Spoilage of Vegetables and fruits
The deterioration of raw vegetables and fruits may result from physical factors action of their own enzymes, microbial action, or combinations of these agencies. Mechanical damage resulting from action of animals, birds or insects or from bruising, wounding, freezing or other mishandling may predispose toward increased enzymatic action or the entrance and growth of microorganisms.
Although each fruit and vegetable has certain types of decomposition and kinds of microorganisms predominant in its spoilage, some general types of microbial spoilage are found more often than rest in vegetables and fruits. The most commonly occurring types of spoilage are as follows:
- Bacterial soft rot caused by Erwina carotovora and related species.
- Gray mold rot caused by species of botrytis e.g cinera a name derived from the gray mycelium of the mold. It is favored by high humidity and a warm temperature.
- Rhizopus soft rot, caused by species of Rhizopus e.g stolonifer. A rot results that often is soft and mushy.The cottony growth of the mold with small, black dots of sporangia often covers masses of the foods.
- Anthracnose, usually caused by Colletotrichum lindemuthianum, C. cocodes and other species.The defect is spotting of leaves and fruits.
- Alternaria rot caused by Alternaria tenuis and other species. Areas become greenish – brown early in the growth of the mold and later turn to brown or black spots.
- Blue mold rot caused by species of Penicillium digitatum and other species. The bluish green color that gives the rot its name results from the masses of spores of the moldd.
- Downy mildew caused by species of Phytophthora, Bremia and other genera. The molds grow in white, woolly masses.
- Watery soft rot caused chiefly by Sclerotinia sclerotiorum is found mostly in vegetables.
- Black mold rot caused by Apergillus niger.The rot gets its name from the dark brown to black masses of spores of the mold termed “smut” by the lyperson.
- Pink mold rot caused by pink spored Trichothecium roseum.
- Fusarium rots a variety of types of rots caused by species of Fusarium.
- Brown rot caused chiefly by Sclerotinia species.
Many fruits and vegetables present nearly ideal conditions for the survival and growth of many types of microorganisms. The internal tissues are nutrient rich and many, especially vegetables, have a pH near neutrality. Their structure is comprised mainly of the polysaccharides cellulose, hemicellulose, and pectin. The principal storage polymer is starch. Spoilage microorganisms exploit the host using extracellular lytic enzymes that degrade these polymers to release water and the plant’s other intracellular constituents for use as nutrients for their growth. Fungi in particular produce an abundance of extracellular pectinases and hemicellulases that are important factors for fungal spoilage (Miedes & Lorences, 2004). Some spoilage microbes are capable of colonizing and creating lesions on healthy, undamaged plant tissue (Tournas, 2005b). Spoilage microorganisms also can enter plant tissues during fruit development, either through the calyx (flower end) or along the stem, or through various specialized water and gas exchange structures of leafy matter.