Open access peer-reviewed chapter

Application and Conversion of Soybean Hulls

Written By

Hua-Min Liu and Hao-Yang Li

Reviewed: 07 November 2016 Published: 03 May 2017

DOI: 10.5772/66744

From the Edited Volume

Soybean - The Basis of Yield, Biomass and Productivity

Edited by Minobu Kasai

Chapter metrics overview

2,829 Chapter Downloads

View Full Metrics


Soybean is one of the most cultivated crops in the world, with a global production of approximately 240 million tons, generating about 18–20 million tons of hulls, the major by-product of soy industry. The chemical composition of soybean hulls depends on the efficiency of the dehulling process, and so, the soybean hulls may contain variable amounts of cellulose (29–51%), hemicelluloses (10–25%), lignin (1–4%), pectins (4–8%), proteins (11–15%), and minor extractives. This chapter provides a review on the composition and structure of soybean hulls, especially in regard to the application and conversion of the compositions. Current applications of soybean hulls are utilizations to animal feed, treatment of wastewater, dietary fiber, and herbal medicine. The conversion of soybean hulls is concerned with ethanol production, bio-oil, polysaccharides, microfibrils, peroxidase, and oligopeptides. On the basis of the relevant findings, we recommend the use of soybean hulls as important source on environment, energy, animal breeding, materials, chemicals, medicine, and food.


  • soybean hulls
  • application
  • conversion
  • dietary fiber
  • polysaccharides

1. Introduction

Soybeans are one of the most worthy crops in the world because of their high protein and oil content, which provides a wide variety of uses [1]. Soybean protein has been used in livestock and aquaculture feeds and is highly digestible, along with many human foods [24]. Soybean oil is used as a food and feed ingredient as well as in biodiesel production and cosmetics [5, 6]. Soybean hulls, accounting for a substantial fraction (7–8%) of the total mass of soybean, are the largest amount of by-products in the soybean process industry. In contrast to the oil and proteins, there is a fairly common perception that hull is a “waste” product of soybean processing [7]. It is predicted that the total world soybean production will be 371.3 million tons by 2030 and there will be 29.7–37.1 million tons of soybean hulls available [8].

The chemical composition of soybean hulls depends on the efficiency of the dehulling process, and so, the soybean hulls may contain variable amounts of cellulose (29–51%), hemicelluloses (10–25%), lignin (1–4%), pectins (4–8%), proteins (11–15%), and minor extractives [911]. Therefore, soybean hulls are primarily lignocellulose material. However, unlike many other lignocellulosic material such as hardwood or switchgrass, soybean hulls are easy degradable [9, 11]. Chemically, cellulose is a linear polymer of 250 to over 10,000 glucose units linked by β-1,4 glycosidic bonds. Pectin is a polysaccharide consisting of a backbone of α-1,4 linked galacturonic acid residues usually up to 100 residues in length. The galacturonic acid residues are commonly methylesterified or acetylated, and the backbone may include substitutions of rhamnose and/or branching chains consisting of arabinose and galactose [12]. Hemicellulose is a group of wall polysaccharide that is characterized by being neither cellulose nor pectin and by having β-1,4-linked backbone of glucose, mannose, or xylose [13]. The backbone is frequently decorated with a variety of sugar side chains or acetyl ester groups [14]. The average degree of polymerization of hemicellulose is in the range of 80–200. Lignin is a heterogeneous biopolymer in lignocellulose formed by radical-mediated oxidative coupling of phenyl-propane unit linked together through various types of ether and carbon-carbon bonds [15].

The low lignin content in soybean hulls makes the residues have a very wide variety of application (Figure 1). Due to this biomass composition, soybean hulls are widely used as animal feed [16]. In addition, soybean hull is lignocellulosic material containing a small proportion of lignin, as compared with other agro-residues, and has a good potential for saccharification, because lignin is a major hindrance for enzymatic hydrolysis of biomass [17]. Soybean hulls also contain a large amount of dietary fibers (DFs), and have been used as a batter ingredient to decrease the fat contents in cakes and cookies [18]. Moreover, soybean hulls have also been identified as a rich source of peroxidases and as an agro-industrial residue; they are a low-cost alternative for resulting in biocatalyst production [19]. This review summarizes the present knowledge on the composition, application, and conversion of soybean hulls.

Figure 1.

Application and conversion of soybean hulls.


2. Compositions and structure of soybean hulls

2.1. Cellulose

Cellulose derived most frequently from wood is widely used in a range of applications including composites, papermaking, food additives, textile, and pharmaceutical industries [20]. More importantly, cellulose is also useful for bio-ethanol production after enzymatic hydrolysis. Cellulose is a linear polymer of anhydroglucose unit linked at the one and four carbon atoms by a β-glycoside bond [21]. This is confirmed by the presence of three hydroxyl groups with various acidity/reactivity, secondary OH at the C-2, secondary OH at the C-3, and primary OH at the C-6 position, and accordingly, by the formation of different strong intermolecular hydrogen bonds [22]. Based on carbon nuclear magnetic resonance (13C NMR) spectra and X-ray diffraction patterns, four major polymorphs of cellulose have been reported and named cellulose I, II, III, and IV [23]. Cellulose I is the most abundant native crystalline form and can be converted into the other polymorphs through a variety of treatments. Cellulose I consists of two phases, Iα and Iβ. Cellulose Iα has one-chain triclinic structure and cellulose Iβ has two-chain monoclinic structure and they differ in hydrogen bonding [24]. The chemical, physical, and biological properties of cellulose depend on its shape properties such as its ease of deformability and its intrinsic form [23]. The noncrystalline cellulose is also important because of higher chemical reactivity of noncrystalline (or amorphous) cellulose.

2.2. Hemicellulose

Hemicellulose, next to cellulose, refers to a large group of complex polysaccharide in cell wall of plants [25]. Unlike cellulose, it is a low-molecular-weight polysaccharide, associated in plant cell wall with lignin and cellulose. It forms covalent bonds (mainly α-benzyl ether linkages) with lignin, hydrogen bonds with cellulose, and ester linkages with hydroxycinnamic acids and acetyl units, which restrict the liberation of hemicellulosic polymers from the cell wall matrix [26]. Large variations in hemicellulose content and chemical structure can occur between various lignocellulosic materials. Many methods have been used to isolate hemicellulosic polymers from plant materials, which include extraction with alkaline, alkali, organic solvent, or twin-screw extrusion and ultrasonication treatments, as well as steam or microwave treatment [26]. For higher lignin content materials, they must be delignified and/or pretreated in some way prior to extraction of hemicelluloses, such as pretreatment by sodium chlorite in acetic acid solution. For soybean hulls, they do not require delignification prior to isolation of hemicelluloses, as compared with other lignocellulosic biomass, because of low content of lignin. The major hemicelluloses in soybean hulls are composed of α-L-arabinofuranosyl, L-arabino-4-O-methyl-D-glucurono-D-xylan, 4-O-methyl-glucuronic acid and α-D-galactose units attached with substituted sugars [27, 28]. These hemicelluloses have the potential to be integrated in a wide variety of applications, including thickeners, film-former substances, emulsifiers, binders, and stabilizers in the food, cosmetic, and pharmaceutical industries [29]. In addition, they can be easily hydrolyzed into hexose (mannose, glucose, and galactose) and pentose (arabinose and xylose), and can be transformed into fuel ethanol and other value-added chemicals, including furfural, 5-hydroxymethylfurfural (HMF), xylitol, and levulinic acid (Figure 2) [30].

Figure 2.

The potential products from hemicelluloses [13].

