1. INTRODUCTION
Black rice (Oryza sativa L.) is a special variety of violet or dark purple rice, and its characteristic dark color is due to the presence of a high amount of anthocyanin as compared to other rice varieties [1]. In India, black rice is mostly cultivated in Puducherry, Odisha, West Bengal, Tamil Nadu, and Jharkhand; and in the North Eastern part of India, the Meitei community of Manipur is involved in the cultivation of black rice that is popularly known as Chak-hao Amubi [2]. It is richer in antioxidant activities, has high protein content and low-fat content, gluten-free, gut-friendly, and is a natural cleaner with many medicinal values in comparison to other rice varieties [3,4]. The rice kernel bran layer is a rich source of many pharmacological compounds such as anthocyanins, phenolic, and flavonoid compounds which have the ability to improve the lipid profiles are anti-inflammatory and anti-cancerous and may also help in the prevention of diabetes and heart diseases, cancer, high blood pressure, and extend the quality of life [5].
Because it has anthocyanin, black rice is usually eaten with the bran and is sold as “unmilled” rice. However, still black rice is not so popular as a staple food as compared to red and white rice [6]. In recent times, black rice has been considered as functional food because of its anti-carcinogenic, curative effect, anti-oxidant properties, and high nutritive value [7].
Musa balbisiana Colla (genome group “AA”) the seeded banana is locally called bhimkol. It belongs to the family Musaceae and is mostly available both in wild and cultivated types in the North Eastern part of India [8]. Bhimkol is wildly grown in the Upper Assam region and is semi-domesticated along river sides where human habitats are present [9]. Bhimkol is robust in growth, very hardy, resistant to pests, diseases, drought, and high yielders [10]. Conventionally, feeding infants with bhimkol is a common practice in the North-east region of India because it is highly nutritious and is a rich source of carbohydrates, vitamins, and proteins. It has also proved to be beneficial for the treatment of diseases such as dysentery and jaundice [11]. The majority of the ethnic groups of Assam use different parts of the plant in the form of food or in their religious and social activities. In a recent study conducted by Borah et al. [12] on low-cost healthy extrudates of low amylose rice and bhimkol formulation, it was found that the developed product at the optimized condition was found to have a calorific value of 175 kcal/100g and protein content of 6.35% with an adequate amount of micronutrients such as magnesium (15.3 mg/100g) and potassium (33.2 mg/100g), respectively.
The market for convenience foods has expanded rapidly in recent years. Ready-to-eat (RTE) products are becoming increasingly popular among consumers due to their low time and effort requirements [13]. Ready-to-eat (RTE) foods are foods that require minimal cooking time and have a good storage shelf life. With the increase in the number of working women, busy lifestyles, and so on, most people prefer an easy and quick way of cooking food over the old traditional method, which takes time. Thus, the entrance of ready-to-eat (RTE) food in the global market and presently in the Indian markets has seen a tremendous shift in the pattern of consumption over the past few years [14]. There is very limited research on RTE functional food prepared from a combination of black rice and bhimkol. The main reason is bhimkol being an underutilized horticultural crop as it contains large number of seeds as compared to its pulp. Therefore, the aim of the present study was to develop RTE functional food prepared from black rice and bhimkol.
2. MATERIALS AND METHODS
Fresh and ripened Bhimkol (Musa balbisiana Colla) and black rice (Oryza sativa L.), were procured from the local market of Mangaldai, Assam, India. The honey (Brand Dabur) was bought from the local grocery shop. It imparts a characteristics sweet flavor to the product. The raw milk (cow milk) was procured from a local milk vendor, Mangaldai. The low density polyethylene (LDPE) pouch for product storage was procured from an online shopping platform (Flipkart).
2.1. Preparation of Black Rice Flour
Black rice was cleaned using clean potable water, and after complete draining of the water, the rice was ground using a kitchen mixer for 5 min, and then it was cooked for 5 min using a microwave oven at 900W. Then, after cooling the cooked rice, it was formed into small ball-like structures and dried at 40°C for 24 h in a tray drier. After that, the grinding of the dried rice balls was carried out using a kitchen mixer, and the flour, after proper sieving, was stored in airtight containers for further use. Rice flour was used as the base material for the product formulation.
