Physical,Mechanical, and Barrier Properties of Kafirin Films from Red and White Sorghum Milling Fractions

Fractions from the sorghum dry milling industry, including bran, are a potential source of kafirin. Free‐standing plasticized cast films were prepared from defatted kafirin preparations from red and white sorghum flour and bran fractions, and from commercial zein. All the kafirin preparations were able to form films. However, there were differences in film thickness, clarity, flexibility, surface texture, odor, and color between the different kafirin films. Bran kafirin films were highly colored, less flexible with a less smooth surface texture compared with films from flour, probably due to higher levels of contaminants in the bran kafirins. The strong color of the bran films could limit their use in certain coating applications. The kafirin films had much higher tensile strength and lower extensibility than zein film, probably because of the presence of β‐ and γ‐kafirins in the kafirin, giving high levels of disulfide cross‐linking in the kafirin films. The kafirin films had poorer water barrier properties than zein film, possibly due to greater thickness or to poorer flexibility, which may have caused microcracks.     

Extraction and Film Properties of Kafirin from Coarse Sorghum and Sorghum DDGS by Percolation

The high cost of kafirin and zein restricts their use for bioplastic and food applications. Effective, simple, and rapid kafirin/zein isolation processes are required. Here a percolation‐type aqueous ethanol solvent extraction process from coarse meals (grits) and coarse sorghum distillers dried grains and solubles (DDGS) for kafirin and zein isolation employing a low ratio of extractant to meal (2.5:1) was investigated, which is potentially applicable in the grain bioethanol industry. Postextraction filtration times were more than twice as fast using coarse meals compared with fine flours. Washing the meals prior to extraction to remove starch improved protein preparation purity to 73–85% compared with 68–72% for unwashed meals. Hence, no subsequent filtration or centrifugation step is required to clean up the kafirin/zein solution prior to solvent evaporation. With a single extraction step, kafirin/zein yields were 48% (protein basis) for DDGS and 53–70% for washed sorghum/maize meals. Cast films were used as a model bioplastic system to evaluate extracted kafirin/zein functional properties. DDGS kafirin films had rough surfaces but had the lowest water uptake and in vitro digestibility, owing to heat‐induced disulfide crosslinking during DDGS processing. Extraction by percolation using coarse meal/DDGS has potential to improve kafirin/zein viability.     

丁香酚对高粱醇溶蛋白可食性膜结构及性能的影响

为开发天然的可降解、可食性包装材料,以高粱醇溶蛋白为原料,采用溶液共混的方法制备可食性丁香酚/高粱醇溶蛋白复合膜,分析不同浓度丁香酚对可食性高粱醇溶蛋白膜物理性能及微观结构的影响并探讨其变化机理。结果表明,添加4%丁香酚可优化蛋白膜的机械性能,提升膜的拉伸强度(TS)和断裂伸长率(EAB);添加丁香酚不影响蛋白膜的水蒸气透过系数(WVP),但略微提高了蛋白膜的溶解度;添加4%丁香酚可增加蛋白膜对紫外光和可见光的吸光度值,即增强膜的光阻隔性能。DSC测量显示,添加丁香酚后降低了高粱醇溶蛋白的玻璃态转变温度(Tg),表明丁香酚提高了丁香酚/高粱醇溶蛋白复合膜的延展性;FTIR分析结果表明,添加丁香酚后使得高粱醇溶蛋白二级结构中的α-螺旋、无规则卷曲转变为β-折叠、β-转角,表明丁香酚有助于提高丁香酚/高粱醇溶蛋白复合膜的机械性能;SEM结果显示,4%丁香酚与高粱醇溶蛋白的相容性良好,制备的复合膜截面光滑紧致。本研究结果为可降解、可食性膜新材料的研究及应用推广提供了理论参考。     

Alteration of kafirin and kafirin film structure by heating with microwave energy and tannin complexation

