Soy Hull, Okara and Molasses)
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Wageningen Academic Quality Assurance and Safety of Crops & Foods, 2015; 7 (5): 651-660 Publishers Chemical composition and functional properties of three soy processing by-products (soy hull, okara and molasses) Y. Zhong1 and Y. Zhao1,2* 1Shanghai Jiao Tong University, Department of Food Science & Technology, School of Agriculture and Biology, 800 Dongchuan Road, 200240 Shanghai, China P.R.; 2Oregon State University, Department of Food Science and Technology, 100 Wiegand Hall, Corvallis, OR 97331, USA; [email protected] Received: 2 July 2014 / Accepted: 7 October 2014 © 2014 Wageningen Academic Publishers RESEARCH ARTICLE Abstract Three soy processing by-products, soy hull, okara, and molasses, were analysed for their amino acids, fatty acids, dietary fibre, and other chemical compounds. Their digestibility and odour variance were also quantified. Okara had the greatest content of protein (306.1 g/kg) and amino acids (340.6 g/kg dry matter; DM), while soy hull had the highest amount of dietary fibre (546.7 g/kg) and extractable pectin (47.4 g galacturonic acid equivalents/kg DM), and molasses possessed the most abundant total phenolics, resulting in its highest radical scavenging activity. The high unsaturated fatty acids presented in soy by-products (accounting for 73.1-82.3% of total lipids) indicated their favourable physiological functions. In simulated digestion test, the by-products generally underwent fast digestion within the first 30 min in gastric digestion step, and then slowed down. However, okara was still digested rapidly in the stimulated intestinal digestion stage. Electronic nose was able to clearly discriminate the odour differences among the three soy by-products. Keywords: chemical composition, digestibility, odour characteristics, radical scavenging activity, soy processing by-products 1. Introduction generated before extraction of soy oil with a US annual production in excess of 9.1×105 tons (Sessa, 2004). Karr- Soy products are favourable nutritional sources which can Lilienthal et al. (2005) reported that soy hull mainly contains provide basic nutrients and various potential functional cellulose, hemicellulose, and acidic polysaccharides, and substances. During the processing of soy products, large suggested soy hull as commercial source of pectin or quantities of residues or by-products are produced, fibre. Soy molasses is a concentrated liquid obtained in which are rich in nutritional and bioactive substances. the production of protein-concentrate soy meal extracted Directly discarding these materials would not only cause with ethanol, and mainly consists of carbohydrates, lipids environmental problems, but also lead to large amounts and protein with the most abundant carbohydrates being of resource wastage. sucrose, raffinose and stachyose (Siqueira et al., 2008). Okara is a by-product of soymilk, soy protein isolate Presently, the by-products of soy processing are generally and tofu processes. Raw okara is white yellowish puree used in the animal feed industry. However, they might be containing insoluble parts of soybeans. Approximately inexpensive sources of value-added products. Wiboonsirikul 8×105 tons of okara are produced from the tofu industry et al. (2013) pointed out that extracts from okara exhibit in Japan every year, and about 3.1×105 and 2.8×106 tons high radical scavenging activity and suppressive activity to in Korea and China, respectively (Li et al., 2012). Okara the autoxidation of linoleic acid. Replacing 30% of coconut contains high amount of protein, lipids, dietary fibre and with wet okara was found to increase fibre content and minerals, and is also a potential source of natural antioxidant decrease fat content of a coconut-based snack, with the (Jimenez-Escrig et al., 2010). Soy hull is a major by-product overall sensory score being significantly higher than that ISSN 1757-837X online, DOI 10.3920/QAS2014.0481 651 Y. Zhong and Y. Zhao of the control sample (Radocaj and Dimic, 2013). A 1.5 Analysis of soluble sugar and 4% substitution of okara flour to meat in frankfurter displayed no significant differences in the physical (colour, One gram of dried sample was extracted in an ultrasonic texture, and emulsion stability) and chemical (pH and unit (Model S-10H; Zealway Instrument Inc., Xiamen, proximate composition) properties from those without China) with 50 ml of 80% ethanol for 15 min at 25 °C okara flour (Grizotto et al., 2012). Soy hull coated on frying for three times (Deng et al., 2011). The extraction was batter could reduce fat uptake during deep fat frying. centrifuged at 10,000×g for 10 min. The combined With increased soy hull content, the inner crust structure supernatant was then evaporated at 50 °C under vacuum showed improved cellular integrity (Kim et al., 2008). Soy (Model RE-52AA; Yuhua Instruments Co., Henan, China) molasses could be used as a combined nitrogen and carbon- to remove solvent and diluted to 50 ml with deionised water. source for microbial growth to produce single cell protein, One ml of the water solution was mixed thoroughly with exopolysaccharides, and sophorolipids (Gao et al., 2012). 