post harvest spoilage of grains

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post harvest spoilage of grains


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Post harvest spoilage of grains:

Post harvest spoilage of grains BY V.DHIVYA BSA10498

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The main objective of proper grain storage is to maintain the quality and characteristics that the grain possessed immediately after harvesting and drying. Grain improperly harvested and dried will remain of low quality no matter how well it is stored In cereal grains loss in quality and quantity during storage is caused by fungi, insects, rodents and mites. The development of fungi is influenced by the: Moisture content of the stored grain Temperature Condition of the grain going into storage Length of time the grain is stored Amount of insect and mite activity in the grain.


Fungi Fungi (molds) are the major cause of spoilage in grain. Losses caused by fungi in cereal grains are related to a decrease in germination discoloration of the seed heating and mustiness biochemical changes possible production of toxins loss in dry matter . Loss of weight Loss of nutritive value Poor milling quality Deterioration in flavor All these changes may occur without the mold becoming visible to the naked eye.

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Fungi usually come from spores, which act like "seeds" of the fungus . Spores are microscopic, dustlike particles that are almost everywhere in the environment. Because they are so widespread, it is impossible to prevent most fungi from inoculating the grain at some point in the production cycle, so the best strategy for preventing contamination is to avoid conditions that will allow these spores to germinate and grow.

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There are two groups of mold that affect grain quality field molds storage molds field molds : Field molds invade kernels while the grain is still in the field. The field molds cause the discoloration of cereal grains often observed in plants exposed to very moist weather before harvest. In addition to affecting grain appearance, field mold may cause a decrease in the germination of the grain seeds. Field mold damage is completed by the time the grain is harvested. Once the grain is dried, these molds die or become inactive.

Storage molds:

Storage molds Grain temperature and moisture content determine the allowable storage time (AST) or how long grain can be kept before it spoils. Notice that as grain moisture content increases for a given temperature, the allowable storage time for drying and storing decreases. Also, as temperature increases, allowable storage time decreases. Adapted to grow under low moisture conditions Normally invade kernels after harvest Generate heat and moisture as they grow

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Mechanical damage to grain and the amount of foreign material also affects allowable storage time. Clean grain and whole seeds are more resistant to mold. For long-term storage grain should be dried as soon as possible after it comes from the field. A delay in drying decreases the allowable storage time

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Example 1. Grain is harvested at 22% moisture content and grain temperature is 21°C (70°F). How much time do we have before the grain spoils? Answer. About 7 days (next slide) If the condition in the bin remains constant, the grain will drop one market grade in about 7 days, with the allowable storage time at 22% moisture content and 21°C (70°F).

 Planned storage time before marketing:

Planned storage time before marketing Crop 6 months 6 to 12 months more than 1 year Corn and sorghum 14 percent 13 percent 12 percent Soybeans 13 percent 12 percent 11 percent Small grains 12 percent 11 percent 10 percent Edible beans 14 percent 12 percent 10 percent


mycotoxins There are many different kinds of fungi that can grow on grains. Some are worse than others in terms of toxins produced . Mycotoxins are poisonous chemical compounds produced by certain fungi There are five mycotoxins , or groups of mycotoxins , that occur quite often in food: deoxynivalenol / nivalenol ; zearalenone ; ochratoxin ; fumonisins , aflatoxin The food-borne mycotoxins likely to be of greatest significance for human health in tropical developing countries are the fumonisins and aflatoxins .


MYCOTOXINS IN STAPLE GRAINS AND SEEDS. Mycotoxin Commodity Fungal source(s) Effects of ingestion deoxynivalenol / nivalenol wheat, maize, barley reported from Fusarium graminearum Human toxicoses India, China, Japan, and Korea. Toxic to animals, especially pigs Fusarium crookwellense Fusarium culmorum zearalenone maize, wheat barley, wheat, and many other commodities ochratoxin A fumonisin B1 Maize aflatoxin B 1 , B 2 maize, peanuts, and many other commodities aflatoxin B 1 , B 2 , G 1 , G2 maize, peanuts


