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The physicochemical properties of fibrous residues from the agro industry
Accepted Manuscript The physicochemical properties of fibrous residues from the agro industry Giselle A. Jacometti, Léa R. P.F. Mello, Pedro H.A. Nascimento, Ana Claudia Sueiro, Fabio Yamashita, Suzana Mali PII:
S0023-6438(15)00060-2
DOI:
10.1016/j.lwt.2015.01.044
Reference:
YFSTL 4425
To appear in:
LWT - Food Science and Technology
Received Date: 14 August 2014 Revised Date:
20 January 2015
Accepted Date: 25 January 2015
Please cite this article as: Jacometti, G.A., Mello, L.R.P.F., Nascimento, P.H.A., Sueiro, A.C., Yamashita, F., Mali, S., The physicochemical properties of fibrous residues from the agro industry, LWT - Food Science and Technology (2015), doi: 10.1016/j.lwt.2015.01.044. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The physicochemical properties of fibrous residues from the agro industry
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Giselle A. Jacomettia, Léa R. P. F. Mellob; Pedro H.A. Nascimentob; Ana Claudia
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Sueirob; Fabio Yamashitac and Suzana Malib* a-
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Technological Federal University of Paraná, Cornélio Procópio - PR, Brazil.
Department of Biochemistry and Biotechnology, CCE, State University of Londrina,
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Londrina - PR, Brazil. c- Department of Food Science and Technology, CCA, State
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University of Londrina, Londrina - PR, Brazil Abstract
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The objectives of this work were to determine some of the physicochemical
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properties of four agro-industrial residues, namely malt bagasse, oat hulls, rice hulls and
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fibrous residue from banana pseudo-stems (FRBPS). Oat hulls contained the highest
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dietary fiber content (89.08 g/100 g), followed by malt bagasse (63.84 g/100 g), rice
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hulls (56.26 g/100 g) and FRBPS (47.99 g/100 g). The insoluble fiber in all residues
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formed the major fraction of the fiber contents, ranging from 43.79 (FRBPS) to 88.0
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g/100 g (oat hulls). FRBPS exhibited the highest soluble fiber content (4.44 g/100 g),
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water (4.71 g/g) and oil-holding capacity (2.68 g/g). Only malt bagasse and FRBPS
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exhibited emulsifying capacity, which was 59.83 and 8.28 mL oil/g, respectively. As
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demonstrated by water sorption isotherms, rice hulls were less hygroscopic and FRBPS
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were more hygroscopic.
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Keywords: malt bagasse; oat hulls; rice hulls; fibrous residue from banana pseudo-
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stems
* To whom correspondence should be addressed: Tel: +55 43 3371-4270, Fax: +55 43 3371-4054, E-mail: [email protected] 1
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1. Introduction Dietary fiber is a class of compounds that includes a mixture of plant
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carbohydrate polymers, both oligosaccharides and polysaccharides, e.g., cellulose,
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hemicelluloses, pectic substances, and gums that may be associated with lignin and
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other non-carbohydrate components (e.g., polyphenols, waxes, saponins, cutin,
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phytates, and resistant protein) (Elleuch, Bedigian, Roiseux, Besbes, Blecker, & Attia,
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2011).
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Fibers extracted from some grains and seeds present physical and functional
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properties that make them useful for the food industry, which encourages researchers to
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search for novel raw materials that meet the needs of these areas, with a particular focus
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on food industry residues, such as malt bagasse, oat and rice hulls, or on residues from
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agriculture, such as the fibrous residue of banana pseudo-stems (FRBPS). These
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materials are used as bedding for animals and livestock feeding, burned in the fields,
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added into soil as green fertilizer, or used as soil conditioners or fertilizers, biofuels,
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thermoplastics, activated charcoal, and components of other composite materials.
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However, the potential of these agro-industrial residues as a source of food dietary fiber
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has not been fully examined (Kuan & Liong, 2008).
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Brazil is the third largest beer producer in the world, with a production of 12.6
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ML, trailing only China (40 ML) and the United States (35 ML) (Mardegan et al.,
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2013). According to Cordeiro, El-Aouar and Araújo (2013), malt bagasse is a byproduct
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of beer brewing, and it is a component of the solid material produced from wort
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filtration before boiling. This solid byproduct primarily consists of the leftover peels
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and pulp of malt and grains and also some additives, such as rice, corn, and wheat.
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Crushed malt makes up 85% of the total product generated by the brewing industry and
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is thus considered to be the most important byproduct of this process.
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ACCEPTED MANUSCRIPT Oat hulls are a poorly used byproduct of oat groat milling and are discarded
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during processing, making them an environmental pollutant. Oat hulls are
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approximately 90g/100 g fiber, which is higher than that of wheat (47 g/100 g) or corn
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bran (62 g/100 g) (Galdeano & Grossmann, 2006), and they are an interesting raw
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material for use as a source of insoluble fiber.
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Every year, billions of pounds of rice hulls are generated by rice-producing
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countries and most are thrown away as a waste byproduct. Rice hulls represent
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approximately 20 % of the dry weight of the rice harvest (Dagnino, Chamorro, Romano,
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Felissia, & Area, 2013). Rice hulls consist in 36–40 g/100g cellulose and 12–19 g/100g
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hemicelluloses (Banerjee et al., 2009), and they also contain fats, gums, alkaloids,
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resins, essential oils and other cytoplasmic components (extractives), and with an ash
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composition of approximately 12g/100g, which are made primarily of silica (80–90
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g/100g) (Dagnino et al., 2013). Due to the high silica content present rice hulls have not
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yet been exploited in the food and feed industry, but the removal of silica can be an
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alternative to convert this residue in a suitable fiber-rich food ingredient (Nenadis,
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Kyriakoudi, &Tsimidou, 2013).
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Brazil is the fifth largest banana producer in the world with a production of 7.3
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million tons, which follows India, China, the Philippines and Ecuador (FAO, 2013).
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Fibrous residue from banana pseudo-stems (FRBPS) is pre-consumption waste that is
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generated during the production phase. According to Saraiva et al. (2012), the current
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destination of pre-consumption residues in South America is not well documented in the
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scientific literature; however, the pseudo-stems produced in China and India are
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normally cut and usually abandoned in the plantation to become organic waste and
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cause environmental pollution after harvesting banana bunches.
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Thus, as part of an effort to determine the potential application for four agro-
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industrial residues (malt bagasse, oat hulls, rice hulls and fibrous residue from banana
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pseudo-stems), the objectives of this work were to determine some selected
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physicochemical properties of these residues.
2. Material and methods
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2.1 Materials
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Malt bagasse was kindly provided by Microcervejaria Fábrica 1 (Londrina,
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Paraná, Brazil). Oat and rice hulls were kindly supplied by SL-Alimentos (Mauá da
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Serra, PR, Brazil) and HT-Nutri (Camaquã, RS, Brazil), respectively. FRBPS from the
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Nanica cultivar (Musa cavendishii) was collected at the Technological Federal
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University of Paraná, and the pseudo-stems were manually defibrillated and dried at
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room conditions (at approximately 25 °C and 70 % relative humidity). After the
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residues were obtained, all of them were dried (12 - 14 h) at 45oC in air circulation oven
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(Marconi MA 415 – Piracicaba-Brazil) and milled (IKA-A 11 Basic Mill - Germany) to
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yield particles < 0.30 mm.
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2.2 Chemical composition
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The centesimal composition of the residues (proteins, lipids, moisture and ash)
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was determined by following Association of Official Analytical Chemists (AOAC)
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methods (2003), and the total carbohydrates were calculated by taking the difference.
