加工方式对木姜叶柯甜茶速溶粉稳定同位素指纹的影响

为了研究加工方式对甜茶速溶粉稳定同位素指纹的影响,进而验证δ¹³ C、δ¹⁵ N用于甜茶及其速溶粉产地溯源的可行性,本试验分别以烘箱烘干和微波杀青2种烘干方式制备甜茶老叶和嫩叶4种原料,采用热水浸提、离心并干燥(喷雾干燥和冷冻干燥)的方法制备甜茶速溶粉,得到喷雾干燥速溶粉(ITSD)、冷冻干燥速溶粉(ITFD)和速溶粉副产物(ITBP)三类加工样品,并采用元素分析-同位素比率质谱仪(EA-IRMS)测定样品中的δ¹³C、δ¹⁵N值。结果表明,不同产地(湖南、四川、江西)甜茶杀青嫩叶δ¹³C、δ¹⁵N值存在显著差异(P<0.05),烘箱烘干法与微波杀青法制得的原料茶δ¹⁵N值存在差异,且 δ¹³C、 δ¹⁵N值在速溶粉加工产品(原料、速溶粉及副产物)间存在显著差异(P<0.05),但不同烘干原料制备的所有样品δ¹³ C、δ¹⁵N值之间存在极显著相关(P<0.01)。本研究结果为基于δ¹³C、δ¹⁵N溯源指纹进行甜茶原料或速溶茶粉的产地溯源提供了理论依据。     

茶多酚对可食性马铃薯淀粉/海藻酸钠复合膜性能影响及表征

为探究茶多酚(TP)对淀粉基复合可食膜功能化改性效果,本试验以马铃薯淀粉和海藻酸钠(7:3,m:m)为成膜基质,甘油为增塑剂,TP为功能活性物质,通过溶液共混法制备马铃薯淀粉/海藻酸钠/茶多酚复合膜,考察不同质量分数TP对复合膜的物理性能、力学性能、阻湿性能、抗菌和抗氧化性等的影响。结果表明,当TP质量分数为5%时,复合膜的综合性能较好,且各项指标均显著高于空白对照组(P<0.05),此时抗张强度为20.78 MPa,断裂伸长率为24.33%,水蒸气透过系数为2.33×10^-12 g·cm^-1·s^-1·Pa^-1, 同时厚度为117.67 μm,总酚含量为7.95 mg GAE·g^-1,DPPH自由基清除率为84.47%,对金黄色葡萄球菌抑菌圈面积为502.15 mm²。本研究结果为TP在基于淀粉等可食性膜的功能化及其在食品包装方面的应用提供了一定的理论指导和数据参考。     

云南3种特色蜂蜜糖组分的稳定碳同位素比值测定与分析

为了研究云南3种特色蜂蜜的碳同位素分布规律,本试验采用元素分析-同位素比质谱法(EA-IRMS)和液相色谱-同位素比质谱法(LC-IRMS)对60份云南特色蜂蜜(苕子蜜、澳洲坚果蜜和橡胶蜜)的六项碳同位素比值,即果糖、葡萄糖、二糖、三糖、蜂蜜和蜂蜜蛋白的δ¹³C值进行了测定。对云南3种特色蜂蜜的六项碳同位素比值的分布区间、果糖与葡萄糖的差值(Δδ¹³C_{果糖-葡萄糖})、蛋白与蜂蜜的差值(Δδ¹³C_{蛋白-蜂蜜})、最大差值(Δδ¹³C_max)、果葡比(F/G)等参数进行了统计和偏最小二乘判别分析,并与现有蜂蜜掺假鉴别的指标进行了比对。结果表明,部分蜂蜜样品(占比20%)不满足现有评价标准(Δδ¹³C_max ≤±2.1‰)。通过构建偏最小二乘法判别分析(PLS-DA)模型可以实现3个蜜种的有效分类鉴别,主要差异性指标为三糖的δ¹³C值、三糖含量和二糖含量。本研究结果为特色蜂蜜的鉴别和品质评价提供了技术支撑,有利于促进云南乃至我国蜂蜜品质和质量的提升。     

添加适量丁香精油提高大豆分离蛋白膜性能

为探索新型生物膜材料的制备方法及抗菌、抗氧化活性,以大豆分离蛋白为成膜基质,添加适量的增塑剂和丁香精油成分,制备可食性复合膜。研究丁香精油添加对膜的物理性能、抗氧化活性和抗菌活性的影响。结果表明,当丁香精油添加量在0～2.0%时,随着添加比例的增加,复合膜的抗拉强度和透明度降低,断裂伸长率和透湿性升高;添加丁香精油显著提高了大豆分离蛋白膜的抗氧化活力(P0.05),具有很好的抑制肉中常见腐败菌和致病菌的效果,对革兰氏阳性菌单增李斯特菌和清酒乳杆菌的抑菌效果好于革兰氏阴性菌大肠杆菌和荧光假单胞菌,其中对单增李斯特菌抑菌效果最好。当丁香精油添加量为1.5%时,制备复合膜具有优良抗菌、抗氧化活性,且综合理化性能较佳。丁香精油可添加到大豆分离蛋白中制备具有抑菌抗氧化性能的可食性膜,此复合膜具有作为活性包装的潜力。     