2.3. Pectin

Pectin is a complex polysaccharide consisting of D-galacturonic acid linked by α-1,4 glycosidic linkages [31]. The molecular weight of pectin varies from 50,000 to 150,000 Da depending on the source materials and extraction procedure. Pectin is a highly valuable functional food ingredient and is very important in creating or modifying the texture of jellies, jams, and confectionery, and in low-fat dairy products. Soybean hulls were potentially inexpensive commercial sources of pectin. Soybean hull pectin (SHP) mainly contains galactose, xylose, galacturonic acid, arabinose, glucose, and rhamnose. The chemical composition of the extracted soybean hull pectin has been comparatively investigated with that of commercially soybean hull pectin (CSHP) and citrus pectin (CP) by Yamaguchi et al. (Table 1) [32]. The results showed that SHP had a molecular weight similar to the CSHP and CP. Glucose content in SHP was higher as compared with CSHP and CP, but other sugar contents were similar between SHP and CSHP. The SHP had a similar galacturonan structure to that of CP, but SHP contains more arabinose and glucose, less rhamnose and fucose, and more xylose as compared with CP. The SHP extracted by Yamaguchi et al. [32] showed the degree of esterification of 18.1%, belonging to low methoxyl pectin.

Galacturonate, % Dry material basis33.018.585.8
(% Esterified galacturonate, % Dry material basis)18.1073.7
Neutral sugar composition, % Dry material basis
Rhamnose + Fucose8.08.025.1

Table 1.

Composition of soybean hull pectin (SHP), commercially available soluble soybean hulls pectin (CSHP), and citrus pectin (CP) [32].

2.4. Lignin

Lignin is a three-dimensional amorphous biopolymer formed by three major monolignols, that is, p-coumaryl alcohol (H), coniferyl alcohol (G), and sinapyl alcohol (S) of various ratios, linked together by different types of ether (β-O-4’) and carbon-carbon (β’-β’ and β’-5’) linkages (Figure 3). Besides, lignin is covalently linked to hemicellulosic polysaccharides, forming a lignin-hemicellulose network made up of phenyl-glycoside, benzyl-ether, and benzyl-ester bonds [34]. Despite the extensive investigations of lignin, the complex and irregular structure of lignin has not been completely understood up to now. Lignin is considered as the most abundant sources of aromatic compound in nature and can be utilized for adhesives or chemical reagents to replace those derived from oil. For the lignin of soybean hulls, it is not usually utilized as a major value product, due to its lower content. However, the soybean hull is a good resource for lipid production due to its low lignin content and it has been proven in the bioconversion process that soybean hulls can be utilized without any pretreatment [9].

Figure 3.

Main lignin structures present in bamboo lignin: (A) β-O-4 alkyl-aryl ethers; (A′) β-O-4 alkyl-aryl ethers with acylated γ-OH with p-coumaric acid; (A″) Cα-oxidized β-O-4 structures; (B) resinols; (B′) tetrahydrofuran; (C) phenylcoumarans; (D) spirodienones; (E) α, β-diaryl ethers; (T) a likely incorporation of tricin into the lignin polymer through a G-type β-O-4 linkage; (I) p-hydroxycinnamyl alcohol end groups; (I′) p-hydroxycinnamyl alcohol end groups acylated at the γ-OH; (J) cinnamyl aldehyde end groups; (p-CE) p-coumarates; (H) p-hydroxyphenyl units; (G) guaiacyl units; (S) syringyl units. (S′) oxidized syringyl units bearing a carbonyl at Cα [33].

2.5. Protein

The chemical composition of soybean hulls depends on the efficiency of the dehulling process. If soybean meal with high protein content is required, the dehulling process is more intense in order to avoid contamination of the meal with pieces of hulls [10]. In general, the soybean hulls may contain 11–15% of proteins. Soybean proteins are commercially and extensively used in food products due to their functional properties, low cost, and high nutritional value. Soybean proteins are composed almost exclusively of two globular protein fractions called 11S (glycinin) and 7S (β-conglycinin) [35].


3. Application of soybean hulls

3.1. Animal feed

The by-products of agro-industrial may become an economical alternative to corn grain in ruminant diets, especially when the price of corn is high due to the increase of demand from the ethanol industry [36]. Soybean hulls are by-product from the soybean-processing industry, where the soybean is de-hulled leaving a highly digestible, fibrous feed [37]. Due to their compositions, the biomass is widely used as animal feed. Many investigations have demonstrated that there are advantages of using soybean hulls as an energy source for ruminants in replacement of corn, as long as they are supplied together with effective fiber sources to reduce the rate of passage and enable ruminant fermentation [3840]. For example, the excessive use of starch in equine diets can lead to fermentation of the ingested material by amylolytic bacteria in the large intestine resulting in an increase in lactic acid production and increased production of short-chain fatty acids, which can cause intestinal disorders such as laminitis or colic [41]. However, studies on the inclusion of soybean hulls in equine diets have shown promising a decrease in starch level without compromising the caloric density of the feed [42]. It was suggested that diets with up to 28% soybean hulls can be used as equine feed without negatively affecting digestibility, the selected microbiota or short-chain fatty acids concentrations, and physicochemical characteristics in the feces [38]. Soybean hulls can also be a resource in maintaining sheep meat production without compromising product quality. Investigation has been carried out for the improvement of sheep diets by soybean hulls, which leads to the improvement of the fatty acid composition of meat and the production of meat with adequate levels of fat which reduce the levels of saturated fatty acids [43]. The investigation found that the inclusion of soybean hulls in the sheep diet increased the total lipid content, conjugated linoleic acid, and omega 3 fatty acids. The increase of unsaturated and polyunsaturated fatty acids ensured greater consumer satisfaction, since the population was increasingly attentive to health. Soybean hulls can also be used replacing ground corn in diets of goats in the early lactation, because they improve the digestibility of the diet and nutrients, do not change the physical and chemical quality or productive performance of the milk, and increase the content of omega 3 fatty acids in the milk [44]. Soybean hulls can replace corn grain to supply about 30% of the dry matter in high-grain content diets without negatively affecting either the digestion of nutrients or fermentation in gastrointestinal tract or the performance of dairy cows [45]. Vinay Kumar [46] investigated the effect of soybean hulls on the physicochemical characteristics, color, texture, and storage stability of chicken meat nuggets. The results showed that the addition of soybean hulls to chicken nuggets improved nutritional value, sustained the desired cooking yield and emulsion stability, and helped in improving instrumental textural and color values. In addition, the inclusion of soybean hulls in the chicken diet increased the storage times of meat.

3.2. Treatment of wastewater

Fresh water is a limited and essential natural resource for the development of a series of living organisms in aquatic environments as well as for humans, all of which require its preservation [46]. The quality of the water is being negatively affected by the world’s population growth along with accelerated industrial development that generally involves processes requiring a huge consumption of water and the release of wastewaters back into water bodies [46]. Current methods used to treat wastewater include chemical precipitation, oxidation and chemical reduction, filtration, electrochemical treatment, ion exchange, reverse osmosis, evaporation, and adsorption [47, 48]. Among these techniques, adsorption is an economic and efficient method, based on flexible and simple operating conceptions and the use of regenerative adsorbents, for the removal of inorganic or organic pollutants with high efficiency in many cases [48]. Biosorption is the binding of radionuclides and metal ions onto the cellular structure of biological materials, which contain their functional groups and ligands [49]. Biosorbent materials that are lignocellulosic, containing cellulose, hemicelluloses, and lignin, have high adsorption properties due to the ion exchange capabilities [50]. Biosorbent materials have some advantages. For example, they can be regenerated for reuse, can recover the biosorbent material, do not require much energy input, and do not produce a toxic sludge [49, 51]. Much attention has been given to the use of soybean hulls in the remediation of heavy metals [46, 49, 52]. Soybean hulls without the soluble dietary fiber (SDF) present good metal-binding property and can be used as novel biosorbent [53]. The preparation of soybean hulls including pretreatment, drying, modification, activation, and so on was presented to make the preparation process feasible and economical [46, 54, 55]. Generally, adsorption of inorganic or organic pollutants in wastewater by soybean hulls has been limited and the hull modification is desirable to enhance adsorption especially of metal ions. Aparecido N. Módenes [46] investigated the absorption characteristic of the soybean hulls absorbent by various modification methods for the removal of Cd2+ and Pb2+. The results showed that an increase in the sorption capacity of Pb2+ ions of around 20% was achieved as compared with the unmodified material and that an insignificant improvement in the sorption capacity of Cd2+ ions was obtained when the soybean hulls were modified by treating them with strong base (0.1–1.0 M NaOH). Functional groups such as phosphoryl, hydroxyl, and carboxyl could be the activated sites on soybean hulls sorbent, with metal ion uptake on a neutral sorbent surface occurring via an ion exchange process [46]. The addition of surface functional groups by chemical reaction with NaOH could be responsible for the increase in the biosorbent surface area and consequently greater metal sorption capacity as compared with the untreated material [56]. Investigation has demonstrated that soybean hulls work well at removing textile dyes from contaminated water [52]. Results of the investigation indicated that the soybean hulls and rice hulls worked well at removing the Safranin T and Direct Violet 51 dyes from solution. The soybean hull samples were more effective at removing the Remazol Brilliant Blue R dye as compared with rice hull samples.

