Conformational changes induced by high-pressure homogenization inhibit myosin filament formation in low ionic strength solutions

Myofibrillar proteins (MPs) of chicken breast are generally insoluble in water. We have developed a new method whereby MPs are solubilized in water by applying high-pressure homogenization (HPH) thus potentially enabling greater utilization of meat in various products. To clarify the mechanism of solubilization of MPs by HPH, we investigated their conformation, solubility and filament forming behavior in low ionic strength solutions induced by 15,000 psi HPH (103 MPa). HPH induces unfolding of MPs which subsequently exposes sulfhydryl and hydrophobic groups to the surface. Our findings, determined by circular dichroism, ATR-FTIR, SDS-PAGE and LC-ESI-MS/MS analysis suggest that HPH leads to unraveling of helical structures and to formation of myosin oligomers through disulfide bond. Due to intermolecular electrostatic repulsion and physical barrier of disulfide bonds in the rod induced by HPH, we suggest that the altered myosin conformation in MPs inhibits filament formation, thus contributing to high solubility of MPs in water.     

Emulsion-forming properties of heat-induced pork myofibrillar protein affected by NaCl

The emulsification characteristics of myofibrillar proteins (MPs) with different NaCl concentrations also affect the quality of meat products after cooking. We investigated the effects of heating (100 °C) on the solubility, emulsifying activity, and conformational and environmental changes of MPs prepared with different NaCl concentrations. Emulsifying activity increased with increasing NaCl prior to heating, but there was no significant effect after heating. The viscosity increased and particle size decreased with increasing NaCl before heating, but these properties did not change after heating. NaCl did not affect the amount of α-helix and β-sheet. We deduced that the different emulsifying activity of myofibrillar proteins with different NaCl concentrations after heating may have been due to changes in the local environment of MPs. An understanding of the physicochemical and functional properties of MPs would unlock an area for development of meat products at different NaCl and temperature in the food industry.     

紫苏叶对红曲菌产色素和莫纳可林K及抗氧化物的影响

以高产莫纳可林K（MK）及红曲色素（MPs）、不产桔霉素的丛毛红曲菌（Monascus pilosus）MS-1为实验菌株,优化已有的固态发酵工艺,考察添加紫苏叶对红曲菌产MPs、MK及抗氧化物的影响。结果表明,添加10%紫苏叶时MPs和MK的产量最高（P＜0.05）。添加紫苏叶及紫苏叶提取液均可显著促进菌株MS-1产MPs和MK（P＜0.05）,但两种添加方式对菌株MS-1产MPs及MK的影响无显著差异（P＞0.05）。添加紫苏叶后色价和MK产量可分别达211.73 U/g和8.15 mg/g,分别为对照的1.35和1.36倍。紫苏红曲粗提物的DPPH清除率显著高于对照（P＜0.05）,可达48.71%。然而,紫苏红曲中迷迭香酸含量仅为0.032 mg/g,而紫苏叶中迷迭香酸含量高达14.71 mg/g。添加紫苏叶不仅可促使红曲菌产MPs及MK,还可能促使红曲菌产抗氧化物质,从而提高其发酵产物的抗氧化能力。     

阿魏酸对·OH诱导的肌原纤维蛋白氧化及凝胶特性的影响

为了探究阿魏酸（FA）对·OH诱导的肌原纤维蛋白（MPs）氧化及凝胶特性的影响,以猪肉肌原纤维蛋白为研究对象,利用Fenton氧化体系模拟实际肉品氧化环境,建立MPs-Fenton氧化体系,研究添加不同浓度水平（0、0.01、0.25、0.50 mg/g蛋白质）阿魏酸对猪肉MPs氧化及其凝胶特性的影响。结果表明:FA可以显著降低MPs羰基含量（P<0.05）,且抑制效果具有浓度依赖性,高浓度（0.50 mg/g）FA对羰基含量的抑制率高达38.2%;高浓度FA在氧化的基础上进一步促进MPs巯基损失,经·OH氧化体系氧化12 h后,其总巯基含量极显著降低了4.02%（P<0.01）。MPs氧化后溶解度降低,且随着FA添加浓度的增大,溶解度降低越明显,表明添加FA可以促进蛋白结构进一步展开,对MPs的氧化状态起到介导调控作用。氧化后的MPs凝胶强度显著降低（P<0.05）,凝胶弹性增强,当添加0.01 mg/g FA时弹性最强,之后随FA浓度的增加而降低,添加高浓度FA可使凝胶蒸煮损失增大,水分损失越多,保水性变差,氧化会导致MPs结构变化,形成较弱的凝胶网络结构。添加适量FA可以抑制MPs氧化及改善凝胶品质,高浓度的FA会影响蛋白成胶能力和凝胶品质。     

