ABSTRACT
Two studies were conducted using 20 broiler chickens with the aim of improving the
yield, quality and shelf-life of meat products. In the first study, eight broiler chickens
were used to investigate the effects of rigor state and curing temperature on yield and
quality of smoke-cooked meat using a 2 x 2 factorial arrangement. The results showed
that the yield was not significantly (P>0.05) affected by rigor states but was affected
(P<0.05) by curing temperatures. The yield of broiler meat was higher in cold cure
(14.60%) than in hot cure (6.31%). Furthermore, the interaction between curing
temperature and rigor state was also significant (P<0.05) with post rigor and cold cure
interacting best with a yield of 15.88%. Effect of rigor on sensory properties of the
product showed no significant difference (P>0.05) except for flavour which was higher
(2.17) in the pre-rigor carcasses, curing temperature showed no significant effect
(P>0.05) while their interaction effect was significant (P<0.05) for the parameters and
ranged between 1.75 and 1.92, 2.00 and 2.06, 2.03 and 2.20, 1.56 and 1.74, 2.03 and
2.20,2.44 and 2.64 for texture, juiciness, colour, saltiness, smoky flavour and general
acceptability respectively were pre-rigor hot cure meat was most preferred. In the
second study, five kilogrammes of manually deboned and comminuted broiler meat was
used to determine the antioxidant and antimicrobial activities of cloves, ginger, pepper,
black pepper and African nutmeg extracts on the quality and shelf-life of nuggets using
a completely randomised design. The results for the antioxidant effect of spice extracts
revealed that lipid oxidation of chicken nuggets was improved by the inclusion of spice
extracts with cloves, ginger, pepper and their combinations performing better (P<0.05)
than the other spices. Total plate count, coliform count and fungal count were
significantly (P<0.05) reduced with the addition of extracts during storage. It is
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concluded that optimum yield can be achieved through cold curing in post- rigor state.
More so, addition of spice (cloves, ginger, and pepper) extracts led to retarded oxidative
rancidity and microbial growth during refrigerated storage, thereby improving the
quality and shelf-life of chicken nuggets.
TABLE OF CONTENTS
COVER PAGE ……………………………………………………………………………………………………….. i
FLY PAGE …………………………………………………………………………………………………………… ii
TITLE PAGE …………………..…………………………………………………………………iii
DECLARATION ………………………………………………………………………………………………….. iii
COPYRIGHT STATEMENT ………………………………………………………………………………….. iv
CERTIFICATION ………………………………………………………………………………………………….. v
DEDICATION ……………………………………………………………………………………………………… vi
ACKNOWLEDGEMENTS ……………………………………………………………………………………. vii
ABSTRACT ……………………………………………………………………………………………………….. viii
TABLE OF CONTENTS ………………………………………………………………………………………… x
LIST OF TABLES ……………………………………………………………………………………………….. xv
LIST OF FIGURES …………………………………………………………………………………………….. xvii
LIST OF APPENDICES …………………………………………………………………………………….. xviii
CHAPTER ONE ……………………………………………………………………………………………………. 1
1.0 INTRODUCTION ……………………………………………………………………………………….. 1
1.1 Justification ……………………………………………………………………………………………….. 3
1.2 Objectives of the study ………………………………………………………………………………… 4
1.3 Hypotheses ………………………………………………………………………………………………… 4
CHAPTER TWO …………………………………………………………………………………………………… 5
2.0 LITERATURE REVIEW …………………………………………………………………………….. 5
2.1 Meat industry in Nigeria: An overview of poultry production …………………………….. 5
2.2 Characteristics and nutritional value of poultry meat ………………………………………… 6
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2.3 Poultry meat products ………………………………………………………………………………….. 6
2.4 Meat quality and safety ……………………………………………………………………………….. 8
2.4.1 Microbial spoilage ………………………………………………………………………………………. 9
2.4.2 Lipid oxidation …………………………………………………………………………………………. 14
2.4.3 Enzymatic actions …………………………………………………………………………………….. 14
2.5 Meat processing ……………………………………………………………………………………….. 15
2.5.1 Curing/ marination ……………………………………………………………………………………. 15
2.6 Effect of rigor and temperature on meat quality ……………………………………………… 16
2.7 Bio-preservation: Spices …………………………………………………………………………….. 19
2.7.1 Ginger (Zingiber officinale) ………………………………………………………………………… 21
2.7.2 Cloves (Eugenia caryophyllus) ……………………………………………………………………. 21
2.7.3 African nutmeg (Monodora myristica) …………………………………………………………. 22
2.7.4 Pepper (Capsicum spp.) ……………………………………………………………………………… 23
2.7.5 Black pepper (Piper guineense) …………………………………………………………………… 23
2.8 Effect of spices on TBARS, microbial load and sensory properties of meat ………… 24
