POSTHARVEST MANAGEMENT OF CEREAL GRAINS

 Introduction:

Cereal grains are essential to our dietary needs, as well as for industrial processing. The cereal species of agricultural significance are wheat, rye, barley, oats, maize, rice, sorghum and the millets, all members of the grass family. Assessment of grain quality is needed at all stages for effective management. The many analytical methods available need to be adapted to the specific needs at each stage of the value-addition chain.

The term "post-harvest losses" means a measurable quantitative and qualitative loss in a given product. These losses can occur during any of the various phases of the post-harvest system. In addition to direct economic losses, there are those resulting from poor management of post-harvest systems. They are evidenced by a lack of growth in production and in the income of the farmers.

Quality losses include those that affect the nutrient/caloric composition, the acceptability, and the edibility of a given product. These losses are generally more common in developed countries

Quantity losses refer to those that result in the loss of the amount of a product. Loss of quantity is more common in developing countries

 Structure and composition of cereal grains and legumes:

Structure:

The basic structure of almost all cereal grains is same having same parts, identified below. An epidermis which is outer layer and number of interior layers makes up the seed coat. The Aleurone is the layer which is just beneath the seed coat. Moreover, oils as well as other elements such as minerals, proteins, and vitamins. The seed coat and Aleurone make up the bran layer, which accounts for about a quarter of the grain. The endosperm is the major part of cereal grain because it makes up the majority of the grain, is surrounded by the Aleurone layer. The endosperm is made up of storage cells that contain starch granules embedded in a protein matrix. The germ is the part of the grain that sprouts. It makes up only approximately 2% of the seed in wheat, yet it includes 65 percent of the B group vitamins and 33 percent of the oil.

Composition of Cereal Grains:

The chemical composition of grains varies greatly and is influenced by the environment, soil, variety, and fertilizers used on it. Cereals are high in vitamins, minerals, carbs, lipids, oils, and protein as whole grains. The remaining endosperm, however, is largely carbohydrate and lacks the majority of the other nutrients when the outer layer removes called bran which is hard in nature and germ is reproductive component and it is rich in polyunsaturated fats, which has a tendency to oxidize and turn rancid when stored that why it is removed.

Barley grains contain 60 to 80 percent starch, 9 to 13 percent protein, 10 to 15% water, and 1 to 2 percent lipids by mass.  They've been linked to changes in the malting process and product yield.

Legumes have a carbohydrate content of roughly 60%. The main carbohydrate is starch. Lower molecular weight carbohydrates like sucrose and sucrosyl oligosaccharides are found in small concentrations. Raffinose, stachyose, and verbascose are oligosaccharides that are related with flatulence.

Pulses are ideal for making composite flours with cereals because of their high lysine and folate levels. The total carbohydrate, fat, niacin, riboflavin, thiamine, and vitamin B6 levels of pulses and cereal grains are similar. Pulses, on the other hand, contain more protein, folate, iron, magnesium, potassium, and zinc than grains.

Rye Wheat and rye have similar levels of cellulose and lignin, but rye has more arabinoxylan and mixed-linked b-glucan. Starch, dietary fibre (DF), protein, and mineral matter are the main chemical constituents of rye grain (ash). The endosperm contains the majority of the starch.

Oats include approximately 60% carbohydrate, 14% protein, 7% fats, and 4% -glucan. Oats are abundant in protein and fats, compared to other grain crops. Oats are notable for their high concentration of dietary fibre, particularly soluble -glucans. When it comes to micronutrients, oats are especially high in potassium. Oats also include other small components such as phenolics.

Pearl millet Crude protein, gross energy, ether extract, acid detergent fibre, amino acid profile, and mineral content were shown to be higher in pearl millet than maize. Pearl millet is gluten-free and is frequently substituted for gluten-intolerant people. It's high in iron, magnesium, calcium, phosphorus, manganese, potassium, copper, zinc, and chromium.

Sorghum grains are similar to maize in composition and feeding value; however their protein content varies significantly. Sorghum is a naked kernel that includes condensed tannins in a thick testa layer under the pericarp. It contains a lot of micronutrients.

Rice mainly consists of the aleurone layer, embryo, and other regions of the grain Brown rice protein content varies from 4.3 to 18.3 percent on average, with a mean of 9.2 percent. After carbohydrates, protein is the second most essential component of rice. Albumin (water soluble proteins) and globulin (salt soluble proteins) are abundant in the rice grain's outer layer, but gluten is abundant in the endosperm.

Corn Carbohydrates make up the majority of corn's chemical structure. The maize corn kernel, on the other hand, is more than just a carbohydrate powerhouse. On a dry weight basis, corn bran contains 70 percent hemicelluloses, 23 percent cellulose, and 0.1 percent lignin. Corn contains only 4.4 percent oil, but it not even being considered an oil seed crop, corn oil is produced on a large scale. Triglycerides contribute for 98.8% of the refined commercial corn oil's content.

