Contamination, Spoilage, Preservation: Sugars, Fruits and Vegetables

Contamination, Spoilage,
Preservation: Sugars, Fruits and
Sugar products include: sucrose (cane and beet sugar),
molasses, syrups, maple sap and sugar, honey and candy.
 The raw juice expressed from sugarcane may become high in
microbial content unless processing is prompt.
 The relevant micro organisms are those from the sugarcane and the
soil contaminating it and therefore comprise slime producers, such
as species of Leuconostoc and Bacillus; representatives of the genera
Micrococcus, Flavobacterium, Alcaligenes, Xanthomonas,
Pseudomonas, Erwinia, and Enterobactor; a variety of yeast, chiefly in
the genera Saccharomyces, Candida, and Pichia; and a few moulds.
 Microbial spoilage of molasses is not common,
although it is difficult to sterilize by heat because
of the protective effect of the sugar.
 Canned molasses or sirup may be subjected to
spoilage by osmophilic yeast that survives the
heat process.
 Molasses or sirup exposed to air will mold, in
time, on the surface, and this also may occur at
the surface of a bottled or canned sirup if air is
left there and contamination has taken place
prior to sealing.
 Sap from the sugar maple becomes contaminated when
Although a moderate amount of growth may improve
flavor and color, the sap often stands under conditions
that favor excessive growth of micro organisms and
hence spoilage.
Five chief types of spoilage are recognized:
Ropy or stingy sap, usually caused by Enterobacter
aerogenes , although Leuconostoc may be responsible.
Cloudy, sometimes greenish sap resulting from the
growth of Pseudomonas fluorescens, with species of
Alcaligenes and Flavobacterium sometimes contributing
to cloudiness,
 Red sap, colored by pigments of red bacteria,e.g.
Micrococcus roseus, or of yeasts or yeast like fungi,
Sour sap ,a catchall grouping for types of spoilage not
showing a marked change in color but having a sour odor
and caused by any of a variety of kinds of bacteria or
yeasts, and
Moldy sap, spoilage by molds.
Maple sirup can be ropy because of Enterobacter
aerogenes, yeasty as the Micrococcus roseus, or moldy at
the surface, where species of Aspergillus, Penicillium, or
other genera may grow.
The sirup may become dark because of alkalinity produce
by bacteria growing in the sap and inversion of sucrose.
 The chief cause of spoilage of honey is osmophilic yeast:
species of Zyggosaccharomyces, such as Z. mellis, richteri,
or nussbaumeri, or Torula (Cryptococcus) mellis.
Species of Penicillium and Mucor develop slowly.
Special theories for initiation of growth of yeast in honey
have been advanced:
Honey, being hygroscopic, becomes diluted at the
surface, where yeasts begin to multiply and soon
become adapted to the high sugar concentrations,
Crystallization of glucose hydrate from honey leaves a
lowered concentration of sugars in solution, or
On long standing, yeasts gradually become adapted to
the high sugar concentrations.
 Most candies are not subject to microbial spoilage
because of their comparatively high sugar and low
moisture content.
 Exceptions are chocolate with soft centers of
fondant or of inverted sugar, which under certain
circumstances, burst or explode.
 Yeast growing in these candies develops a gas
pressure which may disrupt the entire candy or more
often will push out some of sirup or fondant through
a weak spot in chocolate coating.
 Often this weak spot is on the poorly covered
bottom of the chocolate coating.
 Storage conditions should be such that vermin are kept out
and the sugar remains dry.
Can or sugar beet may be stored in a controlled
Fungal growth is inhibited by 6% carbon dioxide and 5%
During the manufacture of raw sugar and the subsequent
refining process the numbers of micro organisms present,
which may have been large during extraction from cane or
sugar beet, are reduced by most subsequent processes, e.g.
clarification, evaporation, crystallization, centrifugation,
and filtration.
Chemical preservatives are effective in reducing microbial
numbers during sugar refining.
 Care should be taken to avoid buildup of organisms and their spores
during processing, and numbers may be reduced by irradiation with
ultraviolet rays or combined action of heat and hydrogen peroxide.
The bursting of chocolate is prevented by a uniform and fairly heavy
chocolate coating and use of fondant or other filling that will not
permit the growth of gas formers.
Sirups and molasses should be stored at cool temperature to
prevent or slow chemical changes and microbial growth.
The boiling process during evaporation of maple sap to maple sirup
kills the important spoilage organisms.
Honey may be subjected to crystallization. Commercially distributed
honey usually is pasteurized at 71 to 77 C for a few minutes.
