The thesis h a s b e e n pr e s e n t e d in the f o l l o w i n g C h a p t e r s s
«
C h a p t e r I It gives an i n t r o du ct io n to t h e p r o c es s of p a r b o i l i n g of p a d d y w i t h r eference to its objectives and principle.
A r e v i e w of lit e r atu r e on the m e c h a n i s m of a b s o r p t i o n of w a t e r b y t he g r a i n along" wit h m a t h e m a t i c a l analysis, and subsequent g ela t ini z a t i o n of starch gr an ules h a s a l s o b e e n incorporated.
P a r b o i l i n g is a p r o c e s s of m o i s t u re-hea t t r e a t m e n t of p a d d y and is f o l l o w e d b y s o ak i n g in w a t e r and subsequent s t e a m i n g and drying b e f o r e m i l l i n g in th e u s u a l way. The p r i m a r y change b r o u g h t about
d u r i n g soaking and p a r t i c u l a r l y d u r i n g steaming, is some sort of c h e m i c a l reaction, cal l ed gelatin iz at io n. This c h a n g e s t h e structure of ric e k e r n e l b y h y d r a t i o n and i r r e v e r s i b l e swe l l i n g of starch
granules. G e l a t i n i z a t i o n and some other second ar y p r o c e s s e s occurring d u r i n g p ar bo iling, b r i n g about m a n y impr o v e m e n t s in the q u a l i t y of f i n i s h e d rice. W h i l e t h e p r o c e s s of s oaking and su bsequent steaming s u p p l y a de qu at e m o i s t u r e and h e a t r e q u i r e m e n t s f o r c o m p l e t e parboiling, a n o t h e r p o s s i b i l i t y is that m e r e s o a ki ng in w a t e r at e l e v a t e d t e m p e r a tu re m a y f u l f i l t h e s e r e q u i r e m e n t s also.
1 *3
T h e r e por t ed l i t e r a t u r e J indi c a t e d little studies on the m e c h a n i s m of a b s o r p t i o n of w a t e r b y paddy. F o l l o w i n g a d e t a i l e d study
Copyright
IIT Kharagpur
on the absorption of water by wheat kernel , earlier workers observed that the basic process of absorption of wate? by paddy daring soaking is diffusion. They also assumed that the integral diffusion equation, developed by Becker for unsteady-state diffusion
in solids of arbitrary shape , describes the absorption of water molecules into paddy. The equation, in the neighbourhood of time
zero, is of the general form :
1 - M = JL- X + BX2 .. (1)
v/jtx„ - x S .
where M = -3--- , X =.
- r r -/D§
x s “ Xq v
(The notations m and t in the original equation have been changed to x and © respectively).
Neglecting.higher power of X, Eq. (1) becomes on rearrangement x - x = J L (xs - x0) ( J L ) t/De, ..(2)
Vat V
x - xD = km /©7 ..(3)
where k m - (xs - x D) (_£_)
< /D ~..(4)
a/ji V
* 1
The analysis of the data of earlier workers , based on Eq.(3),
showed little uniformity in the approach to the problem of diffusion during soaking of paddy and the values of the constants so calculated were not comparable with each other. Regarding gelatinization of
grains during soaking, no attempt has been made so far as to evolve a method of measurement of degree of parboiling and to give a
quantitative picture of the progress of gelatinization during soaking.
Copyright
IIT Kharagpur
This i n v e s t i g a t i o n was, therefore, taken up to study the soaking c h a r a c t e r i s t i c s of some v a ri et ie s of p a ddy with the f o l l o w i n g objectives:
(i) to give a b e t t e r and mo re u n i f o r m p i ct u r e on d i f f u s i o n of w a t e r m o l e c u l e s inside the grain and subsequent
g e l a t i n i z a t i o n of starch granules;
(ii) t o give a ge ne ralized corr e lat i on of t h e d a t a on soaking of v ari o u s i n vestigators; and
«
(iii) t o evolve a m e t h o d f o r evalua t ion of d e g r e e of par b o iling.
C h a p t e r II This chapter incorpo ra te s d e t a i l e d
i n f o r m a t i o n on m a t e r i a l s and e x p e r i m e n t a l procedures. The following f i v e h i g h - y i e l d i n g v a r i e t i e s of p a d d y h a v e b e e n used in th e
i n v e s t i g a t i o n :
TABLE
SI. V a r i e t y # Length,
No. " mm.
9
1. J A Y A 9 . 0 2
2. R AT N A 9 . 2 4
S. PADMA 7.62
4. B A L A ’ 7. 0 1
0
5. PANKAJ 8 . 5 8
M e a n diamete r, mm . Sto ra ge ( B r e a d t h + th ic kn es s) time
2 . 5 1 6 m o n t hs or m o r e
2 . 1 7 "
2 . 4 6 "
2.52 "
2 . 5 7 "
Copyright
IIT Kharagpur
V a r i a b l e s studied f o r m o i s t u r e gain, swelling and d e g r e e of ' * p a r b o i l i n g are as f o l l o w s s
1. Temperature,° C : room t e m p e r a t u r e ( 2 8 - 3 0 ) , 40, 50, 60, 65, 70, 75, 80.
2. Time : 10 m i n t o 12 hrs. and u p t o about 2 8 hrs. in case of r o o m temp.
Th e e x p e r ime n ta l t e ch n i q u e s f o r m e a s ur em en t of m o i s t u r e gain and swellin g we re b a s e d on Ghose et al.^" The d e g r e e of p a r b o i l i n g was m e a s u r e d f r o m the p e r c e n t a g e of grains c o m p l e t e l y g e l a t i n i z e d , i . e . , f r o m p e r c e n t a g e of gra i n s wit h ou t "o pa qu e spot". The " o p a q u e spot"
w as o b s e r v e d in a n u m b e r of soaked grains a f te r c u t t i n g t h e grains into t w o h a l v e s w i th a sharp edge.-
Ch ap t e r I I I . The r e s u l t s of i n v e s t i g a t i o n h a v e b e e n p r e s e n t e d in thi s c h a p t e r in t h e f o l l o w i n g w a y :
(i) M o i s t u r e con te nt h i s t o r y of all the v a r i e t i e s at d i f f e r e n t t e m p e r a tur e s.