蛇龙珠葡萄成熟过程中6种甲氧基吡嗪分析

建立了顶空固相微萃取和气相色谱-氮磷检测器法(HS-SPME-GC-NPD)测定葡萄中6种3-烷基-2-甲氧基吡嗪(MPs)的方法。经优化采用CAR/DVB/PDMS三相SPME萃取头浓缩提取葡萄中MPs,在30℃恒温条件下吸附3h。该方法具有良好的线性,6种MPs标准曲线的线性相关性系数均大于0.99;线性范围在0.78～100ng/L之间;检测限在0.20～1.40ng/L范围内;除2-甲氧基吡嗪(73.12%)外,其他5种MPs的回收率在83.20%～113.09%之间。应用本方法检测蛇龙珠葡萄成熟过程中MPs,发现在果实成熟过程中MPs含量呈递减趋势,其中2-异丁基-3-甲氧基吡嗪最为突出;3-异丁基-和3-异丙基-2-甲氧基吡嗪的含量大于其阈值,对蛇龙珠葡萄的"青椒"气味具有重要贡献。     

Manipulating interfacial behaviour and emulsifying properties of myofibrillar proteins by L-Arginine at low and high salt concentration

The present work examined the impact of L-Arginine (Arg) on the emulsifying properties, interfacial behaviour and conformational characteristics of myofibrillar proteins (MPs) at high (0.6 m ) and low (0.15 m ) salt concentration to maintain good emulsifying properties of MPs at low salt concentration. The data indicated that Arg increased the emulsifying activity index/emulsion stability index (EAI/ESI) and decreased the CI and droplet size of emulsions regardless of salt concentration. Raman spectra revealed that the α-helix content decreased from 60.30% to 51.26% at high salt concentration, and from 60.20% to 54.82% at low salt concentration in the presence of Arg. In addition, MPs treated with Arg exhibited a higher interfacial pressure and more rapidly diffusion to the oil surface. Meanwhile, Arg increased the interfacial protein loading. The results demonstrated that Arg caused the unfolding of MPs, promoting the adsorption of proteins and decreasing the interfacial tension, ultimately improving the stability of emulsions at low salt concentration.     

Effect of microwave heating time on the gel properties of chicken myofibrillar proteins and their formation mechanism

The present work was conducted to illustrate the mechanism of gel formation of myofibrillar proteins (MPs) under different microwave heating times. The results showed that the denaturation enthalpy (ΔH) of the MPs significantly decreased when the heating time increased from 3 to 9 s and then completely disappeared as the heating time progressed, indicating that the MPs gradually denatured and subsequently aggregated with increasing heating time, which was further verified by the changes in the secondary structure, electrophoretic bands, and gel properties (e.g., water holding capacity and textural profiles) of the MPs. Microstructural images indicated that the MP gel formed under 12 s had the most compact network, indicating that extended microwave heating time could induce quality deterioration of MP gels. Moreover, the hydrophobic forces, electrostatic forces, and disulphide bonds of the MPs gradually intensified with increasing microwave heating time, suggesting that both non-covalent and covalent bonds could promote molecular denaturation and subsequent aggregation of MPs. In addition, correlation analysis revealed that the changes in the molecular conformation of MPs induced by different microwave heating times could effectively regulate the formation of MP gels and their related properties.     

Production of three anti-listerial peptides by Lactobacillus curvatus in MRS broth

Three novel bioactive peptides (BAP1–3) from Lactobacillus curvatus CWBI-B28 were isolated and purified using de Man, Rogosa and Sharp (MRS) broth by a three-step protein purification protocol including ammonium sulfate precipitation, hydrophobic C₁₈ Sep-Pak column and reverse-phase high performance liquid chromatography (RP-HPLC). This procedure allowed the recovery of chromatographically pure antimicrobial peptides with the yields of 19%, 10% and 15% of BAP1, BAP2 and BAP3, respectively. The respective apparent molecular masses as determined by tricine-SDS-polyacrilamide gel electrophoresis were 6365, 3426 and 3496. N-terminal amino acid sequencing of the BAPs and comparison of their sequences with those of international data bases indicated that BAP1 is more likely to be a casein-derived bioactive protein produced upon hydrolysis of the tryptone present in MRS broth by Lb. curvatus CWBI-B28 during active growth. However, the identity of BAP2 and BAP3 could not be determined with certainty; yet, they would be novel bacteriocins not fitting in any of the known classes of bacteriocins. Therefore, this strain would have the ability to produce intrinsic antimicrobial substances and also release bioprotective peptides from milk-proteins upon cultivation in milk or casein-containing food products due to its proteolytic activity. Thus, Lb. curratus CWBI-B28 possesses a good potential to be used in food preservation and safety.     

