The difference that  deliberate efforts have been taken to  improve the quality of processed   rice  (Ihedioha and Odoemena  2006)
Harvesting tropical rice is usually at  20 percent or more moisture, when grains will provide optimum total and head role yields. Moisture content at harvest is lower during  the dry season than in the wet season  because of  sun –drying  while the grain are in the intact plant.  The actual period of dry matter production is not  more than  14  to  18 days, after which the grain
undergoes drying. Harvesting is  carried out by cutting  the stem (Juloiano  1993)  by hand sickles or knives combine harvesting are  used in large areas as the muda estate in Malaysia and in the  united  state,  Australia, Europe and Latin  America.  (Juliano  1993). 
            The  moisture content of paddy at harvest ranges between  22-26%  wet asis in order  to prevent deterioration after harvest, paddy should  be dried down to a level of water activity that will enable safte storage by   reducing respiration, inhibiting mould growth and preventing  production of mycotoxins. This  corresponds to a moisture content  of about  13 -14  percent which is  considered adequate for safe storage  milling  and further storage as  milled rice.  (Hall. 1970).  Drying can be done traditionally by sun –drying   if the  whether   permits drying  rice  (Paddy ) by Thinly  spreading it on  a floor or pilling  it over to increase   the  surface  area of the grain bulk   to air and prevent the build up of heat  within the grain bulk, (Alaka,  2005). This method allows  drying  in open air and under strong sunshine for  1 to  2 days. But   the sun-drying method can produce sun –checks which reduces the head rice and increases the   rice bran percentage, also this method requires intensive care and  labour. Drying in more  developed  countries is done  artificially  such as the use of batch dryers in Japan and hot air dryer in United State, this is  an alternative to sun –drying  and can avoid dehydration, which cause  reduce head, rice (Juliano  1993).
Cleaning  /winnowing
            After drying, the rough rice is   winnowed to remove chaff (Juliano  1993).  This  is important to remove foreign seed  and trash.  The three major cleaning methods includes air cleaning by using sieves and  gravity cleaning in rice mill. All impurities, odds and ends such as stones and peaces of soil and straw must be removed by screening or ridding process and fan.  Also because of the  subsequent effect of  the storability and milling quality, unclean rice  increase  maintenance  requirement on  milling  machine (FAO  1993).   
In some countries a popular form of parboiled rice is  subjected to a sterming  or  parboiling process while  still a brown  rice gain, the  parboiling of  rice is an ancient tradition in India and Pakisten but now, is  part of  traditional milling  of rice in many developing countries (Okaka,  2005).  The traditional parboiling  process involves soaking rough rice  over –night or longer in  water  at ambient temperature followed by  boiling or steaming rice at  100% to gelatinize the starch, while the grain  expands  until the hall’s  lemma and palea to separate (GARIBALDI 1984,  Bhattacharys,  1985),  Pullaiyar  1988).  The  parboiled rice is then cooled  and sun-dried before storage or milling  (Juliano  1993). Parboiling had as its original intention the loosing of the hulls, but in addition this  enhances the nutritive  value of milled rice so rerated because water dissolved the vitamins and minerals concentrated in the  bran and hulls  and re –distributed these in the endosperm (Okaka,  2005). Parboiling gelatinizes   the starch granules and hardens   the endosperm making it translucent. Chalky grains, and those with chalky back, belly or core  becomes completely translucent on  parboiling . A white core or  centre  indicate incomplete parboiling of  the  grain  (Juliano  1993) results show that water soluble B  vitamins (thiamine, riboflarin and niacin ) are higher in milled parboiled rice than in milled raw rice (Kik  and Williams,  1945).   Oil and protein are reported to diffuse outward during parboiling, based  on microscopic observations. They cannot diffuse as  readily though cell walls as water, soluble vitamins   but the spherosme is  destroyed. At  similar degree of milling, parboiled milled rice has lower  protein content  than  raw  rice but  parboiled rice  bran  has more protein  and oil than  raw  rice bran (Padua and julieno   1974). Parboiling also   removes cooked rice  volatiles including free fatty acids, in activates enzymes such as lipase  and lipoxygenase, kills  the embryo  and decomposes some antioxidants  (SOwbhagya and bhattacharya,  1976) . hence cooked parboiled rice lack the volatiles   characteristics of freshly cooked raw rice,  hydrogen  sulphide, acetaldehyde and ammonia  (Obata  and Tanaka  1965).  The volatiles identified where mainly Addehydes and Ketnes. (Tsugita,  1996). Parboiled rice takes longer to cook than raw rice and may be presoaked in water to reduce the cooking time to be comparable to that of raw rice.  The cooked grains are less sticky, do not dump and are resistance to disintegration, the grains are also   harder, they also tend to expand more  in  girth rather than in length as  compare to raw rice (Juliano  1993).
Advantages of  parboiled rice parboiled  rice as earlier started  brings  about many  changes in the property of rice
-      Parboiled rice is harder and therefore resists attack during storage
-     It improves the amount of  vitamin  and other nutrient in the rice 
-     The   loss of solid matter into the liquid furing cooking is less than  in raw rice
-     It reduces grain damage during milling shelling paddy becomes  easier because   the husk did split during  parboiling \

