they are separated before eating. From a nutritional point of view, high fat intake has been associated with various health disorders such as obesity, cancer, high blood cholesterol and coronary heart disease. Therefore, there is substantive evidence that an alternative process is required, which allows the functionality of sprayed oil in snacks to be retained, but with less oil or fat and increased spread.

The spreading characteristics of a liquid on a surface is dictated primarily by the surface energy, which is expressed as the hydrophilicity or hydrophobicity of the surface. This is a well-known phenomenon, often encountered in polymer and textile science and in surface engineering. A gas discharge plasma can be defined as a partially ionized gas containing neutral particles as well as an equivalent number of negative electrons and positive ions. Plasma treatment only changes the uppermost atomic layers of a material surface without modifying the bulk properties. Industrial plasma processing of food packaging films is already in practice.

It is an object of the invention to overcome at least one of the above-referenced problems.

Summary of the Invention

The applicant has discovered that viscous liquids such as oils when applied to discrete portions of a food surface such as a snack product can be spread out on the surface by exposing the surface to a non-thermal plasma field prior to application of the viscous liquid. The plasma can be generated by dielectric barrier discharge, floating electrode or jet designs. An embodiment of the invention is the application of oils to a food snack surface. Fig. 1 shows the increased spread of droplets of oil applied to the surface of a biscuit by exposing the surface to a plasma field when compared to a control. In a first aspect, the invention provides a method for enhancing the spread of a viscous liquid on a surface of a product comprising the steps of treating the surface by exposing the surface to a non-thermal plasma field, and subsequently applying the viscous liquid to the treated surface, wherein the spread of the applied viscous liquid on the treated surface is increased compared to the spread on an untreated surface.

In a further aspect, the invention provides a method for reducing the amount of food grade oil or food grade oil-based liquid applied to a surface of a food product, the method comprising the steps of treating the surface of the food product by exposing the surface to a non-thermal plasma field, and subsequently applying the food grade oil or food grade oil-based liquid to the treated surface of the food product, wherein the spread of the applied food grade oil or food grade oil-based-liquid on the treated surface of the food product is increased compared to the spread on an untreated surface.

Typically, the product is a food product. Suitable, the viscous fluid is an oil, or an oil- based liquid. Typically the oil is a food grade oil.

In this specification, the term "oil" should be understood to include oils of animal or vegetable origin, having a saturated fully unsaturated, or partially unsaturated nature. The term also includes emulsions of a water-in-oil type formed from oils, fats and lipids. Typically, the oil is an edible oil. Examples of suitable oils include corn oil, coconut oil, palm oil, rapeseed oil, and fats rendered from animals. In this specification, the term "product" should be understood to mean any article of manufacture, in particular comestible products for human or animal consumption, and ideally baked or fried comestible products for human or animal consumption. The term "comestible" should be understood to mean suitable for consumption by a human or animal, and includes nutritional products, pharmaceuticals, nutritional and health food supplements and the like. Thus, the term can include human or animal food products, including biscuits, crackers, snacks, crisps, fries, dehydrated food products, pharmaceutical unit dose products, food and health supplement unit dose products, and other products for which a surface coating of a viscous fluids such as an oil is desirable. Typically, the product is a comestible product, suitably a baked product, or preferably a comestible baked product. In this specification, the term "snack" should be understood to mean a baked or fried food product including sweet and savoury biscuits, crackers, crisps and snack products including but not limited to pretzels, savoury crackers, and animal feed products such a pellets and animal feed biscuits.

Suitably, the method of the invention enhances (i.e. increases compared to an untreated surface) the spread of the viscous liquid (i.e. oil) on the surface by at least 50% (v/v), as determined using the method embodied below. Typically, the plasma field is generated between two electrodes, and wherein the voltage applied across the electrodes is from 10 to 120kV. Typically, the plasma field is generated with a dielectric discharge barrier, floating electrode or plasma jet and in which the surface is exposed to the plasma field for a period of at least 1 to 300 seconds, typically from 10-300, 10-200, 10-100 second.

