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 + ksorbate 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.
TABLE OF CONTENTS
CERTIFICATION------------------------------------------------------------------- i
DEDICATION----------------------------------------------------------------------- ii
ACKNOWLEDEMENT------------------------------------------------------------ iii
TABLE OF CONTENT------------------------------------------------------------- iv
LIST OF TABLES------------------------------------------------------------------- vii
ABSTRACT-------------------------------------------------------------------------- viii
CHAPTER 1 Introduction---------------------------------------------------------- 1
1.1 Background Information---------------------------------------------------- 1
1.2 Objective of Study----------------------------------------------------------- 2
CHAPTER 2 Literature------------------------------------------------------------- 3
2.1 Physical characteristics of snail-------------------------------------------- 3
2.1.1 The body of snail------------------------------------------------------------ 3
2.1.2 The shell of the snail-------------------------------------------------------- 4
2.1.3 Torsion in snail--------------------------------------------------------------- 5
2.1.4 Respiration and blood circulation----------------------------------------- 5
2.1.5 Aestivation in snail---------------------------------------------------------- 5
2.1.6 Feeding in snail-------------------------------------------------------------- 6
2.1.7 Light reaction of snail------------------------------------------------------- 6
2.1.8 Defeacation in snail---------------------------------------------------------- 7
2.1.9 Ecology of snail-------------------------------------------------------------- 7
2.1.10 Gathering snails-------------------------------------------------------------- 7
2.1.11 Edible snail species---------------------------------------------------------- 8
2.1.12 Biochemical composition of the snail------------------------------------- 10
2.1.13 Nutritional value of snail--------------------------------------------------- 10
2.1.14 Nutritional importance of snail-------------------------------------------- 11
2.1.15 Preparation of snail meat--------------------------------------------------- 11
2.1.16 Microbial qualities of snail meat------------------------------------------ 13
2.2. Methods of meat preservation---------------------------------------------- 13
2.2.1 Food preservation--------------------------------------------------------------- 14
2.2.2 Humectant/Curing ingredients------------------------------------------------ 17
2.2.3 Curing meat, principles and benefits----------------------------------------- 19
2.2.4 Cooking snail meat as a preservative technique---------------------------- 21
2.2.5 Meat smoking------------------------------------------------------------------- 22
CHAPTER THREE- MATERIALS AND METHODS
3.1 Sample Procurement and Processing----------------------------------------- 24
3.1.1 Preparation of Infusing solution----------------------------------------------- 24
3.1.2 Processing of preliminary products------------------------------------------- 27
3.1.3 Production of Intermediate moisture snail meat---------------------------- 27
3.2. Analysis of sample-------------------------------------------------------------- 27
3.2.1 Moisture content determination----------------------------------------------- 27
3.2.2 Ash content determination----------------------------------------------------- 27
3.2.3 Fat content determination------------------------------------------------------ 27
3.2.4 Crude protein determination-------------------------------------------------- 28
3.2.5 pH determination--------------------------------------------------------------- 29
3.2.6 Water activity------------------------------------------------------------------- 29
3.2. 7 Total pigmentation------------------------------------------------------------- 29
3.2.8 Determination of protein solubility------------------------------------------ 29
3.2.9 Mineral determination using atomic absorption spectrophotometer--- 29
3.3.0 TBA determination------------------------------------------------------------ 30
3.3.1 Sensory evaluation------------------------------------------------------------- 30
3.3.2 Microbial Analyses------------------------------------------------------------ 30
3.3.3 Total viable count-------------------------------------------------------------- 30
3.3.4 Mould count--------------------------------------------------------------------- 31
3.3.5 Coliform count------------------------------------------------------------------ 31
3.3.6 Data Analyses------------------------------------------------------------------- 31
CHAPTER FOUR- RESULTS AND DISCUSSION
4.1 Characteristics of washed snail meat----------------------------------------- 32
4.1.1 Sensory characteristics of washed snail meat------------------------------- 32
4.1.2 Proximate composition of washed snail meat------------------------------- 33
4.1.3 Selection of suitably washed sample for snail meat products------------------35
4.2 Effects of curing on snail meat---------------------------------------------------- 35
4.2.1 Effects of curing on sensory characteristics of snail meat--------------------- 35
4.2.2. Effects of curing on the characteristics of snail meat--------------------------- 39
4.3 Quality changes during storage of intermediate moisture (IM) snail meat-- 41
4.3.1 Changes in water activity of IM Snail meat products during storage--------- 41
4.3.2 Changes in protein solubility of IM snail meat products during storage---- 48
4.3.3 Changes in TBA of IM snail meat products during storage-------------------- 54
4.3.4 Changes in pH of IM snail meat during storage------------------------------ 61
4.3.5 Changes in microbial quality of IM snail meat products------------------- 67
5.0 CHAPTER FIVE- RECOMMENDATION AND CONCLUSION 70
References ----------------------------------------------------------------------- 71
Appendix I------------------------------------------------------------------------ 79
Appendix II----------------------------------------------------------------------- 80
