Incorporation of cactus (Opuntia ficus-indica f. inermis) in young goats diets: 2. Effects on meat quality and fatty acid composition

F Zouaghi, M Mahouachi* and N Atti*

INRA-Tunisie, Laboratoire de Productions Animales et Fourragères, 2049 Ariana, Tunisia
* Ecole Supérieure d’Agriculture du Kef, Le Kef, Tunisia
belhaj.naziha@iresa.agrinet.tn

Abstract

The objective of this study was to determine the effects of feeding system based on spineless cactus on meat characteristics, sensory qualities and fatty acid (FA) profile of local male kids. Thirty male kids (initial live weight (LW) =17.4 kg) were assigned randomly to five dietary treatments. All groups received 600 g of oats hay per animal per day. The two first groups received 600 and 400 g of concentrate containing 130 (C130) and 200 (C200) g crude protein (CP) per kg of dry matter (C130 and C200 groups, respectively). Two other groups received spineless cactus (Opuntia ficus indica f. inermis) ad-libitum and 400g of C130 (C130-Cac group) and 300 g of C200 (C200-Cac group). The last group received spineless cactus ad-libitum and 200 g soya bean meal (soya-cac). The experiment lasted 12 weeks and then all animals were slaughtered. Samples of longissimus dorsi muscle were taken for meat quality measurements and FA determination.

Meat color parameters (L*, a*, b*) were not affected by dietary treatments. Also, no significant differences were found among groups for cooking loss. Moreover, dietary treatment had no significant effect on meat moisture, ash, crude fat and protein contents, but meat produced with cactus tended to be leaner than other groups. However, the intra muscular lipid composition in FA showed differences between cactus and no cactus groups. Cactus in the diet was associated with more conjugated linoleic acid as well as a higher proportion of the polyunsaturated fatty acid DPA (C22:5n-3) than other diets. Finally, the tasters perceived that the meat of all groups was considered to be juicy and meat of no cactus kids (C130 and C200) was more tender compared to that produced on cactus.

Keywords: goat kids, spineless cactus, saturated

Introduction

Meat quality is a term used to describe the overall meat characteristics including physical, chemical, sensory, technological, nutritional and culinary properties. It is an important criterion that influences the decision of a consumer. The feeding plan is considered one of the most important factors that affect meat production and quality. Compared to concentrate diet systems, grass feeding has been reported to affect several meat quality characteristics, in particular color, flavor and fatty acid (FA) composition in lambs, beef, cattle and goats (Poulson et al 2004; Varela et al 2004; Gattellier et al 2005). The fatty acid composition of meat has long been studied but still receives a lot of attention in research because of its implications for human health. Besides a lower total fat intake, human nutritionists are recommending a higher intake of polyunsaturated fatty acids (PUFA), and especially of n-3 fatty acids at the expense of n-6 fatty acids (Williams 2000; Semma 2002). On the other hand, conjugated linoleic acids (CLA), in particular c9t11 CLA and t10c12 CLA, are presently the subject of intensive research because of their potent anticarcinogenic effects as well as effects on the immune system and lipid metabolism (Geay et al 2001).

Otherwise, it has been reported that cactus incorporation, as a green forage, in diets influenced FA composition of kid meat lipids, by increasing the levels of C18:2 and CLA as well as the proportion of PUFA (Atti et al 2006) Furthermore, quantifiable properties of meat such as water holding capacity, cooking loss, pH are the important technological characteristics representing the aptitude of the meat to conservation and transformation (Monin 1991). However, no data are available concerning the effects of cactus on meat sensory evaluation which is of importance, to influence the quality judgment by consumers before and after purchasing a meat product. Hence, this paper reports the effects of cactus vs concentrate diet on meat characteristics, organoleptic qualities and FA composition of kids. The results of the growth, digestibility and carcass composition were reported in the companion paper (Atti et al 2009).