-      Parboiled rice may also choke the polisher due to the higher oil content in the  bran
-     Parboiled rice takes time to cook than raw rice
-     The heat treatment during parboiling destroy antioxidant  so  parboiled becomes  rancid   more easily than  raw rice
-     Parboiled rice is more difficult to polish   than the raw rice therefore milling  is more costly in terms of time and power requirement expand more in girth rather than in length as compared to raw rice (Juliano 1993).
Drying Of  Parboiled Rice
Unlike most  cereals, rice is  consumed primarily as unbroken  kernel’s is much greater than that of broken kernels. Therefore, more care is needed to avoid breakage in drying rice than in drying other cereals. Moisture reduction  takes place rapidly during the first drying  from  36-18  percent moisture level, but it is low from  18-14% .  as the  kernels is dried the other portion shrinks setting  up stress and strain  and when moisture is removed too  rapidly, checking or  shattering of  kernel   results. Frying should stop at  18 percent moisture to  allow paddy to equilibrate for  several hours   before continuing the drying  to  14%. Paddy drying  is one of the important steps  in post harvest   handling of rice. It determines storage time, milling out turn and appearance of rice . (Alaka  2005)
Milling in the rice industries can either be referred   as the overall  operation  that includes cleaning, hulling pealing, polishing  and  grading or  simply the removal of the rice bran or  outer  layers.  Typically, the  percicap accounts for   1 to  2%  of the weight of the whole  rice caryopsis seed coat  and aleuronic  5%  embryo  2 to  3%  and  endosperm  89-91%  (Okaka  2005 ).  The edible part of rice grain is  enclosed in the glumes, which need to be  first separated by  hulling.  The most  primitive implement for hulling is the system with wood mortar and   pestle or treadle or water mill.  These hulling method are still used in some of rice grouting region in  Asia and African.   Now mechanical hulling or milling  is popular in most of the rice growing  countries.  The hulled gain are then winnowed in order to remove the chaff and bran.
Rice with the  hulls removed but the bran left on, is called “Brown rice”  the pearling / milling is whitening or securing process in  which  the remaining layer, of  pericap,  tasti and aleuronic materials  on  the  hulled  rice  are removed by passing  it through  services  of pearling cone   milled rice refers to the  rice after removing all hulls, bran layer and   germ  (Okaka, 2005)
            Polishing operation   similar to  pearling operation  further  whiten,  and smoothens the rice gain to  obtain  fine  white rice. Polishing  is necessary for better  appearances  to meet the market needs  with sacrifice  of the flavor   and health  constituent   in the rice grain (Okaka 2005,  Francois  et al;  1997)  during grading operation the broken  grains  are  separated and sorted  to meet market standards. This separation can be accomplished by passing   through a series of staves or cellular cylinder. These broken grains can be reduced to rice flour\grits and put to several useful ways as rice fufu or as raw material for manufacturing of several convenience
foods. (Osaretin 2006). Effect of milling on vitamins and minerals content of Rice.