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All determinations were run in triplicate.
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The total dietary fiber and soluble and insoluble fractions were determined
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according to AACC methods (AACC method 32-07, 1990). Cellulose was determined
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by the Updegraff (1969) method, and the lignin content was determined by the 4
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Because the insoluble dietary fiber (IDF) fraction in cereals is made of cellulose,
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hemicelluloses and lignin (Chawla & Patil, 2009), the hemicelluloses were calculated
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by taking the IDF minus cellulose plus lignin contents.
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2.3 Fourier Transform-Infrared Spectroscopy (FT-IR)
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The samples were dried and compressed into tablets with potassium bromide.
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The FT-IR analyses were performed with a Shimadzu FT-IR 8300 (Shimadzu, Japan),
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which has a spectral resolution of 4 cm-1 and a spectral range of 4000–500 cm-1.
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2.4 Scanning electron microscopy (SEM)
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The dried samples were mounted on bronze stubs using double-sided tape, and
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their surfaces were coated with a thin gold layer (40–50 nm). The analyses were
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performed with an FEI Quanta 200 microscope (Oregon, USA) using an accelerating
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voltage of 30 kV.
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2.5 X-ray diffraction
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The samples were finely powdered (particles < 0.149 mm) and the analysis was
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performed by using a PANalytical X´Pert PRO MPD diffractometer (Almelo, The
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Netherlands) according to Matsuda et al. (2013). The relative crystallinity index (CI)
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was calculated by Ruland method (1961) as follows: CI = ((Ac)/(Ac+Aa))*100, where Ac
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is the crystalline area and Aa is the amorphous area.
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2.6 Water-holding (WHC) and oil-holding capacity (OHC)
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Both capacities were determined according to Chau, Cheung, and Wong (1997)
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with modifications. Each sample (2.00 g) was weighed and then stirred into 20 mL of
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distilled water or soybean oil for 30 min at 200 rpm in a shaker (Quimis Q 225M, 5
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Germany) at 2200 x g for 30 min and the supernatant volumes were measured. The
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water-holding capacity was expressed as g of water held per g of sample, and the oil-
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holding capacity was expressed as g of oil held per g of fiber. All tests were conducted
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in triplicate.
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2.7 Emulsifying capacity
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The emulsifying capacity was determined according to Seibel and Beléia (2009).
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Each sample (1.00 g) was weighed, stirred into 50 mL of distilled water and
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homogenized for 30 s. Soybean oil was then added to the mixture at a rate of 10
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mL/min and mixed at 300 rpm in a shaker (Quimis Q 225M, Brazil). The emulsifying
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capacity was calculated as the amount of oil emulsified by each gram of sample. All
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tests were conducted in triplicate.
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2.8 Swelling
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The swelling capacity was determined according to Robertson, Monredon,
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Dysseler, Guillon, Amado and Thibault (2000). One gram of each sample was mixed
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with 20 mL of distilled water in a 100 mL graduated cylinder. The suspension was
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intermittently stirred for 2 h and then allowed to stand for 18 h to achieve complete
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hydration and sedimentation equilibrium. The bulk volume was recorded and the
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swelling capacity was expressed as the volume occupied by the sample per gram of
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original sample dry weight. All tests were conducted in triplicate.
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2.9 Moisture sorption isotherms
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Samples of the residues (0.5 g) were dried for 15 d over anhydrous calcium
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chloride. The samples were then were placed over saturated salt solutions in separate
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desiccators, each with a specific level of relative humidity (RH) (11, 33, 43, 58, 75 and 6
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equal consecutive measurements had been recorded, it was assumed that the equilibrium
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weight had been reached. The equilibrium moisture content was calculated as the mass
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increase of the dried sample at equilibration for each RH. The GAB (Guggenheim-
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Anderson-de Boer) model was used to fit the data from the sorption isotherms, and
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monolayer values were calculated from the equations (Bizot, 1984). The GAB isotherm
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model can be expressed as follows in Equation 1:
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M=m0CKaw/(1-Kaw)(1- Kaw + CKaw) (Equation 1)
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Where M is the equilibrium moisture content at a given water activity (aw), aw is
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RH/100, m0 is the monolayer value (g water/g solids), and C and K are GAB constants.
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All tests were conducted in triplicate.
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2.10 Statistical analysis
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were performed with Statistica software version 7.0 (Statsoft, OK, USA).
3. Results and discussion
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3.1 Chemical composition
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Analyses of variance (ANOVA) and Tukey's mean comparison test (p ≤ 0.05)
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The chemical compositions of the four residues are presented in Table 1. Oat
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hulls presented the highest total fiber content (89.08 g/100g), followed by malt bagasse
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(63.84 g/100g), rice hulls (56.26 g/100g) and FRBPS (47.99 g/100g). The insoluble
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fibers in all residues formed the major fraction of the fiber contents, and FRBPS
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exhibited the highest soluble fiber content (4.44 g/100g). The soluble and insoluble
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fractions of the dietary fibers exhibited differences in their technological functionality
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and physiological effects. Soluble fibers are attributed with the capacity to increase 7
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viscosity and to reduce the glycemic response and plasma cholesterol, and insoluble
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fibers are characterized by their porosity, their low density and by their ability to
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increase fecal bulk and decrease intestinal transit (Elleuch et al., 2011). The proportion of cellulose, hemicellulose and lignin exhibited large variations
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between residues (Table 1). Oat hulls had the highest cellulose content (48.00 g/100g),
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followed by rice hulls (35.47 g/100g) and FRBPS (29.91 g/100g). Oat hulls also showed
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the highest hemicellulose content (25.50 g/100g), followed by malt bagasse (23.41
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g/100g), FRBPS (14.42 g/100g) and rice hulls (13.35 g/100g). Malt bagasse had the
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highest lignin content (26.13 g/100g) and FRBPS had the lowest (5.31 g/100g).
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Malt bagasse exhibited the highest protein and lipid contents compared with the other residues, with values of 13.60 and 4.44 g/100g, respectively (Table 1). The ash content was higher in FRBPS (16.68 g/100g) and rice hulls (14.74
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g/100g). In FRBPS, the minerals present in higher quantities are potassium, calcium and
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magnesium (Mohapatra, Mishra, & Sutar, 2010), and in rice hulls, silica makes up 95-
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98 % of the total ashes (Della, Kuhn, & Hotza, 2001). There is little information about
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the use of rice hulls for animal or human consumption because of their high silica
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content. Several authors reported that silica induces indigestibility in foods, in addition
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to chronic kidney diseases, autoimmune diseases, nephropathy and skin lesions in
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dialysis patients (Ghahramani, 2010; Kuan & Yuen, 2012). Thus, the use of rice hulls as
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an insoluble dietary fiber source in food products could be useful only if the silica
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content could be partially or totally removed.
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These materials have large potential to be used in production of dietary fiber rich
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powders. In the last years, there is a great interest in food industry residues from which
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dietary fibers powders are obtained (Femenia Lefebvre, Thebaudin, Robertson, &
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Bourgeois, 1997; Larrauri, 1999; Figuerola, Hurtado, Estévez, Chiffelle, & Asenjo, 8
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characteristics of these fibers powders are: total dietary fiber content above 50 g/100g,
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moisture lower than 9 g/100g, low content of lipids, a low caloric value and neutral
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flavour and taste (Larrauri, 1999). The adequate intake of dietary fiber is associated
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with the prevention of chronic diseases such as colon, rectal, breast cancers, coronary
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heart diseases and with improved glycemic control and the World Health Organization
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(WHO) recommends a minimum daily fiber intake of 12.5 g/1000 kcal (Sardinha,
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Canella, Martins, Claro, & Levy, 2014).
