Research paper
Incorporation of yeast and hot melt extrusion 
enhance contents of total polyphenol and 
flavonoids and antioxidant ability in buckwheat 
flour
Min Ook PARK1, 2, Choon Il PARK2, Se Jong JIN2, Mi-Ri PARK3, Ik Young CHOI1, and 
Cheol Ho PARK2
1 Department of Agro-Industry, Kangwon National University, Chuncheon, 24341, Korea
2 Cheorwon Cosmetic Agricultural Cooperation, Cheorwon, 24047, Korea
3 Cheorwon Plasma Research Institute, Cheorwon, 24047, Korea
* Corresponding author: chpark@kangwon.ac.kr
DOI https://doi.org/10.3986/fag0024
Received: March 16, 2022; accepted March 23, 2022.
Keywords: Common buckwheat, yeast, hot-melt extrusion, total polyphenol, rutin, antioxidants
ABSTRACT
A study was conducted to determine the degree of interaction between yeast and hot-melt extrusion on contents 
of total polyphenol, total flavonoid, and rutin and antioxidant ability in common buckwheat. The highest content of 
total polyphenol was 95mg/100g in buckwheat flour, which included 2% yeast and was dried for 8 hours after extrusion 
while that of total flavonoids was 181mg/100g. The highest content of rutin in this study was 4.23mg/100g (156% 
higher than control, non-extrusion without yeast) in buckwheat flour, included 2% yeast, and dried for 8 hours after 
extrusion. Antioxidant ability determined by DPPH free radical scavenging ability was higher in yeast-mixed buckwheat 
flour extruded and dried for 8 hours (23-61%) than non-extruded with or without yeast (19-40%). The highest antioxi-
dant ability (61%) was shown in buckwheat flour mixed with 2% yeast, extruded, and dried for 8 hours after extrusion. 
These results may be attributed to incorporating extruded buckwheat flour with yeast powder during 8 hours of drying 
and fermentation followed. 
Fagopyrum  39 (1): 13-18 (2022)
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INTRODUCTION
Buckwheat (Fagopyrum esculentum Moench.) is annu-
al melliferous crop and a pseudo cereal. For many years, 
the cultivation of buckwheat declined, but recent interest 
in and demand for dietary health care have led to the re-
vival of its cultivation.
As a recognized medicine-food source, buckwheat 
contains a lot of bioactive substances having a variety of 
antioxidants such as flavonoids and phenolic acid along 
with proteins, carbohydrates, lipids, vitamins, and min-
erals (Krkoskova & Mrazova, 2005). In recent years, 
flavonoids and phenolic acids have attracted increasing 
interests due to their various beneficial pharmacolog-
ical effects including antioxidative, anti-inflammatory, 
antiallergic, antiviral, anticancer, and antihyperten-
sive properties (Kreft et al., 1999; Chao et al., 2002). 
Buckwheat is a good source of rutin, a flavonol glyco-
side plant metabolite, able to antagonize the increase of 
capillary fragility associated with hemorrhagic disease 
or hypertension in humans (Kreft et al., 1999; Park et 
al, 2000).
The extrusion process is traditionally employed via 
ram extrusion and screw (single or twin screw) extrusion. 
Twin screw extrusion generates high shear stress with a 
higher degree of mixing capacity than the single screw 
extruder. The solvent-free hot melt extrusion (HME) 
equipped with twin screw is widely used in the pharma-
ceutical and food industries, to develop solid compos-
ites with a nano-sized particle of the active compounds 
(Azad et al., 2019). In general, the high temperature of 
HME softens the polymer and favors the diffusion of 
active compounds such that they are dispersed into the 
polymer matrix. The processing ability in the HME can 
be enhanced by adding plasticizer, which lowers the melt 
viscosity of the extrudate. Hydrophilic plasticizer has a 
significantly positive effect on the increase in dissolution 
rate (Azad et al., 2019; Koo et al., 2019). HME contrib-
utes to enhancing the bioaccesibility, functionality, and 
thermal stability of nutraceutical compounds (Lee et al., 
2019; Azad et al., 2020; Azad et al., 2021). 
