In recent decades, sausage producers have significantly expanded the range of casings for cooked, smoked, and cooked smoked sausages. The latter are highly popular, especially in the summer, due to their sensory characteristics, high nutritional value, long shelf-life, and a relatively low price compared to expensive dry sausages [1, 2]. Aroma is one of the key factors of consumer preference [3–9]. The classical technology of making cooked smoked sausages involves a fairly long cooking process that includes boiling, cooling, smoking (one or two stages), and drying. Such a process demands using only permeable casings [10–12]. Artificial casings made of collagen, cellulose, and polyamide are widely used by modern producers for various reasons. Some of them include standard characteristics of steam and gas permeability, as well as geometrical dimensions, which allow for automatic sausage forming . Growing competition forces sausage producers to focus on technology, rather than the price or outcome, when choosing casings. In particular, they look at the effect that technology has on the product’s sensory characteristics . In this regard, of great scientific and practical interest is a study that aims to objectively assess the composition of volatile substances in the aroma of cooked smoked sausages formed in various types of artificial casings.
ОБЪЕКТЫ И МЕТОДЫ ИССЛЕДОВАНИЯ
Our objects of study were samples of Moskovskaya cooked smoked sausage (whole sausages) produced by the same shift on the same day according to State Standard R 55455-2013. Boiled-smoked meat sausages. Specifications. The sausages were formed in the following casings: sample no. 1 in a fibrous (cellulose) casing, sample no. 2 in a collagen casing, sample no. 3 in a highly permeable polyamide with an oxygen permeability above 40 cm3/m2∙24 h∙bar, and sample 4 in a permeable polyamide casing with an oxygen permeability less than 30 cm3/m2∙24 h∙bar.
All the samples were produced at a sausage factory. After cooling, they were packed in impermeable bags to preserve their aroma and sent to V.M. Gorbatov Federal Research Centre for Food Systems.
The sensory evaluation of sausages was carried out according to State Standard 9959-2015. The taste panel consisted of 7 qualified experts. The results were confirmed by instrumental sensory data produced by the VOCmeter (‘electronic nose’). The device is equipped with highly sensitive nanosensors capable of capturing volatile components released from the surface of the product. Prior to testing, the sausages were crushed and at least three 3 g samples were taken from each of them. The samples were placed in special vials and sealed. The vials were alternately placed into the chamber, where each sample was heated to 50°C. Then, the lid of the vial was punctured with a needle, and the gas phase was taken from near the sample surface. The gas phase entered the surface of the nanosensors sensitive to various classes of chemical compounds. Any physicochemical changes that occurred on the surface of the nanosensors were converted into an electronic signal, transmitted to a computer, and statistically processed by the software. We used four metal oxide nanosensors (M1–M4) sensitive to those aromaproducing volatile substances which are characteristic of meat products. They include products of protein breakdown, fat oxidation, ketones, aldehydes, volatile fatty acids, ammonia and other substances [15–16].
The composition of volatile aroma components was analysed by a 7890A gas chromatograph with a 5975C VLMSD mass-selective detector (Agilent Technologies, USA). For this, volatile substances were preliminarily extracted (1:1) with 40% aqueous ethanol and chloroform-methanol according to the Folch method, followed by methylation with a solution of acetyl chloride in methanol. The composition of aroma components was determined by a HP-5MS capillary column with a diameter of 0.25 mm, a length of 30 m, and a stationary phase layer thickness of 0.25 μm.
The chromatography was carried out under the following conditions:
– carrier gas: He;
– flow rate: 1 ml/min;
– injector temperature in a no-split mode: 250°C;
– initial temperature of the column thermostat: 100°C for 2 minutes;
– programmable heating from 100°C to 290°C at a rate of 20°C/min;
– an isotherm at 290°C: up to 25 min; and
– component analysis duration: 25 min.
The identification parameters were as follows:
– ion source temperature: 230°C;
– quadrupole temperature: 150°C;
– electron energy: 70 eV;
– scan mode: full; and
– mass range: 33–1050 amu.
