Determination of age at slaughter on meat quality characteristics for indigenous Malawian spotted (kawangi) chickens

S R Mussah and R K D Phoya¹

Moyale Barracks, 3^rd Battalion, Malawi Defence Force, P O Box 23, Mzuzu, Malawi
mussahsteven@gmail.com
¹ Department of Animal Science, Bunda campus, Lilongwe University of Agriculture and Natural Resources (LUANAR),
P O Box 219, Lilongwe. Malawi.

Abstract

The effect of age at slaughter on meat flavour, tenderness, drip loss, cooking loss and colour was studied in Malawian indigenous spotted (Kawangi) chickens. Thirty-two chickens (16 cocks and 16 hens) were slaughtered at 4 different ages: 16, 20, 24 and 28 weeks. There were equal numbers of cocks and hens in each age group. Meat tenderness and flavour were determined from the breast muscles and the drumstick using sensory evaluation by a trained taste panel.

The increase in age at slaughter decreased tenderness and drip/cooking loss while increasing colour and flavour. The optimum age at slaughter was around 24 weeks of age.

Key words: colour, cooking/drip loss, flavour, sex, tenderness

Introduction

In Malawi, the poultry industry is going through a gradual but definite change in product differentiation in response to consumer demands. However, some consumers still regard meat derived from indigenous chicken as being tough as compared to exotic breeds. Poultry meat is more nutritionally important in countries like Malawi unlike other industrialized countries where a wide variety of food from all kinds is available. Chicken products are popular and in the coming years, the consumption of chicken meat will rise dramatically [Food and Agriculture Organisation (FAO) 2012]. The trend is similar in many Sub-Saharan Africa (SSA) and Asian countries, where there has been a shift in demand from broiler meat to indigenous chicken meat. This preference is partly explained by colour, chewy texture and flavour of their meat (Wattanachant et al 2005; Guèye et al 1997). Apart from taste, some consumers consider indigenous chicken to contain less drug residues, since their management is mostly free range system which is almost just like organically farmed livestock. To ensure a sustainable continued growth and competitiveness of the indigenous poultry meat industry, it is essential that indigenous chicken meat quality and safety are maintained during production process.

The quality of meat, generally, is judged by its tenderness, succulence, flavour and nutritive value. The quality is mainly influenced by age at slaughter, strain, the nutritional regime and rearing system (Sogunle et al 2010). Apart from other meat quality attributes, texture particularly tenderness, is an important selection criteria used by consumers when purchasing meat (Fanatico et al 2007). Waskar et al 2009, reported that meat tenderness also depends on muscle type and some consumers discriminate meat cuts depending on their tenderness. The other factor influencing meat quality is the age at which the birds are slaughtered. Northcutt et al (2001) indicated that, under traditional systems, often chickens are slaughtered many month post maturity, partly contributed by the slow growth rate resulting in toughness of meat. Consumption of quality meat should be an issue now in Malawi, since reports indicate that malnutrition levels are at 46% (UNICEF 2015) among under five children and underweight growth at 21% (UNICEF 2015) in most growing children particularly in those households with low socio-economic status.

Materials and methods

Location of the study

The experiment was carried out at the students’ farm, Bunda campus of Lilongwe University of Agriculture and Natural Resources (LUANAR), in Lilongwe, Malawi, using 32 Malawian indigenous spotted (Kawangi) chickens comprising 16 cocks and 16 hens.

Experimental design

The chickens were raised under intensive system and fed farm formulated feed with 18% crude protein, and slaughtered in 4 age groups; 16, 20, 24 and 28 weeks. There were an equal number of males and females in each group. Meat tenderness and flavour for each bird from each age group were measured from the breast and drumstick muscles using sensory evaluation by a trained taste panel. Drip and cooking losses were calculated and expressed as percentages of initial weights of the samples. Colour was measured using the CIE colour system, using Konica Minolta CR400 Chroma Meter

Statistical model

The following statistical model was used to analyze the data:

Y_ijk = µ + A_i(1-4) + S_j(1-2) + (AS) _ij +ℇ_ijk

Where;

Y_ijk = jth observation on the ith treatments

µ =Overall mean

A_i = Effect of age (1:16 weeks, 2:20 weeks, 3:24 weeks and 4: 28 weeks)

S_{j =} Effect of sex (1: cock, 2: hens)

AS_ij = Effect of interaction of sex and age

ℇ_{ijk =} Random error component

Statistical analysis

Data were analyzed using the General Linear Model procedures of SAS 12.1

Results and discussion

Effect of age on drip loss, cooking loss, tenderness and flavour

Increase in age resulted in a decrease in both drip/cooking loss and tenderness but improved flavour (Table 1).

