Abstract: Effect of roasting on important physical properties and sensory acceptability of soybean for making sattu formulations was studied at three temperature (180, 200 and 220° C) and time (45, 60 and 75 sec) combinations. In general, GMD of soybean increased with increase in roasting temperature and time except for 75 sec. Hardness, toughness and average rupture force decreased with increase in roasting temperature and time except at 200 and 220° C for 75 sec time. L* value of roasted soybean decreased at increased temperatures while a* values increased with increased roasting temperature and time that affected hue and chroma of soybean. The lower hardness of soybean roasted at 200° C for 60 sec as compared to higher temperature and highest mean sensory scores for different attributes for soybean flour prepared from the soybean roasted at 200° C for 60 sec, make this temperature and time combination best for roasting of soybean for incorporating in sattu formulations. Roasted soybean flour can be incorporated up to 20% level but the best sensory acceptability of sattu formulation was observed with 10% soy flour level with 50% barley and 40% Bengal gram.
INTRODUCTION
Sattu, is a ready-to-eat traditional snack food of northern India and most popular in Bihar and Uttar Pradesh. It is prepared from flour of roasted cereals only, or legumes only or, combination of cereal and legumes with added flavouring agents (Mridula et al., 2004a). It is a convenient food product, containing digestible dietary constituents of vital importance. Roasting which is a simple and more commonly used household and village level technology, pre-cooks the ingredients used in food grains and oilseed based mixes and increases 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 eliminates most of anti-nutritional or toxic effects of legumes, partially or wholly (Liener, 1973).
Amongst various cereals and legumes, barley and bengal gram are the most liked grain for making sattu (Mridula et al., 2004b). Bengal gram sattu is commercially produced in Bihar and eastern Uttar Pradesh, which is the most liked form of sattu but in other parts of Uttar Pradesh, barley and bengal gram based sattu is preferred by the population. Earlier sattu was considered as food of the poor but now a days, it is gaining popularity amongst all because of its protein value and suitability of this product for diabetics due to lower glycemic index of Bengal gram and barley (Shukla et al., 1991). Anonymous (2000) developed an acceptable quality product from roasted flour mixture using wheat, bengal gram, defatted soyflour, groundnut and jaggery called Amirtham. Proportions used for preparing this product were 50% wheat, 25% bengal gram, 8.25% defatted soy flour and 16.66% groundnut.
Soybean, being less expensive, but rich source of good quality 40% protein and 20% fat, has been recognized as a vital ingredient for protein enrichment for ready to eat food product (Kulkarni, 1994). Several workers have explored the possibilities of using soy flour with cereal flour to prepare a variety of food products of Indian taste such as snacks, baby foods, chapatti, beverages and bakery products (Rathod and Williams 1970; Tsen et al., 1973; Sushma et al., 1979; Okeiyi and Futrell, 1983; Chauhan and Bains, 1985; Singh and Singh, 1989; Chauhan and Santosh Kumari, 1990; Vimala et al., 1990; Deshpande et al., 2004; Mridula and Wanjari, 2006) but information on optimum roasting temperature and time combination for soybean for incorporating in sattu is not cited in the literature. As sattu is getting popular amongst diabetics, incorporation of soybean in sattu in acceptable proportion will not only enhance the protein value of the product but also provide benefits of health promoting phytochemicals at an affordable price. The present study was conducted with the objective to standardized roasting temperature and time combination for soybean for making sattu formulations based on barley and bengal gram.
MATERIALS AND METHODS
Soybean with Geometric Mean Diameter (GMD) of 5.249 mm was used for the study. In order to see the effect of roasting on quality of soybean for making sattu with barley and bengal gram, sattu was prepared using the method shown in Fig. 1. Raw soybean with moisture content of 11.09% (d.b.) was dipped in water in a wire mesh basket, twice for washing followed by tempering for 3 h. The moisture content of the tempered soybean sample was 14.22% (d.b.). The tempered samples were roasted in sand using sand grain ratio 10:1 at three different temperatures (180, 200 and 220° C) and time (45, 60 and 75 sec) combinations. The roasted samples were tempered for 4 h and packed in LDPE bags (50 μ) and kept in desiccator. The quality parameters viz., moisture, GMD, colour (L*, a* and b* values) and textural properties were determined after 24 h of roasting. These roasted samples were dehulled in mini dhal mill (capacity 100 kg h-1) at 6 mm dehuller clearance.
