Effect of Beetroot Powder Incorporation on the Textural, Sensory and Nutritional Quality of Legume and Oil Seeds Based Snack Bar

Since past decade, World Health Organization recommends formulation of innovative food products (WHO, 2004) while keeping the customers nutritional requirements in mind.  Nowadays, consumers are demanding such processed snack foods which are less perishable, tastier and convenient and above all contribute to health benefits. Food manufacturers are also coming forward with wide variety of snacks specifically prepared with natural products to satisfy wide consumer spectra.

Snack bars are gaining importance worldwide since these are available with numerous nutritional claims of being rich in fibre, omega-3, protein, antioxidants etc. Mostly these snack bars are formulated using different food groups alone or in combination including fruits, millets, cereals, oil seeds and natural sweeteners. However, the use of synthetic colorants, flavors and antioxidants to enhance the sensory appeal and shelf life of these bars is of prime concern among health conscious consumers due to its adverse health effects (Shahidi and Ambigaipalan, 2015). Therefore, use of natural food ingredients without addition of synthetic chemicals should be the prime focus of manufacturers in order to maximize the health benefits of these nutritious bars.

Beetroot (Beta vulgaris) contains fair amount of protein and fat but considered a good source of dietary fibre, carbohydrates, folate, minerals viz. potassium, phosphorus, magnesium and bioactive compounds like: flavonoids and carotenoids (Georgiev et al., 2010; Longvah et al., 2017). It is also elucidated to have highest phenols and antioxidant activity among all the roots and tubers (Sreeramulu and Raghunath, 2010). The major phenolic compound present in beetroot is betalains, which imparts significant red color and also used as a natural colorant in variety of food systems. It has also been found to possess high antioxidant activity (Georgiev et al., 2010) which is associated with numerous health benefits including inhibition of lipid peroxidation, anti-inflammatory and chemo-preventive properties (Reddy et al., 2005).

Despite the superior nutritional quality, beetroot consumption is very limited owing to its limited availability due to its high moisture content, sustained metabolism and microbial attack, leading to damage during harvesting and storage (Agbor-Egbe and Rickard, 1991). Hence, to curtail its spoilage problem, simple processing method like drying can be applied. Dried beetroots can further be converted into chips or powder for the formulation of nutritious snack foods.

Therefore, the present study aims at 1) formulation of beetroot powder (BRP) incorporated legume and oil seeds based snack bars, 2) analysis of textural and sensory qualities of formulated snack bars and 3) nutrient evaluation of most acceptable snack bars.

Procurement of raw ingredients
 
The study was conducted in year 2017 (January-June) in Foods and Nutrition Department, College of Home Science, G.B.P.U.A. and T., Pantnagar, Uttarakhand, India. For the study, fresh beetroots were procured from Pantnagar haat. Other raw materials viz; flax seeds, roasted bengal gram, honey, sesame seeds, roasted peanuts and dry coconut were purchased from local Pantnagar market.
 
Preparation of BRP and other ingredients
 
Fresh beetroots were peeled, washed properly and cut into thin, round slices (<4 mm) followed by its drying at 60°C temperature for 6 hours in hot air oven. Dried beetroot slices were ground into fine powder using electric grinder. Other ingredients viz; dry coconut was grated into small chips, roasted peanuts were cut into small pieces after skin removal, flax seeds and sesame seeds were roasted for 2 minutes, separately and allowed to cool. Roasted bengal gram and roasted flax seeds were ground into coarse powder using electric grinder.
 
Preparation of snack bars
 
Table 1 represents various ingredients used in different proportions for the formulation of fifteen snack bars. For the preparation of BRP incorporated snack bars (B1-E3), BRP, bengal gram powder, flax seeds powder and honey in different proportions were mixed with roasted sesame seeds, roasted peanuts and coconut chips. Control snack bars (A1-A3) had same ingredients except BRP. Thereafter, well mixed mixture for each combination was placed and spread uniformly using rolling pin on aluminum tray and snack bars weighing 50 g were cut out with the help of moulds measuring 9x3x1.5 cm³ size. Each individual snack bar was packed properly in High Density Polyethylene bags for further analysis.


