DIETARY FIBRE CONTENT IN ETHNIC AND UNCONVENTIONAL VEGETABLES AND FRUITS GROWING IN BANGLADESH

Dietary fibre is known to provide health benefit and protect against degenerative chronic diseases. Thus, the present study reports the total dietary fibre (TDF) content of sixty-nine selected ethnic and unconventional vegetables and fruits growing in Bangladesh. The samples were collected from different locations of Bangladesh and mixed together to ensure sample representativeness. Dietary fibre assay kit according to the AOAC method was utilized for the analysis of TDF in selected vegetables and fruits. In the ethnic varieties, the TDF content ranged from 1.02 ±0.16 to 7.16 ±0.16 g for leafy (LV), 0.18 ±0.01 to 6.71 ±0.49 g for non-leafy vegetables (NLV) and 1.21 ±0.12 to 5.29 ±0.20 g for fruits per 100 g edible portion (EP). In the unconventional items, it arrayed from 3.08 ±0.34 g to 7.75 ±0.13 g for LV and 1.02 ±0.06 to 8.82 ±0.40 g for NLV per 100 g EP. Among the analysed samples, the highest and lowest content of TDF was found in Orohordal and Mairabokong, respectively. The unconventional vegetables contained much higher content of TDF than the ethnics and the commonly consumed similar varieties. Data on TDF content in underutilized vegetables and fruits of Bangladesh is sparse. Thus, the finding of this study would fill up the data gap in the existing food composition table of Bangladesh and also would aware the people to take vegetables and fruits rich in fibres.


INTRODUCTION
In the recent years, health benefits of dietary fibre in reducing the risk of many chronic diseases have extensively been addressed ( Epidemiological and interventional studies reported that consumption of dietary fibre rich foods such as vegetables, fruits, and whole grains reduce the blood cholesterol, especially, low-density lipoprotein and blood pressure, promote weight loss and improve insulin sensitivity  Stewart and Schroeder, 2013). Soluble fibre has been reported to improve immunity, to speed up elimination of toxic waste through the colon and to enhance digestion. They can help treat or prevent overweight or obesity (Takekawa and Matsumoto, 2012; Kamila et al., 2018).
Data on dietary fibre are sparse. Bangladesh does not yet have its own dietary fibre data; some data are being generated for a few common foods. Dietary fibre data for ethnic or unconventional foods have not yet been generated or reported elsewhere. In our present-attempt to prepare a food composition database for Bangladesh with special reference to ethnic foods

Scientific hypothesis
The content of total dietary fibre was evaluated in different types of leafy vegetables, non-leafy vegetables and fruits consumed by specific tribal community of Bangladesh. We presumed that there exist a significant difference with respect to total dietary fibre, measured by AOAC method, in different indigenous leafy and non-leafy vegetables, as well as fruit species.

Food samples
This study included analysis of total dietary fibre content for sixty-nine vegetables and fruits of ethnic and unconventional varieties grown in Chittagong Hill Tracts (CHTs) and in some specific plane lands. Ethnic group comprised twenty-eight leafy and seventeen non-leafy vegetables and six fruits; and unconventional group consisted of fifteen leafy and three non-leafy vegetables.

Sample plan
Multi-region sampling plan was employed for collection of the food sample. To conform to the representative sample principle-"what the mass people consume' and from where they collect it"? (Southgate and Greenfield, 2017), the ethnic samples were collected from weekly local markets at Rangamati and Bandarban, and the unconventional ones were collected from the specific local areas of Gazipur, Mymansingh and from some places of Dhaka, where they were grown. The samples were collected fresh, which were then water sprayed, packed into auto seal plastic poly bags and brought to the lab where the food samples were processed for analysis of dietary fibre. Depending on the availability, two to three samples were collected for each of the food from every market and growing area. These were then mixed to make three analytes or composite test samples.

Identification of vegetable sample
A taxonomist (Dr. Maksuda Khatun) of the Department of Botany, University of Dhaka, who was also accompanied the collection team, and confirmed the sample identity with name and family. The collected samples are listed in the Table 1a, Table 1b and Table 2

Sample processing
Each of the collected samples was cleaned with tap water and then rinsed with distilled water, gently swabbed with tissue paper to remove trace of water and air dried. The airdried sample was diced or cut into small pieces (peeled where needed) using a clean stainless steel knife on a dried clean plastic cutting board. The diced sample was mixed, and a weighted portion was spread in stainless steel plate(s) and then dried in air-oven at 100 -105 °C to constant weight (AOAC, 2007), which was then milled to 0.3 to 0.5 mm mesh powder. The powdered or milled sample was stored in desiccators for analysis of total dietary fibre.

