1.a Agricultural processing are those operations which maintain or raise the quality of raw materials, change its form, or prepare it for market. It is value addition or conditioning of agricultural products.
The operations connected with agricultural processing are: Cleaning, grading, sorting, drying, decortications soaking, steaming, boiling, concentration, dehydration etc (5marks)
1b. Storage is done to fulfill the national and domestic needs of food, feed and seed between two consecutive harvests (5marks)
1c. The advantages of processing and storage of agricultural products are
____ Economy in transport
____ Provision of employment opportunities
____ Change of perishable products to stable commodity
____ Prevention of insect and pest infestation during storage.(5marks)
1d. The four operations that could be portioned on food materials to improve the quality and shelve life of the product are - physical -thermal - hydrothermal and pneumatic operations.
The value addition is referred to as primary processing - secondary processing -Tertiary processing - Combinations of the operations.
2ai. Indigenous Rice Hullers
ii. Disk type Hullers
iii. Roller type hullers (5 marks)
2b. The terms used in rice milling industry are as follows:
i. - paddy - rice in the hull (husk) after threshing.
ii. Husked rice - Kernels with out husk
iii. Milled rice - white rice from brown milled rice
iv. Degree of milling - the extent of the removal of bran layers and germ (4- 6%).
v. Milling yield - head rice + broken after milling.
2ci. Free moisture
ii. Bound moisture
iii. Unbound moisture
Free moisture is retained by the grain before EMC stages.
Bound is contained inside the grain and held by chemical substances.
Grains are not fund with unbound moisture or it will behave like free water surface.
(d) Milling process can be presented diagrammatically thus:
Polishing 3 – 4 step
Grading and packaging
3a. Paddy grain structure shows the presence of voids and spaces which are usually filled by moisture and air which cause cracks during milling.
Parboiling is the process of preheating of rice paddy before drying and milling and the idea is to close the voids and the cracks that usually occur during milling, in addition to other advantages. (5 marks)
3bi. During the cold or hot soaking starch granules swell. During hot soaking energy supplied in the form of heat weakness the granule structure by disturbing hydrogen bonds, giving more surfaces for water absorption by starch granules. This permits irreversible granule swelling and further hydration a process called gelatinization.
3bii. The four methods by which gelatinization of starch may be done include:
- Soaking of paddy in water at or below its gelatinization temperature
- Soaking of paddy at or above its gelatinization temperature.
- Paddy soaking for a short duration may be to steam pressure for gelatinization.
- Paddy soaked fully in water or freshly harvested high moisture paddy may be subjected to conduction heating to achieve parboiling.
3c. Advantages of parboiling are:
i. Shelling of parboiled rice is easier
ii. Broken are reduced to considerable extent
iii. Parboiled rice retains more proteins, vitamins and minerals.
iv. It is more resistant to insect infestation.
v. Less loss of solids during cooking.
vi. It could with stand over cooking.
vii. Superior quality rice bran with 29 – 30% oil. (5 marks)
3d. Parboiling disadvantages include:-
i. Heat destroys some natural antioxidants.
ii. It takes more time to cook
iii. Micro toxins could develop which is hazardous to human health.
iv. Re-drying from moisture content of 45 – 50 percent to 14-16 percent for proper milling.
v. It needs an extra investment of capital.
vi. It has harder shells that are more difficult to polish. (5 marks)
4a. The avoidable reasons that cause breakage of rice during milling are:-
i. Harvesting should be done at the optimum when moisture content is between 19 and 23 percent at maturity.
ii. Paddy should be dried under controlled condition (hot mechanical dryer)
iii. Milling should be done at the suitable moisture content (14%)
iv. Proper storage to avoid weakening of kernels by insects.
v. Non use of Rubber Roll shellers and Emery
vi. Non use of constant feed rate
vii. Degree of milling should be normal
viii. Non pretreatment of parboiling. (5 marks)
4b. Food may spoil through
i. The activities of micro-organisms;
ii. Metabolic process in living foods, leading to decay.
iii. Direct oxidation from the atmosphere, leading to rancidity
iv. Absorption of foreign orders and flavours
v. desiccation and withering.
vi. Faulty preparation.
