ABSTRACT
Sixteen male red deer (age <1.5 year), both farm reared and pastured in Slovakia, were assessed with an emphasis on the variability of pH, chemical, structural, and textural parameters of their Musculus longissimus thoracis et. lumborum. Pastured deer had a higher pH than farmed deer. Regarding chemical compounds, meat from pastured deer contained less protein, fat, and ash, and regarding technological parameters, drip loss and cooking loss was higher when fried at 80°C. Meat cohesiveness was quite similar for both groups, while shear force was lower in pastured deer after being roasted in an oven and being fried, and it had less coefficients of variation than hardness. The total variation higher than 85% was explained by the first five principal components for pH, chemical, and technological parameters, and 86% for textural parameters. The principal component analysis illustratively divided the pastured and farmed deer according to the assessed parameters.
KEYWORDS:
Introduction
The red deer population has significantly increased in Europe during the last decades, both in population density and in occupying new ranges.[Citation1] The increasing interest of consumers in the so-called free-range products was reflected, among others, in the development of wild animal farming in various regions of the world.[Citation2–Citation6] Currently, more than 10,000 deer-farming operations with some 300,000 deer exist in 16 European Union (EU) countries.[Citation7] Consumers expect the meat products on the market to have the required nutritional value, be wholesome, fresh, lean and have adequate juiciness, flavor, and tenderness.[Citation8–Citation10] Venison is recognized to be high in protein and low in fat, energy, and cholesterol.[Citation11] Tenderness is one of the most important parameters rated by consumers in terms of overall meat quality.[Citation12,Citation13] The conditions during rigor development (muscle pH decline, temperature/pH relationship, and carcass treatment) are very important in controlling meat.[Citation14] The objective of the present study was to assess the variability of the pH, chemical, technological and textural parameters of Musculus longissimus thoracis et. lumborum of meat obtained from red deer pastured in free range and deer raised in a commercial farm, using statistical methods, including the principal componentanalysis (PCA).
Materials and methods
Animals and sample collection
A total of 16 male red deer (age <1.5 year; body weight: pastured 78 ± 3 kg, farmed 80 ± 2 kg) were included in the study. Eight animals had had grazed natural pastures located in the central-west part of Slovakia and the other eight had been reared in the deer farm X in south-west Slovakia. The pastured group had grazed on summer herbage pastures. The farmed group received a daily portion of 500 g dry matter/head of supplementary feed: (% dry matter) organic matter 95.0; crude protein 16.1; neutral detergent fiber 25.0. The pastured animals were shot, eviscerated according to regulation[Citation15] and supplied (15 min transport) to the meat processing plant X. The farmed animals were exposed to normal pre-slaughter handling and supplied to the meat processing plant in the deer farm. The carcasses were cut according to regulation[Citation15] and kept for 6 h at room temperature (12–15°C) to avoid cold shortening, and then chilled for 18 h at 4°C according Volpelli et al.[Citation16] The meat samples collected were labeled, placed in plastic bags, and stored at a temperature of 4ºC for 7 days before cooking. The samples of M. longissimus thoracis et. lumborum were collected and measured twice. The muscle samples were analyzed for water, protein, fat, and ash.[Citation17]
pH
The pH of the muscle was measured 9, 24, and 48 h after slaughter, by means of a portable Gryf 259 pH meter (Gryf HB, Czech Republic).
Water-holding capacity (WHC) and drip loss
Water holding capacity was assessed by filter-press method, where samples (500 ± 20 mg) were put under the pressure of 10 kg for 5 min. The pressed juice was determined by the wetted area per unit weight of the sample (cm2g−1). The area was calculated from 8 diameters, assuming the wetted area was a circle.[Citation18] A muscle sample (35 ± 5 g) was suspended in a plastic bag at 1–3°C for 24 h and the liquid collected in the bag was weighed.[Citation19]
Cooking procedure and cooking loss
Three cooking procedures were used:
Meat samples (2 cm thick) were cooked in a plastic bag immersed in a water bath at 75°C for 45 min, iced for 15 min, and chilled at 4°C for 45 min. Cooking loss was expressed as a percentage.
Meat samples (2 cm thick) were roasted in a convection oven at 190°C in aluminum foil to 70°C central temperature of the sample. The cooking loss as a percentage was determined by weighing the sample before it was put in the aluminum foil and immediately after being taken out of the oven and unpacked from the foil.