Heating with microwave energy and tannin complexation of kafirin both increase the tensile strength of cast kafirin bioplastic films. The effects of these treatments on the molecular structure of kafirin and of kafirin in the film were investigated. SDS-PAGE of heated wet kafirin showed an increase in kafirin oligomers. Disulfide groups increased in heated kafirin and in films made from the heated kafirin. Fourier transform infrared (FTIR) spectroscopy of heated kafirin and films made from the heated kafirin indicated an increase in beta-sheet conformation. In contrast, kafirin complexation with tannic acid (TA) and sorghum condensed tannin (SCT) resulted in a slight decrease in beta-sheet conformation in the kafirin and a larger decrease in the kafirin in the films. Raman spectroscopy showed that, with TA, there was a shift in peak from 1710 to 1728 cm(-1) for kafirin-tannic acid complexes, indicating kafirin and tannic acid interaction. The protein conformational changes presumably facilitated cross-linking between kafirin molecules and/or between kafirin and the tannins. Thus, although both heating with microwave energy and tannin complexation cause cross-linking of kafirin to increase film tensile strength, their effects on kafirin structure appear to be different.     

Improvement in water stability and other related functional properties of thin cast kafirin protein films

Improvement in the water stability and other related functional properties of thin (<50 μm) kafirin protein films was investigated. Thin conventional kafirin films and kafirin microparticle films were prepared by casting in acetic acid solution. Thin kafirin films cast from microparticles were more stable in water than conventional cast kafirin films. Treatment of kafirin microparticles with heat and transglutaminase resulted in slightly thicker films with reduced tensile strength. In contrast, glutaraldehyde treatment resulted in up to a 43% increase in film tensile strength. The films prepared from microparticles treated with glutaraldehyde were quite stable in ambient temperature water, despite the loss of plasticizer. This was probably due to the formation of covalent cross-linking between free amino groups of the kafirin polypeptides and carbonyl groups of the aldehyde. Thus, such thin glutaraldehyde-treated kafirin microparticle films appear to have good potential for use as biomaterials in aqueous applications.     

Sorghum Bran as a Potential Source of Kafirin

Sorghum bran, a coproduct of sorghum dry milling, could be a source of protein for industrial applications. Condensed tannin‐free red and white sorghum samples were decorticated by abrasion until ≈10 or 25% grain by weight was removed. Kafirin was then extracted from the milling fractions using an aqueous ethanol based solvent system. The brans were darker and considerably higher in protein and fat compared with the whole grain flours and decorticated grain flours, with the 25% bran having higher protein than the 10% bran. This is due to increased contamination of the bran with protein‐dense, corneous endosperm. The protein extracted from all the milling fractions, including the brans, was pure kafirin. However, the yield of kafirin from the brans (15.9–26.7% of total protein present) was somewhat lower than that from whole grain and decorticated grain flours (45.0–57.9% of total protein present), due to the fact that kafirin is located solely in the endosperm. Also, the kafirin from bran was more contaminated with fat, polyphenols, and other substances, and more highly colored, particularly the kafirin from red sorghum. Thus, sorghum bran could be used as a source of kafirin but further purification steps may be necessary.     

Effect of preparation conditions on protein secondary structure and biofilm formation of kafirin

Various extraction and drying conditions for the isolation of kafirin from dry-milled, whole grain sorghum have been investigated, with a view to optimizing extraction of the protein for commercial food coatings and packaging films. The addition of sodium hydroxide to an aqueous ethanol extractant increased the yield and solubility of kafirin. Subsequent heat drying at 40 degrees C was shown to cause the kafirin to aggregate as indicated by an increase in intermolecular beta-sheets. Extraction of the flour using ethanol (70%, w/w) with 0.5% (w/w) sodium metabisulfite and 0.35% (w/w) sodium hydroxide at 70 degrees C followed by freeze-drying of the protein was found to produce a yield of 54% kafirin with good film-forming properties. The kafirin films were assessed for their sensory properties, tensile strength, strain, and water vapor permeability. Fourier transform infrared spectroscopy was used to study the secondary structure of the extracted kafirins. The best films were made with kafirin containing a large proportion of nativelike alpha-helical structures with little intermolecular beta-sheet content as indicated by the Fourier transform infrared reflectance peak intensity ratios associated with these secondary structures. The principal factor affecting the secondary structure of the protein appeared to be the temperature at which the protein was dried. Heat drying resulted in a greater proportion of intermolecular beta-sheets. Any industrial-scale extraction must therefore minimize protein aggregation and maximize native alpha-helical structures to achieve optimal film quality.     

