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1、第六章 各类农产品贮藏技术第一节 粮食贮藏（储藏）第二节 果品贮藏第三节 蔬菜贮藏Section 1 Grain Storage1.Grain harvesting, threshing and cleaning 2.Drying methods 3.The biodeterioration of grain and the risk of mycotoxins 4.Storage 1、Grain harvesting, threshing and cleaning(i) Harvesting methodsnSometimes, it is desirable to hasten the t
2、ime of crop harvesting. nAfter a grain crop reaches physiological maturity, any delay in harvesting may cause deterioration in quality and yield reduction. nA number of direct and methods may be adopted by crop producers to hasten the time of crop harvesting.Physiological maturityndefined as nmaximu
3、m kernel dry weight, nmoisture percentage ranges from about 20 to 40%（2530%）. ndetermines the readiness of the crop for harvest. nThis stage of crop development is reached prior to the crop being ready for combining as the kernel is relatively soft (easily dented with finger nail) and kernel moistur
4、e percentage is relatively high. nOnce a plant has attained physiological maturity, it cannot accumulate any more dry matter.HarvestingnHarvesting methods differ according to the part of the plant to be used.n As regards forage crops, the whole plant is cut, but for underground crops (eg, groundnuts
5、, roots and tubers), the crop is lifted while the soil sticking to it is removed. nWith cereals, the crop is first cut either as a whole or partially (ears), and then threshed and cleaned to separate the grain from the ears and straw. nIn the latter case two main alternatives exist: separate harvest
6、ing and threshing, or combined harvesting and threshing. HarvestingHarvesting methods Manual harvesting Mechanized harvesting nDIRECT METHODS nDefoliation and DesiccationnLeaving it in the field longer predisposes it to weathering. Sometimes, inclement weather threatens the quality of the harvest, t
7、hereby compelling the producer to make adjustments in the harvesting schedule. Such adjustments include “inducing” early harvest maturity by applying a defoliant or desiccant. HarvestingnA defoliant causes leaf-drop, while a desiccant causes the plant to dry out in the field and die.n In cotton prod
8、uction, green leaves tend to stain the fibers. Defoliation of cotton prior to mechanized harvesting reduces not only the amount of undesirable plant debris in the harvested fiber but also the chance of tainting it with plant pigments. HarvestingnINDIRECT METHODSnGenerally, crops are harvested when t
9、he conditions of the economic product are such that the product can be stored for a reasonable period of time without deterioration.n However, if the product has a facility for drying, the crop may be harvested sooner than normal harvest maturity then dried to storable moisture content at a later da
10、te.Harvesting(ii) Threshing methodsTraditional threshing Mechanized threshing Combined harvesting and threshing methods (iii)Cleaning2、Drying methods nThere is an essential need to dry grain quickly and effectively after harvest and before storage to retain maximum quality, to attain a moisture cont
11、ent sufficiently low to minimise infestation by insects and microorganisms (bacteria, fungi, etc.), and to prevent germination. nNatural methods of drying make use of exposure of the wet grain to the sun and wind. nArtificial dryers employ the application of heat from combustion of fossil fuels and
12、biomass resources, directly or indirectly, and in both natural and forced convection systems. nMechanical dryers, long used in developed countries, are finding increased application as farming and grain handling systems develop.DryingNatural and solar drying nThe traditional practice of grain drying
13、 is to spread crop on the ground, thus exposing it to the effects of sun, wind and rain.n The logic of this is inescapable; the sun supplies an appreciable and inexhaustible source of heat to evaporate moisture from the grain, and the velocity of the wind to remove the evaporated moisture is, in man
14、y locations, at least the equivalent of the airflow produced in a mechanical dryer. DryingDryingMechanical dryers nBatch-in-Bin DryersnThe small capacity version of the batch-in-bin dryer, otherwise known as the flat-bed dryer, has been developed for farm- or village-level use. Its capacity is of th
15、e order of 1-3 tonnes/day with drying times of 6-12 hours. DryingRe-circulating Batch DryersnThe dryer is a self-contained unit with an annular drying chamber, 500 mm thick, around a central plenum chamber, a fan and heater, and a central auger for transporting the grain from the bottom to the top.
