Foods and Raw Materials, 2019, том 7, № 1
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The Ministry of Science and Higher Education of the Russian Federation
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FOODS AND
RAW MATERIALS
Vol. 7, no. 1, 2019
The journal covers promising research in the food industry and related branches. The Journal stimulates scientific communication between academia and manufacturers. We publish scientific papers of theoretical and empirical nature to promote new technologies and innovative ideas, bridge the gap between regional, federal and international scientific publications, and educate qualified specialists.
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Friedhelm Diel, Professor, Institut fur Umwelt und Gesundheit, Fulda, Deutschland;
Sergey A. Eremin, Dr. Sci. (Chem.), Professor, Lomonosov Moscow State University, Moscow, Russia;
Palanivel Ganesan, Ph.D., Associate Professor, College of Biomedical and Health Science, Konkuk University, Chungju, Republic of Korea;
Vladimir P. Kurchenko, Cand. Sci. (Biol.), Associate Professor, Belarusian State University, Minsk, Republic of Belarus;
Andrei B. Lisitsyn, Dr. Sci. (Eng.), Professor, Academician of the Russian Academy of Sciences, The Gorbatov’s All-Russian Meat Research Institute, Moscow, Russia;
Philippe Michaud, Ph.D., Professor, Universite Clermont Auvergne, Polytech Clermont Ferrand, Aubiere, France;
Lev A. Oganesyants, Dr. Sci. (Eng.), Professor, Academician of the Russian Academy of Sciences, Russian Research Institute for Wine, Beer and Soft Drink Industries, Moscow, Russia;
Viktor A. Panfilov, Dr. Sci. (Eng.), Professor, Academician of the Russian Academy of Sciences, Russian State Agrarian University-Moscow Timiruazev Agricultural Academy, Moscow, Russia;
Glaucia Maria Pastore, Ph.D., Professor, Food Science Department, Campinas University, Campinas, Brazil;
Andrey N. Petrov, Dr. Sci. (Eng.), Academician of the Russian Academy of Sciences, All-Russian Scientific Research Institute of Technology of Canning, Vidnoe, Russia;
Joaquin Pozo-Dengra, Ph.D., Research Associate, Clever Innovation Consulting, Biorizon Biotech, Almeria, Spain;
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Rudolf Valenta, MD, Professor for Allergology, Medical University of Vienna, Vienna, Austria.
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Foods and Raw Materials, 2019, vol. 7, no. 1
E-ISSN 2310-9599
ISSN 2308-4057
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CONTENTS
Olasunkanmi O. Arije, Babatunde A. Adewumi, Tajudeen M.A. Olayanju, and Babatunde O. Adetifa. A comparative study of physical properties of selected rice varieties in Nigeria ..................................4
Do Viet Phuong, Le Pham Tan Quoc, Pham Van Tan, and Le Nguyen
Doan Duy. Production of bioethanol from Robusta coffee pulp (Coffea robusta L.) in Vietnam ....................................... 10
Roghieh Talebi Habashi, Shahin Zomorodi, Alireza Talaie, and Sepideh
Kalateh Jari. Effects of chitosan coating enriched with thyme essential oil
and packaging methods on a postharvest quality of Persian walnut under cold storage ......................................................... 18
Igor A. Nikitin, Marina А. Nikitina, Nadezhda М. Allilueva, and Andrey
Yu. Krivosheev. Comprehensive assessment of fruit jelly with an improved carbohydrate profile based on unconventional plant raw materials ......26
Irfan Hamidioglu, Alvija Salaseviciene, and Gintare Zaborskiene. Effects
of natural herbal extracts on hemp (Cannabis Sativa L.) oil quality indicators.35
Ahmed M.S. Hussein and Gamil E. Ibrahim. Effects of various brans on quality and volatile compounds of bread ............................42
Nguyen Phung Tien, Sunisa Siripongvutikorn, and Worapong Usawakesmanee. Effects of Vietnamese tamarind fish sauce enriched with iron and zinc on green mussel quality ............................51
Galina A. Osipova, Svetlana Ya. Koryachkina, Vladimir P. Koryachkin, Tatiana V. Seregina, and Anna E. Zhugina. Effects of protein-containing additives on pasta quality and biological value........................60
Marina N. Shkolnikova, Evgeny D. Rozhnov, and Anastasia
A. Pryadikhina. Effects of Granucol activated carbons on sensory properties of sea-buckthorn (Hippophae rhamnoides L.) wines ...........67
Tatyana V. Voblikova, Saverio Mannino, Lyudmila I. Barybina, Vladimir
V. Sadovoy, Anatoly V. Permyakov, Vyacheslav V. Ivanov, and Magomed
A. Selimov. Immobilisation of bifidobacteria in biodegradable food-grade microparticles ....................................................... 74
Alexandra V. Zaushintsena, Irina S. Milentyeva, Olga O. Babich,
Svetlana Yu. Noskova, Tatyana F. Kiseleva, Dina G. Popova,
Igor A. Bakin, and Andrey A. Lukin. Quantitative and qualitative profile of biologically active substances extracted from purple echinacea (Echinacea
Purpurea L.) growing in the Kemerovo region: functional foods application......84
Sergey T. Antipov, Andrey I. Klyuchnikov, and Viktor A. Panfilov.
System modelling of non-stationary drying processes ...................93
Roman H. Kandrokov, Georgiy N. Pankratov, Elena P. Meleshkina,
Irina S. Vitol, and Danila G. Tulyakov. Effective technological scheme for processing triticale (Triticosecale L.) grain into graded flour . 107
Irina M. Chernukha, Leonid I. Kovalev, Natalia G. Mashentseva,
Marina A. Kovaleva, and Natalia L. Vostrikova. Detection of protein aggregation markers in raw meat and finished products ............... 118
ЙЕЯИ
Foods and Raw Materials, 2019, vol. 7, no. 1
E-ISSN 2310-9599
ISSN 2308-4057
Zaual A. Temerdashev, Alexan A. Khalafyan, Anastasiya A. Kaunova,
Aleksey G. Abakumov, Viktoriya O. Titarenko, and Vera
A. Akin’shina. Using neural networks to identify the regional and varietal
origin of Cabernet and Merlot dry red wines produced in Krasnodar Region...... 124
Islamiyat Folashade Bolarinwa, Mat Gani Hanis-Syazwani,
and Kharidah Muhammad. Optimisation of important processing
conditions for rice bran sourdough fermentation using
Lactobacillus plantarum......................................................................................... 131
Olayinka O. Ajani, Felicia T. Owoeye, Fisayo E. Owolabi, Deborah
K. Akinlabu, and Oluwatosin Y. Audu. Phytochemical screening
and nutraceutical potential of sandbox tree (Hura crepitans L.) seed oil.............. 143
Irina V. Buyanova, Igor V. Altukhov, Nikolay V. Tsuglenok,
Olga V. Krieger, and Egor V. Kashirskih. Pulsed infrared radiation
for drying raw materials of plant and animal origin .............................................. 151
Vladimir D. Kharitonov, Natalia E. Sherstneva, Dmitriy V. Kharitonov,
Date of publishing Elena A. Yurova, and Vladimir P. Kurchenko. Changes
June 10, 2019 in physico-chemical properties of milk under ultraviolet radiation ...................... 161
Circulation 500 ex. Anastasia A. Semenova, Andrey N. Ivankin, Tatyana G. Kuznetsova,
Open price. Andrei S. Dydykin, Viktoria V. Nasonova, and Elena V. Mileenkova.