The peaks were analysed using the NIST08 MS Library, an automated search and identification database, and the substances were named according to the IUPAC. The analysis covered those substances whose mass content in the mixture of volatile compounds exceeded 0.01%. The probability of peak correlation had to be at least 35% .
РЕЗУЛЬТАТЫ И ИХ ОБСУЖДЕНИЕ
The sensory evaluation of the Moskovskaya sausage samples in various casings did not reveal any significant differences in their consistency, colour, taste, or aroma. The tasters noted a more pronounced smoking aroma in samples no. 2 and 3, compared to samples no. 1 and 4, and a firmer surface layer in samples no. 1 and 2. They did not establish any differences in taste and aroma between samples no. 1, 2, and 3; however, they found them less pronounced in sample no. 4.
The ‘electronic nose’ was used to quantitatively identify the minimum differences in the gas phase aroma (Fig. 1).
The highly sensitive nanosensors revealed no significant differences in aroma between the samples. This was evidenced by the general nature of nanosensor responses, with the strongest signal coming from M4 and M2. Moreover, there was an image resembling a geometric figure and no intersection between the lines connecting the scale points that corresponded to the signals of the four nanosensors. The multisensory profiles of samples no. 2 and 3 practically coincided, indeed.
The analysis of sample no. 1 showed stronger signals coming from M2 and M4. These nanosensors are sensitive to the presence of aldehydes, ketones, and heterocyclic aromatic compounds in the gas phase. This might result from more intensive oxidative processes and/or an increased concentration of volatile substances due to a rapid loss of moisture during heat treatment. Another reason might be a more intensive accumulation of substances that enter the product through the casing during smoking.
The statistical processing of the nanosensor signals showed the following multisensory profile areas that characterized the intensity of the samples’ aroma (S·107, cu, P > 0.95): 179.06; 118.91; 106.51; and 84.87 for samples no. 1, 2, 3, and 4, respectively. Thus, if we take the aroma intensity of sample no. 4 (minimum value) as 100%, the intensity of samples no. 1, 2, and 3 was 211%, 140%, and 125%, respectively. These differences indicated a need for further analysis of volatile substances.
It is noteworthy that it was the first study into the composition of volatile co mponents in cooked smoked sausages. The most studied aroma is that of fermented raw and dry sausages [3–6]. Moskovskaya cooked smoked sausage is only made of beef and fatback, as well as a nitrite-curing mixture, sugar, and spices (black pepper, cardamom or nutmeg). Therefore, it was an excellent model for studying aroma in this type of meat products.
Tables 1–4 present the identification and statistical processing results for volatile substances in the sausage samples obtained with the gas chromatograph software and the automated search and identification database .
We used the NIST08 MS Library automated database to identify volatile substances with a peak correlation probability of more than 35%. Of total volatile substances, we identified 85.9; 93.31; 94.43; and 93.72% of substances in samples no. 1, 2, 3, and 4, respectively.These amounts corresponded to the peaks presented in Tables 1–4.
The atomic composition of the identified volatile substances contained 10 elements from Mendeleev’s Periodic Table, including hydrogen, carbon, oxygen, and nitrogen. These elements are the most typical in products of animal and plant origin with a cellular structure. Also present were chlorine, sulphur, silicon, fluorine, bromine, and iron (Table 5).
The presence of organosilicon compounds was due to the use of a capillary column based on (5%-phenyl)-methylpolysiloxane. This group of compounds accounted for 0.36% to 0.64% of total volatilesubstances. Due to their origin and insignificant amount, they were excluded from further analysis.
As can be seen from Table 5, all the studied samples contained two groups of compounds with the general chemical formulas of CiHkOl and CiHkOlNm. Apparently, they were the most significant compounds in the aroma of Moskovskaya sausage. Their content was 33:1, 12:1, 32:1, and 25:1 in samples no. 1, 2, 3, and 4, respectively, which could be summarized as 12–33:1.