16、nWhen drying is complete the grain is discharged from the top. Most dryers of this type are portable and can be moved relatively easily from farm to farm. DryingnContinuous-flow Dryers nContinuous-flow dryers can be considered as an extension of re-circulating batch dryers. However, rather than the
17、grain re-circulating from bottom to top, as in the latter, the grain is removed from the bottom, in some systems, cooled, and then conveyed to tempering or storage bins. DryingDrying3、The biodeterioration of grain and the risk of mycotoxinsnThe condition of stored grain is determined by a complex in
18、teraction between the grain, the macro- and micro-environment and a variety of organisms (including microorganisms, insects, mites, rodents and birds) which may attack it.ecosystemecosystemnGrain provides an abundant source of nutrients, and the natural consequence of the type of stable ecosystem de
19、scribed above will normally be spoilage (biodeterioration) of the grain, caused by the organisms.nThe organisms that are introduced into the storage facility from the field or the air include bacteria and fungi, especially Aspergillus spp. (e.g., A. glaucus, A. flavus, and A. candidus) and Penicilli
20、um, Helminthosporium, and Fusarium. nThese organisms create moldiness in stored grain. Some like the A. flavus, produce deadly toxins (e.g., the mycotoxin aflatoxin in grains such as corn and crops such as peanuts).3.1 microorganismsnFungi may infect grain in the field, the major species being Alter
21、naria链格孢属 , Cladosporium枝孢属 , Helminthosporium 长蠕孢属 , and Fusarium镰孢属 . nTheir role in quality deterioration in storage is minimal. Storage fungi of importance are Aspergillus曲霉, Penicillium青霉, and to a lesser extent Sporendonema丝内霉.mouldsnThe extent of contamination by moulds is largely determined
22、by the temperature of the grain and the availability of water and oxygen. nMoulds can grow over a wide range of temperatures, from below freezing to temperatures in excess of 50C.n In general, for a given substrate, the rate of mould growth will decrease with decreasing temperature and water availab
23、ility. mouldsnThe intergranular water concentration is described either in terms of the equilibrium relative humidity (RH, %) or water activity (aw). nTypical water activities which are necessary for mould growth range from 0.70 to 0.90.mouldsnThe interaction between grain temperature and moisture c
24、ontent also affects the extent of mould colonisation. nThe passage of water from the grain into the vapour phase is encouraged by an increase in temperature. nMaize, for example, can be relatively safely stored for one year at a moisture level of 15 per cent and a temperature of 15C. However, the sa
25、me maize stored at 30C will be substantially damaged by moulds within three months.mouldsnInsects and mites (arthropods) can, of course, make a significant contribution towards the biodeterioration of grain, through the physical damage and nutrient losses caused by their activity. nThey are also imp
26、ortant, however, because of their complex interaction with moulds and, consequently, their influence on mould colonisation.mouldsinsectsnIn general, grain is not infested by insects below a temperature of 17C 17C whereas mite infestations can occur between 3 and 30C and above 12 per cent moisture co
27、ntent. nThe metabolic activity of insects and mites causes an increase in both the moisture content and temperature of the infested grain. nArthropods also act as carriers of mould spores and their faecal material can be utilised as a food source by moulds. nFurthermore, moulds can provide food for
28、insects and mites but, in some cases, may also act as pathogens.mouldsBroken kernelsn Another important factor that can affect mould growth is the proportion of broken kernels in a consignment of grain. nBroken kernels, caused by general handling and/or insect damage, are predisposed to mould invasi
29、on of the exposed endosperm. nIt has been estimated, for example, that increasing the proportion of broken grains by five per cent will reduce the storage-life of that consignment by approximately one order of magnitude; that is from, say, 150 to 15 days.mouldsnMould growth is also regulated by the
30、proportions of oxygen, nitrogen and carbon dioxide in the intergranular atmosphere. nMany moulds will grow at very low oxygen concentrations; a halving of linear growth, for example, will only be achieved if the oxygen content is reduced to less than 0.14 per cent.n Interactions between the gases an
31、d the prevailing water activity also influence mould growth.nIn certain grains, such as wheat that is cultivated principally for flour, the characteristic elastic properties caused by the protein gluten is lost, reduced, or completely destroyed by pests eating it. Such grain is no longer fit for mak