3.3. Dietary fiber

Dietary fiber can be defined as “the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine” [57]. Dietary fiber is a complex component of natural carbohydrate polymer which consists of a variety of nonstarch polysaccharides such as hemicellulose, cellulose, lignin, and pectin [58]. The beneficial role of dietary fiber in health and nutrition has been demonstrated in normal gastrointestinal and physiological functions, including carbohydrate and lipid metabolism, and in the reduction of chronic ailments such as coronary heart disease, diabetes, obesity, and some cancers [59]. Dietary fiber can typically be divided into soluble dietary fiber and insoluble dietary fiber (IDF). SDF includes pectins and some hemicelluloses. Cellulose, lignin, and some hemicelluloses are examples of dietary fiber classified as IDF. Soybean hulls contain the majority of the fibers with a higher level of IDF. Acid-base hydrolysis and autoclaving significantly affect the SDF, IDF, and total DF distribution in soybean hulls [60]. Kumar et al. [61] and Goldnon and Brown [62] reported that 4% addition of soy hull flours had no impact on the cooking yield and texture of chicken nuggets and pork patties, respectively. Investigation by Kumar et al. [63] indicated that 3–5% addition of soybean hull flours slightly improved emulsion stability and water-holding capacity of chicken nuggets. Kim et al. [64] indicated that insoluble fiber from soybean hulls through acid and alkali hydrolysis influenced positive effects on reduction in cooking loss and increase in hardness of meat without any adverse effect on springiness and cohesiveness, and minimized color alteration. The investigation also indicated that acid-base hydrolysis and autoclaving processes in soybean hulls could significantly boost total dietary fiber content, showing the great potential in various food applications due to the functional properties [60].

3.4. Medicine

Soybean with black, brown, yellow, and green seed coats possesses antioxidant capacity varying with color because of differences in phenolic levels and composition which is anthocyanins, phenolic acids (chlorogenic and caffeic acids), isoflavones, and proanthocyanidins [6567]. Black soybean has been used as an herbal medicine to treat edema and jaundice. It has also been used to treat enuresis by affecting the functions of the spleen and kidney [68]. The hull of the black soybean has been used for the treatment of headache and vertigo, as well as for detoxification and diuresis [68]. Black soybeans were reported to contain anthocyanins and only brown and black soybeans contain proanthocyanins [66, 67]. Investigation showed that black soybean had the highest antioxidant activity as compared with other colored seed coat soybeans [65]. The antioxidant activity of back soybeans is related to their phenolic pigments in the seed coats [69, 70]. In vitro anticancer investigation reported that polysaccharides from black soybean may induce differentiation and inhibit proliferation in human leukemic U937 cells [71]. Anthocyanins isolated from black soybean hulls display growth inhibitory effects and strong apoptosis induction effect against human leukemia Molt 4B cells [72]. Animal experiments indicated that the intake of extract from black soybean hulls effectively enhanced memory and learning ability in rats [73]. The extract of the black soybean hulls has also been used as dietary ingredient including pigments and nutraceuticals [68].


4. Conversion of soybean hulls

4.1. Ethanol production

The National Biofuels Action Plan released in October 2008 states that expanding annual biofuels production to 36 billion gallons by 2022 would be a key component in America’s movement toward clean, affordable, and secure energy sources [11]. The interest for ethanol production from renewable resources has increased in the last decade, directly related to environmental and economic concerns over fossil fuels [74]. Currently, ethanol is mainly produced from sugarcane and corn (in the Brazil and USA, respectively), accounting for 66% of worldwide production [75]. However, recently, there has been increasing interest in cellulosic ethanol production, because biomass is an abundant feedstock that is inexpensive and has a high cellulosic content [10, 76]. Lignocellulosic biomass needs to be decomposed into its monomers in order to release fermentable sugars, and which is achieved by using diluted acids or enzymes. The cellulose in the biomass is scarcely affected by the diluted acid hydrolysis, requiring other physicochemical hydrolyses at higher temperatures to result in sugar decomposition, which may lead to metabolic inhibition during fermentation [77]. Lignocellulosic biomass mainly consists of lignin, cellulose, hemicelluloses, and small amounts of extractives. Cellulose structure allows the formation of intermolecular and intramolecular hydrogen bonds, generating organized rigid crystalline regions. The biological role of hemicellulose is the cross-linked interaction with lignin and cellulose, which strengthens the cell wall and embedding of the crystalline cellulose elementary fibrils [78]. The close association between hemicellulose and lignin impedes enzyme access to hemicellulose, which in turn affects accessibility to cellulose [79]. Thus, pretreatment by various technologies is a crucial prerequisite to break down the rigidity of the biomass prior to enzyme hydrolysis process. Soybean hulls are an agricultural residue produced during the processing of soybeans, and the lignocellulosic material contains a small proportion of lignin (1.4–2%) when compared to other biomass. Therefore, soybean hulls are an attractive source of fermentable sugars for cellulosic ethanol production. Hickert et al. [74] investigated the conversion of pentoses and hexoses liberated from high osmotic pressure soybean hull hydrolysate into ethanol by various immobilized cerevisiae. The soybean hulls were hydrolyzed in a two-step sulfuric acid-enzyme pretreatment, resulting in more than 72% of saccharification. The yields of bioconversion of soybean hulls into ethanol were 38–47%. Physicochemical pretreatments of soybean hulls for hemicellulose removal were essential in order to improve the material digestibility at the enzymatic hydrolysis stage. Cassales et al. [80] investigated various acid concentrations in order to achieve high sugar release and low generation of toxic compounds. Yoo et al. [11] studied the pretreatment of soybean hulls by thermomechanical extrusion. Mielenz et al. [9] reported high yields of ethanol by simultaneous saccharification and fermentation of soybean hulls without pretreatment, because of the low lignin content. However, the time of fermentation was very long (about 9 days). Rojas et al. [10] reported a process for the recovery of proteins from soybean hulls, mainly as oligopeptides, and the production of ethanol from the remaining lignocellulosic fraction. In addition to ethanol production from soybean hulls, Zhang and Hu [81] studied a new application of soybean hulls to be converted to fungal lipids for biodiesel production through solid-state fermentation. The results showed that the total final lipid reached 47.9-mg lipid from a 1-g soybean hull after the conversion, which is 3.3-fold higher as compared with initial lipid reserve in the soybean hulls. The solid-state fermentation is a more cost-effective process because of low-energy expenditure, its low capital cost, less expensive downstream processing, high volumetric productivity, low wastewater output, and less fermentation space needed [82].