高压均质处理次数对肌原纤维蛋白水溶液结构及理化特性的影响

以鸡肉中的肌原纤维蛋白（myofibrillar proteins,MP）为对象,研究在103 MPa压力条件下不同高压均质（high pressure homogenization,HPH）处理次数（1～6 次）对MP水溶液结构以及理化特性的影响。结果表明：HPH可以显著提高MP在水中的溶解性（P＜0.05）。随着HPH处理次数的增加,MP在水溶液中的粒径先减小后变大;表观黏度减小,流动能力增强;表面疏水性和活性巯基含量先增加后减少;圆二色光谱结果显示不同HPH处理次数对MP水溶液的二级结构构象的影响不同;过多的HPH处理次数会导致MP水溶液中蛋白质聚集,从而影响其溶解性和稳定性;经过4 次HPH处理的MP水溶液具有较好的溶解性和稳定性。说明通过选择适当次数的HPH处理可以实现对MP在水中溶解性的调控,为其在食品加工中的应用提供新思路。     

Formation of distinct soluble microbial products by activated sludge: kinetic analysis and quantitative determination

Soluble microbial products (SMP) released by microorganisms in bioreactors are classified into two distinct groups according to their different chemical and degradation kinetics: utilization-associated products (UAP) and biomass-associated products (BAP). SMP are responsible for effluent chemical oxygen demand or for membrane fouling of membrane bioreactor. Here an effective and convenient approach, other than the complicated chemical methods or complex models, is developed to quantify the formation of UAP and BAP together with their kinetics in activated sludge process. In this approach, an integrated substrate utilization equation is developed and used to determine UAP and their production kinetics. On the basis of total SMP measurements, BAP formation is determined with an integrated BAP formation equation. The fraction of substrate electrons diverted to UAP, and the content of BAP derived from biomass can then be calculated. Dynamic quantification data are obtained for UAP and BAP separately and conveniently. The obtained kinetic parameters are found to be reasonable as they are generally bounded and comparable to the literature values. The validity of this approach is confirmed by independent SMP production tests in six different activated sludge systems, which demonstrates its applicability in a wide range of engineered system regarding SMP production. This work provides a widely applied approach to determine the formation of UAP and BAP conveniently, which may offer engineers with basis to optimize bioreactor operation to avoid a high effluent soluble organics from SMP or SMP-based membrane fouling in membrane bioreactors.     

花生组织培养及高频率植株再生

以14个花生品种为材料,对花生组织培养及植株再生进行了研究。将花生成熟胚幼叶、子叶和下胚轴外植体接种到添加0—2mg／LNAA和0～10mg／LBAP的MSB,（MS无机盐＋B5有机）培养基上诱导愈伤,再转到添加0～10mg／LBAP的分化培养基上诱导不定芽。结果表明,诱导培养基中添加的激素及其浓度对以后在分化培养基上不定芽分化有重要作用,以添加1mg／LNAA和6mg／LBAP最利于不定芽分化;分化培养基中添加4mg／LBAP利于不定芽伸长及植株再生;幼叶外植体分化不定芽频率明显高于子叶和下胚轴;不同基因型不定芽分化率存在明显差异,白沙1016和花育23幼叶外植体获得了较高的不定芽分化率,分别达到91．8％和88．5％。再生苗经生根培养和驯化后,移栽花盆可正常开花结果。     

