Prediction of end-use quality of Indian wheat varieties by using
SECAbstractThe eminence of molecular weight distribution (MWD) of
gluten proteins has been elucidated by correlation studies in
context with flour characteristics, dough rheological properties
and textural attributes of finished product. Size Exclusion
Chromatography (SEC) chromatogram of wheat varieties was segregated
into five domains depending on the molecular weight of the eluting
protein fractions as peak 1: glutenins along with minor amount of
omega gliadins, peak 2: gliadins with slight portion of low
molecular weight glutenin subunits (LMW-GS), peak 3: low molecular
weight (LMW) monomeric proteins, lastly peak 4 and 5: albumins and
globulins. Absorbance area percentage (AA %) of peak 1 and 2
exhibited divergent influence on the flour characteristics, dough
rheology and gluten protein quality characteristics; reflected the
alliance of MWD patterns with their contrasting performance in
noodle, bread, cookie and chapatti making. This investigation was
subjected to utilization of SEC to indicate the varietal variation
in terms of their peculiarities for a specific type of product.
Moreover, high molecular weight glutenin subunits (HMW-GS) which is
considered as prime determinant for varietal variation is not the
sole root cause, but the discrepancy in the proportion of gluten
protein fractions play an imperative role in deciding the
technological and functional characteristics of a wheat variety. 1.
IntroductionWheat (Triticum aestivum L.) is considered the worlds
most domesticated cereal crop and possesses a great economic
importance for India. The distinct rheological property of wheat is
due to the viscoelastic complex called gluten which lets it to be
processed into a plenitude food as well as non-food products (Dong,
Hao et al. 2009). Gluten is a complex of heterogeneous protein
components that form a three-dimensional network of linearly
cross-linked glutenin subunits and gliadin components through
hydrogen, hydrophobic, and disulfide bonds (Korableva and Kasymova
2010, Ferreira, Ruiz et al. 2012). Quantity and quality of wheat
proteins is considered substantial in relation to baking quality of
wheat (He and Hoseney 1992).The molecular size of wheat gluten
proteins has been demonstrated extensively by SEC. Gliadin was
first fractionated by SEC after extraction with 70% ethanol by
Jones, Babcock et al. (1963) and Beckwith, Neilsen et al. (1966).
Similarly Huebner and Wall (1974) revealed that reduced and
alkylated glutenin resulted in three types of subunits differing in
size and associative tendencies, followed by improvements of
chromatographic procedures by Beitz (1984), Batey, Gupta et al.
(1991) and Larroque and Bekes (2000). Numerous researches had
emphasised on the relation of differences in molecular size of
native flour proteins with wheat quality parameters. Ohm, Ross et
al. (2006), Ohm, Ross et al. (2008), Ohm, Ross et al. (2009b) and
Tsilo, Ohm et al. (2010) have demonstrated distinct associations of
protein fractions with specific molecular weight with various
quality parameters and wheat products related characteristics.
Previous studies has mentioned the significant associations of
protein fractions with wheat quality characteristics such as the
prominent effects of HMW-GS (Uthayakumaran, Stoddard et al. 2000),
LMW-GS (Verbruggen, Veraverbeke et al. 2001), gliadins
(Uthayakumaran, Tmskzi et al. 2001, Khatkar, Fido et al. 2002a,
Khatkar, Barak et al. 2013), the glutenin-to-gliadin ratio
(MacRitchie 1987, Gupta, Batey et al. 1992, Uthayakumaran, Newberry
et al. 2000) and overall protein content (MacRitchie 1992,
Uthayakumaran, Gras et al. 1999) on end-product quality, but much
emphasis has not been laid down on the relationships of variations
in MWD with unique end use quality attributes of wheat variety. The
present study was undertaken to understand the association of MWD
patterns of gluten proteins with functional specialty of different
Indian wheat varieties. The influence of quantitative and
qualitative protein composition, as measured by SEC, on dough
baking and cooking quality was investigated. The main objective of
this research was to examine fundamental advantage of SEC of wheat
proteins, in conjunction with physicochemical, rheological and
textural analysis and to predict the finished product specificity
of diverse background wheat varieties. Thus AA % of each particular
protein fraction could be adapted as a successful marker in
suggesting end use quality of wheat varieties and hence SEC could
hold a potential for rapid assessment of wheat genotypes in
breeding programmes. 2. Material and methodsFour wheat samples
commonly cultivated in India HI 977, HW 2004, DBW 16 and C 306 were
elite among the choices. The samples were tempered at 15.5 g/100 g
moisture for 24 h and milled to 65% extraction rate. Physical
characteristics of grains i.e. thousand kernel weight, test weight,
kernel length and width, hardness of all the varieties were
determined using single kernel characterization system (model 4100,
Perten Instruments, Huddinge, Sweden) according to standard AACC
procedures. Milling was carried out using Chopin laboratory mill
(Model CD1, Villeneuve la Garenne, France). Moisture, ash and crude
protein content were determined by standard AACC methods (2000).
