Effect of extruded flaxseed enriched diet on physico-chemical and sensory characteristics of broiler meat

The aim of this experiment was to examine the effect of the addition of extruded flaxseed to chicken feed on physico-chemical and sensory characteristics of breast and leg-thigh meat. The basic chemical composition, pH value, instrumental colour and sensory characteristics of white (breast) and dark meat (leg-thigh) were examined by feeding two groups (both comprising males and females) of 500 Ross 308 hybrid line chickens by standard feed (control group) and with the addition of 6% of extruded flaxseed mixture (experimental group). Instrumental characteristics of colour were changed, especially in white meat. Both breast muscles of male broilers were significantly lighter, but a* values were significantly lower in m. pectoralis profundus and b* values higher in m. pectoralis superficialis of both genders. In dark meat, a* values were significantly lower in the meat of males, while b* values were higher in the meat of females. The addition of extruded flaxseed to chicken feed did not led to significant changes in the sensory characteristics of meat.


Introduction
Meat is an important source of high biological value proteins, minerals, vitamins and other nutrients. On the other hand, meat lipids do not have such beneficial characteristics, but rather properties such as high fat and cholesterol content, high energy and atherogenic value, bad ratio of saturated (SFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), low content of ω-3 PUFA, as well as a poor ratio of ω-6/ω-3 FA (Delgado-Pando et al., 2010). Dušan Živković u et al. 222 Fatty acid profile of meat lipids can be improved by a diet rich in ω-3 PUFA especially in monogastric animals (pigs, poultry and fish) since their organism absorbs fatty acids in their intact form (Bou et al., 2009).
Poultry meat has become very important in the last several decades and nowadays accounts for about 33% of global meat production (FAO, 2010). Until recently, flaxseed oil was predominantly used in chicken feed, as the use of flaxseed is limited by antinutritional factors such as: cyanogenic glycosides, phytic acid, linatin dipeptide (vitamin B6 antagonist) (Anjum et al., 2013). The extrusion process reduces the content of antinutritional factors by more than 93%, at the same time retaining useful components and rendering extruded flaxseed adequate for use in animal diet (Anjum et al., 2013).
In the process of increasing the level of ω-3 PUFA in meat, it is important to achieve positive nutritional and functional effects on meat and at the same time not diminish the sensory quality. Meat with a higher content of unsaturated fatty acids has a higher nutritional value; however, the higher content of unsaturated fatty acids, especially in dark meats, results in their oxidative instability and poorer sensory characteristics of taste and odour. Poorer taste and odour can be ascribed to the presence of compounds from, for instance, marine products used in animal feed and the oxidation of unsaturated fatty acids (Bou et al., 2009). More pronounced oxidative instability of meat means that sensory changes will also be more noticeable (Palmquist, 2009).
The goal of this experiment was to examine the effect of the addition of extruded flaxseed to chicken feed on physic-chemical and sensory characteristics of breast and leg-thigh meat as the most valuable parts in nutritional and economic terms.

Experimental design and animal management
One thousand unsexed one-day chickens of the Ross-308 hybrid line had ad libitum access to water and to the diets (starter to 28 days, followed by 28-45 day finisher). The experiment was carried out at the chicken farm of meat company "Union MZ", Svilajnac, Serbia. The chicks were reared under standard conditions of housing and management in floor pens with wooden shavings as litter material. Ventilation, lighting and relative humidity were automatically regulated. During the starter period chickens were placed in a single floor pen. On day 28 two equal groups were randomly formed in three replicates each, having an approximately equal sex ratio: control group (CON), fed by standard feed, and experimental group (EXP), fed with the addition of 6% of extruded flaxseed mixture (Croquelin, Walorex SAS, La Messaayais-35210 Combourtille, France). Some research studies indicate that extruded flaxseed level in poultry diet of 5% and more could adversely influence some sensory characteristics of broiler meat such as flavour and aroma (Anjum et al., 2013). In view of these data, the addition of 6% of extruded flaxseed mixture (3% of extruded flaxseed) to the diet was chosen to Effect of extruded flaxseed enriched diet … 223 avoid such changes. The composition of their diet is presented in Tables 1 and 2. At the age of 45 days, 15 male (CONM & EXPM) and 15 female (CONF & EXPF) chickens from each group (5 from each replicate) were selected by the average weight of the group (± 5%) and marked before being slaughtered and then eviscerated. The carcasses were air-chilled for about 2 hours until the temperature of below 4 °C was reached within the breast muscle. After weighing, 12 male and 12 female processed carcasses from each group were randomly selected (4 from each replicate); the meat was apportioned into cuts: back, two leg-thighs, two wings and breasts. Breasts (white meat) and leg-thighs (dark meat) were then deboned, the skin was removed and the meat was used for physicochemical analysis. From each group 3 male and 3 female processed carcasses were used for the sensory evaluation of the meat.

