faster than others and produced the best skins in terms of the grade. Salt with the 5mm crystals didn't cure effectively as the crystals were large there creating ...
ASSESSING THE EFFECTS OF CURING SALT CRYSTAL SIZES ON HIDES AND SKINS MOISTURE CONTENT LEVELS
Contents DECLARATION .......................................................................................... Error! Bookmark not defined. DEDICATION ............................................................................................. Error! Bookmark not defined. ACKNOWLEDGEMNT ................................................................................ Error! Bookmark not defined. LIST OF ABBREVIATIONS AND ACRONYMS ............................................................................................ vi Abstract ................................................................................................................................................. vii 1.0 INTRODUCTION ............................................................................................................................ 1 1.1 Background review: ...................................................................................................................... 1 1.2 Problem statement: ...................................................................................................................... 2 1.3 JUSTIFICATION OF THE STUDY ............................................................................................ 3 1.4 Objectives...................................................................................................................................... 4 1.4.1General objective .................................................................................................................... 4 1.4.2 Specific objectives .................................................................................................................. 4 1.5 HYPOTHESIS TESTING............................................................................................................. 5 2.0 LITERATURE REVIEW ................................................................................................................. 6 2.1Types of salts used today ............................................................................................................... 7 2.2 The relationship between loss in moisture content and the salt crystal size ................................. 9 2.3 Bacterial damage ......................................................................................................................... 10 2.4 Act of degradation....................................................................................................................... 10 2.5 Moisture content of hides and skins ............................................................................................ 11 3.1 Determination of the curing saltcrystals currently being used in the market .............................. 12 3.2 Study area.................................................................................................................................... 12 3.2.1 Geographical location .......................................................................................................... 12 3.2.2 Climate and weather............................................................................................................. 12 3.2.3 Population ............................................................................................................................ 12 3.3 sample collection and preparation............................................................................................... 13 3.4 Determination of moisture content ............................................................................................. 13 3.5 Determination of the extent of bacterial infection in skins by use of different salt crystals for curing of skins ................................................................................................................................... 14 3.6 Determination of mechanical damage on cured hides and skins caused by use of salt with various crystal sizes .......................................................................................................................... 14 3.7 salt crystal sizes used for curing ................................................................................................. 14 ii
Figure 4; 5mm salt crystal size ............................................................................................................. 15 3.8Data analysis ................................................................................................................................ 18 CHAPTER4 RESULTS ........................................................................................................................ 19 4.1 salt crystal sizes used for curing of hides and skins. ................................................................... 19 4.2 Percentage moisture content of the different salt crystal sizes.................................................... 20 CHAPTER 5: Discussion ...................................................................................................................... 22 Chapter 6: Conclusion........................................................................................................................... 23 Chapter 7: Recommendations ............................................................................................................... 25 References ............................................................................................................................................. 26
