高直链玉米淀粉/羟丙基甲基纤维素可食性膜的制备及性能研究

以高直链玉米淀粉(HACS)和羟丙基甲基纤维素(HPMC)为主要成膜基材,采用溶液流延法制备了HACS/HPMC可食性膜。研究了不同配比的HACS与HPMC对可食性膜的结晶性能、力学性能、亲水性能和水蒸气阻隔性能等的影响。结果表明,随着HPMC比例的增大,HACS与HPMC之间的氢键作用减弱,复合膜的水溶性增大,连续相由HACS转变为HPMC,但HACS与HPMC的相容性变差。HPMC可有效降低可食性膜的结晶程度并抑制其在储藏过程中的老化。在复合膜中,当HACS与HPMC比例为8∶2时,可食性膜具有最大抗拉强度(7.5 MPa)、断裂伸长率(14.7%)、水接触角(84.33°)和最低水蒸气透过系数(2.17×10~(-10 )g·m·m~(-2)·s~(-1)·Pa~(-1))。纯HACS膜和纯HPMC膜的透光性能均优于HACS/HPMC复合膜。     

Technical Note: A Method to Quantify Prolamin Proteins in Corn That Are Negatively Related to Starch Digestibility in Ruminants

Compared with floury or high-moisture corns, dry corn with a greater percentage of vitreous endosperm has been demonstrated to be negatively related to starch digestibility and milk yield of lactating dairy cows. Starch granules in corn are encapsulated by hydrophobic prolamin proteins that are innately insoluble in the rumen environment. Corn prolamin proteins are named zein, and laboratory methods to quantify zein exist but are seldom employed in ruminant nutrition because of their arduous nature. In this study, advances in cereal chemistry were combined with rapid turbidimetric methods yielding a modified turbidimetric zein method (mTZM) to quantify zein in whole corn. Ten dry corns containing unique endosperms were evaluated using the mTZM. Corns with flint, dent, floury, or opaque endosperms were found to contain 19.3, 11.3, 5.8, and 4.9 g of zein/100 g of starch, respectively. The ability of mTZM to differentiate corn endosperm types as defined by least significant difference was 2.6 g of zein/100 g of starch. Ten high-moisture corns of varying moisture content were also evaluated using the mTZM. Zein content of high-moisture corns as defined by mTZM ranged from 8.3 to 2.8 g of zein/100 g of starch with a least significant difference of 1.2 g of zein/100 g of starch. The mTZM determined that zein contents of high-moisture, floury, and opaque corns were markedly less than those of flint and dent dry corns, indicating that mTZM has the ability to quantify starch granule encapsulation by hydrophobic prolamin proteins in whole corn.     

Heat-moisture treatment of high-amylose corn starch increases dietary fiber content and lowers plasma cholesterol in ovariectomized rats

ABSTRACT:  The effect of dietary high-amylose corn starch (HACS) of varying dietary fiber (DF) content on plasma cholesterol was examined in ovariectomized (OVX) rats. Gelatinized normal corn starch (G-CS) was used as a reference. OVX rats were fed a fiber-free purified diet containing G-CS, HACS, gelatinized high-amylose corn starch (G-HACS), or heat-moisture treated HACS (HM-HACS) at 400 g starch/kg diet for 21 d. The DF content of G-CS, HACS, G-HACS, and HM-HACS measured by the AOAC method was 0.1, 19.3, 2.4, and 64.5 g/100 g, respectively. The dry weight of cecal contents, cecal wall weight, the amount of short chain fatty acids in cecal contents, the amount of bile acids in small intestinal contents, and fecal excretion of neutral sterols increased logarithmically with increasing DF, while total plasma cholesterol concentration decreased. On the other hand, hepatic CYP7A1 activity, fecal dry weight, and fecal excretion of bile acids increased linearly with increasing DF, while body weight gain decreased. The hypocholesterolemic effect of HACS in OVX-rats appeared to be more effective by heat-moisture treatment.     