| Fig. 1: | Method for preparation of soybean fortified sattu |
Dehulled and cleaned soybean dhal was ground for making roasted soybean flour. The ground samples were evaluated for different sensory attributes to find out the best accepted soybean flour, prepared from soybean roasted at different temperature and time combinations. Different sattu formulations with barley, bengal gram and soybean were prepared using soybean flour at 5, 10, 15 and 20% level. Thus the proportion of barley, bengal gram and soybean in different formulations was 50:50:0 (control), 50:45:5, 50:40:10, 50:35:15, 50:30:20, respectively. Roasted barley and bengal gram was prepared as per the standardized process (Mridula et al., 2004b).
Geometric Mean Diameter
GMD of raw and roasted sample were measured using Vernier Caliper with least
count of 0.02 mm. Geometric mean of the spatial dimensions (length, breadth
and thickness) was calculated as:equivalent diameter = (L x B x T)1/3.
Moisture content of samples was determined by using oven method (105° C) (AOAC, 1990).
Textural Properties
Textural properties of raw and roasted soybean such as hardness, toughness
and average rupture force were measured using Texture Analyzer (TA) TA-HDi.
Stable Micro systems. The TA setting were: Mode-measure force in compression,
option-return to start, pre test speed-3 mm sec-1, test speed-1 mm
sec-1, post test speed-10 mm sec-1, distance-3 mm, stainless
steel cylinder probe-5 mm diameter and 50 kg load cell. Textural properties
were measured for 10 representative grains 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
the 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 Determination
Colour (L*, a* and b* values) of the samples 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. Hue angle
(h°) is the attribute of colour by means of which the colour is perceived.
Chroma (C*) is the attribute of colour used to indicate the degree of departure
of the colour from gray of the same lightness. h° and C* are computed by
using the following formula.
h° = tan-1 (b/a) |
C* = a2+b2 where a = a*, b =
b* |
Sensory Evaluation
Roasted soybean flour (in flour form only) and soybean incorporated sattu
with barley and bengal gram were evaluated in drink form, for different
sensory attributes by a panel of nine scientist of the Institute. The sattu
drink was prepared with 16 g formulation in 100 mL water with salt, cumin
seed powder and white pepper. Sensory attributes like colour and appearance,
body (sensory texture of sattu drink), roasted odour, flavour and taste
and overall acceptability for all samples were assessed using nine point hedonic
scale (IS, 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 and dislike extremely-1
(Larmond, 1977).
Statistical Analysis
Analysis of variance and polynomial regression for the data of the study
were computed using Statistica 7.1.
DISCUSSION
Roasting has a significant impact on the overall quality of grain and the final product i.e., sattu. The roasting odour, a most important quality of sattu is basically depends on the roasting temperature and time combination. Hence, roasting temperature and time combination is of great importance in grain processing for making sattu. It is observed that moisture content of roasted soybean decreased with increase in both roasting temperature as well as time, which is obvious and expected. In general, GMD of soybean increased with increase in roasting temperature and time except for 75 sec. The GMD of soybean roasted at 180° C for 45 sec, the lowest temperature and time combination was 5.23 mm as against 5.34 mm of grain roasted at 220° C for 75 sec. The increase in GMD is attributed to start of puffing of grain at high temperature and time combination. The recovery of de-hulled fraction of roasted soybean was in the range of 79.05 to 81.28%. The roasting temperature affected the recovery of dehulled soybean (p<0.001), may be due to higher powdering in case of grain roasted at 200 and 220° C.