4c. Their growth pattern is as follows:
i. Up to 10oC the growth is slow
ii. At about 300C, the growth rate is rapid, and
iii. At about 360C, the growth stops entirely
iv. At about 75oC, the spores may be killed in about 3 days.
v. At a pH of 4 to 7, mould grows fast whereas the growth is restricted below pH of 2 or very alkaline pH values of 8 to 9.(5 marks)
4d. Feature of food processing industries is that they are engaged in processing highly perishable commodities, such as fruits and vegetables, milk and eggs, fish and meat etc.
Because the products of these industries are for mass consumption availability of adequate funds and other resources are always ensured. We accord higher priority to these industries because they are intensive labour industries which generate employment in rural a areas and thus improve their standard of living.
5a. The basic principles involved in freezing are to inactivate the living micro-organisms causing decay or to change the liquid water present in foods into crystals of ice rendering food assist as if it would have been dried. (5 marks)
5b. Sharp freezing consists of placing foods in a cold room with temperatures maintained from -15 to - 28oC. It is relatively slow process but is still used for freezing boxed poultry, fish, packaged meat and some cold packed fruit.
5c. Foods may be quick frozen by:
i. Freezing by direct immersion in a refrigerating medium (brine or special sugar solution held at – 18oc)
ii. Freezing by indirect contact:(refrigerating medium at - 28oC to -45oC)
iii. Freezing in a blast of could air (- 18oC -62oC)
iv. Fluidized bed freezing.
5d. After freezing as in the methods above, bacterial activities come to stand still, but still there are few enzymes which remain active. To over come this problem, the food (particularly the vegetables) may be blanched in boiling water or low pressure steam before freezing it by one of the above mentioned methods of freezing. (5 marks)
6a. The Ten sequences of order of seed processing include.
i. Receiving (ii).Storing (iii) conditioning and processing (iv) Basic cleaning (v) Separating and upgrading (vi) Drying
(vii) Treating (viii) Bagging (ix) Storage (x) Shipping.(10 marks)
6b. The visibility and percentage germination of seeds may be affected by a number of separate but interacting factors during storage, including moisture content, relative humidity, temperature, breakage, gaseous atmosphere and chemical treatment. (5 marks)
6c. Packaging is done to protect the contents placed inside the package and also to make good impact on the mind of the consumers to attract them. Novelties of good packaging are(i) transparency of the pack giving clear visibility of the content, (ii) thermo stability, (iii) new protective coatings for hard packages (glass etc.), (iv) lighter and thinner tin plates, (v) hygienic aluminum foils and (vi) steel foils.(5 marks)
7a. - Unheated or natural air drying
- Unheated air drying with supplemental heat
- Heated air drying
Unheated air drying refers to the use of atmospheric air forced around the grain for the removal of moisture.
Unheated air with supplemental heat is desirable during periods of high humidity (when atmospheric air cannot accomplish drying with unheated air installation). A small amount of heat is added to the air to decrease the humidity there by increasing the water holding capacity of the air.
Heated air drying makes use of forced air movement around the grain with the addition of large amount of heat for removing moisture rapidly.
7bi. Dried zone;
ii. The drying zone; and
iii. The wet zone
The air pass through the dried zone to the drying zone and finally to the wet zone. The air picks up moisture as it passes.
7c. Agricultural materials are hygroscopic because they have the ability to absorb or give out moisture to the atmosphere depending on their equilibrium moisture content (EMC)
7d. At any given temperature there is a condition of grain MC and RH of the air, when the moisture retaining tendency of grain and moisture withdrawing tendency of the air come into balance. The air and the grain are then said to be in equilibrium. Under these conditions the grain no longer loses moisture to the air nor does it pick up moisture from it. This MC of the grain is called equilibrium moisture content (EMC) and the corresponding RH is called equilibrium Relative Humidity (ERH).