Meat source

A total of 90 whole broiler chicken carcasses were randomly collected from six sources named A, B, C, D, E and F, chosen from a big retail market, in Jeddah, Saudi Arabia during April-June 2014. The sample represented two types of broiler chickens carcasses: imported frozen (A, B and C) and locally produced fresh (cold) carcasses (D, E, and F) . The frozen carcasses were one from France and two from Brazil. The sample size was five carcasses per source, replicated three times, resulting in 15 broiler carcasses per source. The carcasses were from the A grade and 1 kg weight classes, and had similar production and expire dates. However, the details of husbandry practice were not available from the producing companies. The rearing, husbandry and feeding practice were according to broilers management guide. It is well known that broilers are fed commercial diets that meet the requirements for dietary nutrients and were supplied with feed and fresh water ad libitum. Broilers were slaughtered in automatic slaughter houses according to the Islamic method.

Carcass appearance and presence of defects

Carcass appearance and presences of defects were evaluated using a scale of five where 5= excellent. This was conducted using complete carcasses and parts with the whole skin on. A score of 5 signified the following: the skin was free from tears; the flesh was free from drying-out; there was a perfect covering of fat under the skin; and lastly there were no defects such as contusions, unusual colouration, feathers, broken bones and viscera. In addition, complete broilers and parts of broilers were totally fleshed and meaty. Scale 4= good, signifying that carcasses were free of most of the above-mentioned defects and had only one defect. Scale 3= fair, signifying carcasses that had two or three above-mentioned defects. Scale 2= poor, signifying carcasses which had four to five defects. Lastly 1= bad, where carcasses had an unacceptable appearance and most of the defects listed above were in evidence.

Meat yield

Carcasses were cut into different parts such as breast and legs to obtain absolute and relative weights (as relative to the carcass weight). Absolute and relative weights of meat and bone yield were done using the deboning method to obtain the meat and bone of breast and leg parts. Abdominal fat was separated and absolute and relative weights of abdominal fat were calculated relative to the carcass weight. In addition, the carcasses were deboned and absolute and relative weight of meat and bone, abdominal fat, breast and legs were calculated.

Meat physical characteristics

Thaw loss of the frozen carcasses was determined according to loss in carcass weight after keeping the carcass at room temperature for 12 h. Carcasses were cut into two halves, and the right side of the carcasses was skinned and deboned and meat was minced using a meat mincer (Moulinex- HV8, France). Water retention capacity (WRC) was determined according to Hamm²⁶ and adapted by Garcia et al²⁷.

The meat pH was measured with an InoLab digital pH 720 meter (Germany) after homogenisation of 1 g of raw muscles for 30 sec in 10 ml of distilled water ²⁸. The colour of the breast muscle surface was measured according to Combes et al²⁹ using a colorimeter (Model CR-300, Minolta, Co., Ltd., Osaka, Japan) and expressed as Hunter values: L* (lightness), a* (redness) and b* (yellowness). Myoglobin content was determined according to Chaijan et al³⁰.

Cooking loss were determined by measuring the differences in the weight of the leg before and after cooking in boiled water for 30 min³¹ as follows: Cooking loss=(leg after cooking - leg before cooking)/leg before cooking × 100.

A filter paper assay was applied to determine the drip loss³². A 10 g section of breast fillet was kept under conditions that simulate retail sales. Samples were placed on polystyrene trays, covered with permeable plastic film, and stored at 4 ± 1 °C for 24 h. Drip loss was calculated by the difference between initial and final weights, reported on the initial weight and multiplied by 100.

Meat chemical composition

Dry matter, fat, protein and ash contents were determined according to AOAC³³, using five pooled samples per treatment, collecting the same type of meat three times per meat source. The method numbers used were 934.01 for dry matter; 954.01 for crude protein; 920.39 for ether extraction, and 942.05 for ash³³.

Meat mineral composition

Concentrations of Ca, K, Na and Fe were determined using a Varian ICP-Optical Emission Spectrometer (ICP -OEM): Varian 720-ES³⁴. Phosphorus concentrations were determined utilizing flame spectrophotometry technique³⁵.

Statistical analyses

The resulting data were statistically analysed according to SAS(36) using the PROC nested according the following model: Y_ijk= μ + C_i + B_ij + e_ijk. Where Y_ijk= observed value of the dependent variable, μ = Overall mean, C_i= Carcass type effect (Frozen vs fresh), B_ij= Source within type effect, e_ijklm= Experimental error of random distribution (0, σ²). The significance of the differences were tested at P<0.05 for all means³⁷. All percentages were transformed to their corresponding arcsine before running the analyses. Correlation analyses were also done to obtain the relationship between the different meat quality traits.