The invention also relates to an apparatus for treating a food product with a non-thermal dielectric barrier discharge plasma field, the apparatus comprising a pair of spaced-apart electrodes, a step-up transformer in electrical communication with the electrodes adapted to apply a voltage across the electrodes of 10-120kV (peak to peak), and optionally a dielectric in contact with the voltage electrode. Suitably, a working gas is disposed between the electrodes, and in which the working gas is air typically at atmospheric pressure.

Preferably, the spacing between the electrodes is at least 2, 3, 4, 5, 6, 7, 8, 9 or 10 cm for dielectric barrier discharge plasma designs.

The invention provides a system for enhancing the spread of a viscous product (such as a food grade oil or food grade oil-based liquid) or on a surface of a comestible product such as a food product, the system comprising:

- plasma field generating means configured to generate a non-thermal plasma discharge field;

- viscous product application means configured to apply the viscous product to discrete portions of the surface of product; and

- first conveyor means for conveying the products from the non-thermal plasma discharge field to the viscous product application means such that the spread of the viscous product on the surface of the comestible products increases.

Typically, the viscous product is a food grade oil or a food grade oil-based liquid. Typically, the product is a food product. Preferably, the food product is baked or fried food product.

Typically, the plasma field generating means comprises a dielectric discharge barrier, floating electrode or plasma jet. Typically, the plasma field generating means comprises a pair of spaced apart electrodes in which the plasma field is generated between the electrodes, and in which the spacing between the electrodes for dielectric discharge barrier is at least 2, 3, 4, 5, 6, 7, 8, 9 or 10 cm. Suitably, the plasma field generating means comprises means (for example, a step-up generator) for generating a voltage across the electrodes of 10 to 120kV, 50-120kV, 70- 120kV, or 80-90kV.

Suitably, the system comprises an oven for baking the products and, optionally, second conveying means for conveying the baked products from the oven to the plasma field of the plasma field generating means.

Preferably, the system comprises cooking means and conveying means for conveying the food product from the oil application means to the cooking means.

Suitably, the cooking means is an oven for cooking the food product or a fryer for frying the food product.

Typically, the means for applying oil to the surface of the product is configured to apply drops or a flowing curtain of oil to the surface.

Typically, the first conveyor is configured to expose each baked comestible product to the plasma field for a period of from 1 to 300 seconds. In a further aspect, the invention provides plasma field generating means configured to generate a non-thermal dielectric barrier discharge plasma field, a floating electrode design or plasma jet for use in spreading a viscous fluid such as an oil on a surface of a food to reduce oil content. Brief Description of the Drawings

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying figures, in which:-

Figure 1 is a matrix of images depicting typical digital images of the biscuits along with the processed images wherein the oil spots have been picked. Treatment times are (a) 0 minutes (b) 1 minute (c) 3 minutes and (d) 5 minutes.

Figure 2 is a schematic of the non-thermal plasma source and experimental set-up.

Figure 3 displays the typical current and voltage waveforms of the dielectric barrier discharge plasma in air at 80 and 90 kV (p-p), without (Empty) and with biscuit samples (Bisc).

Figure 4 represents overlaid UV-Vis Emission spectra of the dielectric barrier discharge plasma at applied voltages of 80 and 90 kV (p-p), with biscuit samples. Inset: zoom of the spectra between 700 to 800 nm window.

Figure 5 graphically presents the spread area of oil on biscuit surface (expressed as number of pixels) as a function of treatment time.

Detailed Description of the Drawings

Materials and Methods

Wheat flour, bakery shortening, sugar, and Refined-Bleached and Deodorised (RBD) palm oil were all obtained from a local supermarket. Methyl Red-0 dye was obtained from Sigma- Aldrich, Ireland.

Preparation of biscuits and oil spraying The formulation used for biscuit making is presented in Table 1. Briefly, the ingredients were kneaded using a dough mixer (5KPM5 KitchenAid, St Joseph, Michigan, USA) followed by sheeting to a thickness of 2-3 mm and cutting out 7.5 cm diameter pieces. The biscuits were baked at 165°C in an oven (SCC101E Combi-Oven, Rational AG, Landsberg am Lech, Germany). The said baking conditions prevented excessive cracking of the biscuit surfaces, which would otherwise impose difficulties in feature extraction from images.

Table 1 Formulation of ingredients used in the preparation of biscuits.

