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Effect of fermentation and cooking on soluble and bound phenolic profiles of finger millet sour porridge Molly Gabaza, Habtu Shumoy, Maud Muchuweti, Peter Vandamme, and Katleen Raes J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b03090 • Publication Date (Web): 19 Sep 2016 Downloaded from http://pubs.acs.org on September 19, 2016
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Effect of fermentation and cooking on soluble and bound phenolic profiles of finger
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millet sour porridge
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Molly Gabaza1,2,3, Habtu Shumoy1, Maud Muchuweti2, Peter Vandamme3, Katleen
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Raes1
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1
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University, Graaf Karel de Goedelaan 5, 8500 Kortrijk, Belgium
9
2
Department of Industrial Biological Sciences, Faculty of Bioscience Engineering, Ghent
Department of Biochemistry, Faculty of Science, University of Zimbabwe, P.O. Box MP
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167, Mt Pleasant, Harare, Zimbabwe
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3
12
Ledeganckstraat 35, 9000 Gent, Belgium
Department of Biochemistry and Microbiology, Faculty of Science, Ghent University,
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Corresponding author:
[email protected] 15 16 17 18 19 20 21
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Abstract
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The aim of this study was to evaluate the soluble and bound phenolic content of finger millet
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and the impact of process induced changes on phenolic profiles of their sour porridge. Finger
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millet porridge and intermediate products were collected from four groups of households in
26
Hwedza communal area, Zimbabwe, after which soluble and bound phenolic compounds (PC)
27
including condensed tannins (CT) were quantified. Bound PC and CT contributed 95 % of the
28
total PC and CT. The CT were only detected in the red varieties. Major individual PC
29
identified were catechin occurring in the soluble fraction only, while ferulic, sinapic and
30
salicylic acid were mainly present in the bound fraction. Fermentation and cooking caused a
31
more than two fold increase in soluble PC, CT and individual PC. Improved traditional
32
processing techniques optimized for improved bioavailability and health benefits of phenolics
33
are highly relevant for the low income populations.
34 35
Keywords: Phenolic compounds, condensed tannins, finger millet, fermentation, cooking
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Introduction
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Small grains such as sorghum and millets are drought resistant and thus are an important food
43
component to low income populations in many parts of Africa. Finger millet (Eleusine
44
coracana) is a small grain containing high amounts of phenolic compounds (PC), many of
45
which have therapeutic benefits such as heart disease prevention, anticancer, antihypertensive
46
and anti-inflammatory characteristics
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and white varieties with the dark colored varieties possessing higher contents of PC, and also
48
condensed tannins (CT) than the light colored varieties
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finger millet are mainly present in the black varieties compared to other varieties, similar to
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the presence of anthocyanins in sorghum varieties 6, 7. According to Dykes and Rooney 3 and
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Chandrasekara and Shahidi 4, CT have higher antioxidant activity than monomeric PC.
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However, PC may behave like a double edged sword as on the one hand they exhibit positive
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health effects but on the other hand certain PC with catechol and galloyl groups may
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negatively affect mineral absorption
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diets as they have adverse effects on protein digestibility, enzyme activity and mineral
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absorption 10. Phenolic compounds in cereal grains exist as free, in a soluble conjugated or an
57
insoluble bound form 11, 12. PC in cereal grains exist mainly in the bound form, and values of
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bound PC varying between 75 and 91 % have been reported for blue maize, brown rice, red
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sorghum and wheat 11, 12.
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In Africa, fermented thin porridge is quite common. It is consumed by both adults and
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children and is also used as weaning and complementary food for young children.
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Fermentation and cooking are two processing methods widely used in the African cuisine that
63
are able to induce important chemical changes, e.g. the destruction of anti-nutritional factors
64
such as phytates and CT. The effects of processing on PC differ among cereal grains and can
65
be related to the type of grains, the location of the different PC in the cereal matrix and the
1-4
. Finger millet consists of black, dark brown or red
3, 5
. In addition, the anthocyanins in
8, 9
. CT are even considered as anti-nutrients in many
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intensity of the processing method
. There are contradictions in literature pertaining to the
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effect of fermentation and/or cooking on the amount of PC and CT in cereals. Additionally
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there is a paucity of information concerning the changes occurring to soluble and bound PC
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after fermentation and cooking of cereals, as well as regarding different finger millet varieties.
