2.1. Samples
Three-quarter fat butter with a declared 60% fat content, 74% dairy spread and butter with a fat content of 82% were selected for the purpose of this study. The samples (commercially available), consisting of 200 g blocks, were provided by a local dairy company (Mleczarnia Naramowice, Poznań, Wielkopolska, Poland). The samples were collected at the same time (in January). The milk was delivered to the dairy company from a university farm where the cows did not have access to pastures. The fats were produced with no colourants used.
2.3. Colour
In order to provide a physical determination of the colour for the three fats, five colour compounds were read from the device: L*, a*, b*, c and h. The L* component denotes lightness and assumes values from L* = 0 (black colour) to L* = 100 (white), hue (h) was determined with an angle formed by a straight line crossing the centre of the system and measured point with coordinates a*, b* on axis a* (in a* b* coordinate system), and the chroma (c, or depth of colour) was the distance of a point (a*, b*) from the centre of the system. The analyses were conducted using an SP60 X-Rite spectrophotometer (Grandville, MI, USA). The measurements were recorded using illuminant D65 and geometric d/8, with a measurement area of 8 mm and 10° standard observer on the SPIN setting. The spherical geometry in the device had two variants, with the first being SPIN (Specular Component Included (SCI)). In the SPIN mode, the colour is measured independently of the sample’s gloss and texture. The thickness of the sample was 30 mm, and its temperature was 10 °C. Colour differences (ΔE) between the samples were calculated according to Equation (1). The values for L*, a* and b* obtained for the two compared fats were inserted into the following formula:
Value ΔE is interpreted as follows: 0 < ΔE < 1 indicates a normally invisible difference; 1 < ΔE < 2 indicates a very small difference only obvious to a trained eye; 2 < ΔE < 3.5 indicates a medium difference, which is also obvious to an untrained eye; 3.5 < ΔE < 5 indicates an obvious difference; and 5 < ΔE indicates a very obvious difference [
19].
2.4. Texture Tests
The textures of spreads at temperatures of 4–20 °C were tested using a TA.XT plus Texture Analyzer (Stable Micro Systems Ltd., Godalming, Surrey, UK). Two texture tests were selected: cutting force and spreadability.
2.4.1. Cutting Force
The purpose of this test was to determine the “firmness” of the samples by their resistance to cutting by wire. The cutting force of the products was tested. The measurements were taken with the following accessories: a heavy duty platform (HDP/90), a wire cutter (Ø 0.3 mm) and a 5 kg load cell. The conditions of the measurements were as follows: a test speed of 0.5 mm s–1, distance of 25 mm and trigger type of 50 g. (The texture analyser would move the probe down until it detected a force greater than the trigger force setting.) The dimensions of tested samples were 100 mm long × 75 mm wide × 30 mm high. The samples consisted of bars of butter (cuboids). The wire cut the 100 mm × 75 mm surface (the top of the butter bar, positioned flat on the largest side) to a depth of 25 mm (so that 5 mm remained uncut).
2.4.2. Spreadability
Spreadability is the force required to obtain a given deformation and the amount of deformation under a given force. As a result of testing, a mean maximum force called the “firmness” (N) and a mean area called the “work of shear” (N s) were obtained. The equipment was operated under the following conditions: a test speed of 3.0 mm s
−1, distance of 23 mm and trigger type button. (The measurement started as soon as the run command was given and the probe started moving) Male and female perspex cones were used. A sample was placed in a female cone and pressed down to eliminate air pockets. The excess was scraped off the sample with a knife to leave the test area flat. A precisely matching male cone was lowered into the sample, forcing the fat to flow upwards and outwards. The ease with which the sample flowed was the indication of its spreadability [
20].
2.5. Differential Scanning Calorimetry (DSC)
A differential scanning calorimeter 7 (Perkin Elmer, Norwalk) equipped with an Intracooler II and Pyris software was used to examine the melting properties of the butter and reduced fat butters. Nitrogen (99.99% purity) was the purge gas. The calibration was performed using indium (m.p. 156.6 °C, ∆Hf = 28.45 J∙g
−1) and n-dodecane (m.p. −9.65 °C, ∆Hf = 216.73 J∙g
−1). Samples of the fats (9–10 mg) were weighed in aluminum pans of 20 μL (Perkin Elmer, No. 0219-0062) and sealed hermetically. The reference was an empty, hermetically sealed aluminum pan. The following temperature programme was set: (1) cooling at 5 °C∙min
−1 to −40 °C and (2) heating at 5 °C∙min
−1 to 50 °C. Three replicates were analysed for each sample. Melting enthalpy was calculated from the heating curve as the area under the curve, limited by the baseline. From the results of the melting enthalpy percentage area, a curve was plotted vs. temperature, and the solid fat indexes (SFI) for 4 and 20 °C were calculated:
where AT is the area percentage determined at a certain temperature (4 or 20 °C).
2.6. Consumer Opinion
The products were tested by consumers (n = 100) over 18 years of age. The test was performed inside a building for 4 days from 10:00 a.m. to 4:00 p.m. Consumers were recruited among the visitors of a local mass event.
Consumers who declared butter consumption at least once a day were selected for the study. The preliminary tests determined the temperatures of the test samples. The consumers declared eating butter straight from the fridge or stored at room temperature.
The consumers were asked to evaluate the samples at a temperature of 4 °C (taken out directly from the refrigerator) and 20 °C (stored under refrigeration conditions and placed at a room temperature for 3 h before consumer testing to imitate home consumption). The panelists individually evaluated 7 g samples presented in plastic cups. They were given room temperature water and unsalted crackers to cleanse their palates between samples [
21].
The preferences regarding colour, appearance, aroma, spreadability and taste of these spreads were examined. The differentiation criterion was the preference for a sensory attribute (e.g., colour) of a sample in relation to the remaining ones.
The respondents (n = 100) answered six questions: “Which colour/appearance/aroma/spreadability and taste of a sample do you like best?” and “Which sample of the three do you like best?” In these types of questions, the respondents could not say that the products were equal. They were forced to prioritise. A scale of 0–2 was used to specify the degree of meeting expectations either by only one feature or by the product in general. Each respondent had to evaluate 3 products (three-quarter fat butter, 74% dairy spread and butter) using the following scale: 0, 1 and 2, where 0 was the least accepted product, 1 was an accepted product and 2 was the most accepted product. The samples were given in random order. Only products with two points were selected for further analysis. The advantages of this method are simple tasks and quick assessment.
The surveys were once again analysed and the overlapping replies checked for the first and last question), and then for the second and last question, and so on.
Additionally, a new group of respondents (n = 600 over 18 years of age) answered the question of whether they preferred milk fat products of a more white or yellow colouring.
2.7. Statistical Analysis
The values describing colour and texture are the arithmetic means of 9 measurements. Three samples of each product were evaluated in triplicate.
The results obtained for the samples were subjected to one-way ANOVA and Tukey’s honestly significant difference (HSD) test using Statistica data analysis software version 10 (StatSoft, Tulsa, OK, USA). Verification of the statistical hypotheses was accomplished by adopting an α = 0.05 level of significance.