Comparative study of chemical treatments in combination with extrusion for the partial conversion of wheat and sorghum insoluble fiber into soluble

Abstract Dietary fiber has gained greater attention owing to their positive and potential health perspectives. Cereals are the most important and enriched source of dietary fiber with more insoluble dietary fiber than soluble. For dietary fiber modification, chemical treatment with various techniques is considered as significant approach owing to its safety point of view and involves less damage to the molecular structure of the dietary fiber through chemical reagents and content of soluble dietary fiber is increased more efficiently. The current study was aimed to nutritionally characterize the cereal grains and to partially convert insoluble dietary fiber into soluble dietary fiber through chemical treatments in combination with extrusion. For the purpose, two varieties of each cereal were characterized for their chemical composition, mineral profile, and dietary fiber content according to the respective methods. Then, dietary fiber ratio in cereals was modified through chemical treatments, that is, acid, alkaline, and consecutive acid–alkaline followed by extrusion. Results regarding dietary fiber content of cereal grains exhibited that wheat (12.03–12.20 g/100 g) contained higher total dietary fiber followed by sorghum (6.70–6.90 g/100 g). Additionally, modification of SDF (1.97%) and IDF (11.48%) ratio in wheat and SDF (1.19%) and IDF (24.25%) ratio in sorghum through extrusion processing was nonsignificant while acid–alkaline treatment showed highly significant results, that is, 768.2% increase in SDF and 56.5% decrease in IDF in wheat and 952.38% increase in SDF and 71.17% decrease in IDF in sorghum. Among chemical treatments, higher result was given by acid–alkaline method and the lower outputs were observed in case of extrusion in both cereals. Conclusively, soluble dietary fiber was significantly increased through chemical treatments alone or in combination with twin‐screw extrusion.


| INTRODUC TI ON
In recent era, the trend for dietary fiber consumption and utilization is increasing day by day owing to its functional properties (Lorencia & Alvarez, 2016;Singh, 2016). Dietary fiber is a nondigestible carbohydrate that is not absorbed in the largest part of alimentary canal (Park, Subar, Hollenbeck, & Schatzkin, 2011).
Conventionally, based on solubility in water, dietary fiber is classified into two major classes including soluble dietary fiber (mainly pentosans, pectin, gums, and mucilage) and insoluble dietary fiber (cellulose, part of hemicellulose, and lignin) (Fuller, Beck, Salman, & Tapsell, 2016;Esposito et al., 2005;Borderias, Alonso, & Mateos, 2005). About contents of insoluble and soluble dietary fibers in foods, mainly cereals are 65%-80% and 20%-35%, respectively.  (Abutair, Naser, & Hamed, 2018;McRae, 2018). Moreover, these fibers maintain the level of blood glucose and provide heart protection. These fibers have great role in weight management owing to their middle whittling perspective. Furthermore, soluble dietary fiber can pass easily through gastrointestinal tract through softness of stools, while insoluble dietary fibers do not solubilize in water and pass rapidly through gastrointestinal tract by providing bulk to the waste and preventing constipation and hemorrhoids.
Because of these positive and potential health perspectives, trend of fiber utilization in food products is increasing day by day (Brouns, Hemery, Price, & Anson, 2012). As the food applications of dietary fiber are concerned, it can be used in different nutritional products such as beverages, meat, drinks, and bakery products. The principal sources of dietary fibers are cereals, nuts, fruits, and vegetables. Among various sources of dietary fibers, the most important and enriched source of dietary fiber is cereals.
Cereal is a prevalent harvest all over the mild and humid areas of the world from the family Gramineae. Major cereals are wheat, rice, rye, oat, sorghum, barley, and maize. These cereals provide 50% of the food energy worldwide (Awika, 2011 (Huang, He, Zou, & Liu, 2015). Englyst and Cummings (1984) used sulfuric acid and trifluoroacetic acid to hydrolyze hemicellulose. This treatment hydrolyzes the long polysaccharide chain to smaller fractions to increase their solubility. Moreover, in a study, soluble dietary fiber content in black soybean hull was increased by using hydrogen peroxide (Feng et al., 2017). Furthermore, the dietary fiber ratio of whole grain barley was modified by carboxymethylation . Along with chemical treatments, another approach for dietary fiber modification is extrusion. Huang and Ma (2016) applied high temperature, pressure, and shear force to gasify and extend the moisture content present in the cereals. This mechanism depends upon the processing parameters such as temperature and pressure (Chen, Ye, Yin, & Zhang, 2014;Rashid, Rakha, Anjum, Ahmed, & Sohail, 2015). In general, a combined method may have greater effect on the modification of insoluble dietary fiber into soluble dietary fiber in cereal than the use of the single method (Ma & Mu, 2016;Tang et al., 2016).
Keeping in mind all the above-mentioned views, there is a dire

| Mineral profile
The macrominerals (Ca, Mg, Na, K) and microminerals (Fe, Cu, Zn, Mn) of cereal grains were assessed according to the method of AOAC (1990).

