Physical, physicochemical and nutritional characteristics of Bhoja chaul, a traditional ready-to-eat...

Food Chemistry xxx (2014) xxx–xxx

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Food Chemistry

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Physical, physicochemical and nutritional characteristics of Bhoja chaul,a traditional ready-to-eat dry heat parboiled rice product processed byan improvised soaking technique

http://dx.doi.org/10.1016/j.foodchem.2014.10.1440308-8146/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +91 3712 275702; fax: +91 3712 267005.E-mail address: [email protected] (C.L. Mahanta).

Please cite this article in press as: Dutta, H., et al. Physical, physicochemical and nutritional characteristics of Bhoja chaul, a traditional ready-to-heat parboiled rice product processed by an improvised soaking technique. Food Chemistry (2014), http://dx.doi.org/10.1016/j.foodchem.2014.10

Himjyoti Dutta a, Charu Lata Mahanta a,⇑, Vasudeva Singh b, Barnali Baruah Das c, Narzu Rahman c

a Department of Food Engineering and Technology, School of Engineering, Tezpur University, Assam, Indiab Department of Grain Science and Technology, Central Food Technological Research Institute, Mysore, Indiac Department of Food and Nutrition, Assam Agricultural University, Jorhat, India

a r t i c l e i n f o

Article history:Available online xxxx

Keywords:Rice productReady-to-eatDry heat parboilingTPAStarch digestibilityResistant starch

a b s t r a c t

Bhoja chaul is a traditional whole rice product processed by the dry heat parboiling technique of lowamylose/waxy paddy that is eaten after soaking in water and requires no cooking. The essential stepsin Bhoja chaul making are soaking paddy in water, roasting with sand, drying and milling. In this study,the product was prepared from a low amylose variety and a waxy rice variety by an improvised labora-tory scale technique. Bhoja chaul prepared in the laboratory by this technique was studied for physical,physicochemical, and textural properties. Improvised method shortened the processing time and gavea product with good textural characteristics. Shape of the rice kernels became bolder on processing.RVA studies and DSC endotherms suggested molecular damage and amylose–lipid complex formationby the linear B-chains of amylopectin, respectively. X-ray diffractography indicated formation of partialB-type pattern. Shifting of the crystalline region of the XRD curve towards lower values of Bragg’s anglewas attributed to the overall increase in inter-planar spacing of the crystalline lamellae. Resistant starchwas negligible. Bhoja chaul may be useful for children and people with poor state of digestibility.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Rice (Oryza sativa L.) is parboiled to bring about desirableproperties for consumption as staple food (Bhattacharya, 1985).Parboiling often involves soaking of paddy in water followed bysteaming, drying, and milling. Bhattacharya (1985) however hasspecifically termed this as the conventional parboiling processwhile a process where steaming is carried out under elevated pres-sure has been termed as pressure parboiling. A third technique,called dry heat parboiling involves conduction heating of fullysoaked paddy at high temperature for shorter durations using sandor hot air. This method with variations in the processing conditionsis generally used for making certain speciality rice products(Mahanta & Bhattacharya, 2010; Mahanta & Goswami, 2002).While steam parboiling causes starch gelatinisation during steam-ing followed by retrogradation during prolonged drying, gelatinisa-tion and simultaneous rapid loss of water from the paddy occursduring dry heat parboiling which does not allow retrogradationto occur (Ali & Bhattacharya, 1976; Mahanta & Bhattacharya,

2010). This results in development of certain peculiar propertiesin parboiled rice.

Assam, a state in India, produces rice varieties with wide rangeof apparent amylose content (Bhattacharya, Sowbhagya, &Indudhara Swamy, 1980). While the high and intermediate amy-lose varieties are consumed as staple foods throughout the state,the low amylose and waxy varieties are often processed into spe-ciality products (Mahanta & Goswami, 2002). Ready-to-eat (RTE)rice products have gained much popularity in the last few decadesdue to the ease of cooking and fuel economy. Bhoja chaul is apopular RTE product of Assam. The traditional product is conven-tionally processed by soaking low amylose or waxy paddy in waterat room temperature for 3–4 days for maximum hydration. Thesoak-water along with soaked paddy is brought to a boil and boiledfor 6–8 min for enhanced hydration. The water is drained and thepaddy is roasted in an iron vessel over wood fire with constant stir-ring. The roasting temperature is controlled by the intensity of thewood fire and is stopped when the grains sufficiently dry up. Theroasted paddy is then spread over mud floor to cool before millingin a dheki (a foot pounding machine) to get the product. Theprepared Bhoja chaul is soaked in water at room temperature priorto consumption to let it hydrate sufficiently to a softer and some-what sticky texture. After squeezing out the water, the chaul is

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2 H. Dutta et al. / Food Chemistry xxx (2014) xxx–xxx

eaten with milk, cream, curd and jaggery. The roasted aroma,colour, and sticky as well as chewy texture of Bhoja chaul are con-sidered to be its desirable characteristics by the rural householdprocessors. There is no cooking involved. As per the traditionalfood processors, extensive hydration of the soaked paddy followedby extensive roasting without allowing puffing yields high qualityBhoja chaul. This peculiar characteristic of low amylose and waxyvarieties subjected to dry heat parboiling has never been discussedbefore (Bhattacharya, 2011). Improved parboiling techniquesinvolving soaking of paddy in boiling water is practiced in ruralhouseholds of Assam for making parboiled rice products (Dutta &Mahanta, 2014a). This minimises the microbial and enzymaticspoilage of the paddy that occurs on prolonged soaking and alsoaccelerates the rate of water uptake, thereby improves the timeefficiency of the parboiling processes and product safety (KaddusMiah, Haque, Douglass, & Clarke, 2002a, 2002b). Soaking in boilingwater for 1–3 min had been successfully used and studied for mak-ing other important traditional ready-to-eat rice products (Dutta &Mahanta, 2014a, 2014b). Apart from soaking, the other steps ofconventional parboiling have also been improvised. For example,in the last few decades, high pressure steaming and mechanicalroasting using electrically operated specialised machineries havebeen preferred over open steaming and sand roasting using woodfire (Kim et al., 2002; Unnikrishnan & Bhattacharya, 1987). Moderndrying techniques are also being studied for efficient drying ofparboiled paddy (Jittanit, Saeteaw, & Charoenchaisri, 2010).

