第六章 各类农产品贮藏技术ppt课件

1、第六章 各类农产品贮藏技术第一节 粮食贮藏贮藏第二节 果品贮藏第三节 蔬菜贮藏.Section 1 Grain StorageGrain harvesting, threshing and cleaning Drying methods The biodeterioration of grain and the risk of mycotoxins Storage .1、Grain harvesting, threshing and cleaning(i) Harvesting methodsSometimes, it is desirable to hasten the time of cr

2、op 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 maturitydefined as maximum kernel dry

3、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 re

4、latively 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),

5、 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

6、combined harvesting and threshing. Harvesting.Harvesting methods Manual harvesting Mechanized harvesting DIRECT METHODS Defoliation and DesiccationLeaving it in the field longer predisposes it to weathering. Sometimes, inclement weather threatens the quality of the harvest, thereby compelling the pr

7、oducer 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

8、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 METHODSGenerally, crops are harvested when the conditions of the econom

9、ic 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

10、 methodsTraditional 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 m

11、inimise 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, directl

12、y 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 g

13、round, 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 eq

14、uivalent of the airflow produced in a mechanical dryer. Drying.Drying.Mechanical dryers Batch-in-Bin DryersThe 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 wi

15、th drying times of 6-12 hours. Drying.Re-circulating Batch DryersThe 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

16、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 bott

17、om 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 mycotoxinsThe condition of stored grain is determined by a complex interaction between the grain,

18、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 spoilag

19、e (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. The

20、se 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 , Helminthos

21、porium 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.mouldsThe extent of contamination by moulds is largely determined by the temperature of the grain and the av

22、ailability of water and oxygen. Moulds can grow over a wide range of temperatures, from below freezing to temperatures in excess of 50C. In general, for a given substrate, the rate of mould growth will decrease with decreasing temperature and water availability. .mouldsThe intergranular water concen

23、tration 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.mouldsThe interaction between grain temperature and moisture content also affects the extent of mould coloni

24、sation. 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 dam

25、aged by moulds within three months.mouldsInsects 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 interact

26、ion with moulds and, consequently, their influence on mould colonisation.mouldsinsectsIn 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 caus

27、es 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 path

28、ogens.mouldsBroken 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 exam

29、ple, 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.mouldsMould growth is also regulated by the proportions of oxygen, nitrogen and carbon dioxide in the inte

30、rgranular 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 c

31、ertain 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 InsectsThe most common storage pe

32、sts 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

33、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 moistureNotwithstanding the storage facility

34、, 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%. Th

35、is 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.

36、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 co

37、ntent. .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 burnThe brown discoloration of grain in storage caused by intense heat generated from the respiration of organisms in the en

38、closed 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. fermentationUnder conditions of high moisture (greater than 14%) and low oxygen, fermentation occurs in the bin. This i

39、s 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 col

40、d 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

41、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 viab

42、ility. 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. Th

43、ere 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 can

44、not be improved during storage, since quality declines with time.(1) CONDITIONED STORAGESeeds 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 c

45、an hold seed quality for about 1 year. Many commercial seed companies operate such a facility. (2)CRYOGENIC STORAGECryogenic 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 li

46、mited by the small size of the cryogenic tank. It is widely used by germplasm banks for long-term storage.(3)HERMETIC STORAGESeeds 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 sea

47、led, the ambient air inside may be replaced with an inert gas (e.g., argon or nitrogen) for best results.(4) CONTAINERIZED SEED STORAGEIn containerized seed storage, seed (usually high-value germplasm) are maintained in specially constructed rooms, equipped with dehumidifiers and other environmental

48、 control systems. Sometime, a desiccant is used to control the level of humidity of the environment.SUMMARYThe 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,

49、 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 i

50、n quality deterioration of stored grain.reviewEcosystemtreatment before storagephysiological maturityBiodeteriorationtype of storage CONDITIONED STORAGE CRYOGENIC STORAGE HERMETIC STORAGE CONTAINERIZED SEED STORAGE .WHEAT STORAGEWHEAT STORAGE.Preharvest The first step in good stored grain management

51、 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 immed

52、iate 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 1

53、4% 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 grai

54、n 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.M

55、anage 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 an