 
Texture analysis
 
Texture analysis was performed at room temperature using HDTA plus texture analyzer in strain mode with a cylindrical probe using three pieces (2x2x1.5 cm³) of each sample which were compressed twice to 50% of original height. Pre-test, test and post-test speeds were 1, 1 and 5 mm/s respectively. From the resulting curves hardness, cohesiveness, springiness, gumminess and chewiness were determined.
 
Sensory evaluation
 
All the snack bars were evaluated for their sensory quality by a semi-trained panel of 15 members from the Department of Foods and Nutrition, G.B.P.U.A.T., Pantnagar. Nine point Hedonic scale (Amerine et al., 1965) was used to find out the most acceptable snack bar based on various sensory parameters. Most acceptable control bar and BRP incorporated snack bar were further subjected to nutrient analysis and shelf life study.
 
Nutrient composition of control bar and BRP snack bar
                                                                       
For analyzing the nutrient composition snack bars were crushed, dried in hot air oven at 60°C for 120 minutes and then ground into fine powder.
 
Proximate composition and mineral analysis
 
Moisture, total ash, crude protein (using the factor 6.5 x N), crude fat and crude fiber content were analyzed as per the standard methods of AOAC (AOAC, 2000). The carbohydrate content and physiological energy value were calculated using the following equations.
 
% Carbohydrate =
100 - [moisture (%) + ash (%) + crude fat (%) + crude protein (%) + crude fiber (%)]      
 
Physiological energy value (Kcal/100 g) =
[Carbohydrate (%) x 4 + [Protein (%) x 4 + [Fat (%) x 9]
 
The minerals like calcium and iron were estimated using atomic absorption spectrophotometer method (Raghuramulu et al., 2003).
 
Total phenolic content, flavonoids, total antioxidant activity and folic acid
 
Total phenolic content of samples was determined as per Folin-Ciocalteu’s method (Singleton et al., 1999). Total antioxidant activity was estimated by DPPH (2.2-Diphenyl-1-picrylhydrazyl) radical scavenging activity (Brand-Williams et al., 1995). Total flavonoid content was measured according to colorimetric assay (Zhishen et al., 1999) and folic acid content was determined as per method illustrated by Ranganna (1986).
 
Statistical analysis
 
Statistical analysis was performed using WASP version 1, developed by ICAR-CCARI, Goa, India. All the experiments were conducted in triplicate except texture analysis and sensory evaluation (fifteen observations). Data pertaining to textural and sensory properties were analyzed using one way ANOVA. Two sample t-test was used to analyze the data of nutrient composition.

Texture analysis of formulated snack bars
 
For the evaluation of textural qualities, texture profile analysis (TPA) is the most commonly used standard test which quantifies various textural parameters in just one experiment. The textural properties of all the snack bars (A1-E3) have been presented in Table 2. The hardness values for all the snack bars were significantly different (p<0.05) which suggests that the incorporation of BRP altered the textural properties of all snack bars. On increasing the level of BRP from 5%-20%, all the BRP incorporated snack bars (B1-E3) showed decline in the hardness values. Similarly, gradual increase in the amount of honey (32% to 36%) also decreased the hardness values. Higher amount of honey may have resulted in better binding of ingredients at 36% than 32% and 34% which in turn may have decreased hardness properties. Hardness values for all the snack bars ranged from 40.25 N to 129.20 N, which were remarkably lower than the hardness values (99.606 N to 157.956 N) for the cereal bar containing pineapple peel flour (Aparecida et al., 2016) suggesting that snack bars formulated in the present study are softer. Regarding springiness property, gluten free nature of all the ingredients used in this study resulted in very low springiness for snack bars ranging from 0.12 mm to 0.27 mm.

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With respect to cohesiveness, it was observed that cohesiveness increased with increase in amount of honey at same level of BRP which indicates that higher moisture content due to addition of higher amount of honey and BRP, lead to better cohesiveness. An increasing trend was also observed in case of gumminess and chewiness but only up to 10% incorporation level of BRP followed by a gradual decrease in the values with 15% and 20% of BRP, indicating that the force needed to disintegrate the snack bars to a steady state of swallowing decreased at 15% and 20% BRP incorporation level. Results observed in the present study are in agreement with those reported by Bchir et al., (2018) and Mridula et al., (2013) for cereal bar and flax seed enriched bar, respectively.
 
