REDOX POTENTIAL AND DYNAMICS OF PROTEIN AND FAT DESTRUCTION DURING STORAGE OF CANNED MEAT IN PIECES ОКИСЛИТЕЛЬНО-ВОССТАНОВИТЕЛЬНЫЙ ПОТЕНЦИАЛ И ДИНАМИКА ДЕСТРУКЦИИ БЕЛКА И ЖИРА ПРИ ХРАНЕНИИ МЯСНЫХ КУСКОВЫХ КОНСЕРВОВ

Введение Настоящая статья является второй статьей из цикла публикаций по изучению окислительно-восстановительного потенциала (Eh) мясных и мясорастительных консервов. В первой публикации [1] приведены банк значений окислительно-восстановительного потенциала мясных и мясорастительных консервов, выработанных из разных видов мяса в охлажденном и размороженном состоянии; результаты изучения влияния способов предварительной обработки мясного и растительного сырья на величину Eh сырья и консервов; показано, что характер изменения величины Eh продукта после производства зависит от степени измельчения мясного сырья и режимов стерилизации консервов. Так для кусковых мясных консервов стерилизация снижала величину Eh продукта — чем жестче режимы стерилизации, тем сильнее снижение величины Eh. Известно, что мясные кусковые консервы относятся к пищевой продукции, имеющей самый длиKrylova V.B. The V.M. Gorbatov All-Russian Meat Research Institute, Moscow, Russia REDOX POTENTIAL AND DYNAMICS OF PROTEIN AND FAT DESTRUCTION DURING STORAGE OF CANNED MEAT IN PIECES ОКИСЛИТЕЛЬНО-ВОССТАНОВИТЕЛЬНЫЙ ПОТЕНЦИАЛ И ДИНАМИКА ДЕСТРУКЦИИ БЕЛКА И ЖИРА ПРИ ХРАНЕНИИ МЯСНЫХ КУСКОВЫХ КОНСЕРВОВ


Abstract
The studies on the dynamics of the redox potential of systems and its relationship with the processes of protein and fat destruction in canned foods during their storage are fragmented and not systemized, which highlight their topicality.The aim of the research was to obtain the experimental data on the Eh values and physico-chemical indicators of canned food quality during storage in order to establish their possible correlation.It was shown that the dynamics of Eh, the content of free amino acids and fatty acid fractions in the canned products from beef and pork was different during storage.For example, a decrease in the Eh value and free amino acid content in the canned products from beef had a smooth character, while in the canned products from pork several periods were observed, which differed in the character of the change in the quality indicators.
A linear character of the changes in the proportion of fatty acid fractions during storage of the canned products from beef and pork was noticed.With that, both canned food items had an increase in the saturated fatty acid content at the concomitant decrease in the sum of mono-and polyunsaturated fatty acids.The value of an increase in the proportion of saturated fatty ac-