Material and methods 

Animals and feeding

Meat quality from the kids slaughtered at the end of the experiment described in companion paper (Atti et al 2009) was studied. Three kinds of concentrates, soya bean, C130 and C200 (containing 130 and 200 g crude protein per kg dry matter, respectively) were used on 5 groups of five local goat kids 7 months old and 17.4 kg live weight.  All animals received 600 g of oat hay per animal per day and one of five supplements, 600 or 400 g of concentrate C130 or C200 (C130 and C200 groups, respectively), spineless cactus ad libitum plus 400 g of C130, 300 g of C200 or 200 g of soya (C130-Cac, C200-Cac and soya-cac groups, respectively). Animals were allowed 84 days in this growth trial and then were slaughtered. One hour post mortem the carcasses were placed in a chiller room at 4ºC air temperature. At 24 h post mortem, the  longissimus dorsi (LD) muscles (6^th to 13^th rib) which subcutaneous fat removed were separated and conserved at -20°C until  sensorial and instrumental meat quality evaluation, chemical analysis and FA composition.

Meat quality measurements

Instrumental measurements

The pH was measured with an Orion 9106 penetrating probe after calibrating with two buffers (7·00 and 4·01). Color variables (L* (lightness), a* (redness), b* (yellowness)) were measured using a Minolta CR 400 color meter calibrated to a standard white tile. Chroma (C*, the square root of (a*+b*)) and hue angle (H*, tan^-1 (b*/a*) were also calculated (Priolo et al 1998).

For the determination of cooking loss, meat samples were weighed (Wi) and held in plastic bags and then immersed in a water-bath at 75 °C until the internal temperature reached 75°C, which was monitored with a thermocouple (30 minutes). Then the bags were cooled under running tap water for 30 min and blotted dry with paper towels (Boccard et al 1981). The cooked meat was weighed again (final weight, Wf) and cooked loss (g/kg) was calculated as 1000 X (Wi _ Wf) / Wi.

For chemical composition of the Muscle longissimus dorsi, samples of meat were dried by lyophilisation, ground (1 mm screen) and stored for subsequent analyses. Mineral content was then determined by ashing at 600°C for 8 h. Nitrogen was determined by Kjeldahl method (CP = N x 6.25), meat lipids were calculated as DM minus the sum of protein and ash.

Fatty acid composition

The fatty acid composition of the diet (Table1) and the intra muscular (i.m.) fat was analyzed after extraction and methylation with K-OH on chromatograph (HP-5890) equipped with a flame ionisation detector and split (1:24) injector. Separations were performed using a HP-FFAP capillary column (25 cm x.2mm i.d. x .3µm), the injector and detector were set at 230° C.

The sum of saturated fatty acids (SFA), polyunsaturated (PUFA) and desirable fatty acids (DFA) as well as the PUFA: SFA ratios were calculated. The DFA corresponds to the sum of all unsaturated fatty acids and C18:0 (Rhee 1992).

Sensory evaluation

Meat samples were roasted in aluminum paper in a pre-heated oven at 180ºC. No salt was added to the meat. Each cooked meat sample had been cut into six pieces of 1x1 cm and were coded and served in random order for testing. There were five sessions of assessment and each panelist tested 6 different pieces per session. Panelists were trained during two sessions on different species meat before the assessment of this trial meat samples. Bread and water were provided for each panelist to freshen their mouth between each two samples. Panelists evaluated each sample for the following attributes:

Tenderness (scale 1-10; 1=extremely tough, 10=extremely tender)

Juiciness (scale 1-10; 1=extremely dry, 10=extremely juicy).

Flavor (scale 1-10; 1=very poor, 10=very good)

Statistical analysis

Statistical analysis was performed by analysis of variance using the GLM procedure of SAS (1989). The effect of dietary treatment on meat characteristics, organoleptic qualities and FA composition was analysed. Differences between groups were evaluated by t-test; significance was declared at P<0.05. The contrast [C130+C200 vs C130-Cac+C200-Cac+Soya-Cac] was used to compare the effects of cactus diets vs. no cactus diets.

Results 

Meat physical and chemical characteristics

Chemical and physical characteristics determined on LD muscles were shown in Table 2.