4.2. Bio-oil

Lignocellulosic biomass can be converted into useful form of energy using biochemical and thermochemical processes, but thermochemical conversion technology finds its dominance due to high efficient conversion to gas, liquid, and solid products under thermal conditions [83]. The liquid product called bio-oil is a complex mixture of water and organic chemicals, which are alcohols, aldehydes, acids, ketones, esters, heterocyclic derivatives, and phenolic compounds [84]. There are two typical thermochemical processes to produce liquid product with high yield: pyrolysis and liquefaction. During the pyrolysis processes, the biomass feedstock is heated in the absence of air to a high temperature (400–1000°C), resulting in the formation of bio-oils and gaseous products. Another important method to convert the biomass into liquid fuel is liquefaction in solvents (such as acetone, ethanol, water, or their mixtures) by heat. By the method, biomass can be decomposed into liquid at a mild temperature and a high pressure as compared with the pyrolysis process [85]. Oliveira et al. [86] studied soybean hull bio-oil produced by fast pyrolysis. The main components of the bio-oil were analyzed by gas chromatography/mass spectrometry (GC/MS). The results indicated that the soybean hull bio-oil can be used as an alternative source of chemical products with higher added value. As a result of the decomposition of cellulose, hemicellulose, and lignin, the soybean hull can be transformed into products having various molecular structures. The soybean hull bio-oil was proved to be a complex mixture of a variety of organic compounds (more than 60 compounds were identified) [86]. For the aqueous phase of the soybean hull bio-oil (acid extraction), the main compounds were pyridine (17.06%), acetic acid (9.12%), phenol (16.94%), pyrole (5.14%), and acetamide (5.73%). The high acidity presented in the aqueous phase of soybean hull bio-oil is probably because of the thermal degradation of hemicelluloses, which produces acids as the final product of reactions involving the removal of acetyl groups [87]. Cellulose can be decomposed into levoglucosan at first, and then the levoglucosan can be generated by depolymerization reactions, which produce small quantities of acids, such as propionic acid and acetic acid, as well as furans (furfural, furfuraldehydes, and pyrans) [88]. In the organic phase, the main compounds identified in soybean hull bio-oil were phenol (14.88%), 4-methylphenol (12.55%), and 2-methylphenol (7.59%) [86]. The phenol compounds and derivatives were obviously due to the decomposition products from lignin (and maybe hemicellulose and cellulose). Those phenolic compounds can be separated from soybean hull bio-oil by using vapor distillation, reverse osmosis membranes, and solvent extraction [8991].

4.3. Polysaccharides

Polysaccharides are species of macromolecular substance existing widely in organisms. It has been reported that plant polysaccharides or their derivatives have strong antioxidant activities and can be explored as novel potential antioxidants [92]. Some of the polysaccharides have been targeted as important candidates for the development of effective and nontoxic medicines with strong free radical-scavenging and antioxidant activities [93]. The insoluble carbohydrate fraction in soybean hulls contains 50% hemicelluloses, 30% pectins, and 20% celluloses [94]. Therefore, the soybean hulls are potentially commercial source of polysaccharides. Liu et al. [27] studied the extraction of soybean hull polysaccharides by hot-compressed water in a batch system. The results showed that a moderate temperature (160°C) and short extraction time (60 min) were suitable for the preparation of soybean hull polysaccharides. In the sugar composition of the polysaccharide products, arabinose constituted 35.6–46.9%. Nagata et al. [95] investigated the effects of soybean hull polysaccharides on serum immunoglobulin concentration and production of NO and interleukin-1β from peritoneal macrophages. The soybean hull polysaccharides consisted of arabinose, galactose, xylose, glucose, and rhamnose, and the molecular weight was 500,000. The investigation demonstrated that soybean hull polysaccharides enhanced humoral immunity and activation of macrophages, thereby leading to the augmentation of immune responses in rats.

4.4. Microfibrils

Microfibrillated cellulose developed for the first time in the early 1980s by Turbak and coauthors can be obtained through mechanical treatments such as refining and high-pressure homogenization [96]. Microfibrillar cellulose is a bio-based material with interesting intrinsic properties that make it attractive in many applications. It is characterized by a high specific surface area, flexibility, and crystallinity, and contains a large amount of hydroxyl groups [97], all of which influence its interactions in liquid dispersions or in solid films. Merci et al. [98] produced the microfibrillar cellulose from soybean hulls by using a simple method based on reactive extrusion. The reported microfibrillar cellulose produced from soybean hulls was composed of short and rod-shaped fibers, and had a cellulose content of 83.79% and crystallinity index of 70%. Miranda et al. [99] studied the kinetics of degradation process of cellulose extracted from soybean hulls and compared its behavior to commercial microcrystalline cellulose under inert environment. The results indicated that kinetic degradation behavior of soybean hull cellulose was more similar to commercial microcrystalline cellulose. However, the activation energy value of commercial microcrystalline cellulose was higher as compared with soybean hull cellulose. Ferrer et al. [7] isolated cellulosic microfibrils (SMF) and brick-like microparticles (SMP) from soybean hulls by combining mechanical and chemical pretreatments. The SMF and SMP chemical compositions included residual polysaccharides and lignin that endow such biologically derived materials with properties typical of nanocellulosics. As compared with those of micro- and nanofibrillated cellulose obtained from fully bleached wood fibers, the SMF and SMP exhibited enhanced crystallinity and thermal stability. In addition, a strong shear-thinning behavior was observed for aqueous dispersions of SMF and SMP, revealing that cellulose microstructures are of interest for rheology modification, coatings, and films. These SMF and SMP extracted from soybean hulls have been used in films and also combined with wood-based micro- and nanofibrillar cellulose in hybrid systems [100]. The hybrid films displayed similar strength and barrier performance to those of neat nanofibrillar cellulose films, thus offering an option for reduced cost while keeping a performance from synergistic contributions of the components. Furthermore, dense films with low porosity, a characteristic essential for barrier properties, can be easily produced by replacing up to 75% of micro- and nanofibrillar cellulose with SMF or SMP.

4.5. Peroxidase

The extraction of enzymes from agro-industrial residues is an alternative for reducing costs in biocatalyst production. Soybean hull peroxidase (SHP, E.C. is a glycoprotein that belongs to plant peroxidase superfamily that also includes horseradish (HRP), peanut, and barley peroxidases [101]. Because of the high thermostability, broad pH stability, and cheap source for production from soybean hulls [102], SHP is a more promising biocatalyst for industrial use as compared with the widely used HRP. SHP was previously used for the removal of aqueous phenols from wastewaters in stirred membrane reactor, as a bromination catalyst, for luminal oxidation, for the synthesis of polyaniline, and in organic solvents [103106]. Then, higher-value commodities such as diagnosis tests and therapeutics would require more costly alternatives such as purified or recombinant peroxidases. Soybean hull peroxidase has a ferriprotoporphyrin IX prosthetic group located at the active site. The catalytic mechanism follows a peroxidase ping-pong mechanism involving the two-electron transfer from hydrogen peroxide to the heme, creating an oxidized form of the enzyme, “compound I.” Successive one-electron reductions return the enzyme to its native or reduced state via an intermediate oxidized form of the enzyme, “compound II” [107]. As compared with free enzymes, immobilized enzymes offer more advantages, such as enhanced stability against various denaturing conditions, easier product and enzyme recovery, higher catalytic activity, continuous operation of enzymatic processes, reusability, and reduced susceptibility to microbial contamination [108, 109]. Chagas et al. [110] extracted peroxidase from soybean hulls and immobilized the enzymes on chitosan beads cross-linked with glutaraldehyde. The immobilized enzyme showed a potential of 50% in the oxidation of caffeic acid after four consecutive cycles.

4.6. Oligopeptides

Soybean oligopeptides produced by proteolysis or microbial fermentation techniques followed by purification protocols are widely used in the food industry. The soybean hulls may contain 11–15% of proteins, and the proteins can be transferred into oligopeptides by various techniques. Most commercial productions of oligopeptides use batch hydrolysis, which depends on various factors such as protein denaturation, hydrolysis temperature, and protease specificity [111]. The hydrolysate of protein is a complex mixture of peptides with various lengths. Molecular size of the peptides has a major effect on functional properties. In general, smaller peptides with less than six amino acids have the greatest impact on cell growth and production [112]. Rojas et al. [10] published the results concerning the recovery of proteins from soybean hulls by hydrolysis, mainly as oligopeptides, and subsequent ethanol production from the remaining lignocellulosic fraction. The results indicated that soybean hulls might be a promising feedstock for the production of a high-value protein hydrolysate composed mainly of low-molecular-weight oligopeptides.