2.2. Preparation of Bhimkol Powder
Mature and ripe bhimkol were washed in clean and potable water. After peeling, the seeds were removed using a grater, and the pulp was dried using a tray drier for 12 h at 45°C. The dried pulp was then ground into powder using a mixer grinder. The flour obtained after proper sieving was stored in airtight containers for further use. Bhimkol powder was used as the functional ingredient for the product formulation.
2.3. Preparation of the Dough
The dough was prepared by mixing black rice powder, bhimkol powder, and milk as the binding agent and honey as the sweetening agent. The prepared dough was then dried using a hot air oven at 40°C for 6 h, and the product was stored in LDPE pouch for better storage.
2.4. Product Formulation
A total of eight trials were conducted to determine the best product combinations for the composite flour design [Table 1].
Table 1: Ingredient formulation
| Ingredients | T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 |
|---|---|---|---|---|---|---|---|---|
| Black rice powder | 40 | 50 | 40 | 40 | 40 | 30 | 30 | 25 |
| Bhimkol powder | 40 | 40 | 50 | 30 | 30 | 30 | 30 | 25 |
| Milk | 10 | 5 | 5 | 20 | 10 | 30 | 10 | 30 |
| Honey | 10 | 5 | 5 | 10 | 20 | 10 | 30 | 20 |
2.5. Proximate Analysis
For proximate analysis, protein, fat, moisture, and ash were analyzed using the AOAC, 2000 [15] methods. The carbohydrate content was estimated by subtracting the sum of the percentages of moisture, fat, protein, and ash contents from 100% according to AOAC, 2000 [15].
Carbohydrate (%) = 100 – (moisture% + fat% + protein% + ash%)
The total energy value of the food formulation was calculated according to the method of Mahgoub [16] as:
Total energy (kcal/100 g) = [(% available carbohydrates × 4) + (% protein × 4) + (% fat × 9)].
2.6. Color Analysis
The color values of the RTE food prepared from black rice and bhimkol in terms of L, a, b values were measured using a color measurement spectrophotometer [L* = 0 (black) to 100 (white); a*=−60 (green) to +60 (red); and b*=−60 (blue) to +60 (yellow)].
2.7. Total Phenol Content
The total phenol content of the juice was estimated by the Folin-Ciocalteu method with a gallic acid standard, and the absorbance was measured at 650 nm using a UV/VIS spectrophotometer [17].
2.8. Water Absorption Index (WAI) and Water Solubility Index (WSI)
Water Absorption Index and Water Solubility Index were determined using the Anderson [18] procedure.
 |
2.9. Sensory Assessment
The sensory quality of the product was evaluated at Mangaldai College by a panel of ten panelists comprised of students and faculty members ranging in age from 20 to 40 years. The 9-point hedonic scale was used (1: dislike extremely, 9: like extremely), where a score of 5 was the lowest limit of acceptance.
2.10. Storage Study
During the storage period of 6 weeks, different properties such as moisture content and total phenolic content changes were studied. The data were collected during the 1st week and then at an interval of 7 days up to 6 weeks.
2.11. Statistical Analysis
All the experiments were carried out in triplicates and the results were expressed as mean ± standard deviation calculated using MS Excel.
3. RESULTS AND DISCUSSION
Eight different combinations of the product are taken and among them, T4 having black rice powder, bhimkol powder, milk, and honey in the ratio of 40:30:20:10 (all in %) showed the best product combination. In T1 and T5, although the product is formed and is similar to T4 after sensory analysis, it shows the best result thus has been accepted as the final product. In T2 and T3, the product did not form proper dough and it may be due to a high amount of solid ingredients (black rice and bhimkol powder) as compared to liquid components (milk and honey). In T6, T7, and T8, the dough becomes sticky, it may be due to the high amount of liquid component as compared to the solid ingredients.
The moisture content of the final product (T4) was determined to be 8.65±0.06% [Table 2], and it plays an important role in extending the product’s shelf life [19] because chemical and physical deteriorations are less likely to occur at such low moisture content [20]. According to Kumar et al. [21], the protein content of black rice is 8.5 g/100g. Bhimkol powder may have a good contribution toward the high protein content and was found to be 11.48 ± 0.8% which shows that it can have a good impact on the nutritional value as RTE products are basically cereal-based and found to have low nutritional value. The fat and ash content was found to be 2.13 ± 0.1% and 1.81 ± 0.3%, respectively. Similarly, the ash content of pork patties developed using black rice was found to be 1.93 ± 0.01bc% [22] which is slightly higher than our product. Again in the development of Gluten-free rice and bean biscuit [23], the ash content was 1.87b ± 0.04% which is almost similar to our product. The carbohydrate content of the final product accounts for 75.93 ± 0.45% and it falls within the range as per Codex Alimentarius Standards for weaning foods. Total energy (kcal/100 g) was calculated to be 403.41 kcal/100g which is slightly lower than the minimum energy (451 Kcal/100g) recommended in the Codex Alimentarius.