Meat samples (2 cm thick) were fried on a pan. Twenty grams of vegetable frying fat (Planta, Czech Republic) were used to fry each sample. The samples were turned every other minute and the temperature was determined in the center of each sample by a handheld probe. The cooking loss was determined as a percentage when the central temperature of the sample was 60, 70, and 80°C.
Instrumental measurements were performed when the central temperature of samples cooled down to 21°C after it had reached the final cooking temperature (water bath 75°C, oven 70°C, and fried 80°C).
Volodkevich bite—shear force
Shear force measurements were performed using TA.XTplus Texture Analyser (Stable Micro Systems, UK). The Volodkevich bite jaws probe, which simulates the action of an incisor tooth,[Citation20] was used to shear cores that were cut across the fiber. The maximum breaking force (kg) was determined when compression was done until 50% of the sample. Eight cores and two shear values per core were obtained per animal per cooking sample described in the cooking procedure and mean values were reported.
Instrumental texture profile
The texture profile analysis was performed in eight cores and it was repeated twice per core per animal per cooking sample described in the cooking procedure above using the TA.XT plus Texture Analyzer (Stable Micro Systems, UK). The tested sample dimensions were 10 × 10 × 10 mm. A double compression cycle test according to Szczesniak[Citation21] was performed up to 50% compression of the original sample height with an aluminum cylinder probe of 38 mm diameter and the setting was adjusted at a pretest speed of 5 mm/s, a test speed of 10 mm/s and a post-test speed of 5 mm/s. The probe was oriented perpendicular across the muscle fibers. The following parameters were quantified:
Hardness: force needed for the 1st compression
Springiness: ratio between the distance or time of contact for the 2nd compression to the distance or time of contact for the 1st compression
Cohesiveness: ratio between the total areas under the 2nd compression curve to that under the 1st compression curve
Chewiness: product of hardness, springiness, and cohesiveness
Statistical analysis
PCA describes the variation of a set of multivariate data in terms of a set of uncorrelated variables, each of which is a particular linear combination of the original variables. The new variables (principal components), the total number of which equals to the number of the original variables in the studied data, are derived in decreasing order of importance. The first principle component accounts for as much as possible of the variation in the original data. The second component is chosen to account for as much as possible in the remaining variation subject being uncorrelated with the first component. The objective of this type of analysis is to see whether the first few components account for most of the variation in the original data. If so, they can be used to summarize the data with little loss of information. A reduction in dimensionality is thus achieved which might then be useful in visual interpretation of the data represented by two-dimensional graphics. All the computational work, including the graphical presentations, was performed using Tanagra 1.4.50 (2003) package program.
Results and discusion
displays mean values and standard deviations of pH, chemical, technological, and textural parameters of M. longissimus thoracis et. lumborum. There were coefficients of variation lower than 5% in chemical parameters such as water, protein and fat in farmed animals and in technological parameters such as WHC and cooking losses of oven roasted and fried meat. On the other hand, coefficients of variation higher than 5% and lower than 20% were obtained for fat, WHC, and cooking losses measured in pastured animals after roasting the samples in the oven. For pH, ash, and drip loss, coefficients of variation ranged from 0.05 to 0.13%. The highest coefficient of variation in both groups was in pH (0.09–0.13%).
Table 1. Means and standard deviations (SD±) of pH, chemical, technological, and textural parameters of M. longissimus thoracis et. lumborum.
Drew et al.[Citation22] recorded pH 6 in fallow deer muscle longissimus thoracis et. lumborum 8 h after slaughter, which is higher than pH measured after 9 h in both groups in our study. The average ultimate pH of pastured and farmed deer muscles was below 6.0 in the present trial. Smith and Dobson[Citation23] reported that an ultimate pH above 6 is associated with dark cutting meat in red deer. Slow decline of pH after slaughter would reduce problems of exudation of the meat.[Citation2] This study showed higher moisture content of red deer (75.76–76.32%) than Drew et al.[Citation11] who recorded lower values (70–71%). Higher content of protein, fat and ash was found in farmed deer. Protein content in pastured animals was found lower. The average protein content of M. longissimus dorsi of hinds collected in forest habitats was higher (22.02%) than in the present experiment while fat concentration was substantially lower (0.51%).[Citation24] An investigation of the chemical composition of different muscles of farmed deer indicated that, in general, farmed deer have higher intramuscular fat contents compared to free-range roe deer,[Citation25] which is consistent with our results. Low fat content (0.55% pastured–0.67% farmed) was observed in our study, which is consistent with results by Mielnik et al.[Citation26] in Norwegian reindeer meat showing very low amounts of intramuscular fat (0.5–1.6%). High total protein content (22.42%) of venison was also observed by Uherova et al.[Citation27] in forest-dwelling deer and by Stevenson et al.[Citation28] in farm-reared deer stags (23.53–23.79%). The ash content ranged from 1.18% in pastured to 1.23% in farmed deer muscle.