Drying temperature and relative humidity effects on wheat gluten film properties

The mechanical and physical properties of glycerol-plasticized wheat gluten films dried at different temperatures (20, 50, and 80 degrees C) and relative humidities (35 and 70% RH) were investigated. Dispersion of wheat gluten was prepared at pH 11 in aqueous solution. Films were obtained by casting the wheat gluten suspension, followed by solvent evaporation in a temperature and relative humidity controlled chamber. Decreasing relative humidity altered most of the mechanical properties. At 35% RH, tensile strength increased when drying temperature increased. However, at 70% RH, tensile strength decreased when temperature increased. Thickness of the films decreased by increasing temperature. Hypothetical coating strength increased with increasing drying temperature at 35% RH. However, at 70% RH, a maximum value was observed at 50 degrees C. Films produced at 80 degrees C exhibited low solubility in aqueous solution. Addition of 1.5% (w/v) sodium dodecyl sulfate increased solubility of all of the films except the film dried at 50 degrees C and 70% RH. Overall, drying temperature and relative humidity affected mechanical and physical properties of the wheat gluten films. However, the effect of drying temperature was more pronounced than the effect of relative humidity.     

Formulation and Characterization of Drug‐Loaded Microparticles Using Distillers Dried Grain Kafirin

Kafirin, a protein extracted from sorghum grain, has been formulated into microparticles and proposed for use as a delivery system owing to the resistance of kafirin to upper gastrointestinal digestion. However, extracting kafirin from sorghum distillers dried grains with solubles (DDGS) may be more efficient, because the carbohydrate component has been removed by fermentation. This study investigated the properties and use of kafirin extracted from DDGS to formulate microparticles. Prednisolone, an anti‐inflammatory drug that could benefit from a delayed and targeted delivery system to the colon, was loaded into DDGS kafirin microparticles by phase separation with sodium chloride. Scanning electron micrographs revealed that the empty and prednisolone‐loaded microparticles were round in shape and varied in size. Surface binding studies indicated prednisolone was loaded within the microparticles rather than being solely bound on the surface. These findings demonstrate DDGS kafirin can be formulated into microparticles and loaded with medication. Future studies could investigate the potential applications of DDGS kafirin microparticles as an orally administered targeted drug‐delivery system.     

Developments in the Science of Zein,Kafirin, and Gluten Protein Bioplastic Materials

Despite much research, there are very few commercial prolamin bioplastics. The major reason, apart from their high cost, is that they have inferior functional properties compared with synthetic polymer plastics. The inferior functional properties are because the prolamins are complex, each consisting of several classes and subclasses, and the functional properties of their bioplastics are greatly affected by water. Prolamin bioplastics are produced by controlled protein aggregation from a solvent or by thermoplastic processing. Recent research indicates that aggregation occurs by polypeptide self‐assembly into nanostructures. Protein secondary structure in terms of α‐helical and β‐sheet structure seems to play a key but incompletely understood role in assembly. Also, there is inadequate knowledge as to how these nanostructures further assemble and organize into the various forms of prolamin bioplastics such as films, fibers, microparticles, and scaffolds. Many methods have been investigated to improve prolamin bioplastic functionality, including better solvation of the prolamins, plasticization, physical and chemical cross‐linking, derivatization, and blending with synthetic and natural polymers, and some success has been achieved. The most promising area of commercialization is the biomedical field, in which the relative hydrophilicity, compatibility, and biodegradability of, particularly, zein and kafirin are advantageous. With regard to biomedical applications, “supramolecular design” of prolamin bioplastics through control over inter‐ and intramolecular weak interactions and disulfide/sulfhydryl interchange appears to have considerable potential.     