Table 2: Analysis of RTE functional food prepared from black rice and bhimkol flour
| Parameter | Result |
|---|---|
| Moisture content (%) | 8.65±0.06 |
| Protein (%) | 11.48±0.8 |
| Fat (%) | 2.13±0.1 |
| Ash (%) | 1.81±0.3 |
| Carbohydrate (%) | 75.93±0.45 |
| Total energy (kcal/100 g) | 368.69 |
| Total phenolic content ( mg GAE/100 g) | 13.04±0.5 |
| L | 45.11±0.5 |
| A | 0.38±0.05 |
| B | 9.18±0.1 |
| WSI (g/g) | 0.28±0.87 |
| WAI (%) | 34.15±0.6 |
The total phenolic content was found to be 13.04 ± 0.5. A slightly higher TPC has been found by other authors [24] in the study of banana powder as an additive to common wheat pasta. The color values of the RTE food prepared from black rice and bhimkol in terms of L, a, and b values were 45.11 ± 0.5, 0.38 ± 0.05, and 9.18 ± 0.1, respectively, as illustrated [Table 2]. The sensory assessment of the product has been found that T4 shows the best overall acceptability as compared to the others. The comparison among the different trials has been outlined [Table 3].
Table 3: Sensory assessment of the product
| Parameters | T1 | T2 | T3 | T4 | T5 | T6 | T7 | T8 |
|---|---|---|---|---|---|---|---|---|
| Colour | 7±0.3 | 7±0.3 | 6±0.2 | 8±0.2 | 7±0.1 | 6±0.1 | 7±0.2 | 6±0.3 |
| Appearance | 7±0.1 | 7±0.4 | 5±0.4 | 8±0.4 | 7±0.4 | 7±0.4 | 7±0.4 | 7±0.4 |
| Taste | 7±0.3 | 7±0.1 | 6±0.3 | 8±0.5 | 7±0.5 | 6±0.5 | 7±0.5 | 6±0.5 |
| Mouth feel | 6±0.2 | 7±0.1 | 6±0.1 | 8±0.3 | 7±0.2 | 7±0.1 | 7±0.1 | 5±0.1 |
| Overall Acceptability | 6±0.3 | 6±0.1 | 6±0.1 | 8±0.1 | 6±0.1 | 6±0.1 | 7±0.1 | 6±0.3 |
The product does not contain any added preservatives and the storage study was carried out over a period of 6 weeks at a temperature of 37°C and relative humidity of 80% and was stored in an LDPE pouch. The data thus obtained are analyzed to determine the storage stability of the product which is illustrated [Table 3].
After a storage study of 6 weeks, it can be seen that the moisture content goes on increasing with the increase in time [Table 4]. An increase in storage time can have an adverse effect on the storage life of the product because a rise in moisture can aid in the growth of microorganisms, which is one of the major causes of food spoilage. This increase in moisture might be due to improper packaging technique (e.g., not properly sealed) and high relative humidity of the ambient air entering into the LDPE pouch [25].
Table 4: Shelf–life study of the product
| Week | TPC (mg GAE/100g) | Moisture Content (%) | Protein (%) | Ash (%) |
|---|---|---|---|---|
| 1 | 13.04±0.05 | 8.65±0.06 | 11.48±0.8 | 1.81±0.3 |
| 2 | 12.87±0.03 | 8.87±0.02 | 11.23±0.5 | 1.78±0.2 |
| 3 | 12.35±0.04 | 9.05±0.02 | 11.03±0.3 | 1.75±0.2 |
| 4 | 11.84±0.02 | 9.45±0.05 | 10.88±0.5 | 1.72±0.4 |
| 5 | 11.23±0.03 | 9.69±0.02 | 10.46±0.4 | 1.70±0.3 |
| 6 | 10.89±0.06 | 9.78±0.06 | 10.14±0.3 | 1.69±0.3 |
Phenolic compounds are very important constituents of plants bearing redox properties that are responsible for their antioxidant activity [26]. Das et al. [10] reported that at normal room temperature the TPC of bhimkol powder decreases with increasing storage time as compared to that stored at refrigerated storage temperature. In our study, the product containing bhimkol and black rice powder also follows the same trend of decrease of TPC with the increase in storage time of 6 weeks as shown [Table 4]. The decrease in TPC accounts for a 21.5% decrease in the 6th week of the study which is similar to the work reported by Deng et al. [27].