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Many studies report changes occurring to total contents of PC without making a distinction
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between soluble and bound PC
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the content and change in both soluble and bound PC fractions are not well known, thus their
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possible related effects towards health or interactions with other food components are unclear.
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Furthermore, many studies use model food products prepared under standardized laboratory
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conditions and information about ‘real samples’ from the field is lacking.
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The objective of this study is thus to compare the profile and content of soluble and bound PC
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and CT of red and white varieties of finger millet, and to determine the effect of traditional
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household processing, in particular fermentation and cooking, on the content of soluble and
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bound PC and CT, and on changes in PC profile of finger millet porridge.
14-16
. This implies that the impact of processing conditions on
80 81
Materials and Methods
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Materials
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Methanol, sodium hydroxide (NaOH), sodium carbonate (NaCO3), hydrochloric acid (HCl)
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were purchased from Merck (Darmstadt, Germany). Folin-Ciocalteu’s reagent was purchased
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from ChemLab (Zedelgem, Belgium), chemical standards: gallic acid, catechin, p-coumaric
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acid, ferulic acid, syringic acid, sinapic acid, vanillic acid, protocatechuic acid, p-
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hydroxybenzoic acid, caffeic acid, cinnamic acid, were purchased from Sigma Aldrich
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(Bornem, Belgium). HPLC-grade methanol (MeOH), HPLC-grade water, trifluoroacetic acid
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(TFA) were purchased from VWR (Leuven, Belgium).
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Methods
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Sample preparation
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Finger millet products were prepared by four groups of women (n=24) in Ushe communal
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area (Hwedza district, Mashonaland East Province, Zimbabwe). The women were tasked to
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prepare fermented slurries and fermented porridges according to their traditions and to record
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the recipes accurately and with as much detail as possible. The products were prepared from
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two red and two white varieties and each group will be identified according to the variety
98
used i.e. red variety 1 (RV1), red variety 2 (RV2), white variety 1 (WV1), white variety 2
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(WV2). Finger millet grains were cleaned to remove glumes and foreign particles after which
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they were finely milled to pass through a sieve of 1 mm size. The fermentation process was
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done in a thatched kitchen with approximate temperature of 23-25oC. An aliquot of flour was
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measured into a fermentation vessel which could be a plastic or metal container followed by
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carefully adding a measured aliquot of water. The vessel was tightly closed and spontaneous
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fermentation allowed to proceed for 24-36 hours. Successful fermentation was identified by a
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characteristic frothing of the fermented slurry at the surface and a typical fermented aroma
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(measured pH of 4 - 4.5). The fermented slurry was then cooked for 15-20 minutes, with or
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without extra added water, to make the porridge. Table 1 shows the type of products and
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amount of ingredients used by each group, as well as the used preparation conditions.
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Sample collection
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Fermented slurry and porridge samples were collected in aliquots of 50 mL in sterile falcon
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tubes between July 1 and 12, 2014. The sampling was done twice within a time frame of two
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weeks. Samples were always transported under cooled conditions and immediately frozen at -
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80oC. Samples were transported to Belgium under dry ice and stored at -20oC. Flour of the
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different varieties was also collected and stored at -20oC at the Laboratory of Food
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Microbiology and Biotechnology, Ghent University, Campus Kortrijk, Belgium.