Introduction
The present paper is the second in the series of publications on the investigation of the redox potential (Eh) of meat and meat-and-plant canned foods.The first publication [1] presented the bank of values of the redox potential of the meat and meat-and-plant canned foods, produced from different kinds of meat in the chilled and thawed conditions, and the results of the study on the effect of the methods of the preliminary processing of meat and plant raw material on the Eh value in raw material and canned foods.It was shown that the character of the changes in the Eh value of a product after production depended on the degree of meat raw material comminution and the regimes of canned food sterilization.For example, sterilization of canned meat in pieces decreased the Eh value of a product -the stricter sterilization regimes, the greater decrease in the Eh value.
It is known that canned meat in pieces falls in the category of food products with the longest shelf life (up to DOI 10.21323/2114-441X-2016-2-26-33 5 years) depending on the type of consumer packaging.This is conditioned by the hermiticity of consumer packaging and absence of the contact with air oxygen, destruction of the active microflora and inactivation of the meat enzyme systems upon product sterilization.
The complex and interconnected biochemical and chemical processes of destruction of proteins, fats and vitamins, including hydrolysis of the high molecular weight compounds, oxidation of fat and protein substances, destruction of peptides and amino acids, formation of melanoidins, low molecular weight organic and inorganic compounds and other substances at different regimes of thermal treatment of various meat products including canned foods are studied quite thoroughly and systemized in the works of the national and foreign scientists.As for the dynamics of the above mentioned processes, which occur during storage of canned food products in pieces, some experimental material has been accumulated in this field to date, which allows discussing this issue in more detail.For instance, Gunther H. [2] and Hottenroth B. [3], when studying the abiotic processes occurred during storage of canned meat, paid attention to the correlation between the organoleptic characteristics of canned foods and the amino acid composition of muscle tissue.The more profound study of the composition of the low molecular weight compounds using the methods of gel filtration and thin layer chromatography showed that the polypeptide pool in the contents of canned foods was in the dynamic condition; that is, disappearance of some polypeptide fractions was accompanied with the appearance of others.This suggests the continuous occurrence of the processes of protein hydrolysis to polypeptides and polypeptides to free amino acids in canned meat during storage, which is confirmed by the works of the national scientists [4,5,6].The processes of protein hydrolysis are significantly responsible for deterioration in quality of canned foods stored for a long time.In particular, meat can acquire bitterish or sweatish off-taste as a result of the proteolytic processes.
Despite an importance of elucidation of the reasons and driving forces of the transformation processes in the protein constituent of canned meat in pieces during storage, the information on this issue is contradictory to date.In particular, the hypothesis of the foreign and national scientists about the enzyme nature of the process of hydrolysis of the high molecular weight proteins to peptides and amino acids [7,8] can be considered contradictory.
To date, the investigations regarding the dynamics of the redox potential of the systems and its relationship with the processes of protein and fat destruction in canned foods during storage are fragmented and not systemized, which highlights the topicality of the investigations in this direction.

Materials and methods
The canned meat products in pieces «Stewed beef of the top grade» and «Stewed pork of the top grade» produced by the traditional sterilization regimes and stored at a temperature of 37 °С and relative humidity of air not more than 75 % were used as the subjects of research.The choice of this temperature is associated with the use of the accelerated method of canned food analysis during storage.
The changes in the Eh values were measured using the FE20 instrument from the Swiss company METTLER TOLEDO.
The following methods of measurement were used in the work: -peroxide values of fat under GOST R 54346, acid values under GOST R 50457; -thiobarbituric acid (TBA) values under GOST R 55810; -fatty acid composition of lipids by the method of gasliquid chromatography on the apparatus Cristal 5000 (SKB Chromatec, Russia); -free amino acid content by the method of high performance liquid chromatography (HPLC) using the automatic amino acid analyzer PMA GmbH, Aracus; -amino-ammonia nitrogen content under GOST R 55479.