External carcass quality

Fresh (cold) carcasses had significantly superior carcass appearances and lower defects (7.8 %) than frozen carcasses, but lower skin weight (10.7 %) and a lower skin weight percentage (11.8 %) (Table 1). The low quality of frozen carcasses may be due to more handling during distribution, retailing and customers’ selections, and longer storage periods than fresh (cold) carcasses. Bird handling represents the greatest cause of downgrading and loss of quality³⁸. Poor carcass quality will definitely reflect in poorer meat quality³⁹. However, also the freezing technique can affect the carcass and meat quality as freezing process can affect the water fraction of the meat⁴⁰. With the freezing of water, the concentration of the remaining solutes (proteins, carbohydrates, lipids, vitamins and minerals) increases, thereby upsetting the homeostasis of the complex meat system⁴⁰. The changes in the immediate environment of the muscle fibers affect the cell membrane characteristics, which in turn affect the quality of the meat⁴¹.

There was a significant effect (P<0.05) of carcass sources on most of the external carcasses traits except for absolute carcass weight due to the choice of carcasses of the same category of weight. The results showed that source A of the frozen carcasses and D and E of the fresh carcasses had superior carcass appearances compared to the other sources (P<0.05). In addition, source F of the fresh carcasses had higher carcass appearance than sources B and C of the frozen carcasses (P<0.05). The external traits of carcasses can strongly affect consumer purchase decision as it is one of the main factors affecting consumer’s choice⁴² even if other factors as price, convenience, freshness and origin of the product can influence poultry meat purchase¹.

Thawing loss of the frozen carcasses was significantly (P<0.05) greater in C than in B and A sources. In addition, source B had higher thawing loss than source A (P<0.05). Increased thawing loss indicates low quality of carcass and this may be affected by age, handling processes, quality of packaging and storage conditions^38,43 as well as freezing and thawing techniques which can affect drip losses⁴⁰. Meat spoilage increases with increased length of display and storage and varies significantly between fresh and frozen carcasses^44,45,46.

The absolute and relative weights of the skin were significantly greater for source A of the frozen carcasses than that of the other sources of frozen or fresh carcasses. In addition, source B and C of the frozen carcasses had heavier absolute and relative weight of skin than source D of the fresh carcasses. The increase in weight and percentage of the skin may reveal higher fat/collagen content³⁸, and this has been shown to be affected by the strain, age and nutritional plan of broilers⁴⁸.

The absolute and relative weights of the abdominal fat were significantly heavier in source F of the fresh carcasses than those of the other sources of frozen and fresh carcasses. Abdominal fat in broiler carcasses has been found to be affected by broiler genotypes, feed restriction and nutritional plans, particularly in terms of dietary concentrations of protein or essential amino acids or energy^38,49. Increasing abdominal fat may be undesirable and has a negative impact on consumer health⁴⁹, but also in consumer choice as in recent years consumers preference for leaner carcasses has increased⁵⁰.

Breast meat characteristics

Fresh carcasses had significantly (P<0.05) greater absolute and relative weights of breast, absolute breast meat weight and absolute breast bone weight than frozen one (Table 2). However type of meat did not affect percentage of breast meat and breast bone (P>0.05).

The meat sources significantly (P<0.05) influenced not only the breast meat weight percentage, but also the breast bone weight and breast bone percentage. The results showed that within frozen carcasses, the A and B sources exhibited similar breast meat percentages, and were significantly (P<0.05) greater than that of source C. The latter group had also significantly smaller values than the different fresh sources.

Source B of frozen meat had significantly smaller breastbone weight than another frozen source (C) as well as the different sources of fresh carcasses, showing smaller bone to meat ratio: a desired trait. Source C had an intermediate value that did not differ from most of the other groups except for group E of the fresh carcasses. Within the fresh carcasses, source E had greater bone weight than the other sources. The relative weight of breast bone of frozen source C was significantly greater than that of the other sources of frozen carcass as well as the various sources of fresh meat. Carcasses with a high breast meat yield and high meat to bone ratios display a desired trait for consumers, due to increased meat quality in terms of the breast meat and low bone content. Several factors such as protein, amino acid and genotype have been reported to affect breast meat yield of broiler chickens^21,51.