Table 1. Effect of age of indigenous chickens on meat eating quality attributes
Age/attribute	16wks	20wks	24wks	28wks	SEM	p
Tenderness (scores)	5.31a	5.58a	6.93b	4.82c	0.122	0.006
Flavour (scores)	5.31a	5.58b	6.93c	7.10d	0.122	<0.001
Cooking Loss (%)	18.9a	16.3b	16.0c	15.9d	0.062	0.003
Drip loss (%)	1.66a	1.08b	0.64c	0.541d	0.028	0.022
L*	69.2a	62.5b	60.4c	60.3c	0.147	0.002
a*	3.68a	5.74b	8.31c	9.99d	0.207	<0.001
b*	7.92a	10.0b	14.4c	13.2d	0.227	0.001
abcd Means with different superscripts within rows differ at P<0.05. L* = lightness; a* = redness; b* = yellowness

The current results agree with those of Moran (1999), who reported that muscle composition changes with age of chickens, with the greatest changes taking place at the inflection point in growth. Differences in the composition of meat concern, among others, the content of fat, collagen and myoglobin. Studies by Owens and Sams (2000), Van Laack et al (2000) and Fraqueza et al (2006), found that after 24-hour cold storage of the carcasses, the pH of meat in the younger birds decreases to reach lower values than in the older chickens. Such a marked decrease in the pH of muscles from the youngest chickens could thus negatively affect the quality of their meat (e.g. the drip loss or the lightness). Water holding capacity is an important aspect in meat quality for it influences the eating quality (FAO 2010). Meat with high water holding capacity tends to have high pH which is undesirable because it leads to formation of dark, firm and dry (DFD) meat.

On the other hand, the differences in tenderness and flavour could be due to many structures which form in the muscles as the birds grow older. Moran (1999) indicated that muscle composition changes with the age of chickens. The changes in fat, collagen and myoglobin contents make the muscles tougher as the birds’ age increases while at the same time flavour also increases (Albuquerque et al 2003).

The study by Iqbal et al (1999) revealed that the age related decline in meat tenderness is due to many factors. For instance, glucose derived/non-enzymatic collagen cross linkages play a role in the normal aging process as well as accelerated tissue aging associated with hyperglycemic state. The structural, long-lived tissue protein collagen is the major component of connective tissue and functions as the basic supporting structure of tissues and organs. Non enzymatic collagen cross linking in muscle may contribute to the decline in meat tenderness of aged animals. However, it is apparent that there are no differences due to sex in tenderness, flavour, cooking and drip losses.

Effect of age on meat colour

There were differences between different age groups in meat colour. The meat from young birds was lighter in colour changing to yellowness and redness with age (Table 2).

Table 2. Effect of age of indigenous chickens on meat colour
Age/colour	16 weeks	20 weeks	24 weeks	28 weeks	SEM	P
L*	69.2a	62.5b	60.4c	60.3c	0.147	0.002
a*	3.68a	5.74b	8.31c	9.99d	0.207	<0.001
b*	7.92a	10.0b	14.4c	13.2d	0.227	<0.001
abcd Means with different superscripts within rows differ at P<0.05. L* = lightness; a* = redness; b* = yellowness

Table 3. Effect of sex of indigenous chickens on meat attributes
Sex/attribute	Cock	Hen	SEM	p
Tenderness	5.56	5.67	0.086	0.888
Flavour	6.22	6.24	0.085	0.850
Cooking Loss	16.7	16.8	0.044	0.226
Drip Loss	0.97	0.98	0.020	0.663