Subscription index: Volatile aroma compounds in Moskovskaya cooked smoked sausage
for the unified ‘Russian Press’ formed in different types of casings....................................................................... 168
catalogue - 41672, Fahimeh Safaei, Khadijeh Abhari, Nader Karimian Khosroshahi,
for the ‘Informnauka’ Hedayat Hosseini, and Mojtaba Jafari. Optimisation of functional
catalogue - 40539 sausage formulation with konjac and inulin: using D-Optimal mixture
Kemerovo State University design ...................................................................................................................... 177
(KemSU), Georgiana G. Codina, Sorina Ropciuc, Andreea Voinea,
6 Krasnaya Str., and Adriana Dabija. Evaluation of rheological parameters
Kemerovo 650000, Russia of dough with ferrous lactate and ferrous gluconate.............................................. 185
Opinions of the authors Natalia L. Lisina. Environmental regulations in Russian food security.............. 193
of published materials Svetlana I. Artyukhova, Oksana V. Kozlova, and Tatiana Т. Tolstoguzova.
do not always coincide with Developing freeze-dried bioproducts for the Russian military in the Arctic ........202
the editorial staff’s viewpoint. Yousef Naserzadeh, Niloufar Mahmoudi, and Elena Pakina.
Authors are responsible Antipathogenic effects of emulsion and nanoemulsion of cinnamon
for the scientific content essential oil against Rhizopus rot and grey mold on strawberry fruits..................210
of their papers. Guide for Authors ................................................................................................. 217
© 2019, KemSU.
All rights reserved.
Foods and Raw Materials, 2019, vol. 7, no. 1
E-ISSN 2310-9599
ISSN 2308-4057
ЙЕЯИ
Research Article Open Access
DOI: http://doi.org/10.21603/2308-4057-2019-1-4-9
Available online at http:jfrm.ru
A comparative study of physical properties of selected rice varieties in Nigeria
Olasunkanmi O. Arye¹,* , Babatunde A. Adewumi¹, Tajudeen M.A. Olayanju², and Babatunde O. Adetifa³®
¹ Department of Agricultural and Bio-Resources Engineering, Federal University of Agriculture Abeokuta, Abeokuta, Ogun State, Nigeria
² Department of Agricultural Engineering, Landmark University, Omu Aran Kwara State, Nigeria
³ Department of Agricultural Engineering, Olabisi Onabanjo University, Ibogun Campus, Ogun State Nigeria
* e-mail: arijeolasunkanmiomobolaji@gmail.com
Received November 30, 2018; Accepted in revised form March 12, 2019; Published June 08, 2019
Abstract: Rice is now the main food for about 35 million people in Nigeria, and consumption is increasing faster than that of any other food crop in many countries in Africa. This study provided essential engineering data on the physical properties of selected varieties of local rice in Nigeria. Some selected physical properties of Igbemo, Ofa-da and Abakaliki rice varieties at harvest, market, and storage conditions were evaluated as a function of moisture content. The latter ranged from 12.38 to 25.69% (dry base). We also determined the physical properties of the rice samples, such as moisture content, linear dimensions, geometric mean diameter, arithmetic mean diameter, surface area, aspect ratio, sphericity, bulk density, and hundred kernel weights. A result of the linear dimensions for the major diameter was 8.4-10.3 mm, 6.4-6.55 mm, and 5.9-7.4 mm for harvested, marketed, and stored rice, respectively. The minor diameter ranged from 2.70 to 3.29 mm, 2.49 to 2.63 mm, and 2.56 to 2.74 mm, and the intermediate diameter of the rice varieties at harvest, market, and storage conditions was 1.92-2.29 mm, 1.90-2.02 mm, and 1.87-1.99 mm, respectively. Depending on the conditions and varieties, the bulk density, true density, and porosity, was observed to be between 0.59 to 0.90 g/cm³, 2.28 to 5.57 g/cm³ and 70.38 to 85.35% respectively.
Keywords: Rice, moisture content, surface area, aspect ratio, sphericity, bulk density
Please cite this article in press as:. Arije O.O., Adewumi B.A., Olayanju T.M.A., and Adetifa B.O. A comparative study of physical properties of selected rice varieties in Nigeria. Foods and Raw Materials, 2019, vol. 7, no. 1, pp. 4-9. DOI: http://doi. org/10.21603/2308-4057-2019-1-4-9.
INTRODUCTION
Rice is the most widely consumed cereal after maize and sorghum in many parts of Nigeria [1]. Rice grain could be prepared in various forms. Industrially, starch could be made from broken rice which is used in laundry, pharmaceutical, cosmetics, and textile industries. The straw can be used as livestock feed, for thatching of houses, and for making mats and hats. The husk can be used as fuel [2].
The physical properties of rice, which are important in the design and selection of storage structures and processing equipment, depend on grain moisture content. Therefore, the determination and consideration of properties such as bulk density, true density, angle of internal friction, and static coefficient of friction of grain at specific moisture content are essential [3]. Sabbah et al. studied the effect of moisture content on the physical
properties for three Egyptian paddy rice varieties [4]. They recorded the increase occurring in seed sphericity (S) due to the increase of moisture content. The principal axial dimensions of rye seeds are useful in selecting sieve separators and in calculating power during the rye milling process. Knowing the grain’s bulk density, true density and porosity can be useful in sizing grain hoppers and storage facilities: they can affect the rate of heat and mass transfer of moisture during the aeration and drying processes. A grain bed with low porosity will have greater resistance to water-vapour escape during the drying process, which may lead to the need for higher power to drive the aeration fans.
Cereal-grain kernel densities have been of interest in breakage susceptibility and hardness studies [5]. Researchers in [6] reported that various physical properties of green gram (Phaseulus aureus L.) were evaluated as
Copyright © 2019, Arije et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.
