ABSTRACT
This research was carried out to study the influence of three cooking methods (frying, smoking and roasting) on the physicho-chemical properties and the shelf – life of snail meat (Achachatina marginata). The snail meat was first washed using different washing agents (lime, alum, salt and ash) and through sensory evaluation, the best washing agent was selected and used to prepare snail meat samples for subsequent processing. The snail from the best washing agents was divided into 4 portions to correspond to the following curing humectant which were used in cook-soak equilibration: salt alone, salt + glycerol, salt + k-sorbate and salt + k-sorbate + glycerol. The cured samples were analyzed for proximate composition, mineral, microbial characteristics and sensory properties. Portions of products from each curing solution were subsequently subjected to three different methods of cooking namely smoking, frying and roasting. These products were also stored at ambient conditions (280C – 320C) for 31days and analyzed at 6day interval for indices of shelf – stability which included water activity, protein solubility, TBA values, pH and microbial quality. Results showed that lime – washed snail meat had the highest score for overall acceptability and had similar scores for color, odor, texture and proximate composition with samples washed with salt, alum and ash. Lime – washed snail meat was then selected for further processing. Curing with various humectants did not lead to significant differences (p>0.05) in sensory characteristics except that samples cured with salt + glycerol + k-sorbate solution was judged to be tougher/harder and the color was neither liked nor disliked compared to others. Curing also reduced the moisture content due to osmotic dehydration but due to concentration effect, increased the protein, fat, ash, zinc, total pigment and pH. Among the cured products, those containing glycerol were higher in moisture content but lower in water activity. The different methods of cooking/preparation (smoking, frying, roasting) had different effects on the shelf stability of the products. In all the 3 methods, samples containing glycerol were lower in water activity, protein solubility, lipid oxidation (TBA), pH and total viable count. The differences caused by curing humectants were maintained during storage. Products treated with salt and those treated with salt + k-sorbate were so unstable that incipient spoilage, which set in caused discontinuation of storage after 1-2 weeks. Smoking caused all the cured snail meat products to be stable throughout the thirty-day storage. Roasted products were least stable during storage; hence, samples cured with salt alone and those cured with salt + k-sorbate spoiled in 7 days in the roasted samples.
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CHAPTER ONE
INTRODUCTION
1.1 Background Information
Food security is a major problem in the developing countries of the world. Diets of an average citizen in this region is carbohydrate based with little or no protein source with a great potential of reducing insulin level in the blood of the consumer. Moreover, consumption of animal protein, which is known to be a better source of this nutrient, is extremely low in this region (Omole, 1999). Cases of malnutrition are more prevalent in the developing countries than in other parts of the world. Consequently, thousands of children die every year of starvation and malnutrition (FAO, 1996). Animal production is faced by many problem in the developing countries, for instance, high cost of animal feed constitutes a major impediment in most projects as a result of continuous competition between man and animal for most of the ingredients (Adeyemo and Longe, 2001). Animal protein is superior to plant protein as it contains all the essential amino acids in adequate proportions (Tewe, 1997).
Low consumption of animal proteins in the developing countries is borne out of poverty and ignorance. Unavailability and low production of livestock are indeed a major problem. It is very clear that regular livestock can no longer meet the demands of the fast growing population of the world. Therefore, there is an urgent need to encourage the production of mini livestock such as snails, insects and rodents to supplement the current livestock production (Afolayan, 1992).
Snail is one of the mini livestocks with great potentials. The meat is a delicacy for many people both in the rural and urban centers of Nigeria and in many countries in Africa. It is a major source of meat to people in the rural communities where the majority cannot afford the cost of regular livestock meat (Emevbore, 1990). Snail meat has a special taste and is rich in iron, calcium and phosphorus. It is low in fat and cholesterol (Afolayan, 1992). It is high in quality protein, as it contains all the essential amino acids in adequate proportions. In fact, the amino acid profile compares favorably with those of broiler, fish and pork (Omole, 1999). This makes its consumption beneficial and safe to the consumers. This known nutritive value of the snail makes it unthinkable not to harness it for human benefits in view of acute protein shortage. Thus, the idea of its preservation comes in. This is because what is obtained from major sources of meat supply can no longer sustain the growing demand due to increases in human population. In order to bridge the gap between demand and supply of animal protein, preservation of meat is, therefore, necessary. The principles of meat preservation are mainly associated with preventing or delaying microbial spoilage and chemical actions and avoiding,
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as far as possible, weight loss and any change in color, taste, odor, flavor and texture (Cooper and Ledward, 1993).
Preservation methods are designed to prevent deterioration of meat and are absolutely essential for extending the keeping quality during storage of meat and meat products. Methods of preservation include the use of infusion humectants and curing ingredients to produce intermediate moisture meats, refrigeration, freezing, thermal processing and dehydration while including drying and smoking as well as preservation by use of chemical additives, generally recognized as safe.
Intermediate moisture meats (IMM) are semi moist shelf-stable-meat that owe their stability to the infusion humectants which, besides being antimicrobial, depress the water activity (aw) to limits (mostly 0.70-0.85) below the growth requirements of most bacteria. Intermediate moisture meats can also be defined as heterogeneous group of meats which resemble dry meats in their resistance to microbial deterioration but which contain too much moisture to be considered dry (Brockmann, 1970; Obanu et al. 1975b). An intermediate moisture meat has been described as one that can be eaten directly without rehydration, and yet is shelf stable, without refrigeration or thermal processing (Kaplow, 1970). This stability of relatively moist meat is the result of depressing the aw below the growth requirement of most spoilage and pathogenic microorganisms (Anon, 1972; Brockmann, 1970).
1.2 OBJECTIVES OF STUDY
1) To compare shelf stability of smoked, fried and roasted snail meat pretreated with solution containing Sodium chloride, Glycerol and Potassium sorbate.
2) To assess the physical, chemical, microbial and organoleptic qualities of the intermediate moisture (IM) snail meat.
3) To assess the quality changes under ambient room storage condition (280C – 300C ) of intermediate moisture products.
