QUALITY ANALYSIS OF RICE

QUALITY ANALYSIS OF  RICE VARIETIES

Rice that has been harvested from the plant with its hull (husk) intact is known as rough or paddy rice. The hull is not eaten by humans but is sometimes burned for use as an energy source. Timely paddy threshing by recommended method reduces losses and improves grain quality .The more the lapsed time between harvesting, the greater is the decrease in field yield as well as head rice recovery.

Moisture content:

The moisture contents at harvesting are also important for quality rice production. Harvesting at 20-23%grain moisture gives maximum field yields as well as high milling recoveries, At this moisture levels the crop is about 90% straw coloured and the lower portion of the panicles are in the hard dough stage. A report claims 10%paddy loss if the crop left in the field for attaining 14-16% moisture before harvest.

Paddy Cleaning:

Paddy usually contains foreign matter like mud lumps,pebbles,straws chaff, wed seeds, immature grains, animals dung, bird dropping,dirt and even iron or steel particals which substantially reduce the marketability of paddy and badly deteriorate its quality for storage and milling processes.

Using Electrical Proper cleaning of paddy cleaning of paddy is imperative keeping in view the following broad objectives.

• Cleaning reduce drying requirements and cost.
• Removes foreign matters that cause paddy deterioration during storage.
• Removes materials that damages the conveying and milling machinery.

DRYING:

Drying refers to removal of moisture from paddy grains. Paddy drying is imperative as it is usually hervested at high moisture level at 20-23 percent. The higher is the initial moisture content of paddy the longer it takes to dry. If the moisture content is not reduced to 14 percent soon after threshing, paddy quality deteriorates on account of microbial activities and insect demage .Thus immediate and proper paddy drying after threshing is imperative. The most common paddy drying method is sun-drying. Although sun-drying increases breakage durning milling, it is cheap as compared to mechanical drying and may continue to be the major drying procedure despite 1-5 percent losses.

DEHULLING:

The hull is removed from rough rice using a huller to yield brown rice. It’s also called De-hulling.

Brown (unmilled) Rice:

Brown rice is the least processed form of rice, it has the outer hull removed, but still retains the bran layers and germs are still intact. The bran layers give this type of rice its characteristic tan color and nut –like flavor. The outer side layer of the bran gives this rice a chewier texture than white rice. When the hull is removed from rough rice it is called brown rice. However not all dehulled rice is brown in colour .The outer bran layer of the grain and embryo(germ) is what gives rice its colour and can vary from light yellow to red to dark purplish black. Rice bran and germ contain greater amounts of dietary fiber, vitamins, minerals, and other health-related components that the white center portion of the kernels (endosperm).But those outer portion of the kernels also contain lipids (fats) material making brown rice more susceptible to becoming rancid under cool condition will lengthen its shelf life. Cooked brown rice has higher fiber content and is chiewer in texture than its white rice counterpart and is described as described as having a slightly nutty flavor.

MILLING OF BROWN RICE:

Milling is the last post-harvest paddy processing stage which converts paddy into edible rice after passing through its various steps which are paddy, dehusking, milling, and rice grading for better marketability and consumers preference. Therefore, rice obtained after commercial milling enteriely comprises of starch endosperm which is the major milling component. The final step is separation of the whole kernel from the broken kernels using screens sized for use on long, medium or short grains varieties to produce whole grain rice. Head rice milling yield is the percentage of whole kernels recovered after milling and removal of the broken kernels. Producers are paid less for broken kernels than for a whole.

Milling of rice increases its shelf life and provides consumers with a physical property that have come to desire,whiteness.therefore the goal of milling is to remove as much of the colored bran and germ as possible. The quantity of bran remaining on the surface of the surface of the grain after milling is defined as milling degree. A high degree of milling means that the milled rice is very white with relatively light milling. Degree of milling is influenced by to grain hardness, size and shape, depth of surface ridges, bran thickness and mill efficiency. Consumers also have a preference for rice that is transparent and not chalky. Chalky areas of the grains are grains are as a result of air spaces in between the starch granules that make up the endosperm.

GRADING OF RICE:

Grading of rice is primarily according to its grain shape. For improved milling efficiency the adoption of improved technology for each post-harvest stage. The sole factor which affects the head rice and total milled rice yields. Rubber roller mills yield higher values for total milling recovery 70% head rice 62% and lower  values of 40%husk and bran and 30 %broken rice are produced by hand pounding and steel hullers husk and bran are removed in one pass while in shellers and rubber roller mills these are removed in two posses.

Standard Operating Procedure (SOP) for Alkali spreading (digestion) value determination

Principle     

Test describes the response of rice starch to dilute alkali to speculate the temperature at which gelatinization of rice endosperm takes place. Higher value of alkali spread/ digestion indicates lower temperature at which starch gelatinization will occur or vice versa.

A.      Reagents

1.      Potassium hydroxide solution (1.7% KOH)

B.        Requirements

1.      Milled or preferably head rice at least six grains

2.      Clean glass Petri dish

3.      Thermostat at 30 ⁰C

4.      Alkali spread value pictures hedonic scale 1––7

Preparation of Reagent 1.7% KOH

Weigh accurately 17g of KOH (anhydrous) and dissolve it in 1000mL of distilled water.