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Arije O.O. et al. Foods and Raw Materials, 2019, vol. 7, no. 1, pp. 4-9
a function of moisture content in the range of 8.39 to 33.40% d.b. The average length, width, thickness and the mass of thousand seeds were 4.21 mm, 3.17 mm, 3.08 mm, and 28.19 g, respectively at moisture content of 8.39% (d.b.). Also, the geometric mean diameter increased from 3.45 mm to 3.77 mm, whereas sphericity decreased from 0.840 to 0.815. They observed that with the increase of moisture content the bulk and true densities decreased from 807 to 708 kg/m³ and from 1,363 to 1,292 kg /m3, respectively. The corresponding bulk porosity increased from 40.77 to 45.16%. The static coefficient of friction is used to determine the angle at which chutes must be positioned to achieve consistent flow of materials through the chute.
The geometric properties such as size and shape are one of the most important physical properties considered during the separation and cleaning of agricultural grains. Theoretically, agricultural seeds are assumed to be spheres or ellipse because of their irregular shapes [3]. [7] determined the physical and mechanical properties of funnel seed as a function of moisture content. They found that there was a parabolic mathematical equation for sphericity, true density, and deformation on both seed length and width sections with changes of moisture content. The shape of the rice was found to be cylindrical with three perpendicular dimensions, namely length (L), width (W), and thickness (T).
Matouk et al. developed the mathematical relationships relating the changes of the properties with the seed moisture content. The seed principal dimensions, mass of 1,000 seeds and seed projection area generally increased with the increase of seed moisture content. On the contrary, both shape-index and coefficient of contact surface decreased [8]. Thousand grain mass of rice was utilized in determining the effective diameter which can be used in the theoretical estimation of seed volume [9].
Ghasemi et al. designed equipment for processing, sorting, sizing, and other post-harvesting equipment of agricultural products requires information about their physical properties [10]. In their study, various physical properties of rough rice cultivars were determined at a moisture content of 10% (wet basis). In the case of Sorkheh cultivar, the average thousand grain weight, equivalent diameter, surface area, volume, sphericity, aspect ratio, true density, bulk density and porosity were 21.64 g, 3.35 mm, 31.76 mm², 20.27 mm³, 39.71%, 0.28, 1,269.1 kg/m³, 544.34 kg/m³, and 56.98%, respectively. For Sazandegi cultivar, the corresponding values were 20.52 g, 3.4 mm, 32.58 mm², 21.06 mm³, 39.88%, 0.29, 1,193.38 kg/m³, 471.21 kg/m³, and 60.37%. For Sorkheh cultivar, the average static coefficient of friction varied from 0.2899 on glass to 0.4349 on plywood, while for Sazandegi cultivar those varied from 0.2186 to 0.4279 on the same surfaces. Angle of repose values for Sorkheh and Sazandegi cultivars were 37.66° and 35.83°, respectively. Linear model for describing the mass of rough rice grain was investigated. Mass was estimated with single variable of kernel length with a determination coefficient as 0.862 for Sorkheh cultivar whereas for Sazandegi cultivar was as 0.860. These properties considerably differ from one variety to another.
In Nigeria, there are different local varieties of rice, prominent of these varieties are, ‘Ofada’, ‘Igbe-mo’, and ‘Abakaliki’ rice. Ofada is a generic name for local rice produced and processed in the rice producing clusters. It originates from Ofada town and its axes including Owode and Wasimi, Ogun State South-West Nigeria. It has recently gained prominence and is fast gaining international attention. Cooked Ofada rice is usually eaten with a special kind of sauce prepared using pepper (Atarodo and Tatase), onion, locust beans, palm oil and assorted meat [11]. The growing of Igbemo rice is a primary activity among the farmers in Igbemo Ekiti, Ekiti State, where 70% are actively engaged in its production, [12]. Igbemo-Ekiti is acquiring national and international reputation for producing rice [13]. Abakaliki is known in agriculture, especially in rice production. It dates back to years before the 1960s.
Despite the popularity of these rice varieties in Nigeria, there is little or no detail of the properties of these varieties. This factor is one of the major issues affecting the development of suitable equipment/structure for the efficient storage and processing of these local rice varieties. This study, therefore, is aimed at investigating some major properties of Ofada, Igbemo, and Abakaliki rice varieties at different conditions. The study also seeks to find the effect of these conditions on the physical properties.
STUDY OBJECTS AND METHODS
1. Sample preparation. One kilogram each of the three rice grain varieties, namely Ofada, Igbemo, and Abakaliki were obtained from farmers from state of their origin, namely from Ogun, Ekiti and Ebonyi State, respectively. Each of the rice variety was divided into 10 equal parts and one part was randomly selected from each of the parts divided. The process was repeated again by mixing all the divided parts together and then separating them into another 10 equal parts. Another sample of grain was taken from each of the divided parts [14]. The process was continued until 500 g of rice were taken from each of the harvested, marketed, and stored rice varieties. The harvested grains were collected directly from the farm after harvest, while the stored and marketed rice varieties were collected from the farmer stores and market outlets respectively.
2. Determination of the physical properties of the rice varieties. We determined the following physical properties: moisture content, shape, size, 1,000 kernel weight, surface area, bulk density, true density, aspect ratio, and sphericity.
2.1 Moisture content. Oven method was adopted for moisture content determination as recommended by the ASAE standards*. The whole grains were placed on dishes for each of the varieties and conditions. After weighing the dishes and grains, dishes were placed in the oven at 105°C for 8 hours. After drying, the dishes were taken out and placed in desiccators. Then the samples were cooled and weighed with a balance. This procedure was performed in three replications for the
* ASAE standards (ASAE [15]).
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Arije O.O. et al. Foods and Raw Materials, 2019, vol. 7, no. 1, pp. 4-9
harvested, marketed, and stored rice samples. Weight differences before and after heating were used to determine moisture content, %:
... Wi - w.
Moisture content = ------x 100, (1)
w1 - w₀ ’ v ⁷
where W₀ is weight of moisture dish, kg; W1 is weight of dish + sample before drying, kg; and W2 is weight of dish + sample after drying, kg.
2.2 Size. 100 grains selected randomly from 500 g were used, and the basic dimensions of the seed (major, minor, and intermediate) were measured using a digital micrometer (Mitutoyo Digital Micrometer, Series) with accuracy 0.001 mm. The arithmetic and geometric average diameters of rice for each of the varieties and conditions were calculated using equations suggested by K. Shkelqim and M. Joachim [16]:
AMD
L+W+T
(2)
GMD = (LWT^,
(3)
where AMD is arithmetic mean diameter, mm; GMD is geometric mean diameter, mm; L is length, mm; W is width, mm; and T is thickness, mm.