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Extraction of Soluble PC
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Extraction of soluble PC was based on Gonzales, et al. 17. Briefly, 5 g of porridge samples and
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fermented slurries and 2 g of flour samples were added with 15 ml methanol in 50 ml falcon
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tubes. The mixture was homogenized using an ultra turrax (IKA T18 Basic) at 10000 rpm for
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45 s and placed on ice for 15 minutes thereafter. To separate the soluble extract from the
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residue, the mixture was centrifuged (Z 300 K, Hermle Labortechnik, GmbH, Germany) at
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4000 rpm, 15 minutes at 4oC. Re-extraction was done using 80 % methanol following the
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same procedure. The collected supernatants were pooled and filled to 25 ml with 80 %
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methanol. The extract was transferred to storage bottles covered with aluminum foil to protect
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from sunlight and stored at -20oC until further analysis. The residue was dried overnight at
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room temperature and bound PC were extracted from it the next day.
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Extraction of Bound PC
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Bound PC were extracted according to method described by Gonzales, et al.
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residue, obtained after extraction of the soluble PC (0.1 g) was placed in 25 ml screw-capped
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falcon tubes previously flushed with nitrogen and hydrolyzed with 2 ml NaOH in a sonicated
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water bath (UP 400 S, dr.Hielscher, GmbH, Germany) at 60oC for 30 minutes. The mixture
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was neutralized with 4 ml HCl and extracted twice with 0.1 % formic acid in methanol for 2
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minutes under vortex. Supernatants were always separated by centrifugation at 4000 g for 15
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minutes and 4oC. The supernatants were pooled and filled to 25 ml using 80 % methanol and
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stored in storage bottles at -20oC covered in aluminum foil.
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Determination of total PC
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The total PC were determined on both the soluble and bound fractions according to the Folin-
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Ciocalteu method as described by Singleton and Rossi 18. Briefly, extracts from soluble and
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bound fraction (1 ml) were added to test tubes with 1 ml deionized water following by 0.5 ml
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ten times diluted Folin-Ciocalteu’s reagent. After 5 minutes, 1.5 ml of 20 % NaCO3 and 1 ml
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. The dried
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deionized water was added and the mixture was allowed to stand for 2 hours in the dark after
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which the absorbance was read at 760 nm. The phenolic contents for each fraction was
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calculated based on a standard curve generated from gallic acid and expressed as mg Gallic
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Acid Equivalents (GAE)/100g dm.
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Determination of Condensed Tannins (CT)
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Proanthocyanidins or CT were analyzed according to the method described by Price, et al. 19.
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Bound and soluble extracts and standards (1 ml) were added to test tubes followed by 5 ml of
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vanillin reagent (50:50 mixture of 5 % vanillin and 24 % HCl w/v) and incubated for exactly
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20 minutes in a water bath at 30oC. A second set of control tubes was prepared by adding 1 ml
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of sample or standards followed by 12 % HCl, and incubated under the same conditions after
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which the absorbance was read at 500 nm. The final absorbance was determined by
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subtracting the absorbance of the sample control from the corresponding vanillin-containing
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sample. The CT for each fraction was calculated based on a standard curve generated from
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catechin and expressed as mg catechin equivalents (CE)/100 g dm.
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Identification of PC by HPLC
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Identification of PC was done following the method described by Wen, et al. 20. Soluble and
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bound sample extracts were dried under nitrogen, and redissolved in 500 µL of
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MeOH:water:trifluoroacetic acid (TFA) (50: 50: 0.1) and filtered. An internal standard of o-
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coumaric acid was added to the samples and the samples were injected directly into the HPLC
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system. The separation of phenolic acids was carried out with Agilent HPLC equipped with
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column (AlltimaTM –Column 18 5u (4.6 mm × 150 mm), GRACE, Deerfield, USA). The
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mobile phase consisted of solvent mixture A (0.02 % TFA in water) and solvent mixture B
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(0.02 % TFA in methanol). The following program was used for gradient elution: 0-5 mins
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(25 % B), 5-10 mins (25-30 % B), 10-16 mins (30-45 % B), 16-18 mins (45 % B), 18-25 mins
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(45-80 % B), 25-30 mins (80 % B), 30-40 mins (80-25 % B). Samples were injected at a
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volume of 10 µL. The DAD detection was set at four wavelengths namely 254 nm (for
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identification of protocatechuic and vanillic acid), 275 nm (gallic, syringic, cinnamic, catechin
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and internal standard), 305 nm (p-coumaric and salicylic acid) and 320 nm (caffeic, ferulic,
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sinapic and rosmarinic acid). Quantification of identified phenolic acids was done using
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corresponding regression equation and values are expressed as µg/g dm.