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The apparent density of the samples ranged from 0.41 to 0.48 g/cm3, and the oat
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and rice hulls presented the lower density values, and malt bagasse and FRBPS had
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higher values (Table 2). The lower density of oat hulls was most likely related to the
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higher insoluble fiber content of this residue (Elleuch et al., 2011).
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3.2 Scanning electron microscopy (SEM)
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The morphology of the residue surfaces are shown in Fig. 1, and all materials
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exhibited the typical aspect of lignocellulosic fibers, with the original fiber bundles
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together with the nonfibrous components (hemicellulose and lignin), which forms a
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compact structure in all cases. In plant cells, lignin and hemicelluloses are deposited
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between the cellulosic microfibrils, which results in an interrupted lamellar structure
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(Abraham et al., 2011). Fung, Yuen and Liong (2010) reported that the fibers in their
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native state contain waxes and other encrusting substances such as hemicellulose,
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lignin, and pectin that form a thick and smooth outer layer.
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3.3 Fourier Transform-Infrared Spectroscopy (FT-IR)
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Because the primary components of the studied residues are cellulose,
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hemicelluloses and lignin, the observed FT-IR spectra (Fig. 2) have been attributed 9
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corresponding to O–H stretching at approximately 3200–3600 cm-1, which could
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indicate the occurrence of H-bonding interactions in these materials. These interactions
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are characteristic of polymeric associations among the hydroxyl groups present in
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carbohydrates (cellulose + hemicellulose) and lignin.
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The bands observed at 2900 cm-1 correspond to –C-H stretching; H-C-H and –C-
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O-H-conjugated bending vibrations appeared in all spectra (Fig. 2). Bands were
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observed at approximately 1650 cm-1 for all samples, and this value is associated with
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the angular O–H bending of water molecules. Sun, Sun, Zhao and Sun (2004) reported
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that the band at approximately 1650 cm−1 may result from water, but it could also be
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attributed to the aromatic C=C stretch of the aromatic ring in the lignin.
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A large region of absorption involving overlapping bands in the 1500–1100 cm-1
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range caused by C-C, C=C, OH, CO, CH, C-O-C, and CH aromatic linkages (Bilba,
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Arsene, & Ouensanga, 2007) appeared in all samples, which also exhibited bands at
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1043 cm-1 corresponding to the linear and branched (1→4)-β-xylans (Kakurácová
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Capek, Sasinková, Wellner, & Ebringerová, 2000); these bands are characteristic of
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hemicelluloses (Fig. 2).
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3.4 X-ray diffraction
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Fig. 3 depicts the XRD patterns of the agro-industrial residues. The relative
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crystallinity index was 16.5 % for malt bagasse, 23.6 % for oat hulls, 25.4 % for rice
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hulls and 28.7 % for FRBPS. The malt bagasse diffractogram (Fig. 3) was characteristic
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of an amorphous material with only a small peak near 2θ = 22°, which could be
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attributed to the structure of the native cellulose (Nishino, Matsuda, & Hirao, 2004).
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The protein content (13.60 g/100g) of malt bagasse was higher than that of the cellulose
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content (12.29 g/100g), and according to Marengo, Vercelheze and Mali (2013), the 10
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complex special arrangement of protein molecules generates materials with a lower
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crystallization capacity. FRBPS, oat and rice hulls presented the same cellulose characteristic peak at 2θ
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= 22° (Fig. 2). FRBPS presented the highest relative crystallinity, with other peaks at 2θ
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= 14.3°, 18°, 29° and 40.7°. The 29.2° and 40.7° peaks can be attributed to the presence
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of inorganic substances (Guimarães, Frollini, Silva, Wypych, & Satyanarayana, 2009),
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the 29° peak is from silicon and the 40° peak is caused by potassium and calcium
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(Schettino, Freitas, Cunha, Emmerich, Soares, & Silva, 2007).
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Kim, Yoon, Choi and Gil (2008) reported a characteristic peak at 2θ = 22° for
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rice hulls ashes rich in silica. In our work this characteristic peak appeared (Fig. 2) for
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rice hull and was overlapped by cellulose.
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3.5 Water-holding capacity (WHC), oil-holding capacity (OHC), emulsifying capacity
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and swelling
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The water-holding capacity represents the ability of a material to retain water
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when subjected to an external centrifugal gravity force or compression, and it consists
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of the sum of linked water, hydrodynamic water and physically trapped water
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(Vázquez-Ovando,
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Considering our samples, FRBPS presented significantly higher WHC (4.71 g/g) when
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compared with other samples (Table 2), followed by malt bagasse (3.68 g/g), rice hulls
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(2.58 g/g) and oat hulls (2.13 g/g). The higher WHC for FRBPS and malt bagasse could
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be attributed to the higher soluble dietary fiber contents (Table 1) of these samples when
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compared with the oat and rice hulls. According to Robertson and Eastwood (1981), the
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WHC differences between different types of fibers could be caused by either differences
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in the chemical composition or structural differences between the fiber sources. These
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authors also reported that cereal fibers, such as malt bagasse, oat and rice hulls, tend to
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have a lower WHC than vegetable fibers, such as FRBPS. Considering the WHC values, FRBPS could have possible applications in baked
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products requiring hydration, viscosity development and freshness conservation, or in
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meat products requiring water retention. Additionally, the WHC of the fiber is highly
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indicative of its physiological role in intestinal function and blood sugar level control
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(Fung et al., 2010).
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The WHC values of oat and rice hulls (Table 2) observed in this work were
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comparable with those reported for wheat and maize hulls, which presented WHC
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values of 2.48 and 2.32 g/g (Zambrano, Meléndez, & Gallardo, 2001).
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The swelling values (Table 2) followed the same trend observed for WHC, with
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high values observed for FRBPS and malt bagasse. According to Izydorczyk, Chornick,
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Paulley, Edward and Dexter (2008), the swelling capacity is a function of the chemical
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composition and the physical structure of the fiber matrix.
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Natural fibers also have the capacity to hold oil, and this property (the oil
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holding capacity or OHC) represents the amount of oil retained by the fibers after
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mixing, incubating with oil and centrifuging. In our work, the OHC was low for all
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residues, and the higher values were observed in FRBPS and malt bagasse (Table 2),
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followed by rice and oat hulls. According to Vázquez-Ovando et al. (2009), fibers with
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low OHC are potential ingredients in fried products because they would provide a non-
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greasy sensation.
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The emulsifying capacity is related to the ability of a substance to act as an agent
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that facilitates the solubilization or dispersion of two immiscible liquids (Vázquez-
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Ovando et al. 2009). Only malt bagasse and FRBPS presented emulsifying capacities,
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with values of 59.83 and 8.28 mL oil/g solids, respectively (Table 2). These results
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FRBPS (6.80). According to Fung et al. (2010), the higher protein contents in fibrous
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residues positively affect its emulsifying activity. The good emulsification properties of
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dietary fiber can improve the blood cholesterol level, which is mostly attributed to the
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binding of biliary acids, thus limiting its absorption in the small intestine and leading to
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the increased expenditure of cholesterol for biliary acid synthesis (Betancur-Ancona,
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Peraza-Mercado, Moguel-Ordoñez, & Fuertes-Blanco, 2004).
