Effect of Roasting on Texture, Colour and Acceptability of Pearl Millet (Pennisetum glaucum) for Making Sattu
In order to study the effect of roasting on some important
physical properties viz. geometric mean diameter, colour, textural properties
(hardness, toughness, average rupture force) and sensory attributes of
pearl millet for making sattu, it was roasted using three time
(45, 60 and 75 sec) and temperature (160 °, 180 ° and 200 °C)
combinations. In general, geometric mean diameter, hardness, toughness
and average rupture force increased with increase in roasting temperature.
Roasting brought a significant change in colour of pearl millet grain
and its roasted flour samples. h0 and C* of flour increased
with increase in time at the same roasting temperature except at 180 °C
for 45 sec time. The lower hardness of pearl millet roasted at 180 °C
for 60 sec as compared to higher temperature and highest mean sensory
scores for colour and appearance (6.28), roasted odour (6.58) and overall
quality (6.58) for pearl millet flour prepared from the grain roasted
at 180 °C for 60 sec, make this temperature and time combination best
for roasting of it for making sattu. The 10% level of pearl millet
flour with bengal gram (90%) was found the most accepted sattu
formulation with mean sensory score (7.01). Regression equations developed
for hardness, toughness, average rupture force, hue and chroma showed
that temperature had significant effect on these parameters as compared
to roasting time.
Sattu is one of most popular traditional food of northern India.
It is preferred item in the breakfast in some of the State particularly
in Bihar and Uttar Pradesh. Sattu, in drink form, is considered
as one of the best food in breakfast during the summer season due to its
cool effect as believed by the population and good digestibility. Sattu
is basically a product, prepared from roasted cereals, or legumes or,
combination of cereal and legumes with added flavouring agents (Mridula
et al., 2004). Roasting which is a simple and most commonly practiced
household and village level technology, pre-cooks the ingredients used
in food grains and oilseed based mixes and increased shelf life and acceptability
of the products (Gopaldas et al., 1975). Roasting improves the
flavour, texture and nutritive value of the grains (Siegal and Fawcett,
1976) and also eliminates most of anti-nutritional or toxic factors present
in legumes, either partially or wholly (Liener, 1973).
Amongst various legumes, bengal gram is the preferred one for making
sattu, particularly in Bihar and eastern part of Uttar Pradesh
(Mridula et al., 2004) but no legume or cereal alone can provide
balanced amount of nutrients. However, mixing of legume with cereal can
improve the digestibility of the product. Supplementing various types
of millets with chickpea has shown good improvement in the protein efficiency
ratio (Casey and Lorenz, 1977). Addition of cereal and millets to sattu
to the acceptable limit will not only improve the protein quality but
also reduce the cost. Earlier sattu was considered as poor man`s
food but nowadays the popularity of bengal gram sattu amongst the
diabetics is increasing day by day due to its low glycemic index. As the
glycemic response of pearl millet (Shukla et al., 1991) is also
low, pearl millet and bengal gram based sattu can also get popularity
amongst the masses at lower cost than pure bengal gram based sattu.
Studies (Vimala et al., 1990; Dahiya and Kapoor, 1995) have been
carried out to develop weaning mixes based on pearl millet and Bengal
gram but information on optimum roasting temperature and time and their
effect on quality attributes of pearl millet and its flour is not cited
in the literature. As roasting is one of the important unit operation
in sattu making, that effect the textural, colour properties and
flavour and aroma of the product i.e., sattu, it is important to
know the effect of roasting conditions on quality of pearl millet for
making sattu. Therefore, the present study was undertaken with
the objective to study the effect of roasting temperature and time combination
on quality attributes of pearl millet for making sattu in combination
with bengal gram.
MATERIALS AND METHODS
Pearl millet (variety FBC-16), which is commonly known as bajra in India,
was used for the study. In order to see the effect of roasting on quality
of pearl millet for making sattu with bengal gram, it was incorporated
in sattu using the method (Fig. 1). Raw pearl
millet with geometric mean diameter (GMD) -2.28 mm and moisture content
of 9.58% (w.b.) was dipped in water in a wire mesh basket, twice for washing
followed by tempering for 2 h. The moisture content of the tempered samples
was in the range of 15.85-16.02% (w.b.) (p>0.05). The washed and tempered
samples were roasted in hot sand bath using sand grain ratio 8:1, at three
different temperatures (160°, 180°, 200° C) and time (45,
60, 75 sec) combinations. The roasted samples were tempered for 4 hours,
packed in LDPE bags (62.5 μ) and kept in desiccator for determination
of moisture, colour and textural properties. The roasted samples were
subjected to CIAE (Central Institute of Agricultural Engineering, Bhopal,
India) developed cleaner cum grader to remove the sand particles if any
before grinding for making flour. The ground samples were evaluated for
colour and different sensory attributes. Bengal gram and pearl millet
based sattu was prepared from pearl millet flour, prepared from
pearl millet roasted at 180 °C for 60 sec. Different formulations
with roasted Bengal gram were prepared using pearl millet at 10, 20, 30
and 40% level. Roasted Bengal gram was prepared as per the standardized
process (Mridula et al., 2004). Statistica 7.1 was used for statistical
analysis of the results of the study.