Preparation of High‐Quality Protein‐Based Extruded Pellets Expanded by Microwave Oven

The aim of this work was to study the effects of extrusion barrel temperature (75–140°C) and feed moisture (16–30%) on the production of third‐generation snacks expanded by microwave heating. A blend of potato starch (50%), quality protein maize (QPM) (35%), and soybean meal (SM) (15%) was used in the preparation of the snacks. A laboratory single extruder with a 1.5 × 20.0 × 100 mm die‐nozzle and a central composite routable experimental design were used. Expansion index (EI) and bulk density (BD) were measured in expanded pellets, viscosity at 83°C (V₈₃), thermal properties, and relative crystallinity were measured in extruded pellets. EI increased and BD decreased when the barrel temperature was increased, while the feed moisture effect was not significant. V₈₃ increased when feed moisture increased. Extrusion modified the crystalline structures of the pellets and the X‐ray data suggests the formation of new structures, probably due to the development of amylose‐lipid complexes. The maximum expansion of pellets was found at barrel temperatures of 123–140°C, and feed moisture of 24.5–30%. It is possible to obtain a functional third‐generation snack with good expansion characteristics using a microwave oven, and this snack has health benefits due to the addition of QPM and SM.     

Total Phenolics and Antioxidant Activity of Water and Ethanolic Extracts from Distillers Dried Grains with Solubles With or Without Microwave Irradiation

The purpose of this study was to determine the efficacy of extracting phenolic compounds with antioxidant activity from distillers' dried grains with solubles (DDGS) with water, 50% aqueous ethanol, and absolute ethanol, using microwave irradiation or a water bath at various temperatures. DDGS was extracted for 15 min with each solvent while heating at 23, 50, 100, and 150°C by microwave irradiation or in a water bath at 23, 50, and 100°C. Phenolic content of extracts increased with increasing temperature to a maximum of 12.02 mg/g in DDGS extracts that were microwave irradiated in water or with 50% aqueous ethanol at 150°C. Antioxidant activity range was 1.49–6.53 μmol of Trolox equivalents/g of DDGS. Highest antioxidant activities were obtained from 50% aqueous ethanol extracts at all temperatures, and water extracts that were heated at 100 and 150°C. These data indicate that DDGS extracts with high phenolic content and antioxidant activity can be obtained from DDGS, particularly with the use of water or 50% ethanol and high temperature (100 or 150°C). This may be valuable to ethanol manufacturers, livestock producers, and food and nutraceutical companies.     

Influence of Microwave Heating on Biological Activities and Electrophoretic Pattern of Albumin Fraction of Wheat Grain

Microwave treatment is a sufficiently alternative technique to be applied widely in food production and cereals protection against insect pests. Water‐soluble proteins were washed out from microwave‐heated wheat grain for the purpose of assaying the influence on biological activities, reducing sugars content, and SDS‐PAGE electrophoresis proteins patterns. The differences between microwave‐heated grain samples were verified by analysis of variance at the P ≤ 0.05 level of significance. Microwave heating of wheat grain within the temperature range of 28–98°C caused a decrease in water‐extractable proteins, statistically significant when grain temperature reached 79 and 98°C. Statistically significant increase in reducing sugars content was noted in grain samples heated only to 48°C; a decrease was noted above this temperature. All biological activities studied (amylolytic and inhibition activities against α‐amylases from insects (Sithophilus granarius L., Tribolium confusum Duv., Ephestia kuehniella Zell.), human saliva, hog pancreas, antitryptic activity) were distinctly diminished in grain samples heated to 79°C. At the highest grain temperature of 98°C, the loss of all biological activities were even more pronounced due to denaturation of ≈45% of extractable proteins. Among the wheat albumins studied by SDS‐PAGE, only eight and nine protein bands were detected in the grains heated to 98 and 28°C, respectively, whereas 12 bands were present in the control. The highest number of protein bands (13) was found in the grains heated to 48 and 64°C, respectively.     

