THE STUDY OF ODOR PROFILE AND COLOR CHARACTERISTICS IN BEEF DURING HEAT TREATMENT

The article presents the study results of changes in the odor profile and color characteristics in beef under various heat treatment conditions. More than 120 volatile substances are identified. In samples subjected to short-term and minor heat treatment, 2-meth-yl-butene and ethyl hexanoate were found in significant amounts. In samples subjected to prolonged roasting at low temperature, as well as in samples subjected to processing at higher temperature for less time period, was found 3,5-dimethyl–4-octanone. Analysis of changes in color characteristics showed that increase in heating temperature results in significant darkening of the samples. The maximum heating temperature of 210 °C had the most significant effect on the color change. After heating for more than 30 minutes, carbonization of the samples occurred. The results indicate that controlling the temperature and duration of heat treatment helps to obtain the finished product of desired color.


Introduction
During the technological heat treatment of food products, their organoleptic characteristics (color, taste and odor) often change due to the formation of colored substances, melanoidins, as a result of reducing sugars interaction with free amino acids, i.e. the reaction of non-enzymatic browning first described by the French scientist Maillard in 1912. This reaction take place in products of animal and vegetable origin, since all of them contain a certain amount of reducing sugars and free amino acids [1,2,3,4].
The process of melanoidin forming has a certain effect on consumer properties and food quality, because along with the improvement of sensory properties and the formation of substances with antioxidant properties, accumulation of toxic compounds and decrease in nutritional value occur due to utilization of amino acids [5,6]. In this regard, the study of this chemical transformation is important for development of innovative food products.
The process of browning improves sensory properties of various products, since their color transforms into attractive golden or brown (bread crust, coffee beans), which increases consumer demand for them [6,7,8,9].
Browning measurement may be carried out by visual observation or using a spectrophotometer. Spectrometric color determination at a wavelength of 420-460 nm makes it possible to obtain quite satisfactory results when assessing the change in color of food extracts or model systems. Visual color evaluation is often not enough, since it is very subjective and depends on a physiological state of the person. In this regard, it is relevant to study the change in food color under various temperature and teat treatment duration using modern computer technology.
The purpose of the work is to study the odor profile and color characteristics of beef during heat treatment.

Materials and methods
To study the effect of heat treatment on odor forming components and color characteristics, L. dorsi beef muscle previously minced in a meat grinder was used. Roasting was performed in Binder FD-53 drying chamber with forced convection and automatic recording of the temperature inside the chamber, with an accuracy of 2 °C. Minced meat was molded in round-shaped products with a diameter of 50 mm and a height of 5 mm; the weight of each product was about 5 g. For duration measurement, C-01 stop watch was used. The measurements were carried out at temperatures of 120, 150, 180, and 210 °C with periods of 10 minutes for 2 hours. To study the color characteristics, photographs were taken under the same conditions for all samples: D65 light source (standard daylight), viewing angle of not more than 2°, each measurement was performed once; Canon EOS 750D camera; Canon EF-S 17-55mm f/2.8 IS USM lens; ISO 400, f 5.6, shutter speed 1/60. Images of the analyzed samples were processed in Adobe Photoshop CS6 graphic editor.
Color difference is a mathematical representation that allows to numerically express the difference between two colors in colorimetry. To determine the difference in color values between two samples, there are several equations. The results obtained from these equations are in some cases inconsistent with the results of visual assessment. The following general equations are recommended for use by the International Commission on Illumination (CIE): CIE76 in L*, a*, b* values, CIE94 in LCH (L*C*h) color coordinate system and CIEDE2000 including the rotation of the tone angle, compensation for neutral colors, lightness, saturation and tone [10,11,12].
In current work, in order to quantitatively and most accurately assess the color difference of heat-treated meat samples, the online calculator, «CIE2000 Calculator», was used that allows to calculate the color difference in various color coordinates according to CIEDE2000 standards [13].
To obtain the color characteristics of the studied samples, their photo images are used followed by processing in Adobe Photoshop graphic editor, in which color characteristics may be determined. To estimate the change in color, Δ E parameter (color difference) is used, which is defined as the difference between two colors in uniform color space. Using the eyedropper tool (color determination tool) in Adobe Photoshop, the hexadecimal color value and color coordinates in RGB were obtained. RGB is a widely used additive color model. RGB color model may use various shades of primary colors, various color temperatures («white point» setting), and various gammacorrection values.

