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A study has been carried out to prepare a stabilized rice bran with low amounts of antinutritional factors commonly present in rice bran such as sand (silica), phytic acid and trypsin inhibitor. Full fat stabilized rice bran with low silica content has been prepared. The prepared bran had a silica content of 0.99 g / 100 g bran, as against the control bran (4.85 g / 100 g bran) (90% reduction) which is novel in this work. Also, the phytic acid level was brought down to 3.4 g / 100 g bran, as against the control bran (4.65 g / 100 g bran) (30% reduction). The trypsin inhibitor content of rice bran was at 190-198 mg/100 g bran which was low compared to soyabean. The prepared bran has also retained all the oryzanol (359 mg/100 g bran), tocopherols (31 mg/100 g bran) and sterols (81 mg/100 g bran) present originally in the control bran (339 mg/100 g bran, 28 mg/ 100 g bran, 77 mg/100 g bran). The prepared bran was incorporated in to commercial rice flour to obtain a low glycemic index product that can be used to prepare traditional south Indian foods like roti, dosa, idli and others. The reducing sugar content of commercial rice flour (85 mg/100 g) was brought down to 62-68 mg/100 g (20-27% reduction) in bran incorporated rice flours. The bran so produced may be useful as a food supplement in processed foods to provide health benefits.
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50 BEVERAGE & FOOD WORLD - Vol. 41 - No 1 - JANUARY 2014
Development of a Process for
Preparation of Low Silica Stabilized Rice
Bran for use as a Food Supplement
A. S. Bhatnagar, P. K. Prasanth Kumar, G. Suresh Kumar, A. G. Gopala Krishna*
*Chief Scientist & Head, Dept. of Lipid Science & Traditional Foods, CSIR-Central Food Technological Research Institute, Mysore-570020, India
Email: aggk_55@yahoo.com
ABSTRACT
A study has been carried out to prepare a stabilized rice bran with
low amounts of antinutritional factors commonly present in rice
bran such as sand (silica), phytic acid and trypsin inhibitor. Full fat
stabilized rice bran with low silica content has been prepared. The
prepared bran had a silica content of 0.99 g / 100 g bran, as against
the control bran (4.85 g / 100 g bran) (90% reduction) which is novel
in this work. Also, the phytic acid level was brought down to 3.4 g
/ 100 g bran, as against the control bran (4.65 g / 100 g bran) (30%
reduction). The trypsin inhibitor content of rice bran was at 190-
198 mg/100 g bran which was low compared to soyabean. The
prepared bran has also retained all the oryzanol (359 mg/100 g bran),
tocopherols (31 mg/100 g bran) and sterols (81 mg/100 g bran)
present originally in the control bran (339 mg/100 g bran, 28 mg/
100 g bran, 77 mg/100 g bran). The prepared bran was incorporated
in to commercial rice flour to obtain a low glycemic index product
that can be used to prepare traditional south Indian foods like roti,
dosa, idli and others. The reducing sugar content of commercial
rice flour (85 mg/100 g) was brought down to 62-68 mg/100 g (20-
27% reduction) in bran incorporated rice flours. The bran so
produced may be useful as a food supplement in processed foods
to provide health benefits.
Key words: Antinutrients, Rice bran, Low silica rice bran, food supplement
INTRODUCTION
Rice bran (5-10%) is a byproduct from rice milling industry, which is
obtained while milling and polishing of brown rice in to white rice (polished
rice). The annual world production of paddy and white rice was about 652
and 437 million tons (2007-2008) with highest production of rice in China
(125.3 million tons), followed by India (94.6 million tons) and Indonesia
(38.2 million tons) (FAO, 2008) with a potential of 32.8 million tonnes of
bran. Rice bran contains about 12-18% fat, which has health beneficial
nutraceuticals such as tocopherols, tocotrienols, phytosterols, squalene,
and oryzanol (Gopala Krishna, 2002; Sakina & Gopala Krishna, 2004).
For most part, polished rice is the staple food, thus giving rise to an
abundant byproduct, rice bran, obtained during milling of rice (Housten,
1972). Rice bran is rich in proteins, lipids, fibre, vitamins and trace
minerals (Juliano, 1972).