RVA is important for analysing the cooking behaviour that pri-marily decides their targeted use in processed food systems (Sun,Han, Wang, & Xiong, 2014). XRD and DSC give the idea of molecularstructures and their arrangement in a complex polymeric foodmaterial (Ambigaipalan, Hoover, Donner, & Liu, 2014). TPA is usedas a mechanical tool to simulate the sensory attributes of cookedrice that are perceived subjectively (Szczesniak, 2002).

Digestibility is one of the primary factors for determining thenutritional status of the starchy foods (Englyst, Kingman, &Cummings, 1992; Goni, Garcia-Alonso, & Saura-Calixto, 1996;Kawai, Matusaki, Hando, & Hagura, 2013) Mujoo, Chandrasekhar,and Ali (1998) suggested that gelatinised starch in dry heatparboiled rice is more susceptible to enzymatic digestion. Contraryto this, Chitra, Singh, and Ali (2010) worked on in vitro starchdigestibility of three sand roasted rice products and reported for-mation of resistant starch which passes the human digestive tractunhydrolysed (Englyst et al., 1992). The present study aimed atusing an improvised laboratory-scale dry heat parboiling processfor making RTE Bhoja chaul (essentially a dry heat parboiled riceproduct) from a low amylose rice and a waxy rice and characterisethe product for its physical, physicochemical and nutritionalproperties.

2. Materials and methods

Kola chokua as a low amylose variety and Aghoni bora as a waxyvariety were taken for the study. Paddy of both varieties was fromthe recent harvest of 2012 and purchased from local farmers ofJorhat district, Assam. Kola chokua and Aghoni bora contained12.6% and 1.15% (db) apparent amylose contents (Dutta &Mahanta, 2012; Juliano, 1979), respectively. The samples werestored at 4 �C for further use. Enzymes and D-glucose standardswere procured from Sigma–Aldrich (St. Louis, MO, U.S.A.).

2.1. Processing and coding of samples

As the normal process of dry heat parboiling mentioned byBhattacharya (1985) gave Bhoja chaul that had raw rice texturewhile eating (unpublished) due to low moisture absorption on

Please cite this article in press as: Dutta, H., et al. Physical, physicochemical aheat parboiled rice product processed by an improvised soaking technique. Fo

soaking, an improvised method of soaking was developed in thelaboratory. Table 1 gives an idea of the enhanced hydration capac-ity of the paddy subjected to the improvised soaking method.Briefly, 200 g paddy was brought to room temperature and keptfor 5 h. The paddy was then added to 3 L of water at 100 �C in a ves-sel kept over flame with continuous stirring for 1 and 3 min. Suchhot soaking resulted in higher absorption of water by the paddywithin a short soaking duration as was reported elsewhere(Dutta & Mahanta, 2014a) and thereby allowed for extensive starchgelatinisation in the kernel. The vessel was then removed from theflame, immediately covered with a 1 cm thick gunny bag to pre-vent rapid cooling and kept at room temperature (25 ± 2 �C) for18 h. Kola chokua and Aghoni bora attained moisture content above36% (wb) against �30% moisture that would have been attainedwithout the 1 or 3 min boiling steps as revealed by trials in our lab-oratory. The excess water was then decanted and the hydratedpaddy was roasted with hot sand in a drum type roaster (1:3 paddyto sand). The sand particles (less than 3 mm in diameter) were pre-heated to temperatures of 220 �C which came down to 140 �C afteraddition of the paddy (determined from repeated trials) and wascontrolled as such throughout the roasting time by wrapping thedrum of the roaster with a moistened piece of gunny bag (1 cmthick). Sand roasting allowed for rapid gelanisation and simulta-neous drying of the gelatinised starch. The roaster had an internalrotatable shaft which was operated at 110–120 rpm for maximumheat distribution throughout the paddy mass. The paddy sampleswere roasted for 11, 13 and 15 min. The roasted paddy hadmoisture content between 11% and 12% (wb) as was determinedimmediately after roasting. The roasted samples were then cooledat room temperature for 6 h and milled (8–10% milling, w/w) in aSatake dehusker and a polisher (Satake, Japan). A portion of eachsample was ground into flour in a laboratory grain mill (FritschPulverisette 14, Germany) and passed through a 100 lm sieve.All the samples were stored in polypropylene bags at 4 �C until fur-ther analyses were carried out. For ease of identification, the ricevarieties were coded as LK meaning low amylose Kola chokuaand WA meaning Aghoni bora. LK and WA suffixed with (N) indi-cated raw rice. The variety code was suffixed with time of boilingprior to overnight soaking and time of roasting to identify the pro-cessed samples. Thus, LK-1–11 indicated low amylose Kola chokuaboiled for 1 min prior to overnight soaking followed by roasting at140 �C for 11 min.

