Evidence of “ Flat Sour ” Spoilage by Obligate Anaerobes in Marketed Canned Drinks

Abstract

Twenty-five samples of canned drinks incubated at 55C° were examined in microbial aspects during high temperature storage. Forty spoiled cans were found in six kinds of canned coffee samples. The appearance of these was very similar to that of flat sour spoilage. Spoilage ratios ranged from 0.3 percent to 3.6 percent. pH values and degrees of vacuum of the spoiled cans were lower than those of the normal cans. The contents of spoiled cans were more whitish than the normal ones and in some cans separated into clear supernatants and precipitates, but the change of flavor was very slight.
From 15 out of 40 spoiled cans some spore-forming obligate anaerobes were isolated. Among 15 isolates inoculated in normal canned coffee samples, 12 isolates caused flat sour spoilage, and there is a chance that the spores of 10 isolates survive the sterilization processes (F₀: 15-20). These principal characteristics except for the failure of sulfate reduction might indicate the participation of Desulfotomaculum nigrificans.
The flat sour spoilage found in this study was caused by at least 9 obligate anaerobic isolates, and called by the authors“A New Type of Flat Sour Spoilage”(O. A. Flat Sour Spoilage.).