5. Conclusion

Soybean hulls are a major by-product in the soybean-processing industry, and have a variable chemical composition of cellulose (29–51%), hemicellulose (10–25%), lignin (1–4%), pectin (4–8%), proteins (11–15%), and minor extractives. The low lignin content in soybean hulls makes the residues have a very wide variety of applications. Due to their compositions, the soybean hulls are widely used as animal feed and have demonstrated the advantages of using as an energy source for ruminants in replacement of corn. Adsorption of inorganic or organic pollutants in wastewater by soybean hulls has been limited and the hull modification is desirable to enhance adsorption, especially of metal ions. The soybean hulls are potentially commercial source of ethanol production, dietary fiber, microfibrils, polysaccharides, and pectin. Soybean hulls can be converted into useful form of energy such as bio-oil by thermochemical processes. The extraction of peroxidase from soybean hulls is an alternative for reducing costs in biocatalyst production. The peroxidase has been used for the removal of aqueous phenols from wastewaters in stirred membrane reactor, as a bromination catalyst, for luminal oxidation, for the synthesis of polyaniline, and in organic solvents. The protein content in soybean hulls has produced a high-value protein hydrolysate composed mainly of low-molecular-weight oligopeptides.



We sincerely acknowledge the financial support by the Fundamental Research Funds for the Henan Provincial Colleges and Universities (2014YWQN01).