2.2. Grain colour

The CIE (International Commission on Illumination) L⁄a⁄b⁄

colour values of all flour samples were obtained by a colourmeasurement spectrophotometer (Hunter Colour-Lab UltrascanVis, US). The results for L⁄ (lightness), a⁄ (red–green), and b⁄

(yellow–blue) values were used to calculate the correspondinghue angle (H⁄) and chroma (C⁄) values (Falade & Onyeoziri, 2010)using the relations.

H� ¼ tan�1ðb�=a�Þ ð1Þ

C� ¼ ½ða�Þ2 þ ðb�Þ2�1=2

ð2Þ

2.3. L/B ratio, kernel hardness and head rice yield

The length (L) and breadth at the midpoint (B) of the polishedkernels were determined using a Seed dial calliper (Baker, India)and the L/B ratio was calculated. Kernel hardness (H) was testedin a Texture Analyzer (TA.HD.plus, Stable Micro Systems, UK) witha 25 kg load cell by using a single compression test with a 2 cmdiameter stainless steel probe along the kernel thickness at a speed

nd nutritional characteristics of Bhoja chaul, a traditional ready-to-eat dryod Chemistry (2014), http://dx.doi.org/10.1016/j.foodchem.2014.10.144


Table 1Effect of soaking on the moisture level in the paddy.

Improvised laboratory soaking process Traditional process

Stages of processing Moisture content(%, wb)

Stages of processing Moisture content(%, wb)

Raw paddy 12 Raw paddy 12Paddy soaked overnight in water brought to boil and removed from flame 32.6 Paddy soaked at RT for 3 days 31.3Paddy added to boiling water, cooked for 1 min and allowed to soak

overnight in water after removal from flame37.3 Soaked paddy boiled for 8 min

on 4th day35.8

Paddy added to boiling water, cooked for 3 min and allowed to soakovernight in water after removal from flame

41.6 – –

H. Dutta et al. / Food Chemistry xxx (2014) xxx–xxx 3

of 0.5 mm/min followed by return to its original position (Dutta &Mahanta, 2014). The test was repeated for 20 kernels from eachsample and the mean was calculated. The maximum force (inNewton) indicated by the force–time curve generated by theinbuilt software (Exponent Lite) was taken as the hardness (H).Head rice yield (HRY) was determined as the percentage weightof intact kernels obtained after milling to that of total milled rice.

2.4. Porosity

For porosity (e, %) determination, bulk density (qb), and truedensity (qt) were first determined. For qb determination, polishedgrains were allowed to fall into a measuring cylinder from a con-stant height up to a known volume. The top level was adjustedby gentle tapping. The weight of the filled grains was determinedand qb was calculated from the relation:

qb ðg=cm3Þ ¼mass of grain=volume occupied ð3Þ

qt was determined by the solvent displacement method. Pol-ished kernels of known weight were immersed in a known volumeof kerosene taken in a measuring cylinder. The cylinder was gentlyagitated to release any possible air gap. The volume of kerosenedisplaced by the kernels was then recorded and the density (qt)was calculated by the relation:

qt ðg=cm3Þ ¼mass of grain=volume of kerosene displaced ð4Þ

The porosity (e) was determined from Eqs. (3) and (4) by therelation:

e ð%Þ ¼ ½ðqt � qbÞ=qt� � 100 ð5Þ

2.5. Equilibrium moisture content on soaking at room temperature

The method of Indudhara Swamy, Ali, and Bhattacharya (1971)was used to determine the Equilibrium moisture content (EMC-S%,db). Briefly, polished rice kernels were soaked at room temperaturefor 4 h. The excess water was decanted and the surface moisturefrom the kernels was removed with a piece of blotting paper. Themoisture content was then estimated (AOAC, 2000). EMC-S wascalculated from the following equation:

EMC � S ð%;dbÞ ¼ ½Moisture contentðgÞ=Dried weight of kernelsðgÞ� � 100 ð6Þ

2.6. Sediment volume

The test for sediment volume (SV, mL) gives an indirect indica-tion of the degree of gelatinisation of pregelatinised rice flour(Bhattacharya, 1985). Briefly, 1 g each of the flour samples wastaken in a measuring cylinder and 15 mL of 0.05 N HCl was addedto it with agitation after each 5 min for 1 h. The level of the floursediment was observed after 4 h and was reported as the SV ofthe sample.

Please cite this article in press as: Dutta, H., et al. Physical, physicochemical anheat parboiled rice product processed by an improvised soaking technique. Fo

2.7. Cooking time of raw rice

The objective method of Juliano (1982) was used to determinethe cooking times (in min) of the raw rice samples. Sample weigh-ing 20 g was cooked in 200 mL water at 98 �C on a hot plate. After10 min of cooking, ten kernels were brought out from the middle ofthe cooked mass and pressed between two clean glass slides. Thenumber of translucent kernels were counted and recorded. Thepressing test was repeated after each minute and the time at which90% of the kernels were translucent was considered as the cookingtime of that rice. The cooking times were further used to determinethe texture profiles of cooked raw rice (Section 2.10).

2.8. Pasting properties

Flour sample (12% moisture content w/w; 28 g total weight)was added to 25 mL water and allowed to saturate for 5 min. Theslurry was then held at 50 �C for 1 min, heated from 50 to 95 �Cin 3.45 min, held at 95 �C for 2.40 min followed by cooling to50 �C in 3.45 min and finally holding at 50 �C for 1 min in a RapidViscosity Analyser (RVA Starchmaster2, Newport Scientific Instru-ments, US). The pasting curves obtained were compared and thepasting parameters, namely PV (maximum viscosity during heatingphase); HPV (minimum viscosity at 95 �C); CPV (final viscosity at50 �C); BD (PV � HPV) and SB (CPV � HPV) were recorded.