Rice bran has been reported to be equally good as oat bran in lowering
serum cholesterol, increasing water retention in feces and reducing the
risk of heart disease. The primary reason for the non-utilization of rice
bran as food supplement is the presence of an active lipase enzyme in
the bran which gives rise to free fatty acids (Barber & Benedito de Barber,
1980). The lipase enzyme of rice bran can be deactivated through
stabilization process of rice bran. Several rice bran stabilization procedures
have been reported to address the issue of lipase inactivation such as,
by extrusion cooking of bran (Enochian et al., 1981; Randall et al., 1985),
pH lowering of bran (Prabhakar & Venkatesh, 1986), microwave cooking
of bran (Tao et al., 1993), ohmic heating of bran (Lakkakula et al., 2004),
cooking of rice bran (Anil Kumar et al., 2006).
Another reason for non-utilization of rice bran as food supplement is
the presence of high amounts of anti-nutrutional components like silica,
trypsin inhibitor and phytic acid. Phytic acid (myo-inositol 1,2,3,4,5,6
hexakisphosphate) is the most abundant form of phosphorus in rice and
is virtually indigestible by humans or non-ruminant livestock and hampers
the nutritional value of rice and its milling by-product rice bran (Larson et
al., 2000). Silicon dioxide includes both naturally occurring which is
crystalline and synthetic silicas which is amorphous. As a direct use, it
can be naturally present / added directly to food and is currently regulated
under Code of Federal Regulations (CFR) of United States Food and
Drug Administration (USFDA). As per the title 21 part CFR 172.480,
present limit for silicas that may be safely used in food is 2% by weight
of the food (Electronic Code of Federal Regulations, 2012). Consumption
of excess amounts of silica in food may cause thiamine deficiency,
diuresis eating disorders, formation of renal silica calculi and some
nephropathies (European Food Safety Authority, 2004). While phytic
acid is an integral part of rice bran, silica is incorporated in to the bran
through contamination with husk and unhygienic handling/processing of
paddy in the farms and rice milling industries. Stabilized rice bran can be
used as a food supplement provided its lipase enzyme is annihilated,
trypsin inhibitor, phytic acid and silica contents are not beyond deleterious
limits.
India is the diabetic capital of the world with 62.4 million and 77.2
million Indian population suffering from diabetes and pre-diabetes
(impaired fasting glucose and/or impaired glucose tolerence) (Indian
Council of Medical Research-India Diabetes study-ICMR-INDIAB, 2011).
Diabetic and prediabetic patients should consume low glycemic index
foods (foods that have slow digestion and absorption rates in the body,
causing a gradual and sustained release of sugar into the blood, which
reduces the chances of developing diabetes) (National Institute of
Diabetes and Digestive and Kidney Diseases, http://www.nlm.nih.gov,
2012). Rice bran is having a very low glycemic index as compared to
white rice flour, hence incorporation of stabilized rice bran having low
silica and phytic acid to commercial white rice flour would bring down the
glycemic index of white rice flour to be used for traditional Indian foods like
roti, dosa (toasted rice pan cake) and idli (steamed rice cake). With this
background, the present work was carried out with the objective to
prepare full fat stabilized rice bran with low silica and phytic acid contents
for incorporation into white rice flour and/or to be used as a food
supplement.
EXPERIMENTAL PROCEDURES
Materials
Indian variety paddy namely, Sona-Masoori was procured from the local
market of Mysore. Fresh commercial rice bran (CRB) as control bran
was also procured from a local rice milling industry. Standard α-
tocopherol, cholesterol, sodium phytate, D-glucose, trypsin, tris
(hydroxymethyl aminomethane) and BAPA were procured from Sigma
51 BEVERAGE & FOOD WORLD - Vol. 41 - No 1 - JANUARY 2014
Fig.1. Flow sheet for the preparation of low silica stabilized rice bran
Fig.2. Flow sheet for production of rice bran by two step milling process
Chemical Co., St. Louis, USA. Hexane (boiling range 65-67 °C) of
commercial grade was used for the fat extraction. All other chemicals
and reagents used were of analytical grade.