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List of figures Figure 1Very fine salt with grain size of 0-0.2 mm ................................................................................. 7 Figure 2: Medium salt with grain size of 1-3mm .................................................................................... 8 Figure 3: coarse salt with grain size of 10-15mm ................................................................................... 8 Figure 4; 5mm salt crystal size…………………………………………………………………………………………………………15 figure5; 0.5mm salt crystal size………………………………………………………………………………………………………15 figure6; 0.5mm salt crystal size……………………………………………………………………………………………………….15 Figure7; Magadi salt with 5mm
crystal size……………………………………………………………………16
figure8; Magadi salt with 2mm crystal size…………………………………………………………………………………….16 figure9; Magadi salt with 0.5mm crystal size……………………………………………………………………………………16 figure10; Marine salt with 5mm salt crystal size………………………………………………………………………………16 figure11; marine salt with2mm salt crystal size………………………………………………………………………………16 figure12; marine salt with 0.5mm salt crystal size……………………………………………………………………………………………………..16 Figure 13; curing salt which was available to farmers ………………………………………………………………………………………………19 Figure14; A line graph showing loss in moisture content in percentage when Marine salt with different crystal sizes of salt was used for curing……………………………………………………………………………………………………………………………………………..20 Figure15; shows percentage moisture content in hides and skins when Livestock salt with different crystal sizes was used for curing……………………………………………………………………………………………………………………………………………………………………..21 Figure16; shows percentage loss in moisture content when magadi salt with different crystal sizes was used for curing…………………………………………………………………………………………………………………………………………………………………………….21
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List of tables Table 1; showing the moisture content in skins from day 1 to day 21 when Marine salt…………………………………………………………………………………………………………………………………………………20 Table2; shows the percentage hair loosening in the skins and the grades when different crystal sizes were used for curing………………………………………………………………………………………………………………………………………………………………………………23
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List of abbreviations and acronyms CCD
charge coupled devise
FAO
Food and agriculture organization
ISO
International organization for standardization
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Abstract The most common method of hides and skins curing used in Kenya is wet salting where salt is used. The salt should be of good quality as quality affects the curing but besides quality, the crystal size may also affect the quality of the preserved skins. There is no specific salt in the market for curing of hides and skins. The salt is available in various crystal sizes and the manufacturers of the industrial salt are not aware of the correct crystal size required for the salt to be effective if used in hides and skins curing. The project being reported was carried out to identify the correct salt crystal size for curing of hides and skins. This was achieved by use of different types of salts which included Magadi industrial salt, Marine salt and Livestock salt with different crystal sizes i.e. 0.5mm, 2mm and 5mm and determining the moisture content in the skins. The hides and skins were also graded by comparing the hair loosening when different crystal sizes of salt were used. The results obtained showed that the salt with the 2mm crystal size reduced moisture content faster than others and produced the best skins in terms of the grade. Salt with the 5mm crystals didn’t cure effectively as the crystals were large there creating gaps on the skins without salt. This caused putrefaction and also lowered the grade of the skins. It’s clear from the investigation being reported here that most of the putrefaction occurred in the skins that were cured using salt with crystal sizes of 5mm, followed by those cured with 0.5mm. The skins that were cured with crystal sizes that were 2mm had less hair loosening and were grade I. Salt with 0.5mm crystal size wasn’t effective in curing as the crystals were too small and they therefore formed a fused mass slowing the process of curing. It has therefore, been established in this study that the best curing salt for hides and skins is the one with crystal size of 2mm. Key words: Curing salt, salt crystal sizes, putrefaction, hairslip, moisture content, cake formation, staining vii
1.0 INTRODUCTION 1.1 Background review: Hides and skins after flaying contains water to about 60-70% water (Eduard et al., 2008) and are known as green hides (Chapter 359 – Laws of Kenya). This is because they are fresh and without any preservation. The presence of this amount of moisture and their chemical constituents (mainly consisting of proteins) favors bacterial growth, which cause damage to the hides and skins due to bacterial degradation (Eduard et al., 2008). Putrefying bacteria are usually present in the hides and skins or get access to them from the air and then when conditions are favorable for their activity, the bacteria secrete enzymes which degrade the molecular structure of proteins resulting in the formation of amino acids and ammonia evident by hair slipping (Humdin et al., 2016), surface sliming (Pekhtashera et al., 2012) and offensive odour in a pack of hides (www. leathermag.com). Several different types of microorganisms are responsible for putrefaction, these include; staphylococcus, micrococcus, bacillus and corynebacterium (Rother, 1995). Putrefaction is prevented by curing of hides and skins and the main method of curing used in Thika is wet-salting comprising 85% of the total hides and skins cured (Mwinyikione et al., 2011).Curing stabilizes the hides and skins rendering them non putrescible, converts the hides and skins into a convenient form for transportation or storage, ensures that changes brought about by curing are reversible, so that the cured hides and skins can be brought back to a condition similar to that of the freshly- flayed material, creates a cured stock which can be handled, sorted and graded by the tanner on receipt and minimizes the effluent produced during curing and subsequent processing (Sarkar, 1997).