(ii) S w e l l i n g or v o l u m e gain in part /p ar t in i t i a l v o l u m e , a s a f u n c t i o n of t i m e ar\d t e m p e r a t u r e of soaking f o r v a r i e t i e s JAYA,
PADMA, B A L A and P A N K A J •
a
(iii) D e g r e e of p a r b o i l i n g as a f u n c t i o n of t im e and t e m p e r a t u r e of s o a k i n g f o r all t h e v a r ie ti es .
C h a p t e r I V . Th i s c h a p t e r i nc lu de s a na ly s i s of th e res u lts p r e s e n t e d in C h a p t e r III.
Copyright
IIT Kharagpur
C hapter V » The important findings and c o n c l u s i o n s of the^
i n v e s t i g a t i o n h a v e b e e n p r e s e n t e d in t h i s c h a p t e r as l i s t e d b e l o w :
1. The d ata on m di s t u r e gain can b e ad e q u a t e l y c o r r e l a t e d b y the d i f f u s i o n equation, Eq.(3), f o r all t h e v a r i e t i e s of p a d d y in the t e m p e r a t u r e r a n g e studied. However, the e quation is valid for a short d u r a t i o n of s oaking and up t o a l i m i t i n g m o i s t u r e content w h i c h is at t a i n e d b y t h e grai n s either Just b e f o r e reaching a point of e q u i l i b r i u m b e l o w a t e m p e r a t u r e of 60-65 C or at th e onset of r apid o h y d r a t i o n above 60-65°C.
2. The A r rh e n i u s plot of d i f f u s i o n co ef ficient f o r all t h e
6 0
v a r i e t i e s exhibi t s a b r e a k a r ou n d a t e m p e r a t u r e of 70 C. S imilar o b s e r v a t i o n ha s a lso b e e n n o t e d w i t h the d a t a of other workers.7 This p h e n o m e n o n h a s b e e n expl ai n ed b y conside rin g t w o differ en t m e c h a n i s m s p r e d omi n ant in th e t w o d if f e r e n t t e m p e r a t u r e regions.
L a r g e r v a l u e s of a c t i v a t i o n e n e r g y a b ov e t h e t e m p e r a t u r e of b rea k c o r r e s p o n d t o g e l a t i n i z a t i o n of s ta r c h granules w h i c h is p r e d o m i n a n t l y a c h e m i c a l process. The t emp e r a t u r e of b r e a k is v e r y close to g e l a t i n i z a t i o n t e m p e r a t u r e of rice starch granules. The results on s w e l l i n g and d e g r e e of p a r b o i l i n g of grains h a v e conf ir me d this
f i n d i n g .
»
3. Another i m po r t a n t f i n d i n g of t hi s i n v e s t i g a t i o n is tha t ad e q u a t e d e g r ee of p a r b o i l i n g is a c h i e v e d at a m o i s t u r e con te nt of about 0. 55 g«/g. d r y b a s i s b y s oaking alone near about g e l a t i n i z a t i o n t e m p e r a t u r e . This c o n f i r m s t h e f i n d i n g s of Ali .3
Copyright
IIT Kharagpur
'
*
c o l l e c t e d b y v a r i o u s w o rk e r s h a v e b e e n prese nt ed b y a sing le semi- e mpi ri ca l c o rr e l a t i o n w i t h f a i r m e a s u r e of accuracy. This gives an unifi e d a pp roach t o p r o b l e m of m o i s t u r e d i f f u s i o n in p a d d y during
soaking.
N o m e n c l a t u r e :
X 0 initial, uniform moisture content, g./g. dry basis.
X
•#
average moisture content at given absorption time, g./g. dry basis.
xs effective surface moisture content
than zero, g./g. dry basis. at times greater
e absorption time, sec.
( s / v ) surface-to-volume ratio of a solid
D diffusion coefficient, cm^/sec.
B dimensionless constant.
R e f e r e n c e s *
1. B a n d o p a d h y a y , B . & Ghose, T.K., Indian J. Technol, 3 (11), 1965, 360.
2. Biswas, D.K.
&
Ghose, T.K., T r a n s . I n d i a n Inst.Chem.Engrs.„ 15(1), 1973, 43.
3. Ali,N., S t u d i e s on some e n g i nee r ing a s pe c t s of p a r b o i l i n g of paddy, 1974, Ph.D. thesis, I.I.T., K h a r a g p u r , I n d i a .
4. B e c k e r , H . A . , C e r e a l Chem., 37, 1960, 309.
5. B e c k e r , H . A . , J. appl. Polym. Sci., 1, 1959, 212.
6. B a n d y o p a d h y a y , S . & ^oy, N.C., Indian J. Technol.
(in p r e s s ) .
7. Ibid, J. Fd. Sci. Technol. 12(4), 1975, 197.