Methods
Washing of Paddy
The paddy was washed under a stream of running water for 5 minutes.
The washing was repeated thrice (Fig.1).
Drying of paddy
The washed paddy was sun dried (35-40 °C) for 4 h. The dried paddy
was packed in polyethylene bags and then the same day, it was taken
for milling (Fig.1).
Milling of Paddy
The paddy was milled by using a 25 Kg capacity two step integrated rice
miller (CFTRI make). The husk obtained was discarded. The brown rice
obtained was subjected to further milling and polishing and fresh bran
was obtained. Fresh bran was transported from rice mill in polyethylene
bags to the laboratory (Fig.2)
STABILIZATION OF RICE BRAN FOR USE AS FOOD SUPPLEMENT
CRB was immediately heat stabilized to arrest the lipase activity and
stabilized bran (SB) was obtained as shown in Figure 1. Briefly, CRB
(100 g) contained 10% moisture. It was treated with 20 ml distilled water
to get a moisture content of 30% and then allowed for equilibration for
1hr at room temperature, followed by drying at 110°C for 5 hrs to get a
moisture content of around 2.0% (Fig.1). The data of commercial rice
bran stabilized in this way is provided in Table 1. After stabilization of
the bran, it was analyzed for moisture and fat content and was stored at
-20 °C for further analysis. The stabilized bran (SB) sample was subjected
to physico-chemical characteristics analysis such as fat and moisture
content and the extracted fat was investigated for oryzanol, tocopherols,
and phytosterols.
Incorporation of Rice Bran to Rice Flour
Commercial white rice (polished rice) was finely ground by electrical
grinder and rice flour (RF) was obtained. The RF was mixed with SB
and CRB in different proportions and various mixtures were obtained,
i.e., 75% RF + 25% CRB; 50% RF + 50% CRB; 75% RF+ 25% SB; 50%
RF + 50% SB (Fig.1).
Proximate Composition
The moisture content of RF, CRB and SB was determined by oven drying
the sample at 105 °C for 4 h and expressed as g/100 g bran/flour,
according to AOCS Method No: Ai 2-75 (11). The fat content of RF, CRB
and SB was determined by Soxhlet’s extraction method. Percent nitrogen
content of RF, CRB and SB was determined by Kjeldahl method and
multiplied by a factor of 6.25 to obtain crude protein and expressed as g/
100 g bran/flour (AOAC, 2000). The total ash content was determined by
incineration and ashing in a muffle furnace at 550 °C for 6 h. Calculations
were done gravimetrically and total ash content expressed as g/100 g of
either bran or on flour basis (AOAC, 2000). Total carbohydrates was
calculated by the difference in total dry matter. All the analyses were done
in triplicate and the mean values ± standard deviation are provided.
Acid soluble and Insoluble Ash
The total ash of CRB and SB obtained after ashing in muffle furnace
was dissolved in 2N hydrochloric acid (HCl). The part of total ash which
dissolved in HCl was considered as acid soluble ash (minerals ash) while
the part of total ash insoluble in HCl was considered as acid insoluble
ash (silica). Calculations were done gravimetrically and acid soluble ash
(mineral ash) and acid insoluble ash (silica) contents expressed as g/
100 g of either bran or on flour basis (AOAC, 2000).
Phytic Acid Content
Phytic acid contents of RF, CRB and SB and their mixtures was
determined according to Gao et al., 2007. Briefly, Samples of 0.50 g of
ground powder were thoroughly mixed with 10 mL of 2.4% HCl. Sample
tubes were shaken at 220 rpm for 16 h in a incubator shaker and
centrifuged at 1000 g at 10 °C for 20 min. The crude extracts were used
for determination of phytic acid by the modified colorimetric (Wade
reagent) method according to Gao et al., (2007) by reading the
absorbance of sample and standard sodium phytate (Sigma, St. Louis,
MO) at 500 nm (UV-1601, Shimadzu) and expressed as mg/100 g bran.