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Curing removes the excess water from hides and skins where water flows from the inside because of difference in osmotic pressure thus the moisture content of hides and skins is reduced producing an environment unfavorable for bacterial growth. Preservation using salt remains the most popular curing technique worldwide due to its ease of application, costeffectiveness and the quality of the finished product (Gurdo et al., 2004). The hides and skins are piled one on top of each other with 30% -50% of their weight of salt spread on the flesh side for 21 days (FAO 2000). The measures taken during wet salting are to ensure that the salt used is enough and evenly distributed across the cross section but despite the above measures being used, putrefaction still occurs in hides and skins leading to great loses. This can be as a result of the size of salt crystals being used for wet-salting which is critical as has been observed in this study. The objective of this project was to review the different sizes of salt crystals currently being used in the preservation of hides and skins today, to analyze the loss in moisture content from the hides and skins when salt of different crystal sizes is used and to determine the extent of bacterial damage in the hides and skins produced when different salt crystal sizes are used during wet- salting. This investigation has led to the establishment of the correct crystal size of salt that produces the maximum preservation through reduction moisture hence bacterial damage and at the same time reducing other adverse effects like formation of cake, patchy curing, and cutting the hides and skins due to the sharp corners of the salt crystals. 1.2 Problem statement: Despite wet salting being the most common method used for preservation of hides and skins, at times putrefaction continues to take place and this is evident by hair slip leading to poor quality of leather after processing. This may be as a result of the size of the crystals of salt used for wet salting.
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The commonly used curing salt is the rock salt, which occurs in various crystal sizes (either too small or too large for effective curing of hides and skins) (Covington, 2009). Most manufactures of industrial salt are not aware of the correct crystal size required for the salt to be effective if used in hides and skins curing. The rock salt crystals used for curing should be neither too small nor too large. When objectionably small they dissolve so rapidly in the fluids of the hide surface that too much brine drains from the pack before a sufficient amount of salt is absorbed; when too large, the formation of brine is retarded to such a degree that insufficient salt is absorbed in the early stages of curing to slow down satisfactorily the natural process of autolysis which sets within 5 to 6 hours after slaughter (O’Flaherty, 1978). 1.3 Justification of the study Damages caused by putrefaction accounts for 5% of the total damages in hides and skins in Kenya which accounts for 0.2 billion loss in Kenya’s leather value chain (Mwinyihija, 2010). The determination of the correct crystal size of salt is a way of reducing the damages caused by putrefaction. Theoretically, the granular type of salt is the most appropriate type of curing salt although it is not commonly used in practice as it is not readily available to raw hides and skins dealers as compared to all the other types of salt namely; vacuum, rock, marine and Khari salts. It has the advantage of not becoming caked when wet by brine. Caking not only reduces the surface available for dissolution of the salt but also interferes with the free flow of the resulting brine into or away from the skins (O’Flaherty, 1978). Granular salt is also high in purity, but the crystal size is larger, 2-4 mm, and it is cheaper than vacuum salt, which is considered the most pure salt (99.9% NaCl) and therefore a relatively high cost product (Covington, 2009). The 2-4 mm crystal size for granular salt means the rate of crystal growth is slower and contact with the surface is maintained as it is dissolved into the pelt’s moisture. The other two types of salt that is; marine and khari salts are unsuitable for curing hides and skins. Marine salt (usually prepared by evaporating sea water) is highly 3
contaminated with calcium, magnesium and other salts; and in addition to this, unlike sea salt prepared for the food industry, which is sterilized by the boiling processes, the salt destined for industrial applications is evaporated by solar action and is likely to be contaminated with halophilic and halo tolerant bacteria (Covington, 2009). On the other hand, khari salt cannot strictly be considered as a grade of salt. It is very impure, composed of variable amounts of sodium, magnesium, chloride, sulfate, bicarbonate and carbonate ions, typically a mixture of sodium and magnesium sulfates (BLMA, 1948). The presence of alkaline impurities in this grade of salt, which is also contaminated with halophilic and halotolerant bacteria, causes protein hydrolysis under warm conditions (Covington, 2009). It was against this background therefore, the present study concentrated on investigating the most appropriate crystal size of rock salt for effective curing of raw hides and skins as the coarse crystals usually obtained after mining and crushing this type of salt tend to have sharp edges which are likely to cause indentation and cutting on the cured hides during storage, making this grade of salt unsuitable for curing purposes (Covington, 2009). 1.4 Objectives 1.4.1General objective To determine the size of salt crystals suitable for adequate wet salting in Thika sub county. 1.4.2 Specific objectives
1. To review the sizes of salt crystals currently being used for preservation of hides and skins. 2.To analyze the loss in moisture content in hides and skins when different crystal sizes of salt are used for wet salting 3. To analyze the extent of bacterial damage in hides and skins produced by use of different crystal sizes of salt during curing.