32、ing bread flour.3.2 Insects3.2 InsectsnThe most common storage pests that damage stored grain include the rice weevil (Sitophilus oryzae), granary weevil (Sitophilus granatius). Angoumois grain moth (Sitotroga cerealella), Australian wheat weevil (Rhizoperha dominica), and the lesser grain borer fou
33、nd in elevators.n Others are Ploidia interpunctella, which damage corn in particular; cadelle (Tenebroides mauritanicus); khapra beetle (Trogoderma granarium); saw-tooth grain beetle (Oryzaephilus surinamensis); and confused flour beetle (Tribolium confusum).n常见的贮粮害虫有米黑虫、黄粉虫、玉米象、常见的贮粮害虫有米黑虫、黄粉虫、玉米象、
34、豌豆象、蚕豆象、绿豆象、麦蛾、谷蠹、螨类豌豆象、蚕豆象、绿豆象、麦蛾、谷蠹、螨类等等 3.3 Temperature and moisturenNotwithstanding the storage facility, two factors are critical to the retention of grain quality for a long period of time: the temperature and moisture content of grain.n Seeds in a single head do not ripen uniformly but over a
35、 period of about 3 to 10 days. At this stage, the average moisture content of the seed is about 25 to 30%. This moisture is too high for bin storage. nFor storage in winter, the grain moisture should be more than 14% in most case. nIn the Coastal Plains and Gulf Coast, a lower moisture content of 11
36、 to 12% is recommended. nLower percent of moisture (1% lower on the average) is required in the summer months. nA combination of high moisture (13% or greater) and high temperature (70,or 21.1) promotes infestation by microorganisms and insects that leads to spoilage. nUnder such conditions, the gra
37、in respires, producing heat, carbon dioxide, and water.n This additional water further increases grain moisture content. nThe respiratory activities of the organism raise the heat in the grain bin, sometimes to 90 to 160. The intense heat is responsible for the browning of grain (call bin burn（The b
38、rown discoloration of grain in storage caused by intense heat generated from the respiration of organisms in the enclosed storage bin.）) and even a charred appearance and off-taste. nAt temperatures above 130 (54.4), heat sterilization occurs in the bin, killing insects and inactivating microbes. fe
39、rmentationnUnder conditions of high moisture (greater than 14%) and low oxygen, fermentation occurs in the bin. nThis is more of a problem when deep bins (such as those used in terminal elevators) are used for grain storage. It is important to aerate these bins to avoid condensation of moisture.n Th
40、is happens by convectional current (warm air at the bottom of the bin rising through the grain and being replaced by cold air). The rising warm air may condense near the top of the bin where the cool grain is. nTo avoid this condition, an exhaust fan is installed to draw up the warm up the warm air
41、at the bottom of the bin through a metal pipe. This pipe has perforations neat the bottom and is installed in the center of the bin to draw up the warm air at the bottom of the bin.4、StorageTHE GOALS OF GRAIN STORAGE 1.The product should have high purity. 2.It should be in good physical condition (s
42、hape, size, color). 3.There should be minimal mechanical damage (breakage, cracks, and splits). 4.The seed should have high viability. 5.There should be no damage from insects (holes, devoured contents). 6.There should be no molds or disease infection. 7.There should be no contamination from rodent
43、droppings. 8.There should be no pesticide residue. 9.There should be no toxic microbial metabolites. 10.There should be no loss of flavor. 11.There should be no foul odor. 12.There should be adequate moisture in the productnThere are four general ways in which seed can be stored for varying lengths
44、of time. nThe method chosen depends on the duration over which it is desired for seed to maintain its quality, among other factors. nSeed quality cannot be improved during storage, since quality declines with time.n(1) CONDITIONED STORAGEnSeeds are maintained in a dry and cool environment. For most
45、grain crops such as corn, wheat, and barley, seed moisture at storage should be about 12 to 13% and the temperature 20 (68) or less. nThese conditions can hold seed quality for about 1 year. nMany commercial seed companies operate such a facility.n (2)CRYOGENIC STORAGEnCryogenic storage of seed is u
46、sed when seed to be stored for a very long period. nSuch seeds are held in liquid nitrogen at -196 (-295). The practical use of this method of storage is limited by the small size of the cryogenic tank. nIt is widely used by germplasm banks for long-term storage.(3)HERMETIC STORAGEnSeeds under this
47、type of storage are sealed in moisture-resistant containers. nMetal containers are used when very long storage periods are desired. Before the container is sealed, the ambient air inside may be replaced with an inert gas (e.g., argon or nitrogen) for best results.(4) CONTAINERIZED SEED STORAGEnIn co
