Defects Produced by Spoilage Organisms in Cottage Cheese Sterilized by Cathode Rays

Abstract

Seventeen organisms representing five genera of bacteria, two genera of yeast and three genera of mold were inoculated individually and in combination with Streptococcus lactis into cottage cheese which had been sterilized by subjection to cathode rays at a dosage of 5.5 x 106 rep (Roentgen equivalent physical). Achromobacter butyri and A. eurydice produced gelatinous slime and a fermented aroma. Alcaligenes metalcaligenes and Pseudomonas desmolyticum produced a tapioca slime. The coliform and Pseudomonas bacteria, and the Rhodotorula and Torulopsis yeasts produced surface slime the characteristics of which varied with the species of organism. Geotrichum candidum, Mucor plumbeus, and Penicillium frequentana produced pigmented mold characteristic of the particular species. Achromobacter and Escherichia produced defects more rapidly when inoculated individually, than when combined with S. lactis. The yeasts and three of the Pseudomonas cultures produced defects more rapidly when combined with S. lactis than when inoculated alone. The appearance and odor of the spoiled cheese was the same regardless of whether the cultures were introduced individually or in combination with S. lactis. Most of the organisms caused increases in pH during the period required for spoilage; exceptions being the two species of Micrococci and the Rhodotorula yeast combined with S. lactis which produced acid and whey.