Physicochemical analysis of meat
It was explained in Experimental design and animal management section. The chemical composition of meat was determined in the following manner: water content by drying samples at 105 °C (ISO 1442(ISO , 1997; protein content by the Kjeldahl method and multiplying by factor 6.25 (ISO 937, 1978); fat content by the Soxhlet method (ISO 1443(ISO , 1973; ash content by sample mineralization at 550-600 °C (ISO 936, 1998). pH value was measured by pH-meter Hanna, HI 83141 (Hanna Instruments Srl, Sarmeola di Rubano, Italy).

Determination of meat colour
The CIE L*a*b* colour coordinates were determined by MINOLTA Chroma Meter CR-400 (Minolta Co., Ltd., Osaka, Japan) using an 8 mm aperture size, illuminant D65 and a 2º standard observer angle. The Chroma Meter was calibrated using a Minolta calibration plate (Y=87.2, x=0.3173; y=0.3348; ). C* (chroma) and h (hue angle) were calculated according to Tapp et al. (2011). The colour was measured on two breast muscles (m. pectoralis superficialis -MPS and m. pectoralis profundus -MPP) and one leg muscle (m. biceps femoris -MBF), with two measurements on each sample.

Sensory evaluation
Meat is sensory evaluated by a quantitative descriptive analysis (ISO 6658, 2005) using the scales with 5 or with 8 points, depending on the sensory property. Sensory evaluation was performed by eight assessors, previously trained for detection and recognition of various tastes (ISO 3972, 2011) and odours (ISO 5496, 2006a). Samples of leg-thigh and breast meat with bones and skin were thermally treated in the oven at 150 °C until the temperature of 80 °C was achieved in the Effect of extruded flaxseed enriched diet … 225 inner part of the meat pieces. Then, samples were served to the assessors in an identical way on white plastic plates.

Statistical analysis
The results of the chemical composition, pH value, instrumental colour measurement and sensory analysis were processed by a two-factorial analysis of variance (ANOVA). Tukey's HSD test was used to identify significant (P < 0.05 and P < 0.01) differences between groups. Calculations were done with software Statistica 6.0 (2001).

Chemical composition
Chemical composition is an important meat characteristic, not only because of the nutritional value, but also because of its effect on the sensory quality. The results of the analysis of the impact of nutrition and gender on the chemical composition of white and dark meat of broilers are presented in Table 3.
The diet to which extruded flaxseed was added did not have a large influence on the chemical composition. Statistically significant influence was established only in terms of ash content in the white meat of male broilers and protein in the dark meat of females. Crespo and Esteve-Garcia (2002) reached rather similar results and concluded that the protein content in meat was somewhat higher in animals fed by the control diet.