||Method for preparation of pearl millet incorporated
Geometric Mean Diameter
Geometric mean diameter is the geometric mean of the spatial dimensions
of raw and roasted grain, were measured using Vernier Caliper with least
count of 0.02 mm (Mohsenin, 1970). The spatial dimensions namely length
(L, longest dimension), breadth (B, second longest dimension), thickness
(T, third longest dimension) were measured for 10 representative seeds
under each roasting condition. Geometric mean of the spatial dimensions
was calculated as: Equivalent diameter = (L x B x T)1/3.
The textural properties of raw and roasted pearl millet grain such
as hardness, toughness and average rupture force were measured using Texture
Analyzer (TA) TA-HDi. Stable Micro systems (U.K.). The TA setting
were: mode- measure force in compression, option-return to start, pre
test speed- 3 mm/s, test speed - 1 mm sec-1, post test speed
- 10 mm sec-1, distance- 1 mm, trigger force - 20 g, stainless
steel cylinder probe -5 mm diameter (P/5) and 50 kg load cell. Textural
properties were measured for 10 representative seeds of each replication
under each roasting condition. During the test, the graph was drawn between
force and distance as the result of the force resisted by the grain sample
against the probe of texture analyzer with the help of software (Texture
Expert Exeed TM, MS Windows). The maximum force experienced
by the probe is considered as hardness and the area under this maximum
force on the graph is considered as toughness of the grain. The average
force experienced by the probe throughout the test is considered as average
rupture force of the grain.
Colour (L*, a*, b* values) of the samples was determined by using
Handy Colorimeter; Model No. NR-3000, NIPPON Denshoku, Japan. L* is known
as the lightness and extends from 0 (black) to 100 (white). The other
two coordinates (a*) and (b*) represents redness (+ a) to greenness (-
a) and yellowness (+ b) to blueness (-b), respectively. h0 (hue
angle) is the attribute of colour by means of which the colour is perceived.
C* (chroma) is the attribute of colour used to indicate the degree of
departure of the colour from gray of the same lightness. h0
and C* are computed by using the following formula.
h0 = tan-1 (b*/a*)
a2 + b2
Roasted pearl millet flour incorporated sattu with bengal gram
were evaluated for different sensory attributes by a panel of nine trained
judges. Sensory attributes like colour and appearance, body (textural
property of sattu drink), roasted odour, flavour and taste and
overall acceptability for all samples were assessed using nine-point hedonic
scale (IS: 6273, 1971). Hedonic scale was in the following sequence- like
extremely -9, like very much - 8, like moderately -7, like slightly -
6, neither like nor dislike - 5, dislike slightly 4, dislike moderately,
- 3, dislike very much - 2, dislike extremely -1 (Larmond, 1977).
RESULT AND DISCUSSION
Roasting is an important unit operation in processing of grain for making
sattu due to its significant effect on the odour in the final product
sattu, which is the most desired quality of sattu. As the
sale of the product is basically depend on the roasted odour in sattu,
the optimum roasting temperature and time combination is of great importance.
It is observed from Fig. 2 that moisture content of roasted
grain decreased with increase in both roasting temperature as well as
time (R2 = 0.99). The increase in Geometric Mean Diameter (GMD)
in linear fashion may be attributed to start of puffing of grain at higher
temperature and time combination (Fig. 3).
Textural properties of the roasted pearl millet are very important because
energy requirement for grinding may be in proportion to the hardness and
average rupture force of the grain. From the Fig. 4,
in general, hardness of pearl millet grain increased with increase in
roasting temperature and time. The reason for the increase in hardness
at increased temperature and time may be attributed to decrease in moisture
content of the grain during the roasting process as also reported in other
studies (Srivastav et al., 1994). Hardness of pearl millet decreased
when roasted at 160°C for 45 sec time as compared to raw grain hardness,
which was 30.38 N, but when roasting time increased, hardness also increased.
This trend was also observed at other temperatures i.e., 180° and
200°C. The formation of a continuous protein matrix, which physically
traps the starch granules, leads to difficulty in separating starch from
protein and makes the grain harder (Stenvert and Kingswood, 1977; Moss
et al., 1980). This may also be one of the reasons for increased
hardness of grain. Hardness was also increased with increase in the roasting
temperature for the same roasting time. The hardness of pearl millet at
200 °C for 60 sec, although not significant but lowered as compared
to 75 sec roasting time than at 160° and 180 °C.