48、ntainerized seed storage, seed (usually high-value germplasm) are maintained in specially constructed rooms, equipped with dehumidifiers and other environmental control systems. Sometime, a desiccant is used to control the level of humidity of the environment.SUMMARYnThe best time of harvesting depe
49、nds on the economic part of the plant, utilization, and the method of storage.nImproper timing of harvesting causes yield reduction, reduction in product quality, and loss of economic value.nTo prevent spoilage in storage, the grain should be in proper condition prior to being placed in storage (e.g
50、., right moisture content of material). The storage conditions should be appropriate (temperature and moisture).nSaprophytic fungi are the most important microbes in quality deterioration of stored grain.reviewnEcosystemntreatment before storagenphysiological maturitynBiodeteriorationntype of storag
51、e nCONDITIONED STORAGE nCRYOGENIC STORAGE nHERMETIC STORAGE nCONTAINERIZED SEED STORAGE WHEAT STORAGEPreharvest nThe first step in good stored grain management is to thoroughly clean bins and handling equipment three to four weeks before harvest. Since old grain and fines under perforated floors, in
52、 aeration ducts, in grain handling equipment, and inside and outside grain bins are likely to be contaminated with insects, remove this material to avoid immediate infestation of the new crop. Consider fumigating any areas that cant be cleaned. nAfter the bin and equipment are cleaned, consider spra
53、ying the bin with an approved, residual-type insecticide. Make Sure Grain is Dry Enough nInsects and molds are less active in dry grain, so make sure wheat is 14% moisture or less for 9 months storage and 13% moisture or less for more than 9 months storage. nBarley should be about 0.5 percentage poi
54、nts drier than these values. Insecticide Treatment nIf grain will be stored into next summer or if you often have problems with insects, consider applying a grain protectant as the crop is moved into storage. Contact your county extension office for the latest information on approved protectants. Co
55、ntact potential buyers to see if they will accept treated grainsome will not. Rusty Grain Beetle on Wheat Red Flour Beetle on Wheat Mites on Wheat AspergillusManage Fines nFines tend to congregate in pockets in storage bins, they restrict airflow, and they are more susceptible to attack by molds and
56、 insects. Try to limit the amount of fines in storage by setting combines for minimum grain damage and maximum cleaning, operate grain augers slowly and full of grain to reduce kernel breakage, and consider cleaning grain before storage to remove fines. Either use a grain spreader to fill bins and d
57、istribute fines uniformly throughout the grain mass, or dont use a spreader and periodically remove fines that accumulate in the bin center during filling (Figure 1). nFigure 1. Removing fines during bin filling. Use Aeration to Cool Grain nKeeping grain cool reduces mold and insect activity. Activi
58、ty slows at temperatures below 60 degrees F and almost ceases below 40 degrees F. Because daytime temperatures are usually greater than 60 degrees F in late summer and early fall, it might be necessary to operate fans at night to start the cooling process. Dont worry too much about high nighttime re
59、lative humiditygrain rewetting is unlikely to be a problem. nAnother reason for aerating grain is to keep its temperature within about 20 degrees F of the average outdoor temperature to prevent moisture migration. If warm grain is stored into cold weather, natural moisture movement from warm grain t
60、o cold results in rewetting and spoilage of grain at the top of the bin (Figure 2). The recommended winter grain storage temperature in northern Minnesota is about 25 degrees F. Watch forecasts for 20 to 30 degrees F weather and operate aeration fans 24 hours/day in late fall to cool grain for winte
61、r storage.Figure 2. Moisture migration in unaerated grain. Figure 3. Measuring exhaust-air temperature. Check Stored Grain Frequently nCheck stored grain monthly during cold weather and every 2 weeks during warm weather. Look for evidence of mold on the surface and in probe samples. Also, use probes
62、 and insect traps to check for insects.n Measure and record temperatures at several locations and watch for spontaneous heatinga sure sign of mold or insect activity.n Permanently installed temperature cables make this job a lot easier (Figure 4). Also, start the fan briefly on cool, dry days and smell the first exhaust air leaving the bin for musty or sour odors.Figure 4. Permanently-installed grain temperature cables. RICE STORAGE