An interesting method of obtaining food of improved 
bioactive potential, increased digestibility, high nutrition-
al value and favorable taste is solid-state fermentation of 
plant seeds. Yeast cells derived from Saccharomyces cerevi-
siae and related species have gained increasing attention 
as oral delivery systems for bioactive agents, including 
pharmaceuticals, supplements, and nutrients (Ten et al., 
2021). Yeast cells have a rigid outer cell wall comprised 
of dietary fibers and glycoproteins that provide unique 
features for these applications. Indeed, yeast cells have 
several potential advantages such as their ability to de-
liver both hydrophobic and hydrophilic compounds and 
protect encapsulated substances from heat, light, oxygen, 
and moisture. The food-related bioactive compounds that 
have been successfully encapsulated using yeast cells in-
clude flavors, vitamins, carotenoids, phenolics, and other 
nutraceuticals (Ten et al., 2021).
This study is a preliminary trial for buckwheat flour 
to enhance contents of total polyphenol and flavonoids, 
including rutin, and antioxidant ability by incorporating 
hot melt extrusion with yeast powder during processing 
buckwheat flour for food or cosmetic materials. 
MATERIALS AND METHODS
Sample preparation of common buckwheat
For experiment 200g of common buckwheat flour 
(Chuncheon Makguksu Agricultural Cooperation, Mae-
milgaru) was mixed with 1 or 2 percent of yeast powder 
(Beoma Food. Co., Instant yeast). Control was not mixed 
with yeast powder. With those mixed flour, t Three tri-
als were done for hot melt extrusion (Han Kook Tech., 
AL-300); flour was non-extruded, flour dried just after 
extrusion, and flour dried for 8 hours after extrusion. 
Drying of buckwheat flour was conducted at 70 °C of dry-
er. Hot melt extrusion was done with an extruder at a 
temperature of 95-115 °C and pressure of 15 bar. Screw-
ing speed was 160 rpm and time to ejection after extrud-
ing was 60-90 seconds. 
Determination of total phenolic contents (TPC)
The total phenolic contents (TPC) were determined 
by the Folin-Ciocalteu assay (Singleton and Rosi, 1963). 
A sample aliquot of 200 μl was added to a test tube con-
taining 200 μl phenol reagent (1N). The volume was 
increased by adding 1.8 ml of distilled deionized water. 
The solution was allowed to stand for 3 min for reaction. 
To continue the reaction, 400 μl of Na2CO3(10% in 
water v/v) was added and vortexed (Daihan Scientific, 
VM-30). The final volume 4 ml was adjusted by adding 
1.4 ml of distilled water. The prepared sample was then 
incubated for 1 hour at room temperature. The absorb-
ance was measured at 725 nm using a spectrophotometer 
(UV-1800 240V, Shimadzu Corporation, Kyoto, Japan). 
Park et al., (2022): Yeast and hot melt extrusion enhance polyphenol and flavonoids
14
The total phenolic content was expressed as tannic acid 
equivalents (TAE) in dry weight basis (DW)
Determination of flavonoid contents (TF)
The total flavonoid content (TF) was determined ac-
cording to Ghimery et al. (2009) with slight modification. 
Briefly, an aliquot of 0.5 ml of sample (1 mg/ml) was 
mixed with 0.1 ml of 10% aluminum nitrate and 0.1 ml 
of potassium acetate(1M). In the mixture, 3.3 ml of dis-
tilled water was added to make the total volume 4 ml. 
The mixture was vortexed and incubated for 40 minutes. 
The total flavonoid was measured using spectrophotom-
eter (UV-1800 240V, Shimadzu Corporation, Kyoto, Ja-
pan) at 415 nm. Total flavonoid content was expressed as 
μg/g quercetin equivalent in dry weight basis.
DPPH free radical scavenging ability (AA)
The antioxidant activity was determined on the basis 
of the scavenging activity of the stable 2, 2-diphenyl-1 
picryl hydrazyl (DPPH) free radical according to methods 
described by Braca et al. (2003) with slight modification. 
