Oil and Fat Technology Lectures III

OIL AND FAT TECHNOLOGY LECTURES II (Handling & Storage of

Oil-Bearing Materials - Pretreatments) Prof.Dr.Aytaç SAYGIN GÜMÜŞKESEN Yrd.Doç.Dr.Fahri YEMİŞÇİOĞLU

Handling & Storage of Oil-Bearing Materials The handling and storage of oil-bearing materials is one of the most important phases of oil seed processing. The vegetable oils and feed industries are dependent for successful operation upon obtaining high yields and product of good quality from their raw material. Excessive biological activity in the seeds, either in the field prior to harvesting or subsequently during storage, will result in a reduction both in the quality and the yield of oil and meal.

The handling and control of the raw materials for the oil seed industry can be primarily characterized by the short harvest season, by the necessity to move them into protected storage in minimum time, and by the required care before they can be processed. But they can be treated and stored successfully with minimal deterioration long enough to allow the processing industry to operate throughout the year.

Sunflower seed, soybeans, cottonseed, rape seed and other oil seeds are subject to damage primarily from biological actions, which are accelerated by high moisture content, foreign material, physical damage, and such adverse climatic conditions as frost or rain before harvest.

Effects accompanying deterioration of seed during storage  Respiration : In the presence of oxygen as the oxidizing agent, organic food stuffs are oxidized to form water and carbon dioxide as the end product. exothermic reaction

C6 H12 O 6 + O2

6 CO2 + 6 H2O + energy

Respiration intensity; Sound seed

–

Damaged seed –

low m.c.

0.1ml CO2 /g seed.day

high m.c. 5.0ml CO2 /g seed.day

The respiratory quotient, defined as the ratio of carbon dioxide evolved to oxygen absorbed, is an indication of the class of substances undergoing oxidation. In aerobic respiration; it is theoretically unity if the subctances are carbonhydrates, but less than unity if they are proteins or fats, which are less rich in oxygen.



Enzymes :

(a)Lipase. This enzyme catalyzes the reaction; 1 glycerol + 3 fatty acid

triglycerid + 3 water 2

1

synthesis t.g

2

hydrolysis t.g

(b) Catalase and peroxidase. Both of these enzymes react with hydrogen peroxide.Catalase will decompose hydrogen peroxide while peroxidase utilizes it for further oxidation. 2 hydrogen peroxide

2 water + oxygen

 Influence of moisture content : Oil seeds are best stored at low moistures where respirotary and enzymic activities, germination and mold growth are inhibited. This maximum acceptable moisture level is known as “critical moisture level (CML) ”. The moisture content of the nonoil portion of the seed rather than the whole seed is the important factor in oil seed deterioration.  CML is relatively high for seeds of low oil content.  CML is relatively low for seeds of high oil content.

Safe humidity for starchy food grains

16% Oil content of soybean Non-oily part of soybean

……. 22% ……. 78%

Critical moisture level 0.78 x 16% = 12.5%

CML of oil seeds Hulls (%) Rape seed 14 Palm kernel Sunflower seed 28 Cottonseed 48 Soya beans 8

Fat (%) 40 52 43 18 20

CML(%) 7.0 8.0 8.5 10.0 12.0

 Influence of temperature. In the case of soya beans and similar oilseeds where deterioration appears to b primarily a result of the growth of microflora, the storage temperature does not appear to be a major factor. However, temperature is very important factor in storage of cotton seed. The respiration of cotton seed is markedly temperaturedependent. The insulating effect of linters on cottonseed contributes to the peculiar tendency of this seed to heat in storage. It is because of the undesirable effect of high temperature that most seed houses are equipped with aeration ducts and large ventilating blowers to cool the seed.

 Storage method Warehouses (Muskogee type seed houses) Bulk storage in warehouses on flat floors has the advantage of easy control of oil seeds, like cottonseeds, sunflower seed, corn germ, further meals etc. To prevent self heating or autocombustion of the seeds, recycling by horizantal and vertical transportation means is recomended.

Muskogee type seed store

Oil seed

Belt conveyer

Oil seed bulk

Section through storage building

Preparation of Oil-bearing Materials  Cleaning

foreign materials

 Delinting for cottonseed  Dehulling

hulls

 Flaking  Cooking

moist

lints

CLEANING  Cleaning

is important not only to ensure the good quality of the final products oil and meal but also to avoid premature wear of the preparation equipment.  The removal of foreign materials from oil seeds is done by cleaning machines working on mechanical, pneumatic and magnetic principles.

Cleaning machines; Screens Aspirators Magnets Shape sorters

 SCREENS Screening is the seperation of mixtures of different sizes into fractions; the portion staying behind being oversize, the portion passing through being undersize.  Rotating screens  Vibrating screens

Drum screen

Vibrating screen

 ASPIRATORS In order to seperate impurities or fractions of different density, pneumatic means, like air nozzles and aspirators are used.

