Development of Finger Millet and Sapota based Ready-to-Reconstitute Halwa Mix

Millets are one of the early foods domesticated by humans. They are also known as nutria-cereals and are a source of food, feed and fodder (Bhat et al., 2018). They come from the family Poaceae. Modern acquired lifestyles have paved the way for micronutrient deficiencies along with diabetes, cardiovascular diseases and hypertension. Thus, millets have revived as a plausible alternative for living a healthy lifestyle (Singh et al., 2020). In 2019, the global millet production was 27.8 million tons. India ranks 1^st in millet production, accounting for 41.0 per cent of the global market share (Research and Markets, 2019). With an aim of creating domestic and global demand, the Indian Government have proposed the year 2023 as International Year of Millets which have been approved by FAO (FAO, 2022).

Eleusine coracana (finger millet) is a staple crop in Asian and African countries, particularly India and Nigeria. The principal botanical components of the finger millet kernel are the seed coat, embryo (germ) and endosperm. There are varieties that are yellow, white, tan, red, brown, or violet in color, but only the red-colored ones are widely cultivated worldwide. Finger millet is as healthy as other cereals, with high calcium content (300-350 mg/100 g) and a good amount of protein, dietary fiber and micronutrients (Tiwari et al., 2018). The anti-oxidant and immune-modulating properties of finger millet’s rich phytochemical profile guarantees a positive health impact and make finger millet a powerhouse of health benefiting nutrients (Chandra et al., 2016). However, finger millet is still an underutilized crop due to lack of awareness of its nutritional quality and health benefits.

Sapota is a climacteric fruit used for its sweet and delectable taste. Sapota contains a diverse range of sugars, vitamins (A, C, niacin, pantothenic acid and folate), acids, protein, minerals (Fe, K, Cu), phenolics and carotenoids. Sapota is deemed to be one of the healthiest fruits to alleviate micronutrient malnutrition (Srivastava et al., 2014). Sapota is also utilized as a traditional medicine in India (Divya et al., 2014).  Many researchers and practitioners have turned their focus to sapota because of its vast range of phenolic compounds (as natural antioxidants) and flavonoids.

Halwa is a traditional dessert which is popular not only in the Indian cuisine but also in Asian and Middle Eastern cuisines. Traditionally it is prepared using semolina, ghee, seeds and nuts during festivities and occasions. It is also called as sheera or kesari in some regions.

The ready to cook (RTC) and ready to Reconstitute (RTR) food demand is increasing. The ingredients used in Indian traditional foods have tremendous health advantages (Mangalassary, 2016). There is a lack of research on development and mechanization of convenience type traditional food products. Considering the great importance of millets, fruits and milk in a balanced diet and the potential for RTC/RTR food products in market, a study was carried out to develop finger millet and sapota based RTR halwa mix.

The study was conducted at College of Food Processing Technology and Bio Energy, Anand, Gujarat, India from November 2021 to May 2022.
 
Materials
 
Finger millet (Gujarat Nagli 8 variety) was procured from Hill Millet Research Station, Dahod, Gujarat. Sapota fruits of Kalipatti variety were purchased from a local farm in Navsari, Gujarat. Other materials required for halwa preparation such as milk, sugar, ghee and cardamom powder were purchased from local market in Anand, Gujarat.
 
Experimental design
 
Central composite design of the response surface methodology was adopted for the optimization of ingredients for the development of finger millet and sapota based RTR halwa mix. Level of milk (ml), sugar (per cent of weight of the dried halwa) and dried sapota chunks (per cent of weight of the dried halwa) were taken as independent factors. The responses taken into consideration were sensory attributes (color and appearance, body and texture, taste and aroma and overall acceptability) and rehydration ratio. The experimental plan along with the actual levels of the three ingredients is shown in Table 1.


 
Preparation of dried sapota chunks
 
Fresh ripe sapota fruits were washed, peeled and seeds and other inedible portion were removed. The edible portion was cut into 4-5 mm chunks using a stainless steel square mesh of a fruit chopper. The prepared sapota chunks were vacuum dried at 70°C and 650 mm Hg pressure. The drying process was continued until the final moisture content of sapota chunks reached 8 per cent or below. The dried chunks were packed in polyethylene pouches for further use.
 