Table1: Mineral content.
Extraction rate(%)
Calcium (mg/g)
phosphorus (mg/g)
zinc (ppm)
Iron (ppm)
Copper (ppm)

100(Rough Rice)





82 (brown rice)
72 (milled rice)

Vitamins content
Extraction  rate (%)
Thiamin  mg/100
Riboflavin  mg/100
Niacin microgram
Pyridoxine microgram
Folate (m/g)
Biotin ng/g
100(Rough Rice)
82 (Brown Rice)
72 (Milled Rice)
  Soruce. Baurent friend and Derither (1991)

A lot of losses are encountered during  milling of brown rice to white or polished rice. Milled or white rice represent 40 to  70%  extraction of rough rice. The  B. vitamins and iron are found primarily  in the germ and bran layer, and are therefore  removed in the  cause of   milling it has been estimated that in the cause of milling brown rice to  white rice, approximately  80  percent of the thiamins  is removed Baurent fiend  and Dertter (1991) 

Alaka, i.c (2005). Upgrading the quality of local  rice for local  and internation market   paper  presented at  NIFST symposium  on the challengers  of theNigierian Rice processing industry in  the  21st Century Abakaliki , Nigeria  October  2005 
Deritter (1991)  food   considered for nutrient addition  cereal grain  product , nutrients additions  to food  pg  19.
Bhattacharya,  K (1985)  parboiling  of  rice . in  Julian,  B.ed  Rice chemistry and  technology st paul, NIN, USA,  America  association of cereal chemists  P  289-384
Brudevold f, govlet D, Auarzadeh  of and  Tlehrani A, and  Van  Houte J  (1985) . intraoral  demineralization and maltose clearance from   wheat  starch caries  res 9,  136 -144
R.P  Central R.P  and  Reeves TG (2002),  the cnetral of the worlds poor takes centre  stage , science,  296,53
Ebuchi  Oat, Ikanone CE, Nwamadi ULM  (2004)  Sugar,  Vitamin C  and Mineral content in indigenous as foreign  fruit  guile in Nigeria. Nigeria Food  J. 22:2k 222
Enwere J.N  (1998)  foods of  plant origin afro-orbis publication, Nigeria  p. 108
FAO (1954)   rice and rice  diets  a nutritional  survey , rev ed Rome, FAO P 78
FAO  (1972)  Effect of milling on rice  kernels res.  Edition Rome food and  agriculture 
FAO (1994)  African  experience in the improvement of post harvest techniques synthesis  based on workshop  held in Accra, Ghana , July  1994 .  Agricultural support system division,  Rome
Oxford,  P.D. ring, S.G Carroll, v. Miles,  M.J  Morris, V.J (1987) the effect of concentration and botanical source on the gelation and  retrogradation  of  starch  journal of science of food and agri.  39  :169-177  Firestone AR  Schimid R &  Mulitemann HR  (1985)  demineralization  potential
Garibaldi, f  (1984) . rice parboiling FAO agric. Serve bill  56   Rome FAO P  73.
Gibson R.S (1994)  content and bioavailability  of trace elements in vegetarian  diets am.j  clini Nutri  59 (5) .  5 1223-1232 
Hall, C.W  (1970)  handling and  storage  of  food grains in  gropical  and subtropical  area   FAO agricultural Development   paper No  90.
BEMILLIER JN  and whistler R.L  (2006)  CARBOHYDRATE. IN FOOD CHEMISTRY o.r  Fennema  (Ed),  CRC press TAYLOR AND Francis Group : Goca ration F 157-223 PP 
Haumann, B.F  (1989)Rice  brarlinked tolower cholesterol J A M OIL  Chem Soc.  66:615-618
Henry C J. K and  Massey D (2005)  Micro  Nutrient Changes during  processing and storage. National   resources  international Ltd,  PARK, HOUSE,  KENT UK
IRRI  (19976)  IRRI WARDA CIAT international rice research institute  merila Philippines
Ihekoronye A.I  and  Ngoddy  P.O  (1985).  Intergrated FST  for the tropics, Macmillan publisher  Ltd  London  pg  139 -  148, 236-258 industry. www NITST . org/eeditiorial articles.
Iwasaki t (1987)  measure  for  the enhancement of rice consumption and  diversification  of rice  utilization, international of  rice  utilization  12-12 october  Bangkok pg  3
Ihedioha d and odoemena  b (2006)  towards appropriate pricing of locally processed rice . paper at the training workshop on  rile   proc packaging and marketing instate of fod sex tech ai  july  2006 
Jones m.p (1995) ,  he rice plant and  its envrironment , WARDA trauining , Guide  2 , 27   -30 
Uliano B.O  (1979).  THE CHEMICAL BASIS OF RICE GRAIN Quality in proc chemical aspect   or rice grain quality. IRRI  Philippines p   69-90 
Juliano B.O  (1993)  Rice in  Human Nutrition, Rome, FAO  p  162
Kahlon , T.S  Saunders, R M, Chon,  fi:  chu! M.C  and  Betschart, A.A. (1990): INFLUENCE OF RICE   BRAN, OAT AND WHEAT BRAN ON CHOLESTEROL AND TRIGLYCERIDE IN HAMSTERS.  CERAL CHEM  -  67: 439-443
Kennedy  G Burlingame, B and  Contribution  of rice as important  impact of biotechnology and biodiversity in rice consuming  contries published by FAO  remeltaly
Khatum mm, ali, MH  and delacrus , Q D (2003)  correlation studies   on grain physicochemical characteristic\s of  aromatic rice , paskistar journal of biological sci pub by asian network for  scientific  information  6 (5)  p. 511 -512
Kik  M.C  and Williams R.R.  (1945)  The nutritional improvement of  white  rice  Nat  acad.  Sci bull  112  Washington  D.C   Natioanl  council  76pp 
Lee, M.H.N.S Hettiarachy, R.W  M.C  new, R  gnanasam banadam  (1995) phys, co chemical properties  of calcium for tified rice  areal  chemistry  pg  72 ,  333-355
Miyoshi h : OKUDA t Okuda K and   Koishi , it  (1987)  effect of branch rice  on apparent digestibility and balance  of nutrient in young man on low  protein  diet J nutr sci vitamin  33 . 207 -218
E. IMOLEHIN E.O  and Wada  A.E  (2000) meeting the rice production and consumption demand in Nigeria with improved technologies.  International rice  commission  newsletter  49,23-41
Nkama (2005)  modern method  of rice processing . an invited paper  at  the Nigerian institute of food  science and technology (NIFST) Conference  Abakaliki  Nigeria