CHAPTER THREE ………………………………………………………………………………………………. 27
3.0 MATERIALS AND METHODS …………………………………………………………………. 27
3.1 Study location ………………………………………………………………………………………….. 27
3.2 Study 1: Effect of rigor state and curing temperature on quality and carcass
yield ……………………………………………………………………………………………………….. 27
3.2.1 Slaughter and processing treatments …………………………………………………………….. 27
3.2.2 Curing …………………………………………………………………………………………………….. 28
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3.2.3 Primal cuts and smoking…………………………………………………………………………….. 29
3.2.4 Processing yield ……………………………………………………………………………………….. 29
3.2.5 Proximate, nitrite and salt analysis ……………………………………………………………….. 29
3.2.6 pH… ……. ……………………………………………………………………………32
3.2.7 Sensory analysis ……………………………………………………………………………………….. 33
3.2.8 Statistical analysis …………………………………………………………………………………….. 33
3.3 Study 2: Effects of spice extracts on the quality and shelf-life of chicken
nuggets ……………………………………………………………………………………………………. 34
3.3.1 Preparation of extracts ……………………………………………………………………………….. 34
3.3.2 Bacterial culture preparation ……………………………………………………………………….. 34
3.3.3 Antimicrobial activity testing of extracts in agar media …………………………………… 35
3.3.4 Chicken nugget preparation ………………………………………………………………………… 35
3.3.5 Optimization of spice extracts …………………………………………………………………….. 36
3.3.6 pH… ……. ……………………………………………………………………………36
3.3.7 Thiobarbituric acid ……………………………………………………………………………………. 36
3.3.8 Antimicrobial activity testing ……………………………………………………………………… 37
3.3.9 Sensory analysis ……………………………………………………………………………………….. 38
3.3.10 Statistical analysis …………………………………………………………………………………….. 38
CHAPTER FOUR ………………………………………………………………………………………………… 40
4.0 RESULTS ……………………………………………………………………………………………….. 40
4.1 Effect of rigor state, curing temperature and their interaction on the physicochemical
properties of cured and smoked-cooked broiler meats ………………………… 40
4.2 Effect of rigor state, curing temperature and their interaction on the sensory
properties of smoked-cooked broiler meat …………………………………………………….. 45
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4.3 Antimicrobial activities of individual and combined spice extracts at various
concentrations of agar media ………………………………………………………………………. 49
4.4 Effect of spice extracts and storage time on pH and thiobarbituric acid reactive
substances (mg of malondialdehyde/kg of chickens) of chicken nugget stored at
4°C for 12 days ………………………………………………………………………………………… 53
4.5 Microbial count (Log cfu/g) of chicken nuggets stored at 4ºC for 12 days ………….. 56
4.6 Effect of spice extract inclusion on the sensory properties of chicken nuggets
stored at 4ºC for 12 days …………………………………………………………………………….. 60
CHAPTER FIVE ………………………………………………………………………………………………….. 67
5.0 DISCUSSION ………………………………………………………………………………………….. 67
5.1 Effect of rigor state, curing temperature and their interaction on the physicochemical
properties of cured and smoked-cooked broiler meat …………………………. 67
5.2 Effect of rigor state on the sensory properties of smoked cooked broiler meat …….. 68
5.3 Antimicrobial activity of individual spice extracts at various concentrations in
agar media ……………………………………………………………………………………………….. 69
5.4 Effect of spice extracts and storage time on pH and thiobarbituric acid reactive
substances (mg of malondialdehyde/kg of chicken) of chicken nugget stored at
4°C for 12 days ………………………………………………………………………………………… 70
5.5 Effect of spice extracts and storage time on microbial count of chicken nugget
stored at 4°C for 12 days ……………………………………………………………………………. 71
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5.6 Effect of spice extracts inclusion on the sensory properties of chicken nuggets
store at 4ºC for 12 days………………………………………………………………………………. 72
5.7 Effect of spice extracts on the proximate analysis of chicken nuggets ………………… 73
CHAPTER SIX ……………………………………………………………………………………………………. 74
6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS …………………………. 74
6.1 Summary …………………………………………………………………………………………………. 74
6.2 Conclusion ………………………………………………………………………………………………. 75
6.3 Recommendation………………………………………………………………………………………. 75
REFERENCES…………………………………………………………………………………………………….. 76
APPENDICES …………………………………………………………………………………………………….. 91
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CHAPTER ONE
1.0 INTRODUCTION
The demand for livestock products, including poultry is increasing in West Africa as a
result of population growth and urbanisation, but the sector faces constraints. The
constraints include safety concerns due to inadequate sanitary controls, processing
technology and marketing, adversely affecting the supply of meat, an important source
of animal protein in the region (Dupaigre et al., 2004).