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1.5 Hypothesis testing H1: There are different salt sizes being used in the market for curing of hides and skins in Thika HI: There is a difference in loss of moisture content in hides and skins when different crystals sizes of salt are used for wet salting H1: There is bacterial damage in hides and skins produced by use of inappropriate crystal sizes of salt during curing
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2.0 LITERATURE REVIEW Preservation of hides and skins is important as deterioration of the skin starts within 5-6 hours after flaying (Gudro et al., 2004). Wet salting is the process of hides and skins curing by dehydrating the fresh hides and skins (through abstraction of water) in order to prevent the development of bacteria causing putrefaction by creating an environment in which bacteria cannot thrive and storing them in a pile in such a way that the pickling brine resulting from the dehydration can be easily drained off (Eduard, 2008). Different methods of preservation of hides and skins have been used over the years. Some of them are; 1. Sun drying and suspension drying (Kagunyu et al., 2011) 2. Preservation using vacuum salt (Gurdo et al., 2014) 3. Preservation using indigenous azadirachta indica leaf (Ahmed et al., 2015) 4. Curing by use of potassium chloride (Kagunyu et al., 2011) 5. Curing by silica gel (Ahmed et al., 2015) The use of salt for preservation of hides and skins remains the most popular curing method worldwide (Gurdo et al., 2004). In Kenya, wet salting is the most widely practised method of preservation of hides and skins and comprises 85% of the total hides and skins cured (Mwinyihija et al., 2011). This is because the method is easy, cheaper than other methods, highly efficient (Palanisamy et al., 2005) and the quality of the finished leather is better compared to other methods. Salt has high solubility, is easy and safe to handle and is easily removed from the hides and skins during soaking (FAO, 1995). Despite wet salting being the most popular method of curing of hides and skins, few producers in the pastoralists 6
communities are aware of the wet salting method of curing of hides and skins and this leads to poor quality of hides and skins (Ahmed, 2016). 2.1Types of salts used today Different types of curing salts are available to the hides and skins dealers and the slaughterhouses globally (Vankar and Dwivedi, 2009). These are: The marine salt Magadi salt Rock salt (Mwinyihija et al., 2011) Khari salt Sea salt (www.leathermag.com) Granular salt and vacuum salt (Covington, 2009) These types of curing salts have different crystal sizes and different characteristics.