Reducing Sugars Content
Reducing sugars content of RF, CRB and SB and their mixtures was
determined according to Goni et al., 1996. Briefly, available starch/
carbohydrates in the sample was hydrolyzed by using digestive enzymes
and final hydrolyzed derivative was estimated for reducing sugars by
DNS method. D-glucose (Sigma, St. Louis, MO) was used as the standard
and the standard curve was plotted by reading the absorbance of different
concentrations of D-glucose at 540 nm (UV-1601, Shimadzu) and
expressed as mg/100 g bran.
Trypsin Inhibitors
Trypsin inhibitors content (TI) in RF, CRB and SB and their mixtures
was determined according to the modified AACC procedure by
Hamerstrand et al., 1981. Briefly, sample was extracted with 0.01N
NaOH. Aliquot (2 ml) of the extract was mixed with 2 ml of trypsin solution
(0.0040 g trypsin dissolved in 200 ml of 0.001 N HCl) and incubated at
37°C for 10 min. To the above solution, a 5 ml of BAPA solution {0.080
g of BAPA dissolved in 2 ml of dimethyl sulfoxide and made up the
52 BEVERAGE & FOOD WORLD - Vol. 41 - No 1 - JANUARY 2014
TABLE 2 Proximate and Nutraceutical Composition of Rice Bran
Parameters Rice Flour Stabilized Commercial Rice bran
Rice bran (SB) (Control) (CRB)
Moisture 5.0 (0.2)a2.0 (0.1)b8.0 (0.3)c
(g /100 g bran)
Fat (g /100 g bran) 0.5 (0.05)a15.9 (0.6)b16.0 (0.4)c
Free Fatty acids —7.5 (0.3)a0.8 (0.2)a8.0 (0.4)a0.8 (0.2)a8.0 (0.3)a
value g/100 g bran
Protein (g /100 g bran)
Total Carbohydrates 85.0 (1.2)a66.0 (1.2)b56.0 (0.9)c
(g /100 g bran)
Total Ash 2.0 (0.08)a7.3 (0.4)b11.2 (0.5)c
(g /100 g bran)
Acid insoluble 0.99 (0.09)a4.85 (0.3)b
ash (Silica)
(g /100 g bran)
Acid soluble 6.30 (0.3)a6.35 (0.6)a
ash (Minerals
Ash) (g /100 g bran)
Oryzanol 359 (2.5)a339 (3.0)b
(mg /100 g bran)
Phytosterols 81 (0.5)a77 (1.5)a
(mg /100 g bran)
Tocopherols 31 (0.2)a28 (0.5)a
(mg /100 g bran)
Values in parenthesis are standard deviation of the mean values (n=6) reported.
Values in the rows followed by different alphabetical superscripts are significantly
different at p d” 0.05.
The FFA content of stabilized rice bran was 0.2 g / 100 g over a period of 12 months at
room temperature.
volume to 200 ml with Tris buffer (1.21 g of hydroxymethyl aminomethane
and 0.59 g of CaCl2.2H2O, dissolved in 180 ml of distilled water, pH
adjusted to 8.2 and made upto 200 ml with distilled water)}. The contents
were vortexed and incubated at 37 °C for 10 min. The reaction was
ceased by addition of 1 ml of 30% acetic acid. The absorbance of the
solution was measured at 410 nm (UV-1601, Shimadzu) against the
blank solution (2 ml of distilled water instead of extract aliquot). The
absorbance of sample was subtracted from the absorbance of trypsin
standard and the trypsin inhibitor content was calculated by using the
formula: TI, mg/g of sample = ({differential absorbance / 0.019 x 1.000}
x dilution factor).
Tocopherols Determination
The tocopherols content was determined in the extracted oil from CRB
and SB in triplicate by using AOCS O.M. no. Ce 8-89 (Firestone, 1998)
by HPLC, model LC-10 AVP Shimadzu Corp., Kyoto, Japan, fitted with
silica column, CLC-SIL(M) 250 mm x 4.6 mm i.d., Shimadzu Corporation,
Kyoto, Japan and flourescence detector. The mobile phase was hexane-
isopropanol (99.5:0.5) at a flow rate of 1ml/min and excitation wavelength
of 290 nm and emission wavelength of 330 nm. Standard α-tocopherol
(Sigma, St. Louis, MO) was taken as the reference standard. The
individual tocopherol isomers were calculated on fat basis and expressed
as α-tocopherol as mg/100 g bran.