A recommended treatment is to heat fairly rapidly to at least 71 C,
hold there for 5 minutes, and cool promptly to 32.2 to 38 C.
It is estimated that one-fourth of all produce
harvested is spoiled before consumption. Spoilage of fresh
fruits and vegetables usually occurs during storage and
transport and while waiting to be processed.
 During transportation to market or the processing plant,
mechanical damage may increase susceptibility to decay
and growth of micro organisms may take place.
 Recirculated or reused water for washing of fruits and
vegetables likely to add organisms and the washing process
may moisten surfaces enough to permit growth of
 Sorting spoiled fruits or vegetables or trimming spoiled
parts removes micro organisms, but additional handling
may result in mechanical damage and therefore greater
susceptibility to decay.
 Spraying with water or packing with chipped ice is done. This
spraying gives a fresh appearance to the vegetables and delays
decomposition but also adds organisms, e.g. psychrotrophs, from
water or ice and gives a moist surface to encourage their growth on
longer storage.
Sweating of products during handling increases the number of micro
organisms in them.
Processes such as trimming, mechanical abrasion or peeling, cutting,
pitting or coring, and various methods of disintegration may add
contaminants from the equipment involved.
Examples of possible source of contaminants of foods with micro
organisms are trays, bins, tanks, pipes, flumes, tables, conveyer
belts and aprons, filters, blanchers, presses, screens, and filters.
Inclusion of decayed part of fruits increases the number of micro
organisms in fruit juices.
Added ingredients such as sugars and starch may add spoilage
organisms, specially spores of thermophilic bacteria.
The deterioration of raw vegetables and
fruits may result from physical factors, action of their own enzymes,
microbial action, or combination of these agencies. Mechanical
damage resulting from action of animals, birds, or insects or from
bursting, wounding, cutting, freezing, desiccation, or other
mishandling may predisposed towards increased enzymatic action
or the entrance or growth of micro organisms. Contact with spoiling
fruits and vegetables may bring about transfer of organisms, causing
spoilage and increasing the wastage. If oxygen is available, the plant
cells will respire as long as they are alive, and hydrolytic enzymes
can continue their action after death of their cells. Disease of
vegetables and fruits may result from the growth of an organisms
that obtains its food from the host and usually damages it or from
adverse environmental conditions that cause abnormalities in
functions and structures of the vegetables or fruits.
General types of microbial
 Bacterial soft rot, caused by Erwinia carotovora and related
Grey mold rot caused by species of Botrytis.
Rhizopus soft rot, caused by species of rhizopus.
Anthracnose, usually caused by Colletotrichum lindemuthianum.
Alternaria rot, caused by Alternaria tenuis and other species.
Blue mold rot, caused by species of Penicillium digitatum and
other species.
Downy mildew, caused by species of Phytophthora, Bremia, and
other genera.
Watery soft rot, caused chiefly by Sclerotinia sclerotiorum.
Stem end rots, caused by species of molds of several genera, e.g.
Diplodia, Alternaria, Phomopsis, Fusarium, and others.
 Black mold rot, caused by Aspergillus Niger.
 Black rot, often caused by species of Alternaria but sometimes of
Ceratostomella, Physalospora and other genera.
 Pink mold rot, caused by pink spored Trichothecium roseum.
 Fusarium rots, a variety of types of rots caused by species of
 Green mold rot, caused usually by species of Cladosporium but
sometimes by other green spored molds, e.g. Trichoderma.
 Brown rot, caused by Sclerotinia species.
 Sliminess or souring, caused by saprophytic bacteria in piled, wet,
heating vegetables.
 Adequate control of temperature and humidity will reduce the
growth of micro organisms.
 Boxes, lugs, baskets and other containers should be practically
free of the growth of micro organisms, and some will need
cleaning and sanitation between uses.
 Contamination from equipment at the time of processing plant
can be reduced by adequate cleaning and sanitizing.
Preservation is done by various methods:
 Removal of micro organisms through washing of vegetables
which removes most of the contamination on the surface but
leaves much of the natural microbial flora. Unless the washed
water is of good bacteriological quality, it may add organisms
and subsequently growth may take place at the moist surface.
 Use of heat: Vegetables to be dried or frozen, and some to be
canned, are scalded or blanched to inactivate their enzymes.
 Use of low temperature: A few kinds of vegetables that are relatively
stable, such as root crops, potatoes, cabbage, and celery, can be
preserved for a limited time by common or cellular storage.
