DETERMINATION OF C O -VALUE AS AN INDICATOR OF NUTRITIVE VALUE OF PÂTÉ STERILISED BY REGULAR AND OPTIMIZED REGIMES

Introduction . Heat treatment of food provides appropriate shelf life and safety, as well as adequate sensory properties and better digestibility, but excessive thermal processing leads to the loss of nutritive value. In practice, sterilised meat products are usually overheated, which leads to a loss of nutritive value. Therefore, it is necessary to find the optimum between the preservative effect of heat treatment and maintenance of the nutritive value of food. Control of the sterilisation efficiency is based on the F o value, an indicator of the lethal effect of heat treatment, while the cooking (C o ) value indicates a reduction of the nutritive value of heat treated products. Materials and Methods . During pâté sterilisation processes, two working heat treatment regimes were used: the regime used in regular, commercial production and an optimised regime. Heat treatment measurements were carried out using six thermocouple probes placed in the geothermal centres of six chosen cans. For each heat treatment, schematic diagrams were produced. F C o values achieved during the sterilisation process can make a significant contribution to obtaining products with a better nutritional value through an optimised sterilisation process, without jeopardising product safety.

C o values achieved during the sterilisation process can make a significant contribution to obtaining products with a better nutritional value through an optimised sterilisation process, without jeopardising product safety.

INTRODUCTION
Heating is a form of energy input in the process of processing and preparing food. It can be of varying intensity (pasteurisation, cooking, sterilisation), and in food processing, depends on the nature and composition of the foods. Heat transfer is carried out by conduction or convection (flow) (Wareing, 2010).
Heat treatment is a physical method of preserving food that uses high temperature to destroy microorganisms and inactivate tissue enzymes. The heat treatment process should eliminate pathogenic and spoilage microorganisms to the extent that they do not pose a threat to consumer health, but heating should not deleteriously affect the quality of the final product. The degree of applied temperature is proportional to the antimicrobial effect (Nitsch and Vuković, 2002;2003;2006;FAO, 2010). However, this is not straightforward, since microorganisms are grouped non-homogenously in solid foods, and the applied heat can have difficulty penetrating to the centre of a microbial colony, while the microorganisms in the centre of a can are more difficult to destroy than those at the periphery. Food is also altered during heat treatment, which causes appropriate sensory property changes (e.g., to flavour, texture) in the food. Excessive, non-optimised heat treatment leads to loss of nutritional value of food. Therefore, it is necessary to find the optimum between the conserving effects of heat treatment and preservation of the nutritional value of food (meat) products (Teodorović et al., 2015).
In the system of integrated control of production and processing of meat according to the Hazard Analysis Critical Control Points (HACCP), a special place is held by the control of heat treatment. In all HACCP plans, heat treatment is designated as a critical control point (CCP) and is represented on a flow diagram as the process where a hazard is eliminated or reduced to the lowest acceptable measure (Surak and Wilson, 2014).
For the purpose of reliable control of heat treatment process efficiency, the F o value is useful. The F o value is based on the fact that during humid environment heating, microorganisms die in a logarithmic pattern. F o value expresses the lethal effect of a reference heat treatment temperature during one minute. If F o = 3 or more is achieved, it is considered that any thermoresistant Clostridium botulinum types A and B spores are destroyed (Nitsch and Vuković, 2002;2003;2006).
The cooking value (C o ) expresses the reduction in the nutritional value of heat treated products. There are no norms or recommendations for C o values, so the optimal process of heat treatment is the one that has a lower C o value for a given F o value (Vuković, 2012).
Pâtés are meat products derived from meat, fat tissue, connective tissue, intestines, blood, blood products and additives that are conserved by heat treatment in hermetically sealed containers or appropriate envelopes after various forms of heat treatment (Anonymous, 2015). Meat as a raw material for making canned products must have optimal hygienic and technological qualities, provided by measures such as selection of animals, adequate preparation for slaughter and adoption of suitable slaughtering operations, until the meat is sealed in the can. During heat treatment of canned meat products, the characteristic sensory properties (e.g., colour, flavour and texture) of the final product are formed, while the temperature affects the viability of microorganisms, thereby ensuring the product's safety and shelf-life (Rubén et al., 2018). Notably, the canning process uses packaging (cans) which remains its basic hermetic characteristic during the product's shelf-life (Teodorović et al., 2015).
Sterilisation is the process of the heat treatment of cans at a temperature higher than 100 °C, wherein in the thermal centre of the product at least a lethal value of F o = 3 must be achieved (Anonymous, 2015). Sustainability of the cans depends primarily on the degree of destruction of the bacteria (biological sterility), which is extremely difficult to attain without irreversible loss of the organoleptic properties of the product. The sterilisation regime is, therefore, adjusted to achieve commercial sterility (FSIS/USDA, 2005). Commercial sterility involves the destruction of vegetative forms and spores of Clostridium botulinum and Clostridium perfringens, destruction of Enterobacteriaceae and staphylococci, absence of toxins, enzymes and microorganisms which could produce them, but with a tolerance for non-pathogenic Bacillus spp. spores, when these are not capable of causing product spoilage within at least 6 months (FAO, 2010). If the pH value of the filling is lower, the effect of the heat treatment will be higher (Clostridium botulinum cannot produce toxin at a pH less than 4.6) (Codex Alimentarius 2011). However, since meat products belong to the group of low acid foods (pH >4.5), spores of Clostridium botulinum have to be destroyed (Anon, 2011).
The higher the applied sterilisation temperature, as well as the longer the effective operating time, the greater the loss of nutritional value will be. In addition to ensuring food safety and sustainability, an important task of heat treatment is the preservation of the biological value of meat and meat products (Pither, 2003). Also, during the heat treatment of liver, which is an important component of liver pâté, irreversible changes occur to the protein ferritin at temperatures above 80 °C, when it can precipitate (Prochaska et al., 2000). Often, therefore, microbiologically flawless, practically sterile canned liver pâtés have a softer consistency, more or less pronounced brown colour and false aroma. These methods of intense, long-term sterilisation are applied by producers who have problems with hygiene practices in their facilities, in order to produce products with a commercially acceptable shelf-life. Liver pâtés heat treated in this way have a lower biological value, while because of higher energy consumption, the profitability of production is always questionable (Pither, 2003).
The aim of this research was to determine F o and C o values for the heat treatment regime used in regular liver pâté production as well as for an optimised regime. The two heat treatment regimes were compared in order to determine opportunities for improving the current sterilisation regime used in the industry, while still producing a safe product with better nutritive value.