  1. 1. Long CC, Gibbons W. Enzymatic hydrolysis and simultaneous saccharification and fermentation of soybean processing intermediates for the production of ethanol and concentration of protein and lipids. Isrn Microbiology. 2012;2012(5):278092-278092. DOI:10.5402/2012/278092
  2. 2. Choct M, Dersjant-Li Y, Mcleish J, Peisker M. Soy oligosaccharides and soluble non-starch polysaccharides: A review of digestion, nutritive and anti-nutritive effects in pigs and poultry. Asian Australasian Journal of Animal Sciences. 2010;23(10):1386–1398. DOI:10.5713/ajas.2010.90222
  3. 3. Singh P, Kumar R, Sabapathy SN, Bawa AS. Functional and edible uses of soy protein products. Comprehensive Reviews in Food Science and Food Safety. 2008;7(1):14–28. DOI:10.1111/j.1541-4337.2007.00025.x
  4. 4. Takamatsu K, Tachibana N, Matsumoto I, Abe K. Soy protein functionality and nutrigenomic analysis. Biofactors. 2004;21(1–4):49–53. DOI: 10.1002/biof.552210110
  5. 5. Suszkiw J. Soy-based hydrogel ready for biomedical exploration. Agricultural Research. 2008(5).
  6. 6. Suszkiw J. How about some soybeans with that tan? Agricultural Research. 2002;50(12):13–14.
  7. 7. Ferrer A, Salas C, Rojas OJ. Physical, thermal, chemical and rheological characterization of cellulosic microfibrils and microparticles produced from soybean hulls. Industrial Crops and Products. 2016;84:337–343. DOI:10.1016/j.indcrop.2016.02.014
  8. 8. Masuda T, Goldsmith PD. World soybean production: Area harvested, yield, and long-term projections. International Food and Agribusiness Management Review. 2009;12(4):143–162.
  9. 9. Mielenz JR, Bardsley JS, Wyman CE. Fermentation of soybean hulls to ethanol while preserving protein value. Bioresource Technology. 2009;100(14):3532–3539. DOI:10.1016/j.biortech.2009.02.044
  10. 10. Rojas MJ, Siqueira PF, Miranda LC, Tardioli PW, Giordano RLC. Sequential proteolysis and cellulolytic hydrolysis of soybean hulls for oligopeptides and ethanol production. Industrial Crops and Products. 2014;61:202–210. DOI:10.1016/j.indcrop.2014.07.002
  11. 11. Yoo J, Alavi S, Vadlani P, Amanor-Boadu V. Thermo-mechanical extrusion pretreatment for conversion of soybean hulls to fermentable sugars. Bioresource Technology. 2011;102(16):7583–7590. DOI:10.1016/j.biortech.2011.04.092
  12. 12. Mohnen D. Pectin structure and biosynthesis. Current Opinion in Plant Biology. 2008;11(3):266–277. DOI:10.1016/j.pbi.2008.03.006
  13. 13. Peng F, Peng P, Xu F, Sun RC. Fractional purification and bioconversion of hemicelluloses. Biotechnology Advances. 2012;30(4):879–903. DOI:10.1016/j.biotechadv.2012.01.018
  14. 14. Gilbert HJ. The biochemistry and structural biology of plant cell wall deconstruction. Plant Physiology. 2010;153(2):444–455. DOI:10.1104/pp.110.156646
  15. 15. Vanholme R, Morreel K, Ralph J, Boerjan W. Lignin engineering. Current Opinion in Plant Biology. 2008;11(3):278–285. DOI:10.1016/j.pbi.2008.03.005
  16. 16. Chee KM, Chun KS, Huh BD, Choi JH, Chung MK, Lee HS, et al. Comparative feeding values of soybean hulls and wheat bran for growing and finishing swine. Asian Australasian Journal of Animal Sciences. 2005;18(6):861–867. DOI:10.1128/AEM.70.12.7413-7417.2004
  17. 17. Mosier N, Wyman C, Dale B, Elander R, Lee YY, Holtzapple M, et al. Features of promising technologies for pretreatment of lignocellulosic biomass. Bioresource Technology. 2005;96(6):673–686. DOI:10.1016/j.biortech.2004.06.025
  18. 18. Ku K-H, Park D-J, Kim S-H. Characteristics and application of soybean hull fractions obtained by microparticulation/air-classification. Korean Journal of Food Science and Technology. 1996;28(3):506–513.
  19. 19. Silva MC, Torres JA, Chagas PMB, Corrêa AD. The use of soybean peroxidase in the decolourization of remazol brilliant blue r and toxicological evaluation of its degradation products. Journal of Molecular Catalysis. 2013;89(3):122–129. DOI:10.1016/j.molcatb.2013.01.004
  20. 20. Bras J, Hassan ML, Bruzesse C, Hassan EA, El-Wakil NA, Dufresne A. Mechanical, barrier, and biodegradability properties of bagasse cellulose whiskers reinforced natural rubber nanocomposites  [2010]. Industrial Crops & Products. 2010;32(3):627–633. DOI:10.1016/j.indcrop.2010.07.018
  21. 21. Sun XF, Sun RC, Fowler P, Baird MS. Isolation and characterisation of cellulose obtained by a two-stage treatment with organosolv and cyanamide activated hydrogen peroxide from wheat straw. Carbohydrate Polymers. 2004;55(4):379–391. DOI:10.1016/j.carbpol.2003.10.004
  22. 22. Kadla JF, Gilbert RD. Cellulose structure: A review. Cellulose Chemistry & Technology. 2000;34(3):197–216.
  23. 23. Sun JX, Xu F, Sun XF, Xiao B, Sun RC. Physico-chemical and thermal characterization of cellulose from barley straw. Polymer Degradation & Stability. 2005;88(3):521–531. DOI:10.1016/j.polymdegradstab.2004.12.013
  24. 24. Sugiyama J, Vuong R, Chanzy H. Electron diffraction study on the two crystalline phases occurring in native cellulose from an algal cell wall. Macromolecules. 1991;24(14):4168–4175. DOI:10.1021/ma00014a033
  25. 25. Peng P, Peng F, Bian J, Xu F, Sun RC, Kennedy JF. Isolation and structural characterization of hemicelluloses from the bamboo species phyllostachys incarnata wen. Carbohydrate Polymers. 2011;86(2):883–890. DOI:10.1016/j.carbpol.2011.05.038
  26. 26. Bian J, Peng F, Peng XP, Xu F, Sun RC, Kennedy JF. Isolation of hemicelluloses from sugarcane bagasse at different temperatures: Structure and properties. Carbohydrate Polymers. 2012;88(2):638–645. DOI:10.1016/j.carbpol.2012.01.010
  27. 27. Liu HM, Wang FY, Liu YL. Hot-compressed water extraction of polysaccharides from soy hulls. Food Chemistry. 2016;202:104–109. DOI:10.1016/j.foodchem.2016.01.129
  28. 28. Wang FY, Li HY, Liu HM, Liu YL. Fractional isolation and structural characterization of hemicelluloses from soybean hull. Bioresources. 2015;10(3):5256–5266.
  29. 29. Spiridon I, Popa VI. Hemicelluloses: Major Sources, Properties and Applications. In: Belgacem MN, Gandini A, editors. Monomers, polymers and composites from renewable resources Oxford: Elsevier; 2008. p 289–304. DOI:10.1016/B978-0-08-045316-3.00013-2
  30. 30. Canilha L, Silva JBAE, Felipe MGA, Carvalho W. Batch xylitol production from wheat straw hemicellulosic hydrolysate using Candida guilliermondii in a stirred tank reactor. Biotechnology Letters. 2003;25(21):1811–1814. DOI: 10.1023/A:1026288705215
  31. 31. Thakur BR, Singh RK, Handa AK. Chemistry and uses of pectin--a review. Critical Reviews in Food Science & Nutrition. 1997;37(1):47–73. DOI: 10.1080/10408399709527767
  32. 32. Yamaguchi F, Kojima H, Muramoto M, Ota Y, Hatanaka C. Effects of hexametaphosphate on soybean pectic polysaccharide extraction. Bioscience Biotechnology & Biochemistry. 1996;60(12):2028–2031. DOI:10.1271/bbb.60.2028
  33. 33. Shi ZJ, Xiao LP, Jia D, Xu F, Sun RC. Physicochemical characterization of lignin fractions sequentially isolated from bamboo (Dendrocalamus brandisii) with hot water and alkaline ethanol solution. Journal of Applied Polymer Science. 2012;125(4):3290–3301. DOI:10.1002/app.36580
  34. 34. Wen JL, Sun SL, Xue BL, Sun RC. Quantitative structural characterization of the lignins from the stem and pith of bamboo (Phyllostachys pubescens). Holzforschung. 2013;67(6):613–627. DOI:10.1515/hf-2012-0162
  35. 35. Xu DX, Zhang JJ, Cao YP, Wang J, Xiao JS. Influence of microcrystalline cellulose on the microrheological property and freeze-thaw stability of soybean protein hydrolysate stabilized curcumin emulsion. Lwt-Food Science and Technology. 2016;66:590–597. DOI:10.1016/j.lwt.2015.11.002
  36. 36. Ferreira EM, Pires AV, Susin I, Mendes CQ, Gentil RS, Araujo RC, et al. Growth, feed intake, carcass characteristics, and eating behavior of feedlot lambs fed high-concentrate diets containing soybean hulls. Journal of Animal Science. 2011;89(12):4120–4126. DOI:10.2527/jas.2010-3417
  37. 37. Bittner CJ, Erickson GE, Mader TL, Johnson LJ. Utilization of soybean hulls when fed in combination with MDGS in finishing diets. Nebraska Beef Cattle Reports. 2013.739.
  38. 38. Kabe AMG, de Souza AD, Sousa RLD, Bueno ICD, Mota TP, Crandell K, et al. Soybean hulls in equine feed concentrates: Apparent nutrient digestibility, physicochemical and microbial characteristics of equine feces. Journal of Equine Veterinary Science. 2016;36:77–82. DOI:10.1016/j.jevs.2015.10.008
  39. 39. Moore JA, Poore MH, Luginbuhl JM. By-product feeds for meat goats: Effects on digestibility, ruminal environment, and carcass characteristics. Journal of Animal Science. 2002;80(7):1752–1758.
  40. 40. Ipharraguerre IR, Ipharraguerre RR, Clark JH. Performance of lactating dairy cows fed varying amounts of soyhulls as a replacement for corn grain. Journal of Dairy Science. 2002;85(11):2905–2912. DOI:10.3168/jds.S0022-0302(02)74378-6
