Abstract: Biscuits prepared from flour blends containing varying proportions of sorghum flour (0, 10, 20, 30, 40, 50 and 60%) and fortified with 5% defatted soy flour, were evaluated for different quality parameters. Spread ratio was decreased with increased proportions of sorghum flour in biscuits. Dough strength decreased but hardness, toughness, average breaking force and average breaking energy of biscuits increased (p<0.001) with increased proportions of sorghum flour. L* values decreased while a* value increased (p<0.001) with increased proportion of sorghum flour, resulting in the darkening of biscuit samples but on sensory evaluation, mean sensory scores for different level of sorghum flour incorporated biscuits fortified with 5% defatted soy flour, for all the sensory attributes, were more than the minimum acceptable score of 6 with highest overall acceptability at 10% sorghum flour level.
INTRODUCTION
Sorghum is a staple food for a large section of the people especially in dryland regions but nowadays coarse cereals and millets are gaining popularity amongst those who are accustomed to softer cereals like wheat and rice because of the presence of soluble and insoluble dietary fibre, beneficial in various degenerative diseases. Insoluble fraction of dietary fibre in cereal grains contains large proportion of cellulose, which has beneficial effects in the gastrointestinal tract (Riaz, 1999). The soluble fractions, which consists mainly pectin, arabinoxylan and β-glucans has the ability to lower blood serum cholesterol, through its tendency to increase viscosity in the intestine. Earp et al. (1983) identified the mixed linked β-glucans in sorghum pericarp, aleurone and endosperm. These β-glucans are water-soluble and form viscous, sticky solutions. Klopfenstein and Hoseney (1987) observed that rats fed bread prepared from white flour fortified with β-glucan (7% by weight) had serum cholesterol significantly lower than those fed bread from unfortified flour.
Sorghum, for human consumption, is generally utilized in the form of roti, snacks (puffed grain), porridges and noodles. Several studies indicated the possibility of incorporating sorghum in wheat flour at various levels for producing bread, biscuits and other snacks (Hulse et al., 1980; Chavan and Kadam, 1993). Elmonienm et al. (2002) suggested that biscuit with acceptable quality could be made from wheat dough containing 20% sorghum flour. The demand of biscuit, named Deliken, produced with 20% flour from the sorghum variety - Ntenemissa was very high (Anonymous, 2002). It has been reported that replacing wheat with 20% non-wheat flour for the manufacture of bakery products would result in an estimated savings in foreign currency of US$320 million annually (FAO, 1982). By making extensive use of cereals, other than wheat, like sorghum and other millets, grown widely in India, diversified food products with special features could be prepared. Incorporation of Defatted Soy Flour (DSF) in a small quantity will improve the protein quality of cereal based products without causing significant difference in the acceptability of the developed product. Mridula and Wanjari (2006) observed that the flavour and taste of full fat soy flour incorporated biscuit at 5% level was comparable with the biscuits prepared from refined wheat flour only. Therefore, the present study was carried out to examine the effect of incorporation of higher levels of pearled sorghum flour to wheat flour and fortified with 5% Defatted Soy Flour (DSF) on physical properties, texture, colour, proximate composition and sensory characteristics of biscuits.
MATERIALS AND METHODS
Preparation of Biscuits
Biscuit samples were prepared, using creamery method. The ingredients (g)
used in preparation of biscuits were wheat flour or flour blends 100, fat 60,
sugar 50, egg 20, baking powder 0.8, vanilla essence 0.02 and required amount
of water. Flour blends for making biscuits were prepared using refined wheat
flour, substituted with 10, 20, 30, 40, 50 and 60% pearled sorghum flour. All
the samples of flour blends were fortified with 5% DSF. Thus, the proportion
of wheat flour, sorghum flour and defatted soy flour in flour blends was 95:0:5
(control), 85:10:5, 75:20:5, 65:30:5, 55:40:5, 45:50:5, 35:60:5, respectively.
Each biscuit sample was prepared from 500 g flour blend.
The particle size of wheat flour, sorghum flour and defatted soy flour used for making biscuits was 0.254, 0.397 and 0.429 mm, respectively. The particle size of the flour was determined by using sieve shaker machine which carries a set of sieve No. 100, 65, 48, 35, 20, 14, 10 and 8 with pan and cover. A sample of 250 g flour was placed in the upper most sieve and the set of sieves was placed on a sieve shaker machine and was shaken for 5 min. Then material on each sieve was collected and weighed. Average particle size was determined by using following formula:
Dp (average particle size) = 0.135 (1.366)fm |
Where, fm = Fineness modulus (Total percent material retained/100)
Sorghum flour was prepared from sorghum, pearled at 12% moisture for 5 min in a grain pearler (capacity 50 kg h-1), followed by grinding in a sample mill. The dough was prepared in a Hobart mixer and sheeted by using the dough sheeter to a thickness of 6 mm, cut into round shape of 50 mm diameter, transferred to a baking tray and baked at 180°C for 12 min. The cooled biscuits were packed in LDPE bags (50 μ) and evaluated for all different quality parameters after 12 h.