2.3 Surface area. Surface area is an important property of grain. It helps the designer in estimating the hopper, processing chamber and the chute. The surface area was found by analogy with a sphere of some geometric mean diameter using the expression cited by Amin et al. [17]:
S = Dg, (4)
where S is surface area (mm²) and Dg stands for geometric mean diameter (mm) respectively.
2.4 Sphericity. The sphericity was calculated using the equation reported by [18]:
0 = ⁽™2* , (5)
where 0 is sphericity; L is the major diameter; W is the minor diameter; and T is the intermediate diameter.
2.5 True density, bulk density and porosity. The bulk density was determined by filling a container of known mass and volume to the brim with each variety of rice and condition for three replicate each. The net mass of rice was obtained by subtracting the mass of the container from the mass of the rice. To achieve uniformity in bulk density, the container was tapped 10 times in the same manner in all measurements to consolidate as reported by Aderinlewo et al. [18]. This experiment was carried out inthree replicates. The bulk density was then calculated using the equation:
Bulk density = ~ , (6)
V°
where Mₛ is the mass of sample in the container, g; Vₒ is the volume occupied, c m³.
The true density and porosity were calculated as follow: „ мд
True density = — vg, _ . True density—Bulk density
Porosity =------------------------True density
(7)
(8)
Table 1. Average moisture content of Igbemo, Ofada, and Abakaliki rice varieties under different conditions
Conditions Moisture content, %
Igbemo Ofada Abakaliki
Harvest 25.64 20.25 12.85
Storage 12.63 12.44 13.20
Market 12.72 13.41 13.40
2.6 1,000 kernel weight. 1,000 kernel weight was measured by counting 1,000 grains and weighted them on an electronic balance to an accuracy of 0.001 g. This experiment was carried out in three replicates.
2.7 Aspect ratio. Aspect ratio relates the width of a grain to its length which is indicative of its tendency towards being oblong in shape [19]. The aspect ratio Rₐ was estimated using the equation reported by Aderinle-wo et al. [18]:
Ra = 7 , (9)
where W is the minor diameter; L is the major diameter. This experiment was conducted for 100 replicates for the width and length.
RESULTS AND DISCUSSION
1. Moisture content. Table 1 shows the moisture content in the Igbemo, Ofada, and Abakaliki rice at different conditions. The moisture content in the marketed and stored samples was lesser (12.72 and 12.63%) compared with the harvested sample (25.64%). The moisture content of Ofada rice was 20.25%, 12.44%, and 13.41% at harvest, storage, and market conditions, respectively. The Abakaliki rice had the moisture content of 12.85%, 13.20%, and 13.40% for harvested, stored, and marketed samples, respectively.
A one can see in Table 1, the increase in moisture content of the Abakaliki rice occurred after harvest. The rice would have absorbed moisture after harvest unlike the Igbemo and Ofada rice that had a decrease in their moisture content. The Abakaliki rice was usually allowed to dry before harvesting in September with 85% humidity. This led to lower moisture content in the harvested sample when compared to the other rice varieties.
The results are in agreement with [20] that stated that the optimum moisture content of stored grains was 12-13%, while that for harvested grains ideally was 20-25% (wet basis). It also referred to rice as hygroscopic material, which explains why the Abakaliki rice had decreased moisture at harvest condition but increased moisture at market and storage conditions.
2. Geometric properties. The axial dimensions, arithmetic mean, geometric mean diameter, surface area, sphericity, and aspect ratio of the Igbemo, Abakaliki, and Ofada rice at different conditions are presented in Table 2.
2.1 Axial dimension. Table 2 summarizes axial properties of the Igbemo, Ofada and Abakaliki rice at harvest, storage, and market conditions.
Major diameter. We found that the major diameter of the Igbemo, Ofada, and Abakaliki rice was 10.35;
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Arije O.O. et al. Foods and Raw Materials, 2019, vol. 7, no. 1, pp. 4-9
Table 2. Geometric properties of Igbemo, Abakaliki, and Ofada rice varieties under different conditions (n = 100).
Variety Condi- Major Minor Inter- Arithmetic Geometric Surface area, Sphericity Aspect ratio
tion diameter, diameter, mediate mean mean mm2
mm mm diameter, diameter, diameter,
mm mm mm
Igbe- Harvest e10.35 ± 1.09 f2.90 ± 0.23 f2.29 ± 0.12 d5.18 ± 0.38 f4.09 ± 0.25 h52.66 ± 5.74 a0.40 ± 0.07 b0.23 ± 0.08
mo Storage b6.55 ± 0.34 b2.57 ± 0.16 a1.87 ± 0.14 b3.66 ± 0.14 a3.15 ± 0.13 c31.28 ± 2.59 e0.48 ± 0.03 f0.29 ± 0.03
Market b7.46 ± 0.54 c2.62 ± 0.15 b2.02 ± 0.12 e4.04 ± 0.23 c3.40 ± 0.17 f36.49 ± 3.58 c0.46 ± 0.02 d0.27 ± 0.02
Ofada Harvest c8.44 ± 0.48 g3.29 ± 0.13 e2.23 ± 0.15 g4.66 ± 0.20 e3.96 ± 0.16 i49.23 ± 3.99 d0.47 ± 0.02 c0.26 ± 0.02
Storage a5.93 ± 0.39 d2.74 ± 0.14 d1.99 ± 0.11 a3.55 ± 0.14 b3.18 ± 0.11 d31.84 ± 2.20 g0.54 ± 0.03 h0.34 ± 0.03
Market b6.42 ± 0.46+ c2.63 ± 0.17 c1.95 ± 0.12 b3.67 ± 0.16 b3.20 ± 0.12 e32.20 ± 2.51 f0.50 ± 0.03 g0.30 ± 0.03
Abaka- Harvest d8.72 ± 0.68 e2.70 ± 0.26 b1.92 ± 0.18 c4.45 ± 0.27 d3.55 ± 0.20 g39.80 ± 4.44 b0.41 ± 0.02 a0.22 ± 0.02
liki Storage b6.54 ± 0.41 b2.56 ± 0.42 a1.85 ± 0.06 b3.65 ± 0.21 a3.13 ± 0.16 b30.90 ± 3.57 e0.48 ± 0.03 e0.28 ± 0.02
Market b6.51 ± 0.44 a2.49 ± 0.14 b1.90 ± 0.11 b3.63 ± 0.17 a3.13 ± 0.12 a30.75 ± 2.29 e0.48 ± 0.02 f0.29 ± 0.03
Note: Parameters with the same superscripts in each column have no significant difference at 5% level of significance
8.44; and 8.73 mm respectively at harvest conditions; 6.55; 5.93; and 6.54 mm at storage condition; and 7.46; 6.42; and 6.51 mm at market conditions. Statistical analysis with t-test revealed that there was no significant difference in the major diameter between the three varieties at market condition and Abakaliki rice at storage condition.