  41. 41. Fombelle AD, Jullianda V, Drogoul C, Jacotot E. Feeding and microbial disorders in horses: 1 - effects of an abrupt incorporation of two levels of barley in a hay diet on microbial profile and activities. Journal of Equine Veterinary Science. 2001;21(9):439–445. DOI:10.1016/S0737-0806(01)70018-4
  42. 42. Geor RJ, Equine carbohydrate nutrition: implications for feeding management and disease avoidance. In: Proceedings of the 5th Mid-Atlantic Nutrition conference; 28–29 March 2007; Maryland. p. 154–161.
  43. 43. Costa LS, Silva RR, da Silva FF, de Carvalho GGP, Simionato JI, Marques JD, et al. Centesimal composition and fatty acids of meat from lambs fed diets containing soybean hulls. Revista Brasileira De Zootecnia-Brazilian Journal of Animal Science. 2012;41(7):1720–1726. DOI: org/10.1590/S1516-35982012000700023
  44. 44. Zambom MA, Alcalde CR, Kazama DCD, Martins EN, Hashimoto JH, Matsushita M, et al. Soybean hulls replacing ground corn in diets for early lactation Saanen goats: Intake, digestibility, milk production and quality. Revista Brasileira De Zootecnia-Brazilian Journal of Animal Science. 2012;41(6):1525–1532. DOI: 10.1590/S1516-35982012000600029
  45. 45. Ipharraguerre IR, Clark JH. Soyhulls as an alternative feed for lactating dairy cows: A review. Journal of Dairy Science. 2003;86(4):1052–1073.DOI:10.3168/jds.S0022-0302(03)73689-3
  46. 46. Módenes AN, Espinoza-Quiñones FR, Colombo A, Geraldi CL, Trigueros DEG. Inhibitory effect on the uptake and diffusion of cd 2+ onto soybean hull sorbent in cd–pb binary sorption systems. Journal of Environmental Management. 2015;154:22–32. DOI:10.1016/j.jenvman.2015.02.022
  47. 47. Bueno BYM, Torem ML, Carvalho RJD, Pino GAH, Mesquita LMSD. Fundamental aspects of biosorption of lead (ii) ions onto a rhodococcus opacus strain for environmental applications. Minerals Engineering. 2011;24(14):1619–1624. DOI:10.1016/j.mineng.2011.08.018
  48. 48. Fu F, Wang Q. Removal of heavy metal ions from wastewaters: A review. Journal of Environmental Management. 2011;92(3):407–418. DOI:10.1016/j.jenvman.2010.11.011
  49. 49. Rizzuti AM, Ellis FL, Cosme LW. Biosorption of mercury from dilute aqueous solutions using soybean hulls and rice hulls. Waste & Biomass Valorization. 2015;6(4):1–8. DOI:10.1007/s12649-015-9391-2
  50. 50. Krishnani KK, Meng X, Christodoulatos C, Boddu VM. Biosorption mechanism of nine different heavy metals onto biomatrix from rice husk. Journal of Hazardous Materials. 2008;153(3):1222–1234. DOI:10.1016/j.jhazmat.2007.09.113
  51. 51. Volesky B. Biosorption and me. Water Research. 2007;41(18):4017–4029. DOI:10.1016/j.watres.2007.05.062
  52. 52. Rizzuti AM, Lancaster DJ. Utilizing soybean hulls and rice hulls to remove textile dyes from contaminated water. Waste & Biomass Valorization. 2012;4(3):647–653. DOI:10.1007/s12649-012-9167-x
  53. 53. Jia LI, Chen E. Biosorption of pb~(2+) with modified soybean hulls as absorbent. Chinese Journal of Chemical Engineering. 2011;19(2):334–339. DOI:10.1016/S1004-9541(11)60173-0
  54. 54. Marshall WE, Wartelle LH, Boler DE, Johns MM, Toles CA. Enhanced metal adsorption by soybean hulls modified with citric acid. Bioresource Technology. 1999;69(69):263–268. DOI:10.1016/S0960-8524(98)00185-0
  55. 55. Marshall WE, Wartelle LH. Acid recycling to optimize citric acid-modified soybean hull production. Industrial Crops & Products. 2003;18(18):177–182. DOI:10.1016/S0926-6690(03)00060-8
  56. 56. Asadi F, Shariatmadari H, Mirghaffari N. Modification of rice hull and sawdust sorptive characteristics for remove heavy metals from synthetic solutions and wastewater. Journal of Hazardous Materials. 2008;154(1–3):451–458. DOI:10.1016/j.jhazmat.2007.10.046
  57. 57. Devries JW, Camire ME, Cho S, Craig S, Gordon D, Jones JM, et al. The definition of dietary fiber. Cereal Foods World. 2001;46(3):112–129.
  58. 58. Abirami A, Nagarani G, Siddhuraju P. Measurement of functional properties and health promoting aspects-glucose retardation index of peel, pulp and peel fiber from citrus hystrix and citrus maxima. Bioactive Carbohydrates & Dietary Fibre. 2014;4(1):16–26. DOI:10.1016/j.bcdf.2014.06.001
  59. 59. Mann JI, Cummings JH. Possible implications for health of the different definitions of dietary fibre. Nutrition Metabolism & Cardiovascular Diseases Nmcd. 2009;19(3):226–229. DOI:10.1016/j.numecd.2009.02.002
  60. 60. Yang J, Xiao AH, Wang CW. Novel development and characterisation of dietary fibre from yellow soybean hulls. Food Chemistry. 2014;161:367–375. DOI:10.1016/j.foodchem.2014.04.030
  61. 61. Kumar V, Biswas AK, Chatli MK, Sahoo J. Effect of banana and soybean hull flours on vacuum-packaged chicken nuggets during refrigeration storage. International Journal of Food Science & Technology. 2011;46(1):122–129. DOI:10.1111/j.1365-2621.2010.02461.x
  62. 62. Dcgms RD, Nebpdrd LD. Effects of fat level and addition of soy fiber on sensory and other properties of ground pork patties. Foodservice Research International. 2006;7(1):1–13. DOI:10.1111/j.1745-4506.1992.tb00197.x
  63. 63. Kumar V, Biswas AK, Sahoo J, Chatli MK, Sivakumar S. Quality and storability of chicken nuggets formulated with green banana and soybean hulls flours. Journal of Food Science & Technology. 2013;50(6):1058–1068. DOI:10.1007/s13197-011-0442-9
  64. 64. Kim HW, Yong JL, Yuan HBK. Efficacy of pectin and insoluble fiber extracted from soy hulls as a functional non-meat ingredient. LWT - Food Science and Technology. 2015;64(2):1071–1077. DOI:10.1016/j.lwt.2015.07.030
  65. 65. Slavin M, Kenworthy W, Yu LL. Antioxidant properties, phytochemical composition, and antiproliferative activity of Maryland-grown soybeans with colored seed coats. Journal of Agricultural & Food Chemistry. 2009;57(23):11174–11185. DOI: 10.1021/jf902609n
  66. 66. Xu B, Chang SKC. Antioxidant capacity of seed coat, dehulled bean, and whole black soybeans in relation to their distributions of total phenolics, phenolic acids, anthocyanins, and isoflavones. Journal of Agricultural & Food Chemistry. 2008;56(18):8365–8373.DOI: 10.1021/jf801196d
  67. 67. Todd JJ, Vodkin LO. Pigmented soybean (glycine max) seed coats accumulate proanthocyanidins during development. Plant Physiology. 1993;102(2):663–670. DOI: 10.1104/pp.102.2.663
  68. 68. Fukuda I, Tsutsui M, Yoshida T, Toda T, Tsuda T, Ashida H. Oral toxicological studies of black soybean (glycine max) hull extract: Acute studies in rats and mice, and chronic studies in mice. Food & Chemical Toxicology An International Journal Published for the British Industrial Biological Research Association. 2011;49(12):3272–3278. DOI:10.1016/j.fct.2011.09.022
  69. 69. Takahashi R, Ohmori R, Kiyose C, Momiyama Y, Ohsuzu FA, Kondo K. Antioxidant activities of black and yellow soybeans against low density lipoprotein oxidation. Journal of Agricultural & Food Chemistry. 2005;53(11):4578–4582. DOI: 10.1021/jf048062m
  70. 70. Furuta S, Takahashi M, Takahata Y, Nishiba Y, Oki T, Masuda M, et al. Radical-scavenging activities of soybean cultivars with black seed coats. Food Science & Technology International Tokyo. 2003;9:73–75. DOI 10.3136/fstr.9.73
  71. 71. Liao HF, Chou CJ, Wu SH, Khoo KH, Chen CF, Wang SY. Isolation and characterization of an active compound from black soybean [glycine max (l.) merr.] and its effect on proliferation and differentiation of human leukemic u937 cells. Anticancer Drugs. 2001;12(10):841–846. DOI: 10.1097/00001813-200111000-00008
  72. 72. Katsuzaki H, Hibasami H, Ohwaki S, Ishikawa K, Imai K, Date K, et al. Cyanidin 3-o-β-d-glucoside isolated from skin of black glycine max and other anthocyanins isolated from skin of red grape induce apoptosis in human lymphoid leukemia molt 4b cells. Oncology Reports. 2003;10(2):297–300. DOI: 10.3892/or.10.2.297
  73. 73. Shinomiya K, Tokunaga S, Shigemoto Y, Kamei C. Effect of seed coat extract from black soybeans on radial maze performance in rats. Clinical & Experimental Pharmacology & Physiology. 2005;32(9):757–760. DOI:10.1111/j.1440-1681.2005.04263.x
  74. 74. Hickert LR, Cruz MM, Dillon A. Fermentation kinetics of acid-enzymatic soybean hull hydrolysate in immobilized-cell bioreactors of Saccharomyces cerevisiae, Candida shehatae, Spathaspora arborariae, and their co-cultivations. Biochemical Engineering Journal. 2014;88(28):61–67. DOI:10.1016/j.bej.2014.04.004
  75. 75. Taherzadeh MJ, Karimi K. Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: A review. International Journal of Molecular Sciences. 2008;9(9):1621–1651. DOI: 10.3390/ijms9091621