Figure 1: Very fine salt with grain size of 0-0.2 mm
Source; Zoutman Industries official website
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Figure 2: Medium salt with grain size of 1-3mm
Source; Zoutman Industries official website
Figure 3: coarse salt with grain size of 10-15mm
The use of the correct grain size for curing salt is important because use of improper grain size lowers the value of hides and skins (Behailu, 2015) and the weight loss during salt curing depends on several factors among them the type of salt used (Mwinyikione et al., 2011). The size of the grain is determined by use of the sieve analysis method (Miller, 1978).The particles are passed through a sieve mesh and the size is determined by the ratio of the particle size to the sieve openings. During sieve analysis, the sample is subjected to horizontal or vertical movement in accordance with the method. This causes a relative movement between the particles and the sieve. Depending on their size, the individual particles either pass through
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the sieve mesh or are retained on the sieve surface. The likelihood of a particle passing through the sieve mesh is determined by the ratio of the particle size to the sieve openings, the orientation of the particle and the number of encounters between the particle and the mesh. Standardized sieves in accordance with ISO 3310 are used and different sizes are obtained and they are expressed in terms of mm, the smallest being from 0.045mm to >15mm (ISO 3310). A modern method of determination of the size and the shape of salt is by use of the CAMSIZER dynamic image analysis which is more efficient than the sieve analysis( ISO 3310).The sample is transported to the measurement field via a vibratory feeder where the particles drop between a planar light source and 2 CCD cameras. The projected particles shadows are recorded at a rate of more than 60 images per second and analyzed. It’s possible to measure a wide range of particles from 20 micrometers to 30 millimeters. The CAMSIZER dynamic image analysis method has advantages over the sieve method which include; reduction of sample analysis time, analysis costs, manpower, reduced workload and perfect matching of sieve results (i.e. identical product specifications). Also, more information on each sample is obtained (i.e. size and shape, higher resolution, etc.), results are available faster and at higher frequency, results saved in 1000 sizes classes more frequent and better calibration and similar and accurate results in absolute size at different locations due to low instrument to instrument variability ratio (Horiba particle characterization, 2010). 2.2 The relationship between loss in moisture content and the salt crystal size Moisture content is responsible for the growth of bacteria. The moisture content of fresh hides and skins is about 60-70 % (Covington, 2009) and is adequate to support bacterial growth. However, if reduced by salting, the bacterial activity lowers and eventually stops when moisture content is below the critical moisture content which is about 35%. (Kanagaraj and Babu, 2002). Salt has two functions as a curing agent; 9
1. Has dehydrating ability, therefore acts as a preservative reducing the water content from 60-70% to 35-40%. 2. Bacteriostatic effects (Sivabal and Jayanthi, 2009). 2.3 Bacterial damage Different types of bacteria are associated with putrefaction after flaying. They include the Bacillus species, Micrococcus and the Staphylococcus species (Covington, 2009). The micrococcus is a halophilic bacterium which grows in 20% salt concentration and causes poor grain and red heat (Putrefaction; 2002).The bacillus and staphylococcus are halophilic bacteria which can survive in 5-15% salt concentrations. The bacteria are responsible for leather decay and low grading (Mohamed et al., 2016). 