Instrumental colour and pH value
Colour is one of the most important sensory characteristics of meat; it is the first thing we perceive about food, it attracts buyers or puts them off, and is often related to flavour, tenderness and safety (Girolami et al., 2013). A whole series of factors affect the colour of meat, some independently, and some through mutual interactions. The physical and chemical characteristics of meat have an additional impact on colour (King and Whyte, 2006), while the pH value of meat also plays an important role. It is known that animal feed can affect meat colour, but there are few data about the effect of the addition ω-3 FA to the feed. The results of instrumental colour measurements and pH values are presented in Table  4.
Lightness (L* values) increased in light muscles due to the addition of extruded flaxseed, though significantly only in males (P < 0.05). No differences were established between genders in either group or in either light or dark muscles. Measured pH values were between 5.67 and 5.77 (MPS) and somewhat higher in MPP, 6.00-6.15, while the differences in either case were not statistically significant which indicates that the pH value was not significantly changed by the diet and that different values of lightness can be most likely attributed to nutrition. Our results correspond to the data of Betti et al. (2009) who established that the addition of flaxseed, as well as the length of the feeding period, affects the increase of lightness of white meat. The redness, a* values, in the MPS of CON groups was somewhat lower (2.48 and 2.08) relative to MPP (3.77 and 3.54). The addition of extruded flaxseed to the diet resulted in a decrease of a* values in both of the tested muscles of both genders, but significantly (P < 0.01) only in MPP -"the redder" muscle. The yellowness, b* values, was higher in test groups, though considerably only in MPS (both genders). In general, the white meat of test groups of both genders had slightly poorer characteristics in terms of colour -it was lighter, less red and more yellow.
The influence of diet on changes in parameters of instrumental colour of dark meat (MBF) differs relative to white meat. Significant changes were not determined in terms of lightness and hue angle. The a* values in EXP were considerably lower in the meat of males, while b* values were significantly higher in the meat of females. pH values of dark meat were higher (6.11-6.26) than those of white meat, which contributed (in addition to higher myoglobin content) to lower lightness and a more intensive red colour (Dadgar et al., 2012). As was the case with both white meat muscles, the diet did not significantly affect the change in the pH value ofMBF.

Sensory Evaluation
When assessing white meat, no statistically significant differences were detected in any of the observed parameters (data not shown). The panellists assessed the colour of white meat with relatively high grades, from 4.19 (CONF) to 4.31 (EXPM), while the structure of meat of all groups was assessed as fine [3.69 (CONF)-4.06 (EXPF)]. Juiciness and softness were assessed as being between juicy and moderately juicy [6.06 (CONF)-6.50 (EXPF)] and soft and moderately soft [6.13 (CONF)-6.56 (EXPF)], respectively. Taste and odour were given high grades, between good and very good (6.81-7.31).
Dark meat grades (data not shown) were very similar to the grades for white meat, and none of the observed parameters of the sensory evaluation showed statistically significant differences.
Our results confirm to the findings of Betti et al. (2009) who compared the sensory characteristics of pates made from the white meat of broilers fed by flaxseed, and concluded that texture, flavour, aftertaste, liking and the overall opinion of breast samples were not different across the range of treatments compared. Stanaćev et al. (2014) also concluded that the addition of 4% of flaxseed oil in finisher diet did not lead to major changes of sensory characteristics of breast meat. Schreiner et al. (2005) observed that panellists noticed the differences between the sampled variants of chicken meat quite rarely and with difficulty, while Lopez-Ferrer et al. (1999) believe that the use of fish oil can have bad sensory effects, and that the use of plant oils considerably improves the sensory parameters of meat compared to fish oil.

Conclusion
The addition of extruded flaxseed to broiler diet affected the instrumental characteristics of colour, most notably in white meat. Both breast muscles of male broilers were significantly lighter. Breast muscles (m. pectoralis superficialis and m. pectoralis profundus) of both EXP groups were more yellow -higher b* values and significantly higher h values, whereas a* values were significantly reduced in m. pectoralis profundus. However, these changes did not cause significant differences during the sensory evaluation of the colour of white meat. As for the dark meat of males, a* values were significantly higher in CON, while b* values in the meat of females were significantly higher in EXP. Based on the results of this experiment, we may conclude that the addition of extruded flaxseed to chicken feed did not led to major changes in the sensory characteristics of meat. Dušan Živković, Slobodan Lilić, Slaviša Stajić, Danijela Vranić, Dejana Trbović, Nikola Stanišić