  76. 76. Saxena RC, Adhikari DK, Goyal HB. Biomass-based energy fuel through biochemical routes: A review. Renewable & Sustainable Energy Reviews. 2009;13(1):167–178. DOI:10.1016/j.rser.2007.07.011
  77. 77. Galbe M, Zacchi G. A review of the production of ethanol from softwood. Applied Microbiology & Biotechnology. 2002;59(6):618–628. DOI: 10.1007/s00253-002-1058-9
  78. 78. Wang K, Yang H, Xi Y, Feng X, Sun RC. Structural transformation of hemicelluloses and lignin from triploid poplar during acid-pretreatment based biorefinery process. Bioresource Technology. 2012;116(116):99–106. DOI:10.1016/j.biortech.2012.04.028
  79. 79. Kumar R, Wyman CE. Access of cellulase to cellulose and lignin for poplar solids produced by leading pretreatment technologies. Biotechnology Progress. 2009;25(3):807–819. DOI: 10.1002/btpr.153
  80. 80. Cassales A, Souza-Cruz PBD, Rech R, Ayub MAZ. Optimization of soybean hull acid hydrolysis and its characterization as a potential substrate for bioprocessing. Biomass & Bioenergy. 2011;35(11):4675–4683. DOI:10.1016/j.biombioe.2011.09.021
  81. 81. Zhang J, Hu B. Solid-state fermentation of Mortierella isabellina for lipid production from soybean hull. Applied Biochemistry & Biotechnology. 2012;166(4):1034–1046. DOI:10.1007/s12010-011-9491-9
  82. 82. Hölker U, Höfer M, Lenz J. Biotechnological advantages of laboratory-scale solid-state fermentation with fungi. Applied Microbiology & Biotechnology. 2004;64(2):175–186. DOI:10.1007/s00253-003-1504-3
  83. 83. Zhang X, Xu M, Sun R, Sun L. Study on biomass pyrolysis kinetics. Journal of Engineering for Gas Turbines & Power. 2006;128(3):401–405. DOI:10.1115/GT2005-68350
  84. 84. Liu W, Changwei HU, Yu Y. Effect of the interference instant of zeolite hy catalyst on the pyrolysis of pubescens. Chinese Journal of Chemical Engineering. 2010;327(2):351–354.
  85. 85. Liu HM, Feng B, Sun RC. Enhanced bio-oil yield from liquefaction of cornstalk in sub- and supercritical ethanol by acid–chlorite pretreatment. Indengchemres. 2011;50(19):10928–10935. DOI: 10.1021/le2014197
  86. 86. Oliveira TJP, Cardoso CR, Ataíde CH. Fast pyrolysis of soybean hulls: Analysis of bio-oil produced in a fluidized bed reactor and of vapor obtained in analytical pyrolysis. Journal of Thermal Analysis & Calorimetry. 2015;120(1):427–438. DOI: 10.1007/s10973-015-4600-6
  87. 87. Sheng C, Azevedo JLT. Estimating the higher heating value of biomass fuels from basic analysis data. Biomass & Bioenergy. 2005;28(5):499–507. DOI:10.1016/j.biombioe.2004.11.008
  88. 88. Pattiya A, Suttibak S. Production of bio-oil via fast pyrolysis of agricultural residues from cassava plantations in a fluidised-bed reactor with a hot vapour filtration unit. Journal of Analytical & Applied Pyrolysis. 2012;95(95):227–235. DOI:10.1016/j.jaap.2012.02.010
  89. 89. Sagehashi M, Nomura T, Shishido H, Sakoda A. Separation of phenols and furfural by pervaporation and reverse osmosis membranes from biomass--superheated steam pyrolysis-derived aqueous solution. Bioresource Technology. 2007;98(10):2018–2026. DOI:10.1016/j.biortech.2006.08.022
  90. 90. Žilnik LF, Jazbinšek A. Recovery of renewable phenolic fraction from pyrolysis oil. Separation & Purification Technology. 2012;86(8):157–170. DOI:10.1016/j.seppur.2011.10.040
  91. 91. Kanaujia PK, Sharma YK, Garg MO, Tripathi D, Singh R. Review of analytical strategies in the production and upgrading of bio-oils derived from lignocellulosic biomass. Journal of Analytical & Applied Pyrolysis. 2014;58(105):183–193. DOI:10.1016/j.jaap.2013.10.004
  92. 92. Jiang YH, Jiang XL, Wang P, Xiao-Ke HU. In vitro antioxidant activities of water-soluble polysaccharides extracted from isaria farinosa b05. Journal of Food Biochemistry. 2005;29(3):323–335. DOI:10.1111/j.1745-4514.2005.00040.x
  93. 93. Li XM, Li XL, Zhou AG. Evaluation of antioxidant activity of the polysaccharides extracted from Lycium barbarum fruits in vitro. European Polymer Journal. 2007;43(2):488–497. DOI:10.1016/j.eurpolymj.2006.10.025
  94. 94. Liu H, Guo X, Li J, Zhu D, Li J. The effects of mgso 4, d -glucono-δ-lactone (gdl), sucrose, and urea on gelation properties of pectic polysaccharide from soy hull. Food Hydrocolloids. 2013;31(2):137–145. DOI:10.1016/j.foodhyd.2012.10.013
  95. 95. Nagata J, Higashiuesato Y, Maeda G, Chinen I, Saito M, Iwabuchi K et al. Effects of water-soluble hemicellulose from soybean hull on serum antibody levels and activation of macrophages in rats. Journal of Agricultural & Food Chemistry. 2001;49(49):4965–4970. DOI: 10.1021/jf0104883
  96. 96. Turbak AF, Snyder FW, Sandberg KR. Microfibrillated cellulose, a new cellulose product: Properties, uses, and commercial potential. Journal of Applied Polymer Science: Applied Polymer Symposium (United States); 1983.
  97. 97. Dat Nguyen H, Thi TTM, Bich Nguyen N, Duy Dang T, My LPL, Dang TT, et al. A novel method for preparing microfibrillated cellulose from bamboo fibers. Advances in Natural Sciences Nanoscience & Nanotechnology. 2013;4(1). DOI:10.1088/2043-6262/4/1/015016
  98. 98. Merci A, Urbano A, Grossmann MVE, Tischer CA, Mali S. Properties of microcrystalline cellulose extracted from soybean hulls by reactive extrusion. Food Research International. 2015;73:38–43. DOI:10.1016/j.foodres.2015.03.020
  99. 99. Miranda MIG, Bica CID, Nachtigall SMB, Rehman N, Rosa SML. Kinetical thermal degradation study of maize straw and soybean hull celluloses by simultaneous dsc–tga and mdsc techniques. Thermochimica Acta. 2013;565(6):65–71. DOI:10.1016/j.tca.2013.04.012
  100. 100. Ferrer A, Salas C, Rojas OJ. Dewatering of MNFC containing microfibrils and microparticles from soybean hulls: Mechanical and transport properties of hybrid films. Cellulose. 2015;22(6):3919–3928. DOI: 10.1007/s10570-015-0768-y
  101. 101. Kamal JKA, Behere DV. Thermal and conformational stability of seed coat soybean peroxidase. Biochemistry. 2002;41(41):9034–9042. DOI: 10.1021/bi025621e
  102. 102. Liu J, Liu H, Zhang Y, Qiu L, Su F, Li F, et al. A simple preparation method of crystals of soybean hull peroxidase. Applied Microbiology & Biotechnology. 2007;74(1):249–255. DOI: 10.1007/s00253-006-0639-4
  103. 103. Flock C, Bassi A, Gijzen M. Removal of aqueous phenol and 2-chlorophenol with purified soybean peroxidase and raw soybean hulls. Journal of Chemical Technology & Biotechnology. 1999;74(4):303–309. DOI:10.1002/(SICI)1097-4660(199904)74:4<303::AID-JCTB38>3.0.CO;2-B
  104. 104. Alpeeva IS, Sakharov IY. Soybean peroxidase-catalyzed oxidation of luminol by hydrogen peroxide. Journal of Agricultural & Food Chemistry. 2005;53(14):5784–5788. DOI: 10.1021/jf0506075
  105. 105. Cruz-Silva R, Romero-García J, Angulo-Sánchez JL, Ledezma-Pérez A, Arias-Marín E, Moggio I, et al. Template-free enzymatic synthesis of electrically conducting polyaniline using soybean peroxidase. European Polymer Journal. 2005;41(5):1129–1135. DOI:10.1016/j.eurpolymj.2004.11.012
  106. 106. Prokopijevic M, Prodanovic O, Spasojevic D, Stojanovic Z, Radotic K, Prodanovic R. Soybean hull peroxidase immobilization on macroporous glycidyl methacrylates with different surface characteristics. Bioprocess & Biosystems Engineering. 2013;37(5):799–804. DOI:10.1007/s00449-013-1050-z
  107. 107. Steevensz A, Madur S, Alansari MM, Taylor KE, Bewtra JK, Biswas N. A simple lab-scale extraction of soybean hull peroxidase shows wide variation among cultivars. Industrial Crops and Products. 2013;48(3):13-18. DOI:10.1016/j.indcrop.2013.03.030
  108. 108. Ashraf H, Husain Q. Stabilization of DEAE cellulose adsorbed and glutaraldehyde crosslinked white radish (Raphanus sativus) peroxidase. Journal Of Scientific & Industrial Research. 2010;69(8):613–620.
  109. 109. Kulshrestha Y, Husain Q. Decolorization and degradation of acid dyes mediated by salt fractionated turnip (Brassica rapa) peroxidases. Toxicological & Environmental Chemistry. 2007;89(89):255–267. DOI:10.1080/02772240601081692
  110. 110. Chagas PMB, Torres JA, Silva MC, Corrêa AD. Immobilized soybean hull peroxidase for the oxidation of phenolic compounds in coffee processing wastewater. International Journal of Biological Macromolecules. 2015;81:568–575. DOI:10.1016/j.ijbiomac.2015.08.061
  111. 111. Kenji S, Yasunori O. An integrated bioreactor system for biologically active peptides from isolated soybean protein. Annals of the New York Academy of Sciences. 1995;750(1 Enzyme Engine):435–440. DOI:10.1111/j.1749-6632.1995.tb19992.x
  112. 112. Franěk F, Fussenegger M. Survival factor-like activity of small peptides in hybridoma and CHO cells cultures. Biotechnology Progress. 2005;21(21):96–98. DOI:10.1021/bp0400184

Written By

Hua-Min Liu and Hao-Yang Li

Reviewed: 07 November 2016 Published: 03 May 2017