2.9. X-ray diffraction

An X-ray diffractometer (Rigaku Miniflex, Japan) with a k valueof 1.54 Å, operating at an acceleration potential of 30 kV with15 mA current and a copper target was used to obtain wide angleX-ray diffractograms (XRD) of the flour samples. The scanningrange was 10�–40� of 2h values in steps of 0.05�. The total areaunder the curve and the area under each prominent peak weredetermined and the percentage crystallinity was calculated(Singh, Ali, Somashekar, & Mukherjee, 2006).

% crystallinity ¼ ðarea under peaks=total area under the curveÞ� 100

ð7Þ

Inter-planar space (d) of the crystalline lamellae of starch wascalculated from the Bragg’s equation.

k ¼ 2d sin h ð8Þ

Gaussian fit curves of the diffractograms were obtained usingOrigin 8 software (OriginLab Corporation, US) to study any notablechange in the overall diffraction patterns of the flour samples.

2.10. Differential scanning calorimetry

Flours of raw rice and samples processed for 15 min wereanalysed for their thermal profiles. Saturated flour slurries wereprepared by mixing 4 mg each of sample and deionised water

d nutritional characteristics of Bhoja chaul, a traditional ready-to-eat dryod Chemistry (2014), http://dx.doi.org/10.1016/j.foodchem.2014.10.144


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(1:2 flour to moisture ratio, db) in aluminium pans and keeping for1 h at 4 �C. The pans were then hermetically sealed and heated in aDifferential Scanning Calorimeter (DSC, model DSC-60; Shimadzu,Tokyo, Japan) against an empty reference pan from 30 to 130 �Cat a heating rate of 5 �C/min under N2 atmosphere. The onset(To), peak (Tp), and conclusion (Tc) temperatures and enthalpy ofgelatinisation and/or crystallite melting (DH, J/g) were obtainedfrom the thermograms using the inbuilt TA-60WS software.

2.11. Enzymatic hydrolysis of starch and resistant starch content

The in vitro starch hydrolysis rate of each sample was estimatedby the method of Goni et al. (1996). 50 mg of flour was firstdeproteinised with 0.2 mL of a solution containing 1 g of Pepsinin 10 mL of HCl–KCl buffer (pH 1.5) and incubating at 40 �C for1 h. The volume was then made up to 25 mL with Tris–maleatebuffer (pH 6.9) and 5 mL of a Tris–maleate buffer solution contain-ing 2.6 IU pancreatic a-amylase was added before incubating at37 �C for 180 min. One millilitre aliquot was taken out after each30 min, boiled to inactivate the enzymes and stored under refriger-ation. 3 mL of 0.4 M sodium acetate buffer (pH 4.75) containing60 lL of amyloglucosidase (Sigma–Aldrich) was then added andfurther incubated at 60 �C for 45 min. The glucose liberated wasestimated using a D-glucose oxidase–peroxidase assay kit (Robo-nik, India) and a previously prepared glucose standard curve. Thevalue was converted to starch by multiplying by a factor of 0.9.The total starch content of each sample was calculated by the stan-dard protocol of AOAC (2000) and the degree of hydrolysis (%, db)was calculated as the percentage of starch degraded from eachsample after each time interval.

Degree of hydrolysis ð%Þ¼ ðStarch hydrolysed=Total starch contentÞ�100 ð9Þ

Resistant starch (RS) present in the flour samples was measuredby a method modified from Englyst et al. (1992). Briefly, 100 mgflour was first added to 7 mL acetate buffer (pH 5.2) and incubatedat 37 �C for 20 min in a shaking water bath (Voltam, India). Then,3 mL of an enzyme mixture composed of invertase (220 U/mL),pancreatic a-amylase (3000 U/mL) and amyloglucosidase (15 U/mL) was added and incubated further. Aliquots were taken outafter 20 min and 120 min and measured for rapidly released andslowly released glucose (G20 and G120) respectively using the glu-cose assay kit and standard curve. Rapidly digestible starch (RDS)and slowly digestible starch (SDS) expressed as a percentage ofdry matter were evaluated by the following formulae:

RDS ð%Þ ¼ ½ðG20 � 0:9Þ=TS� � 100 ð10Þ

SDS ð%Þ ¼ ½ðG120 � G20Þ � 0:9� � 100 ð11Þ

As mentioned by Patindol, Guraya, Champagne, Chen, andMcClung (2010), the difference between total starch (TS) and thestarch digested during the incubation period was calculated asresistant starch (RS) and expressed as percentage of dry matter.

RS ð%Þ ¼ ½TS� ðRDSþ SDSÞ� � 100 ð12Þ

Tabl

e2

Colo

urva

lues

and

phys

ical

prop

erti

e

Sam

ples

Col

our

read

ings

L*a

LK(N

)57

.5±

0.34

k2

LK-1

–11

31.0

±1.

21h

2LK

-1–1

325

.3±

0.83

c3

LK-1

–15

21.1

±0.

29b

3LK

-3–1

129

.8±

1.44

f2

LK-3

–13

24.8

±0.

99c

2LK

-3–1

520

.3±

0.39

a2

WA

(N)

66.7

±0.

22l

2W

A-1

–11

33.3

±1.