The meat ultimate pH ranged between 6.5 and 6.9 in the five groups, it was not affected by the feeding treatment and the contrast [no cactus vs cactus] was not significant. Also, meat from different treatments did not differ significantly (P>0.05) for cooking loss and color parameters (a*, b*, L*, hue angle and chroma). However, compared to no cactus animals meat from kids given cactus tended to be darker with lower values of lightness (L*: 41.3 vs 43.1), more red with a higher redness values (a*: 16.9 vs 15.5%) and more yellow with a higher b* (9 vs 7.5). No differences were found for moisture, crude protein and ash contents between treatment groups. The crude fat varied between 91 and 151 g/kg DM for C200-Cac and C130 groups respectively. So, cactus fed kids had a tendency to be leaner than no cactus ones, but the difference between groups was not significant.

Fatty acid composition

The major fatty acids were C16:0, C18:0 and C18:1 for all groups without significant difference between them. The intra muscular (i.m.) lipid composition showed differences between animals receiving cactus and those not receiving for CLA and DPA (C22:5n-3). They were significantly higher (P<0.001) in the group receiving the lowest quantity of concentrate with the highest quantity of cactus (Soja-Cac) compared to other groups. The contrast (no cactus vs cactus) was significant only for CLA (P<0.01). For C22:5n-3, values increased with increasing cactus incorporation in kid diets. There was no significant influence of feeding (P>0.05) on the SFA, PUFA and the PUFA/SFA ratio (Table 3).

Meat sensory evaluation

Results of sensory evaluation were shown in Table 4.

Meat from no cactus kids was more tender than cactus-fed ones (P<0.001); furthermore meat was judged more tender when increasing the level of concentrate in the kids ration. No significant differences (P>0.05) were reported for juiciness between dietary treatments, meat from all groups was judged juicy (7.2-7.6). Finally, there was no significant effect of diet on meat flavor, this criterion was considered medium.

Discussion  

Meat physical and chemical characteristics

Meat from all dietary treatments had similar pH at 24 h post slaughter. No significant differences in relationship with dietary difference were reported for meat pH for cattle (French et al 2000; Varela et al 2004) and lambs (Diaz et al 2002). However, other authors indicated that grass-fed animals had higher ultimate pH values than grain-fed animals (Muir et al 1998; Vestergaard et al 2000; Nũernberg et al 2005). Inversely, Atti et al (2006) mentioned that the inclusion of cactus in kids diet showed a lower ultimate pH compared to meat from the control diet. Moreover, the ultimate pH of muscles can have a large effect on meat color (Kadim et al 2006), meat becoming darker as its ultimate pH increases from 5.4 to 7.0 (Muir et al 1998).

The cooking loss from muscles was in the range of 150–180 g/kg, which is within the normal range for goat muscles (Kannan et al 2001, Atti et al 2006). However, higher cooking losses (210-370) were reported (Kadim et al 2003, Choi et al 2005) for goat meat.

Muscle color is an important criterion by which many consumers evaluate meat quality and acceptability (Sami et al 2004). Cactus incorporation in kid’s diet had no effect on color parameters, although a tendency to a darker meat. Yang et al (2002), Poulson et al (2004) and Gattellier et al (2005) found darker meat in forage-fed animals than in concentrate-fed ones. However, Nũernberg et al (2005) hypothesized that grass feeding was found to improve the stability of meat resulting in improvements of color and shelf life. This is related to the naturally high content of α-Tocopherol (vitamin E) in grass (O’Sullivan et al 2002; Gattellier et al 2005). This very important antioxidant helps to stabilise the fats and color pigment in stored meat.

The inclusion of cactus tends to reduce intramuscular fat proportion, which in accordance with other results (Atti et al 2006). The modification of kids feeding to substitute energy-dense concentrate ingredients with grass of lower energy concentration resulted in carcasses with lower intramuscular fat content. This result was in line with that of Sami et al (2004) showing that bulls intensively fed had higher fat contents in comparison with the extensively fed bulls, to hypothesize that the high energy diet resulted in a high intramuscular fat content. French et al (2003) did not find differences between percentages of intramuscular fat when steers finished on autumn grass, grass silage and concentrate-based diets were compared at the same carcass growth rate.

