MOLD SPOILAGE IN FOOD PRODUCTS 253 



of such products are due to organisms which have invaded the fruit 

 on the Hving plant. Even with those which invade during storage 

 we must remember that the plant tissues are alive, and presumably 

 possess a mechanism which can be overcome only by certain species 

 having to a certain degree parasitic qualities. It is not surprising, 

 therefore, that we find some species of fungi occurring characteris- 

 tically on each kind of fruit or vegetable. Thus, various fruits, 

 especially the plums and cherries, are spoiled by pathogenic species 

 of Sclerotinia, which also cause disease in the trees. R. nigricans 

 is especially important as a cause of spoilage of fruits and stored 

 potatoes, especially sweet potatoes. The small fruits, especially 

 strawberries, are particularly susceptible. The disease in straw- 

 berries is known as leak, because of the softening and dripping of 

 the fruit. It occurs as a source of considerable loss in shipment and 

 is prevented by refrigeration. In sweet potatoes, a characteristic 

 soft rot is produced, the main factors determining which are injury 

 to the potatoes and humidity of the storage bins. For a bibliog- 

 raphy of the rots caused by R. nigricans, see Heald.^^ The common , 

 soft rot of apples in storage is due to P. expansum. Although other 

 organisms may at times cause spoilage of apples, certainly in the 

 great majority of cases this Penicillium is responsible. An injury to 

 the skin is apparently necessary for infection to take place. The 

 spoilage of citrus fruits is caused by two species, P. digitatum and 

 P. italcum. P. digitatum is sometimes referred to as P. olivaceum, 

 since it forms conidia of an olive-green color. On oranges the olive- 

 colored area is generally surrounded by a broad white zone of my- 

 cehtiin which has not formed conidia. P. italcum produces spores of 

 a light blue-green color. Both species may frequently be found 

 growing on one orange. As with the apples, these organisms are 

 wound parasites, and losses may be avoided by care in handling 

 and packing. IVIucors occur frequently on fresh fruits, especially 

 during shipment. A hairy, greyish growth of these molds often 

 develops on grapes, thus preventing their sale. A similar growth of 

 Sclerotinia may also develop on grapes, the mycelium penetrating 

 the skin and the mold obtaining nourishment from the juice. It 

 causes a rapid evaporation of water from the juice, without having 

 a deleterious effect on the flavor of the grapes. It thereby increases 

 the concentration of sugar to such a degree that grapes too sour for 

 the manufacture of wine become sweet enough for this purpose. 

 However, the mold may cause economic loss if allowed to develop 

 unchecked. Species of Dematium and Alternaria have also been 

 observed on grapes. 