Minor diameter. The minor diameter for the Igbe-mo, Ofada, and Abakaliki rice was 2.90; 3.29; and 2.70 mm respectively at harvest condition; 2.57; 2.74; and 2.56 mm at storage condition; and 2.62; 2.63; and 2.49 at market conditions. The result in Table 2 also showed that there was a significant difference between the minor diameter in all the varieties and conditions, except for the stored Igbemo and Ofada rice that had no significant difference (p < 0.05). This is also the case for the market condition of Igbemo and Abakaliki rice.
Intermediate diameter. According to Table 2, the intermediate diameter of the Igbemo, Ofada, and Abaka-liki rice was 2.29; 2.23; and 1.92 mm respectively in harvested samples; 1.87; 1.99; and 1.85 mm in stored samples; and 2.02; 1.95; and 1.90 mm were marketed rice. The t-test result revealed the rice varieties and conditions whose intermediate diameters are significant at 5% level of significance. At storage and market conditions, the intermediate diameters of Igbemo and Abakaliki rice were observed not to have any significant difference. Besides, the harvested and marketed Abaka-liki rice were also observed not to differ significantly in their intermediate diameter.
2.2 Arithmetic mean diameter. Table 2 also contains the arithmetic mean diameter of the Igbemo, Ofa-da, and Abakaliki rice under different conditions. The arithmetic mean diameters were 5.18; 4.66; and 4.45 mm, respectively, in the harvested samples; 3.66; 3.55; and 3.65 mm in the stored samples; and 4.04; 3.67 mm; and 3.63 mm in the marketed samples. Further analysis revealed that there was no significant difference in the arithmetic mean diameters among the stored Igbemo rice, the marketed Ofada rice, and the stored and marketed Abakaliki rice.
2.3 Geometric mean diameter. The geometric mean diameters under harvest condition were 4.09; 3.96; and 3.55 mm for the Igbemo, Ofada, and Abakaliki rice, re
spectively. These values for the stored samples were 3.15; 3.18; and 3.13 mm, and the marketed samples had he geometric mean diameters 3.40; 3.20; and 3.13 mm. Statistical analysis revealed that there was no significant difference between the geometric mean diameters of the stored Igbemo rice and the stored and marketed samples of the Abakaliki rice. In addition, there was no significant difference between the geometric mean diameters of Ofada rice at market and storage conditions. This result implies that a multi-variety screen can be used to clean, sort, or grade Igbemo and Abakaliki rice at storage conditions, Ofada rice at storage and market conditions, and Abakaliki rice at storage and market conditions. This will not be appropriate for the other samples because the discrepancy in their GMD will not allow the use of a screen with a particular diameter. The only possible solution is to have a screen with adjustable size or to replace the screens in the machines when the rice is to be changed.
2.4 Surface area. The surface area of the Igbe-mo, Ofada, and Abakaliki rice was 52.66; 49.23; and 39.80 mm² respectively in the harvested samples; 31.28; 31.84; and 30.90 mm² in the stored samples; and, and 36.49; 32.20; and 30.75 mm² in the marketed samples. The result also showed that there was no significant difference between the surface area of each condition across the rice varieties (p > 0.05). Without varying the air speed or the water pressure in a multi-variety or multi-condition aerodynamic or hydrodynamic applications of these rice varieties, the efficiency will be affected.
2.5 Sphericity. Acording to Table 2, sphericity of the Igbemo, Ofada, and Abakaliki rice was 0.40; 0.47; and 0.48, respectively, at harvest condition; 0.48; 0.54; and 0.48 at storage condition; and 0.46; 0.50; and 0.48 at market condition. In line with the result of GMD, statistical analysis revealed that there was no significant difference in sphericity between the stored Igbemo rice and the samples of the stored and marketed Abakaliki rice. It should be noted that the mean values of sphericity for all the three investigated varieties, which ranged between 0.40 and 0.54, decreased to 0.32-1.00 for most of agricultural products [3].
2.6 Aspect ratio. The aspect ratio of the Igbemo, Ofada, and Abakaliki rice was 0.23; 0.26; and 0.22 for
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Table 3. Gravimetric properties of the rice varieties under different conditions (n=3).
Variety Condition Bulk density, g/cm3 True density, g/cm3 Porosity, % 1,000 kernel weight, g
Igbemo Harvest a0.68 ± 0.01 a2.28 ± 0.02 a70.38 ± 0.49 a39.93 ± 0.06
Market b0.87 ± 0.01 b5.97 ± 0.31 b85.35 ± 0.77 b28.47 ± 0.64
Storage b0.90 ± 0.03 c4.50 ± 0.24 c80.06 ± 0.67 c23.73 ± 0.23
Ofada Harvest a0.61 ± 0.01 a2.84 ± 0.07 a78.62 ± 0.68 a31.57 ± 0.25
Market b0.89 ± 0.01 a4.54 ± 1.29 a79.30 ± 5.56 b23.50 ± 0.26
Storage b0.89 ± 0.01 a4.23 ± 0.24 a78.97 ± 1.26 c24.30 ± 0.20
Abakaliki Harvest a0.59 ± 0.01 a2.61 ± 0.25 a77.15 ± 2.20 a22.20 ± 0.10
Market b0.89 ± 0.00 b4.13 ± 0.29 a78.40 ± 1.49 a22.30 ± 0.20
Storage b0.89 ± 0.00 b4.36 ± 0.44 a79.44 ± 2.16 a22.40 ± 0.30
Note: Parameters with the same superscripts in each column have no significant difference at 5% level of significance
the harvested samples; 0.29; 0.34; and 0.28 for the stored samples; and 0.27; 0.30; and 0.29 for the marketed samples (Table 2). This result did not indicated any significant difference among all the varieties and conditions (p > 0.05), except the stored Igbemo rice and the marketed Abakaliki sample.
3. Gravimetric properties. Table 3 presents the bulk density, true density, porosity and 1,000 kernel weight of the three selected local varieties of rice in Nigeria at different conditions.