MYCOTOXINS IN MAIZE Harvesting of maize is often carried out at moisture contents which are >14-15% which requires drying to reduce the available water to <0.70 aw (=14%) which is safe for storage. Often harvested maize is left at drying facilities during this critical part of the chain if drying facilities are working at full capacity. This can create problems with an opportunity for growth and mycotoxin contamination of maize, especially by Fusarium , F.graminearum and Aspergillus flavus ( aflatoxins ). For maize, the pre-harvest selection of hybrids, time of planting, plant density and insect control have all be found to have an impact on contamination of maize with these mycotoxins pre-harvest and during drying and storage

ochratoxin A :

ochratoxin A Ochratoxin A is a mycotoxin . A mycotoxin is a toxin produced by fungi that grow in certain conditions. Ochratoxin A can be found in cereal grains and a variety of other food products like coffee or grapes. In Canada, a fungus called Penicillium verrucosum produces ochratoxin A. It develops after harvest while grain is in storage only if temperature and moisture content are high enough. Unlike Fusarium head blight, which produces deoxynivalenol , commonly known as vomitoxin , ochratoxin A and the fungus that produces it cause no visible damage to grain and can't be detected through visual inspection and grading we can prevent ochratoxin A by keep temperature and moisture content low and aerate our grain regularly

Scanning electron micrograph of Penicillium verrucosum:

Scanning electron micrograph of Penicillium verrucosum Barley (all except Select): 14.8% moisture or less Barley (Select): 13.5% moisture or less Wheat (all classes): 14.5% moisture or less Oats (all classes): 13.5% moisture or les s


RESPIRATION AND DRY MATTER LOSSES Grain itself and the microbial contaminants respire slowly when stored dry. However, if the water availability is increased to 15-19% moisture content ,activity (wheat) spoilage fungi, particularly Eurotium spp., Aspergillus and Penicillium species grow, resulting in a significant increase in respiratory activity. This can result in an increase in temperature and sometimes spontaneous heating from the colonisation by a succession of fungi resulting in colonisation by thermophilic fungi and actinomycetes ( Fleurat-Lessard , 2002; Maganet al., 2004). The chemical process involved in heat generation is predominantly aerobic oxidation of carbohydrates such as starch. C6H12 O6+ 6 O2 --> 6 CO2 + 6 H2O+ 2835 kJ

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The requirement for oxygen increases with temperature, to a maximum of 40oC, but does not decrease greatly until the temperature exceeds 65oC. At this temperature, microbial growth is largely inhibited and heating results from exothermic chemical oxidation. Thus the respiratory quotient (RQ) may be 0.7 to 0.9 up to 65oC but <0.5 at higher temperatures. The greater the CO2 production, the shorter the safe storage period without dry matter loss. The moulds such as P.verrucosum in stored grain and effects on germinability , fungal biomass and maximum safe storage times.

Spoilage by insects:

Spoilage by insects Indian meal moth ( Plodia interpunctella ) Rice weevil ( Sitophilus oryzae ) Granary weevil ( Sitophilus granarius ) Sawtoothed grain beetle ( Oryzaephilus surinamensis Tropical warehouse moth ( Ephestia cautella ) Lesser grain borer ( Rhyzopertha dominica ) Rust-red flour beetle ( Tribolium castaneum )

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Indian meal moth ( Plodia interpunctella ) Attacks oilseeds and cereals. Adults have a wingspan of 20 mm; the outer portion of the forewing is reddish-brown and the inner portion creamy- white.Eggs are laid on the surface of the grain. Larvae spin webs on the surface of the grain and consume kernels within the webbing. Indian meal moths feed externally on intact and broken grains

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SAW-TOOTHED GRAIN BEETLE, Oryzaephilus surinamensis (Linnaeus) Along with flour beetles, the saw-toothed grain beetle is one of the most common insects in stored grain and cereal products. The larvae develop in flour, cereal products and many other dried foods, For this reason, it is a common pest not only in grain bins, but also in elevators, mills, processing plants, warehouses and kitchens. In grain bins, it feeds on broken kernels and grain residues.