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3.6 Moisture sorption isotherms
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As shown in Figure 4, all samples exhibited similar sigmoidal isotherm patterns,
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and the equilibrium moisture content of the samples increased with increasing RH, but
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the increase in the equilibrium moisture content was more pronounced when the
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samples were stored at RH ≥ 75%. The FRBPS exhibited a higher increase in the
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equilibrium moisture content at RH ≥ 75%. Berkün, Balköse, Tihmnhoglu and
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Altinkaya (2008) observed that cellulosic materials have low equilibrium moisture
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contents under reduced RH, but an exponential increase could be observed at higher RH
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values.
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The GAB parameters were calculated from our experimental water sorption
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isotherm data and in all cases, the coefficient of determination (R2) was 0.99, indicating
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that this model was consistent with the experimental data. Rice hulls exhibited the
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lowest monolayer value (0.032 g/g), followed by malt bagasse (0.042 g/g) and oat hulls
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(0.042 g/g), and FRBPS had the highest value (0.059 g/g), which is indicative of the
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higher hygroscopicity of this residue in relation to the others. The monolayer value
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indicates the maximum amount of water that can be adsorbed in a single layer per gram
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of dry matter; this value is a measure of the number of sorbing sites in the water sample
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(Strauss, Porcja, & Chen., 1991). The constants of the GAB model (C and K) were calculated as follows: malt
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bagasse (C = 5.95 and K = 0.88), oat hulls (C = 26.51 and K = 0.89), rice hulls (C =
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13.98 and K = 0.88) and FRBPS (C = 1.47 and K = 0.99). The C parameter is related to
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the water adsorption energy of a layer (Strauss et al., 1991), and in our samples, the
319
lower value was observed for FRBPS, which is the more hydrophilic material.
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Considering the K parameter, some authors reported that it is effectively independent of
321
the composition (Coupland, Shaw, Monahan, O'Riordan, & O'Sullivan, 2000).
322
4. Conclusions
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All residues presented high fiber contents, and the oat hulls exhibited the highest
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total fiber content, followed by malt bagasse, rice hulls and FRBPS; thus, they can all
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be employed as dietary fiber sources by the food industry in health and diet food
326
products such as fiber-rich powders, nutrition bars, breads and cookies. It is important
327
to highlight that the use rice hulls as fiber source for food products is conditioned to
328
silica removal.
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FRBPS showed the highest soluble fiber content, in addition to the higher water
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holding capacity and swelling, making it a potential ingredient for use in baked products
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requiring hydration, viscosity development and freshness conservation, or in meat
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products requiring water retention.
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All the residues presented low oil-holding capacities and could be used in fried
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products to provide a non-greasy sensation. Only malt bagasse and FRBPS presented
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emulsifying capacities, making them possible emulsifiers for the food or pharmaceutical
336
industries. 14
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Acknowledgments
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The authors wish to thank the Laboratory of Microscopy and Microanalysis (LMEM)
341
and the Laboratory of X-Ray Diffraction (LDRX) at the State University of Londrina
342
for the analyses, and also to CNPq-Brazil for financial support (No. 479768-2012).
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Tecnología y Salud (pp. 195–209). Brasil: Livraría LTDA.
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FIGURE CAPTIONS
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Figure 1 - Micrographs obtained using MEV: malt bagasse (a), oat hull (b), rice hull (c)
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and FRBPS (d).
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Figure 2 - FT-IR spectra of the agro-industrial residues.
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Figure 3 - X-ray diffractograms of the agro-industrial residues.
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Figure 4 – Water sorption isotherms of the agro-industrial residues: () malt bagasse,
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() oat hull, () rice hull and () FRBPS. The lines were derived from GAB model.
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Malt bagasse
Oat Hull
Rice Hull
Moisture (g/100g)
5.34 ± 0.12
5.12 ± 0.52
9.38 ± 0.88
Ash (g/100g)
2.78 ± 0.25
3.27 ± 0.37
14.74 ± 0.90
16.68 ± 0.05
Lipid (g/100g)
4.44 ± 0.14
1.94 ± 0.15
0.28 ± 0.01
0.86 ± 0.01
Protein (g/100g)
13.60 ± 0.90
1.85 ± 0.56
4.65 ± 0.35
6.80 ± 0.59
Carbohydrates (g/100g)
73.84 ± 1.87
90.02 ± 2.19
70.95 ± 0.82
66.08 ± 0.5
Total dietary fiber (g/100g)
63.84 ± 0.60
89.08 ± 2.58
56.26 ± 3.20
47.99 ± 0.02
1.08 ± 0.15
0.11 ± 0.01
4.20 ± 0.02
88.0 ± 5.18
56.15 ± 0.85
43.79 ± 0.01
35.47 ± 4.48
29.91 ± 0.55
2.01 ± 0.12
Insoluble dietary fiber (g/100g)
61.83 ± 0.52 12.29 ± 0.14
FRBPS
9.58 ± 0.06
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Table 1 – Chemical compositions of malt bagasse, oat hulls, rice hulls and fibrous residue from banana pseudo steam (FRBPS).
Hemicellulose (g/100g)
23.41 ± 2.30
25.5 ± 1.96
13.35 ± 2.88
14.42 ± 0.82
Lignin (g/100g)
26.13 ± 3.15
14.5 ± 0.99
7.24 ± 0.59
5.31 ± 0.12
Data are the means of triplicate determinations ± standard deviation.
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Table 2-Physical and functional properties of malt bagasse, oat hull, rice hull and fibrous residue from banana pseudo-steam (FRBPS). Oat Hull
Rice Hull
FRBPS
Apparent density (g/cm3)
0.48 ± 0.01a
0.41 ± 0.05b
0.45 ± 0.08a,b
0.46 ± 0.07a,b
Water holding capacity (g water/ g solid)
3.68 ± 0.08b
2.13 ± 0.11c
2.58 ± 0.28c
4.71 ± 0.31a
Swelling (mL water/ g solid)
4.53 ± 0.30a
3.56 ± 0.52b
3.27 ± 0.58b
4.98 ± 0.89a
Oil holding capacity (g oil/ g solid)
2.46 ± 0.27a
1.37 ± 0.06b
1.85 ± 0.15b
2.68 ± 0.08a
Emulsifying capacity (mL oil/g solid)
59.83 ± 0.28a
ND
ND
8.28 ± 0.58b
pH
5.73 ± 0.14a
5.58 ± 0.25a
5.68 ± 0.28a
5.52 ± 0.41a
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Data are the means of triplicate determinations ± standard deviation. Different letters in the same line indicate significant differences
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ACCEPTED MANUSCRIPT HIGHLIGHTS The physicochemical properties of four agro-industrial residues were determined. Malt bagasse, oat hulls, rice hulls, fibrous residue from banana pseudo-stems.
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In all the residues, insoluble fibers formed the major fraction of the fiber content.
Banana residue with highest soluble fiber content, water and oil-holding capacities.
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The residues had potential for use as a dietary fiber source in health food products.
S0023-6438(15)00060-2
DOI:
10.1016/j.lwt.2015.01.044
Reference:
YFSTL 4425
To appear in:
LWT - Food Science and Technology
Received Date: 14 August 2014 Revised Date:
20 January 2015
Accepted Date: 25 January 2015
Please cite this article as: Jacometti, G.A., Mello, L.R.P.F., Nascimento, P.H.A., Sueiro, A.C., Yamashita, F., Mali, S., The physicochemical properties of fibrous residues from the agro industry, LWT - Food Science and Technology (2015), doi: 10.1016/j.lwt.2015.01.044. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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The physicochemical properties of fibrous residues from the agro industry
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Giselle A. Jacomettia, Léa R. P. F. Mellob; Pedro H.A. Nascimentob; Ana Claudia
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Sueirob; Fabio Yamashitac and Suzana Malib* a-
4 b-
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Technological Federal University of Paraná, Cornélio Procópio - PR, Brazil.