1 ml of extract was added to 3 ml of DPPH. The mixture 
was shaken vigorously and left to stand at room temper-
ature in the dark for 30 minutes. The absorbance was 
measured at 517 nm using a spectrophotometer (UV-
1800 240V, Shimadzu Corporation, Kyoto, Japan). The 
percent inhibition activities of the purple potato sample 
were calculated against a blank sample using the follow-
ing equation. Inhibition (%) = (blank sample extract sam-
ple/blank sample) x 100. 
RESULTS AND DISCUSSION
Buckwheat flour processed by hot melt extrusion 
showed 43-89% higher contents of total polyphenol and 
30-48% higher total flavonoid than control, non-extrud-
ed treatment without yeast (Table 1). Rutin content was 
also 43-47% higher than control. Addition of yeast pow-
der to buckwheat flour induced higher contents of total 
polyphenol and flavonoid as well as rutin content. In the 
treatment of non-extrusion, 1% and 2% of yeast increased 
29% and 51% of total polyphenol contents and 38% and 
42% of total flavonoid contents. Rutin content in the 
treatment of non-extrusion increased from 1.65mg/100g 
without yeast to 1.96mg/100g (19% higher) in 1% of 
yeast and 3.96mg/100g (140% higher) in 2% of yeast. Two 
types of extrusion caused increases of total polyphenol, 
total flavonoid, and rutin. Drying 8 hours after extrusion 
induced higher contents of total polyphenol, total flavo-
noid, and rutin than those obtained just after extrusion, 
indicating that fermentation in buckwheat flour hot-melt 
extruded by solid-state yeast was continuously proceeded 
during drying of 8 hours after extrusion. Addition of 2% 
yeast induced higher contents of total polyphenol, total 
flavonoid, and rutin rather than addition of 1% yeast. 
The highest content of total polyphenol was 95mg/100g 
in buckwheat flour included 2% yeast and dried for 
8 hours after extrusion wwhile that of total flavonoid was 
181mg/100g. The highest content of rutin in this study 
was 4.23mg/100g (156% higher than control, non-extru-
sion without yeast) in buckwheat flour included 2% yeast 
and dried for 8 hours after extrusion. Antioxidant ability 
determined by DPPH free radical scavenging ability was 
higher in yeast-mixed buckwheat flour extruded and dried 
for 8 hours (23-61%) than non-extruded with or without 
yeast (19-40%). The highest antioxidant ability (61%) was 
shown in buckwheat flour mixed with 2% yeast, extruded 
and dried for 8 hours after extrusion. These results in-
dicate that extruded buckwheat flour incorporates with 
yeast powder during 8 hours of drying and following fer-
mentation. HME processing technology was applied to 
several crops to maintain higher nutraceutical or pharma-
ceutical compound contents. HME increased the reactive 
surface area of compounds and de-structures the fibre 
matrix, thereby causing enhance decursin and decursinol 
angelate to be released into the solution in Angelica gigas 
(Azad, et al., 2020). HME resulted in prolongation of the 
thermal stability of anthocyanins in a biopolymer-medi-
ated purple potato (Azad et al, 2021). This study showed a 
high potential of improvement from nutraceutical points 
of view. Effect of fermentation on buckwheat flour was 
determined in several cases of study using diverse mi-
crobials including yeast, Saccharomyces spp. The total 
phenolic content and antioxidant potential of fermented 
buckwheat dough significantly increased using Lactoba-
cillus delbrueckii (Gandhi & Dey, 2013). Amino acid, glu-
tamate and tryptophan in buckwheat increased through 
the serial repitching of Saccharomyces pastorianus (yeast) 
on the composition of the barley, buckwheat and quinoa 
fermentation medium (Deželak et al., 2015). Buckwheat 
groats fermented with Rhizopus oligosporus are a potential 
source of flour of advantageous antioxidant parameters 
for application as a food additive (Starazynska-Janisze-
wska et al., 2016). Raw buckwheat flour fermented with 
liquid-state fermentation by lactic acid bacterial and 
Fagopyrum  39 (1): 13-18 (2022)
15
Rhizopus oligosporus fungi contained higher amount of ru-
tin and total polyphenol contents (Zielinski et al., 2019). 
