Process optimization of Gulabjamun utilizing pearl millet (Pennisetum glaucum L.)

Introduction

India is immerged as major milk producing nation in the globe sharing 24% of the global milk production (Ministry of Fisheries, Animal Husbandry & Dairying, 2023) [14] . India has the world's highest production of milk and about 50-55% of its production is applied for manufacture of various traditional dairy products (Baladhiya et al., 2020) [3] . Traditional dairy products have always been an integral element of India's socio-cultural life. Traditional dairy products are always offered to celebrate festivals, wedding ceremonies, inauguration of a new house, baby birth, getting a job and social occasions. Traditional dairy products have more acceptability and longer shelf life than milk. It is also considered that the conversion of milk into milk products is more gainful than the sale of milk. The most significant benefit of this segment is the huge consumer demand for the products. Gulabjamun is a traditional Indian heat desiccated product in which khoa is a basic ingredient. In the category of traditional dairy products, khoa is in the paramount place. Dhap variety of khoa with 50 to 60% total solids is preferred for gulabjamun production. Traditionally, gulabjamun is made from dough containing mainly maida and khoa. This dough is formed into small round balls, which are deep-fried till golden to dark brown colour, soft and slightly spongy body. The product should have no lumps and rigid inner midst and have a consistent grainy structure. Soaking in sugar syrup is a key operation in the preparation of gulabjamun. Soaking of gulabjamun not only gives sweetness but also gives its typical texture. Maida contains a protein called gluten that provides the flour with its pliability and thickness as well as the capacity to be kneaded and binds the dough together. The preparation of gulabjamun utilising maida as a binder is unsuitable for people who suffer from celiac disease. So, using pearl millet (Pennisetum glaucum) flour in place of maida or its combination is the best way to reduce or make it free from gluten in gulabjamun. Millets are the oldest food grains and they may have been the first cereal used for domestic purposes. Millet growing region decreases by dint of low recognized support for millet compared to wheat, rice and maize. But at present to promote millets as a major component of food UN declares 2023 as the "International Year of Millets" (Kumari et al., 2023) [10] . In many nations, pearl millet (Pennisetum glaucum) has been recognised as a component of gluten-free cereals. In India, pearl millet is also known as "bajra". It is a major crop for poor farmers, especially the tribal people in India. Pearl millet is soothing and easy to digest. The chemical composition of gulabjamun varies greatly based on variables including the type and quality of khoa, constituents and syrup concentration. Gulabjamun contains moisture, fat, protein, total carbohydrates and ash ranging from 25 to 35%, 9 to 11%, 6 to 7%, 48 to 52% and 0.9 to 2%, respectively.

Materials and Methods

Raw components like milk, maida, pearl millet, sugar and ghee were used in the experiment. Milk received from the Mini Dairy plant of Sardarkrushinagar Dantiwada agricultural University for the study. Good quality Maida and Pearl millet which is free from stones, dust, insects and other impurities was procured from local market. Good quality sugar for preparation of sugar syrup and ghee is also procured from local market.

The pearl millet flour had an average composition of 4.38% fat, 10.82% protein, 8.96% moisture and 2.13% Ash.

Preparation of Khoa

Khoa was made from fresh standardised milk. Khoa was produced using heat desiccation in an open, steam-jacketed stainless steel pan that was run at 0.75 kg/cm2 steam pressure while being constantly stirred and scraped. The procedure of heating and stirring was carried out until the end product achieved the necessary consistency (60-% TS). After removing khoa from the kettle, it was allowed to cool at ambient temperature before being utilized within 24 hours to make gulabjamun.

Preparation of Gulabjamun

Gulabjamun was developed using a method described by Ghosh et al. (1986) [7] with minor alterations. It involves proper blending of khoa, Pearl millet/Maida at different rate, baking powder and water (optional) to make homogenous and smooth dough. Small amount of water was added in case of dough is hard. The small balls formed from the dough were deep fried in ghee to golden brown colour and subsequently transferred to 60 °Brix sugar syrup maintained at about 65 °C.

Sensory evaluation

Sensory evaluation of control gulabjamun and experimental gulabjamun was done by eight semi-trained judges. The 9-point hedonic scale method was used to evaluate sensory perception. Judges were also asked to record their thoughts and observations for each quality listed on the scorecard.