Sensory evaluation of formulated snack bars
 
Formulated snack bars (A1-E3) were evaluated for various sensory parameters viz; taste, after taste, color and appearance, texture and overall acceptability using nine- point Hedonic scale (Table 3). In case of BRP incorporated snack bars (B1-E3) sensory quality declined with increase in the level of BRP. Mean sensory scores for taste and after taste decreased significantly (p<0.05) which may be due to geosmin, an endogenously produced volatile compound in beetroot, which imparts undesirable earthy taste (Bach et al., 2015). Bars incorporated with 20% of BRP (E1-E3) received lowest scores for all the sensory parameters due to unpleasant taste, appearance and after-taste. Increased level of BRP also resulted in darker earthy red color in snack bars which could be attributed to pigments betalains and betaxanthins in beetroot (Bach et al., 2015). Among control bars (A1-A3 with 0% BRP), A3 bar received highest scores for all the sensory parameters including overall acceptability (7.57). However, in case of BRP incorporated bars, all the bars with 5%-15% of BRP (B1-D3) were highly acceptable and showed no significant difference with control bar A3 (0% BRP) in terms of overall acceptability. Therefore, D3 snack bar with 15% of BRP and A3 control bar were selected for nutrient analysis and shelf life study. Singh et al., (2016) in their study reported 10% BRP level to be the most acceptable for BRP incorporated corn extrudates. However, in another study noodles prepared with 30% of beetroot pulp were found most acceptable (Chhikara et al., 2019).

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Proximate composition and mineral analysis of A3 control bar and D3 snack bar
 
Beet root is a fair source of protein (1.95%), fat (0.14%), total dietary fibre (3.31%), ash content (1.46%), energy (35 Kcal) and minerals viz. calcium (17.28 mg/100g), iron (0.76 mg/100g) (Longvah et al., 2017). Therefore, incorporation of 15% BRP resulted in significantly higher (p<0.05) moisture, ash and carbohydrate content in D3 snack bar (Table 4). High total dietary fiber content of BRP which allows good water holding capacity (Kohajdováet_al2018) may be the suggestive of higher moisture content in D3 snack bar. BRP incorporation also increased total phenol, flavonoids and antioxidant activity significantly (p<0.05) in D3 snack bar, which may be elucidated by the fact that beetroot is the richest source of phenols (169.41 GAE mg/100 g) and antioxidant activity (125.10 TE mg/100 g) among all the roots and tubers (Sreeramulu and Raghunath, 2010). In a similar study, beetroot juice alone significantly affected the total phenol and antioxidant activity of beetroot and ground nut meal incorporated pasta (Mridula et al., 2016). On the contrary, A3 control bar, prepared with comparatively higher amount of flax seed and bengal gram (24 g each), had significantly higher (p<0.05) crude protein and fat content than D3 snack bar. Bengal gram is a good source of protein (18.77%) while flax seeds are considered rich in both protein (18.55%) and fat (35.67%) (Longvah et al., 2017) which in turn resulted in higher protein and fat content in A3 control bar. However, the crude fibre and folic acid content were found comparable in both the snack bars. Ingle et al., (2017) and Reddy et al., (2014) developed cookies with 15% of BRP and extruded snacks with 20% BRP, respectively and reported similar results for nutrient composition.

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The present study revealed that snack bar prepared with 15% of BRP was the most acceptable among all the snack bars on the basis of textural and sensory evaluation. Also, incorporation of 15% BRP resulted in improved nutrient profile (ash, carbohydrate, folic acid, antioxidants content) of snack bar, which validates great potential of beetroot as a functional food. Keeping in view all these facts, 15% of BRP with other ingredients may be considered for nutritious snack bar formulation at commercial level. Being rich in antioxidants, BRP incorporated snack bars can also be offered to the patients with hypertension and atherosclerosis to ascertain its benefits in such clinical conditions.

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