||Moisture content of roasted bajra grain
||Effect of roasting temperature and time on geometric
mean diameter of bajra grain
||Effect of roasting temperature (160, 180 and 200°
C) and time (45, 60 and 75 sec) on hardness, toughness and ARF of
pearl millet grain
This may be due to the fact that surface gelatinization of starch took
place initially and fissures developed on the grain upon further heating,
resulted in the reduced hardness. The effect of temperature and time of
roasting on grain hardness, toughness and average rupture force is presented
in non-linear multiple regression equations. Both the independent variable
i.e., temperature and time were considered for computation of coefficient
of determination. After deleting the non-significant variable (time or
temperature as the case may be), the regression equation can be written
H = 218.408 + (-) 2.758 T + 0.008 T2
Coefficient of determination = 0.72
ln Ts = -14.009 + 0.163
T + (-)0.0004 T2
Coefficient of determination = 0.49
ARF = 116.31 + (-) 1.32 T + 0.004 T2
Coefficient of determination = 0.404
||Average rupture force,
The colour of the sattu is very important from consumer points
of view because it is the colour, which appeal first to a person to purchase
or consume any food. Roasting, in general, affected the colour of pearl
millet grain (Fig. 5). L* values of pearl millet grain
at 160 °C decreased with increased roasting time while at 180°
and 200°C, L* values slightly decreased at 60 sec as compared to 45
sec and further increased at 75 sec time. The variation in L* values at
different time and temperature combinations may be due to degree of puffing
of pearl millet grain. At the same temperature when roasting time was
increased, no significant changes were observed in a-values except at
||Effect of roasting on colour (L*, a* and b* values,
h0 and C* (chroma) of pearl millet roasted at 160, 180
and 200° C temperature and 45, 60 and 75 sec time
The decrease in a*-value at 200°C may be due to slight puffing of
some of grains, which increased the L* values i.e., whiteness and decreased
the redness i.e., a*-values. Overall Colour changes during heating takes
place due to Maillard reaction (Ibanoglu, 2002). When the roasted pearl
millet was milled into flour, h0 (hue) and C* (chroma) showed
a different pattern because of the colour of the endosperm. In the seed
form, colour basically represents the colour of the seed coat while in
ground form; it is the mixed effect of the colour of all component of
the grain. L* values for pearl millet flour, prepared from grain roasted
at different time and temperature were not significant but effect of roasting
on a* and b* values for pearl millet flour (Table 1)
brought a significant change in h0 (hue) and C* (chroma) of
pearl millet flour, which has also affected the acceptability of the product.
The effect of temperature and time of roasting on h0 and C*
for roasted pearl millet grain and its flour is presented in non-linear
multiple regression equations and after deleting the non-significant variable
(time or temperature as the case may be), the regression equation can
be written as:
ln h0 (g) = 14.257 + 7.732
t + 7.762 t2
Coefficient of determination = 0.51
ln C*(g) = 0.75 + 0.029 T + (-)0.00007
T2 + (-)0.025 t + 0.0002 t2
Coefficient of determination = 0.87
||Effect of roasting temperature and time on colour (L*,
a*, b*, h0 and Chroma (C*) of pearl millet flour
||Effect of roasting on mean sensory scores for important
sensory attributes of pearl millet flour
||Mean sensory scores for different attributes of bengal
gram and pearl millet based sattu with bengal gram
ln h0 (f) = 1.491 + 0.031
T + (-)0.00008 T2
Coefficient of determination = 0.63
ln C*(f) = -1.976 + 0.050 T + (-)0.00013
Coefficient of determination = 0.75
Mean sensory scores of roasted pearl millet flour for making sattu
are given in Table 2. The mean scores for all the attributes
and overall acceptability were more than 5, indicated that the samples
of pearl millet flour prepared from grain roasted at different roasting
conditions were accepted by the panelist with highest score for roasted
odour (6.58) and overall quality (6.58) of the samples prepared from the
grain roasted at 180 °C for 60 sec, hence this sample was used for
making bengal gram and pearl millet based sattu. The acceptability
of pearl millet flour for making sattu (Table 2)
and pearl millet flour incorporated sattu drink with bengal gram
(Table 3) for different sensory attributes was significantly
different for all the attributes.
Roasting of pearl millet grain at different roasting conditions affected
the GMD and textural properties of pearl millet and colour of pearl millet
and its flour. In general, hardness of pearl millet grain increased with
increase in roasting temperature from 160 to 200 °C for 45 to 75 sec
time. The lower hardness of pearl millet, roasted at 180 °C for 60
sec as compared to higher temperature and highest mean sensory scores
for colour and appearance (6.28), roasted odour (6.58) and overall quality
(6.58) for the pearl millet flour prepared from the grain roasted at 180
°C for 60 sec, make this temperature and time combination best for
roasting of pearl millet for making sattu. The 10% level of pearl
millet flour with Bengal gram (90%) was found the most accepted sattu
formulation. The regression equations developed for hardness, toughness
and average rupture force revealed that temperature of roasting had significant
effect on these quality attributes as compared to time. Whereas, regression
equations for colour showed that both roasting temperature and time had
effect on hue and chroma in case of roasted grain but it was only temperature
in case of flour.
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