Compositional and Physico-chemical analysis

A sugar syrup soaked gulabjamun was heated for 20 minutes at 40 °C. They were then left on a sieve with a mesh size of about one centimetre square for 10 minutes to let the sugar syrup drain. Gulabjamun was then divided into small pieces and thoroughly mixed to create a paste that used for various analysis. Fat content of gulabjamun was determined using the Gerber method as per the procedures described by Ladkani and Mulay (1974) [13] . The total protein content was determined by semi-micro Kjeldahl method mentioned in AOAC (2002) [2] . Total solids were estimated by the protocol described in Laboratory Manual (1959) [11] . The BIS (IS: 1479-1961) method for determining ash content was used for determination of ash content of gulabjamun. Total carbohydrate was derived by difference of sum total of the major constituents like moisture, protein, fat and ash from 100. The BIS (IS: 1166-1986) method for condensed milk measurement was used to determine the acidity of gulabjamun. The pH of gulabjamun was measured using digital pH meter. The method described by Patel (2020) [17] was used for the sugar syrup absorption of gulabjamun.

Rheological properties

Rheological properties viz. hardness, cohesiveness, gumminess, springiness and chewiness of gulabjamun was determine by using Food Texture Analyzer of Lloyd Instruments LRX Plus Material Testing Machine, which operates on the parallel plate uniaxial compression principle.

Statistical analysis

Statistical analysis of data obtained from various experiments during optimization was done by using statistical software SPSS with completely randomized design (CRD).

Results and Discussion

Selection of Rate of Pearl Millet for the Acceptable Gulabjamun

Pearl millet: maida ratios of 25:75, 50:50, 75:25 and 100:00 were tested as binders for gulabjamun production during the preliminary studies. During the frying process, gulabjamun made with less than 20% binder was disintegrated. Based on the preliminary studies, different proportions of pearl millet: Maida by 20% weight of khoa was selected for further study. Four different levels of pearl millet: maida at ratios of 25:75 (G1), 50:50 (G2), 75:25 (G3) and 100:0 (G4) along with control 0:100 (C) were used for the manufacture of gulabjamun.

The compositional, physico-chemical, sensorial and rheological properties of each lot of gulabjamun were examined after each batch was manufactured using the technique shown in Figure 1. Selection of rate of pearl millet flour was optimised on the basis of sensory evalution.

Effect of Pearl Millet Flour on the Sensory Attributes of Gulabjamun

The consumption of dairy products is strongly correlated to the human senses, odour and taste. Sensory quality has most important for the market acceptance of any product. Effect of pearl millet flour on sensory attributes of gulabjamun was shown in Table 1. The most crucial factor in determining whether a food will be accepted is its flavour. The flavour score of gulabjamun added with different rates of pearl millet, control scored highest (8.35) among all treatments followed by G1, G2, G3 and G4 were found to be 7.86, 7.74, 7.38 and 6.80, respectively. The flavour score of gulabjamun declined significantly (p<0.05) from 8.35 to 6.80 as the level of pearl millet addition increased, as shown in Table 1. Treatments G1, G2 and G3 were discovered to be statistically equivalent to one another among all treatments. Texture plays a key role in consumer's acceptance and market value of any food stuff. The range for body and texture score of gulabjamun was found to be 8.25 (C) to 6.81 (G4). Compared to other treatments, the body and texture score was found to be higher in the control (8.25) sample. It can be shown from Table 1 that with an increased in the rate of pearl millet flour in gulabjamun, there was a gradually decreased in the body and texture score of gulabjamun except for G1 and G2 from 8.25 to 6.81. Among all treatments, C, G1 and G2; G1, G2 and G3 were found to be statistically equivalent to one another, while G3 and G4 were also statistically not significantly differed. The body of gulabjamun was found slightly loose with increasing the level of pearl millet because pearl millet gives more porous gulabjamun than maida. Therefore, they absorb more ghee during frying and also absorb more sugar syrup. The most attractive feature of a food product is its colour and its appearance is another factor in how well-liked it is on the market. The scores for gulabjamun's colour and appearance ranged from 8.44 (C) to 6.71 (G4). It can be seen from the tabulated value that as the rate of pearl millet increased, there was a successive decreased in the colour and appearance score of gulabjamun except for G1 and G2 from 8.44 to 6.71. Among all treatments, G1 and G2, G3 and G4, C and G2 were found to be statistically at par with each other. The colour of pearl millet was darker than the colour of maida, so it was discovered that adding more pearl millet to gulabjamun caused colour to become slightly blackish. The incorporation of pearl millet flour had a significant (p<0.05) effect on the overall acceptability of gulabjamun. The overall acceptability of control gulabjamun scored highest (8.35) among all treatments followed by G2, G1, G3 and G4 was found to be 8.01, 7.84, 7.24 and 6.76, respectively. As the amount of pearl millet increased, there was a progressively decreased in the overall acceptability score of gulabjamun except for G1 and G2 from 8.35 to 6.76. Among all treatments, G1, G2 and G3 were found statistically equivalent to each other, while G3 and G4 were also not significantly differed. From the above discussion on the effect of pearl millet flour on sensory score of gulabjamun, it could be concluded that the average sensory score of gulabjamun i.e. flavour, body and texture, colour and appearance and overall acceptance ranged from 8.35 to 6.80, 8.25 to 6.81, 8.44 to 6.71 and 8.35 to 6.76, respectively.