2.4 Act of degradation The degradation of skin is believed to begin approximately in 5 to 6 hours after the death of the animal. A process called autolysis governs the onset followed by putrefaction. In autolysis, intracellular enzyme cathepsin is involved (Tancous, 1970; Tancous and Jayasimhalu, 1973; Bienkiewicz, 1983). The process of decay does not proceed uniformly in all areas of the skin. Some skin components are more resistant to bacteria than others. The components most resistant to bacteria are fibrous proteins, collagen, elastin and hair keratin, whereas the albumins, globulins, mucoproteins, fats and soft keratin in hair root are the least resistant (Tancous, 1970). Decay starts in areas of high metabolic activity and in those containing soluble materials (Humdin, 1999). Blood remaining in the veins and soft proteins in the hair follicle will be the first sites. The first visible signs of decay will therefore be a loosening of hair or wool, which is popularly known as hairslip (Tancous, 1964, 1972; Sharp house, 1979). Fats will become softer and yellow. The attack on collagen itself will begin at the base of the hair root at the
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grain- corium junction causing at the worst, delamination of the grain layer and in milder cases increasing the grain looseness in the leather made from it (Tancous, 1986). 2.5 Moisture content of hides and skins Moisture content of the raw hides and skins is an important factor responsible for the growth of the bacteria. The moisture content which is about 65% is adequate to support bacterial growth. However if the water content is reduced by methods such as drying and salting, the bacterial activity decreases and eventually stops when the moisture content is less than 35% ( Sharphouse;1979). At this level, mould growth may still continue particularly on fatty hides and skins. The moisture content should therefore be reduced to less than 20% to provide complete preservation in the absence of any bactericide or bacteriostatic agent (Covington, 2011). If the level of water is reduced to 10% or less, two problems become apparent. First such an over dried hide or skin become brittle and may crack during handling. Secondly and more importantly, low moisture content materials rehydrate only slowly and perhaps incompletely during the course of soaking and subsequent tanning operations. Stuart and Frey, (1996) reported that the growth of bacteria ceases below the critical moisture content. The preservative action of salt is most often described in terms of its osmotic effect but a better explanation involves availability of water or AW (water activity) which is the vapour pressure of the test materials divided by the vapour pressure of water (Sweet and Hendrickson, 1982). The water activity of pure water is 1 and that of hides and skins is about 0.99 (Rockland and Nishi, 1980) Most bacteria grow best in an Aw close to that of pure water but will tolerate an Aw of 0.7. During the course of preservation procedures like salting, the high Aw of fresh hides or skins is reduced by dissolving large quantities of a soluble chemical into the moisture inside the material being preserved (Rockland and Nishi, 1980).
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3.0 MATERIALS AND METHODS 3.1 Determination of the curing saltcrystals currently being used in the market The study was carried out in the curing premises in Thika Sub County. Two of the curing premises were located in Ngoliba and 4 were located in Thika municipality. The type of salt used to cure hides and skins in the curing premises, the size of the salt crystals being used for the preservation of the hides and skins and the effectiveness in reduction of moisture in the cured hides and skins were determined by checking for any signs of putrefaction which included hairslip and ammoniacal odour in the hides and skins. The size of the salt crystals was determined by comparison of the sizes with the standard salt sizes which were determined by use of the sieve analysis method or the CAMSIZER image analysis method (Miller, 1978). 3.2 Study area 3.2.1 Geographical location The determination of the salt crystal sizes currently being used in the market was done in Thika Sub- County. Two of the curing premises were located in Ngoliba and 4 were located in Thika municipality. It lies between longitude 01003ꞌS and latitude 37005ꞌEof the equator. 3.2.2 Climate and weather The Sub-County enjoys a warm climate with temperatures ranging between 120C and 200C. The rainfall average is 1200mm each year. June and July are the coldest months while January February, March September and October are the hottest months. 3.2.3 Population The population tally in the Sub County according to the Kenya National Bureau of Statistics report of 2009 is 139853.