我国有机茶稳定同位素特征与δ15N标识相关性研究

为探明我国有机茶稳定同位素分布情况及δ¹⁵N标识的相关因素,本研究收集了全国不同地区申请有机茶认证企业的145个样品,采用元素分析-稳定同位素比率质谱仪测定稳定同位素比率(δ¹³C、δ¹⁵N、δ²H、δ¹⁸O),结合单因素方差分析和正态分布模型探究稳定同位素特征分布规律。结果表明,有机茶样品δ¹³C分布于-31.0‰ ~ -23.7‰之间,不同产地间差异不显著。δ²H和δ¹⁸O范围分别为-107.1‰ ~ -24.8‰和17.2‰ ~ 32.0‰,均存在显著地域差异。我国有机茶δ¹⁵N正态分布范围为-4.6‰ ~ 7.0‰,平均值为1.2‰。其中有机茶生产面积大的地区样品δ¹⁵N范围为1.6‰ ~ 5.8‰,显著高于生产面积小的地区(-2.5‰ ~ 0.4‰,P<0.01),表明δ¹⁵N指标作为有机茶标识特征与产区生产面积之间存在一定的相关性。本研究为基于稳定同位素技术的有机茶真伪鉴别提供了研究基础,为有机茶的认证与监管提供了一定的理论依据。     

元素分析-同位素比值质谱法同时测定蔬菜中碳、氮同位素的前处理方法优化

为探究过筛目数和热风干燥对蔬菜中碳、氮同位素的影响规律,本试验在验证了基于CO₂稀释的元素分析-同位素比值质谱(EA-IRMS)法可靠性的基础上,研究了过筛目数(20、40、60、80、100、200目)、杀青(105℃,30 min)与未杀青处理、热风干燥温度(45、60、75℃)对6种蔬菜(菠菜、豇豆、韭菜、莲藕、茄子、马铃薯)δ¹³C、δ¹⁵N值的影响。结果表明,以89%CO₂稀释比例下EA-IRMS同时测定δ¹³C、δ¹⁵N值的标准偏差满足检测精度要求;当过筛目数超过80目时,6种蔬菜样品的δ¹³C、δ¹⁵N值均趋于稳定且达到测定精度要求;以真空冷冻干燥处理所测的δ¹³C、δ¹⁵N值为参照,采用不同热风干燥温度(45、60和75℃)处理的茄子、菠菜、莲藕和杀青后韭菜中δ¹³C、δ¹⁵N值均无显著差异,但未杀青的韭菜在45℃热风干燥后其δ¹³C、δ¹⁵N值与参照值之间有显著差异(P<0.05),且热风干燥处理的豇豆(δ¹³C和δ¹⁵N值)和马铃薯(δ¹³C值)与参照值相比也表现出不同程度的差异。因此,采用89%CO₂稀释比例下EA-IRMS法同时测定蔬菜中δ¹³C、δ¹⁵N值是可行的;蔬菜样品在进行碳、氮同位素测定前应以不低于80目的过筛处理。茄子、菠菜、莲藕和韭菜蔬菜样品在制备过程可采用热风干燥方式,其中韭菜需进行杀青处理,而豇豆、马铃薯则建议采用真空冷冻干燥方式。本研究为蔬菜样品中碳、氮同位素同时测定及样品制备提供了一定的参考。     