WHC is one of the most important attributes of the processing quality of meat. [Citation29] WHC decides about meat weight loss during storage as well as about the ability of meat to retain its water during heat treatment.[Citation29,Citation30] Meat from farmed deer had a higher WHC, cooking loss after the water bath (75°C), roasting in an oven (190°C), and frying (60 and 70°C) procedure than the meat from pastured animals. Due to the fact that the experiments on WHC, drip loss, and cooking loss using different procedures are scant and carried out with the use of different methods, it is difficult to compare the obtained results with those reported by other authors studying red deer meat.
There were no coefficients of variation lower than 5%, while there were other measurements for which coefficients of variation were higher than 30%, such as coefficients of variation for hardness in all cooking procedures. Water bath (WB) shear force was slightly higher for the M. longissimus thoracis et. lumborum of the pastured deer measured after water bath and lower after the oven roasting and frying procedures. Campo et al.[Citation31] showed the absence of correlation between WB of the cooked meat and compression data of the raw meat, and attributed it to the effect that cooking can have on texture and to the different structures that each device measures. Researchers use WB test as an indicator of sensory hardness in meat.[Citation32–Citation35] In the present work, shear force showed less coefficients of variation than texture profile analysis (TPA) hardness in all cooking procedures for all animals, therefore, shear force can indicate a precise value. The coefficient of TPA variation was very high and in many cases more than five times higher than that of WB shear force. Only in fried meat, variances for chewiness (both groups) and cohesiveness (farmed) were lower.
The first five PCs explain more than 85% of total variation for pH, chemical, and technological parameters and higher than 86% for textural parameters. Analyzing 76 morphometric variables from young Charolais bull carcasses, Laville et al.[Citation36] found that the first 10 PCs explained 80% of the total variability of those measurements. However, in rabbits, Hernández et al.[Citation37] reported the four first PCs for meat quality explained 62% of the total variation. They analyzed meat quality using 23 variables, including pH, meat color, WHC, cooking loss, fatty acid composition, and sensory parameters. Analyzing 20 variables from light lambs, Cañeque et al.[Citation38] found that the first five PCs explained 77% of total variation.
displays all variables of pH, chemical, technological, and textural parameters. The most important variables for the first PC include protein, cooking loss when fried (60 and 70°C), cooking loss when roasted in the oven, fat and drip loss. The second PC is characterized by cooking loss when fried (80°C), WHC, pH 24. The third PC is defined by pH (24, 48, and 9) and ash, which was not within the technological quality that defined the first PC. Ultimately, the fourth PC is characterized by cooking loss in water bath and water, which had little importance in the previous PCs.
Table 2. Variables of pH, chemical, technological, and textural parameters of M. longissimus thoracis et. Lumborum.
The first PC of textural parameters consists primarily of hardness after water bath, chewiness and springiness after being roasted in the oven. The second PC consists of chewiness, springiness, and cohesiveness after being fried. The third PC is mostly defined by cohesiveness after being roasted in the oven, cooked in the water bath and fried and the fourth PC by shear force after being fried, roasted in the oven and cooked in the water bath. The eating quality explains a large part of the observed variation for meat quality. All variables are placed in the loading plots ( and ). PCA was a very effective statistical tool to determine the quality of food samples[Citation39–Citation41] and this fact was also confirmed by our results.
Figure 1. Plot of the first two PC loading vectors. The labels correspond to pH, chemical, and technological parameters.
Figure 2. Plot of the first two PC loading vectors. The labels correspond to textural parameters.
Conclusion
The PCA has shown how meat quality characteristics are grouped in independent sets. The observed variations in the meat quality traits are explained by pH, chemical, and technological parameters grouped in first PCA and textural parameters grouped in second PCA. Using PCA can better explain the underlying relationships between a lot of variables affecting texture quality by reducing data and visualization. PCA provides a meaningful tool for food authenticity analysis of meat and meat products such as meat from farmed and pastured deer. PCA proved to be an effective procedure to obtain an assessment of deer meat origin.
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