Journal of Agriculture & Life Sciences

Halophilic Archaea Cause the „Red Cheese Spoilage‟ of the Boiled White Cheese ─ Fulfillment of Koch‟s Postulates
Mohammed I. Yamani, Ph.D; Mohammed I. Saleh, Ph.D.

Abstract
Boiled white cheese is seasonally produced by renneting a mix of sheep and goat milk, pressing and cutting the formed curd into pieces which are boiled in brine containing ~ 25% salt (NaCl). Cheese pieces are usually kept in the cooled brine, without refrigeration, for up to one year in tin cans. Producers and consumers have been complaining about spoilage of the boiled white cheese in which cheese pieces and brine show a pink to red discoloration accompanied by unwanted changes in flavor. (“The red cheese spoilage”.)Boiled white cheese samples with red color deviations were collected and tested for the halophilic Archaea. Salt concentration in the brine ranged from 16 to 29% (w/v), with an average of 22.7%, and the pH ranged from 4.2 to 6.3 with the average of 5.2. Counts of halophilic Archaea were determined by applying the surface or spread plate method using a halophilic agar medium containing 25% (w/v) NaCl. Red, pink or orange colonies observed after incubation in plastic bags at 37oC for up to 4 wks were counted and were found to belong to the halophilic Archaea. The counts ranged from 1.5x105 to 5.1 x 107cfu/ml, with an average of 6.1 x 106cfu/ml. The halophilic Archaea belonged to Halobacterium, Haloferax, Haloarcula and Halococcus of the family Halobacteriacea. These findings and the ability of these Archaea experimentally to cause red cheese spoilage in freshly produced boiled white cheese after inoculation from active pure species cultures and storage at room temperature and to re-isolate the corresponding halophilic Archaea from the experimentally spoiled cheese could confirm that halophilic Archaea are responsible for the "red cheese spoilage” of the boiled white cheese, and thus fulfilling Koch’s postulates for red cheese spoilage halophilic Archaea.

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