Leg meat characteristics

Fresh carcasses had significantly greater leg meat characteristics than frozen carcasses except for the percentage of leg meat (Table 3). Source of carcass had a significant effect on the different characteristics of leg meat. Within frozen carcasses, source C had significantly greater leg weight and percentage than sources A and B. In addition, source F had greater leg percentage than the various sources of frozen carcasses. These trends are contrary to the findings with regards to breast meat characteristics, indicating a reverse relationship between breast meat and leg meat formation. The leg meat percentage of frozen source A was significantly greater than the other frozen sources as well as the different sources of fresh carcasses, which in turn did not show significant differences between them.

Absolute and relative weights of leg bone were significantly lower for frozen source A than for other sources of both types of carcasses. In addition, frozen source C had significantly smaller leg bone weight than the other sources of fresh carcass. The increase in leg meat of frozen source A concurred with a decrease in leg bone, indicating an increase in the meat to bone ratio: a desired trait. Differences in leg meat could be attributed to: strains, age, and the nutritional regimen^48,51.

The carcass weights show weak to moderate positive correlations with: thaw lass (r=0.817; P=0.001); breast weight (r=0.218; P=0.039); breast meat (r=0.237; P=0.025); leg weight (r=0.402; P=0.001); and leg meat (r=0.447; P=0.001). Similarly found correlation between the intact upper arms and the skin, bone and muscle to be significant at r=0.60, 0.50 and 0.95, respectively⁴⁵. In addition, there was a positive relationship between thaw loss and carcass defects (r=0.433; P=0.003), and a negative relationship between carcass defects and breast weight (r= -0.218; P=0.0388), breast meat (r=-0.305; P=0.003), leg weight (r=-0.259; P=0.0125) and leg meat (r=- 0.320; P=0.002). Skin weight similarly showed a slight negative correlation with leg weight (r=-0.279; P=0.007) and leg meat (r= -0.241; P=0.0219). Breast weight had a positive correlation with breast meat (r=0.894; P=0.001); breast bone (r=0.600; P=0.001); leg weight (r=0.452; P=0.001); leg meat (r=0.288; P=0.006); and leg bone (r=0.463; P=0.001). Breast meat showed a similar magnitude of correlation with breast bone, leg meat and bone. A weak positive correlation between breast bone and breast meat (r=0.344; P=0.009), and leg bone (r=0.359; P=0.005) was observed. In addition, leg weight showed a positive, moderate correlation with leg meat (r=0.633; P=0.001) and leg bone (r=0.629; P=0.001).

Meat physical characteristics

Fresh carcasses had significantly (P<0.05) lower: pH, drip loss, yellowness (Table 4). However their lightness was greater. This indicated that fresh carcasses were of superior quality compared to the frozen meat. Consistent with these results, other study⁴⁵ found also a strong relationship between physical appearances and odour of the meat: both criteria were negatively influenced by increasing length of display or storage. The differences in pH and drip loss could be attributed to different glycolysis rates post-mortem, and are in line with those reported by other researchers^52,53. On the other hand, it is reported⁴⁷ that frozen storage had no marked influence on pH change and organoleptic attributes such as appearance, flavour, texture and overall palatability, except for juiciness, however there are very important freezing and thawing techniques³⁹.

Differences between frozen and fresh carcasses in WRC, cooking loss, redness and myoglobin were not significant (P>0.05). However, the different sources did have a significant (P<0.05) effect on the meat colour. The results demonstrated that within the frozen carcasses, source A had significantly greater lightness, redness and yellowness than sources B and C. There was only a small difference (P<0.05) between sources B and C in terms of yellowness, showing a greater value for B than for C. Within the fresh carcasses, a significant difference (P<0.05) was only shown in redness with source F having a lower value than D and E. Differences in meat colour could be attributed to the genetic origin of the broilers, as well as dietary pigmentation content^38,48. These differences may also reflect differences in carotenoid content and hence antioxidants. In addition, meat colour can be influenced by: the age, sex, and stress of birds; as well as, intramuscular fat, moisture content, pre-slaughter conditions, and several processing variables^54,55. Furthermore, amount of pigments such as myoglobin and haemoglobin within the muscles can also affect the meat colour. Pearson correlation coefficient analyses among the dry matter and the different physical characteristics of meat demonstrated a lack of relationship except for pH correlated with dry matter (r=0.605; P=0.001) and weakly with WRC (r=0.428; P=0.001).

