Pink fruit

Pink disease can be found at very low levels in most pineapple production areas of the world (Rohrbach, 1983). However, economically significant epidemics are only known to occur in Hawaii, the Philippines and Taiwan. When epidemics occur in Hawaii and Taiwan, the highest incidences occur in February, March and April. In the Philippines, however, epidemics occur from August to September (Hine, 1976).

Pink disease of pineapple fruit is characterized by the typical symptom of brown to black discoloration of the fruit tissue when heated during the canning process. Depending on the bacterial strain and the severity of the disease, symptoms in uncooked fruit may be completely absent or may include extremely severe fruit translucence, light pinkish to brownish colour of the fruit cylinder, and/or a 'cantaloupe-like' odour (Rohrbach and Apt, 1986). E. herbicola in uncooked pineapple fruit is essentially symptomless and very difficult to detect. G. oxydans in uncooked fruit induces pinkish brown to dark brown discolorations and may have a 'cantaloupe-like' odour. A. aceti - more recently classified as Acetobacter liquefaciens (Gossele and Swings, 1986) in uncooked fruit with only a few fruitlets infected can be symptomless. However, in moderately to severely infected fruit (many fruitlets infected), symptoms range from pinkish brown to dark brown (Rohrbach and Pfeiffer, 1976a; Kontaxis and Hayward, 1978). The symptom is reported to be caused by the bacteria producing 2,5-diketogluconic acid, which reacts with amino acids to form brown to black pigments (Buddenhagen and Dull, 1967). Strains of the acetic acid bacteria, such as A. liquefaciens, have been reported to produce browning and rotting of apples and pears and to have been isolated from guava, mango and Surinam cherry (Gossele and Swings, 1986).

In contrast to the other fruit diseases, the economic significance of pink disease is the inability to detect diseased fruit prior to processing, with the result of brown to black slices in a sealed can. Thus, quality control during processing is critical to detection of low levels and management of diseased fruit in the cannery (Rohrbach and Apt, 1986). In fresh-fruit production, low levels of pink disease are not of major economic importance. However, when high incidences occur, with strains having symptoms prior to cooking, economic loss can occur.

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