Ingredients Formulation

Refined Wheat Flour 42.5%

Icing Sugar 21.3%

Ground Almonds 4.2%

Unsalted Butter 21.3%

Whole Egg 8.5%

Water 2.1 %

Plasma treatment

A schematic of the experimental set-up employed in the study is presented in Figure 2. The DBD system comprises of two circular aluminium plate electrodes (outer diameter = 158 mm) with a 10 mm thick Perspex dielectric in contact with the voltage electrode. A polypropylene (PP) package containing the biscuit sample is placed directly in the field between electrodes. The high voltage step-up transformer (Phenix Technologies, Inc., USA) powered at 230 V, 50 Hz delivers a high voltage output in the range 0-120 kVRMS. Two different voltages were applied across the electrodes for the experimentation viz. 80 and 90 kV (peak to peak) at 50 Hz. The rigid PP package had dimensions of 212 mm x 154 mm x 22 mm and also served as a dielectric material. All treatments were done with atmospheric air as the working gas. The atmospheric air condition at the time of packaging and treatment was 22% relative humidity (RH) and 20°C, as measured using a humidity-temperature probe connected to a data logger (Testo 176 T2, Testo Ltd., UK). The biscuit samples were subjected to direct plasma field for 1, 3 and 5 min (in a randomised manner). Direct exposure refers to placement of biscuits within the area of coaxial electrodes.

Simulation of oil spray

An organic dye, Oil Red-0 was introduced into the oil at a level of 10 ppm, followed by centrifugation at 10,000 rpm for 10 min (Sanio MSE Mistral 3000ii, UK), to remove any suspended dye particles in the oil. The Oil Red-0 is a lipophilic dye, which was added to improve contrast of the oil in images, whereby it allows accurate identification of the pixels. Oil droplets of 10 μΐ, volume were drained on the surface of biscuits using a micropipette. Ten droplets were spotted on each biscuit (control as well as plasma treated). The biscuits were left undisturbed for 5 min to allow spreading and diffusion, following which images were acquired. All treatments and further evaluations were performed in duplicate.

Electrical Characteristics

The electrode bias voltage was monitored in the time domain using a high voltage probe (North Star PVM-6) coupled to a 10: 1 voltage divider to allow recording of the full voltage waveforms on an Agilent InfiniVision 2000 X-Series Oscilloscope (Agilent Technologies Inc., USA). A current transformer probe (Bergoz CT-E1.0S) was used to record the current waveforms. The voltage was analysed both in the time and frequency domain, the latter by means of Fast Fourier Transform (FFT) analysis.

Optical Emission Spectroscopy

Emission spectra of the discharge emissions within packages were acquired at 1.5 nm resolution with a computer controlled Stellarnet EPP 2000C-25 spectrometer, in which light from the plasma is coupled via an optical fibre. The diffraction grating in the spectrometer had a radius of curvature of 40 mm, 590 grooves per mm and an entrance slit width of 25 μιη. The fibre had a numerical aperture of 0.22 with optimum performance in the ultraviolet and visible portion of the spectrum. The spectrometer operates in the wavelength range 190 nm to 850 nm. The spectra were evaluated qualitatively to identify the active species generated by the discharge. Image Analysis

Control and plasma treated biscuits were photographed using an Olympus digital single- lens reflex (DSLR) camera (Olympus E5, Olympus, Melville, NY, USA), held on a tripod. The obtained digital images were then imported into R software (R 2.11.1, R Foundation for Statistical Computing, Vienna, Austria). Analysis of the digital images was conducted using existing routines within the EBImage package and in-house routines.

The digital images corresponding to the different biscuit samples studied were segmented to isolate the dyed-oil spots from the biscuit background. The segmentation was achieved by subtracting the green channel image from the red channel to create a greater contrast between the dyed-oil spots and the biscuit background. For the quantification of the spread of the oil in the control and plasma-treated samples, the number of pixels in each of the extracted spots were enumerated and used as an estimate of the spread of oil.

Statistical Analysis

The effect of treatment time and applied voltage on the spread area of the oil was evaluated by ANOVA and Tukey's multiple comparison method available from SPSS (SPSS v. 19, SPPS Inc., Chicago, IL, USA). Significance of effects was evaluated within 95% confidence intervals (p<0.05).