Textural properties of the roasted soybean are very important because energy requirement for dehulling and grinding may be in proportion to the grain hardness. Various studies indicated the affect of grain hardness on particle size of milled grain and energy consumption in milling (Symes 1969; Moss et al., 1980; Tran et al., 1981). Grain hardness is affected by size, direction of applied force, moisture content (Zoerb and Hall, 1960; Bilanski, 1966), chemical composition (Bennett, 1950) and heat treatment (Abdelrahman and Hoseney, 1984). From the Fig. 2, it is observed that in general, hardness of soybean decreased with increase in roasting temperature and time of roasting except at 200 and 220° C for 75 sec time. The reason for the increase in hardness at 200 and 220° C for 75 sec, temperature and time combination may be due to drastic reduction in moisture content of the soybean grain that made the grain harder as also observed in case of bengal gram (Srivastav et al., 1994). The similar trend was observed in toughness and average rupture force of roasted soybean (Table 1 and Fig. 2). The effect of temperature and time of roasting on grain hardness, toughness and average rupture force is presented in non-linear polynomial regression equations. Both the independent variable i.e., temperature and time were considered for computation of coefficient of determination (Multiple R). The regression equation can be written as:
H = 2593.154-19.402 T+0.045 T2-13.177 t+0.099 t2 |
(1) |
| Fig. 2: | Effect of roasting on hardness, toughness and Average Rupture
Force (ARF) of soybean roasted at 180, 200 and 220° C temperature for
45, 60 and 75 sec time |
| Fig. 3: | Effect of roasting on colour (L*, a* and b* values) of soybean
roasted at 180, 200, 220° C temperature for 45, 60 and 75 sec time |
| Table 1: | Analysis of variance for textural properties and colour of
roasted soybean |
| ***p<0.001; **p<0.01; ns = non-significant | |
Ts = 2307.104-15.586 T+0.034 T2-15.937 t+0.12 t2 |
(2) |
ARF = 1439.83-10.288 T+0.023 T2-8.344 t+0.061 t2 |
(3) |
Where, H = hardness; Ts = toughness; ARF = average rupture force; T = temperature; t = time
The colour of the food product is the first attribute that affects the decision of consumer for purchasing or consuming any food. Roasting, in general, affected the colour of soybean grain. In general, L* value of roasted soybean decreased while a* values increased with increased roasting temperature that resulted in the darkening of the grain at higher temperatures and poor acceptability of that sample during sensory evaluation. Whereas, increase in roasting time at 180 and 200° C did not brought significant changes in L*, a* and b* values but at 220° C, L* values slightly decreased with increased roasting time (Table 1 and Fig. 3). The effect of temperature and time of roasting on hue angle (h°) and chroma (C*) for roasted soybean is presented in non-linear polynomial regression equations and after deleting the non-significant variable (time or temperature as the case may be), the regression equation can be written as:
h° = -57.4385+1.5956 T-0.0043 T2 |
(4) |
C* = -52.5473+0.6311 T+0.3419 t |
(5) |
The roasting temperature and time affected the sensory quality of soybean flour (Table 3). The mean sensory scores for all the attributes for roasted soybean flour, prepared from the grain roasted at 180 and 200° C for different time combination and 220° C for 45 sec were more than the minimum acceptable score of 5 (Table 2).
| Table 2: | Effect of roasting on mean sensory scores for different attributes
of soybean flour* |
| *Evaluated in powder form | |
| Table 3: | Analysis of variance for different sensory attributes of roasted
soybean flour for making sattu |
| ***p<0.001; ns = non significant | |
| Table 5: | Mean sensory scores for different attributes of soybean incorporated
sattu formulations* |
| *Evaluated in drink form | |
| Table 5: | Analysis of variance for different sensory attributes for
soybean incorporated sattu |
| *Sensory feeling of texture of sattu drink; ***p<0.001; ns: non significant | |
The results thus indicated that these samples of roasted soybean flour were accepted by the panelist with highest sensory scores for roasted odour and overall quality (7.21) for the samples prepared from the soybean roasted at 200° C for 60 sec, hence this sample was used for making barley, bengal gram and soybean based sattu formulations. The mean sensory scores of different sattu formulations for flavour and taste and overall acceptability were in the range of 8.04 (for control) to 5.21 (20% soy flour) and 8.01 to 6.04, respectively (Table 4). Although, the incorporation of soybean affected the sensory quality of sattu formulations (Table 5) but the sensory scores for flavour and taste and overall acceptability for sattu formulation up to 10% soy flour levels were comparable with the control sample drink form.
CONCLUSIONS
Roasting of soybean at different temperature and time combination affected the physical properties of soybean and sensory acceptability of soybean flour for making sattu. In general, hardness of soybean decreased with increase in roasting temperature from 180 to 220° C. The lower hardness of soybean roasted at 200° C for 60 sec as compared to higher temperature and highest mean sensory scores for colour and appearance (7.14), roasted odour (7.21) and overall quality (7.21) for soybean flour, prepared from the soybean roasted at 200° C for 60 sec, make this temperature and time combination best for roasting of soybean for incorporating in sattu formulations. The study showed that soybean can be incorporated up to 20% level but the best sensory acceptability of sattu formulation was observed with 10% soy flour level with 50% barley and 40% bengal gram.