171 172
Statistical Analysis
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All statistical analysis were done using IBM SPSS software version 20. The differences of
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mean values among the varieties were determined using one-way analysis of variance
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(ANOVA) followed by Tukey’s Honestly Significant Differences (HSD) multiple rank test at
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P < 0.05 significance level.
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Results
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Soluble and bound PC and CT of finger millet flour
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Figure 1 shows the soluble and bound PC found in red and white finger millet samples from
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Ushe communal area, Zimbabwe. The total content of PC of the red and white finger millet
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ranged from 1108-1330 and 334-359 mg GAE/100g dm, respectively. The bound fraction
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accounted for approximately 95 % of the total PC for both red and white millet samples.
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Figure 2 shows the content of CT in the red finger millet. The CT in the white varieties could
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not be detected. Higher amounts of CT in the bound fraction (89-94 % of the total CT
186
content) than in the soluble fraction was also observed, due to the association of CT with cell
187
walls. The white varieties of finger millet contain lower amounts of PC than the red varieties.
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PC profile of finger millet flour
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Seven phenolic acids i.e. cinnamic acid, syringic acid, p-coumaric acid, salicylic acid, sinapic
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acid, ferulic acid, protocatechuic acid, caffeic acid and one flavonoid namely catechin were
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identified in the different millet samples (Table 2). Caffeic acid was only found in the bound
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fraction. Catechin was the only flavonoid identified in the soluble fraction where its peak
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occupied more than 50 % of the total area in soluble extracts. The major phenolic acids
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identified were ferulic acid, sinapic acid and salicylic acid. Ferulic acid was the most
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abundant phenolic acid in the bound fractions of both the white and red varieties with values
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ranging from 107-193 µg/g. Sinapic acid was higher in the white varieties (241-330 µg/g)
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than in the red varieties (49.1-110 µg/g) and 37-59 % was found in the bound fraction.
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Sinapic acid appeared to be the major phenolic acid in white variety and also appeared to be
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the dominant soluble phenolic acid in all the varieties. Salicylic acid was also found in high
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amounts with up to 195 µg/g in the bound fraction of WV2 and 75-98 % existing in the bound
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fraction.
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Effect of fermentation and cooking on soluble and bound PC and CT of finger millet
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porridge
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The soluble, bound and total PC and CT of fermented and finger millet porridges from red
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and white varieties are shown in Tables 1 and 2. After fermentation, there was a general
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reduction in the content of bound and total PC and CT while there was a significant increase
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in the soluble PC in all the varieties (p < 0.05). This shows that despite different household
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processing conditions, in general, fermentation reduced the content of bound and total PC and
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increased the content of soluble PC. Total PC were reduced by 6-31 % while bound PC were
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reduced by 17-37 % with the lowest reductions observed for WV1. Soluble PC were increased
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by 16-167 % and the highest increase was observed for WV1 and lowest increase for RV2. In
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terms of CT, a decrease of 32-52 % and 43-47 % was observed for total and bound CT,
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respectively while an increase of 34-55 % was seen for the soluble CT. The level of reduction
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of PC and CT in all varieties was different which could be explained by the different
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fermentation conditions used as this influences the microbial diversity of the fermented
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slurries.
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After fermentation, cooking of fermented slurries follows to make the porridge. In
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comparison with fermented slurries, soluble PC significantly increased in porridges by 33-186
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% with the highest increase observed for RV2 and WV2 while soluble CT increased by 76
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and 92 % in RV1 and RV2, respectively (p < 0.05). The bound PC increased by 22 and 34 %
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in RV1 and RV2 while they decreased by 26 and 44 % in WV2 and WV1. In general, cooking
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after fermentation caused an increase in total PC for the red varieties while there was a
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decrease for the white varieties. In terms of the CT in the porridges, no significant change was
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observed for the bound and total CT after cooking compared to fermented slurries. The
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overall effect of cooking combined with fermentation caused more than two times increase in
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both the soluble PC and CT. Bound PC decreased by 4-53 % while total PC decreased by 14-
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36 % for all varieties except for RV2 where no change in total PC was observed. For CT,
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bound CT decreased by up to 63 % and total CT was reduced by up to 35 %.