Results

Electrical Characteristics of Discharge

The use of very high voltage in the present study allowed generation of stable non-thermal plasma discharge, also at wider gaps (of up to 2.2 cm). The waveform shown in Figure 3 revealed that the applied voltage was sinusoidal, while the total current comprised of the displacement current superposed by numerous current pulses per half-cycle of the applied voltage. The discharge in the air can be characterized as operating in a typical filamentary regime with a microdischarge zone in each half-cycle of the applied voltage, which is organized by numerous streamer clusters at different durations up to the maximum of the applied voltage. This pattern can be observed for all operating situations under consideration. However, the intensity and number of current filaments increased with the introduction of biscuits. It may be noted that the gas gap became smaller in the presence of biscuits, as the inter dielectric gap was kept constant at 22 mm. The frequency specta of the applied voltage (Figure 3) are characterized by the fundamental frequency at 50 Hz. The FFT of the applied voltage showed little contribution to other harmonic effects (resonance).

Optical Emission Spectroscopy

A fraction of the energy input to the plasma discharge results in excitement of several chemical species to higher energy states, which can be detected by optical spectroscopy of the emissions. Optical emission spectroscopy (OES) is a non-intrusive technique that can monitor the concentrations of the plasma species. In OES, the spectrum of the radiation emitted by the plasma is grated and its intensity measured as a function of the wavelength. The emission spectra of the discharge (in arbitrary units) obtained in the presence of biscuit samples is presented in Figure 4. Emission measurements were taken within the first few seconds of the plasma initiation. Most of the distinct peaks obtained in the near UV region corresponded to strong emissions from N ₂ (C- B) second positive system and N ₂ ⁺ (B- X) first negative system. Many peaks associated with optical transitions of O atom are observed at low intensities (inset in Figure 4): 725.4 from O (5 s ³ S→3p ³ P), 533.0 nm from O (5d ⁵ D-3p ⁵ P), 777.4 from O (2s ² 2p ³ 3p ⁵ P→2s ² 2p ³ 3s ⁵ S), and 752.76 from O (2s ² 2p ² ( ³ P)3d→2s ² 2p ² ( ³ P)4p). It should be noted that the relatively lower intensities of peaks associated with oxygen is due to quenching of 0( ³ P) and 0( ⁵ P) in the air plasma. The highest intensity among these corresponds to the 777.4 nm line. An OH peak around 300 nm can also be observed at very low emission intensity, in spite of 22% relative humidity prevailing at the time of experimentation. The loss of the OH' (A ² ∑ ⁺ ) state has been primarily attributed to the process of radiative de-excitation and the quenching by collisions with different sorts of molecules (for example, quenching time by H2O is about 100 ns). The system employed in this study also generates a significant amount of ozone.

Effect ofDBD treatment on oil spreading

The images provide evidence to the fact that there is a positive correlation between spread area growth and increase in treatment time and voltage. The number of pixels versus treatment time is presented in Figure 5. A statistically significant difference (p<0.05) in spreading of the oil was observed between the control and treated biscuits, with the spreading being higher for DBD treated biscuits. The difference between the spreading of oil was significantly different (p<0.05) between the two voltages for treatment times of up to 1 min. However, for treatment times of 3 min and beyond, the effect of voltage was insignificant (p>0.05). Thus, treatments of up to 1 min at 90 kV (p-p) is recommended for the purpose.

To understand the observed effects, it may be recalled that a droplet of a liquid of lower surface tension will spread upon a surface whose energy level is higher. This lowers the energy of the combined system. Conversely, when the surface tension of the liquid is higher than that of the surface it will spread to a lesser extent. This implicitly means that DBD plasma treatment increases the surface energy of the biscuits, which is reflected by the enhanced spreading of oil. Immediately after spraying the oil, two simultaneous processes occur: the absorption of oil into the biscuit and its spreading effected by surface forces. The degree to which these processes occur relative to each other dictates the extent of spreading of the oil. Following plasma treatment, the latter process exceeds the oil absorption.

Following DBD plasma treatment, we did not notice any obvious changes in the biscuits. There was no perceivable change in colour, smell or overall appearance of the biscuits.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail without departing from the spirit of the invention.