02j

2W

A-1

–13

30.9

1±

0.69

h3

WA

-1–1

528

.1±

1.12

e3

WA

-3–1

132

.2±

0.92

i2

WA

-3–1

330

.1±

0.12

gh3

WA

-3–1

527

.5±

0.34

d3

*Th

em

ean

sin

each

colu

mn

foll

o

2.12. Texture comparison of cooked rice and the RTE product

The raw LK and WA rice samples were cooked at 100 �C for 18and 16 min respectively, as were their cooking times determinedpreviously (Section 2.5). Processed samples were soaked in waterat room temperature for 20 min as generally practiced in house-holds for Bhoja chaul. Excess water from both was decanted andsurface water soaked out with a blotting paper. The samples werethen subjected to texture profile analysis (TPA). For this, a Texture

Please cite this article in press as: Dutta, H., et al. Physical, physicochemical and nutritional characteristics of Bhoja chaul, a traditional ready-to-eat dryheat parboiled rice product processed by an improvised soaking technique. Food Chemistry (2014), http://dx.doi.org/10.1016/j.foodchem.2014.10.144



Analyzer (TA.HD.plus, Stable Micro Systems, UK) with a 5-kg loadcell fitted with a cylindrical probe of 2 cm diameter was used.The two-cycle compression test involved compressing singlekernels collected from the middle of each sample mass to 70% at0.5 mm/s (Suzuki, 1979). The time between two chews was 3 s.All the TPA parameters, namely hardness, adhesiveness, springi-ness, and chewiness were determined by the inbuilt software(Exponent Lite). Twenty kernels from each sample were testedseparately and average values were taken.

2.13. Statistical analysis

All the experiments were carried out in multiple replicates andthe means are reported. Significant differences between the meanswere analysed by Duncan’s multiple range test at a significancelevel of 0.05 using SPSS 11.5 (SPSS Inc., USA).

3. Results and discussion

3.1. Grain colour

None of the processed samples exhibited formation of whitebelly indicating extensive gelatinisation throughout the kernels.Colour values of rice flour samples are presented in Table 2. Thedecreased lightness value (L⁄) with simultaneous increase in Hue(H⁄) and chroma (C⁄) angle values was indicative of extensive

Fig. 1. (a) Equilibrium moisture content on soaking (%, dry weight basis); (b) sediment vrespectively. The representations of the symbolic RVA curves are as follows: native (( ).


gelatinisation of starch, Maillard browning and uniform distribu-tion of the colour compound (Lamberts et al., 2006). Althoughinward migration of pigments from husk and bran layers into thekernel was proposed by Bhattacharya (1985), Lamberts et al.(2006), it was negated by the work of Lamberts and Delcour(2008) who found that the carotenoids present in the epidermallayers got reduced to trace levels after steam parboiling and hencedo not contribute to the final colour of parboiled rice. The extent ofcolour change after dry heat parboiling that involved higher tem-perature of conduction heating was higher than the colour changein steam parboiled rice as was reported by Dutta and Mahanta(2012). Hence, the colour development in Bhoja chaul may be solelyattributed to Maillard browning reaction as a result of thermalbreakdown of starch.

3.2. L/B ratio, kernel hardness and head rice yield

Values for L/B, H and HRY (%) are given in Table 2. Notablereduction in length with simultaneous increase in breadth resultedin reduction of L/B ratio. The Bhoja chaul samples were hencebolder in shape than the raw rice kernels. This was howevercontradictory to the findings of Sowbhagya, Ali, and Ramesh(1993) who observed increase in length of kernels after parboiling.Varietal difference plays an important role in determining raw andparboiled rice properties. Difference in the gap between the rawkernel and the husk and the shape and size of the kernel and

olume (mL); (c and d) RVA pasting curves of raw and processed LK and WA samples), 1–11 ( ), 1–13 ( ), 1–15 ( ), 3–11 ( ), 3–13 ( ), 3–15



Tabl

e3

RVA

past

ing

para

met

ers

ofra

wan

dpr

oces

sed

sam

ples

.

LK(N

)LK

-1–1

1LK

-1–1

3LK

-1–1

5LK

-3–1

1LK

-3–1

3LK

-3–1

5W

A(N

)W

A-1

–11

WA

-1–1

3W

A-1

–15

WA

-3–1

1W

A-3

–13

PV(c

P)16

87±

3.44

f17

71±

2.98

i24

95±

2.13

m16

64±

2.34

e10

02±

1.26

b24

90±

1.54

l15

28±

2.43

d17

20±

3.92

h22

73±

2.43

k17

01±

3.21

g80

3±

3.69

a19

09±

2.47

j16

74±

1.69

e

HPV

(cP)

1305

±1.

09d

1487

±2.

11e

2100

±1.

56i

1835

±4.

21f

991

±2.

45a

2155

±3.

22j

2079

±3.

11i

1179

±3.

24c

2018

±3.

21h

2192

±2.

12k

1146

±2.

67b

1472

±3.

42e

1198

±2.

47c

CPV

(cP)

2880

±1.

45h

2291

±2.

15e

3141

±3.

25j

2811

±4.

12g

1337

±2.

56a

3462

±2.

64m

3385

±2.

35k

1557

±1.

68b

3426

±2.

02l

3436

±3.

00m

1610

±2.

22c

2495

±3.

13f

2092

±3.

21d

BD(c

P)38

2±

2.12

j28

4±

1.00

h39

5±

2.64

k�

171

±2.

69e

11±

394f

335

±1.

69i

�55

1±

2.64

a54

1±

2.18

n25

5±

0.34

g�

491

±1.