e. imolehin E.O  AND Wada  A;E  (2000)  meeting the rice  production   and consumption demand in Nigeria with   improved technologies  international  rice commission newsletter,  49.23-41
Nkama (2005  ) modern method  of rice processing . an  invited paper  at the Nigerian institute of   food science and  technology (NIFST ) CONFERENCE ABAKALIKI Nigeria   
Obata y and tanuka H (1965)  studies on the photolysis of l cysteine and lcystine formateion  of   the flabour of cooked rice from  L-cysteine and lcyrtine   
Agric . boil, chem.  29: 191  - 195 
Okaka j c and  francosi D (1997)  cereal and  legumes storage AND   processing technology data, micro  system published at Enugu pg  13:  17 -  50 
Okaka  J.C (2005)  handling  storage and processing of plant   foods , O.C  Academic publishers p  16  -30
Osuji, C.M  (2006)  Waster  From Rice Industry  . Utilization  and  economic value  paper  presented on  workshop   on rice  processing packaging and marketing organized by  Nigerian institute  of food science and  technology . (NIFST)  Abakaliki, Nigeria July  2006
Padua , A. B.  and  Juliano, B.O   (1974)  effect of parboiling on thiamine, protein and fat or rice  Sci food   agric,  25   667- 701
Perez C.,  Juliano  B.O  PAscaual C.G  , novenario V.G    

Share on Google Plus


NB: All Material Work on this Library is for Educational Purposes Only to assist Scholars writing related Topics. Owners Rights belongs to different original authors who wrote the work. All admin editors of this Library are crime prevention activists. Materials are sent to us anonymously. Please contact us via email only if you unauthorized your work to be in this library so that we can take it down immediately. Join the Social Network Google Plus | Facebook | Twitter
    Blogger Comment
    Facebook Comment