各类农产品贮藏技术课程介绍

,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,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 Storage,Grain harvesting, threshing and cleaning,Drying methods,The,biodeterioration,of grain and the risk of,mycotoxins,Storage,1、Grain harvesting, threshing and cleaning,(i),Harvesting methods,Sometimes, it is desirable to hasten the time of crop harvesting.,After a grain crop reaches,physiological maturity, any delay in harvesting may cause deterioration in quality and yield reduction.,A number of direct and methods may be adopted by crop producers to hasten the time of crop harvesting.,Physiological maturity,defined as,maximum kernel dry weight,moisture percentage ranges from about 20 to 40%（2530%）.,determines the readiness of the crop for harvest.,This 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 moisture percentage is relatively high.,Once a plant has attained physiological maturity, it cannot accumulate any more dry matter.,Harvesting,Harvesting methods differ according to the part of the plant to be used.,As regards forage crops, the whole plant is cut, but for underground crops (eg, groundnuts, roots and tubers), the crop is lifted while the soil sticking to it is removed.,With 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.,In the latter case two main alternatives exist: separate harvesting and threshing, or combined harvesting and threshing.,Harvesting,Harvesting methods,Manual harvesting,Mechanized harvesting,DIRECT METHODS,Defoliation and Desiccation,Leaving it in the field longer predisposes it to weathering. Sometimes, inclement weather threatens the quality of the harvest, thereby compelling the producer to make adjustments in the harvesting schedule. Such adjustments include “inducing” early harvest maturity by applying a,defoliant,or,desiccant.,Harvesting,A defoliant causes leaf-drop, while a desiccant causes the plant to dry out in the field and die.,In cotton production, 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.,Harvesting,INDIRECT METHODS,Generally, crops are harvested when the conditions of the economic product are such that the product can be stored for a reasonable period of time without deterioration.,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 date.,Harvesting,(ii) Threshing methods,Traditional threshing,Mechanized threshing,Combined harvesting and threshing methods,(iii)Cleaning,2、Drying methods,There is an essential need to dry grain quickly and effectively after harvest and before storage to retain maximum quality, to attain a moisture content sufficiently low to minimise infestation by insects and microorganisms (bacteria, fungi, etc.), and to prevent germination.,Natural methods,of drying make use of exposure of the wet grain to the sun and wind.,Artificial dryers,employ the application of heat from combustion of fossil fuels and biomass resources, directly or indirectly, and in both natural and forced convection systems.,Mechanical dryers, long used in developed countries, are finding increased application as farming and grain handling systems develop.,Drying,Natural and solar drying,The traditional practice of grain drying is to spread crop on the,ground, thus exposing it to the effects of,sun,wind,and,rain,.,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 many locations, at least the equivalent of the airflow produced in a mechanical dryer.,Drying,Drying,Mechanical dryers,Batch-in-Bin Dryers,The 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 the order of 1-3 tonnes/day with drying times of 6-12 hours.,Drying,Re-circulating Batch Dryers,The 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.,When 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.,Drying,Continuous-flow Dryers,Continuous-flow dryers can be considered as an extension of re-circulating batch dryers. However, rather than the 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.,Drying,Drying,3、The biodeterioration of grain and the risk of mycotoxins,The condition of stored grain is determined by a complex interaction between the grain,the macro- and micro-environment,and a variety of,organisms,(including,microorganisms, insects, mites, rodents and birds,) which may attack it.,ecosystem,Grain provides an abundant source of,nutrients,and the natural consequence of the type of stable,ecosystem,described above will normally be spoilage (biodeterioration) of the grain, caused by the organisms.,The 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,Penicillium,Helminthosporium, and,Fusarium,.,These 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,microorganisms,Fungi may infect grain in the field, the major species being,Alternaria,链格孢属, Cladosporium枝孢属,Helminthosporium 长蠕孢属, and,Fusarium镰孢属,.,Their 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.,moulds,The extent of contamination by moulds is largely determined by the,temperature,of the grain and the availability of,water,and,oxygen,.,Moulds can grow over a wide range of temperatures, from below,freezing to,temperatures in excess of,50,C,.,In general, for a given substrate, the rate of mould growth will decrease with decreasing temperature and water availability.,moulds,The intergranular water concentration is described either in terms of the equilibrium relative humidity (RH, %) or water activity (aw).,Typical water activities which are necessary for mould growth range from,0.70 to 0.90,.,moulds,The interaction between grain temperature and moisture content also affects the extent of mould colonisation.,The passage of water from the grain into the vapour phase is encouraged by an increase in temperature.,Maize, 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 same maize stored at 30C will be substantially damaged by moulds within three months.,moulds,Insects 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.,They are also important, however, because of their complex interaction with moulds and, consequently, their influence on mould colonisation.,moulds,insects,In general, grain is not infested by,insects,below a temperature of,17C,whereas mite infestations can occur between 3 and 30C and above 12 per cent moisture content.,The metabolic activity of insects and mites causes an increase in both the moisture content and temperature of the infested grain.,Arthropods also act as carriers of mould spores and their faecal material can