Results and discussion
We set the task of obtaining the experimental data on the Eh values and physico-chemical indicators of canned food quality during storage to establish their possible correlation.At the first stage of the work, we studied the dynamics of Eh and pH values of two canned food items during storage.The obtained results are given in Figure 1.
Attention is drawn to the big difference in the Eh values in canned food products from beef and pork, which is associated with the objective differences in the values of the redox potential of these types of meat caused by the significantly higher content of the heme pigment, myoglobin, and its oxi-and meta-forms in beef, especially, from old animals [1,9].The analysis of the Eh dynamics in canned beef showed a stable and smooth character of a decrease in this value.This suggests that the reduction-oxidative processes in canned beef are shifted towards the oxidative ones during storage.
The second period (up to 10.5 months) is accompanied by a decrease in the Eh values, which suggests the shift of the processes towards oxidation.Nevertheless, after 10.5 months of storage, the Eh value was 14.3 % higher than the corresponding value of the indicator in canned foods after production.The obtained regression equations (see Figure 1) adequately describe the dynamics of the Eh values of canned beef and pork during storage.
Different characters of the changes in the pH values of the canned foods during storage were also noticed.For instance, in canned beef, pH value grew smoothly and gradually; an increment was not more than 0.4 by the end of the 10.5 months of storage.In canned pork, pH decreased by 0.1.This can be explained by the fact that pH of canned beef is determined by the weakly alkaline or neutral products of protein destruction, pH of canned pork by free fatty acids.
At the next stage of the investigation, the dynamics of the sum of the free amino acids (ΣFAA) in the canned foods was studied.The obtained results are given in Figure 2.
Анализ данных свидетельствует о линейном характере изменения содержания фракций жирных кислот при хранении консервов из говядины и свинины.При этом в обоих наименованиях консервов отмечен прирост доли насыщенных жирных кислот при одновременном снижении сумм моно-и полиненасыщенных жирных кислот.Интересно, что величина прироста содержания насыщенных жирных кислот, связанная destruction to the low molecular weight substances was retarded or other processes occurred in parallel: the first one was the destruction of amino acids; the second was the accumulation of free amino acids due to the destruction of peptides and proteins.This picture was observed up to 7 months of storage.After 7.5 months of storage, ΣFAA slightly increased, which suggests deepening of the destructive processes in proteins and peptides in the canned foods.
The character of the changes in the amino acid content in canned pork is more complex and allows distinguishing three principally different periods.During the first period (up to 4.5 months of storage), the dynamics of ΣFAA was absent; by the 6 th month, the slight growth in the indicator value was observed.Beginning from the 6 th month and up to the 9 th month of storage, inclusive, the intensive growth in the amino acid content was observed suggesting the high intensity of the protein and peptide destruction processes, which were accompanied by the release of amino acids.
The dynamics of the amino-ammonia nitrogen (AAN) content in the canned foods presented in Figure 3 is consistent with the peculiarities of the process of protein destruction to the low molecular weight compounds.
The dynamics of the changes in the content of saturated, monounsaturated and polyunsaturated fatty acids during canned food storage is indicative of the processes of fat transformation.The obtained results are presented in Figure 4 and 5.
The analysis of the data suggests the linear character of the changes in the content of the fatty acid fractions during storage of the canned foods from beef and pork.With that, an increase in the proportion of saturated fatty acids and a concomitant decrease in the sum of mono-and polyunsaturated fatty acids were observed in both canned food items.It is interesting to note that the value of an increase in the saturated fatty acid content associated with с процессом восстановления моно-и полиненасыщенных кислот, одинакова для консервов из говядины и свинины и составила в среднем 6%.Снижение доли моно-и полиненасыщенных жирных кислот в консервах из свинины интенсивнее, чем в консервах из говядины и, в среднем, составляет 4,5-5,6% соответственно.Для консервов из говядины убыль моно-и полиненасыщенных жирных кислот составила 1,1-1,6%.the process of reduction of mono-and polyunsaturated fatty acids was the same for canned beef and canned pork and was equal to 6% on average.A decrease in the proportion of mono-and polyunsaturated fatty acids in canned pork was more intensive than in canned beef and was on average 4.5-5.6%,respectively.For canned beef, a decrease in mono-and polyunsaturated fatty acids was 1.1-1.6%.quately describe the dynamics of the Eh and pH values, the content of free amino acids and amino-ammonia nitrogen in proteins, saturated, mono-and polyunsaturated fatty acids in fats of canned beef and canned pork during storage.To date, the obtained experimental material is new.3. The character of occurrence of the oxidation and reduction processes in the product main constituents can be judged from the character of the changes in the Eh values in canned beef and pork in pieces.

Figure 5 .
Figure 5. Dynamics of the fractions of fatty acids in canned pork during storage Рис. 5. Динамика фракций жирных кислот консервов из свинины при хранении Conclusions 1.A database of new knowledge on the dynamics of the Eh values in the canned meat products in pieces «Stewed beef of the top grade» and «Stewed pork of the top grade» stored at a temperature of 37 °С was accumulated.2. The analytical dependences were obtained, which ade-