Oryzanol
The oryzanol content was determined in the extracted oil from CRB and
SB in triplicate by using spectrophotometric method (Gopala Krishna et
al., 2001) by dissolving 0.01 g of the sample in 10 ml of hexane and
reading the absorbance at 314 nm in a 1cm cell (double beam uv-visible
recording spectrophotometer model UV-1601, Shimadzu corporation,
Kyoto, Japan). Triplicate samples were used for the determination.
Oryzanol content (mg/100 g bran) was calculated by using the formula:
((A / W) x (100 / 358.9)); Where, A = absorbance of the sample, W =
weight of the sample in gram / 100 ml, 358.9 = E1%1cm for oryzanol. The
oryzanol content of the oil samples were expressed as mg/100 g bran.
Phytosterols
The sterol content was determined in the extracted oil from CRB and SB
in triplicate by using spectrophotometric method according to Raja Rajan
& Gopala Krishna, 2009. Briefly, the phytosterol concentration in the
sample was quantitated from a standard curve generated with 10%
solution of standard cholesterol (Sigma, St. Louis, MO) in groundnut oil
read at 490 nm (UV-1601, Shimadzu) and expressed as total phytosterol
content as mg/100 g bran.
Statistical Analysis
All samples were taken in triplicate and analysis carried out in duplicate
making six determinations and mean ± standard deviation value reported.
The data were analyzed using the statistical program - GraphPad InStat
Demo- (DATASET1.ISD). The two-tailed p value was determined to show
the significant changes. A significant change was considered only when
the p value 0.05.
RESULTS AND DISCUSSION
Figure 1 provides the experimental plan of the study. The objective of the
study was to prepare full fat stabilized rice bran with low silica, phytic acid
and trypsin inhibitor contents for incorporation into white rice flour and/or
to be used as a food supplement.
Figure 2 illustrates the milling details of the paddy used in the study.
The paddy cultivar Sona-Masoori was used for milling in a 25 Kg capacity
two step integrated rice miller (CFTRI make). Dehulling of paddy yielded
18.7% and 79.3% of hulls and brown rice respectively, which agreed well
with the literature reports (Houston, 1972; Juliano, 1972). The polishing
of brown rice yielded rice bran (8.7% paddy basis and 10.9% brown rice
basis) and white rice (69.3% paddy basis and 89.4% brown rice basis).
The yield values obtained in the present study for brown rice polishing
agreed well with the literature reports (Houston, 1972; Juliano, 1972).
Table 1 shows the characteristics of the bran and FFA content of the
oil of treated Rice bran (100:30) with water and dried at 110 °C, packed
in polyethylene pouches and stored at ambient temperature and humidity
(27 °C & 65% RH). The rice bran must be stabilized immediately upon
production. Otherwise, the FFA level in the bran will increase during
storage and it mainly depends on the moisture content and lipase present
in the rice bran. The one way to arrest the activity of enzyme is to
deactivate the enzyme by heat treatment, but the activity is not completely
arrested. In the present study the deactivation of rice bran is carried out
TABLE 1 Characteristics of Rice Bran and FFA content of the Oil of Rice Bran treated
(100:30) with water and dried at 110 °C, packed in Polyethylene Pouches
and stored at Ambient Temperature and Humidity (27 °C & 65% RH)
0 Days 36 Days 160 Days 485 Days
MoistureaFataFFAaFataFFAaMoistureaFataFFAaFFAa
I (3h dried) 4.1 17.22 4.34 17.27 4.78 4.15 17.69 5.1 5.5
II (4h and 3.46 16.08 4.25 17.97 3.94 3.43 17.06 4.6 4.85
30 min dried)
III (5h dried) 2.23 17.95 4.07 17.76 3.94 2.78 17.48 4.9 5.1
Values reported are the mean values of six determinations (n=6).
a The content of moisture, fat and FFA were expressed as, % as is basis, % on dry
basis and % on fat basis respectively.
by mixing rice bran with water in the ratio of 100:30 (w/w) and dried at
110 °C for 3 to 5 hrs. The dried bran was analysed for moisture, fat and
FFA contents at different storage periods. The results show that the
moisture content depends on the drying period and ranges from 2.23%
for 5h dried to 4.1% for 3 h dried samples. During the storage of 160
days, the moisture content did not increase significantly (2.78% to 4.15
%). The fat content of the samples showed that there is no significant
change during storage. The initial FFA of content of the oil extracted
from bran showed 4.07% to 4.34% and during the storage of 485 days
showed the FFA was 4.85% to 5.5%. This shows that the present
treatment is effective in stabilizing the rice bran which helps to store the
rice bran for prolonged periods without increase in its FFA content
indicating stabilization of rice bran.