Fatty acids

Values obtained for proportions of total fatty acid in longissimus dorsi muscle were similar to those obtained on other goats breeds (Banskalieva et al 2000) and on the same Tunisian local goat (Atti et al 2006), showing the prevalence of oleic (C18:1), palmitic (C16:0), stearic (C18:0) and linoleic (C18:2) FA, which accounted for about 910 g/kg of total fatty acids.

In the current study, kids raised on cactus showed higher proportions of C22:5n-3 and C9t11-CLA than kids raised with concentrate; furthermore, lowering the proportion of concentrate in the diet increases the CLA concentration. These results are in accordance with other reports, which compared fatty acid composition of grass-fed to concentrate-fed lambs (Dermirel et al 2006), steers or cattle (French et al 2000; Nũernberg et al 2005) and goats (Atti et al 2006). They reflect the beneficial effect of green forage (grass or cactus) particularly rich in C18:3 (French et al 2003; Ward et al 2003) on meat FA composition. However, in the present study, the 18:2 and 18:3 percentages were not markedly different between groups. Their percentages were much lower for intramuscular fat (<50 g/kg) than for the diets (>500 g/kg in both diets), because much of the dietary 18:2 and 18:3 would have been hydrogenated in the rumen to 18:1 and 18:0 (Rhee et al 2000).

Organoleptic qualities

The three main components of eating quality according to consumer studies are tenderness, juiciness and flavour (Wood et al 1999). Tenderness is the most important textural characteristic of meat and has the greatest influence on consumer acceptance of meat (Kim and Lee 2003). Meat of cactus groups was less tender than that of other ones. This difference may be caused by different intramuscular fat content. Tenderness values were indeed positively correlated (r=0.44; P<0.05) with intramuscular fat content, a higher content of intramuscular fat was found leading to better tenderness of the concentrate groups meat.  Many authors found that tenderness was positively related to intramuscular fat content (Wheeler et al 1996; Fiems et al 2000). Wood et al (1999) indicated that a high intramuscular fat content decreases muscle resistance to shearing because fibrous protein dilution by soft fat. However, Renand et al (2001) found that tenderness or mechanical strength was not closely related to the intramuscular fat content.

The juiciness is an organoleptic characteristic related to both the capacity of muscle to release its constitutive water (initial juiciness) and the infiltration fat content (sustained juiciness). Results of our study confirmed the conclusion of French et al (2000) that there are no detectable differences in juiciness of beef from grass-fed steers and grain-fed steers when compared at similar weights. Priolo et al (2002) found differences in juiciness between forage- and grain-fed lambs; meat from stall fed animals was juicier than meat from grass-fed animals. They also reported that juiciness is mostly influenced by cooking loss. In the present study, juiciness was poorly correlated with cooking loss (r=-0.015, P>0.05).

Meat obtained from kids fed cactus has a similar flavor compared with other groups, although, red meat consumers generally consider meat of grass animals different when compared to that of concentrate ones, especially in terms of flavors. Melton et L (1992) found more intense strong flavor with forage feeding vs. grain feeding. Among factors affecting meat flavor figure meat ultimate pH and FA composition; in the present study, pH had the same value for all dietary treatments. Furthermore, feeding system influenced muscle FA composition, which can affect meat flavor (Elmore et al 2000). There are important flavor implications with this pattern because products of oxidation of linolenic acid have been associated with species flavors of meat as result of the formation of volatile compounds during cooking (Manner et al 1984).

Conclusions

• Kids reared by cactus feeding produce meat with enhanced nutritional quality for the consumer due to lower intramuscular fat content and a higher accumulation of beneficial fatty acids, n-3 FA and CLA, compared with kid's meat from a concentrate feeding system.

  
  

• Incorporating cactus in goat kids diets did not affect the overall acceptability of the meat but resulted in harder meat; further research is needed to improve the meat tenderness.

Acknowledgements 

The authors gratefully acknowledge the technical assistance of B. Chourabi and general Ouesslatia farm staff in the conduct of this study, and Dr Soufia with her team from Beja slaughtering house for their assistance.

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Received 15 April 2009; Accepted 20 October 2009; Published 3 December 2009

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