复合增塑剂对玉米醇溶蛋白膜性能的影响

以木糖醇和甘油为复合增塑剂制备出木糖醇/甘油/玉米醇溶蛋白膜。通过TGA、扫描电镜、红外光谱及电子织物强力机研究玉米醇溶蛋白膜的热性能、微观结构及力学性能。结果表明:在160℃之前膜性能稳定,与纯玉米醇溶蛋白膜相比,添加复合增塑剂后玉米醇溶蛋白膜表面产生了多孔结构,随木糖醇含量增加孔洞结构有增大的趋势,抗拉强度略有下降,伸长率有所提高。     

两种分子量的海藻酸钠对高直链玉米淀粉物化性质的影响

为探讨海藻酸钠及其分子量(AGNa)对高直链玉米淀粉(HACS)物化性质的影响,采用快速黏度分析仪(RVA)、差示扫描量热仪(DSC)、动态流变仪、物性测定仪(TA)等,研究了不同分子量的海藻酸钠-高直链玉米淀粉复合体系(AGNa-HACS)的糊化、凝胶及老化性质。结果表明,随着AGNa分子量的增加,其本身的黏度与亲水的能力增加,导致AGNa-HACS的稠度增加。分子量较低的AGNa易与HACS发生相互作用,使HACS糊化能耗增加,抑制HACS的短期老化。分子量较高的AGNa对HACS的增稠作用更为显著,有利于维持HACS淀粉糊的均一稳定,提高HACS的热稳定性,抑制HACS的长期老化。     

玉米皮油提取及其理化指标的分析研究

为了开发和利用玉米皮资源,对玉米皮的营养成分以及玉米皮油的理化指标和脂肪酸组成及甘三酯组成进行了分析测定。结果表明,玉米皮粗脂肪含量为5.99%,粗蛋白质4.86%,粗纤维含量为12.45%;玉米皮油富含不饱和脂肪酸,含量高达80%以上,玉米皮油的理化指标为相对密度d2400.9135,碘值112.4 gI/100 g,皂化值189.1 mgKOH/g,不皂化物3.75%。     

Effect of plasticizing sugars on rheological and thermal properties of zein resins and mechanical properties of zein films

Zein is the most important protein in corn. Zein has good film forming properties. One of the film forming methods is production of zein resin and then thermomolding by hot press. Pure zein film is very brittle. Plasticizers can improve mechanical and film making properties of zein. In this research, sugars (fructose, galactose and glucose) were used as plasticizers and rheological properties of zein resin were studied by dynamic oscillatory tests for determination of plasticization effectiveness. Effect of plasticizers on thermal properties of resins was investigated by DSC at −100 to 150 °C. No crystallization and melting peaks related to zein and plasticizers were observed. As well as there was not significant difference at glass transition temperature between zein resins containing various sugars. Zein films were prepared from zein resins by rolling and hot press and then mechanical properties of films were measured. Films containing galactose had better tensile properties than other films and showed higher tensile strength, strain at break, and Young modulus than films containing fructose and glucose.     

玉米-小麦淀粉/玉米醇溶蛋白双层膜热学及微观特性

研究了玉米-小麦淀粉成膜液与玉米醇溶蛋白成膜液不同配比制作的5 种可食用复合膜理化特性的差异, 并分别通过扫描电子显微镜观察、热重分析、差示扫描量热分析、X射线衍射分析、傅里叶变换红外光谱分析对其 热学特性和微观结构进行研究。结果表明：添加一层玉米醇溶蛋白后,双层膜阻水性提高,机械性能得到改善,由 扫描电子显微镜观察结果可知双层膜间结合紧密,热重分析和差示扫描量热分析结果显示双层膜热稳定性得到提 高,X射线衍射结果表明生物大分子之间相容性较好,傅里叶变换红外光谱分析结果发现双层膜间产生了新的氢键 等作用力,为玉米-小麦淀粉/玉米醇溶蛋白双层膜在食品包装中的应用提供了重要的参考依据。     

Development of Antioxidant Packaging Material by Applying Corn‐Zein to LLDPE Film in Combination with Phenolic Compounds

Abstract: Functional active packaging materials were successfully developed by incorporating antioxidant agents into corn‐zein‐laminated linear low‐density polyethylene (LLDPE) film. The minimum effective concentrations of the active compounds (for example, thymol, carvacrol, eugenol) were determined and these compounds were then laminated into LLDPE films to develop corn‐zein‐laminated films with antioxidant agents. The release rate of antioxidant agents in gas and liquid media were determined along with the mechanical and water barrier properties of the films containing these compounds. Tensile strength and percentage elongation at break were reduced in the corn‐zein‐laminated LLDPE films when compared to typical LLDPE film. Furthermore, the ability of the corn‐zein‐laminated films to repel moisture decreased by approximately 12.2%, but was improved by incorporating hydrophobic antioxidant compounds in the corn‐zein layer. Examination of release kinetics in the gas and liquid phases verified that antioxidants were effectively released from the films and inhibited oxidation during testing. Finally, the films were used for fresh ground beef packaging, and effectively inhibited lipid oxidation and had a positive effect on the color stability of beef patties during storage. These results indicate that the developed antioxidant films are a novel active packaging material that can be effectively implemented by the food industry to improve the quality and safety of foods. Practical Application: Zein protein, a by‐product of corn processing industry, was laminated into plastic films in combination with natural phenolic compounds to develop antioxidant packaging films. The films demonstrated their efficient release patterns of antioxidant compounds, which are suitable for packaging applications and food protection.     

