The leather industry is an important sector in the world economy. Almost 23 billion square feet of leather is produced annually (1, 2) and the total value of this is estimated to be more than US$100 billion (3). Most of the global earnings are accrued from footwear sales. This sector represents 60% of the industry's total income, with annual production of 13 million pairs of shoes (4, 5). Because many consumers can perceive when leather products are manufactured from an inferior hide grade, producers are perforce obliged to dispose of damaged hides. Ignorance of effective preservation techniques therefore causes important economic losses in the industry.

Studies have shown that hides contain extensive populations of Gram-positive and Gram-negative bacteria which may be either resident or transient bacteria. As soon as the animal is slaughtered, these bacteria can grow on the raw hides and degrade the hide quality (6–8). A mixture of salt and boric acid is commonly used to prevent the growth of these microorganisms and preserve the hides. If hides are preserved with only crude solar salt, they can be contaminated by different species of extremely halophilic archaea (9–12). These microorganisms are easily detected on hides as they are revealed by red to orange pigments. Extremely halophilic archaea produce red, orange and pink coloured colonies because of the presence of C 50 carotenoids (9–12). Red discolorations on the salted hides, caused by microorganisms, have been scrutinised by researchers since 1929; even at that early date, proteolytic activity of halophilic microorganisms was recognised (13). In addition, occurrence of red colouration produced by extreme halophiles has been noted in the Great Salt Lake (14), Dead Sea (15), Lake Magadi (16) and Tuz Lake (11). Salt lakes and solar saltern crystalliser ponds contain 107–108 CFU of extremely halophilic archaea per ml (9). In previous studies, salt samples which were obtained from Tuz Lake in Turkey contained 104–107 CFU g–1 extremely halophilic archaea (11). In another study, the viable cell number of extremely halophilic archaea in water samples collected from Tuz Lake was found to be 1.38 × 107 CFU ml–1 (17).

Salt collected from Tuz Lake, located in Central Anatolia, Turkey, is used to preserve hides in the Turkish leather industry. If the salt obtained from Tuz Lake is directly used in hide preservation, it may contaminate hides with halophiles. During long storage or overseas transportation of the salted hides, viable cell numbers of extremely halophilic archaea on the hides can multiply excessively. In an earlier study, extremely halophilic archaea were observed in considerably high numbers (103–108 CFU g–1) on 36 salt-pack cured hides. Extremely halophilic archaeal counts were fairly high in 72% of the hides (105–107 CFU g–1) as a consequence of inadequate salt-pack curing method. 94% and 81% of the samples contained proteolytic extremely halophilic archaea (102–106 CFU g–1) and lipolytic extremely halophilic archaea (102–106 CFU g–1), respectively (18). These findings were consistent with previous studies' reports of the extremely halophilic archaeal counts (105–108 CFU g–1) on the brine cured hides (19, 20).

The destructive effect of extremely halophilic archaea on salted hides has been observed. It was detected that proteolytic extremely halophilic archaea, originating in unprocessed solar salt, digested the grain surface of the hide and caused a complete disruption of collagen fibers (21). Furthermore, it was noted that proteolytic and lipolytic extremely halophilic archaea produced sponge-like vesicles within the hide and light stains on the suede surface of finished double-face leathers (22, 23). Therefore, inadequately preserved hides and skins may adversely affect final leather quality.

Due to these destructive effects of extremely halophilic archaea on the salted hides, an effective, easy and inexpensive method should be applied to eradicate these archaea in salt. Thus, using sterile salt in hide preservation will increase leather quality and prevent substantial economical losses in the leather industry.

1.1 Use of Electric Current