Impacts of Kafirin Allelic Diversity,Starch Content,and Protein Digestibility on Ethanol Conversion Efficiency in Grain Sorghum

Seed protein and starch composition determine the efficiency of the fermentation process in the production of grain‐based ethanol. Sorghum, a highly water‐ and nutrient‐efficient plant, provides an alternative to fuel crops with greater irrigation and fertilizer requirements, such as maize. However, sorghum grain is generally less digestible because of extensive disulfide cross‐linking among sulfur‐rich storage proteins in the protein– starch matrix. Thus, the fine structure and composition of the seed endosperm directly impact grain end use, including fermentation performance. To test the hypothesis that kafirin (prolamin) seed storage proteins specifically influence the efficiency of ethanol production from sorghum, 10 diverse genetic lines with allelic variation in the β‐, γ‐, and (δ‐kafirins, including three β‐kafirin null mutants, were tested for ethanol yield and fermentation efficiency. Our selected lines showed wide variation in grain biochemical features, including total protein (9.96–16.47%), starch (65.52–74.29%), and free amino nitrogen (FAN) (32.84–73.51 mg/L). Total ethanol yield (ranging from 384 to 426 L/metric ton), was positively correlated to starch content (R² = 0.74), and there was a slight positive correlation between protein digestibility and ethanol yield (R² = 0.52). Increases in FAN content enhanced fermentation efficiency (R² = 0.65). The highest ethanol producer was elite staygreen breeding line B923296, and the line with the highest fermentation efficiency at the 72 h time point was inbred BT×623. A large‐seeded genotype, KS115, carrying a novel γ‐kafirin allele, was rich in FAN and exhibited excellent short‐term fermentation efficiency at 85.68% at the 20 h time point. However, the overall ethanol yield from this line was comparatively low at 384 L/metric ton, because of insufficient starch, low digestibility, and high crude protein. Multivariate analysis indicated an association between the β‐kafirin allele and variation in grain digestibility (P = 0.042) and FAN (P = 0.036), with subsequent effects on ethanol yield. Reversed‐phase HPLC profiling of the alcohol‐soluble kafirin protein fraction revealed diversity in protein content and composition across the lines, with similarities in peak distribution profiles among β‐kafirin null mutants compared with normal lines.     

Molecular structure, physicochemical characterization, and in vitro degradation of barley protein films

Barley protein films were prepared by thermopressing using glycerol as a plasticizer. The combined effects of heating temperature and amount of plasticizer interacted to determine protein conformation and, subsequently, the properties of the film matrix. The film barrier and mechanical properties were systematically investigated using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), SDS-PAGE, and protein solubility tests. These experiments demonstrated that heat treatment induced barley protein unfolding and then protein aggregation and the formation of covalent disulfide bonds to enhance film strength. Increasing the amount of plasticizer reduced protein denaturation and limited protein interactions, resulting in significantly improved film flexibility at the cost of reduced film moisture barrier property and tensile strength. In vitro degradation experiments demonstrated that barley films were resistant in gastric conditions, yet can still be completely degraded by intestinal enzymes, and they possess low cytotoxicity to Caco-2 cells. The prepared barley films have potential for development as delivery systems for gastric-sensitive bioactive compounds to the intestine for release.     