Corn Zein Packaging Materials for Cooked Turkey

Mechanical and barrier properties of corn zein films with butylated hydroxyanisole (BHA), bacterial enzyme, and emulsifier additives were investigated and compared to those of polyvinylidine chloride (PVDC) films. No significant differences (P < 0.05) occurred in elongation, tensile strength, or Young's modulus among corn zein films. PVDC had the lowest apparent water vapor permeability (WVP_app), and no significant differences in WVP_app were found between zein films and PVDC. Cooked turkey breast was packaged, evaluated by a trained sensory panel, and analyzed for hexanal content. Turkey breast wrapped in corn zein film with antioxidant and emulsifier had lower hexanal content than samples packaged in PVDC.     

甘油与甲基纤维素对高直链玉米淀粉- 壳聚糖复合膜性能的影响

以高直链玉米淀粉(HACS)和壳聚糖(CS)为基本材料,甘油为增塑剂,甲基纤维素(MC)为增强剂制备可食性复合膜,研究高直链玉米淀粉与壳聚糖的质量比,甘油的添加量以及甲基纤维素的添加量对复合膜物理性能的影响,包括抗拉强度(TS)、断裂伸长率(E)、水蒸气透过系数(WVP)和色度。结果表明,壳聚糖添加量的增大与甘油添加量的增加都使高直链玉米淀粉- 壳聚糖复合膜的抗拉强度降低,断裂伸长率和WVP 显著增大,膜颜色变黄;甲基纤维素的添加改善了复合膜的机械性能和WVP,随着甲基纤维素添加量的增加,复合膜的抗拉强度和断裂伸长率都随之增大,WVP 逐渐降低,且对膜的颜色没有显著影响。     

玉米后熟期间醇溶蛋白结构和理化特性

将新采收的玉米在温度15 ℃及25 ℃、相对湿度55%条件下进行恒温恒湿贮藏,研究玉米后熟期间玉米醇溶蛋白结构特征及理化特性,并分析二者之间的构效关系。结果发现,玉米在15 ℃及25 ℃后熟56 d期间内,玉米醇溶蛋白的游离巯基含量降低,二硫键含量升高,表面疏水性降低,Zeta电位的绝对值增加,粒径和分散指数降低。玉米后熟期间玉米醇溶蛋白中氢键缔合下降,更多有序的β-折叠转化至无序结构,且后熟作用导致玉米醇溶蛋白热稳定性和α-玉米醇溶蛋白亚基的分子质量降低。此外,玉米后熟显著改变了蛋白的理化特性,在15 ℃后熟42 d和25 ℃后熟28 d,玉米醇溶蛋白的溶解性和持水性均达到最大,在2 个温度下后熟14 d时乳化活性和起泡性均显著增加,而后熟作用导致持油性下降。玉米后熟过程中玉米醇溶蛋白理化特性的改善可能与蛋白质聚集程度降低及其柔性结构相关。结果表明,适当的玉米后熟能够修饰玉米醇溶蛋白结构,进而改善其理化特性。     

The effect of chemically‐modified resistant starch,RS type‐4, on body weight and blood lipid profiles of high fat diet‐induced obese mice

This study was conducted to investigate the effects of feeding chemically‐modified resistant starch type‐4 (RS4) of normal (NCS) and high‐amylose corn starch (HACS) on weight gain and plasma and liver lipid profiles of mice fed a high‐fat diet (HFD). The experimental four groups were, respectively, fed following diets: A 40% HFD with NCS, HACS, NCS‐ and HACS‐RS4. A normal diet (ND) group of mice fed the standard diet was also used as control. In order to produce RS4 by chemical modification, corn starches were treated with STMP/STPP. Total RS (TRS) and total dietary fiber (TDF) levels of chemically‐modified NCS were 26.4 and 44.0%, respectively, while TRS and TDF levels in chemically‐modified HACS were 78.1 and 78.5%, respectively. Onset gelatinization temperatures of both modified corn starches clearly shifted to higher temperatures after STMP/STPP treatment. At the end of the diet trial, the mice on the HACS diet decreased body weight gain compared to the NCS‐fed mice. Adding NCS‐ and HACS‐RS4 to the diet significantly reduced the weight gain relative to NCS and HACS groups. Both RS4 diets were effective in improving the lipid profile compared to their respective controls. They significantly reduced the level of total lipid and total cholesterol.     