 MAGNETS Permenant or electromagnets enclosed in a rotating aluminium drum are used in feeders to distribute the material uniformly over the whole active width of the drum.The magnetic material collected is removed by a blade on the onomagnetized half and, in this way, it remains seperated even in the case of power failure

Self cleaning rotary magnets aspirator

Seed inlet

Rotating drum

Stationary magnet

Cleaned seed

İron parts

DELINTING (for cottonseed) cottonseed

lints (8-12%)

Hull (40-45%)

Delinting process

to remove the remaining lint from cotton seed

Aims of delinting : 1)increase oil yield 2)obtain first- and second- cut linters

Delinter

Cutting operation cottonseed seed feeder cut lints saws delinted seed

brush

Saw teeth

Method of delinting cotton seed comprises the steps of passing the cotton seed through a saw delinter to remove a substantial portion of the lint, preferably at least 40%, and thereafter passing the partially delinted seed through a brush delinter to remove substantially all of the remaining lint.

Cottonseed Delinting Equipment

DEHULLING Dehulling is a process of removing hulls from the oilseeds for obtaining high quality edible oil by the processing of kernels. This reduces fibrous content of the meal and increases the marketability as stock feed. About 99% of oil is stored naturally in kernels and the hulls contain not more than 1% oil. If the hulls are not removed they reduce the total yield of oil by absorbing or retaining oil in the pressed cake. In addition to this the wax and colouring matters present in the hulls get mixed with the expressed edible oil. This necessitated the refining process, and therefore, increase the production cost of edible oil. Moreover, processing oilseeds without dehulling reduces the capacity of the extraction equipment in addition to more repair and maintenance charges.

Approximate Hulls and Kernels Percentage in different seeds % oil % kernel

% hull

whole

kernel

husk

Cottonseed

55

45

19

30

1-2

Rapeseed

82

18

42

-

-

Sunflower

75

25

22-36

Soybean

93

7

18

36-55 19

1-2 0.6

HULLER The hulling machines used for the decortication of medium-sized oil seeds with a flexible seed coat, such as cottonseed, sunflower seed and peanuts, are of two principle types;  Bar hullers  Disc hullers

Bar huller The rotating member of a bar huller is a cylinder equipped on its outer surface with a number of slightly projecting, longitudinally placed, sharply ground, square-edged knives or bars.Opposed to the cylinder over an area corresponding to about one-third of its surface is a concave member provided with similar projecting bars.The seed are fed between the rotating cylinder and the concave member, and the hulls are siplitted as the seeds are caught between the opposed cutting edges.The clearence between the cutting edges may be adjusted for seed of different sizes. seed Bars (concave surface 1/3)

Square-edged knives

Disc huller The disc huller consists of vertically mounted discs, one of which is stationary and the other rotating.The seeds are fed to the center of the discs and are discharged at their periphery by centrifigal force. Adjust according to seed size

Rotating disc seeds

Stationary disc

The moisture content of seed effects the efficiency of dehulling operation.  Wet seeds are difficult to split cleanly and may clog the huller.  If the seeds are very dry, the kernels may disintegrate excessively.

Universal dehulling Seed First huller (coars huller) Hull beater Kernel Hull Uncut seed Second huller Hull beater Kernel Hull Uncutseed

FLAKING The extraction of oil from oil seeds, either by mechanical extraction or solvent extraction, is facilitated by reduction of the seed to small particles. Flaking is achieved on corrugated roll stands. Cracking mills with one or two pairs of rolls are used. Hammer mills are used for certain raw materials like palm kernel.

Crushing rolls A roll assembly commonly used for the reduction of oil seeds consists of a series of five rolls placed one above the other. The seed is introduced by a feeding mechanism between the two top rolls.Seed travels from the top to the bottom of the system, hence it is rolled four times.

kernel

Corrugated roll Speed 0.05 m/sec knife Smooth rolls

flake

Crushing rolls

COOKING – HEAT TREATMENT Effects of cooking process on the physical and chemical properties of oil seeds;  The oil droplets in the oil seed are ultramicroscopic in size. Because of the increase in temperature they come together and form larger droplets to flow from the seed.  Heating of the seeds causes the protein to denature and as a consequence, the emulsion to break and the oil to seperate from the solid surface of the seed.

 Cooking of the seed gives the seed mass the proper plasticity for efficient pressing.  Insolubulization of phosphatides and other impurities.  Destruction of molds and bacteria.  Increase of the fludility of the oil through increase in temperature.  In the case of cottonseed, detoxification of gossypol or related substances.

A four – high stack cooker The cooking of oil seeds is usually carried out in “stack cookers”.These consist of a series of four to eight closed, cylindirical kettles. Each kettle is normally jacketed for steam heating on the bottom and is equipped with a sweep-type stirrer mounted close to the bottom.There is an automatically operated gate in the bottom of all kettles. The top kettle may be provided with spray jets for the addition of moisture to the seed, and each of the lower kettles is provided with an exhaust pipe with natural or forced draft for the removal of moisture, thus it is possible to control moisture content of the cooked seed. Seed flakes

Direct steam

T (0C)

2-3.5 m diameter 50-70 cm high Sweeper-type stirrer Exhaust pipe

gates

Cooked flakes

STACK

COOKER

Cooking of cottonseed Detoxification Before cooking, moisture 12.% Cooking time 90 mn Final cooking temperature 115 0C Final moisture 3%

Conventional preparation system