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3.3 sample collection and preparation The samples used for the experiment were collected from Kiamaiko slaughterhouse. A total of 5 goatskins grade I, medium sized were purchased immediately after slaughter. The skins were trimmed to remove the unwanted parts and washed with cold water to remove blood, dung and dirt. The skins were transported to the curing premises using sealed plastic bags to avoid any contamination. They were placed in a clean place in the curing premises in a slanted position and then curing salt with different crystal sizes was spread evenly on the flesh side of the respective skins. The samples were labeled A, B, C and D; where A represented the hide with the largest crystal size, B with medium crystal size of salt and C with the finest crystal size and D was the sample without any curing salt (control). 3.4 Determination of moisture content The moisture content and the rate of bacterial infection was determined in day1, day 5, day 10 and day 21 and then the results tabulated as shown in the results section. Apparatus used for determination of moisture:
An air oven fitted with a fan and a regulator capable of maintaining the temperature at 100 ± 20C
A desiccator
Analytical balance
3.4.1 Procedure for determination of moisture content: The leather was chopped into small pieces and 10g of sample weighed. The sample was placed in an oven and drying was done for 3hrs. The samples were cooled in a desiccator for 20 minutes and then weighed. 13
The process of drying and weighing was repeated until 2 readings at an interval of 1 hour did not differ by more than 2mg. The final mass of the samples was recorded. Calculation The moisture content Mc was determined using the following formula; 𝑀2 − 𝑀1 × 100 𝑀2 Where: M2 – moisture content before salting M1- moisture content after salting (Elliot, 1967). The moisture content in the skins was recorded when different salt crystals were used for curing. 3.5 Determination of the extent of bacterial infection in skins by use of different salt crystals for curing of skins The extent of bacterial infection in goatskins was determined by the observation of hairslip which was an indicator of putrefaction and the presence of ammoniacal odour in the skins. The results were expressed in terms of quantitative evaluation and expressed as percentage putrefaction and their grades were also indicated as shown in Table 2 below. 3.6 Determination of mechanical damage on cured hides and skins caused by use of salt with various crystal sizes The mechanical damage on cured skins caused by the use of salt with various crystal sizes was determined by observation and recorded in Table 2 below. 3.7 salt crystal sizes used for curing The types of salts used for curing of hides and skins were Magadi industrial salt, Livestock salt and Marine salt.
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The crystal sizes used were 2mm. 0.5mm and 5mm which were determined using the sieve method of analysis.
Figure 4: 5mm salt crystal size
Figure 5: 0.5mm salt crystal size
Figure 6: 0.5mm salt crystal size
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Figure 7: Magadi salt with 5mm crystal size
Figure 8: Magadi salt with 2mm crystal size
Figure 9: Magadi salt with 0.5mm crystal size
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Figure10: Marine salt with 5mm salt crystal size
Figure11: Marine salt with2mm salt crystal size
Figure12: Marine salt with 0.5mm salt crystal size
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3.8 Data analysis The different salt crystal sizes used in the curing of hides and skins were compared to the standard sizes that had been previously determined either by the use of the sieve analysis method or the CAMSIZER image analysis method (Miller, 1978). The mechanical damage caused by use of various salt crystal sizes was determined by observation and then quantitative evaluation was done. The data obtained from the determination of moisture content when various salt crystal sizes were used was analyzed to get analysis of variance ( ANOVA) using Genstat 15th edition statistic software and presented in form of tables and line graphs. Differences considered significance at 95% confidence interval (p≤0.05).
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4.0 RESULTS 4.1 salt crystal sizes used for curing of hides and skins. Different types of curing salts were used in Thika Sub County. These salts included Magadi industrial salt, Marine salt and Livestock salt. These salts were obtained from traders in the market and they came in different crystal sizes but the crystal sizes were mostly mixed up. The salts were bought in sacks as shown in the Figure 13 below.
Figure 13: curing salt available to hides and skins dealers in Thika municipality
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4.2 Percentage moisture content of the different salt crystal sizes The data obtained was as follows Table 1: Percentage moisture content in skins from day 1 to day 21 after using Marine salt, Magadi industrial salt and Livestock salt for curing Type of salt
Magadi industrial salt Marine salt
Livestock salt
Salt crystal sizes
0.5mm 2mm 5mm 0.5mm 2mm 5mm 0.5mm 2mm 5mm
Day1
65
65
65
65
65
65
65
65
65
Day5
59.3
46.4
54.9
53.8
43.2
50.3
57.6
47.9
58.6
Day10
50.2
35.7
45.3
46.2
29.2
38.6
52.1
33.5
49.2
Day 21
48.6
20.8
30.3
37.5
16.5
25.3
47.3
19.6
38.3
The results were presented in form of Line graphs showing the percentage moisture content in the skins when different crystal sizes of salt were used as shown below.