| Dietary fiber content
Total, soluble, and insoluble dietary fibers of cereal grains were analyzed by followed the principles of AACC (2000) method No. 32-05.

| Chemical treatments of cereal fiber
Dietary fiber from wheat and sorghum varieties was chemically modified and extruded for the partial conversion of insoluble dietary fiber into soluble dietary fiber according to the method of Ning, Villota, and Artz (1991). In brief, a mixture of wheat and sorghum fiber and water, at a ratio of 1:5, was used. Its pH values were adjusted acidic (pH 2.0-4.0) and alkaline (pH 9.0-11.0) by using 6.0N HCl (acid treatment) and 6.0N NaOH (alkaline treatment), respectively. After pH adjustment, the mixtures were then heated at 90°C for different periods of time ranging from 1 to 4 hr. At the end of each treatment, the supernatant was removed, neutralized, and then centrifuged at 700 g for 10 min. Pentose and hexose contents were measured for the acid treatment using high-performance liquid chromatography, and total sugar content was determined for the alkaline treatment according to the procedure of Folkes and Taylor (1982) and Dubois et al. (1956), respectively. The precipitate was washed with water and dried using an air drier (Proctor Schwartz, Philadelphia, PA) at 75°C for 2 hr, followed by grinding and screening through a 2-mm sieve. The acid-alkaline treatment involved consecutive acid and alkaline treatments, according to the aforementioned procedures. For the acidic treatment, the mixture was adjusted to pH 2.0 with 6.0N HCl, while for the alkaline treatment, the mixture was adjusted to pH 11.0 with 6.0N NaOH.

| Extrusion of native and chemically modified cereal fiber
Native, and acid-and alkaline-treated wheat and sorghum fiber were extruded using a ZSK-30 twin-screw extruder (Werner and Pfleiderer Crop., Ramsey, NJ) according to the Ning et al. (1991).
Conditions of extrusion were selected according to preliminary work to ensure conditions suitable for bran modification. The barrel temperatures of the first two sections were maintained at 40 and 90°C, and the remaining three sections were held at 120°C. Extrusion was carried out at 50% moisture and a dry feed rate of 200 g/min. The screw speed used was 350 rpm. A dual-orifice die (3 mm in diameter) was used. The extrudate was gently dried in an air dryer at room temperature for 24 hr, and then grounded and sieved.

| Statistical analysis
The data obtained for each parameter were subjected for completely randomized design (CRD) and Latin square design (LSD) and later on ANOVA to determine the level of significance (Steel, Torrie, & Dickey, 1997). Means carrying same letter are significantly identical.

| Partial conversion of IDF into SDF in wheat through chemical treatments
Soluble dietary fiber was increased from 3.05 to 5.61 and from 3.02 to 6.12 g/100 g, while insoluble dietary fiber was decreased from 9.15 to 8.70 and 9.02 to 9.44 g/100 g in Ujala-16 and FSD-08, respectively.
F I G U R E 1 DF content of chemically modified Ujala-16 After that, alkaline treatment and acid treatment were applied simultaneously in two sequences (i.e., alkaline-acid treatment and acid-alkaline treatment). The results of acid and alkaline treatments were significant (p < 0.05). Alkaline-acid treatment increased soluble dietary fiber from 3.05 to 8.12 g/100 g and from 3.02 to 8.90 g/100 g and decreased insoluble dietary fiber from 9.15 to 8.25 g/100 g and from 9.02 to 9.74 in Ujala-16 and FSD-08, respectively. Whereas, acid-alkaline treatment increased the soluble dietary fiber from 3.05 to 26.48 g/100 g (768.2%) whereas decrease in insoluble dietary fiber was from 9.15 to 3.98 g/100 g (56.5%) in Ujala-16 while, in FSD-08, soluble dietary fiber was increased from 3.02 to 24.28 g/100 g (703.97%) and insoluble dietary fiber was decreased from 9.02 to 4.08 g/100 g (54.77%).
Keeping in view all these results, acid-alkaline treatment showed

| CON CLUS ION
Both wheat and sorghum varieties were found to be rich source of protein and potassium. The ratio of dietary fiber in wheat and sorghum was modified through chemical treatments along with extrusion. All treatments significantly increased soluble dietary fiber and decreased insoluble dietary fiber but acid-alkaline treatment was highly significant. This modification opens the door for the betterment of physiochemical, physiological, and functional prop-

CO N FLI C T O F I NTE R E S T
Authors declare that they have no conflict of interest.

E TH I C A L A PPROVA L
This article does not contain any studies with human participants or animals performed by any of the authors. It is further certified that human and animal testing is unnecessary in this study.

I N FO R M E D CO N S E NT
For this type of study, formal consent is not required.