Results and discussion
The study results for the color change in the samples depending on the different temperature and duration are presented in Figure 1. The change from red in the control sample to light gray through beige is due to myoglobin denaturation. Further heating of the samples led to their browning. The higher the temperature was the more intensely melanoidin pigments formed. Moreover, even prolonged exposure to a temperature of 120 °C did not lead to a significant change in the color of the studied samples. At a temperature of 180 °C, a significant change in color was observed even during 30 minutes of heating. Then, with an increase in temperature up to 210 °C, carbonization of the samples occurred regardless of heating duration [14,15].
Images of the analyzed samples are shown in Figure 1.
The results of the color difference study, the visual and numerical characteristics of the color change in the studied beef samples roasted at various temperatures and time periods are presented in Table 1.
The visual perception of the samples subjected to heat treatment showed that at a temperature of 120 °С and 150 °С sample color practically did not change. However, comparison of color numerical values makes it possible to determine the changes occurring in the samples.
The values in Red Green Blue system changed according to the change in color during heating.
The most significant changes were noted in color difference, i.e. after 10 minutes of heating, it changed by more than 2 times compared to the control. Heat treatment at a temperature of 180 °C showed that an increase in temperature led to more intense color. At a temperature of 180 ° C, a more significant change was observed in the values of Red Green Blue system compared to the control. A significant decrease in Blue value during the entire period of heat treatment was noted, and after 120 minutes its value decreased by 2 times in comparison with the control.
The maximum heating temperature of 210 °C had the most significant effect on color change. After heating for more than 30 minutes, carbonization of the samples occurred.
The values in Red Green Blue system at this temperature were as low as possible, tending to zero (absolutely black color) in comparison with all other treatments. Increased duration of temperature exposure slightly effected the color difference.
Odor forming compounds were identified by comparing the test mass spectra with the reference spectra of the NIST (National Institute of Standards and Technology)   172, 79, 71 224, 183, 164 204, 170, 150 180, 143, 116 175, 142, 115 128, 92, 66 117, 87, 55 141, 112, 79 135, 107, 75 145, 112, 66 139, 110, 65 138, 100, 54 145 database [16]. The compounds were identified on the basis of high similarity of the mass spectra and taking into account the retention time order of the compounds in accordance with the Kovats index. The total content of components and component groups was calculated by summing the peak areas of individual components. The relative content of individual components and their groups was calculated relative to the total content of components and expressed as a percentage of the sum of all peak areas, with the exception of background and unidentified peaks.
In the research, more than 150 volatile substances were detected, of which 115 were identified and which significantly contribute to minced meat odor during heat treatment. These are mainly carbonyl compounds and alcohols, esters, and some other compounds. The following substances were detected: 11 esters, 14 heterocyclic compounds, 3 unsaturated hydrocarbons, 5 terpenes, 9 alcohols, 4 acids, 19 aldehydes including 9 unsaturated aldehydes, and 4 azo compounds.
During heat treatment at a temperature of 120 ºС for 60-90 minutes and at a temperature of 150 ºС for 30-60 minutes, propen-2-amine-1 was detected in significant concentrations. During heat treatment at 120 ºС, hexanal and methoxyphenyl oxime were detected, which were not detected under the other temperature conditions of minced meat processing.
3-ethyl-2,5-dimethyl pyrazine was detected during short-term and long-term medium-temperature processing of minced meat, whereas 2-pentyl pyridine was detected in significant amounts in samples subjected to hightemperature processing at 180-210 ºС.

Conclusions
In the studies of the effect of heat treatment on odor forming components and color characteristics in animal products (beef), more than 120 volatile substances were detected: carbonyl compounds and lower fatty acids, alcohols, esters, and some sulfur-containing compounds. After short-term and low-temperature treatment, 2-methyl-butene and ethyl hexanoate were found in large quantities. In samples subjected to prolonged roasting at low temperatures, as well as in samples subjected to processing at a higher temperature but for less time period, 3,5-dimethyl-4-octanone was detected. Carvone was found in samples subjected to long-term and low-temperature treatment or shorter but higher temperature treatment. Many samples contained a significant amount of furfural, benzaldehyde and phenylethyl alcohol, which is in good agreement with the data reported in the literature.
Analysis of changes in color characteristics showed that a significant darkening of the samples was observed with increasing temperature. At a temperature of 120 °C, there is still a slight color change even after 2 hours of exposure, but as the temperature rises up to 180 to 210 °C, the samples darken in the first 10 minutes and subsequently their color changes slightly.
Color evaluation using computer technology as an artificial vision showed that the maximum heating temperature of 210 °C had the most significant effect on color change. After heating for more than 30 minutes, carbonization of the samples occurred. At this temperature, the values in Red Green Blue system were as low as possible, tending to zero (absolutely black color) in comparison with all other treatments.
The results obtained indicate that controlling the temperature and duration of the heat treatment helps to obtain the finished product of desired color, which is important for creating products with given sensory characteristics.