SDS Sedimentation values of flours were determined according to
Axford, McDermott et al. (1979). Damaged starch was evaluated by
the Chopin SDmatic. Gluten yield and gluten index were estimated by
Glutomatic (Model GM 2200, Perten Instruments). 2.1 Gluten
Extensibility TestMeasurements were performed with a TA-XT 2i
texture analyzer (Stable Micro System) using Kieffer dough/gluten
extensibility rig with the test speed of 3.3 mm/s and data
acquisition rate of 200 pps. The test mode of the instrument used
was force in tension.2.2Dough Rheological PropertiesRheological
characteristics of dough were investigated using Chopin Mixolab by
adopting Standard Chopin S protocol (Kahraman, Sakyan et al. 2008).
It determines a comprehensive qualitative profile of the wheat
flour and plots, in real time, the torque (expressed in Nm)
produced by mixing dough between two kneading arms with a constant
mixing speed of 80 rpm. The information recorded from the curves
contained the percentage of water required for dough to produce a
torque of 1.10.07 Nm i.e. water absorption (%); the time to reach
maximum torque at 30o C i.e. dough development time (min); the slip
away time at which the torque produced is maintained at 1.1 Nm i.e.
dough stability (min); the difference between the maximum torque at
30o C and the torque at the end of holding time at 30o C i.e.
mechanical dough weakening recorded in Farinograph Units (FU), was
used to evaluate the rheological characteristics of various
flours.2.3Fractionation of wheat gluten into gliadin and
gluteninWheat flours were defatted by successive extraction with
chloroform according to MacRitchie (1987). Flour (100g) was
defatted using 200ml of chloroform, filtered through filter paper
at room temperature and process is repeated thrice. The defatted
flour was dried at room temperature. Gluten was isolated from
defatted flour using glutomatic instrument as per standard ICC
method. Dry gluten, wet gluten and gluten index were
determined.2.4Product preparation and analysis2.4.1Instant
NoodleInstant noodles were prepared by using the standardized
formulation and processing conditions (Gulia and Khatkar 2013). The
ingredients in noodle recipe (on 100 g flour basis) comprised of
water (30.97%), alkaline salt (0.23%) (Potassium carbonate and
sodium carbonate, 1:1), guar gum (0.28%) and salt (1.54%). Noodle
dough was thoroughly mixed by incorporating wheat flour with all
other ingredients dissolved in water using mixer (Kitchen Aid Inc.,
Michigan, USA) for 4 min. Crumbled dough was then sheeted using
noodle machine (ATLAS, Marcato, Italy) by passing it four times
through roller no. 1 and compounding it after every pass. A resting
period of 10 min was given to the dough sheet in zip lock pouch to
prevent surface moisture loss and later passed over through roller
unit attachment five times to get a final thickness of 1.2 mm with
a regulating knob set at position no. 2, 3, 4 and 5, respectively.
Resting period of final sheeted dough was anew for 30 min and dough
sheet was sent to cutter attachment to get the desirable shape of
noodles. The culminated noodles were stowed uniformly on a sieve
and steamed into a preheated (100C) steamer (Rice Cooker-Ultimate,
UL-255, China) for 6.4 min. Steamed noodles were fried in soybean
oil at 142C for 2 min in deep fat fryer (Friendz, FZ-591, China)
and cooled for 15 min. The samples were stored for further
analysis.Oil Uptake: Oil uptake was calculated according to the
approved AACC (2000) method. Instant fried noodles were ground
evenly and oil was extracted with petroleum ether (60-80C) using a
solvent extractor (SER148, Velp Scientifica, Usmate, Italy). Oil
uptake was expressed in terms of percentage on dry basis.Cooking
quality: As per the procedure of Oh, Seib et al. (1983), fried
noodles (10 g) were put into 400 ml of boiling water, cooked to the
optimal cooking time and subsequently cooled for 1 min under
running tap water. Ultimately, the noodles were reweighed and
stocked in a capped petriplate at room temperature for texture
analysis. The total water remaining after cooking in addition to
that utilized for rinsing was collected to estimate cooking loss.
An aliquot of 50 ml was evaporated in an oven at 100C for 4 h and
outcome was recorded as per cent weight loss during cooking. The
cooked weight was measured as exhibited by Wang, Huang et al.