Effects of Boiling,Refrigerating, and Microwave Heating on Cooked Quality and Stability of Lipids in Macaroni Containing Ground Flaxseed

Research was conducted to determine the effects of boiling, refrigerating, and microwave heating on the cooked quality and stability of lipids in macaroni containing 15% (w/w) ground flaxseed. Boiling increased brightness but decreased redness and yellowness of macaroni containing ground flaxseed. Boiled macaroni and boiled‐refrigerated‐microwave heated (BRMH) macaroni had similar appearance. After boiling, cooking loss was lower and cooked firmness was greater for macaroni dried at ultra‐high temperature (90°C) than at low temperature (40°C). Macaroni fortified with ground flaxseed had lower cooking loss than did nonfortified macaroni. Firmness was greatest with boiled, intermediate with boiled‐refrigerated (BR), and least with BRMH macaroni. Cooking in boiling water reduced extractable lipid content of macaroni with flaxseed. Boiled‐refrigerated and BRMH macaroni with flaxseed had similar extractable lipid contents and were lower than that for boiled macaroni with flaxseed. Free fatty acid content was greatest with dried, intermediate with boiled, and least with BR and BRMH macaroni with flaxseed. Boiling, refrigerating, and microwave heating did not affect conjugated diene content in lipid extracted from macaroni with flaxseed, regardless of drying temperature.     

秸秆料包微波加热过程的温度分布的数值模拟

为深入了解微波加热过程,该文主要对秸秆料包微波加热过程的升温特性进行研究。将微波加热考虑成内热源,并使用Lambert定律对内热源分布进行简化计算,进而采用具有内热源形式的导热微分方程对微波加热过程中大尺寸物料内的温度分布进行了数值计算。最后,采用自制的微波加热装置,对秸秆料包微波加热过程中的温度分布进行了测量,并与模拟结果进行了对比。结果表明：数值模拟结果能较好地反映微波加热过程中大尺寸物料内部的温度分布,进而揭示大尺寸物料内部的传热规律。研究结果对微波热解装置的设计和优化,以及微波热解技术的推广利用有一定帮助。     

Desorption behavior of sorbed flavor compounds from packaging films with ethanol solution

Desorption behavior of sorbed flavor compounds such as ethyl esters, n-aldehydes, and n-alcohols from LDPE and PET films was investigated in 0 to 100% (v/v) ethanol solutions at 20 degrees C, 50 degrees C, and 60 degrees C. In both films, the desorption apparently increased with increasing ethanol concentration and treatment temperature, depending on the compatibility of the flavor compound with the solvent. Namely, the partition coefficient of ethyl esters, n-aldehydes, and n-alcohols in the LDPE film turned out to be approximately zero at >/=60%, >/=80%, and >/=40% (v/v) ethanol, respectively (for PET film, >/=80%, >/=80%, and >/=40% (v/v) ethanol concentrations were required for complete desorption, respectively). As for physical properties (heat of fusion, melting point, and tensile strength and elongation at break) of LDPE and PET films, there were no significant differences between intact film and the treated film with 60% (v/v) ethanol for 30 min at 60 degrees C. These results suggest that it is possible to apply a desorption solvent such as ethanol solution for desorption of sorbed flavor compounds from packaging films with no physical change in the film properties by this desorption treatment.     

微波技术在食品和农产品加工中应用研究进展

微波加热技术具有速度快、可控性高等特点,在食品和农产品的热加工过程中具有较强的应用潜力。该文在分析微波加热原理的基础上,从技术应用、设备研制和仿真研究等方面介绍微波加热应用现状,如在农产品干燥、杀菌、萃取和膨化等方面进行深入研究和应用。指出微波加热在机理解析、工艺局限性、加热不均匀性和能量利用低等问题,尤其是微波场对物料内极性成分作用机制的研究深度、微波加热时在物料内温度和水分分布的不均匀性规律定量表征等方面,严重影响产品质量稳定性和能量充分利用。从揭示微波在加热腔体内传递和物料内吸收的机理,提高微波加热均匀性和改善加工质量,以及研制智能化工业用微波加工设备等方面,指出微波加热技术在食品和农产品加工中应用热点研究方向。针对微波加热技术在农产品和食品加工中科学问题、技术需求和设备现状,为发挥技术优势、拓展应用领域,该文提出微波加热理论研究与技术应用的发展趋势,以期提高微波热加工技术工业化应用适用性、保证产品质量和能量利用率。