Rust-red flour beetle (Tribolium castaneum) :

Rust-red flour beetle ( Tribolium castaneum ) Capable of infesting both whole grain and oilseeds, but a more serious problem in stock feed and processed grain ( ie flour). Adults are reddish brown and range from 2.3-4.4 mm in length. Females produce from 10-20 eggs per day, and over a lifetime of 200 days – 2 years, produce more than 1000 eggs. Larvae and adults feed on broken grain and flour. Granary weevil ( Sitophilus granarius ) They are easily distinguishable from the borers and beetles by their long snout, characteristic of the true weevils. Females produce from 200-300 eggs in their 2-3 month lifespan Eggs are deposited in whole kernels of grain; emerging larvae feed on whole grain. Adults feed in and on whole and broken grain.

Control of stored grain insects:

Control of stored grain insects Stored grain insects may also be controlled by: Cooling stored grain through aeration Treating grain with an insecticide powder such as Dryacide ® or liquid residual chemicals Treating infested grain with dichlorvos Fumigating grain with phosphine Controlled atmosphere such as carbon dioxide in a gas-tight silo Treating storage areas and equipment with residual chemicals


mites Mites are the smallest of the stored-product pests. They are common in grain stored at 14-17% moisture content but, because of their microscopic size, often go unnoticed Some mites, such as the cannibal mite, feed on their own members, other mites or insect eggs. Cannibal mite with large holding mouthparts Mould mite Longhaired mite Glossy grain mite

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Grain mite This mite attacks the germ (embryo) of seeds, which reduces germination, and spreads fungi (moulds), which are also eaten. Heavily infested grain becomes tainted and unpalatable as animal feed. In some cases, dairy cattle and other farm animals develop gastric disorders and other symptoms after eating mite-infested feed Grain mite populations can increase up to sevenfold in 1 week in stored grains and oilseeds, particularly during the fall. Adult females can lay about 500 eggs during a lifespan of 42 days

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Longhaired mite This species is the most common stored-product mite. It is cold-hardy and can live in both straight-grade and tough grains and oilseeds In farm granaries, chronic infestations of this mite generally occur between June and November

IPM Tactics for On-Farm Stored Grain:

IPM Tactics for On-Farm Stored Grain Clean the storage bin thoroughly to eliminate starter colonies of insects . Every few years, remove the bin floor to clean underneath it, or fumigate to kill insects hiding beneath the floor. Don't forget the auger pit. Seal any gaps or holes in the sides of the bin, using caulk or polyurethane foam. Apply an EPA-approved insecticide on the floors and sides of bins to eliminate insects hiding in cracks and crevices Clean the grain to remove excess fine particles and other foreign debris. Fine particles reduce aeration efficiency as well as the effectiveness of grain protectants and grain fumigants.

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Moisture accumulates in a grain peak . Microbial activity in the wet area will heat the grain and attract secondary insects. The peak also reduces aeration efficiency, as does overfilling--do not fill the bin all the way to the top. Leave at least a few feet of air space. Aerate the grain to cool it to at least ambient temperature A 0.1 cfm (cubic feet per minute per bushel) aeration fan can be used to reduce the grain temperature. Using a fan, it will take approximately 120 hours of cooling to reduce the grain temperature by 10 degrees F, such as from 90 degrees to 80 degrees F. Automated aeration controllers make this job simple by turning the fan on and off to admit air only when the outside air temperature is between the desired temperatures.

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Check the grain every 20 days from spring to fall and every 30 days in winter for the presence of insects Five trier samples or probe traps should be sufficient on each sampling date. Pheromone traps in the head space may also be useful Five samples, one from the center and four from about 2 feet from the rim, will be sufficient to monitor insects in most on-farm bins.

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Probe traps can be inserted into the top layer of grain for 1 to 5 days to detect insects. Pheromone traps are available for Indian meal moth and other insects Good storage practices, like aeration, can prevent insect infestations from starting. If grain is kept below -5°C for 12 weeks, insects cannot survive and reproduce.