Physical Properties
Diameter, thickness and spread ratio of biscuit samples were calculated
as per the AACC (1967) methods. Expansion in diameter and thickness was the
ratio of biscuit diameter and thickness before and after baking.
Proximate Composition
Moisture, Protein, crude fat, dietary fiber and ash content were determined
as per standard methods (AOAC, 1984).
Textural Properties
Dough strength, hardness of biscuits, breaking strength (peak breaking force),
peak breaking energy (toughness), average breaking force and average breaking
energy were measured using Texture Analyzer (TA) TA-HDi. Stable Micro Systems.
The dough strength was measured by using SMS/Chen-Hoseney Dough Stickiness Cell
(A/DSC) and 25 mm perspex cylinder probe (P/25P). The TA setting was pre-test
speed 2.0 mm sec-1, test speed 2.0 mm sec-1, post test
speed 10.0 mm sec-1 and distance 4 mm. The dough strength was computed
from the resulting curve. The distance the sample is extended on probe return
on the graph was considered as dough strength.
The hardness of biscuits was measured by using cylindrical probe P/5. The TA setting for all tests, was kept as pre-test speed 3 mm sec-1, test speed 2 mm sec-1, post test speed 10 mm sec-1 and distance 5 mm. The individual samples of biscuits were placed on the platform and the probe was attached to the crosshead of the instrument. The peak force from the resulting curve was considered as hardness of biscuits.
Breaking test of biscuit was conducted using HDP/BS blade of texture analyzer. The individual samples of biscuits were placed on the platform such that they were supported at two points and the blade was attached to the crosshead of the instrument. This test simulates the evaluation of hardness by consumer holding the biscuit in hands and breaking by bending. The peak force from the resulting curve was considered as breaking strength of the biscuit and the area under the peak force on the graph is consider as peak breaking energy i.e., toughness. The average force experienced by the probe throughout the breaking test is considered as average breaking force and the total area under the breaking force on the graph is considered as average breaking energy.
Colour Determination
Colour (L*, a* and b* values) of the biscuits was determined by using Handy
Colorimeter NR-3000. 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.
Sensory Characteristics
Sensory characteristics of biscuits were evaluated for different sensory
attributes by a panel of nine scientist of the Institute. Sensory attributes
like appearance and colour, texture, aroma, 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).
Statistical Analysis
Analysis of variance, F-Ratio and multiple R2 (regression coefficient)
for the data of the study were computed using Statistica 7.1.
RESULTS AND DISCUSSION
Biscuits samples were prepared using the flour blends containing different
levels of pearled sorghum flour (0, 10, 20, 30, 40, 50 and 60%) to wheat flour
with 5% defatted soy flour in all the samples to investigate the influence of
sorghum flour on quality of biscuits. During the dough preparation for biscuits,
it was observed that sorghum incorporated dough samples were crumbly than the
control dough and also comparatively difficult to sheet at 50 and 60% sorghum
flour levels. Incorporation of sorghum flour to wheat flour affected the dough
strength significantly (Table 2). As the proportion of sorghum
flour in flour blends increased, dough strength was decreased (p<0.001).
Decreased gluten and higher fiber content in the dough samples with higher level
of sorghum flour and reduced proportion of wheat flour are the possible reasons
for decreased dough strength.
| Table 1: | Analysis of variance for some physical properties of sorghum
flour incorporated biscuits fortified with DSF |
| *p<0.001 | |
| Table 2: | Analysis of variance for different textural properties of
sorghum flour incorporated biscuits fortified with DSF |
| *p<0.001 | |
Morad et al. (1984) reported the deterioration in rheological properties with increasing levels of sorghum in blends, could be attributed to the dilution of wheat gluten upon sorghum substitution. Studies indicated a decline in quantity and quality of gluten content in blends with the increased proportion of sorghum flour (Rao and Rao, 1997). The study carried out by Brennan and Samyue (2004) showed a reduction in the viscopasting properties of the flour dietary systems with increased fibre content.
