Chapter 6
Vegetable and Fruit Products
The microbial biota of land-grown vegetables may be expected to reflect that of the soils in which
they are grown, although exceptions occur. The actinomycetes (Gram-positive branching forms) are
the most abundant bacteria in stable soils, yet they are rarely reported on vegetable products. On the
other hand, the lactic acid bacteria are rarely found in soil per se, but they are significant parts of the
bacterial biota of plants and plant products. The overall exposure of plant products to the environment
provides many opportunities for contamination by microorganisms. The protective cover of fruits and
vegetables and the possession by some of pH values below which many organisms cannot grow are
important factors in the microbiology of these products.
An attempt is made in this chapter to treat fruits and vegetables separately even though this is
difficult. In common usage, products such as tomatoes and cucumbers are referred to as vegetables
and yet from the botanical standpoint they are fruits. Lemons, oranges, and limes are fruits botanically
as well as in common usage. By and large, the distinctions between fruits and vegetables are based on
pH, irrespective of the lack of scientific merit.
FRESH AND FROZEN VEGETABLES
The incidence of microorganisms in vegetables may be expected to reflect the sanitary quality of
the processing steps and the microbiological condition of the raw product at the time of processing.
In a study of green beans before blanching, Splittstoesser et al.
50 showed that the total counts ranged
from 5.60 log 10 to over 6.00 log 10 in two production plants. After blanching, the total numbers were
reduced to 3.00–3.60 log 10 /g. After passing through the various processing stages and packaging,
the counts ranged from 4.72 to 5.94 log 10 /g. In the case of French-style beans, one of the greatest
buildups in numbers of organisms occurred immediately after slicing. This same general pattern was
shown for peas and corn. Preblanched green peas from three factories showed total counts per gram
between 4.94 and 5.95 log 10 . These numbers were reduced by blanching but again increased successively with each processing step. In the case of whole-kernel corn, the postblanch counts rose
both after cutting and at the end of the conveyor belt to the washer. Whereas the immediate postblanch count was about 3.48 log 10 , the product had total counts of about 5.94 log 10 /g after packaging.
Between 40% and 75% of the bacterial biota of peas, snap beans, and corn was shown to consist of
leuconostocs and “streptococci,” whereas many of the Gram-positive, catalase-positive rods resembled
corynebacteria.
48,49
125
Vegetable and Fruit Products
The microbial biota of land-grown vegetables may be expected to reflect that of the soils in which
they are grown, although exceptions occur. The actinomycetes (Gram-positive branching forms) are
the most abundant bacteria in stable soils, yet they are rarely reported on vegetable products. On the
other hand, the lactic acid bacteria are rarely found in soil per se, but they are significant parts of the
bacterial biota of plants and plant products. The overall exposure of plant products to the environment
provides many opportunities for contamination by microorganisms. The protective cover of fruits and
vegetables and the possession by some of pH values below which many organisms cannot grow are
important factors in the microbiology of these products.
An attempt is made in this chapter to treat fruits and vegetables separately even though this is
difficult. In common usage, products such as tomatoes and cucumbers are referred to as vegetables
and yet from the botanical standpoint they are fruits. Lemons, oranges, and limes are fruits botanically
as well as in common usage. By and large, the distinctions between fruits and vegetables are based on
pH, irrespective of the lack of scientific merit.
FRESH AND FROZEN VEGETABLES
The incidence of microorganisms in vegetables may be expected to reflect the sanitary quality of
the processing steps and the microbiological condition of the raw product at the time of processing.
In a study of green beans before blanching, Splittstoesser et al.
50 showed that the total counts ranged
from 5.60 log 10 to over 6.00 log 10 in two production plants. After blanching, the total numbers were
reduced to 3.00–3.60 log 10 /g. After passing through the various processing stages and packaging,
the counts ranged from 4.72 to 5.94 log 10 /g. In the case of French-style beans, one of the greatest
buildups in numbers of organisms occurred immediately after slicing. This same general pattern was
shown for peas and corn. Preblanched green peas from three factories showed total counts per gram
between 4.94 and 5.95 log 10 . These numbers were reduced by blanching but again increased successively with each processing step. In the case of whole-kernel corn, the postblanch counts rose
both after cutting and at the end of the conveyor belt to the washer. Whereas the immediate postblanch count was about 3.48 log 10 , the product had total counts of about 5.94 log 10 /g after packaging.
Between 40% and 75% of the bacterial biota of peas, snap beans, and corn was shown to consist of
leuconostocs and “streptococci,” whereas many of the Gram-positive, catalase-positive rods resembled
corynebacteria.
48,49
125