不同品种和生长期嘉宝果叶片酚类及挥发性物质研究

为研究不同品种和生长期嘉宝果叶片酚类及挥发性物质的含量和组成,分别通过比色法、水蒸气蒸馏法和顶空-气相色谱/质谱联用技术,对沙巴、四季早生、福冈等9个品种嘉宝果老/嫩叶的总酚、总黄酮、精油含量和挥发性成分进行测定。结果表明,沙巴嫩叶的总酚含量(31.87%)最高;阿根廷嫩叶总黄酮含量(24.81%)最高;沙巴老叶精油含量(2.78‰)最高,其次为沙巴嫩叶(2.42‰)。老叶中相对含量在0.05%以上的挥发性化合物有31~44种,均以萜类为主;嫩叶中相对含量在0.05%以上的化合物有28~40种,同样以萜类为主。除沙巴、阿根廷、大红钻老/嫩叶和福冈老叶外,其余老/嫩叶均以倍半萜为优势成分。沙巴老叶主要成分为α-蒎烯、桉叶油醇;沙巴嫩叶为β-蒎烯和α-蒎烯;阿根廷老/嫩叶、大红钻嫩叶和白艾斯老叶为β-蒎烯;福冈老/嫩叶为β-石竹烯;四季早生、大巨红晶、艾斯卡老/嫩叶为β-胡椒烯;乔尼尔老/嫩叶为β-石竹烯、β-胡椒烯。主成分分析结果表明,单萜含氧衍生物、α-蒎烯、单萜烯、β-蒎烯、α-芹子烯是导致不同品种间嘉宝果老叶香气差异的主要物质;倍半萜烯、单萜烯、β-蒎烯、α-蒎烯、β-石竹烯是导致不同品种间嘉宝果嫩叶香气差异的主要物质。综上,沙巴嫩叶总酚含量最高,精油含量较高,活性挥发性物质蒎烯(α-蒎烯+β-蒎烯)相对含量高达62.41%,在抗菌、抗炎、抗氧化、抗肿瘤等方面有潜在的利用价值,在医药领域有极大的研究价值和开发潜力。     

黑布林籽β-葡萄糖苷酶聚合物的制备与稳定性研究

为探究β-葡萄糖苷酶聚合物的制备方法及其稳定性,以黑布林籽β-葡萄糖苷酶为原料制备交联酶聚合物(CLEAs),优化了制备过程中沉降剂的种类及比例、戊二醛交联剂的浓度等工艺参数,并采用扫描电镜分析其表面结构特征;在此基础上,以红景天苷的酶促合成为模型反应,研究CLEAs在有机溶剂中的热稳定性和操作稳定性。结果表明,制备β-葡萄糖苷酶CLEAs的最佳沉降剂为95%乙醇,其适宜添加量为酶液体积的3倍;戊二醛交联剂的最适浓度为30 mmol·L^-1,交联时间为1.0 h,酶活回收率高达91.4%。扫描电镜结果表明,在此条件下制备的CLEAs有较大的比表面积和致密的多孔道结构。稳定性结果表明,将β-葡萄糖苷酶CLEAs在60℃下保温2.0 h,其酶活回收率为75.1%,是游离酶的6.1倍;重复使用8次后,仍保持73.5%的初始酶活性。综上,黑布林籽β-葡萄糖苷酶CLEAs具有良好的生物催化活性、热稳定性和操作稳定性,可用于糖苷类化合物的高效合成。本研究为β-葡萄糖苷酶CLEAs的研究提供了理论依据,对工业化生产具有现实意义。     

不同产地羊肉稳定同位素特征差异及其溯源应用

为了探讨稳定同位素碳、氮、氧、氢对羊肉产地溯源的可行性,本研究分别从内蒙古、新疆、宁夏、新西兰、意大利5个地区采集羊肉样品,利用稳定同位素比率质谱仪(IRMS)测定脱脂羊肉的碳、氮、氧、氢稳定同位素比值(δ¹³C、δ¹⁵N、δ²H、δ¹⁸O),结合多元统计学方法对不同地区间脱脂羊肉的δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值组成特征及变化规律进行分析。结果表明,δ¹³C值在5个地区间均存在显著性差异,而δ¹⁵N值和δ¹⁸O值除了在新西兰和意大利2个地区差异不显著外,在其他地区差异均显著;δ²H值仅在宁夏和新疆地区间以及内蒙古和新西兰地区间差异不显著。结合Fisher判别分析发现,利用δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值可以实现对羊肉产地区分,且利用δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值组合指标对羊肉产地的初始判别的整体正确率和交叉验证的整体判别正确率均达100%。本研究结果为δ¹³C、δ¹⁵N、δ²H、δ¹⁸O值在羊肉产地溯源中的应用提供了参考。     

样本干燥方法对甜瓜稳定同位素分析及产地溯源的影响

为了评估制样方法对高含糖量甜瓜样本轻稳定同位素分析的影响,本研究以甜瓜果皮、果肉匀浆样本为材料,分别采用热风喷粉干燥、真空冷冻干燥(-80℃,24 h)、真空微波干燥(2 min)、真空直接烘干(60℃,24 h)制备干燥样本,所有样本研磨制备精细粉末用于碳、氮、氢、氧稳定同位素比率(δ¹³C、δ¹⁵N、δ²H、δ¹⁸O)分析。对比4种方式制备样本在低温(-20℃)干燥箱存储60 d内重复测定结果的稳定性。结果表明,4种方式制备的高糖甜瓜果肉精细粉末极易吸湿潮解而干扰其δ²H、δ¹⁸O的测定,存储期长时样本值差异显著(P<0.05)。其中,真空冷冻干燥方式制备的瓜皮样本4种稳定同位素比率测定结果更稳定。真空冷冻干燥方式制样更易将甜瓜组织细胞壁破解后剩余的水分完全干燥,精细粉末样本在储藏过程中表现得更稳定,在不同储藏期的检测结果一致性高。通过对真空冷冻干燥方式制样的果皮样本稳定同位素比率进行偏最小二乘判别分析(PLS-DA)建模,区分新疆、广西、海南3个产地的58份甜瓜样本,判别准确度分别为100%、98.7%、89.1%。结果证明,真空冷冻干燥制备甜瓜果皮稳定同位素分析可以作为其产地确证的可靠方法,溯源模型可用于确证甜瓜原产地标签标识、保护地理标志产品。本研究为提升甜瓜产地溯源提供了新策略。     

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.     