两种辅料对固态发酵红曲米莫纳可林K与红曲色素产量的影响

红曲霉在发酵过程中会产生莫纳可林K(MK)和红曲色素(MPs)等多种对人体有益的次级代谢产物。为同时在红曲米固态发酵产物中获得一定量的MK和MPs,实验在大米基质基础上,分别添加豆粕、豆渣两种辅料,对红曲霉MPs-7进行固态发酵培养,分析两种代谢产物产量,并对辅料影响机制进行了探究。结果表明:在发酵基质中添加两种辅料均促进了MK的产生,但同时抑制了MPs的产生。豆粕添加量为质量分数15%时,发酵产物MK产量最高,但几乎无MPs产生;豆渣添加量为质量分数15%时,提高MK产量的同时也保证了一定的MPs产量,且成本比豆粕低,更适合作为辅料添加到红曲霉固态发酵基质中。研究表明:基质含氮量会影响红曲霉固态发酵过程中菌丝体量的积累,从而影响次级代谢产物的产量。     

l‐histidine improves water retention of heat‐induced gel of chicken breast myofibrillar proteins in low ionic strength solution

The effects of 5 mm l ‐histidine (l ‐His) on water‐binding capacity, gel strength, thermal gelling properties of chicken breast myofibrillar proteins (MPs) in 1 mm NaCl or 0.6 m NaCl solutions (pH 7.0) were investigated. l ‐His could significantly increase the solubility and thermal gelling ability of MPs in 1 mm NaCl. l ‐His at 1 mm NaCl shortened the water relaxation time and decreased the water mobility of MPs gel. l ‐His promoted the formation of MPs gel structure with small pores and thin strands at 1 mm NaCl. These resulted in the enhanced water retention and weak gel strength of MPs in low ionic strength solution. The water‐binding capacity of MPs gels formed in 1 mm NaCl containing 5 mm l ‐His was equivalent to that with 0.6 m NaCl. The information could offer certain theoretical foundation to apply l ‐His as sodium salt substitute for developing low‐salt meat gelling product with high yield.     

食品中微塑料的来源、分布特征及毒理学研究进展

食品已成为人体摄入微塑料（Microplastics,MPs）的主要来源。食品中的MPs主要来源于食品原料（包括鱼类、贝类、农作物、食盐和水等）、食品加工过程以及食品包装。MPs在食品中的丰度、形状、粒径及聚合物类型等分布特征与地理位置、人类活动以及食品工业类型等因素相关。目前,MPs的检测方法包括扫描电子显微镜和能量色散x射线光谱联用（Scanning Electron Microscope-Energy Dispersive X-Ray Spectroscopy,SEM-EDS）,傅里叶变换红外光谱（Fourier Transform Infrared Spectroscopy,FT-IR）,拉曼光谱（Raman Spectroscopy,RS）,热分析法与气相色谱-质谱（Gas Chromatography-Mass Spectrometry,GC-MS）联用法及上述方法的组合使用。此外,MPs内在的化学添加剂、从环境中吸附的污染物和有害微生物附着可能对人体产生健康风险,包括直接毒性、易位毒性以及复合毒性。已有研究证实炎症,氧化应激,细胞凋亡和线粒体功能障碍与MPs摄入量密切相关。该文综述了食品中MPs污染的来源、分布特征、检测方法和毒理作用,以期为食品中的MPs风险防控与未来研究提供参考。     

Physicochemical and structural properties of myofibrillar proteins isolated from pale,soft, exudative (PSE)-like chicken breast meat: Effects of pulsed electric field (PEF)

The present study was performed to clarify the effects of pulsed electric field (PEF) on the physicochemical properties and conformations of myofibrillar proteins (MPs) extracted from pale, soft, exudative (PSE)-like chicken breast meat. Various PEF parameters, including the electric field intensity (0–28 kV/cm) and pulse frequency (0–1000 Hz), were varied. The results showed that as the PEF intensity increased, the solubility, surface hydrophobicity and sulfhydryl group content of the MPs were significantly improved. However, when the intensity exceeded 18 kV/cm, these properties declined, which was possibly due to protein aggregation caused by functional group interactions. Additionally, the PEF treatment altered the rheological properties of PSE-like MPs and induced the formation of low-elasticity MPs. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that the primary structure of the MPs was not altered after the PEF treatment. According to the circular dichroism (CD) spectroscopy results, the α-helix contents of the PEF-treated samples were increased but the β-turn and random coil contents were reduced.Industrial relevanceThe occurrence of PSE-like chicken meat is one of the most serious quality issues worldwide and can decrease the consumer's purchasing desire and result in extensive economic losses for the poultry processing industry. MPs play a vital role in the qualitative characteristics of chicken products. As a potential novel processing technology, PEF has potential applications for improving the functionality of PSE-like chicken protein to expand its application in the food industry.     