It was concluded from the sensory assessment of gulabjamun by eight semi-trained judges that the G2 sample of gulabjamun which contain pearl millet: maida @ 50:50 gave the most acceptable gulabjamun in terms of sensory quality.

Effect of Pearl Millet Flour on the Chemical Composition of Gulabjamun

Chemical composition has been very important aspect in term of the nutritional value of any product. Effect of pearl millet flour on chemical composition of gulabjamun was shown in Table 2. The fat content of gulabjamun ranged from 9.53 (C) to 11.28% (G4). As the rate of adding pearl millet flour to gulabjamun increased, there was a significant (p<0.05) rise in the fat content of gulabjamun from 9.53 to 11.28% as the pearl millet flour contain higher fat compare to maida. Among all treatments, there was not any treatment found to be statistically at par with each other. The average protein content of gulabjamun varied from 6.26 (C) to 6.63% (G4). Table 2 demonstrated that the protein content of gulabjamun increased statistical significantly (p<0.05) from 6.26 to 6.63% with an increase in the rate of pearl millet flour addition. The protein content for C and G1; G1 and G2; G2 and G3; G3 and G4 were discovered to be statistically equivalent to one another among all treatments. The range for ash content of gulabjamun was found to be 1.31 (C) to 2.20% (G4). Compared to other treatments, ash content was found to be higher in G4 i.e. 2.20%. Data obtained from Table 2 shows that as the rate of pearl millet addition increased, there was a significant (p<0.05) increased in the ash content of gulabjamun from 1.31 to 2.20%. Among all treatments, there was not any treatment found to be statistically at par with each other. The average values of total solid content in gulabjamun ranged from 66.26 (C) to 71.85% (G4). Table 2 demonstrated that the total solid content of gulabjamun increased significantly (p<0.05) from 66.26 to 71.85% as the level of pearl millet addition increased. Among all treatments, C and G1 were found to be statistically at par with each other. The average total carbohydrate content of gulabjamun varied from 49.17 (C) to 51.74% (G4). Among all treatments, total carbohydrate content was found to be higher in G4 (51.74%). Table 2 provide evidence that the total carbohydrate content of gulabjamun significantly (p<0.05) increased from 49.17 to 51.74% as the rate at which pearl millet flour was added to the gulabjamun was increased. Among all treatments, G2 and G3 were discovered to be statistically equal, while C, G1 and G2 were also statistically non-significantly differed.

Effect of Pearl Millet Flour on the Physico-Chemical

Properties of Gulabjamun Physico-chemical properties have very vital role on shelf life of any product due to the microbiological quality of any product depend mainly on physico-chemical properties of product. The mean values of physico-chemical properties by different levels of addition of pearl millet flour in gulabjamun are narrated in Table 3. The addition of different rates of pearl millet flour had not any statistically significant impact on the acidity of gulabjamun. The acidity of gulabjamun added with five various proportions of pearl millet: maida i.e. 25:75 (G1), 50:50 (G2), 75:25 (G3), 100:0 (G4) and 0:100 (C) were found to be 0.32, 0.32, 0.32, 0.33 and 0.31% LA, respectively. Statistics revealed that the treatment G1, G2, G3 and G4 were at par with each other, while C, G1 and G2 also statistically non-significantly differed. According to the tabulated data and relevant statistical analysis, the pH of gulabjamun did not varied statistical significantly when pearl millet flour was added at various rates. The pH of gulabjamun varied in a small range from 6.57 (G3) to 6.66 (G1). Data obtained from Table 3 showed that as the rate of pearl millet increased, there was not any specific trend was observed in the pH of gulabjamun. Statistics revealed that all treatments were comparable to one another. The production of gulabjamun involves several steps, one of which is the soaking of gulabjamun balls in sugar syrup. It promotes sugar syrup absorption, which raises gulabjamun's weight and sweetness. The average results for the sugar syrup absorption of gulabjamun produced with various amounts of pearl millet flour addition are narrated in Table 3. The addition of varied rates of pearl millet flour significantly (p<0.05) affects the gulabjamun's capacity to absorb sugar syrup. The average values for sugar syrup absorption of gulabjamun varied from 130.15 to 136.55 g/100 g. The sugar syrup absorption was found to be higher in G4 (136.55 g/100 g) as compared to other treatments. Table 3 demonstrated that the rate at which pearl millet flour was added to gulabjamun increased, there was a significant (p<0.05) increased in the amount of sugar syrup that the gulabjamun absorbed from 130.15 to 136.55 g/100 g. Among all treatments, G1 and G2 were found to be statistically at par with each other, while G2 and G3 were also statistically non-significantly differed.