229 230
Effect of fermentation and cooking on soluble and bound individual PC of finger millet
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In all varieties, an increase of all individual soluble phenolic acids was observed after
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fermentation and cooking while an inconsistent trend was seen for bound phenolic acids
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(Table 2). Catechin increased more than four times after fermentation and cooking, with the
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highest increase in the red varieties. There was an increase of bound phenolic acids after
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fermentation for RV1 and WV1, while a decrease of bound phenolic acids was observed for
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WV2 and RV2. After cooking, levels of phenolic acids increased in bound fraction except for
237
samples from WV1 where all bound phenolic acids decreased after cooking.
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Discussion
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The PC in finger millet are known to be mainly concentrated in the seed coat of the grain
242
and are present both in soluble and bound form and also occurring more abundantly in the red
243
varieties than in the white varieties. A major proportion of PC found in cereal grains are in the
244
bound form and can be up to 91 % for some maize varieties
245
approximately 95 % of the total PC were in the bound form and, to our knowledge, such
246
associations have never been reported in finger millet. A high amount of phenolic acids in
247
both red and white varieties was also found in the bound fraction. The chief hydroxycinnamic
248
acids, ferulic, p-coumaric, caffeic and sinapic acid are known to be ester linked to various cell
249
wall polymers such as arabinoxylans thus they exist in high amounts in the bound fraction
250
21
251
also in the present study the most abundant phenolic acid in the bound fraction of both the
252
white and red varieties. Subba Rao and Muralikrishna
253
µg/g in finger millet and this is in agreement with our findings of 107-193 µg/g. The phenolic
254
acids identified in the present study have also been reported by others 3, 4, 24 but their amounts
255
varied largely showing that the occurrence of different PC in grains may depend on several
256
factors such as environmental, edaphic agricultural and varietal differences.
257
Fermentation caused an increase in the soluble PC, CT and individual PC and a decrease in
258
the bound ones. Different mechanisms have been suggested to explain the changes occurring
259
to PC and CT after fermentation. The low pH attained during fermentation can cause the
260
removal of hydride ions and reorganization of PC 9, some PC may self-polymerize and also
261
interact with other macromolecules such as proteins thus decreasing their extraction,
262
polymerized PC may be degraded into oligomeric PC thus increasing the content of the
5
11, 12
. In the present study,
7,
. Ferulic acid was reported as the major bound phenolic acid in cereal grains 12, 21-23 and was
22
reported ferulic acid content of 186
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263
soluble PC
. Also the synthesis or enzymatic transformations of PC may occur during
264
fermentation
265
microflora may result in structural breakdown of cell walls thereby increasing the
266
accessibility of bound PC to enzymatic attack. Tannin-protein and tannin-iron complexes are
267
hydrolyzed during fermentation therefore the reduction of PC and CT after fermentation could
268
improve the digestibility of proteins and the bioaccessibility of trace minerals such as iron and
269
zinc
270
for degradation of PC and CT could result in improved protein and mineral nutrition. The
271
increase of phenolic acids in the soluble fraction suggest that esterase and glucosidase
272
activities may have been rampant during fermentation as their activities are known to release
273
phenolic acids bound to cell walls in particular protocatechuic and p-hydroxybenzoic acids 27.
274
The effect of thermal processes on PC is dependent on the type of thermal process employed,
275
i.e. wet cooking, steam cooking, extrusion cooking, baking and roasting15. In our case, wet
276
cooking was employed during the preparation of porridge. The further increase of soluble PC,
277
soluble CT and individual soluble PC after cooking was consistent in all millet samples as
278
shown in Table 2-4. In contrast to soluble PC, there was a variable response to bound PC and
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CT after cooking. According to Duodu 25, PC in grains can increase, decrease or not change
280
after processing depending with the mechanism of action of the processing method employed.