Meat is the flesh of animals used as food (Lawrie and Ledward, 2006), and is one of the
most perishable commercial foods (Aymerich et al., 2008). The nourishing components
of meat are susceptible to degradable modification by microbiological and physico–
chemical agents. In fact, meat represents an ideal substratum for the growth of potential
pathogens such as Escherichia coli, Salmonella spp., Listeria monocytogenes,
Staphylococcus aureus and Bacillus cereus (Kotula and Kotula, 2000). It is, therefore,
essential that adequate preservation technologies are applied to maintain its safety and
quality. Food safety and shelf-life are both important microbial concerns in relation to
broiler meat production. The shelf-life of meat is generally determined by appearance,
texture, flavour, colour, microbial activity and nutritive value (McMillin, 2008). The
production of high-quality meat with good appeal to consumers is expected to translate
into increased revenue for meat producers and processors; consequently, boosting the
entire meat industry. The quality of meat and its overall acceptability are determined by
its juiciness, flavour, tenderness and colour. Reduced product quality results in
decreased consumer acceptance (Kotula and Pandya, 1995). Therefore, improving
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customer satisfaction and maintaining the consistency of meat products are a major
concern and challenge for the meat industry (Behrends et al., 2005).
Meat processing enables the processor to convert low-priced meat cut into high-priced
processed product (FAO, 1995). Processing of meat to products also facilitates the
packaging, handling, distribution and marketing of the products (Omojola et al., 2004).
Meat products include chicken nuggets, frankfurters, sausages, bologna, and local meat
products such as kilishi, suya and dambun nama. Chicken nugget is a comminuted meat
product of chicken, which offers an alternative avenue for better utilization of the meat
especially from spent chicken. These pre-processed products are ready-to-fry and serve,
and are gaining importance in the consumer market. Thermal processing, curing and
smoking may be considered as the three most commonly encountered operations in
meat preservation and processing (Kordylas, 1990). Current meat-curing practice, based
on the ancient art of preserving meat with salt, employs the addition of nitrite along with
salt, sugar, reducing agents and phosphates to meat (Rubin et al., 1992). There are two
methods of curing namely: wet and dry curing which can be done at the pre-rigor or
post-rigor state. In the wet cure method, the curing solution can be either hot or cold.
Some researchers (Lauritzsen et al., 1993; Ogunsola and Okubanjo, 2001) have reported
that curing temperature and state of rigor prior to curing affects the quality and yield of
the processed product. Lauritzsen et al. (1993) report on fish showed that pre-rigor
salting resulted in a greater reduction in weight, higher water loss and a lower sodium
chloride uptake than the post-rigor salted. Pre-rigor curing treatment with hot brine at
450C has also been shown to accelerate curing process of rabbit carcass (Ogunsola and
Okubanjo, 2001).
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Over the past 10 years there has been an on-going development of curing processes with
natural ingredients designed to meet consumer demands and safety requirements for
natural and organic processed meats (Sebranek et al., 2012). Bio-preservation has
gained increasing attention as a means of naturally-controlling the shelf-life and safety
of meat products (Ogunbanwo and Okanlawon, 2006). The utilization of spices
possessing antimicrobial and antioxidant properties in various forms like powder and
extract or essential oils have been variously reported (Meena and Sethi, 1997;
Subbulakshmi and Naik, 2002; Rajkumar and Berwal, 2003). Examples of such spices
are clove, rosemary, cassia bark, liquorice, aniseed, pepper, round cardamom, nutmeg
and angelica. Their addition also affects the taste, flavour, texture, water activity, pH
and colour of some meat products (Zhang et al., 2009; Ibrahima et al., 2011).
1.1 Justification
Over 10 per cent of animal producers in Nigeria are involved in poultry production on
small-scale or medium-scale farms. However, availability of quality animal proteins to
the populace, especially in the developing countries is still a mirage (Ogunbanwo and
Okanlawon, 2006) due to marketing inefficiency at the end of the production season,
unstable power supply for preservation of dressed carcass and inadequate knowledge of
an alternative processing/preservation procedure. There is also paucity of literature on
the interactive effect of rigor state and curing temperature; and organic spices on meat
quality and shelf-life of poultry meat in Nigeria.
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1.2 Objectives of the study
The objectives of this study were:
1. To compare the effect of rigor state and curing temperature on the yield and
meat quality of processed broiler chickens.
2. To determine the antioxidant activities of ginger, African nutmeg, pepper, black
pepper and cloves on the quality and shelf-life of chicken nugget, stored at 40C
for 12 days.
3. To determine the antimicrobial activities of Ginger, African nutmeg, Pepper,
Black pepper and Cloves on the quality and shelf-life of chicken nugget, stored
at 40C for 12 days.
1.3 Hypotheses
The present work was, therefore, designed to evaluate the following alternate
hypotheses:
HA: Pre-rigor and post-rigor hot and cold cure have effect on the quality of smokedcooked
broiler meat.
HA: The antioxidant activities induced following the incorporation of spice extracts in
chicken nugget have effect on the quality and shelf-life of the product.
HA: The antimicrobial activities induced following the incorporation of spice extracts in
chicken nugget have effect on the quality and shelf-life of the product.
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