3.1 Bulk density. As one can see in Table 3, bulk density of the harvested samples was 0.68; 0.61; and 0.58 g/cm³ for Igbemo, Ofada, and Abakaliki rice, respectively. There was not observed any significant differences at 5% level of significance. The values for the stored and marketed samples were 0.90; 0.89; and 0.89 g/cm³ and 0.87; 0.89; and 0.89 g/cm³, respectively. The samples did not show a considerable difference in the bulk density values.
3.2 True density. True density values are also presented in Table 3. In the harvested samples of the Igbemo, Ofada, and Abakaliki rice, the true density was observed to be 2.28; 2.84; and 2.61 g/cm³, respectively. The values of true density were 5.67; 4.54; and 4.13 g/cm³ in the marketed rice and 4.50; 4.23; and 4.36 g/cm³ in the stored rice. The stored samples showed a significant difference unlike the other samples which did not differ considerably.
3.3 Porosity. According to Table 3, porosity of the Igbemo, Ofada, and Abakaliki rice samples was 70.38; 78.62; and 77.15%, respectively, at harvest condition. They did not show a significant difference at 5% level of significance. In the marketed samples, porosity values were 85.35; 79.30; and 78.40% for the Igbemo, Ofada, and Abakaliki rice, respectively. There was no significant difference between the marketed Ofada and Abaka-liki rice. In the stored samples, the porosity was 80.06; 78.97; and 79.44%. Similar to market conditions, no sig
nificant difference existed between the stored Ofada and Abakaliki rice.
3.4 1,000 kernel weight. This parameter was 39.93; 31.57; and 22.20 g for the stored Igbemo, Ofada, and Abakaliki rice, respectively. The samples did not demonstrate any significant difference at 5% level of significance. For the marketed rice, the 1,000 kernel weight was 28.47; 23.50; and 22.30 g for Igbemo, Ofada, and Abakaliki rice respectively. There was no significant difference existed between the Ofada and Igbemo rice. At storage conditions, the 1,000 kernel weight was 23.73; 24.30; and 22.40 g. Similar to market condition, no significant difference exist between the stored Ofada and Igbemo rice samples.
CONCLUSION
An investigation was carried out to determine and compare the physical properties of Igbemo, Abakaliki, and Ofada rice at harvest, storage, and market conditions. The values of the major diameter, minor diameter, intermediate diameter, arithmetic mean diameter, geometric mean diameter, surface area, sphericity, aspect ratio, bulk density, true density, porosity and 1,000 kernel weights were presented for each variety at the three conditions. Depending on the condition, the moisture content of the Igbemo, Ofada and Abakaliki rice varied from 12.63-25.64, 12.44-20.25 and 12.85-13.40% respectively. The rice condition (or moisture content) influenced some of the axial dimensions, other geometrical properties, and gravimetric properties, likewise the variety. The result presented can be of use in the design of multi-variety or multi-condition separators, pneumatic conveyors, bins, etc. for these three major local rice varieties in Nigeria.
CONFLICT OF INTEREST
The authors declare no conflict of interests.
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2. Onwueme I.C. and Sinha T.D. Field Crop Production in Tropical Africa. Netherlands, Wageningen: CTA Technical Publ., 1991. 480 pp.
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3. Mohsenin N. Physical properties of plant and animal materials. New York: Gorden and Breach Sci. Publ., 1986. 159-165 pp.
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8. Matouk A.M., Abd El-latiff S.M., and Tharwt A. Aerodynamic and mechanical properties of some oil crops. Journal of Agricultural Science Mansoura University, 2008, vol. 33, no. 6, pp. 4195-4211.
9. Ogunjimi L.A.O., Aviara N.A., and Aregbesola O.A. Some engineering properties of locust bean seed. Journal of Food Engineering, 2002, vol. 55, no. 2, pp. 95-99. DOI: https://doi.org/10.1016/S0260-8774(02)00021-3.
10. Ghasemi H., Mobli H., Jafari A., et al. Some physical properties of rough rice (Oryza Sativa L.) grain. Journal of Cereal Science, 2008, vol. 47, no. 3, pp. 496-501. DOI: https://doi.org/10.1016/j.jcs.2007.05.014.
11. CMDG 2006. Draft Report on Project Delicacy (Ofada Rice Attributes Evaluation Study) submitted to PrOpCom. Abuja: Research Group Limited Publ., 2006.
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13. Longtau S.R. Multi-Agency Partnership in West African Agriculture: A review and description of rice production system in Nigeria. Jos, Nigeria: Eco-system Development Organization Publ., 2000. 47pp.
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ORCID IDs
Olasunkanmi O. Arije https://orcid.org/0000-0003-1999-700X
Babatunde O. Adetifa О https://orcid.org/0000-0002-1952-2381
9
йгаи
Foods and Raw Materials, 2019, vol. 7, no. 1
E-ISSN 2310-9599
ISSN 2308-4057
Research Article DOI: http://doi.org/10.21603/2308-4057-2019-1-10-17
Open Access Available online at http:jfrm.ru
Production of bioethanol from
Robusta coffee pulp (Coffea robusta L.) in Vietnam
Do Viet Phuong¹,⁴,* ®, Le Pham Tan Quoc¹®, Pham Van Tan²®, and Le Nguyen Doan Duy³
¹ Industrial University of Ho Chi Minh City, Ho Chi Minh, Vietnam
² Sub-Institute of Agricultural Engineering and Post-Harvest Technology, Ho Chi Minh, Vietnam
³ Ho Chi Minh city University of Technology, Ho Chi Minh, Vietnam
⁴ Can Tho University, Can Tho, Vietnam
* e-mail: dovietphuong@iuh.edu.vn
Received December 23, 2018; Accepted in revised form February 02, 2019; Published June 08, 2019
Abstract: Coffee pulp is the first waste product obtained during the wet processing of coffee beans. Coffee pulp makes up nearly 40% of the total weight of the coffee cherry. Coffee pulp contains 25.88% of cellulose, 3.6% of hemicelluloses, and 20.07% of lignin. Coffee pulp is considered as an ideal substrate of lignocellulose biomass for microbial fermentation to produce such value-added products as ethanol. In this study, we used alkaline pre-treatment of the coffee pulp with NaOH (0.2 g/g biomass) in a microwave system at 120°C during 20 min. This method gave the best results: 71.25% of cellulose remained, and 46.11% of hemicellulose and 76.63% of lignin were removed. After that, the pre-treated biomass was hydrolyzed by Viscozyme Cassava C (enzyme loading was 19.27 FPU/g) at 50°C for 72 hours. The results showed that the highest reducing sugars and glucose concentration after hydrolysis were 38.21 g/l and 30.36 g/l, respectively. Then, the hydrolysis solution was fermented by S. cerevisiae (3.10⁸ cells/ml) at 30°C for 72 hours. The highest concentration of ethanol obtained was 11.28 g/l. The result illustrated that, available and nonedible as it is, coffee pulp could be a potential feedstock for bioethanol production in Vietnam.