Contamination of table salts from Turkey with microplastics

Microplastics (MPs) pollution has become a problem that affects all aquatic, atmospheric and terrestial environments in the world. In this study, we looked into whether MPs in seas and lakes reach consumers through table salt. For this purpose, we obtained 16 brands of table salts from the Turkish market and determined their MPs content with microscopic and Raman spectroscopic examination. According to our results, the MP particle content was 16–84 item/kg in sea salt, 8–102 item/kg in lake salt and 9–16 item/kg in rock salt. The most common plastic polymers were polyethylene (22.9%) and polypropylene (19.2%). When the amounts of MPs and the amount of salt consumed by Turkish consumers per year are considered together, if they consume sea salt, lake salt or rock salt, they consume 249–302, 203–247 or 64–78 items per year, respectively. This is the first time this concerning level of MPs content in table salts in the Turkish market has been reported.     

Preparation and physicochemical characterisation of resveratrol–ovalbumin microparticles

Resveratrol (RES) is a phenolic compound which has many biological activities, but its poor stability and water solubility limit its function and application. This study developed microparticles (MPs) using ovalbumin (OVA) as a matrix to encapsulate RES. Encapsulation efficiency, solubility and structural characteristics have been evaluated. The antioxidant activity of encapsulated RES has also been examined using the methods of the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) and 2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) radical scavenging assays. Moreover, the stability of the MPs in simulated gastric and intestinal fluid has been studied. In conclusion, RES can be effectively encapsulated by OVA to form spherical MPs resulting in its high water solubility. RES–OVA MPs may not only keep the antioxidant activity of RES but also promote its stability. This kind of MPs can have a potential application in the formulation of functional soft drink based on RES.     

贻贝中微塑料检测的消解方法比较

目的 比较贻贝中微塑料(microplastics, MPs)检测常用的酸消解、碱消解、氧化消解和酶消解等方法,推荐适用于贝类中微塑料检测的通用型消解方式。方法 以常用的指示性双壳贝类贻贝作为研究对象,确定食品样品检测通用的消解条件。在这些条件下对聚苯乙烯(polystyrene, PS)、聚丙烯(polypropylene, PP)、聚碳酸酯(polycarbonate, PC)、聚乙烯(polyethylene, PE)、聚对苯二甲酸乙二醇酯(polyethylene terephthalate, PET)、聚酰胺6 (polyamide, PA6)和聚酰胺66 (polyamide, PA66) 7种微塑料进行消解,考察不同条件下微塑料粒子消解前后重量、红外光谱、粒径分布和形貌特征的变化。结果 采用不同的消解方式对不同的微塑料影响不同,其中重量受影响较大的是PA6和PA66,在硝酸-高氯酸混合溶液和高氯酸-双氧水混合溶液中完全溶解损失,PC和PET在氢氧化钾溶液中损失严重。通过结构表征, PE、PA6和PC的粒径增加, PC的形貌结构发生彻底改变。结论 对微塑料含量甚微的双壳贝类...     

红曲黄色素和红曲橙色素的稳定性研究

为了研究不同色素组分的稳定性差异,利用大孔树脂柱层析分离得到了黄色组分Fl和橙色组分F2,其中Fl主要含有红曲素(monascin)和安卡红曲黄素(ankaflavin),F2主要含有红曲玉红素(monascorubrin)和红斑红曲素(rubropunctatin).以Fl和F2为材料,从光谱特征及色素残留率等方面分...     

紫外-化学诱变筛选高产莫纳可林K或色素的红曲菌株

为获取能稳定高产莫纳可林K（MK）或红曲色素（MPs）的红曲菌株,以不产桔霉素的丛毛红曲菌（Monascus pilosus）MS-1为 出发菌株,经紫外诱变、氯化锂化学诱变及紫外-氯化锂复合诱变分别得到红曲菌11株、2株和3株,对16株诱变菌进行复筛和遗传稳 定性试验研究,得到4株产MPs或MK能力提高且遗传稳定性较好的诱变菌株。 其中诱变菌株ZWS5产MPs总色价为1 476.25 U/g,与出 发菌株MS-1相比产MPs能力提高了23.36%;诱变菌株ZWN2、LHL1和FH2的MK产量分别为7.34 mg/g、7.03 mg/g、和7.16 mg/g,比出发 菌株MS-1产MK能力分别提高了27.65%、22.26%和24.52%。