 Factors for grains losses after harvesting:

Causes of post-harvest loss in this stage include limited availability of suitable varieties for processing, lack of appropriate processing technologies. Lack of knowledge, storage and cooling facilities, inadequate harvesting techniques, poor infrastructure, and inefficient harvest management practices are considered critical contributors to the losses.

Also, Bad weather, insect damage and a shortage of labor will increase the harvest loss. In addition, harvesting attitude, household income and other factors will also affect the losses.

According to a most conservative estimate, about 10% of the cereals harvested in developing countries are lost annually, found considerable grain losses of wheat during the threshing activity. They concluded that threshing losses were mainly in the form of broken grains.

Harvest Losses 10 to improve their livelihoods). There are internal and external factors contributing to postharvest loss 

External Factors:

Factors outside of the food supply chain can cause significant postharvest loss. These factors can be grouped into two primary categories: environmental factors ic and socio-economic patterns and trends.

Environmental factors:

Climatic conditions, including wind, humidity, rainfall, and temperature influence both the quantity and quality of a harvest

Temperature:

In general, the higher the temperature the shorter the storage life of horticultural products and the greater the amount of loss within a given time, as most factors that destroy the produce or lower its quality occur at a faster rate as the temperature increases

 Socio-economic:

Social trend such as urbanization has driven more and more people from rural area to large cities, resulting in a high demand for food products at urban centres, increasing the need for more efficient and extended food supply

Humidity:

Storing food at high altitudes will therefore tend to increase the storage life and decrease the losses in food provided it is kept out of direct rays of the sun

Time:

The longer the time the food is stored the greater is the deterioration in quality and the greater is the chance of damage and loss. Hence, storage time is a critical factor in loss of foods especially for those that have a short natural shelf life.

Internal Factors:

The following sections describe PHL occurring at all stages in the food supply chain from the moment of harvesting, to handling, storage, processing and marketing

Harvesting:

 The time of harvesting is determined by degree of crop maturity and weather conditions. Primary causes of losses at the harvest stage include:

Poor weather at harvesting time which affects the operations and functionality of harvesting machines or human labour and usually increases the moisture content of the harvested products.

Pre-cooling:

Loss at this stage is primarily due to the high cost and lack of availability of pre-cooling facilities, inadequate training on pre-cooling technology at the commercial scale, and lack of information on cost benefits of pre-cooling technology

Transportation:

Primary challenges in the transportation stage of the supply chain include poor infrastructure (roads, bridges, etc.), lack of appropriate transport systems, and a lack of refrigerated transport. In most developing countries, roads are not adequate for proper transport of horticultural crops. Also, transport vehicles and other modes of transport, especially those suitable for perishable crops, are not widely available.

Storage:

Facilities, hygiene, and monitoring must all be adequate for effective, long‐term storage. In closed structures (granaries, warehouses, hermetic bins, silos), control of cleanliness, temperature, and humidity is particularly important. It also very important to manage pests and diseases since damage caused by pests (insects, rodents) and molds can lead to deterioration of facilities (e.g. mites in wooden posts) and result in losses in quality and food value as well as quantity.

Grading:

Proper packing and packaging technologies are critical in order to minimize mechanical injury during the transit of produce from rural to urban areas. Causes of PHL in the grading stages are: lack of national standards and poor enforcement of standards, lack of skill, awareness, and financial resources.

Packaging and labelling:

After harvest, fresh fruits and vegetables are generally transported from the farm to either a packing house or distribution centre. Farmers sell their produce in fresh markets or in wholesale markets. At the retail level, fresh produce is sold in an unpackaged form or is tied in bundles. This type of market handling of fresh produce greatly reduces its shelf life if it is not sold quickly.

Secondary processing:

Causes of post-harvest loss in this stage include limited availability of suitable varieties for processing, lack of appropriate processing technologies, inadequate commercialization of new technologies and lack of basic infrastructure, inadequate facilities and infrastructure, and insufficient promotion of processed products.

Further losses incudes biological, physical and chemical losses:

Biological:

Biological causes of deterioration include respiration rate, ethylene production and action, rates of compositional changes (associated with color, texture, flavour, and nutritive value), mechanical injuries, water stress, sprouting and rooting, physiological disorders, and pathological breakdown. The rate of biological deterioration depends on several environmental factors, including temperature, relative humidity, air velocity, and atmospheric composition (concentration of oxygen, carbon dioxide, and ethylene), and sanitation procedures.

Microbiological:

Micro-organisms cause damage to stored foods (e.g., fungi and bacteria). Usually, microorganisms affect directly small amount of the food but they damage the food to the point that it becomes unacceptable. Toxic substances elaborated by molds (known as mycotoxins) cause loss in food quality and nutritional value.

Chemical:

Many of the chemical constituents naturally present in stored foods spontaneously react causing loses of colour, flavour, texture and nutritional value. One such reaction is the “maillard relation’ that causes browning and decolouration in dried fruits and other product. There can also be harmful chemicals such as pesticides or obnoxious chemical such as lubricating oil.