Preparation of halwa mix
 
For the preparation of RTR halwa, 100 g of finger millet flour was roasted on a low flame followed by cooking with milk. Ghee (at the rate of 5 per cent of flour weight) was added. The prepared halwa was spread into a uniform layer (3 to 4 mm thick) on to stainless steel tray and vacuum dried at 60°C and at a pressure of 720 mm Hg. The dried halwa was ground using a mixer grinder. Depending upon the weight of powdered halwa obtained, powdered sugar (per cent of weight of dried halwa) and dried sapota chunks (per cent of weight of dried halwa) were dry blended with the mix. Total weight of halwa mix was recorded and cardamom powder was added at the rate of 0.075 per cent of the total weight of dry blended halwa mix. The prepared RTR halwa was reconstituted by adding hot boiling water to the mix in the ratio of 1 : 1. The mix was uniformly stirred and kept covered for 3 minutes.
 
Analysis
 
The nutritional parameters such as moisture, protein, fat, crude fiber, ash and total carbohydrate were estimated according the methods described in Ranganna (2007) and AOAC (2019). Mineral estimation was carried out using ICP-OES (Model: Optima 700DV) as per the method given by Kumaravel and Alagasundaram (2014). Total phenolic content and antioxidant activity was estimated as per the procedure described by Camargo et al., (2016) and Upadhyay et al., (2015) respectively, with slight modifications. The microbial quality was analyzed as per the procedure described by Ranganna (2007).
 
Sensory evaluation
 
The sensory evaluation of rehydrated halwa was carried out in terms of color and appearance, body and texture, taste and aroma and overall acceptability using a 9-point hedonic scale. The sensory evaluation was conducted by 9 panelists.
 
Rehydration ratio
 
The rehydration ratio of the RTR halwa mix was calculated using the following equation Vaghela et al., (2016) :
 

      

Statistical analysis
 
The finger millet and sapota based RTR halwa developed using various runs were analyzed using Design Expert (V. 13.0.5) software. All the sensory scores were average of nine scores and the rehydration ratio was average of three readings. The responses of the product prepared using the experimental design and the actual values of the independent variables are shown in Table 1.

Analysis of responses
 
Color and appearance
 
The color and appearance score of the reconstituted halwa ranged from 6.9 to 7.9 (Table 1). The F, R², adjusted R²and adequate precision values were 60.55, 0.9820, 0.9658 and 28.5289 respectively, indicates the model was highly significant (P<0.0001) and can be used to predict the color and appearance score within the design space.
       
The following quadratic model may be used for representing the variation of color and appearance score:
 

Color and appearance= 7.87 - 0.1421A + 0.0196B + 0.0073C 
                                        - 0.0125AB + 0.0375AC - 0.0125BC
                                        - 0.2451A² - 0.0330B² - 0.0153C²   

       

It can be observed from Fig 1 that the color and appearance score increased with increase in the amount of milk upto about 210 ml after which the scores decreased. Milk fat imparted a glossy and rich visual appearance which might have affected the initial increase in color and appearance scores. Further addition lead to dilution of the dark chocolate brown color resulting in declined scores. Similar results were obtained by Vaghela et al., (2016) on addition of khoa to carrot halwa.


 
Body and texture
 
The body and texture of the reconstituted halwa ranged from 6.3 to 8.2 (Table 1). The F, R², adjusted R² and adequate precision values were 32.82, 0.9673, 0.9378 and 20.82 respectively, indicates the model was highly significant (P<0.0001) and can be used to predict the body and texture score within the design space.
       
The following quadratic model may be used to represent the variation of body and texture score:

Body and texture = 8.11 - 0.3185A + 0.0073B - 0.0196C
                               +0.0125AB + 0.0875AC - 0.0375BC
                               -  0.4835A² - 0.0769B² - 0.1299C² 

The body and texture scores were significantly affected by addition of milk after a certain level (Fig 2). The use of high fat milk for development of halwa formed a slimy skin at powder/water interface. The hydrophobic nature of the fat prevented water penetration into the halwa mix during reconstitution, which resulted in poor body of the reconstituted halwa. Similar effect was observed by Fitzpatrick et al., (2016), Velpula et al., (2019) and Vaghela et al., (2016).


 
Taste and aroma
 
The taste and aroma of the reconstituted halwa ranged from 5.8 to 8.2 (Table 1). The F, R², adjusted R² and adequate precision values were 41.83, 0.9959, 0.9923 and 60.54 respectively, indicates the model was highly significant (P<0.0001) and can be used to predict the taste and aroma scores within the design space.
       