Effect of plasticizing sugars on water vapor permeability, surface energy and microstructure properties of zein films

Sugars are natural plasticizers for food biopolymers and zein is the most important protein of corn. In this research, sugars (fructose, galactose and glucose) were used as plasticizers and the water vapor permeability (WVP), contact angle and microstructure of the zein films were studied. The pure zein film had high WVP and adding of sugars to 0.7 g/g zein caused to decrease of WVP. Films containing galactose had the lowest WVP.All samples had the lowest contact angle with ethanol and the highest contact angle with water. The zein films containing galactose had the highest water contact angle within the plasticized films. The pure zein films and the films containing fructose had higher critical surface tension of wetting (γ_c) than the films containing glucose and galactose. Adding sugar plasticizer to zein films increased the surface tension of zein films. In the unplasticized zein films, loose structures with a lot of cavities and voids were observed. The films plasticized by fructose had smooth surface and plasticizer particles distributed throughout of the films.     

高直链玉米淀粉复合膜的应用特性及其对荷兰豆的保鲜研究

以高直链玉米淀粉(HACS)、壳聚糖(CS)和甲基纤维素(MC)为原料制备可食性复合膜,研究了HACS/CS质量配比分别为1∶0、2∶1、1∶1、1∶2及0∶1,MC添加量(占干基淀粉)分别为0%、2%、4%、6%及8%时的成膜性能,并从中选取HACS/CS质量比为2∶1、1∶2、1∶1添加8%MC的3种膜进行荷兰豆保鲜实验。结果表明:3种膜均能有效降低荷兰豆的失重率和霉变率,减缓叶绿素和Vc的损失。其中,质量比HACS/CS为2∶1的膜,综合保鲜效果最好。     

有机酸改性对玉米醇溶蛋白膜机械性能的影响

玉米醇溶蛋白成膜性好,然而其膜机械性能差,影响了它的实际应用效果。改性是弥补这一缺点的有效手段。选用乙酸、乳酸、琥珀酸、苹果酸、酒石酸与柠檬酸6种有机酸来对玉米醇溶蛋白改性,结果表明:在玉米醇溶蛋白含量为0.1 g/mL;乙醇体积分数90%;羧酸添加量0.03 g/mL;加碱改性溶液pH 5.0;反应温度60℃;反应时间30 min条件下,无碱苹果酸改性膜延展率达到(228.17±26.53)%,相比对照组提升154%,而其抗拉强度仅为(0.70±0.05)MPa。碱催化柠檬酸改性膜抗拉强度由(7.18±0.54)MPa提升至(12.73±1.05)MPa,延展率为(3.65±0.21)%,与对照组差距不大。经改性后的玉米醇溶蛋白膜机械性能良好,不仅为它在食品保藏方向的应用打下基础,而且有利于我国玉米产业链的延伸,促进产业成熟。     

油酸与甘油对玉米醇溶蛋白膜机械性能的影响及机理探讨

主要研究了两种性质不同的增塑剂(油酸和甘油)对玉米醇溶蛋白(zein)膜机械性能的影响和可能的机理,以抗拉伸强度(TS)、伸长率(E)、透水率(WVP)为指标,结果发现油酸和甘油都能显著改善zein膜的机械性能,且添加量都以20%(g/g zein)最优;复合增塑研究发现,当添加20%混合增塑液对zein膜进行增塑时,以油酸∶甘油为3∶1复合增塑的效果最好,其中与未增塑的zein膜相比,TS提高190%,E提高70%。进一步统计学分析表明,油酸与甘油在对zein膜增塑时有正协同作用。对未增塑、20%油酸增塑、20%甘油增塑及20%复合增塑(油酸∶甘油为3∶1)zein膜的玻璃态转化温度(Tg)及红外光谱(FT-IR)分析发现,增塑后的zein膜Tg有所下降,其中复合增塑降幅最大;FT-IR图谱分析发现,复合增塑时甘油的特征峰向高波长方向移动,显示增塑作用加强;蛋白二级结构分析发现,复合增塑后,二级结构虽有小幅改变,但并未达到显著水平,因此增塑剂与zein之间的非共价键相互作用(疏水力和氢键)可能是其增塑的化学基础。     