Effect of Pearl Millet Flour on the Rheological Properties of Gulabjamun

The sensory characteristics and overall quality of gulabjamun are significantly influenced by a rheological property of gulabjamun. The type of raw material utilized, its composition and the manufacturing procedure used all have a considerable impact on the textural appearance of gulabjamun.

Hardness, cohesiveness, chewiness, gumminess and springiness were the characteristics taken into consideration for gulabjamun's rheological appearance. Effect of pearl millet flour on chemical composition of gulabjamun was shown in Table 4. The amount of pearl millet flour used had a significant (p<0.05) impact on the hardness of gulabjamun. The mean score for the hardness of gulabjamun varied from 7.36 N (G4) to 9.00 N (G2). It can be seen from the tabulated values that as the rate of addition of pearl millet flour increased, the hardness of gulabjamun was significantly (p<0.05) decreased except G2 sample of gulabjamun. It was revealed from the tabulated values that sample G1 and G3 were statistically equivalent to one another, while sample C, G1 and G2 were also statistically non-significantly differed. The average values for the cohesiveness of gulabjamun varied from 0.25 (G1) to 0.31 (G2). Data obtained from Table 4 showed that as the level of addition of pearl millet increased, there was not any specific trend was observed in the cohesiveness of gulabjamun. Statistics revealed that among all treatments, samples C, G2 and G4; C, G3 and G4 were comparable to one another and samples G1 and G3 were also equivalent. The gumminess of gulabjamun varied from 2.07 N (G1) to 2.79 N (G2). Among the different treatments studied, gumminess was found to be higher in G2 (2.79 N) sample as compared to other treatments. Table 4 showed that there was not any noticeable trend found for the gumminess of gulabjamun as the level of pearl millet addition increased. The tabulated values showed that sample C and sample G2 were statistically comparable to each other, while samples G1, G3 and G4 were also statistically non-significantly different. The springiness of gulabjamun varied from 6.49 mm (C) to 8.08 mm (G3). It can be shown from Table 4 that except G4 sample of gulabjamun, there was a statistically significant (p<0.05) rise in the springiness of gulabjamun with an increased in the rate of addition of pearl millet flour. The values of springiness for C, G1, G4 and G1, G2, G4 were discovered to be statistically equivalent among all treatments. The inclusion of pearl millet flour at varying rates significantly (p<0.05) impacted the chewiness of gulabjamun. The mean values for the chewiness of gulabjamun varied from 14.62 Nmm (G4) to 20.00 Nmm (G2). Table 4 showed that there was not any noticeable trend found for the chewiness of gulabjamun as the level of pearl millet addition increased. It is revealed from the tabulated values that sample C and G3; G2 and G3 were statistically at par with one another, while sample C, G1 and G4 also did not differ statistically. The rheological properties of gulabjamun varied noticeably with the type of milk utilized for the development of khoa for the production of gulabjamun. The rheological properties of gulabjamun are also affected by the proportion of different ingredients like khoa, maida, pearl millet and baking soda. The amount of water used for the preparation of dough also influences the rheological properties of gulabjamun (Lad, 2016) [12] . Thus, differences in rheological properties of gulabjamun prepared from various levels of addition of pearl millet flour as well as the values stated in the literature may be attributed to such reasons. Published data on proximate composition, physico-chemical attributes, rheological property and sensory attributes of gulabjamun affected by addition of pearl millet (bajra) are not available for comparison; however the values observed in the present study are very close to those reported by Patel et al. (2020) [17] , Rathava et al. (2018) [21] , Vasava et al.

(2018) [23] , Patil et al. (2017) [20] , Lad (2016) [12] , Chaudhari (2016) [6] , Kardule (2015) [8] , Nalawade (2014) [15] , Patil (2014) [19] , Krishnaveni (2010) [9] , Singh et al. (2009) [22] , Adhikari (1993) [1] and Patel et al. (1992) [16] . After completion of compositional analysis, physicochemical analysis, sensory attributes and rheological properties of all treatment's gulabjamun, it was concluded based on the sensory evaluation that the G2 (pearl millet and maida @ 50:50) sample of gulabjamun was selected as optimized product for further storage studies, cost calculations and consumer acceptance trial.

Conclusion

It can be concluded on the basis of sensory evaluation of this investigation that a proportion of pearl millet: Maida @ 50:50 by 20% weight of khoa was most appropriate for development of gulabjamun. This developed gulabjamun contained pearl millet (bajra) flour which provides better nutrition value and also reduce gluten content of the final product which is essential for person who have celiac diseases. So, it is a reasonably well balanced food with functional properties that have been show to provide some medicinal benefits.

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