Department of Biochemistry and Biotechnology, CCE, State University of Londrina,
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Londrina - PR, Brazil. c- Department of Food Science and Technology, CCA, State
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University of Londrina, Londrina - PR, Brazil Abstract
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The objectives of this work were to determine some of the physicochemical
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properties of four agro-industrial residues, namely malt bagasse, oat hulls, rice hulls and
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fibrous residue from banana pseudo-stems (FRBPS). Oat hulls contained the highest
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dietary fiber content (89.08 g/100 g), followed by malt bagasse (63.84 g/100 g), rice
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hulls (56.26 g/100 g) and FRBPS (47.99 g/100 g). The insoluble fiber in all residues
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formed the major fraction of the fiber contents, ranging from 43.79 (FRBPS) to 88.0
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g/100 g (oat hulls). FRBPS exhibited the highest soluble fiber content (4.44 g/100 g),
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water (4.71 g/g) and oil-holding capacity (2.68 g/g). Only malt bagasse and FRBPS
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exhibited emulsifying capacity, which was 59.83 and 8.28 mL oil/g, respectively. As
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demonstrated by water sorption isotherms, rice hulls were less hygroscopic and FRBPS
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were more hygroscopic.
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Keywords: malt bagasse; oat hulls; rice hulls; fibrous residue from banana pseudo-
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stems
* To whom correspondence should be addressed: Tel: +55 43 3371-4270, Fax: +55 43 3371-4054, E-mail: [email protected] 1
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1. Introduction Dietary fiber is a class of compounds that includes a mixture of plant
25
carbohydrate polymers, both oligosaccharides and polysaccharides, e.g., cellulose,
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hemicelluloses, pectic substances, and gums that may be associated with lignin and
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other non-carbohydrate components (e.g., polyphenols, waxes, saponins, cutin,
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phytates, and resistant protein) (Elleuch, Bedigian, Roiseux, Besbes, Blecker, & Attia,
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2011).
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Fibers extracted from some grains and seeds present physical and functional
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properties that make them useful for the food industry, which encourages researchers to
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search for novel raw materials that meet the needs of these areas, with a particular focus
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on food industry residues, such as malt bagasse, oat and rice hulls, or on residues from
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agriculture, such as the fibrous residue of banana pseudo-stems (FRBPS). These
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materials are used as bedding for animals and livestock feeding, burned in the fields,
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added into soil as green fertilizer, or used as soil conditioners or fertilizers, biofuels,
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thermoplastics, activated charcoal, and components of other composite materials.
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However, the potential of these agro-industrial residues as a source of food dietary fiber
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has not been fully examined (Kuan & Liong, 2008).
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Brazil is the third largest beer producer in the world, with a production of 12.6
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ML, trailing only China (40 ML) and the United States (35 ML) (Mardegan et al.,
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2013). According to Cordeiro, El-Aouar and Araújo (2013), malt bagasse is a byproduct
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of beer brewing, and it is a component of the solid material produced from wort
44
filtration before boiling. This solid byproduct primarily consists of the leftover peels
45
and pulp of malt and grains and also some additives, such as rice, corn, and wheat.
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Crushed malt makes up 85% of the total product generated by the brewing industry and
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is thus considered to be the most important byproduct of this process.
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during processing, making them an environmental pollutant. Oat hulls are
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approximately 90g/100 g fiber, which is higher than that of wheat (47 g/100 g) or corn
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bran (62 g/100 g) (Galdeano & Grossmann, 2006), and they are an interesting raw
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material for use as a source of insoluble fiber.
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Every year, billions of pounds of rice hulls are generated by rice-producing
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countries and most are thrown away as a waste byproduct. Rice hulls represent
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approximately 20 % of the dry weight of the rice harvest (Dagnino, Chamorro, Romano,
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Felissia, & Area, 2013). Rice hulls consist in 36–40 g/100g cellulose and 12–19 g/100g
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hemicelluloses (Banerjee et al., 2009), and they also contain fats, gums, alkaloids,
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resins, essential oils and other cytoplasmic components (extractives), and with an ash
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composition of approximately 12g/100g, which are made primarily of silica (80–90
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g/100g) (Dagnino et al., 2013). Due to the high silica content present rice hulls have not
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yet been exploited in the food and feed industry, but the removal of silica can be an
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alternative to convert this residue in a suitable fiber-rich food ingredient (Nenadis,
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Kyriakoudi, &Tsimidou, 2013).
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Brazil is the fifth largest banana producer in the world with a production of 7.3
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million tons, which follows India, China, the Philippines and Ecuador (FAO, 2013).
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Fibrous residue from banana pseudo-stems (FRBPS) is pre-consumption waste that is
67
generated during the production phase. According to Saraiva et al. (2012), the current
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destination of pre-consumption residues in South America is not well documented in the
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scientific literature; however, the pseudo-stems produced in China and India are
70
normally cut and usually abandoned in the plantation to become organic waste and
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cause environmental pollution after harvesting banana bunches.
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Thus, as part of an effort to determine the potential application for four agro-
73
industrial residues (malt bagasse, oat hulls, rice hulls and fibrous residue from banana
74
pseudo-stems), the objectives of this work were to determine some selected
75
physicochemical properties of these residues.
2. Material and methods
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2.1 Materials
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Malt bagasse was kindly provided by Microcervejaria Fábrica 1 (Londrina,
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Paraná, Brazil). Oat and rice hulls were kindly supplied by SL-Alimentos (Mauá da
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Serra, PR, Brazil) and HT-Nutri (Camaquã, RS, Brazil), respectively. FRBPS from the
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Nanica cultivar (Musa cavendishii) was collected at the Technological Federal
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University of Paraná, and the pseudo-stems were manually defibrillated and dried at
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room conditions (at approximately 25 °C and 70 % relative humidity). After the
85
residues were obtained, all of them were dried (12 - 14 h) at 45oC in air circulation oven
86
(Marconi MA 415 – Piracicaba-Brazil) and milled (IKA-A 11 Basic Mill - Germany) to
87
yield particles < 0.30 mm.
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2.2 Chemical composition
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The centesimal composition of the residues (proteins, lipids, moisture and ash)
90
was determined by following Association of Official Analytical Chemists (AOAC)
91
methods (2003), and the total carbohydrates were calculated by taking the difference.
92
All determinations were run in triplicate.
93
The total dietary fiber and soluble and insoluble fractions were determined
94
according to AACC methods (AACC method 32-07, 1990). Cellulose was determined
95
by the Updegraff (1969) method, and the lignin content was determined by the 4
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97
Because the insoluble dietary fiber (IDF) fraction in cereals is made of cellulose,
98
hemicelluloses and lignin (Chawla & Patil, 2009), the hemicelluloses were calculated
99
by taking the IDF minus cellulose plus lignin contents.
100
2.3 Fourier Transform-Infrared Spectroscopy (FT-IR)
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The samples were dried and compressed into tablets with potassium bromide.
102
The FT-IR analyses were performed with a Shimadzu FT-IR 8300 (Shimadzu, Japan),
103
which has a spectral resolution of 4 cm-1 and a spectral range of 4000–500 cm-1.