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The decrease of bound PC, CT and phenolic acids could be a result of leaching of PC into the
282
cooking water with subsequent increase of the soluble PC. Increases of soluble PC observed
283
in this study are caused by processes that release bound PC making them more extractable and
284
assayable. Such processes may involve depolymerization reactions. The increase of the
285
soluble PC and CT in our study could be mainly attributed to the increase of catechin,
286
particularly in the red varieties. This is because finger millet contains proanthocyanidins,
287
large polymers of catechin, which were depolymerized during fermentation and cooking. The
10, 13
. During fermentation, enzymes from both the cereal matrix and the
26
. It also implies that a controlled fermentation with the use of starter cultures suitable
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catechin data shows that it is the main flavonoid occurring in the soluble fraction. Catechin
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accounts for 84 % of the soluble fraction in finger millet
290
measure CT is a crude method that unfortunately, also measures catechin, explaining the
291
observed increase of CT in the soluble fraction. The CT in finger millet have not been
292
characterized in detail like CT in sorghum but they are likely to be oligomers of catechin as
293
catechin, epicatechin, gallocatechin, epigallocatechin, trimers and tetramers of catechin and
294
procyanidin dimers B1 and B3 have been identified in finger millet
295
bound PC increased in the red varieties but decreased in the white varieties after cooking. The
296
decrease of bound PC and phenolic acids in WV1 may be as a result of the cooking process
297
employed. After fermentation, the slurry was decanted and the coarse particles containing the
298
seed coat with the highest PC was discarded. The red varieties of finger millet contain CT
299
whose extractability could have been increased after thermal treatment. Several authors have
300
found a decrease of total PC after cooking of sorghum, fonio, pearl, kodo, finger, foxtail,
301
proso and little millet 7, 15, 29, 30 while others reported increases 31. Varying effects of thermal
302
treatment on bound PC and CT of different type of grains have also been reported by other
303
workers 15, 27, 32.
304
Soluble phenolics are stored in the intracellular space of cells while bound phenolics are
305
located in proximity and in association with cell walls
306
coupled with general decrease of bound phenolics after fermentation and cooking alludes to
307
the fact that there is depolymerisation of bound phenolics and their transportation into the
308
intracellular space. As the decrease of the bound phenolics does not add up with the increase
309
of the soluble phenolics, it suggests that some other chemical and physical interactions come
310
into play. The changes occurring to soluble and bound phenolics can thus allow for prediction
311
of localization, transport mechanism and chemistry of phenolics during processing 33.
24
. The vanillin method used to
24, 28
. The content of
33
. The increase of soluble phenolics
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Several studies have shown improved mineral bioaccessibility after reduction of PC and CT 9,
313
34
314
astringency, improved color, acceptance, protein digestibility and mineral bioavailability
315
On the other hand, fermentation and/or cooking has also been shown to effect changes on PC
316
and CT which subsequently increase the antioxidant capacity of the products 16, 31, 36. Kumari
317
et al
318
finger millet, the antioxidant activity of the soluble extract measured by various antioxidant
319
tests i.e. DPPH radical scavenging activity, trolox equivalent antioxidant activity, β-carotene-
320
linoleate model system and ferrous ion-chelating activity, was consistently at least twice that
321
of the bound extracts. Yeo and Shahidi
322
phenolics as an estimate to predict the localization, transportation mechanisms and
323
antioxidant activity of phenolics in germinating lentils. The ratio of bound to soluble
324
phenolics of our samples decreased from 16.7-20.8 in the flour to 2.18-5.67 after fermentation
325
and cooking. Using this ratio of bound to soluble phenolics, we can postulate that the
326
antioxidant activity after fermentation and cooking will increase by a large magnitude.