MATERIALS AND METHODS
Systematic monitoring of heat treatments (sterilisation) of liver pâté was carried out in a meat processing facility. Pâté (90 g amounts) was packed in aluminium containers. Sterilisation was carried out under saturated aqueous vapour conditions in a horizontal autoclave with an overpressure valve (Steriflow Roanne France, type 1341 EA, year 2013) that accommodated four trolleys. Heat treatments were carried out on three trolleys filled with product, due to the limitation in the time of loading the filled mass in cans of two hours (FSIS/USDA, 2005). During the pâté sterilisation process, two working modes were used: A mode, used in regular production and the optimised B mode. The heat treatment formulas are given in Table 1. The heat regime defines the heating time, effective sterilisation and cooling time.  The measurements were carried out by means of a thermocouple (Ellab model CTF 84). Thermoelements with compensating cables were used, including a total of six probes. The probes were placed in the geothermal centres of the six chosen cans which were placed at different points in three trolleys. The positions of the cans with inserted probes were the same for both sterilisation regimes and are shown in Figures  1 and 2.
The F o values for each treatment were determined in real time immediately using original Ellab software, which could be observed on the display along with the temperature in the geothermal centres of the examined cans.
The graphic method described by Vuković (2012) was used to determine C o values, using a semi-logarithmic Thermal Death Time (TDT) diagram (Figures 3 and 5), on which two strait lines were previously constructed, representing: C o = 1 (1 minute at 100 °C, z = 33 °C, blue line in Figures 3 and 5) and F o = 1 (1 minute at 121.1 °C, z = 10 °C, rose line in Figures 3 and 5). In order to determine the C o value of the examined heat treatment, it is necessary to know the F o value of the sterilisation process and  the time (in minutes) the temperature measured in the geothermal centre of the cans is equal to or higher than 100 °C. C o value is obtained by drawing a line (green line in Figures 4 and 6) parallel to the line C o = 1, which passes through the intersection point of the line drawn on the basis of the measured F o value (it is parallel to the line F o = 1, red line in Figures 4 and 6) and the line drawn on the basis of time operating temperature higher than 100 o C for the heat treatment regime (black line in Figures 4  and 6). There are no norms or recommendations for C o values, unlike for F o values, so the optimal process of heat treatment is the one that, for a given F o value, has a lower C o value (Vuković, 2012).