104
2.4 Scanning electron microscopy (SEM)
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The dried samples were mounted on bronze stubs using double-sided tape, and
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their surfaces were coated with a thin gold layer (40–50 nm). The analyses were
107
performed with an FEI Quanta 200 microscope (Oregon, USA) using an accelerating
108
voltage of 30 kV.
109
2.5 X-ray diffraction
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The samples were finely powdered (particles < 0.149 mm) and the analysis was
111
performed by using a PANalytical X´Pert PRO MPD diffractometer (Almelo, The
112
Netherlands) according to Matsuda et al. (2013). The relative crystallinity index (CI)
113
was calculated by Ruland method (1961) as follows: CI = ((Ac)/(Ac+Aa))*100, where Ac
114
is the crystalline area and Aa is the amorphous area.
115
2.6 Water-holding (WHC) and oil-holding capacity (OHC)
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Both capacities were determined according to Chau, Cheung, and Wong (1997)
117
with modifications. Each sample (2.00 g) was weighed and then stirred into 20 mL of
118
distilled water or soybean oil for 30 min at 200 rpm in a shaker (Quimis Q 225M, 5
ACCEPTED MANUSCRIPT Brazil). These fibrous suspensions were centrifuged (Centrifugal Boeco U-32,
120
Germany) at 2200 x g for 30 min and the supernatant volumes were measured. The
121
water-holding capacity was expressed as g of water held per g of sample, and the oil-
122
holding capacity was expressed as g of oil held per g of fiber. All tests were conducted
123
in triplicate.
124
2.7 Emulsifying capacity
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The emulsifying capacity was determined according to Seibel and Beléia (2009).
126
Each sample (1.00 g) was weighed, stirred into 50 mL of distilled water and
127
homogenized for 30 s. Soybean oil was then added to the mixture at a rate of 10
128
mL/min and mixed at 300 rpm in a shaker (Quimis Q 225M, Brazil). The emulsifying
129
capacity was calculated as the amount of oil emulsified by each gram of sample. All
130
tests were conducted in triplicate.
131
2.8 Swelling
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The swelling capacity was determined according to Robertson, Monredon,
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Dysseler, Guillon, Amado and Thibault (2000). One gram of each sample was mixed
134
with 20 mL of distilled water in a 100 mL graduated cylinder. The suspension was
135
intermittently stirred for 2 h and then allowed to stand for 18 h to achieve complete
136
hydration and sedimentation equilibrium. The bulk volume was recorded and the
137
swelling capacity was expressed as the volume occupied by the sample per gram of
138
original sample dry weight. All tests were conducted in triplicate.
139
2.9 Moisture sorption isotherms
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Samples of the residues (0.5 g) were dried for 15 d over anhydrous calcium
141
chloride. The samples were then were placed over saturated salt solutions in separate
142
desiccators, each with a specific level of relative humidity (RH) (11, 33, 43, 58, 75 and 6
ACCEPTED MANUSCRIPT 90 %) and held at 25 °C. Each sample was weighed at regular intervals, and when two
144
equal consecutive measurements had been recorded, it was assumed that the equilibrium
145
weight had been reached. The equilibrium moisture content was calculated as the mass
146
increase of the dried sample at equilibration for each RH. The GAB (Guggenheim-
147
Anderson-de Boer) model was used to fit the data from the sorption isotherms, and
148
monolayer values were calculated from the equations (Bizot, 1984). The GAB isotherm
149
model can be expressed as follows in Equation 1:
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M=m0CKaw/(1-Kaw)(1- Kaw + CKaw) (Equation 1)
151
Where M is the equilibrium moisture content at a given water activity (aw), aw is
152
RH/100, m0 is the monolayer value (g water/g solids), and C and K are GAB constants.
153
All tests were conducted in triplicate.
154
2.10 Statistical analysis
156 157
were performed with Statistica software version 7.0 (Statsoft, OK, USA).
3. Results and discussion
159
3.1 Chemical composition
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Analyses of variance (ANOVA) and Tukey's mean comparison test (p ≤ 0.05)
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The chemical compositions of the four residues are presented in Table 1. Oat
161
hulls presented the highest total fiber content (89.08 g/100g), followed by malt bagasse
162
(63.84 g/100g), rice hulls (56.26 g/100g) and FRBPS (47.99 g/100g). The insoluble
163
fibers in all residues formed the major fraction of the fiber contents, and FRBPS
164
exhibited the highest soluble fiber content (4.44 g/100g). The soluble and insoluble
165
fractions of the dietary fibers exhibited differences in their technological functionality
166
and physiological effects. Soluble fibers are attributed with the capacity to increase 7
ACCEPTED MANUSCRIPT 167
viscosity and to reduce the glycemic response and plasma cholesterol, and insoluble
168
fibers are characterized by their porosity, their low density and by their ability to
169
increase fecal bulk and decrease intestinal transit (Elleuch et al., 2011). The proportion of cellulose, hemicellulose and lignin exhibited large variations
171
between residues (Table 1). Oat hulls had the highest cellulose content (48.00 g/100g),
172
followed by rice hulls (35.47 g/100g) and FRBPS (29.91 g/100g). Oat hulls also showed
173
the highest hemicellulose content (25.50 g/100g), followed by malt bagasse (23.41
174
g/100g), FRBPS (14.42 g/100g) and rice hulls (13.35 g/100g). Malt bagasse had the
175
highest lignin content (26.13 g/100g) and FRBPS had the lowest (5.31 g/100g).
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Malt bagasse exhibited the highest protein and lipid contents compared with the other residues, with values of 13.60 and 4.44 g/100g, respectively (Table 1). The ash content was higher in FRBPS (16.68 g/100g) and rice hulls (14.74
179
g/100g). In FRBPS, the minerals present in higher quantities are potassium, calcium and
180
magnesium (Mohapatra, Mishra, & Sutar, 2010), and in rice hulls, silica makes up 95-
181
98 % of the total ashes (Della, Kuhn, & Hotza, 2001). There is little information about
182
the use of rice hulls for animal or human consumption because of their high silica
183
content. Several authors reported that silica induces indigestibility in foods, in addition
184
to chronic kidney diseases, autoimmune diseases, nephropathy and skin lesions in
185
dialysis patients (Ghahramani, 2010; Kuan & Yuen, 2012). Thus, the use of rice hulls as
186
an insoluble dietary fiber source in food products could be useful only if the silica
187
content could be partially or totally removed.
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188
These materials have large potential to be used in production of dietary fiber rich
189
powders. In the last years, there is a great interest in food industry residues from which
190
dietary fibers powders are obtained (Femenia Lefebvre, Thebaudin, Robertson, &
191
Bourgeois, 1997; Larrauri, 1999; Figuerola, Hurtado, Estévez, Chiffelle, & Asenjo, 8
ACCEPTED MANUSCRIPT 2005; Peerajit, Chiewchan, & Devahastin, 2012; Yang, Xiao,& Wang, 2014). The main
193
characteristics of these fibers powders are: total dietary fiber content above 50 g/100g,
194
moisture lower than 9 g/100g, low content of lipids, a low caloric value and neutral
195
flavour and taste (Larrauri, 1999). The adequate intake of dietary fiber is associated
196
with the prevention of chronic diseases such as colon, rectal, breast cancers, coronary
197
heart diseases and with improved glycemic control and the World Health Organization
198
(WHO) recommends a minimum daily fiber intake of 12.5 g/1000 kcal (Sardinha,
199
Canella, Martins, Claro, & Levy, 2014).