Characterization of Residues from Partially Hydrolyzed Potato and High Amylose Corn Starches by Pancreatic α‐Amylase

High amylose corn starch (HACS) and potato starch were hydrolyzed by pancreatic α‐amylase in vitro. Residues after hydrolysis were collected and characterized for their physicochemical properties and molecular structure. Compared with raw starches, residues had lower apparent amylose contents and higher resistant starch contents. The gelatinization enthalpy of residues from HACS increased while enthalpy of residues from potato starch decreased from 15.4 to 11.3 J/g. Peak viscosity and breakdown values of the residues from potato starch were markedly decreased but final viscosity values did not show much change. Chain length distribution of debranched amylopectin from the residues indicated that the relative portion of short chain in the residue decreased for both starches. More molecules with intermediate chain length (DP 16—31) were found in residue after 48‐h hydrolysis of potato starch.     

Influence of ensiling time and inoculation on alteration of the starch-protein matrix in high-moisture corn

The fates of hydrophobic zein proteins, which encapsulate corn starch to create vitreous endosperm, have not been investigated in high-moisture corn (HMC). To assess influences of ensiling time and inoculation on zein proteins in HMC, quadruplicate samples of 2 random corn hybrids (A and B), containing 25.7 and 29.3% moisture, were ground, inoculated with (I) or without 600,000 cfu/g of Lactobacillus buchneri 40788 (Lallemand Animal Nutrition, Milwaukee, WI), and ensiled for 0, 15, 30, 60, 120, and 240 d. Nutrient composition [crude protein (CP), starch, acid detergent fiber, and neutral detergent fiber], fermentation (pH, lactate, and acetate), and protein degradation markers (buffer-soluble CP, isopropanol-soluble CP, and NH₃-N) were evaluated. At 0 and 240 d, α, γ, δ, and β zein subunits were profiled using HPLC. Data were evaluated as a split-split plot using the PROC MIXED procedures of SAS. Ensiling time and inoculation decreased pH, and altered lactate and acetate contents of HMC. Lactate and acetate contents of A, AI, B, and BI at 240 d were 0.40, 0.32, 1.11, 0.73, and 0, 0.35, 0.30, and 0.87% of DM, respectively. Buffer-soluble CP in HMC increased from 1.5 to 2.0% of DM at 0 d to >4.0% of DM at 240 d. Inoculation had no effect on buffer-soluble CP but increased NH₃-N content of HMC. Corn A contained more isopropanol-soluble CP than did corn B and peak areas for 6 α, and all γ and δ zein regions were greater for corn A. Ensiling (0 vs. 240 d) decreased all zein subunits with the exception of 2 α and 1 δ subunit. Ensiling decreased (42.2-73.2%) γ zeins, which are primarily responsible for cross-linking in the starch-protein matrix. Despite altering lactate and acetate contents, inoculation had no effect on degrading hydrophobic zein proteins in HMC. Data suggest that hydrophobic zein proteins in the starch-protein matrix of HMC are degraded by proteolytic activity over an extended ensiling time.     

Mechanical and microstructural properties of soy protein – high amylose corn starch extrudates in relation to physiochemical changes of starch during extrusion

Mechanical and microstructural properties of expanded extrudates prepared from blends of high amylose corn (Zeamays L. ssp. Mays) starch (HACS) and soy protein concentrate (SPC) were studied in relation to the physicochemical changes in starch. Effects of screw speed (230 and 330 rpm) and SPC level (10%, 20%, 30% and 50%) on expansion and mechanical properties were determined. Compared with 230 rpm, screw speed at 330 rpm resulted in increased specific mechanical energy, expansion ratio, water absorption and water solubility indices and decreased bulk density and piece density. Varying screw speeds did not significantly affect the mechanical strength of extrudates or starch molecular weight distribution. Bulk and piece densities, and water absorption index (WAI) only slightly increased or exhibited no significant trends as SPC level increased to 20%. A substantial increase in bulk and piece densities and decrease in expansion ratio and WAI were observed as SPC level increased from 20% to 30%. The trends were either reversed or moderated as SPC increased to 50%. These results in combination with average crushing force and water solubility index data provided a significant insight into the interactions between HACS and SPC during extrusion processing. As compared to an earlier baseline study by our research group on normal corn starch – SPC extrudates, results from the current study indicated that the expansion of extrudate containing HACS alone was lower than that of extrudates containing normal corn starch. However, expansion of the HACS–SPC blends was not significantly impacted at 10–20% SPC levels, whereas the expansion of normal corn starch was significantly reduced.