 Chilling: Most vegetables to be preserved without special processing
are cooled promptly and kept at chilling temperature. The chilling is
accomplished by use of cold water, ice, or mechanical refrigerator or
by vacuum cooling. In many cases precooling, i.e. cooling before
normal cold storage is done immediately after harvesting by use of a
cold water spray, a practice referred to as hydro cooling.
 Freezing: The washing of vegetables reduces the numbers of some
organisms and add some organisms, and scalding or blanching( 86
to 98 C) brings about a great reduction in numbers, as much as 90 to
99% in some instances. During storage in frozen conditions there is a
steady decrease in number of organisms, but there are at least some
survivors of most kind of organisms after the usual storage periods.
 Drying: Dried vegetables and vegetable products are used in dried
soups, and dried species and condiments are used as flavoring
material. Many vegetables can be dried by the process of explosive
puffing. Usually small pieces of the diced, partially dehydrated
vegetables are placed in a closed rotating chamber. Heat is applied,
and the chamber is pressurized to a predetermined level; then the
pressure is released instantaneously. This results in an additional loss
of water, but more important, a porous network of capillaries is
formed in the product. The increased porosity simplifies further
drying and imparts good reconstituting ability.
 Use of preservatives: The addition of preservatives to vegetables is
not common, although the surfaces of some vegetables may receive
special treatment. Rutabagas and turnips some times are paraffined
to lengthen their keeping time. Zinc carbonate has been reported to
eliminate most mold growth on lettuce, beets, spinach. Biphenyl
vapors will control Fusarium on potatoes. Sodium chloride is the only
added chemical preservatives in common use. There are added
preservatives and developed preservatives which are used.
Fruits may be subjected to contamination
between harvesting and processing from containers and
from spoiling fruits, and care should be taken to avoid such
contamination as much as possible. Before harvest, fruits
are usually exposed to insecticides and fungicides and may
have their flora altered by such treatments.
 Through washing of fruits serves to remove not only dirt
and hence causal contaminating micro organisms but also
poisonous sprays.
 Washing may be with water, detergent solutions, or even
bactericidal solutions such as chlorinated water.
 T rimming also removes micro organisms.
 Fruits seldom are blanched before other processing
because blanching causes excessive physical damage.
 A steam pressure sterilizer is not required for most fruits,
since heating at about 100 C is sufficient and can be
accomplished by flowing steam or boiling water.
 In general, the more acidic the fruit, the less heat required
for its preservation.
 A few fruits, such as apples, can be preserved for a limited
time in common or cellar storage, but controlled lower
temperatures usually are employed during most of the
storage periods of fruits.
 Each fruit has its own optimum temperature and relative humidity
for chilling storage; even varieties of the same fruit may differ in
their requirement.
 Controlled atmosphere storage implies the altering of various gases
from normal atmospheric concentrations. Usually this is done by
increasing the CO2 concentration and decreasing the O2
 Modified atmosphere storage is usually used to describe controlled
atmosphere conditions which are not accurately maintained or
conditions where the air is initially replaced with gas but no further
measures are taken to keep the gas atmosphere constant.
 Ozone in concentration of 2 to 3 ppm in the atmosphere has been
reported to double the storage time of loosely packed small fresh
fruits, such as strawberries, raspberries, currants, and grapes and of
delicate varieties of apples.
 During preparation of fruits for freezing, undesirable
changes may take place, such as darkening, deterioration in
flavor, and spoilage by micro organisms, especially molds.
Washing the fruits removes most of the soil micro
organisms, and adequate selection and trimming will
reduce many of the molds and yeasts involved in spoilage.
 Yeasts (Saccharomyces, Cryptococcus) and molds
(Aspergillus, Pencillium, Mucor, Rhizopus, Botrytis, Fusarium,
Alternaria, etc.) have been reported to be the predominant
organisms in frozen fruits, although small numbers of soil
 The decrease in numbers of organisms during storage in
the frozen condition is slow but is faster than in most
neutral foods.
 The number of micro organisms in dried fruit is comparatively low and
that spores of bacteria and molds are likely to be the most numerous.
 Chemicals have been applied to fruits chiefly as a dip or spray or
impregnated in wrappers for fruits.
 Among substances that have been applied to the outer surfaces of fruits
are waxes, hypochlorites, biphenyl, and alkaline sodium
o-phenyl phenate.
 Wrappers for fruits have been impregnated with variety of chemicals
including iodine, sulfite, biphenyl, o-phenyl phenol plus hexamine, and
 Green olives are the only fruits which are preserved on a commercial
scale with assistance from an acid fermentation.
 Locally, other fermented fruits sometimes are prepared, such as
fermented green tomatoes and Rumanian preserved apples.

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