Metabiosis and pH of Moldy Fresh Tomatoes.

Two hundred twenty eight locally grown, garden variety, moldy tomatoes were examined. The dominant molds were Alternaria , Fusarium and Cephalosporium . Geotrichum , Epicoccum and Mucor were seen in a small number of tomatoes. Seventy eight per cent of the tomatoes were infected with a single mold, and mixed infections were seen in 21% of tomatoes. The pH at the site of infection varied from 4.4 to 8.1, with pH less than 4.8 observed in only 21 moldy tomatoes. The pH of sound tissue increased as pH at the site of the lesion increased. Bacteria were seen in wet mounts from the site of the lesion of 26% of the tomatoes. Bacteria were cultured from an additional 38% of the tomatoes at the site of the lesion and from 13% of the juice cavities at the site across from the infection. Most bacteria were members of the acid tolerant genera Erwinia and Enterobacter . Members of the genera Pseudomonas , Flavobacterium and Alcaligenes were also isolated. Leuconostoc mesenteroides , rennin-proteolytic Streptococcus faecalis and yeasts were obtained in culture, but were not seen in wet mounts. Gram-negative bacteria were seen in two of 13, and recovered in culture from 6 of 13 severely bruised, non-molded tomatoes. The bacteria appear to be present in a metabiotic relationship in which the molds created a favorable pH for bacterial growth.

Survival of Klebsiella pneumoniae Heated in Buffer and in Tomato Juice.

Klebsiella pneumoniae survived nonexponentially when heated in phosphate buffers at pH 7.0 and 4.3 and in tomato juice at pH 4.3. At 60 C, an initial inoculum of 109 cfu/ml decreased by 6 log units in 15 min, with a long tailing of the survivors to 75 min of heating. At 67 C, total destruction of K. pneumoniae was attained in both buffers at 25 min, and in tomato juice at 40 min. Factors influencing heat resistance of the bacterium are discussed.

Effect of Mold Growth on the pH of Tomato Juice.

Fifty-eight species of 21 genera of molds were grown on tomato juice for 35 days to determine the effect on pH. The molds included members of the class Phycomycetes and the families Moniliaceae , Dematiaceae , and Tuberculariaceae . All molds except two raised the pH from the initial pH 4.1 to a range from 4.9 to greater than 9.0. Thirty-three of the Fungi lmperfecti (53%) raised the pH to values above 7.0. None of the Phycomycetes tested raised the pH above 7.0.

Description and Microbiology of Home-Canned Tomatoes and Tomato Juice.

Home canners completed questionnaires and submitted 378 jars of tomatoes and 382 jars of tomato juice for analysis. Nearly 50% of the containers were non-canning jars, and 25 jars had held food items such as instant tea or coffee or jelly. A few closures were reused from grocery stock; the remainder were the two-part rim and lid or zinc cap and ring. The headspace in 14% of the jars was below 16/32 inch and in 17% between 31/32 and 64/32 inch. Serum layers in 70% of the jars of tomato juice ranged from 20 to 64% of the volume. Eleven percent of the samples were processed with the method of hot fill and seal only, 66% were processed in boiling water, and 23% in the pressure canner. Vacuums of 13 to 15 inches of mercury were most frequently recorded in jars processed with any of the three methods. The pH ranged from 3.5 to 4.7. The average titratable acidity as citric acid, of tomatoes was 0.444% and of tomato juice 0.471%. Microorganisms were recovered from 33% of the jars of tomatoes and from 15% of the tomato juice; however, the percentage of recovery decreased during the period of analysis, suggesting autosterilization. The microorganisms recovered included three fermentative yeasts, one Rhodotorula , three filamentous fungi, 15 Bacillus licheniformis , and the remainder were Klebsiella pneumoniae . It is concluded that directions given to home canners are adequate for home preservation of tomatoes and tomato juice, and that most canners engage in good canning practices.