Expansion in diameter (multiple R2 = 0.93), thickness (multiple R2 = 0.64) and spread ratio (multiple R2 = 0.98) were decreased significantly with increased proportions of sorghum flour (Table 1), may be due to decreased dough strength with increased proportion of sorghum flour. Brennan and Samyue (2004) observed that dietary fiber of the biscuit formulations also affected the thickness development during cooking.
Textural properties of biscuits are one of the most important quality parameter, which affect the demand for biscuits. The hardness of sorghum flour incorporated biscuits up to 20% was comparable with the control biscuits. Thereafter biscuit hardness increased at 30 and 40% sorghum flour levels but again a decrease was observed at 50 and 60% sorghum flour levels (Fig. 1). The similar trend was also observed in the breaking strength (peak breaking force) of different biscuit samples. As the proportion of sorghum flour increased, peak breaking energy (toughness), average breaking force and average breaking energy of biscuit samples also increased (Table 2). Higher fibre content in sorghum flour than wheat flour may be attributed to the increased toughness of the biscuits in proportion to the sorghum flour levels. Although the biscuits samples with higher proportion of sorghum flour were tougher as compared to control biscuits but found acceptable on sensory evaluation.
The colour of the food products is the first attribute that affects the decision
of consumer for purchasing or consuming any food products. The results (Table
2) indicated that the proportions of sorghum flour affected the colour of
biscuits significantly. The L* values (whiteness) of biscuit samples decreased
while a* value (redness) increased with increased proportion of sorghum flour,
but no specific trend was observed on change in b* values of different biscuit
samples (Fig. 2). The decreased L* values and increased a
values resulted in the darkening of the biscuits, which ultimately affected
the sensory scores for appearance and colour but the appearance and colour of
biscuits, even with higher proportions of sorghum flour, was well accepted during
sensory evaluation. Crabtree and Dendy (1977) also stated the darkening of colour
of the product, as the proportion of millet increased.
| Fig. 1: | Effect of different levels of sorghum flour in flour blends
(0, 10, 20, 30, 40, 50 and 60%) on textural properties of biscuits fortified
with 5% DSF |
| Fig. 2: | Effect of different levels of sorghum flour in flour blends
(0, 10, 20, 30, 40, 50 and 60%) on colour (L*, a* and b* values) of biscuits
fortified with 5% DSF |
The proximate composition (% dry weight basis) of wheat flour, sorghum flour and defatted soy flour used in the preparation of biscuits were protein 10.47, 9.67 and 56.31; fat 1.4, 1.11 and 1.09; ash 0.73, 1.14 and 6.42; total dietary fibre 0.42, 3.18 and 3.78 and carbohydrates 86.98, 84.73 and 32.40%, respectively. Moisture content of the different biscuit samples, baked at same temperature and time was similar (p>0.05). Although the protein content in control biscuit samples was slightly higher but the higher percentage of dietary fibre and mineral content (Fig. 3) with overall acceptability scores in the range of 7.69 to 7.08 for biscuits containing sorghum flour from 10 to 50% and fortified with 5% DSF, showed the possibility of incorporation of sorghum flour with 5% DSF in biscuits on commercial scale.
As level of sorghum flour increased (Table 3) the sensory
scores for sensory texture, flavour and taste and overall acceptability decreased.
The effect of sorghum flour was also found significant on other attributes like
appearance and colour and odour of biscuits. The mean sensory scores, for different
sorghum flour incorporated biscuits, for all the sensory attributes were more
than the minimum acceptable score of 6. The results thus indicated that the
biscuits prepared from different level of sorghum flour with 5% defatted soy
flour were accepted by the panelist with highest acceptability at 10% sorghum
flour level.
| Table 3: | Effect of different levels of sorghum flour in flour blends
on sensory quality of biscuits fortified with 5% DSF |
| Fig. 3: | Effect of different levels of sorghum flour in flour blends
(0, 10, 20, 30, 40, 50 and 60%) on proximate composition of biscuits fortified
with 5% DSF |
CONCLUSION
Substitution of wheat flour with pearled sorghum flour and fortified with 5% DSF affected the physical, textural, nutritive and sensory characteristics of biscuits in general. However, the study showed that pearled sorghum flour can be utilized for making acceptable quality biscuits up to 50% levels with 5% DSF but the best sensory acceptability of biscuits with highest mean sensory scores for appearance and colour (7.75), texture (7.74), flavour and taste (7.56) and overall acceptability (7.69) of the biscuits was observed for the biscuits containing 10% sorghum flour.