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The apparent density of the samples ranged from 0.41 to 0.48 g/cm3, and the oat
201
and rice hulls presented the lower density values, and malt bagasse and FRBPS had
202
higher values (Table 2). The lower density of oat hulls was most likely related to the
203
higher insoluble fiber content of this residue (Elleuch et al., 2011).
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3.2 Scanning electron microscopy (SEM)
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The morphology of the residue surfaces are shown in Fig. 1, and all materials
206
exhibited the typical aspect of lignocellulosic fibers, with the original fiber bundles
207
together with the nonfibrous components (hemicellulose and lignin), which forms a
208
compact structure in all cases. In plant cells, lignin and hemicelluloses are deposited
209
between the cellulosic microfibrils, which results in an interrupted lamellar structure
210
(Abraham et al., 2011). Fung, Yuen and Liong (2010) reported that the fibers in their
211
native state contain waxes and other encrusting substances such as hemicellulose,
212
lignin, and pectin that form a thick and smooth outer layer.
213
3.3 Fourier Transform-Infrared Spectroscopy (FT-IR)
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Because the primary components of the studied residues are cellulose,
215
hemicelluloses and lignin, the observed FT-IR spectra (Fig. 2) have been attributed 9
ACCEPTED MANUSCRIPT primarily to these components. All the spectra showed a wide absorption band
217
corresponding to O–H stretching at approximately 3200–3600 cm-1, which could
218
indicate the occurrence of H-bonding interactions in these materials. These interactions
219
are characteristic of polymeric associations among the hydroxyl groups present in
220
carbohydrates (cellulose + hemicellulose) and lignin.
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The bands observed at 2900 cm-1 correspond to –C-H stretching; H-C-H and –C-
222
O-H-conjugated bending vibrations appeared in all spectra (Fig. 2). Bands were
223
observed at approximately 1650 cm-1 for all samples, and this value is associated with
224
the angular O–H bending of water molecules. Sun, Sun, Zhao and Sun (2004) reported
225
that the band at approximately 1650 cm−1 may result from water, but it could also be
226
attributed to the aromatic C=C stretch of the aromatic ring in the lignin.
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A large region of absorption involving overlapping bands in the 1500–1100 cm-1
228
range caused by C-C, C=C, OH, CO, CH, C-O-C, and CH aromatic linkages (Bilba,
229
Arsene, & Ouensanga, 2007) appeared in all samples, which also exhibited bands at
230
1043 cm-1 corresponding to the linear and branched (1→4)-β-xylans (Kakurácová
231
Capek, Sasinková, Wellner, & Ebringerová, 2000); these bands are characteristic of
232
hemicelluloses (Fig. 2).
233
3.4 X-ray diffraction
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Fig. 3 depicts the XRD patterns of the agro-industrial residues. The relative
235
crystallinity index was 16.5 % for malt bagasse, 23.6 % for oat hulls, 25.4 % for rice
236
hulls and 28.7 % for FRBPS. The malt bagasse diffractogram (Fig. 3) was characteristic
237
of an amorphous material with only a small peak near 2θ = 22°, which could be
238
attributed to the structure of the native cellulose (Nishino, Matsuda, & Hirao, 2004).
239
The protein content (13.60 g/100g) of malt bagasse was higher than that of the cellulose
240
content (12.29 g/100g), and according to Marengo, Vercelheze and Mali (2013), the 10
ACCEPTED MANUSCRIPT 241
complex special arrangement of protein molecules generates materials with a lower
242
crystallization capacity. FRBPS, oat and rice hulls presented the same cellulose characteristic peak at 2θ
244
= 22° (Fig. 2). FRBPS presented the highest relative crystallinity, with other peaks at 2θ
245
= 14.3°, 18°, 29° and 40.7°. The 29.2° and 40.7° peaks can be attributed to the presence
246
of inorganic substances (Guimarães, Frollini, Silva, Wypych, & Satyanarayana, 2009),
247
the 29° peak is from silicon and the 40° peak is caused by potassium and calcium
248
(Schettino, Freitas, Cunha, Emmerich, Soares, & Silva, 2007).
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Kim, Yoon, Choi and Gil (2008) reported a characteristic peak at 2θ = 22° for
250
rice hulls ashes rich in silica. In our work this characteristic peak appeared (Fig. 2) for
251
rice hull and was overlapped by cellulose.
252
3.5 Water-holding capacity (WHC), oil-holding capacity (OHC), emulsifying capacity
253
and swelling
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The water-holding capacity represents the ability of a material to retain water
255
when subjected to an external centrifugal gravity force or compression, and it consists
256
of the sum of linked water, hydrodynamic water and physically trapped water
257
(Vázquez-Ovando,
258
Considering our samples, FRBPS presented significantly higher WHC (4.71 g/g) when
259
compared with other samples (Table 2), followed by malt bagasse (3.68 g/g), rice hulls
260
(2.58 g/g) and oat hulls (2.13 g/g). The higher WHC for FRBPS and malt bagasse could
261
be attributed to the higher soluble dietary fiber contents (Table 1) of these samples when
262
compared with the oat and rice hulls. According to Robertson and Eastwood (1981), the
263
WHC differences between different types of fibers could be caused by either differences
264
in the chemical composition or structural differences between the fiber sources. These
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Chel-Guerrer,
&
Betancur-Ancona,
2009).
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11
ACCEPTED MANUSCRIPT 265
authors also reported that cereal fibers, such as malt bagasse, oat and rice hulls, tend to
266
have a lower WHC than vegetable fibers, such as FRBPS. Considering the WHC values, FRBPS could have possible applications in baked
268
products requiring hydration, viscosity development and freshness conservation, or in
269
meat products requiring water retention. Additionally, the WHC of the fiber is highly
270
indicative of its physiological role in intestinal function and blood sugar level control
271
(Fung et al., 2010).
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The WHC values of oat and rice hulls (Table 2) observed in this work were
273
comparable with those reported for wheat and maize hulls, which presented WHC
274
values of 2.48 and 2.32 g/g (Zambrano, Meléndez, & Gallardo, 2001).
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The swelling values (Table 2) followed the same trend observed for WHC, with
276
high values observed for FRBPS and malt bagasse. According to Izydorczyk, Chornick,
277
Paulley, Edward and Dexter (2008), the swelling capacity is a function of the chemical
278
composition and the physical structure of the fiber matrix.
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Natural fibers also have the capacity to hold oil, and this property (the oil
280
holding capacity or OHC) represents the amount of oil retained by the fibers after
281
mixing, incubating with oil and centrifuging. In our work, the OHC was low for all
282
residues, and the higher values were observed in FRBPS and malt bagasse (Table 2),
283
followed by rice and oat hulls. According to Vázquez-Ovando et al. (2009), fibers with
284
low OHC are potential ingredients in fried products because they would provide a non-
285
greasy sensation.
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286
The emulsifying capacity is related to the ability of a substance to act as an agent
287
that facilitates the solubilization or dispersion of two immiscible liquids (Vázquez-
288
Ovando et al. 2009). Only malt bagasse and FRBPS presented emulsifying capacities,
289
with values of 59.83 and 8.28 mL oil/g solids, respectively (Table 2). These results
12
ACCEPTED MANUSCRIPT could be attributed to the high protein content of the malt bagasse (13.60) followed by
291
FRBPS (6.80). According to Fung et al. (2010), the higher protein contents in fibrous
292
residues positively affect its emulsifying activity. The good emulsification properties of
293
dietary fiber can improve the blood cholesterol level, which is mostly attributed to the
294
binding of biliary acids, thus limiting its absorption in the small intestine and leading to
295
the increased expenditure of cholesterol for biliary acid synthesis (Betancur-Ancona,
296
Peraza-Mercado, Moguel-Ordoñez, & Fuertes-Blanco, 2004).