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.     

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.     

Transgenic sorghum with altered kafirin synthesis: kafirin solubility, polymerization, and protein digestion

Transgenic sorghum (TG) lines with altered kafirin synthesis, particularly suppression of γ-kafirin synthesis, and improved protein quality have been developed. The proportion of kafirin extracted with 60% tert-butyl alcohol alone was greatly increased in the TG lines. However, the total amount of kafirin remained unchanged. Further, in the TG lines, the kafirin was much less polymerized by disulfide bonding. There was also evidence of compensatory synthesis of other kafirin proteins. Cooked protein digestibility was increased in the TG form, even after removal of interfering starch. The TG protein bodies were intermediate in appearance between the normal type and the invaginated high digestibility mutants. Hence, the increased protein digestibility of these TG lines is probably related to their lower levels of disulfide-bonded kafirin polymerization, allowing better access of proteases. This work appears to confirm that disulfide bond formation in kafirin is responsible for the reduced protein digestibility of cooked sorghum.     

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.     

氨基酸对明胶膜结构及性能的影响

为了探索氨基酸作为明胶膜增塑剂的潜力,本试验研究了不同氨基酸(脯氨酸、亮氨酸、谷氨酸、丝氨酸和甲硫氨酸)对明胶膜厚度、机械性能、水蒸气透过率、透光率、颜色以及结构等的影响。结果表明,与对照组相比,除了甲硫氨酸外,其余的氨基酸都能增加明胶膜柔韧性;除了脯氨酸外,其余的氨基酸都增加了明胶膜的黄度值,并降低了明胶膜透光率和透明度;而添加脯氨酸的明胶膜的柔韧性最好、具有更好的表观特征,表面光滑紧致,同时具有更高的透明度、透光率和柔韧性。根据傅里叶变换红外光谱和二级结构分析发现,添加脯氨酸、丝氨酸和甲硫氨酸能通过氢键与明胶相互作用,降低明胶的无规则卷曲结构含量,增加β-折叠和β-转角结构含量。综合分析认为,脯氨酸可以作为明胶膜的天然增塑剂。本研究结果为增塑剂在明胶膜中的应用提供了新视角。     

柚子皮基可食性膜的制备及性能研究

为了促进果蔬加工副产物的高附加值利用,以柚子皮干粉为材料,海藻酸钠为增稠剂,甘油为增塑剂,采用流延法制备了柚子皮基可食性膜,分析柚子皮干粉质量分数、海藻酸钠、甘油质量分数对柚子皮基膜力学性能、阻湿性能和透光率等的影响,并对柚子皮基膜的制备配方进行优化。结果表明,柚子皮基膜的最佳制备配方为:柚子皮干粉质量分数3%、海藻酸钠质量分数0.15%(以柚子皮粉浆料质量为基础,下同)、甘油质量分数0.5%,此配方制备的柚子皮基膜外观平滑、颜色淡黄,具有较好的综合性能,其拉伸强度为17.53±0.35 MPa,断裂伸长率为19.46%±0.43%,水蒸气透过系数为(2.327±0.128)×10^-12g·cm^-1·s^-1·Pa^-1,透光率为63.2%±0.15%。本研究结果为柚子皮基可食性膜在食品包装等领域的应用提供了理论参考。     

pH值和温度对燕麦蛋白溶解与聚集特性的影响

为研究燕麦蛋白的理化性质,本研究采用碱提酸沉法提取燕麦蛋白,并分析不同pH值与温度对燕麦蛋白溶解性、ζ-电位和粒径分布的影响。结果表明,在等电点附近(pH值5.0),燕麦蛋白的表面电荷数最低,蛋白粒度较大,溶解性和乳化性较低。当pH值远离等电点时,燕麦蛋白的表面电荷增加,蛋白粒度逐渐减小,溶解度升高,乳化性也随之升高;随着温度升高(55~95℃),燕麦蛋白聚集体解离,粒度变小,溶解度增加,稳定性变好;温度进一步升高(121、130℃),燕麦蛋白重新聚集形成粒径较大的聚集体,溶解度降低,稳定性变差。本研究结果为燕麦蛋白资源的利用提供了重要的理论指导。