Nutrient profiles

Fresh carcasses had lower (P<0.05) dry matter and crude protein than the frozen carcasses (Table 5); and also superior juiciness than the frozen meat. Differences in the lipid and ash percentage were not significant (P>0.05). Onibi⁴⁵ found that moisture and lipid contents of meat samples were 69.89 and 4.58 % respectively, and they were similar to the values in this report. The meat sources had no significant effect within either frozen or fresh types, in relation to the nutrient profiles of meat. Similar conclusions were cited by several researches^48,52,56, attributing the differences in chemical composition of broiler meat to genetic origin and nutrition plans^10-12. On the other hand, Santosh et al⁴⁶ indicate fresh chicken dressed under different condition reveal marked differences in their physic-chemical and microbiological qualities. These differences among different experimental results could be attributed to genetic factors i.e. stress, age and sex of birds and non-genetic factors such as feeding regimen, housing condition and husbandry practice¹².

Correlation between three (organic compounds) out of four nutrients in meat was significant with moderate to high magnitudes of correlation. The relationship between dry matter and protein (r=0.796; P=0.001) and lipids (r=0.906; P=0.001) were positively significant and high. In addition, the correlation between protein and lipids were positively significant and moderate (r=0.595; P=0.0005). However, ash percentage did not correlate with dry matter, protein or lipids. Hence, dry matter showed a strong relationship with the organic compounds in meat rather than the inorganic compounds. This could be explained by the greater distribution of protein and lipids (96 %) compared to ash (3 %).

Mineral content

Table 6 displays the impacts of the various types and sources of meat on their minerals content (Ca, P, Na, K and Fe). The overall mean of minerals content of meat are in acceptable range reported by USDA in National nutrient data base standard references release 27 for broilers and mature, and those reported by different studies^57-60. However, it should be mentioned that source A of frozen carcasses showed the lowest values of minerals, except for phosphorus and iron and can account for the variability in mineral contents of the present samples. Mineral contents in meat were found to be affected by feeding, management practice, slaughter age, storage and handling conditions and instruments used in mineral determination^59-61. The results showed that K is the predominant element followed by Na, Ca, P and Fe. Similar findings were reported by other research groups^57-59. These authors reported that the mineral content of broiler meat was affected by dietary vitamin and mineral contents, sex of chickens, dark vs light meat (i.e. breast vs leg), disease status, and age at slaughter.

Fresh meat had significantly (P<0.05) higher Ca, Na, and K than frozen carcasses, but P was lower. On the other hand, iron was not significantly (P<0.05) different among types (frozen vs fresh) and sources of meat. The lower Ca, Na and K measurements in the frozen meat demonstrate the negative effects of freezing, handling and thaw on the cell membranes, causing loss of essential elements and hence reducing the nutritious value of meat. It was found that source F of fresh meat had the greatest levels of Ca while source A of frozen meat had the lowest value. The F and A groups were also different (P<0.05) than the other groups of frozen and fresh meat. In addition, source B and C of the frozen carcasses and D and E of fresh meat had similar Ca concentrations.

There was no significant difference in meat P among different sources of frozen and fresh meat. Differences in Na content was obvious within the frozen meat, showing greater Na in source C than that of the other sources. Within the fresh meat, sources E and F exhibited greater Na content than source D. The potassium content of fresh source E was significantly (P<0.05) greater than that of the other sources. Differences within the frozen meat were not significant (P> 0.05), but sources D and F of fresh meat did exhibit significantly greater K content than only source A of the frozen meat. K is an essential element, needed for many body functions^22,60.

The negative effect of freezing process on nutritive value of meat, in terms of its mineral content (Na, Ca, P and K), may be due to cold shock, which results in damage of the cell membranes and leakage of minerals. It is well known that meat minerals play a significant role in enzymatic processes, influencing muscle pH and hydration of protein. In this regard, elements such as Na, K, Ca and Mg play an important role in maintaining osmotic pressure and the electrolyte balance in the cells and tissues, hence they also play an essential role in regulating the hydration of meat^21,23. Moreover, P found in meat, in the form of phosphates, plays a significant role in maintaining WRC^61,62.

In most cases, correlation analyses between the mineral contents of meat showed that correlation between the five minerals was generally absent except for a significant positive moderate correlation between Na and Ca (r=0.575; P=0.003) and K (r=0.449; P=0.011). In addition, a weak, negative correlation was observed between Fe and K (r=-0.479; P=0.015). The correlation between physiochemical characteristics of meat and meat mineral Na, Ca, K, P and Mg was low in most cases (61). Furthermore, it depends on the cut type, such as breast vs leg. In red muscle, an increase in K is correlated with lower WRC, with a pH of 2, at 15 min and 24 h post- mortem, along with higher cooking loss. They also reported a moderate positive relationship between P content and pH at 15 min, but a moderate negative correlation between P and yellowness.