Modification of barley dietary fiber through thermal treatments

Abstract The current research was carried out to observe the effect of different thermal treatments on soluble and insoluble dietary fiber ratio to improve functional properties of barley. Two varieties of barley labeled as Haider‐93 and Jau‐87 were milled and then wet and dry heat‐treated. Soaking and then cooking of soaked and nonsoaked barley was performed. Untreated barley contained more insoluble dietary fiber (12.00–12.40 g/100g dm) than soluble dietary fiber (4.73–5.70 g/100g dm). Additionally, the modification of soluble (13.32%) and insoluble dietary fiber (8.79%) ratio through pressure cooking was nonsignificant while roasting showed significant results, that is, 53.91% increase in soluble dietary fiber and 8.79% decrease in insoluble dietary fiber. In phase II, cooking without soaking gave highest results, that is, 68.08% increase in soluble dietary fiber and 15.48% decrease in insoluble dietary fiber. Conclusively, among all treatments of phase I and II, the better results were shown by cooking without soaking.

is more as compared to soluble dietary fiber in cereals and other grain-based foods. Barley (Hordeum vulgare L.) is at fourth position in cereals in worldwide production. It has been a considerable staple food in the Arabian Peninsula since earlier eras, and its applications in the food industry are quite limited. It is used as feed or malt. Although barley is a low cost, food grade cereal fiber source, its use as an ingredient in foods has been relatively unsatisfactory due to its poor functionality. Therefore, the need for the modification of the functional characteristics of cereal grains before their incorporation into foods is evident.
For the purpose, thermal processes are considered as most important approach for the modification of soluble and insoluble fibers ratio and physicochemical properties of dietary fiber (Zhou, Qian, Zhou, & Zhang, 2012). Different methods are used for thermal modification such as sterilization, sun drying, steam processing, boiling, frying mainly deep fat frying, microwave drying, vacuum-belt drying, roasting, and pressure cooking. These treatments significantly change the content and accessibility of nutrients and ameliorate the physiological effects of these nutrients by changing the plant cell wall composition. The amount of soluble dietary fiber produced is highly dependent on the temperature of the processes. This high temperature breaks the glycosidic bonds in polysaccharide, which can lead to the release of oligosaccharides and thus increase the quantity of soluble dietary fiber (Wang et al., 2015;Yi, Wang, Zhuang, Pan, & Huang, 2014). The effect of steam processing and sun drying on Polygonatum odoratum was probed, and it was found that the steam processing significantly increased the oil holding capacity whereas, sun drying significantly increased the water-holding capacity and swelling power of P. odoratum fiber (Lan, Chen, Chen, & Tian, 2012). Moreover, in the study of Yan and Kerr (2013), continuous vacuum-belt drying (VBD) was applied to the apple pomace at three different temperatures (80ºC, 95ºC, 110ºC).

| Procurement of raw material
Two barley varieties, that is Haider-93 and Jau-87 were procured from Ayub Agriculture Research Institute (AARI) Faisalabad. Seeds were cleaned to remove any debris or field dirt and sealed in polyethylene bags.

| Determination of dietary fiber
The contents of soluble, insoluble, and total dietary fibers in both barley varieties were determined according to the method of AOAC 991.43 enzymatic gravimetric method (AOAC, 2005).

| Phase 1 2.3.1 | Milling
The cleaned grains were pulverized using a plate mill to obtain whole flour (WF). A part of the whole flour was further sieved through a 44 mesh sieve (BSS). The "+"fraction was termed as the bran rich fraction (BRF), and the "-" fraction was termed as semi-refined flour (SRF) (Pushparaj & Urooj, 2011).

| Wet and Dry Heat Treatment
Each batch of the two commercially available barley varieties was pressure cooked for 10 min (9.8 × 104 Pa) and boiled for 30 min, respectively. The processed grains were dried in an oven at 50˚C and milled

| Phase 2 2.4.1 | Soaking
Soaked barley refers to barley soaked in tap water overnight at room temperature (300 ml of tap water were added to 100 g of barley grains; soaking took place for 18 hr at 20˚C); the soaked grains were drained, dried on a paper towel, lyophilized, ground for 3 min in a coffee mill and stored in polyethylene bags at room temperature prior to analyses (Kutos, Golob, Kac, & Plestenjak, 2003).

| Cooked-soaked barley
Cooked-soaked barley refers to barley soaked in tap water overnight at room temperature (300 ml of tap water were added to 100 g of barley grains, soaking took place 18 hr at 20˚C) then drained and dried on a paper towel and consequently cooked in fresh tap water (volume ratio beans to water being 1-6) boiling in a covered pot (98-100˚C) until these became suitable for consumption (approx. 40 min). Cooked grains were drained and treated in the same way as soaked barley (Kutos et al., 2003).

| Cooked nonsoaked barley
Cooked nonsoaked barley refers to nonsoaked barley directly cooked in boiling water until these became suitable to consumption.
Nonsoaked barley (50 g) was cooked in 400 ml of tap water boiling in a covered pot (98-100˚C) until these became suitable for consumption (approx. 2 hr). Cooked grains were drained and treated in the same way as soaked barley (Kutos et al., 2003).

| Canned barley
Canned barley (CnB) refers to barley directly from a commercial can, which have been drained and treated in the same way as soaked baryley (Kutos et al., 2003).

| Statistical analysis
The data obtained for each parameter were subjected for Latin square design (LSD) to determine the level of significance (Steel, Torrie, & Dickey, 1997).

| Dietary fiber content of barley
The soluble and insoluble fiber contents of the native and all the thermally modified barley of two different varieties were measured.
Mean values for dietary fiber content of two barley varieties before treatment were exhibited in Table 1. Results showed that soluble dietary fiber content was higher in Haider-93 (5.70 g/100 g dm) than in Jau-87 (4.73 g/100g dm) whereas insoluble dietary fiber was more in Jau-87 (12.00 g/100g dm) than in Haider-93 (12.40g/100g dm).
Literature showed similar results as of present study. Beloshapka, Buff, Fahey, and Swanson (2016) explicated that barley contained about 8.6%, 4.8%, and 13.4% insoluble, soluble, and total dietary fiber, respectively.  In 2nd phase, barley varieties were firstly soaked and then cooking of soaked and nonsoaked barley was performed. Canning of both barley varieties was also included in this phase. The results of soaking revealed significant modification of soluble and insoluble dietary fiber ratio. In Jau-87, soluble dietary fiber was increased from 4.73 to 6.67 g/100 g (41.01%) and insoluble dietary fiber decreased from 12.40 to 9.48 g/100 g (23.55%), whereas, in Haider-93, increase in soluble dietary fiber was from 5.70 to 7.92 g/100 g (38.95%) and decrease in insoluble dietary fiber was from 12.00 to 9.15 g/100 g (23.75%).
Furthermore, when the soaked barley was cooked, the results were less significant than soaking, that is, 33.51%-35.10% increase in soluble and 10.91%-11.00% decrease in insoluble dietary fiber in both barley varieties. These results were almost similar to the findings of canned barley, that is, 34.91%-35.10% increase in soluble dietary fiber and to 9.05 g/100 g, and decrease in insoluble dietary fiber was from 12.00 to 10.07 g/100 g. This modification was significant (p < 0.05).
Among all treatments, the highest results were shown by cooking without soaking. Therefore, it was concluded that thermal processes can also change the ratio of soluble and insoluble fibers and physicochemical properties of dietary fiber (Zhou et al., 2012).