The following quadratic model may be used to represent the variation of taste and aroma score:
 

Taste and aroma = 0.0130 - 0.0002A - 0.0023B - 0.0004C
                              + 0.0002AB - 0.0001AC + 0.0001BC
                              +0.0003A² + 0.0031B² + 0.0002C²

From Fig 3 it can be observed that sugar had a positive effect on the taste and aroma scores up to certain limit after which it negatively affected the taste and aroma scores. After a certain amount, the excessive sweetness imparted by high levels of sugar was not preferred by the panelists and was evident from the decreased scores of taste and aroma. With increase in addition of sapota chunks the taste and aroma scores increased from 6.7 to 7.1, which might be due to the sweet and delicate taste offered by the sapota chunks.


 
Overall acceptability
 
The overall acceptability score of the reconstituted halwa ranged from 7.0 to 8.1 (Table 1). The F, R², adjusted R² and adequate precision values were 41.21, 0.9737, 0.9501 and 17.97 respectively, indicates the model was highly significant (P<0.0001) and can be used to predict the overall acceptability within the design space.
The following quadratic model may be used to represent the variation of overall acceptability:
 

Overall acceptability= 8.04 - 0.1544A + 0.1444B + 0.0320C
                                   - 0.0375 AB + 0.0625AC - 0.0375BC
                                   - 0.2815A² - 0.2461B² - 0.1047C²

       
The overall acceptability of halwa was found to increase up to a certain range for both milk and sugar, beyond which the scores decreased. With an increase in the level of dried sapota chunks from 4 to 15 percent, the overall acceptability of reconstituted halwa also increased. From Fig 4 and 5, it can be inferred that overall acceptability of reconstituted halwa was maximum at the center point for both milk and sugar and at a high level of sapota chunks.




 
Rehydration ratio
 
The rehydration ratio ranged from 1.66 to 2.40 (Table 1). The F, R², adjusted R² and adequate precision values were 42.99, 0.8896, 0.8689 and 22.52 respectively, indicates the model was highly significant (P<0.0001) and can be used to predict the body and texture score within the design space.
       
The following linear model may be used for representing the variation of rehydration ratio:

Rehydration ratio= 0.3074 + 0.0543A - 0.0008B - 0.0125C
       
The level of milk negatively impacted the rehydration ratio (Fig 6). The rehydration ratio was found to decrease significantly with increase in the amount of milk. The high proportion of fat from milk formed a thin film around the particles of the halwa mix. This layer prevented penetration of water into the bulk and thereby resulted in lower rehydration ability of the halwa mix. From Fig 6, it can be observed that with increase in amount of dried sapota chunks, the rehydration ratio increased slightly. This dehydrated sapota chunks also absorbed water during rehydration to acquire fresh fruit like characteristics. Thus, greater the amount of sapota chunks, greater amount of water was absorbed resulting in a higher rehydration ratio. Similar results were obtained for rehydration ratio by Vaghela et al., (2016) on addition of fatty ingredients to RTR halwa.


 
Optimization of independent variables
 
Numerical optimization technique of the Design Expert 13.0.5 software was used for simultaneous optimization of level of each ingredient to obtain the best product. During the optimization process, specific constraints were applied on the responses. The sensory analysis parameters such as color and appearance, body and texture, taste and aroma and overall acceptability were maximized and rehydration ratio was kept within range for desirability analysis. Out of the two solutions obtained, the solution having 208.8 ml of milk, 52.9 percent sugar (percent weight of the dried halwa) and 9.4 percent dried sapota chunks (percent weight of the dried halwa) was selected as best formulation, with a desirability of 0.991.The experimental values (average of 6) of the RTR halwa prepared using optimized formulation and the values predicted using the model equations are shown in Table 2. The predicted and experimental values of responses were almost similar and within the range at 95 percent level of confidence.

The nutritional, bio-chemical, sensory and microbial attributes of the optimized finger millet and sapota based RTR halwa mix was carried out and the average values of 3 replication (average of 9 for sensory) is reported in Table 3.

The optimized halwa mix contained 208.8 ml of milk, 52.9 per cent sugar (percent weight of the dried halwa) and 9.4 per cent dried sapota chunks (per cent weight of the dried halwa). The RTR halwa provided 439.32 kcal of energy per 100 g. The optimized halwa mix had a score of 7.8, 7.9, 8.0 and 8.0 for color and appearance, body and texture, taste and aroma and overall acceptability respectively and the rehydration ratio was 2.1. The RTR halwa was rich in calcium (330 mg/100 g) and magnesium (145 mg/100 g). It had an antioxidant activity of 71.3 per cent and the total phenolic content was 119.2 mg/100 g. Considering the overall nutritional, as well as sensory attributes, the developed RTR halwa can fulfill the objective of providing consumers with a nutrient dense, delicious and convenient RTR healthy traditional food. The optimized millet based RTR halwa mix can be suitably employed for commercial production.

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