250 200 150
2mm 5mm
100
0.5mm
50 0 day1
day5
day10
day21
Figure14: percentage loss in moisture content after using Marine salt with different crystal sizes of salt for skins curing
20
250
200
150
2mm 5mm
100
0.5mm
50
0 day1
day5
day10
day21
Figure15: percentage loss in moisture content after using Livestock salt with different crystal sizes for skins curing
250
200
150
2mm 5mm
100
0.5mm
50
0 day1
day5
day10
day21
Figure16: Percentage loss in moisture content after using Magadi salt with different crystal sizes for skins curing.
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5.0 DISCUSSION From the line results obtained above, it was clear that Marine salt removed moisture from the skins faster followed by livestock salt. Magadi industrial salt removed water the least from the skins. In terms of the salt crystal sizes, the skins that were cured using salt with 2mm crystal sizes had the least amount of moisture at the end of the curing process, they were of good quality and no stains were observed. This was followed with the 5mm crystal size of salt and 0.5mm crystals removed moisture the least from the skins. There was hair loosening and odour coming from the skins that were cured using 0.5mm and 5mm crystal sizes. There was formation of a cake on the skins that were cured using the 0.5mm crystal size of salt. Quantitative evaluation of the preserved skins: Table2: Percentage hair loosening in the skins and the grades after using different salt crystal sizes for curing Salt crystal size
Percentage
hair Grade
loosening/ putrefaction 0.5mm
30%
III
2mm
2%
I
5mm
40%
III
From Table 2 above, it’s clear that most of the putrefaction occurred in the skins that were cured using salt with crystal sizes of 5mm, followed by those cured with 0.5mm. The skins that were cured with crystal sizes that were 2mm had less hair loosening and were grade I.
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6.0 CONCLUSION Different salt sizes were available in the market and were being used for curing of hides and skins and were available to farmers involved with curing. The salt crystal sizes ranged from 0.5mm to more than 10mm although there was no salt with grains which were purely of the same crystal size rather the crystal sizes of the salt were mixed up. From the results obtained, it was concluded that salt with crystal size of 0.5mm is unsuitable for curing of hides and skins because in the presence of moisture, the crystals fuse and grow. This effect occurs to reduce the surface free energy. The result of this mechanism is that the salt can create a fused mass when the area of contact between the salt and the pelt surface is reduced, slowing the process and therefore risking bacterial damage. Salt with 5mm crystal size was also found to be unsuitable for curing of hides and skins because the crystal sizes were too large and created areas with gaps in the hides and skins which were not in contact with the salt. These areas were evidenced by hairslip and mild odour which came from the skins. The skins were also grade III after curing and this showed that curing of the skins with salt of 5mm crystal size lowered the grade from grade I to grade III. Salt with 2mm crystal size reduced moisture content in hides and skins fast and the skins when graded were grade I. There was no hair loosening or odour in the skins. It was therefore concluded that salt with 2mm crystal size was the best for curing of hides and skins.
The null hypotheses which stated that different salt sizes were being used in the market for curing of hides and skins, that there was a difference in loss of moisture content in hides and skins when different crystal sizes of salt are used for wet salting and that there was bacterial damage in hides and skins produced by use of inappropriate crystal sizes of salt during curing were accepted. 23
It was also concluded that though livestock salt reduced moisture content in the skins faster than Magadi Industrial salt and when the best crystal size was used the salt could be used for curing of hides and skins, the salt caused discoloration to the skins and this affected the overall grade of the skins which were cured using livestock salt.
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7.0 RECOMMENDATIONS 1. Use of the correct salt crystal size for curing of hides and skins is important as the crystal size of the salt affected the loss on moisture content in the skins and the overall quality of the skins. 2. Either too large or too small crystal sizes of salt were inappropriate for curing of hides and skins which was evidenced by hair loosening and odour from the skins 3. The producers of salt should produce salt with pure sizes of the crystals and should avoid mixing up the crystal sizes as this affects curing of the hides and skins.
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References
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