The greatest variety of compounds was found in sample no. 1 (fibrous casing) and sample no. 4 (permeable polyamide casing). The total amount of oxygen-containing compounds was slightly higher in sample no. 3 (highly permeable polyamide casing) than in sample no. 4 (polyamide casing with lower permeability). At the same time, the content of oxygencontaining compounds in sample 1 (fibrous casing) was 11.88% (absolute value) lower than in sample no. 3. Thus, the formation of a significant amount of oxygencontaining substances in the gas phase of a product could not be explained by the choice of casing or its degree of permeability.
Table 6 shows the content of volatile substances belonging to different classes of chemical compounds. As can be seen, carboxylic acid esters were the main class of identified compounds in all the samples. Their mass fraction in the total amount of identified substances ranged from 76.61% to 81.60%. Another 4 classes of compounds, present in all the samples, were represented less evenly. For example, the content of alcohols, oxygen-containing heterocycles (except ketones and aldehydes), and nitrogen-containing heterocycles (except heterocyclic amines, amides and hydrazides) ranged from 0.3% to 0.51%, 0.2% to 8.03%, and 0.26% to 5.02%, respectively.
A detailed analysis of the classes of substances present in the aroma of the samples, as well as their elemental analysis, did not reveal any relationship between the type and permeability of the casing and the characteristics of volatile substances.
Carboxylic acid esters were mainly represented by methyl esters and less frequently by ethyl esters. On the one hand, this could be explained by the sample preparation method using methylation. On the other hand, methyl and ethyl esters could already be present in the product during its manufacture. The esters identified in the samples differed in their molecular weight, chain length, and the presence of not only carbon, hydrogen, and oxygen, but also nitrogen, chlorine, and fluorine.
In total, we found over 35 compounds with a number of carbon atoms from 6 to 23. The most represented in all the samples were the methyl esters of oleic acid with the number of carbon atoms С19 (Table 7). The predominance of this ester was due to the fatty acid composition of fatback: the content of this monounsaturated acid ranged from 30% to 45% of the total fatty acids.
We were mostly interested in those groups of substances which were found in all Moskovskaya sausage samples as a result of the sensory evaluation and the “electronic nose” tests. The data allowed us to check our hypothesis about a correlation between the aroma intensity established by the “electronic nose” and the total content of substances in the gas phase of the samples (Table 8).
The correlation analysis produced an unexpected result: an increase in the aroma intensity was proportional to the increase in the content of nitrogen-containing heterocycles and chlorine-containing substances. In that case, it was reasonable to consider only positive values of the correlation coefficients, since the hypothesis that the nanosensor signals increased as the concentration of certain substances decreased had no physical sense.
The study produced original data on the qualitative composition and the quantitative content of substances that form the aroma of Moskovskaya cooked smoked sausage. It involved a detailed comparative analysis of the main classes of compounds present in the gas phase of the samples formed in various types of casings. We found that all the samples contained two groups of compounds with the general chemical formulas of CiHkOl and CiHkOlNm. With a ratio of (12–33):1, they appeared to be the most significant in the formation of the Moskovskaya sausage aroma. Furthermore, we established that carboxylic acid esters were the main class of compounds identified in all the samples. Their mass fraction ranged from 76.61% to 81.60% of the total substances.
The data revealed no relationship between the oxidative processes and the degree of casing permeability. The correlation analysis identified the main chemical compounds that increase the intensity of cooked smoked sausages.
The practical significance of the study lies in creating a database of over 200 aromatic compounds. This database allows for a deeper understanding of aroma formation processes in cooked smoked sausages under various technological conditions. As a result, we can exert a purposeful influence on the quality indicators and create various flavour compositions to adjust the sensory properties of the finished product.
The authors declare no conflict of interest.
The authors are grateful to OOO Atlantis-Pak, a manufacturer of packaging materials, for supplying us with casings for the test samples of Moskovskaya cooked smoked sausage.
The study was carried out within the Centre’s Research and Development Plan.
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