Analysis of total dietary fibre
The total dietary fibre was estimated by the enzymatic and gravimetric method of the Association of the Official Analytical Chemists (AOAC, 2007) using a total dietary fibre assay kit (TDF-100A, Sigma-Aldrich, Saint Louis, USA). The assay procedure as described in the kit was strictly followed. In brief, the dried meshed sample was incubated with α-amylase at pH 6.0 for 15 min at 95 o C for gelatinization, which was then digested by incubation with protease at pH 7.5 for 30 min at 60 o C, then with amyloglucosidase at pH 4.5 for another 30 min at 60 o C to remove protein and starch present in the sample. Ethanol was added in excess to precipitate the soluble dietary fibre.
The residue was filtered and washed with ethanol and acetone; which was then dried overnight in an air-oven until it reduced to constant weight or nearest 0.1 mg. After

Statistical analysis
The analysis was carried out in triplicates. Descriptive statistics were performed and values were expressed as mean ± standard deviation. One-way analysis of variance (ANOVA) was employed to evaluate the differences among varieties for total dietary fibre content and was declared significant when p <0.05 at 5% level of significance. Minitab version 18.0. (Minitab Inc., State College, PA, USA) was used to analyze the data. Table 3 and Table 4 represent the total dietary fibre contents in the ethnic leafy and non-leafy vegetables and Table 5 and Table 6 represent the total dietary fibre contents in the ethnic fruits, and unconventional leafy and non-leafy vegetables. In the ethnic vegetables, the dietary fibre ranged from 1.02 ±0.16 to 7.16 ±0.16 g per 100 g fresh edible portion (pooled mean ±SD: 2.25 ±1.34) for leafy vegetables (Table 3), 0.18 ±0.01 to 6.71 ±0.49 g per 100 g fresh edible portion (pooled mean ±SD: 2.75 ±1.64) for non-leafy vegetables (Table 4) and in the ethnic fruits (Table 5), the content varied from 1.21 ±0.12 to 5.29 ±0.20 g per 100 g fresh edible portion (pooled mean ±SD: 3.11 ±1.44). Although the combined data for ethnic fruits showed high amount of dietary fibre compared to ethnic leafy-and nonleafy vegetables, but we did not observe any statistical significance. In unconventional vegetables (Table 6), the content ranged from 3.08 ±0.34 to 7.75 ±0.13 g per 100 g fresh edible portion (pooled mean ±SD: 5.79 ±1.42) for leafy vegetable and 1.02 ±0.06 to 8.82 ±0.40 g per 100 g fresh edible portion (pooled mean ±SD: 4.93 ±3.29) for nonleafy vegetable. Like ethnic vegetables and fruits combined data, unconventional vegetables also failed to show statistical significance between leafy and non-leafy vegetables. Gondhobatali 7.16 ±0.16 a Note: Different superscript letters in each column indicates the significant differences in the mean at p <0.05.  Jongli/Bonaam 5.29 ±0.20 a Note: Different superscript letters in each column indicates the significant differences in the mean at p <0.05. Note: Different superscript letters in each column indicates the significant differences in the mean at p <0.05.

RESULTS AND DISCUSSION
The present study indicates that amongst the vegetables and fruits those were tested, Orohordal contains the highest amount of total dietary fibre (8.82 ±0.40 g per 100 g fresh edible portion).
It was followed by Chimtishak, Telakucha, Betgach, Gondhobatali, Muktajhuri, Orhorpata, Oraibalai, Roktodrone, Tetulpata, Bondhonia, Sornolota, which also contain rich amount of dietary fibre ranging from 7.75 ±0.13 to 6.12 ±0.36 g per 100 g fresh edible portion. The other vegetables such as Jolpaipata, Jonglaam, Jamalu, Missayanu, Shimeful, Mulachi, Bonpalong, Titbegun, Vennapata, Rosko, Betagi, Kochi aampata, Sakumubakla also contain a high amount of TDF (5.74 ±0.06 to 4.06 ±0.30 g per 100 g fresh edible portion). For leafy vegetable, the lowest TDF was present in Simeialupata (1.02 ±0.16 g per 100 g fresh edible portion). Among the fruits, Jongliaam or Bonaam has the highest amount of TDF (5.29 ±0.20 g per 100 g fresh edible portion), followed by Rosko (4.38 ±0.46 g per 100 g fresh edible portion) and Jonglikola (3.06 ±0.09 g per 100 g fresh edible portion). The study findings also indicate that the unconventional vegetables contain higher amount of total dietary fibre (5.65 ±1.85 g per 100 g fresh edible portion) as compared to the ethnic vegetables (2.52 ±1.48 g per 100 g fresh edible portion). In case of most food items, the content of dietary fibre in ethnic vegetables was found to be, somewhat, comparable to that of commonly consumed vegetables in Bangladesh  Table 5 it can be seen that, among ethnic fruits, Rosko, which looks like Plum or Black berry, was found to contain much higher amount of dietary fibre (4.38 g per 100 g edible fresh) than the Plum (2.80 g per 100 g edible fresh) or higher than or similar to the Black berry Similarly, Jongliaam and Joglikola were found to contain higher amount of dietary fibre (5.29 and 3.06 g per 100 g fresh edible portion respectively) as compared to the mango (3.65 or 1.5 g per 100 g fresh edible portion) and banana (1.90 or 2.6 g per 100 g fresh edible portion) In the ethnic Mulachi and Green Chilli, the total dietary fibre was found to be almost same (4.74 vs 4.90 g per 100 g fresh edible portion). The recommended dietary intake (RDI) of TDF for an adult human is 30 -38 g per day and the consumption of these ethnic and unconventional vegetables and fruits can contribute up to 30% of RDI of TDF.

CONCLUSION
Some of ethnic vegetable and fruits such as Gondhobatali, Oraibalai, Shimeful, Rosko, Betagi, Kochi aampata, Jongliaam and most of the unconventional vegetables were found to contain rich amount of total dietary fibre. The findings of present study would encourage people to adapt dietary diversity. Cultivation and regular intake of plant foods rich in fibre might reduce the risk of many diseases. It would also go a long way in filling up the data gap that exists in food composition database for Bangladesh.