32b

�34

3±

1.38

d43

7±

2.32

l47

6±

1.89

m

SB(c

P)15

75±

1.93

m80

4±

2.19

d10

41±

3.21

h97

6±

2.54

f34

6±

3.12

a13

07±

1.08

k13

06±

2.10

k37

8±

3.45

b14

08±

4.12

l12

44±

1.21

j46

4±

1.45

c10

23±

2.22

g89

4±

3.16

e

The

mea

ns

inea

chro

wfo

llow

edby

aco

mm

onle

tter

are

not

sign

ifica

ntl

ydi

ffer

ent

byD

un

can

’sm

ult

iple

ran

gete

stat

p<

0.05

.


swelling tendency of starch can definitely be considered as majordetermining factors for the shape of the kernel after parboiling.Adding to it, conduction heat from the sand probably causedhigher tension to develop along the horizontal axis of the kernelwhich was more exposed to the heating sand. The L/B ratio andH values were indicative of the fact that no puffing occurred duringthe dry heat parboiling process. Processed kernels were markedlyharder than the raw rice. With increased H, the HRY also increasedindicating development of kernel integrity upon processing.Almost all the kernels were intact in the severely dry heat par-boiled samples. This indicates suitability of the laboratory-scaleprocess for developing into a commercial parboiling method.

3.3. Porosity

Increase in porosity was observed for both the varieties (Table 2)which can be attributed to the change in kernel shape obtainedafter parboiling. Although the changing pattern of the values weresame for both the rice types, porosity was comparatively higher forLK(N) and its Bhoja chaul samples as compared to the WA samples(Ashogbon & Akintayo, 2012) reflecting the effect of size and shape.

3.4. Equilibrium moisture content on soaking at room temperature(EMC-S)

The improvised soaking method in the dry heat parboilingprocess followed to make Bhoja chaul increased the water uptakecapacity of the rice kernels (Bhattacharya, 2011). Processed LKsamples showed lower values of EMC-S than WA samplesprocessed under similar conditions. Unnikrishnan andBhattacharya (1987) also observed a negative correlation betweenamylose content and EMC-S of parboiled rice. EMC-S increased withprocess severity indicating progressively developed water uptakecapacity (Fig. 1a) which is indicative of extensive gelatinisation.The values were hence highest for the WA-1–15 and WA-3–15samples (174.6% and 189.4% respectively). Additionally, consider-ing our previous findings (Dutta & Mahanta, 2012), it can be saidthat waxy varieties attained higher water absorption propertyupon any kind of parboiling.

3.5. Sediment volume

Water absorption in dry heat parboiled rice below its gelatinisa-tion temperature is enhanced due to the gelatinised starch ascompared to steam parboiling (Bhattacharya, 1985) because ofthe lower level of retrograded starch in it (Ali & Bhattacharya,1976). LK(N) and WA(N) exhibited SV values of 2.5 and 2.6 mLrespectively which increased on dry heat parboiling into Bhojachaul (Fig. 1b). The sediment volume increased with increase inprocess severity. The extent of gelatinisation, similar to EMC-S,was hence highest for the severely processed WA-3–15 sampleswith SV of 6.4 mL. Samples with boiling time of 3 min gave higherSV than the 1 min boiled samples for both the varieties. This was inaccordance with the EMC-S and reflected more extensive gelatini-sation of starch in those samples (Chitra et al., 2010). However,comparison of SV values between dry heat parboiled rice flourand steam parboiled rice flour for the same varieties (Dutta &Mahanta, 2014b) revealed that the dry heat parboiled rice flourdid not swell as much as steam parboiled samples. The conductionheating during the roasting process with sand must have produceddextrinised starch that did not have impact on SV.

3.6. Pasting properties

The pasting curves that are indicative of extensive change instarch molecular structure upon roasting are given in Fig. 1 (c

Please cite this article in press as: Dutta, H., et al. Physical, physicochemical and nutritional characteristics of Bhoja chaul, a traditional ready-to-eat dryheat parboiled rice product processed by an improvised soaking technique. Food Chemistry (2014), http://dx.doi.org/10.1016/j.foodchem.2014.10.144



and d) and the values of the pasting parameters are given inTable 3. Processing for 11 and 13 min resulted in increased PV forLK variety. For WA, the rise was only for the samples roasted for11 min. Varavinit, Shobsngob, Varanyanond, Chinachoti, andNaivikul (2003) suggests that the starch granules in waxy rice flourdisrupt more easily on cooking and retrogrades to a lesser extent ascompared to non waxy rice. Processed WA samples were also seento be more resistant to swelling on cooking as was evident fromthe time required to attain PV (Gunaratne & Hoover, 2002).Processed LK samples showed patterns opposite to it. Similarobservations were also earlier reported for open steam parboilingof LK sample (Dutta & Mahanta, 2014b). Besides increased PV,there were distinct BD and SB like those exhibited by raw LK sam-ples. This peculiar change in pasting property of parboiled low

Fig. 2. The XRD patterns of raw and processed flour samples of (a) LK and (b) WA withthermographs of pastes of raw and roasted (for 15 min after hot soaking for 1 and 3 mi


amylose and waxy rice hence requires further research involvingmolecular weight characterisation (Lai & Cheng, 2004; Zhu, Liu,Sang, Gu, & Shi, 2010). Other factors like amylose–lipid complexesand protein (Derycke et al., 2005) also may affect the pasting prop-erties which need further investigation. Increase in viscosity onhydrothermal processing by low amylose and waxy rice varietieswas earlier reported by Biswas and Juliano (1988). On the otherhand, severe processing caused drop in the PV and loss of BD(Dutta & Mahanta, 2014b; Mir & Bosco, 2013) like steam parboiledhigh amylose rice but peculiarly with increased SB for both varie-ties giving an almost continuously rising pasting curve. This maybe attributed to excessive breakdown of amylopectin during thehigh temperature roasting; forming irreversible simpler leachablefractions (Mahanta & Bhattacharya, 1989) that continuously got

insets showing Gaussian fit curves; (c) change in % crystallinity with roasting; DSCn) (d) LK and (e) WA samples.




released into the slurry, making it increasingly thicker and viscous.This property may prove to be useful for the prepared Bhoja chaulpowder to be used as thickening agent in cooked food systems.