Keywords: Bioethanol, coffee pulp, Coffea robusta, lignocellulose biomass, hydrolysis, pre-treatment
Please cite this article in press as: Phuong D.V., Quoc L.P.T., Tan P.V., and Duy L.N.D. Production of bioethanol from Robusta coffee pulp (Coffea robusta L.) in Vietnam. Foods and Raw Materials, 2019, vol. 7, no. 1, pp. 10-17. DOI: http://doi. org/10.21603/2308-4057-2019-1-10-17.
INTRODUCTION
Vietnam is currently the world’s largest exporter of Robusta coffee, as well as the world’s second-largest exporter of coffee beans after Brazil. In 2016, the total production of coffee beans in Vietnam was about 1,636,500 tons. About 450,000 tons of dried coffee pulp is produced here annually. Coffee pulp is mainly used as a fuel for fruit/coffee beans drying or as a compost and fertilizer on coffee plantations, which causes serious environmental pollution.
All over the world, there have been many researches on the use of coffee pulp. For instance, feeding and digestibility studies were conducted in concrete ponds to evaluate the use of coffee (Coffea robusta) pulp as a partial and total replacement for yellow maize in low-cost diets for catfish [1]. The research evaluated the effect of
adding coffee husks to animal feed as a substitute for a mixture of corn grain, husks, and cobs. In addition, there have been many studies on how coffee solid wastes can be used. For example, Flammulina velutipes mushroom can be cultivated on coffee spent-ground and coffee husk [2]. Coffee husk can be used as a carbon source for citric acid production in a solid-state fermentation system [3] or for wastewater treatment [4]. However, researchers are more concerned with producing ethanol from coffee pulp using chemical methods [5]. The problem is that these methods remain limited and eco-un-friendly as coffee pulp hydrolysis requires acid and alkali, which means expensive sophisticated equipment. In addition, coffee pulp has a high concentration of carbohydrates and, thus, can be used as a potential raw material for bioethanol production [6]. Besides, recent
Copyright © 2019, Phuong et al. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material for any purpose, even commercially, provided the original work is properly cited and states its license.
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studies indicate that residue utilization has an excellent potential for bioethanol production, given that it does not involve costs related to raw material growth. Furthermore, it is estimated that ethanol production from agricultural residues could be sixteen times higher than the current production [7].
Vietnam possesses large quantities of coffee pulp that need utilization. This is also in line with the current global trends to seek alternative renewable energy sources to replace traditional fossil fuels and solve the problem of environmental pollution and climate change. Thus, the present study offers a good solution for these problems.
STUDY OBJECTS AND METHODS
Materials. Robusta coffee pulp was collected at Pong Drang commune, Krong Buk district, Dak Lak province, Vietnam. The berries were of bright-red colour, ripe, neither crushed nor moldy. After harvesting, the pulp was removed and dried at 65°C until the moisture content was 5-8%. After that, the pulp was crushed and sieved; the diameter of the powder was 0.5-1 mm. Finally, the powder was packaged in plastic bags and stored under ambient conditions.
Analytical methods. The moisture content was analyzed according to AOAC method 934.06.
The total ash content was determined by using AOAC method 942.05.
The analysis of total fat was performed by using AOAC method 948.16.
The quantitative analysis of caffeine was performed by using a Genesys UV-Vis Spectrometer (Genesis 10S) [8].
The total polyphenol content in the extracts was determined according to the Folin-Ciocalteu colorimetric method with some modifications [9].
The micro-Lowry method [10] was used to determine the protein content.
The calcicum pectate method was applied to determine the pectin content [11].
Phenol sulphuric acid was used to estimate the total reducing sugars (TRS) using maltose as standard [12].
The reducing sugars (RS) in the hydrolysate were measured by using the DNS method adapted from Miller [13].
A Clever Check blood glucose meter (model TD 4230, Germany) [14] was used to determine the monomeric sugars (glucose).
The cellulose, hemicellulose, and lignin contents were determined by the crude fibre analysis [15].
The ethanol concentration was determined with the help of a Genesis UV-Vis Spectrometer (Genesis 10S) [16].
Pre-treatment method. 50 g of the dried coffee pulp was treated by 500 ml of sodium hydroxide solution (0.2 g NaOH/g biomass). After that, the mixture was pre-treated at 195W and 120°C for 20 min in the microwave system. The pre-treated biomass was recovered by filtration and washed with 1,000 mL of hot water (70°C) to remove the remaining lignin and alkaline
substances according to the method offered by Chen et al. (2007) [17]. Then the pre-treated residue was pressed to remove excess water and dried at 65°C until moisture content stabilized between 5% and 8%. The concentrations of cellulose, hemicellulose, and lignin remaining in the pre-treated material were calculated by the following equation:
Rx = Aₚ/A x 100, (1)
where Rₓ is the percentage of cellulose (RC), hemicellulose (RH), or lignin (RL) remaining in the pre-treated pulp, %; Aᵢ is the amount of the constituent in the initial dried coffee pulp, g; and Aₚ is the amount of the constituent after the pre-treatment of the dried coffee pulp, g.
Hydrolysis method (enzyme loading). 5 mL of Vis-cozyme Cassava C preparation, 150 ml of 0.05 mol/l citrate buffer (pH 4.8), and 15 g (equivalent to 10% of dry material per 100 ml of solution, w/v) of pressed pre-treated dried pulp were mixed in a flask. The containers were incubated in a thermal shaker at 50°C and 150 rpm for 72 hours. After that, the material from each treatment was centrifuged at 2,500 rpm for 10 min [19]. The supernatant was removed to determine RSₛ, total reducing sugars (TRSₛ), and glucose concentrations. The control samples were not treated by heat and alkaline. The yield from the enzymatic hydrolysis process, %, was calculated using the following equation. Only the cellulose present in the pre-treated coffee pulp was taken into account:
YEH = 0.9(Gₑ-Gw)/Cₚ x 100, (2)
where Gₑ is the glucose concentration at the end of the enzymatic hydrolysis, g glucose/l [18]; Gw is the glucose concentration without enzyme treatment, g glucose/l; and Cₚ is the cellulose concentration in the pre-treated material, g cellulose/l.