Procedure

1. Take six head rice grains and place them in clean glass Petri dish at distant apart.
2. Pour 10mL of 1.7% KOH into Petri dish.
3. Place # 2 in the thermostat at 30 ⁰C for 23 hours.
4. Observe the condition of grains and score the grain status by matching it with the alkali spreading value pictures hedonic scale 1––7

 Aromatic Rices, 2000; Little et al., 1958

Standard Operating Procedure (SOP) for Gel Consistency Determination

Principle:

 Consistency in mm of cold paste of 4.4% rice starch flour in 0.2N KOH

Requirements

1. 0.2 N KOH
2. Samples flour mesh size 100 weigh 100mg ±1mg
3. Ethanol (95%)
4. 0.025% Thymol Blue in Alkohal
5. Vortex at speed Knob up to 6 position  or shaker
6. Culture tubes (13 X 100 m  or 12 X 75mm)
7. Water bath with Boiling temperature
8. Millimeter scale
9. Ice bath or freezer

Reagents

0.2 N KOH

Procedure:       Dissolve 11.2 g of Potasium Hydorixde ( dehydrated) in 1000 mL D-water

0.025% Thymol Blue in Alkohol

Take 0.025 g of Thymol Blue and dissolve in 100 mL of 95% Ethanol

Procedure:

1. 100mg flour of test sample (mesh 100mm) in culture tube

(Place 10 Whole /Head rice grains and grind for 40seconds to give 100mesh.)

2. Add 0.2 ml of Thymol Blue in the test tube only to wet.
3. Shake the tubes well to suspend the starch
4. Add 20 ml of 0.2 N KOH
5. Dispersed the mixture immediately with glass rod
6. Mouth Covered Tubes are placed in boiling water bath cum for 8 min to reflux with constant speed till the surf comes up to ⅔ height of the test tube
7. Let the tube come to cool at temperature for 5- minutes
8. Place the tubes in Ice water/ Bath for 20 minutes
9. Laid the tubes on the Bench top horizontally
10. Measure the Gel length from bottom of tube to the Gel front through millimeter scale

PROFICIENCY TEST FOR NEW AMYLOSE METHOD

REAGENTS

Use only reagents of recognized analytical grade, unless otherwise specified and distilled or demineralized water or water of equivalent purity

1.1              Ethanol 95%

1.2              Sodium hydroxide 1M

1.3              Acetic acid 1M

1.4              Iodine solution 0.2% iodine in 2%KI

SAMPLES

1. Shaheen  Basmati 0.1g
2. Basmati  198  0.1g

Apparatus

2.1 Spectrophotometer with matching cells, usually of 1 cm path length, capable of measuring absorbance at 720nm.

2.2 Volumetric flasks 100ml.

2,3 Boiling water bath

2.4 Analytical balance capable of weighing to the nearest 0.0001g.

2.5 test tubes 20ml

2.6 Pipettes, capacity of 0.2ml,1ml,5ml,and 10ml.

PROCEDURE

Preparation of provided already ground.

PREPARATION OF THE TEST SOLUTION

Take 0.1g of Shaheen in a 100ml of volumetric flask and basmati 198 in another volumetric flask after that prepare a blank solution using a 100ml volumetric flask without sample.

3.21 Add 1ml of ethanol using a pipette, washing down any of the flour adhering to the side of the flask. Shake slightly in order to wet the entire sample.

3.22 add 9.0ml of sodium hydroxide solution 1M and mix. Ensure that the starch is dissolved completely by either heating or standing overnight .allow it to cool to room temperature make up to volume with water.

PREPARATION OF THE BLANK SOLUTION

Prepare a blank solution using a 100ml volumetric flask without sample.

PREPARATION OF THE CALIBRATION GRAPH

Preparation of the five calibrated rice standards with known amalyose contents.

COLOUR DEVELOPMENT AND SPECTROPHOTOMETRIC  MEASUREMENTS

Pipette a 0.5ml aliquot of each calibration solution in to two test tubes.add 5.00ml of water.0.10ml of acetic acid and 0.20ml of iodine solution .put an additional 4.20ml of water in to tube to make the total volumn of reaction mixture 10.00ml .mix well in a vortex mixer or by inverting parafilm covered tube several times.

Measure the absorbance at 720nm against the blank solution,using the spectrophotometer immediately after adding the last chemical.

PLOTTING THE CALIBRATION GRAPH

Enter the absorbance values for each calibration solution.

DETERMINATION OF AMALYOSE CONTENT OF TEST TUBE

 Pipette a 5.00ml of water,0.10ml of acetic acid and 0.20ml of iodine solution . put an additional 4.20ml  of water in to each tube to make the total volume of reaction mixture 10.00ml.mix  wel in a vortex mixer or by inverting parafilm covered tube several times. Measure the absorbance immediately at 720nm against the blank solution using the spectrophotometer .enter the absorbance values for each test tubes for each of the amylase calculator. Amylase content will be calculated automatically.

COOKING QUAILTY OF RICE KERNEL

Cooking means absorption of water until gel of the rice is formed.

Elongation Ratio

Elongation ratio was determined by the method given by Azeez and Shafi, (1966). 20 raw rice grains were selected at random and their length was measured. Rice was then cooked for 10 minutes in vigorously boiling water. After cooking rice grains were placed on table in straight line and length was measured with the help of ruler.

 Elongation ratio was determined as under

 Elongation Ratio= Average length of twenty rice kernels after cooking

                               Average length of twenty rice kernels before cooking

Water Absorption Capacity

Twenty grams of rice kernels were soaked in water for 25-30 minutes and placed in vigorously boiling water and cooked. The rice was cooked till complete gelatinization of kernel. The temperature of water was maintained at 95+1⁰C. The cooked rice drained out completely over filter paper and weighed.

      

 Water absorption capacity = Weight of cooked rice   *100

                                                Weight of raw rice

Volume expansion ratio

Volume expansion ratio was determined by the method given by Juliano (1970). Twenty grams of rice kernels were added in 250 ml cylinder having 100 ml water and increase in volume was noted. After cooking rice were dried over a filter paper and poured in 250ml cylinder having 100ml water and increase in volume was recorded. Volume expansion ratio was determined by the formula as under.

         Volume expansion ratio = Volume of cooked rice

                                                     Volume of raw rice