In the research study by Akhtar et al. [28], it has been reported that there is a progressive decrease in protein content of mango pulp over the entire storage period of 90 days. Again, Oessoe et al. [29] reported that different types (four rice varieties) show a decrease in protein content over storage, and the largest decrease in protein contents was experienced by the red rice which was 10.69% in the initial month and decreased to 5.24% at the end of 6 months and the percentage reduction in protein content accounts for 54.5%. Thus, it can be summarized from the mentioned research study that the protein content of the product containing bhimkol and black rice flour shows decreasing trend with an increase in storage time [Table 4]. The decrease in protein content accounts for a 13.4% decrease as compared to that of the initial week. The decrease in protein content may be due to the Maillard reaction occurring between different components present in the product, and in the case of milk products, it is very important since these are the only naturally-occurring protein foods with a high content of reducing sugar Hurrell et al. [30] and our product contain milk as the binding agent which also imparts a characteristic flavor to the product.
Ash refers to the inorganic residue remaining after either ignition or complete oxidation of organic matter in a food sample [31]. It is a part of proximate analysis for nutritional evaluation. On storage, at normal room temperature, the ash content of the product shows a decreasing trend with increasing time, and the decrease in ash content on storage accounts for a 12% decrease on the 6th week. The ash content shows the opposite trend of increasing on an increase in time from 0.80% to 0.82% during the storage duration of 6 months in the work by Khadra et al. [32].
4. LIMITATIONS OF THE STUDY
The seeds present in bhimkol are one of the main limitations faced during the study, because the seeds are to be removed before preparation of the bhimkol flour and also the flour has high tendency to agglomerate with increase in storage time and temperature.
5. CONCLUSION
Bhimkol flour, along with black rice flour used for the development of RTE functional food, can prove to be the best alternative flour for gluten-free snacks as well as a source for baby food development. However, the processed form of bhimkol is very negligible, although it is a very rich source of minerals. The product formulated without the use of any preservatives and stored at room temperature in an LDPE pouch shows a good shelf life without much change in the sensory attributes. However, the other properties, such as moisture, protein, ash, and mineral content, had a significant change over a storage period of 6 weeks. With the increase in urbanization, the incorporation of healthier foods such as bhimkol (seeded banana) and others has lost its value in food habits; thus, the addition of bhimkol powder (seeded banana) can prove to be a healthier option for food processing industries. Functional foods are foods that have an additional function often one related to health promotion and disease prevention by adding new ingredients or more of existing ingredients. The ready-to-eat functional food with bhimkol and black rice powder as the main ingredients will essentially try to serve itself as a medicinal food, as both black rice and bhimkol have several health benefits while also providing a characteristic taste. The study thus standardized an RTE functional food using black rice and seeded banana flour which can provide both nutrition and health benefits both to the younger as well as the adult section of the population.
6. ACKNOWLEDGMENT
The authors are grateful to the Department of Biotechnology, Government of India, which financed the Institutional Level Biotech Hub at Mangaldai College for providing the essential resources.
7. AUTHORS’ CONTRIBUTIONS
Himakshi Baishya participated in the concept and research design, data analysis, interpretation of analysis results, and writing the manuscript. Ranjita Goswami participated in designing the research and statistical analysis. Lakhya Jyoti Gogoi participated in designing the research, revising the important content of the manuscript, and correspondence. All authors read the final draft and approved it for communication
8. FUNDING
The study was not supported by any kind of research grant.
9. CONFLICTS OF INTEREST
The authors report no financial or any other conflicts of interest in this work.
10. ETHICAL APPROVALS
This study does not involve experiments on animals or human subjects.
11. DATA AVAILABILITY
The authors confirm that all the data underlying the findings are fully available without restriction. All the data is included within the manuscript.
12. PUBLISHER’S NOTE
This journal remains neutral with regard to jurisdictional claims in published institutional affiliation.
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