Fermentation method. After the hydrolysis, the solution was divided into equal portions of 250 ml each and put in an Erlenmeyer flask. Then (NH₄)₂SO₄ (1 g/l), K₂HPO₄ (0.1 g/l) and MgSO₄.7H₂O (0.2 g/l) were added into the solution. The medium was autoclaved at 121°C for 20 min and cooled at room temperature. Fermentation was carried out in an Erlenmeyer flask with 3.10⁸ cells/ml of S. cereviciae at 30°C, 120 rpm, and pH of 5 [20]. The yeast was collected from the Laboratory of the Food Technology Department at the Industrial University of Ho Chi Minh City. Ethanol concentration was analyzed by using a Genesis UV-Vis Spectrometer at different fermentation times:
Yₚ/ₛ = EC(Gb-Gₑ), (3)
where EC is ethanol concentration at the end of fermentation, g/l; Gb is glucose concentration at the beginning of the fermentation, g/l; Gₑ is glucose concentration at the end of the fermentation, g/l. The percentage of the theoretical ethanol yield was calculated as follows:
Yₑₜ = Yₚ/ₛ/0.51 x 100, (4)
where 0.51 is the maximum theoretical ethanol yield when converting 1g glucose to ethanol.
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Table 1. Chemical composition of coffee pulp, g/100g dry basis
Components, Present a b c d e
% study
Moisture 73.85 - - 77.9 82.0 15.0
content
Total sugars 9.18 9.70 - - 28.7
Reducing 8.34 9.63 12.40 - 24.25
sugars
Starch 10.20 - - - -
Pectin 4.37 11.37 6.50 -
Protein 9.52 10.47 10.1 - 7.0
Cellulose 25.88 20.7 17.7 23.0 20.6 16.0
Hemicellu- 3.60 3.60 2.30 20.0 17.2 11.0
lose
Lignin 20.07 14.30 17.5 22.0 15.5 9.0
Lipids 1.22 1.20 - - 0.3
Ash 6.29 7.33 8.30 15.4 7.9 5.4
Caffeine 0.78 - 1.3 - 1.0
Polyphenols 8.69 - 1.8-8.56 - 5.0
Note: a[22]; b[23]; c[24]; d [18]; e [25]
Statistical analysis. All treatments in this study were conducted in triplicate, and 95% of confidence level was applied for the data analysis. ANOVA was used by the one-way analysis of variance, and Statgraphics software (Centurion XV) was used to determine the statistical differences between the treatments.
RESULTS AND DISCUSSION
Characteristics of the solid fraction of coffee pulp. Table 1 shows that the cellulose and lignin content in the coffee pulp (Robusta coffea) was 25.88% and 20.07%, respectively. These results were higher than those received by Bonilla-Hermosa et al., Elias, and Menezes et al. However, the hemicellulose content was similar with the result obtained by Elias (1979) [18, 22, 23]. These differences can be explained by the fact that the previous studies used Arabica, whereas the present research was based on Robusta coffee.
Coffee husks and pulp are comprised of the outer skin and the attached residual pulp, and these solid residues are obtained after de-hulling of the coffee cherries during dry or wet processing, respectively [4]. The coffee pulp only included outer skin and fruit pulp. The sticky coffee husk included skin, fruit pulp, and, perhaps, an insignificant amount of pectin and parchment. Therefore, the total sugars (28.7%) and the reducing sugar content (24.25%) of the sticky coffee husk were higher than those of the coffee pulp (9.7 and 9.63%) [22, 25].
According to Palonen and Hetti [26], lignocellulose biomass is a major structural component of woody plants and other plants, such as grass, rice, and maize. The major constituents of lignocellulose are cellulose, hemicellulose, and lignin. The crude fibre in coffee pulp included: 25.88% of cellulose, 3.6% of hemicelluloses, and 20.07% of lignin. The content of cellulose in the coffee pulp was similar to that in rice husk (24.3%) [27] but lower than in wheat straw (38.2%) [28] and bagasse (38%) [29]. However, there was also a similar proportion between the cellulose content in the coffee pulp (equivalent to
Table 2. Percentages of Rₓ remaining in pre-treated coffee pulp
Lignocellu- Before pre-treat- After pre-treat- Percentages
losic biomass ment, g/100g ment, g/100g of R
dry basis dry basis x
Cellulose, % 25.88b 18.44a 71.25
Hemicellu- 3.60b 1.94a 53.89
lose, %
Lignin, % 20.07b 4.69a 23.37
Note: aand b in the same row denote a significant difference (p < 5%)
52.23%, g cellulose/100g crude fibre) and the typical proportion of lignocellulose (40-60%) [30]. Therefore, coffee pulp is also considered a source of lignocellulose biomass, which can be used in the production of bioethanol (second generation ethanol production).
Alkali pretreatment. According to Sun and Cheng [31], the pre-treatment process has a number of advantages: it reduces cellulose crystallinity, removes lignin and hemicellulose, and increases the porosity of the materials. Pre-treatment should meet a number of requirements:
- it cannot produce by-products that are inhibitory to the subsequent hydrolysis and fermentation processes;
- it cannot result in a loss or degradation of carbohydrate;
- it should improve the formation of sugars or the ability to subsequently form sugars by enzymatic hydrolysis; and
- it has to be cost-effective. Currently, pre-treatment of lignocellulosic materials can be chemical, physical, physico-chemical, and biological. As for materials that are rich in lignin, alkaline pre-treatment method seems to be the most efficient one.
The efficiency of pre-treatment depends entirely on the type of alkalis, concentration, time, and temperature of the pre-treatment process. To increase the efficiency of lignin removal, the above factors need to be increased. However, the increase in these factors means more cellulose loss. In this study, the coffee pulps were pre-treated with 0.2 g NaOH/g biomass at 120°C for 20 min in a microwave system. The results showed th at 71.25% of cellulose was retained, while 46.11% of hemicellulose and 76.63% of lignin were removed. Although the result was not high, the conversion efficiency could not be regarded as low.
It was necessary to go through the next stages (hydrolysis and fermentation) to evaluate the ethanol conversion efficiency. According to [18], when coffee pulp was pre-treated with 4% NaOH (w/v) at 121°C for 25 min, the commercial efficiency removal of lignin and hemicellulose was 78,41% and 55.85%, respectively, while 69.18% of cellulose was obtained. Wang and Cheng [32] pre-treated coastal Bermuda grass with sodium hydroxide (1% NaOH) and calcium hydroxide (0.1 g Ca(OH)₂) (in g/dry biomass) at 121°C during 30 min and obtained about 75% and less than 20% of lignin removal, respectively. In addition, the results of Kim and Holtzapple [33] showed that the optimal conditions of pre-treatment for corn stover were 0.5 g Ca(OH)₂/g
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