The ethanolic extracts of buckwheat fermented with 
three strains of Agaricus exhibited the higher total phe-
nolic contents and superoxide anion radical scavenging 
ability (Kang et al., 2017). 
CONCLUSIONS
This study was attempted through the combination 
of biological (yeast) and mechanical (hot-melt extrusion) 
approaches for improving quality of buckwheat flour. In 
this preliminary study, we found a potential of incorpora-
Treatment DPPH free radical 
scavenging ability
(%)Yeast(%) Extrusion
0.0
Non-extrusion (Control) 18.5
Just after extrusion 23.1
Drying for 8 hrs after extrusion 31.8
1.0
Non-extrusion 35.7
Just after extrusion 47.5
Drying for 8 hrs after extrusion 57.0
2.0
Non-extrusion 39.7
Just after extrusion 50.9
Drying for 8 hrs after extrusion 60.6
Treatment
Total polyphenol 
content (mg/100g)
Total flavonoid 
content (mg/100g)
Rutin content
(mg/100g)Yeast
(%) Extrusion
0.0
Non-extrusion (Control) 35 64 1.65
Just after extrusion 50 83 2.36
Drying for 8 hrs after extrusion 66 95 2.43
1.0
Non-extrusion 46 88 1.96
Just after extrusion 52 101 2.96
Drying for 8hrs after extrusion 77 117 3.21
2.0
Non-extrusion 53 91 3.96
Just after extrusion 59 131 3.69
Drying for 8 hrs after extrusion 95 181 4.23
Table 2. Antioxidant ability in different conditions of yeast and extrusion on buckwheat flour
Table 1. Total polyphenol, total flavonoid, and rutin in different conditions of yeast and hot melt extrusion on buckwheat flour
Park et al., (2022): Yeast and hot melt extrusion enhance polyphenol and flavonoids
16
tion of yeast with hot melt extrusion to enhance antiox-
idant parameters including rutin content of buckwheat 
flour. Further studies are needed to clarify a decisive 
mechanism of the incorporation based both biological 
and mechanical approaches resulting in quality improve-
ment of buckwheat flour. 
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IZVLEČEK
Uporaba kvasa in vročega ekstrudiranja poveča vsebnost celotnih polifenolov, flavonoidov in antioksidacijsko 
sposobnost pri ajdovi moki 
Namen raziskave je bil ugotoviti interakcijo dodanega kvasa in vročega ekstrudiranja mešanice ajdove moke s kvas-
om na vsebnosti celotnih polifenolov, flavonoidov in antioksidacijske sposobnosti pri moki navadne ajde. Ajdovi moki je 
bilo dodanega 2% kvasa, rezanci so bili sušeni 8 ur po ekstruziji. Najvišja vsebnost skupnih polifenolov je bila 95mg/100g 
z dodatkom 2% kvasa, vsebnost celotnih flavonoidov je bila 181mg/100g. Najvišja vsebnost rutina je bila 4,23mg/100g 
(156% več kot kontrola, brez ekstrudiranja, s kvasom) pri ajdovi moki z 2% kvasa in sušeno 8 ur po ekstruziji. Antiok-
sidativna sposobnost, določena z DPPH, je bila višja pri uporabi kvasa, ekstruzije in sušenja 8 ur (23-61%), kot brez 
uporabe kvasa in ekstruzije (19-40%). Najvišja antioksidacijska sposobnost (61%) je bila določena pri ajdovi moki z 
dodatkom 2% kvasa, ekstrudirano in po ekstruziji sušeno 8 ur. Pričakovati je, da bodo rezultati te raziskave prispevali k 
uspešni uporabi ekstrudiranja ajdove moke z uporabo kvasa in osem urnega sušenja ter fermentacije. 
Park et al., (2022): Yeast and hot melt extrusion enhance polyphenol and flavonoids
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