Table 2 shows the proximate and nutraceutical composition of rice
flour (RF), stabilized bran (SB) and commercial rice bran (CRB) (control
bran). RF, SB and CRB contained moisture, 5, 2, 8 g / 100 g bran; fat, 0.5,
15.9, 16.0 g / 100 g bran; protein, 7.5, 8.0, 8.0 g / 100 g bran; total
carbohydrates, 85, 66, 56 g / 100 g bran and total ash, 2.0, 7.3, 11.2 g /
100 g bran, respectively. The moisture, fat, total carbohydrates and total
ash contents of RF, SB and CRB were found to be significantly different
(p 0.05), however the protein content was almost equal and not
significantly different (p0.05). The results agreed well with the literature
reports (Houston, 1972; Juliano, 1972). Acid insoluble ash (silica) content
53 BEVERAGE & FOOD WORLD - Vol. 41 - No 1 - JANUARY 2014
TABLE 3 Phytic acid, Reducing Sugar and Trypsin Inhibitor Contents of the Flour,
Bran and their mixtures
Samples Phytic Total Trypsin Reducing
Acid (g / 100 g) Inhibitors(mg / 100 g Sugar Conten
Defatted Flour) (mg / 100 g)
Stabilized Bran (SB) 3.40 (0.35)a198.4 (2.5)a34 (0.55)a
Commercial Rice 4.65 (0.55)b190.6 (1.8)a35 (0.80)a
Bran (Control) (CRB)
Rice Flour (RF) 0.25 (0.02)c35.9 (0.6)b85 (0.75)b
RF 75% + CRB 25% 0.84 (0.05)d74.4 (0.8)c78 (1.05)c
RF 50% + CRB 50% 1.47 (0.06)e112.9 (1.2)d62 (0.40)d
RF 75% + SB 25% 0.77 (0.03)d76.5 (0.5)c80 (0.65)e
RF50% + SB 50% 1.35 (0.08)e116.9 (1.3)d68 (1.10)f
Values in parenthesis are standard deviation of the mean values (n=6) reported.
Values in the columns followed by different alphabetical superscripts are significantly
different at p 0.05.
of SB (0.99 g / 100 g bran) was very significantly reduced (p 0.01) as
compared to CRB (4.85 g / 100 g bran). This was achieved due to the
washing treatment given to paddy prior to milling. Despite the reduction
in total ash and acid insoluble ash contents of SB as compared to CRB,
the acid soluble ash (mineral ash) of SB and CRB remained equal (6.30
and 6.35 g / 100 g bran, respectively). The oryzanol, tocopherols and
phytosterols contents (determined on fat basis) of SB were 359, 81, 31
mg / 100 g bran and were found to be slightly higher than those of CRB
(339, 77, 28 mg / 100 g bran), however only oryzanol content of SB was
found to be significantly higher (p 0.05) than that of CRB.
Table 3 shows the phytic acid and reducing sugar contents of RF, SB
and CRB. Phytic acid content of SB (3.4 g / 100 g bran) was found to be
significantly lesser (p 0.05) than that of CRB (4.65 g / 100 g bran),
however RF contained the least amount of phytic acid (0.25 g / 100 g
bran). The phytic acid contents of the products formulated out of RF, SB
and CRB were found to be within the range of 0.77-1.47 g / 100 g bran.