be utilised as a food source by moulds.,Furthermore, moulds can provide food for insects and mites but, in some cases, may also act as pathogens.,moulds,Broken kernels,Another important factor that can affect mould growth is the proportion of broken kernels in a consignment of grain.,Broken kernels, caused by general handling and/or insect damage, are predisposed to mould invasion of the exposed endosperm.,It 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.,moulds,Mould growth is also regulated by the proportions of oxygen, nitrogen and carbon dioxide in the intergranular atmosphere.,Many 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.,Interactions between the gases and the prevailing water activity also influence mould growth.,In 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 making bread flour.,3.2 Insects,3.2 Insects,The 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 found in elevators.,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,).,常见的贮粮害虫有米黑虫、黄粉虫、玉米象、豌豆象、蚕豆象、绿豆象、麦蛾、谷蠹、螨类等,3.3 Temperature and moisture,Notwithstanding 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.,Seeds in a single head do not ripen uniformly but over a 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.,For storage in winter, the grain moisture should be more than 14% in most case.,In the Coastal Plains and Gulf Coast, a lower moisture content of 11 to 12% is recommended.,Lower percent of moisture (1% lower on the average) is required in the summer months.,A combination of high moisture (13% or greater) and high temperature (70,or 21.1) promotes infestation by microorganisms and insects that leads to spoilage.,Under such conditions, the grain respires, producing heat, carbon dioxide, and water.,This additional water further increases grain moisture content.,The 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 brown 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.,At temperatures above 130 (54.4), heat sterilization occurs in the bin, killing insects and inactivating microbes.,fermentation,Under conditions of high moisture (greater than 14%) and low oxygen, fermentation occurs in the bin.,This 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.,This 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.,To avoid this condition, an,exhaust fan,is installed to draw up the warm up the warm air 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、Storage,THE GOALS OF GRAIN STORAGE,The product should have high purity.,It should be in good physical condition (shape, size, color).,There should be minimal mechanical damage (breakage, cracks, and splits).,The seed should have high viability.,There should be no damage from insects (holes, devoured contents).,There should be no molds or disease infection.,There should be no contamination from rodent droppings.,There should be no pesticide residue.,There should be no toxic microbial metabolites.,There should be no loss of flavor.,There should be no foul odor.,There should be adequate moisture in the product,There are four general ways in which seed can be stored for varying lengths of time.,The method chosen depends on the duration over which it is desired for seed to maintain its quality, among other factors.,Seed quality cannot be improved during storage, since quality declines with time.,(1) CONDITIONED STORAGE,Seeds are maintained in a dry and cool environment. For most 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,.,These conditions can hold seed quality for about 1 year.,Many commercial seed companies operate such a facility.,(2)CRYOGENIC STORAGE,Cryogenic storage of seed is used when seed to be stored for a very long period.,Such 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.,It is widely used by germplasm banks for long-term storage.,(3)HERMETIC STORAGE,Seeds under this type of storage are sealed in moisture-resistant containers.,Metal 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 STORAGE,In containerized 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.,SUMMARY,The best time of harvesting depends on the economic part of the plant, utilization, and the method of storage.,Improper timing of harvesting causes yield reduction, reduction in product quality, and loss of economic value.,To prevent spoilage in storage, the grain should be in proper condition prior to being placed in storage (e.g., right moisture content of material). The storage conditions should be appropriate (temperature and moisture).,Saprophytic fungi are the most important microbes in quality deterioration of stored grain.,review,Ecosystem,treatment before storage,physiological maturity,Biodeterioration,type of storage,CONDITIONED STORAGE,CRYOGENIC STORAGE,HERMETIC STORAGE,CONTAINERIZED SEED STORAGE,WHEAT STORAGE,WHEAT STORAGE,Preharvest,The 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 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.,After the bin and equipment are cleaned,consider spraying the bin with an approved, residual-type insecticide.,Make Sure Grain is Dry Enough,Insects 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.,Barley should be about 0.5 percentage points drier than these values.,Insecticide Treatment,If 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. Contact 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,Aspergillus,Manage Fines,Fines tend to congregate in pockets in storage bins, they restrict airflow, and they are more susceptible to attack by molds and 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 distribute 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),.,Figure 1. Removing fines during bin filling.,Use Aeration to Cool Grain,Keeping grain cool reduces mold and insect activity. Activity 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 relative humiditygrain rewetting is unlikely to be a problem.,Another 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 to 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 winter storage.,Figure 2. Moisture migration in unaerated grain.,Figure 3. Measuring exhaust-air temperature.,Check Stored Grain Frequently,Check 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 and insect traps to check for insects.,Measure and record,temperature,s at several locations and watch for spontaneous heatinga sure sign of mold or insect activity.,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,