(2011) as per cent enhancement in weight of noodles after
cooking.Texture analysis: Texture profile analysis of cooked
noodles was demonstrated using Texture Analyzer TA-XT 2i within 15
min after cooking. Pre-test speed, test speed and post-test speed
used were 2.0, 3.0 and 3.0 mm/sec, respectively with the
compression plate probe of 45 mm 30 mm. Five noodle strands were
placed closer to each other in flat position. The texture analysis
results were presented as noodle hardness, springiness,
adhesiveness, cohesiveness and chewiness.2.4.2Bread Bread making
method of Finney (1984) was followed to compute the bread making
efficiency of different wheat flours by performing optimized baking
tests. The test baking formulation for 30 g bread was: refined
flour (30 g, 14 % moisture basis), compressed yeast (1.59 g), salt
(0.45 g), sugar (1.8 g), fat (0.9 g), malted barley flour (0.075 g)
and ascorbic acid (100 ppm, flour basis). Salt, sugar and ascorbic
acid were added in solution form and yeast was added as a
suspension, which was mixed well each time before
dispensing.Farinograph was utilized to prepare dough. After
adequate mixing, dough was placed in a bowl, capped with a wet
muslin cloth and proved for 90 min at 30oC and 98 % R.H. Punching
of dough was rendered after 52, 77 and 90 minutes in a machine
moulder by passing through a set of rollers with a gap setting of 9
mm. Dough was placed in a lightly greased baking tin after the
ultimate punching and later proved at 30oC and 98 % R.H. Bread
loaves were placed in a preheated baking oven at 230o C for 25 min
and allowed to cool for 2 h on a wire mesh. Specific loaf volume of
bread was measured by rapeseed displacement method. The breads were
baked in triplicate for each cultivar.Texture analysis: The bread
firmness was evaluated using AACC approved (74-09) standard method
on Texture Analyzer TA-XT 2i with 25 mm cylindrical probe (P/36 R).
The pre test speed, test speed and post test speed were 1.0, 1.7
and 10.0 mm/s, respectively, with data acquisition rate of 250
pps.2.4.3CookiesCookies were prepared according to AACC approved
method 10-50D (2000) with slight modifications. The ingredients
formulated were flour (225 g), sugar (130 g), shortening (64 g),
dextrose solution (33 ml), sodium bicarbonate (1.6 g), ammonium
bicarbonate (0.9 g), sodium chloride (2.1 g) and distilled water
(16 ml). The dough was prepared and sheeted to a thickness of 10 mm
on a dough sheeter and round shaped cut was given using cutter of
60 mm diameter. Cookies were baked in a lightly greased tray in
baking oven at 205o C for 15 min followed by cooling and
consecutively measured for diameter and thickness (six cookies) and
average was calculated. The spread ratio was calculated by dividing
diameter (mm) with thickness (mm). Cookies were prepared in
triplicate.Texture analysis: The texture of cookies was persuaded
via textural analyzer (Stable Micro Systems TA-XT 2i, Godalming,
U.K.). The probe used was Knife Edge Insert (HDP/BS) to apply
braking force required to fracture the cookies with 5 kg load cell
Heavy Duty Platform (HDP/90) at pre test speed, test speed and post
test speed of 1.5, 2.0 and 10.0 mm/s respectively and data
acquisition rate of 400 pps. 2.4.4 ChapattiChapatti was prepared
using method of Haridas Rao, Leelavathi et al. (1986) with minor
modifications. Whole wheat flour (200 g) was mixed with adequate
amount of salt and water in farinograph for 3 min to obtain dough
of moderate stiffness. About 40 g of dough was rounded and sheeted
to 2 mm thickness using rolling pin and desired shape was achieved
using chapatti circular sharp edged die of 15 cm diameter. The
shaped chapatti was baked on a hot plate at 210o C from both the
sides, puffing was performed at 290-320o C for 15-20 s followed by
cooling and packaging. Puffing height was immediately measured
after puffing using a specifically designed system having a ruler
attached to it in centimetres. Chapatti quality score was analysed
via physical and sensory quality parameters which were assessed by
trained panel.Texture analysis: The biaxial extensibility
(softness) of wheat flour chapatti was determined on Texture
Analyzer TA-XT 2i with tortilla/ pastry/ bursting (HDP/TPB) and
heavy duty platform (HDP/90). The ball probe SMSP/1SP was used with
the pre-test speed, test speed and post-test speed of 1.0, 1.0 and
10.0 mm/s respectively. Data acquisition rate was 200 pps during
test.2.5Sample Preparation and Size Exclusion ChromatographyGluten
was extracted with solvent 3M urea as suggested by Huebner and Wall
(1974) with minor modifications. Acetic acid was added to maintain
buffer pH 4.6. Sample was sonicated (Power Sonic 410, Hwashin
Technology) for 10 min, centrifuged at 12,000 x g for 30 min (Remi
Cooling Centrifuge) and filtered through syringe filter (0.22 m HV
Millipore, DuraPore). SEC was performed on Sephacryl S-200 column
(HI PrepTM 16/60 Sephacryl S-200 HR, GE Healthcare). The mobile
phase was 3M Urea, 0.15 M NaCl, pH 4.6 with a flow rate of
0.5ml/min. Selected eluted fractions were then assayed by SDS-PAGE
as described by Laemmli (1970).2.6Data AnalysisData was analysed
using SPSS software version 16.0 (SPSS Inc.). Correlation among
various quality characteristics of kernel, flour, dough, gluten, AA
% and finished product were derived using Pearsons test (p