RESULTS
The following Table 2.
According to Figure 3, the obtained F o value of the chosen regular regime example was 8.58, the temperature of 100 °C was reached after 24 minutes of the process, and it decreased below 100°C after 82 minutes of the process, which means that the temperatures above 100°C lasted for 58 min. Figure 4 shows the process of C o value determination for the regime described in Figure 3. Based on the F o value of 8.58 (red line) and temperature above 100 o C which lasted 58 minutes (black line), a C o value of 112 min (green line) was calculated.
According to Figure 5, the obtained F o value of the chosen optimised regime (B) was 3.1, the temperature of 100 °C was reached after 27 minutes of the process, and it decreased below 100°C after 72 minutes of the process, which means that the temperatures above 100°C lasted for 45 min. Figure 6 shows the process of C o value determination for the regime described in Figure 4. Based on the F o value of 3.10 (red line) and temperature above 100 o C which lasted 45 minutes (black line), a C o value of 82 min (green line) was calculated.  By comparing the results obtained from the regular and optimised regimes, the reductions in the parameters of interest are presented in Table 3. The results obtained showed that the C o value was reduced on average by 19.26%, indicating that the products processed by the optimised regime B had a 19.26% better nutritive value than products processed by the regular regime A.  (Anon, 2015) states that sterilisation is a process for the heat treatment of cans at a temperature higher than 100 °C, and that in the centre of the product, an F o value of at least 3 must be achieved. According to FAO (2010), in order to provide product safety as well as product quality, the sterilisation of meat products packed in cans must achieve F o values between 2.52 and 5.5, whereby the temperature of the medium itself should range from 117 to 130 °C, depending on the characteristics of the products themselves. The optimised regime B meets both requirements, but the F o value of the regular regime A is much higher (7.90) than the FAO recommended maximum of 5.5. According to the national regulations (Anon, 2015) as well as FAO (2010) recommendations, the optimised regime B should produce a product shelf-life of four years at storage temperatures up to 25 °C.
The regular heat treatment regime A (Table 1) lasted 1 hour and 30 minutes. For this sterilisation regime, the average F o value in the geothermal centre was 7.90 ± 0.43, which ensured the safety of the product, but this was 2.63 times higher than the value required by regulations. Such a process ensures that any spores of thermoresistant Clostridium botulinum types A and B are destroyed (Nitsch and Vuković, 2002;2003;2006;Teodorović et al., 2015), but overly excessive heat treatment is not recommended because of the negative influence on the biological value of meat and meat products (Pither, 2003).
In the optimised heat treatment regime, with identical sterilisation conditions (temperature and pressure of the product), but with the effective sterilisation time shortened by 10 minutes, the entire heat treatment process lasted 1 hour and 20 minutes. The average F o value 3.81±0.5 also ensured the safety of the product, but was only 1.27 times higher than the value required by regulations. As temperatures higher than 100 °C significantly affect the biological and nutritive value of meat (Pither, 2003;Vuković, 2012), shortening the operating time by 10 minutes also shortened the influence of temperatures higher than 100 °C by 17.32%. Compared to the regular heat treatment regime A, this resulted in an average decrease of C o value by 19.26%. Consequently, products processed using the optimised B regime may be considered to have a 19.26% better nutritional value than products processed using regime A.

CONCLUSION
During the sterilisation of pâté in aluminium foil (90 g), with an effective time of 55 minutes (regular regime), at 114 °C and pressure of 3.2 bar, an average F o value of 7.90±0.43 was achieved. By reducing the effective sterilisation time to 45 minutes (optimised regime), an average F o value of 3.81±0.5 was achieved. Both heat treatment regimes were sufficient to ensure product safety (F o >3). Average C o values were 109.83±1.33 and 88.67±4.27 minutes for the regular and optimised regimes, respectively. The optimised sterilisation regime provided a 51.77% reduction in F o value, while the operating time at temperatures higher than 100 °C was shortened by 17.32%. The C o value was reduced by 19.26% which corresponds to a proportionally higher nutritional value of the product treated with the optimised regime, while the safety of the product was not compromised.
Analysis of F o and C o values achieved during sterilisation processes can make a significant contribution to obtaining products with better nutritional value through milder sterilisation regimes and without compromising product safety.