297
3.6 Moisture sorption isotherms
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As shown in Figure 4, all samples exhibited similar sigmoidal isotherm patterns,
299
and the equilibrium moisture content of the samples increased with increasing RH, but
300
the increase in the equilibrium moisture content was more pronounced when the
301
samples were stored at RH ≥ 75%. The FRBPS exhibited a higher increase in the
302
equilibrium moisture content at RH ≥ 75%. Berkün, Balköse, Tihmnhoglu and
303
Altinkaya (2008) observed that cellulosic materials have low equilibrium moisture
304
contents under reduced RH, but an exponential increase could be observed at higher RH
305
values.
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The GAB parameters were calculated from our experimental water sorption
307
isotherm data and in all cases, the coefficient of determination (R2) was 0.99, indicating
308
that this model was consistent with the experimental data. Rice hulls exhibited the
309
lowest monolayer value (0.032 g/g), followed by malt bagasse (0.042 g/g) and oat hulls
310
(0.042 g/g), and FRBPS had the highest value (0.059 g/g), which is indicative of the
311
higher hygroscopicity of this residue in relation to the others. The monolayer value
312
indicates the maximum amount of water that can be adsorbed in a single layer per gram
AC C
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ACCEPTED MANUSCRIPT 313
of dry matter; this value is a measure of the number of sorbing sites in the water sample
314
(Strauss, Porcja, & Chen., 1991). The constants of the GAB model (C and K) were calculated as follows: malt
316
bagasse (C = 5.95 and K = 0.88), oat hulls (C = 26.51 and K = 0.89), rice hulls (C =
317
13.98 and K = 0.88) and FRBPS (C = 1.47 and K = 0.99). The C parameter is related to
318
the water adsorption energy of a layer (Strauss et al., 1991), and in our samples, the
319
lower value was observed for FRBPS, which is the more hydrophilic material.
320
Considering the K parameter, some authors reported that it is effectively independent of
321
the composition (Coupland, Shaw, Monahan, O'Riordan, & O'Sullivan, 2000).
322
4. Conclusions
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All residues presented high fiber contents, and the oat hulls exhibited the highest
324
total fiber content, followed by malt bagasse, rice hulls and FRBPS; thus, they can all
325
be employed as dietary fiber sources by the food industry in health and diet food
326
products such as fiber-rich powders, nutrition bars, breads and cookies. It is important
327
to highlight that the use rice hulls as fiber source for food products is conditioned to
328
silica removal.
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FRBPS showed the highest soluble fiber content, in addition to the higher water
330
holding capacity and swelling, making it a potential ingredient for use in baked products
331
requiring hydration, viscosity development and freshness conservation, or in meat
332
products requiring water retention.
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333
All the residues presented low oil-holding capacities and could be used in fried
334
products to provide a non-greasy sensation. Only malt bagasse and FRBPS presented
335
emulsifying capacities, making them possible emulsifiers for the food or pharmaceutical
336
industries. 14
ACCEPTED MANUSCRIPT 337
338
Acknowledgments
340
The authors wish to thank the Laboratory of Microscopy and Microanalysis (LMEM)
341
and the Laboratory of X-Ray Diffraction (LDRX) at the State University of Londrina
342
for the analyses, and also to CNPq-Brazil for financial support (No. 479768-2012).
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Kim, M., Yoon, S.H., Choi, E.; Gil, B. (2008). Comparison of the adsorbent
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FIGURE CAPTIONS
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Figure 1 - Micrographs obtained using MEV: malt bagasse (a), oat hull (b), rice hull (c)
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Figure 2 - FT-IR spectra of the agro-industrial residues.
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Figure 3 - X-ray diffractograms of the agro-industrial residues.
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Figure 4 – Water sorption isotherms of the agro-industrial residues: () malt bagasse,
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() oat hull, () rice hull and () FRBPS. The lines were derived from GAB model.
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Malt bagasse
Oat Hull
Rice Hull
Moisture (g/100g)
5.34 ± 0.12
5.12 ± 0.52
9.38 ± 0.88
Ash (g/100g)
2.78 ± 0.25
3.27 ± 0.37
14.74 ± 0.90
16.68 ± 0.05
Lipid (g/100g)
4.44 ± 0.14
1.94 ± 0.15
0.28 ± 0.01
0.86 ± 0.01
Protein (g/100g)
13.60 ± 0.90
1.85 ± 0.56
4.65 ± 0.35
6.80 ± 0.59
Carbohydrates (g/100g)
73.84 ± 1.87
90.02 ± 2.19
70.95 ± 0.82
66.08 ± 0.5
Total dietary fiber (g/100g)
63.84 ± 0.60
89.08 ± 2.58
56.26 ± 3.20
47.99 ± 0.02
1.08 ± 0.15
0.11 ± 0.01
4.20 ± 0.02
88.0 ± 5.18
56.15 ± 0.85
43.79 ± 0.01
35.47 ± 4.48
29.91 ± 0.55
2.01 ± 0.12
Insoluble dietary fiber (g/100g)
61.83 ± 0.52 12.29 ± 0.14
FRBPS
9.58 ± 0.06
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Table 1 – Chemical compositions of malt bagasse, oat hulls, rice hulls and fibrous residue from banana pseudo steam (FRBPS).
Hemicellulose (g/100g)
23.41 ± 2.30
25.5 ± 1.96
13.35 ± 2.88
14.42 ± 0.82
Lignin (g/100g)
26.13 ± 3.15
14.5 ± 0.99
7.24 ± 0.59
5.31 ± 0.12
Data are the means of triplicate determinations ± standard deviation.
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Table 2-Physical and functional properties of malt bagasse, oat hull, rice hull and fibrous residue from banana pseudo-steam (FRBPS). Oat Hull
Rice Hull
FRBPS
Apparent density (g/cm3)
0.48 ± 0.01a
0.41 ± 0.05b
0.45 ± 0.08a,b
0.46 ± 0.07a,b
Water holding capacity (g water/ g solid)
3.68 ± 0.08b
2.13 ± 0.11c
2.58 ± 0.28c
4.71 ± 0.31a
Swelling (mL water/ g solid)
4.53 ± 0.30a
3.56 ± 0.52b
3.27 ± 0.58b
4.98 ± 0.89a
Oil holding capacity (g oil/ g solid)
2.46 ± 0.27a
1.37 ± 0.06b
1.85 ± 0.15b
2.68 ± 0.08a
Emulsifying capacity (mL oil/g solid)
59.83 ± 0.28a
ND
ND
8.28 ± 0.58b
pH
5.73 ± 0.14a
5.58 ± 0.25a
5.68 ± 0.28a
5.52 ± 0.41a
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ACCEPTED MANUSCRIPT HIGHLIGHTS The physicochemical properties of four agro-industrial residues were determined. Malt bagasse, oat hulls, rice hulls, fibrous residue from banana pseudo-stems.
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In all the residues, insoluble fibers formed the major fraction of the fiber content.
Banana residue with highest soluble fiber content, water and oil-holding capacities.
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The residues had potential for use as a dietary fiber source in health food products.