Contamination Spoilage Preservation Sugars Fruits and Vegetables CONTAMINATION

Contamination, Spoilage, Preservation: Sugars, Fruits and Vegetables

CONTAMINATION OF SUGARS: Sugar products include: sucrose (cane and beet sugar), molasses, syrups, maple sap and sugar, honey and candy. SUCROSE: 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.

MOLASSES AND SIRUPS: 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.

MAPLE SAP AND SIRUP: Sap from the sugar maple becomes contaminated when drawn. 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.

HONEY: 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.

CANDY: 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.

PRESERVATION OF SUGARS: 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 atmosphere. Fungal growth is inhibited by 6% carbon dioxide and 5% oxygen. 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.

CONTAMINATION OF FRUITS AND VEGETABLES: 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 organisms. 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.

SPOILAGE OF FRUITS AND VEGETABLES: 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 spoilage: Bacterial soft rot, caused by Erwinia carotovora and related species. 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 Fusarium. 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.

PRESERVATION OF 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 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 added preservatives and developed preservatives which are used.

PRESERVATION OF FRUITS AND FRUIT PRODUCTS: 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. REMOVAL OF MICRO ORGANISMS: 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.

USE OF HEAT: 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. USE OF LOW TEMPERATURE: 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.

CHILLING: 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 CO 2 concentration and decreasing the O 2 concentration. 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.

FREEZING: 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 organisms. The decrease in numbers of organisms during storage in the frozen condition is slow but is faster than in most neutral foods.

DRYING: 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. USE OF PRESERVATIVES: 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 others. 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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