3.7. X-ray diffraction

XRD of raw rice samples exhibited A-type starch crystallinepattern with strong peaks at 2h = 15.2, 17.4, 18.1 and 23.3(Fig. 2a and b). Feeble peaks at 2h positions near 20.0 and 22 indi-cating V-type and B-type starch polymorphs were observed in thediffractograms of Bhoja chaul samples. While the amylose–lipidcomplex giving V-type diffraction pattern forms during heatprocessing (Tufvesson, Wahlgren, & Eliasson, 2003), the B-typepolymorphic structures are of retrograded starch (Lamberts,Gomand, Derycke, & Delcour, 2009). Formation of retrogradedstarch despite of insufficient water is however contradictory tothe statement of Bhattacharya (1985). Initiation of formation of

Fig. 3. Enzymatic starch hydrolysis rates of raw and processed (a) LK and (b


these minor structures during cooling and storage of the roastedrice may however be considered responsible for the feeble peaks.In addition to that the minor peak retained at 2h value of 18.1was representative of the native A-type crystalline structure sug-gesting either incomplete gelatinisation or partial recrystallisationinto the native structure. These native starch fractions in the pro-cessed samples may be related to the distinct PV shown in theRVA pasting curves. Superimposition of the diffractograms of thethree basic starch crystalline structures was earlier reported byMahanta, Ali, Bhattacharya, and Mukherjee (1989) and was alsoobserved by us in XRD of steam parboiled rice (Dutta & Mahanta,2012). Gaussian fitting of the diffractograms of the Bhoja chaulsamples (Fig. 2a and b ‘insets’) indicated that the crystalline peakregions of the curves shifted towards lower values of 2h. In LK sam-ples, it shifted from 20.2 (LK-1–11) to 18.4 (LK-1–15) and 18.1 (LK-3–15) and in WA samples the shift was from 20.3 (WA-1–11) to18.8 (WA-1–15) and 19.0 (WA-3–15). This indicated progressive

) WA samples; percentage of (c) RDS, (d) SDS and (e) RS in the samples.




reduction in the average inter-planar space (d) of the crystallinelamellae of starch with process severity (Claver, Zhang, Li, Zhu, &Zhou, 2010) as calculated from the Bragg’s equation.

Moisture acts as a principal factor for inter-chain interaction ofstarch (Zhou, Baik, Wang, & Lim, 2010). Excessive reduction inmoisture during the roasting step may be considered as the prob-able reason behind the development of weaker lamellae in dry heatparboiled rice. This may also be related to the significant loss in%crystallinity of both the rice varieties after processing (Fig. 2c).The loss was marginally greater in processed WA samples as theyattained higher degree of starch gelatinisation.

3.8. Differential scanning calorimetry

DSC thermograms of the native and Bhoja chaul samples arepresented in Fig. 2d and e. While the gelatinisation temperature(Tp) of LK(N) was 79.2 �C, WA(N) exhibited a lower Tp of 71.4 �C.LK-1–15 and LK-3–15 however showed minor peaks at tempera-tures of about 79 �C indicating melting of native starch fractionsin the samples as was also suggested by their pasting curve andXRD spectra. Bhoja chaul samples from waxy rice however didnot show this peak indicating higher loss in native crystallinityas shown in Fig. 2c. Bhoja chaul samples of both the varieties exhib-ited major peaks at 100 ± 10 �C for melting of amylose–lipid com-plexes. Bhoja chaul samples from LK exhibited notably highervalues of DH for amylose–lipid complex melting (57.3 and 56.3 J/g for LK-1–15 and LK-3–15 respectively) than those from WA(52.2 and 50.0 J/g for WA-1–15 and WA-3–15 respectively). Higherapparent amylose content in LK may be attributed for thissignificant difference in crystallite formation. Interestingly, forma-tion of such complexes in samples despite of very little amyloseindicated that there is scope for further research on this aspect of

Fig. 4. TPA parameters of raw and


the product. Murugesan and Bhattacharya (1989) reported signifi-cant formation of the complexes when popped rice was hydratedup to 30% moisture content prior to the DSC analysis as was alsodone here during sample preparation. Iturriaga, Lopez, and Anon(2004) also observed formation of such compounds in waxy ricesamples. It may be proposed that occurrence of long B-chains inthe amylopectin and probable debranching of the same due tothermal treatment led to generation of glycosidic chains capableof starch-lipid complex formation. The present study hence sug-gests that gelatinised starch may form amylose–lipid complexwhen in contact with excess amount of water. No distinct peaksfor melting of retrograded starch (Abd Karim, Norziah, & Seow,2000) were however observed which indicates that the B-typecrystalline polymorph indicated by minor peaks in XRD spectraof the samples were either not detected by the DSC conditions usedor were temporary lamellae that became amorphous once waterwas added for DSC sample preparation.