327
However, the benefits of finger millet phenolics go beyond their antioxidant activity. Future
328
research should thus focus on determining whether the increase in soluble PC also improves
329
the absorption of phenolics via in vivo and in vitro studies. Increased absorption is a
330
prerequisite for the phenolics to demonstrate their purpoted health effects.
331
The improvement of processing techniques is highly relevant for low income populations
332
subsisting on finger millet. Household processing techniques such as fermentation and
333
cooking can induce important changes to phenolic phytochemicals which could influence
334
their function both as anti-nutrients and functional ingredients. The increase of soluble PC
335
after household processing is beneficial as simpler and soluble PC are more bioaccessible and
336
may lead to improved bioaccessibility of minerals. The adequacy of household processing in
. The reduction of CT in cereals is encouraged as it leads to products with reduced
37
35
.
revealed that even though bound phenolics were higher than soluble phenolics in
33
proposed to use the ratio of bound to soluble
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terms of improving mineral bioaccessibility and improved utilization of PC as functional
338
foods should be tested by in vitro and in vivo assays.
339 340
Abbreviations
341
CT: condensed tannins; PC: phenolic compounds; TFA: trifluoroacetic acid
342 343
Acknowledgements
344
The authors are very grateful to the women from Hwedza communal area and to the
345
agricultural extension workers for provision of the raw materials and preparation of the
346
products. Further gratitude goes to SOFECSA (Soil Fertility Consortium of Southern Africa)
347
team led by Prof. Paul Mapfumo at the University of Zimbabwe for being advisors in the
348
study and for assisting in field work.
349 350
Funding information
351
We are thankful to VLIR-UOS for PhD funding of Molly Gabaza.
352 353
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Figure Captions
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Figure 1. Soluble and bound PC (mg GAE/100g dm) of red and white finger millet samples.
458
Figure 2. CT (mg CE/100g dm) of soluble and bound extracts of red finger millet samples
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Table 1: Levels of ingredients and processing parameters used in preparation of finger millet fermented slurries and porridges, as noted by the women preparing the porridges Variety
RV1
RV2
WV1
WV2
100 g flour
100 g flour
100 g flour
100 g flour
300 mL water
200 mL water
300 mL water
400 mL water
24 h fermentation
24-30 h fermentation
24 h fermentation
36 h fermentation
Extra 200 mL water
Extra 300 mL water
No extra water added. Extra 400 mL water
Products Fermented slurry
Cooked porridge (~20 minutes cooking for
Fermented slurry was
all porridges)
decanted
and
coarse
particles discarded.
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1600
mg GAE/100g dm
1400
b
1200
a
b
a
1000 800 600 c
400 200
b
a
c
c
c
c
c
0 RV1
RV2 soluble PC
WV1 Bound PC
WV2
Total PC
Figure 1: Soluble and bound PC (mg GAE/100 g dm) of red and white finger millet samples. Bars with the same color with different letters are significantly different (p ≤ 0.05), n=2.
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b
900 b
mg CE/100g dm
800 700 600
a
a
500 400 300 200 100
b a
0 RV1
RV2
CT in soluble extract
CT in bound extract
Total CT
Figure 2: CT (mg CE/100 g dm) of soluble and bound extracts of red finger millet samples. Bars with the same color with different letters are significantly different (p ≤ 0.05), n=2.
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Table 2: PC in finger millet flour, fermented slurries and porridges of finger millet RV1 Soluble Flour
RV2 Bound
Total
WV1
Soluble
Bound
55.1±0.1a 1053±5.2a 1108±4.2a 75.1±4.7a 1255±89a
Fermented 107±1.9b
WV2
Total
Soluble
Bound
1330±84a
20.1±0.6a 339±12a
982±98b
53.7±4b
Total
Soluble
Bound
Total
359±11a 15.3±0.9a 318±42a 334±41a
662±70.5b 769±70b
87.2±6.2a 895±100b
281±24a,b 336±21a 21.7±2.1a 215±13b 237±12b
142±24c
805±21c
947±49c
249±4.9b
1200±4.6a 1450±0.3a 71.6±10c
156±85b
255±91a 51.4±8.6b 159±14b 213±21b