2 ml of 75% H2SO4 and 4 ml of anthrone reagent (0.5 mg anthrone in 250 ml 75% H2SO4), and incubated at 100 °C for Amino acid, fatty acid, pectin and dietary fibre are the 15 min. After cooling to room temperature, the absorbance important bioactive components in soy by-products. Their of the sample or glucose standard was measured at 578 nm fractions represent different physiological functionalities, (UV-1800; Shimadzu Co., Ltd., Kyoto, Japan). Results were thus critical for developing specific applications of the by- expressed as g glucose (GLU)/kg DM. products. Besides, the digestion abilities of different soy by-products may vary that directly relate to the processing Analysis of total phenolic content conditions. Unfortunately, few studies have compared the above constituents in different soy processing by-products. Five gram of dried sample was extracted once with acetone Comprehensively analysing the functional components containing 0.1 ml/l HCl and then twice with 700 ml/l aqueous of the soy processing by-products could help clarify their acetone containing 0.1 ml/l HCl under ultrasonication potential functionality, thus providing useful information (Model S-10H; Zealway Instrument Inc.) for 30 min (Deng for further industrial applications. Therefore, the objectives et al., 2011). The mixture was centrifuged at 4,000×g for 5 of this study were: (1) to investigate the types and contents min, and the combined supernatant was evaporated at 40 °C of pectin, dietary fibre, amino acid, and fatty acid of three under vacuum to remove organic solvent. The extract was soy processing by-products; (2) to evaluate the antioxidant diluted to 50 ml with deionised water and the total phenolic capacity of certain functional components; and (3) to content (TPC) was measured using Folin-Ciocalteau (FC) analyse in vitro digestibility and odour differences of three reagent (Deng et al., 2011). A 1.5 mL of diluted extract soy processing by-products. or gallic acid standard was mixed with 7.5 ml of distilled water and 0.5 ml of FC reagent, and allowed to stand at 2. Materials and methods 25 °C for 10 min. The solutions were then mixed with 3 ml of 20% (w/v) Na2CO3 and placed in water bath at 40 °C for Soy hull, fresh okara and soy molasses were donated by 20 min. Then samples were immediately cooled to room the Wilmar International (Shanghai) Co., Ltd. (Shanghai, temperature and the absorbance was measured at 765 nm China). Samples were freeze dried, milled to pass a 40-mesh (UV-1800; Shimadzu Co., Ltd.). TPC was calculated as g of screen, packaged in the polyethylene bags, and stored in a gallic acid equivalents/kg DM. desiccator at 25 °C until used. Trypsin from bovine pancreas (≥10,000 BAEE U/mg protein) was obtained from Sigma- Analysis of amino acids Aldrich (Shanghai) Trading Co. Ltd. (Shanghai, China). Pepsin (≥1,200 U/g) and all other chemical reagents were Amino acid profiles were analysed using a L-8900 automatic purchased from Sinopharm Chemical Reagent Co., Ltd. amino acid analyser (Hitachi, Ltd., Kyoto, Japan) based on (Shanghai, China). the method by Liu et al. (2013) with some modifications. Ten mg of dried sample was mixed with 10 ml of 6 M HCl Analysis of basic chemical component and hydrolysed at 110±1 °C for 22 h and then cooled to ambient temperature. The hydrolysate was filtered and Basic chemical components were determined according diluted to 50 ml using distilled water. One ml of diluted to the methods of Iqbal et al. (2006). Crude protein was filtrate was dried and dissolved in 2 ml of distilled water, and determined by Kjeldahl method and calculated using the the process was repeated twice. The solution was then dried conversion factor of 6.25. Crude lipid was determined and the residue was dissolved in 1 ml of citrate buffer (pH by Soxhlet extraction using hexane as solvent. Ash was 2.2). Finally, 20 μl of the sample was injected into the amino obtained using a muffle furnace at 550 °C for 4 h. Data acid analyser for quantitation. The amino acid content was were expressed as g/kg dry matter (DM). expressed as g/kg DM. 652 Quality Assurance and Safety of Crops & Foods 7 (5) Composition and properties of soy by-products Analysis of fatty acids dialysed in 1 l of distilled water for 36 h and the water was changed at each 8 h. The dialysed SDF was then freeze- Briefly, known quantity of dried sample (3 g for soy hull, dried and hydrolysed in 72% sulfuric acid at 121 °C for 1 h. 1 g for okara, and 2 g for molasses) was mixed with 100 NSs was quantified with spectrometric assay by anthrone mg pyrogallic acid, 5 mg/ml triundecanoin solution, 95% method as D-glucose equivalent and UAs was determined ethanol, and 8.3 mol/l HCl in order, and then incubated for using galacturonic acid as standard.