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.



CHAPTER 1: Introduction
1.1       Background Information
1.2       Objective of Study

CHAPTER 2: Literature
2.1       Physical characteristics of snail
2.1.1    The body of snail
2.1.2    The shell of the snail
2.1.3    Torsion in snail
2.1.4    Respiration and blood circulation
2.1.5    Aestivation in snail
2.1.6    Feeding in snail
2.1.7    Light reaction of snail
2.1.8    Defeacation in snail
2.1.9    Ecology of snail
2.1.10  Gathering snails
2.1.11  Edible snail species
2.1.12  Biochemical composition of the snail
2.1.13  Nutritional value of snail
2.1.14  Nutritional importance of snail
2.1.15  Preparation of snail meat
2.1.16  Microbial qualities of snail meat
2.2.      Methods of meat preservation
2.2.1    Food preservation
2.2.2    Humectant/Curing ingredients
2.2.3    Curing meat, principles and benefits
2.2.4    Cooking snail meat as a preservative technique
2.2.5    Meat smoking

3.1       Sample Procurement and Processing
3.1.1    Preparation of Infusing solution
3.1.2    Processing of preliminary products
3.1.3    Production of Intermediate moisture snail meat
3.2.      Analysis of sample
3.2.1    Moisture content determination
3.2.2    Ash content determination
3.2.3    Fat content determination
3.2.4    Crude protein determination
3.2.5    pH determination
3.2.6    Water activity
3.2. 7   Total pigmentation
3.2.8    Determination of protein solubility
3.2.9    Mineral determination using atomic absorption spectrophotometer
3.3.0    TBA determination
3.3.1    Sensory evaluation
3.3.2    Microbial Analyses
3.3.3    Total viable count
3.3.4    Mould count
3.3.5    Coliform count
3.3.6    Data Analyses

4.1       Characteristics of washed snail meat
4.1.1    Sensory characteristics of washed snail meat
4.1.2    Proximate composition of washed snail meat
4.1.3    Selection of suitably washed sample for snail meat products
4.2       Effects  of curing on snail meat
4.2.1    Effects of curing on sensory characteristics of snail meat
4.2.2.   Effects of curing on the characteristics of snail meat
4.3       Quality changes during storage of intermediate moisture (IM) snail meat
4.3.1    Changes in water activity of IM Snail meat products during storage
4.3.2    Changes in protein solubility of IM snail meat products during storage
4.3.3    Changes in TBA of IM snail meat products during storage
4.3.4    Changes in pH of IM snail meat during storage
4.3.5    Changes in microbial quality of IM snail meat products





2.1.1    The body of snail

The body of snail consists of foot (sole), head and a coiled visceral mass that is located in the shell. Movement takes place by means of contracting and expanding muscles in the foot. This is clearly visible when the snail is placed on a glass surface and traced from below (Gomot, 1998). Mucus glands located in the anterior (front) part of the foot secrete mucus. There are also mucus glands on the rest of the body protecting the snail against loss of water. Two pairs of tentacles are placed on the head. The upper pair bears the eyes.

The shell is secreted by thick fold of skin, called the mantle. The shell is connected to the body through a strong mantle which is attached to the collumella. It branches on the head and tentacles. Contracting this muscle enables the snail to withdraw into its shell. Inside the shell, it forms mantle cavity, which opens to the foot and in the root is a pulmonate or pectinate gill. The mouth has a tongue called radulla. In the top of the mouth is a hard ridge and the food is being mashed between the radulla and this ridge. The front of the radulla wears very fast but the radulla grows from the back end (Pavlova, 1996). Near the opening of the mouth salivary glands release digestive enzymes. The salivary glands’ secretions moisten the digested food and envelop them, thereby making it easier for food to go into the oesophagus. The oesophagus ends in the stomach. The intestines release large quantities of brown digestive juice in the stomach. The intestinal glands consists of smaller and bigger follicles. A steady back and forth movement of the digestive juice between stomach and intestines enhances the process of absorption of food. The muscles of the intestinal gland ciliae cause the movement of the digestive juices (Gomot, 1998).

The digested food flows over the liver cells, which absorb food. The smaller intestines start at the visceral sac, it follows the edge of the kidney and enters the pulmonary cavity. It ends near the pneumostome (breathing pore). In the smaller groove, which is located with ciliae, it takes over all non- absorbed solids and directs them into the small intestine. There the solids are compressed and enveloped with a layer of slime after which they leave the body (Pavlova, 1996). The kidney of the snail is a yellowish, triangular organ in the rear segment of the lungs. One of the sides of the kidney runs parallel to the intestines; the other side is arranged closely to the periscard. The kidney consists of two parts: the kidney cavity where the excrements are secreted and the primary urethra, in which the first part of the discharge of the excrements takes place. This goes then to a second segment, the secondary urethra, which leaves the body. Snails living on the land are uricotellic, this means that to preserve water they secrete almost solid uric acid. Snails living in the water excrete ammonia and are not uricotellic.

2.1.2    The shell of snail

The most eye catching part of the snail is the shell. It consists of several layers:

1)     A thin layer called periostracum made of organic substances called conchiolin, the color pigments of the shell are usually coated here. Often, when snail gets older, the periostracum starts flaking and wears off.

2)     Thinner layers called ostracum made of inorganic calcium carbonate in some species, color pigments are located here as well.

3)     An inner layer called hypostracum. This is also the layer where nacre or mother of pearl can be found (Dupont-Nivet et al., 2001).

The shell grows larger by secretions of the mantle’s epithelium near the shell edge. The shell wall is made thicker by calcium carbonate crystals, which are secreted by gland, which are located on the epithelium of the mantle (Malouf, 1996). The snail shells have many shapes. The fundamental shape is globose while some are conical tubes; some are spirally coiled around a central axis- the collumella. The separate coils of the spiral are called the whorls. Most shells are coiled in a clockwise direction. In the family of Clausitidae and some species of the genera Vertigo, they are coiled to the left. One can tell which way the shell is coiled by holding it with the aperture towards you. If the aperture is on the right side, it is dextral (clockwise), if it is in the left side, it is sinistral (anticlockwise) (Rogers and Chase, 2002). The body is attached to the shell by a muscle which is attached to the central column, the collumella. The oldest part of the shell is the apex. From the apex, the shell grows downwards; every 3600 turn is a whorl. The area where two whorls meet is called the suture. This can be shallow or deep. The last whorl of the shell is called the body whorl, this leads to the shell mouth or aperture (Hardouin et al., 1995). Some shells have a hollow part on the underside called the navel or umbilicus. This is very narrow to wide and shallow to deep or might not be visible at all. When the snail grows older, the shell grows wider. This happens evenly so that the shell grows regularly. The mouth of the shell is called an aperture, it can be round, semicircular, tribolate or auriculate. The edge of the mouth, the margin can be shaped in a number of ways (e.g. family Zonitide), or folded outwards (genus Helicigona). Sometimes it is folded outwards and then tucked in again, this is an infolded margin (genus Granaria). Often the margin is made stronger by a thickening, this is known as the lip. The thickening of the lip is a sign that the snail has reached adulthood. Shell with an abnormal....

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