3.9. Enzymatic hydrolysis of starch and resistant starch content

While starch in waxy WA(N) flour got digested up to 24.3% and71.2% in 30 min and 180 min respectively, starch in low amyloseLK(N) flour was digested up to 21.2% and 63.7% respectively(Fig. 3a and b) during the same period. This was in accordance withthe findings of Zhu, Liu, Wilson, Gu, and Shi (2011). For both thevarieties, hydrolysis rates increased markedly after roasting. Whilemore than 30% of the starch in the processed samples werehydrolysed within 30 min, the moderate and severely roasted sam-ples of both the varieties, namely 1–13, 1–15, 3–13 and 3–15 werehydrolysed up to more than 85% (db) after 180 min of incubation.Gelatinised starch formed during the roasting step becomes moreexposed to favour enzymatic digestion than that from steam

dry heat parboiled samples.




gelatinised starch (Mujoo, Chandrasekhar, & Ali, 1998). Increaseddigestibility was related to damage to amylopectin structures byJaiboon, Prachayawarakorn, Devahastin, Tungtrakul, andSoponronnarit (2011). Gunaratne, Kao, Ratnayaka, Collado, &Corke (2013) reported up to 50% reduction of RS in one rice varietyafter parboiling. The increase in hydrolytic rate was higher for theBhoja chaul samples of WA. Increased digestibility was alsoreflected by the amounts of RDS, SDS and RS contents in the sam-ples (Fig. 3c–e). RDS increased from 67.1% to 95% (db) for raw andprocessed LK and from 66.6% to 95% for WA samples. SDS was lowfor all the Bhoja chaul samples (5.7–9.2%, db). Severely processedsamples did not contain any RS. The results indicated that gelatin-isation, uncoiling and thermal degradation on dry heat parboilingexposed starch to the enzymes used and thereby significantlyenhanced the hydrolysis rate (Mujoo et al., 1998). Bhoja chaul pro-duced by roasting at 140 �C for 15 min can hence be well targetedfor people with poor state of digestibility who require rapid andnon-residual digestion.

3.10. Texture comparison of cooked rice and the RTE product

Values for the TPA parameters are plotted in Fig. 4. Hardness ofthe soaked Bhoja chaul samples were higher than cooked rice (Kar,Jain, & Srivastav, 1998; Sareepuang, Siriamornpun, Wiset, & Meeso,2008). Process severity however resulted in marginal lowering ofhardness values (Fig. 4a) in samples from both the rice varietiesprobably because of thermally degraded starch. Cooked rice wasmarkedly adhesive as compared to the soaked Bhoja chaul samples(Fig. 4b) because of complete gelatinisation of starch that occurredduring cooking (Kar et al., 1998). Breakdown of amylopectin toshorter fragments also resulted in progressive increase in adhe-siveness of the processed samples (Radhika Reddy, Ali, &Bhattacharya, 1993). Significantly lower values of springiness(Fig. 4c) in both raw and processed WA samples were due to thehigher adhesiveness and lower hardness values than LK samples.LK samples exhibited lower adhesiveness and marginally higherspringiness. Chewiness increased progressively with process sever-ity for the Bhoja chaul samples (Fig. 4d). Chewiness is a positivequality attribute for Bhoja chaul acceptability. Cooked rice samplesexhibited the lowest chewiness value.

3.11. The ready to eat (RTE) product

As no marked differences were observed among the samplesboiled for 1 and 3 min in water before overnight hydration, hotsoaking for 1 min can be considered suitable for the laboratoryprocess used for making Bhoja chaul. Severe sand roasting of Kolachokua paddy at 140 �C for 13–15 min gave superior texture tothe RTE product as per our general observation. Aghoni bora sam-ples showed higher adhesive property and such sticky texture isliked by some sections of the consumers. Roasted aroma, anotherquality parameter of the product could however be sensed in eachof the Bhoja chaul samples. Industrial processes for making theproduct may further be developed based on the present findings.

4. Conclusions

The improvised soaking method and the roasting techniquecould give good quality Bhoja chaul from low amylose rice andwaxy rice. The improvised roasting method allowed for greaterhydration of the paddy that allowed for extensive gelatinistionsof the starch during roasting. Sand roasting allowed for extensiveand uniform gelatinisation of starch that also dried within a shortperiod. Bhoja chaul obtained was uniformly darker in colour due topigment migration during processing. The increased hardness of


the Bhoja chaul as compared to the raw prevented grain breakageduring milling. The product obtained from the laboratory-scalemethod had desirable texture. The increased hydration ability ofBhoja chaul was due to the extensive gelatinisation of starch. DSCcurves revealed absence of retrograded starch. However, peak foramylose–lipid complex melting was evident in the Bhoja chaulsamples that were given severe roasting treatments. Dry heat par-boiling led to significant loss in crystallinity with minor reforma-tion of each type of starch crystalline polymorphs during coolingand storage. The product was highly digestible with very highamount of rapidly digestible starch. There was almost no resistantstarch in the severely processed samples. This product cantherefore be provided to children and patients with poor digestiveconditions. Roasting of the low amylose Kola chokua variety for 13and 15 min at 140 �C gave RTE product with better texture. Bhojachaul from waxy Aghoni bora had sticky characteristic that maybe liked by consumers who prefer sticky rice. There is scope forwider use of Bhoja chaul as a ready to eat product.

Acknowledgements

One of the authors is availing the Senior Research Fellowship ofthe Council of Scientific and Industrial Research (India) for carryingout this work. The authors are thankful to the Director of CentralFood Technological Research Institute (Mysore, India) where a partof this work was done.

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Physical, physicochemical and nutritional characteristics of Bhoja chaul, a traditional ready-to-eat...

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