Methods of grain grading and recent technologies and practices to reduce post-harvest losses:

USDA grain grading have put grains into place to measure levels of value and quality for agricultural commodities. These are commonly utilized to assess the quality of various agriculture products such as grain, rice, corn, and others. During grain processing, there is a concern for food safety and product quality. The physical process includes the cleaning of the kernel, and then the moisture content is adjusted so that it reaches the desired particle size. A safety concern is that higher levels of microbial contamination may be present on the surface of the kernel. There is an unknown level of contamination present in the grain supplied to the miller before processing, and without proper handling, puts the consumer at risk.

There are many examples of promising practices. These range from training in improved handling and storage hygiene to the use of hermetically sealed bags and household metallic silos, and are supported by enhancing the technical capabilities of local tinsmiths in silo construction.

Harvesting:

 In tropical countries in general, most grains have a single annual harvesting season, although in bimodal rainfall areas there may be two harvests. African producers harvest grain crops once the grain reaches physiological At this stage the grain is very susceptible to pest attacks. Poor farmers sometimes harvest crops too early due to food deficiency or the desperate need for cash. In this way, the food incurs a loss in nutritional and economic value, and may get wasted if it is not suitable for consumption.

Drying:

 Most farmers in Africa, both small and large, rely almost exclusively on natural drying of crops by combining sunshine and movement of atmospheric air through the product; consequently, damp weather at harvest time can be a serious cause of postharvest losses. Grains should be dried in such a manner that damage to the grain is minimized and moisture levels are lower than those required to support mold growth during storage (usually below 13-15%)

Storage system at farm:

Post-harvest losses at storage are associated with both poor storage conditions and lack of storage capacity. It is important that stores be constructed in such a way as to provide: -dry, well-vented conditions allowing further drying in case of limited opportunities for complete drying prior to storage; -protection from rain and drainage of ground water; and -protection from entry of rodents and birds and minimum temperature fluctuations

Threshing:

For some grains, particularly millet and sorghum, threshing may be delayed for several months after harvest and the un threshed crop stored in open cribs. In the case of maize, the grain may be stored on the cob with or without sheathing leaves for some months, or the cobs may be shelled and grain stored.

Cleaning:

Usually done prior to storage or marketing if the grain is to be sold directly. For the majority of the smallholder. this process is done manually.

Various drying operations:

Sun drying:

It is a method of drying. Drying takes place through radiation mode of sun's electromagnetic waves. The main purpose is to remove moisture so to avoid any fungal incorporation.

Radiation drying:

Based on absorption of radiant transformation into heat energy by grain. Moisture movement and evaporation is caused by temperature difference and partial pressure of water vapor b/w surrounding energy of sun and air. Ex: sun drying

Conduction: Heat is transferred to wet material mainly by conduction mode through solid surface. Surface temperatures may vary widely. Dryers can be operated under low pressure and in inert atmosphere. Dust and dusty material can be removed easily.

Freeze drying:

 Drying is based on the sublimation (solid to gas) of frozen moisture from wet product placed in a drying chamber. Works at low pressure. Heat is supplied by radiation or conduction mode.

Convection drying:

Drying agent is hot gas or hot air and supplies heat to the wet grain. Steam heated air, direct flue gases of agricultural waste etc. can be used as drying agents. Drying temperature varies widely. If atmospheric humidity is high, natural air-drying needs dehumidification. Fuel consumption is high as compare to conduction drying for same capacity. Ex: fluidized bed dryer, hot air oven dryer.

Grain Storage Handling:

The condition of the grains as you harvest it is going to determine how well it’s going to store. Grain might be a little immature, be lower in test weight, and likely not be corn that would have as good a chance of making long-term storage as good-quality.

They can be stored in these of the followings:

·       Use of rhombus

·       Traditional cribs

·       Underground pits

·       Open stack storage

·       Woven baskets

·       Grain silos

·       Farm store

·       Communal warehouses

·       Domestic storage techniques

Most of the storage methods experience the problem of insect infestation though at varying level depending on the structure. The use of metal silo is the most effective method of storing grains. Facilities are prepared for the grain going in.

Clean out your bins and get rid of any grain left that might have insects in it. Also, check under floor areas. If you had an insect infestation, make sure you fumigate or thoroughly clean the bin. The maximum allowable storage of different grains must be known at different moisture contents at different temperatures.

For long-term storage, you will need to dry grain to a lower moisture level. Properly distributing fines with a grain spreader or by practicing repetitive coring will help improve aeration. It’s important to have fines spread out in the bin, so they aren’t all in the center. Air takes the path of least resistance.

The ability to control the temperature of grain during storage is critical. It should be putting grain into a storage system that has a good aeration system so you can control the grain temperature. The other important is temperature cables in the bin so you have a safe way to monitor the grain. In warmer temperatures, you can go from one or two insects to a major infestation in a period of two to three weeks. If you aren’t checking every week or so, you aren’t able to take corrective action. You will end up reacting to major problems.

Recommendations:

The recommendation has been to keep the grain cool, about 40°F., during spring and summer. Some are now suggesting warming the grain up to 50°F for storage over summer.