Trypsin inhibitor content of SB (198.4 mg / 100 g bran) was found to be
equal to that of CRB (190.6 mg / 100 g bran). RF contained the least
amount of trypsin inhibitors (35.9 mg / 100 g bran). The trypsin inhibitor
contents of the products formulated out of RF, SB and CRB were found
to be within the range of 74.4-116.9 mg / 100 g bran. The reducing sugar
content of SB and CRB was almost equal (34 and 35 mg / 100 g bran,
respectively) and significantly much lower (p0.005) to that of RF (85 mg
/ 100 g bran). Foods containing high reducing sugars content have
generally high glycemic index. The reducing monosaccharides like
glucose, galactose and disaccharides like lactose, maltose, have the
tendency to assimilate quickly and release energy rapidly as compared
to non-reducing sugars like, sucrose and trehalose. The high reducing
sugar content of RF indicates its high glycemic index which may provide
adverse effect on diabetic and prediabetic patients on consumption.
Keeping this in view, the products prepared out of RF, SB and CRB were
found to contain reducing sugars within the range of 62-80 mg / 100 g bran
and provided an improvement over RF.
Full fat stabilized rice bran can be used as a food supplement provided
its lipase enzyme is annihilated and its silica, phytic acid and trypsin
inhibitor contents are not beyond deleterious limits. Incorporation of
stabilized rice bran having low silica, phytic acid and trypsin inhibitors to
commercial white rice flour would bring down the glycemic index of white
rice flour to be used for traditional Indian foods like roti, dosa (toasted rice
pan cake) and idli (steamed rice cake). However, a slight bitter after taste
was observed in roti prepared using rice flour fortified with bran. The
products prepared in this study may provide health benefits to the general
consumers and particularly to diabetic and prediabetic patients.
ACKNOWLEDGEMENTS
The authors thank Prof. Ram Rajasekharan, Director, and previous
Directors Dr. V. Prakash and Dr. G. Venkateshwara Rao, CFTRI, Mysore,
for providing infrastructural facilities. The authors thank Mr. Sathyendra
Rao, GST Dept., for helping in milling of paddy to prepare rice bran.
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Chapter
Rough rice, or paddy, consists of a white starchy endosperm kernel surrounded by a tightly adhering bran coat, an adhering germ with the total enclosed within a loose outer hull or husk. All rice is milled before consumption, producing hull, bran, germ, and white rice. Although a small amount of rice is consumed as brown rice, which still contains the bran and germ, white rice is the principal food staple of over 2.5 billion people worldwide.
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Experimental evidence obtained from physical, thermal and nutritional studies have shown that microwave heating is an effective method for the inactivation of lipase that is responsible for rice bran degradation and instability. Rice bran, stabilized by microwave heating at 2450MHz for 3 min was found to be stable for up to four weeks in storage. Free fatty acid (FFA) content of microwave stabilized bran increased from 4.0% to 4.9% in long grain rice bran and from 4.6% too 6.25% in medium grain rice bran, even when stored under unfavorable storage conditions (33°±2°C, 75±5% relative humidity). In contrast, increases in the untreated bran FFA ranged from 4.0% to 68.3% and 4.6% to 56.8% in long and medium grain bran, respectively.
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An extrusion cooking procedure was developed which produces stabie rice bran which shows no significant increase in free fatty acid content for at least 30–60 days. In the optimum process, 500 kg/hr of 12 - 13% moisture bran was extruded at 130°C and held 3 min at 97 - 99°C before cooling. Stabilized bran contained 6 - 7% moisture and was in the form of small flakes with 88% larger than 0.7 mm (25 mesh). Energy required to extrude the bran was 0.07 - 0.08 kW-hr/lcg bran, and wear on the extrusion surface indicated a life of 500 hr for the cone and 1000 - 2000 hr for other wearing parts.
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A new simple chemical method for stabilization of rice bran is described. The process, based on the principle that lipase activity will be low at low pH, uses hydrochloric acid at 40 l/ton of bran for lowering the pH of rice bran from 6.9–6.0 to 4.0. The acid can be applied easily by sprinkling or spraying. The operation on small lots can be done by hand mixing of bran, but it is more efficient and effective if mechanical mixing, like a rotary or a trough mixer, is used. This simple method, which takes less than 4 min for a batch of 15 kg, will be useful for stabilization of rice bran in rice mills or where steam or electricity is unavailable. The process is being evaluated in commercial trials.