磁场对酵母菌的影响

某些食品的腐败变质与酵母菌有关,而静态磁场对酵母菌有一定作用,因而可望用于酵母菌对食品的危害控制。但迄今关于静态磁场对酵母菌的影响尚缺乏系统研究,制约了磁场处理技术的应用。本文通过静态磁场强度、磁场处理时间对酵母菌影响的研究,探讨静态磁场对酵母菌的作用规律。研究结果为磁场处理技术在食品工业上的应用提供初步理论分析和实验依据。     

高强度脉冲磁场对牛奶杀菌的研究

采用10T以上高强度脉冲磁场处理鲜牛奶,研究脉冲强磁场对牛奶中微生物的影响.结果表明:高强度脉冲磁场对牛奶杀菌效果显著,随磁场强度或脉冲数的增大,菌落总数、大肠杆菌和霉菌酵母的存活率基本呈下降趋势,但出现谷值后,存活率随着磁场强度和脉冲数的进一步增大有所回升.在磁场强度16.02T,脉冲数为6时,对牛奶中菌落总数和大肠杆菌杀菌效果最好;而磁场强度16.02T,脉冲数8时,对霉菌酵母杀菌效果最好.与菌落总数和大肠杆菌相比.霉菌酵母对脉冲磁场有较强的抵抗力.在最佳处理条件下,经脉冲磁场处理的牛奶可达到商业无菌的要求.     

高压静电场对桔青霉菌的作用效果与机理

利用自制高压静电场装置,对桔青霉菌进行不同场强度、时间及温度的处理来考察高压静电场对其孢子萌发率的作用效果;用典型作用参数处理观察青霉菌芽管长度、接种于健果上的菌斑大小及孢子形态来进一步验证对萌发率作用结果及作用机理的探讨。结果表明,高压静电场对青霉菌孢子的萌发具有促进和抑制两种完全不同的作用。场强小于40000V/m和处理时间小于20min能促进孢子萌发,场强大于62000V/m和处理时间超过60min能抑制孢子萌发,中间剂量的处理效果依据不同的处理而有所变化。温度对电场处理效果有着显著的影响,当温度升高到50℃,高剂量的场强处理可以完全抑制青霉菌孢子萌发。高压静电场对青霉菌的芽管长度、桔果上的菌斑大小的作用有着相似的结果。62000V/m、60min的处理使青霉菌的孢子形态结构受损,导致其孢子失去萌发能力。结果表明高压静电场为柑橘类的果蔬保鲜提供了一条物理处理新途径。     

磁阻垢对纺织空调水质的影响

通过水质静态试验研究磁处理在纺织厂循环水的应用效果。通过综合对比化学添加阻垢剂、超声波技术、反渗透技术和磁阻垢法的原理、优劣和设备初投资,选择磁阻垢对循环水进行处理。研究发现：对循环水施加外部磁场能够有效缓解水垢生成,当磁场强度为14 000 GS时,抑垢率最高,最大值为94.41%;外加磁场能够促进CO₂溶于水中,使水的pH值显著降低,有效抑制水垢生成;磁化处理的水CaCO₃的溶解度明显提高,水中离子浓度增加,电导率升高。     

低强交变磁场促进灰树花液体发酵及其生物学窗效应研究

使用实验室自制磁场摇床,以灰树花为研究对象,通过改变交变磁场作用各参数条件,研究其对灰树花菌丝体生长促进效果的影响,并借助发酵液pH值的变化对窗效应的发生原因进行了初步探讨。通过扫描电镜、红外光谱、一般性化学成分分析等手段,对比常规液态发酵和磁场辅助液态发酵所得菌丝体的差别。研究表明,当磁感应强度为35 Gs、初次磁处理介入时间为接种后1 h、作用时长为3 h时,磁场对灰树花菌丝体的生长促进作用最强,灰树花的菌丝体干质量提高率达11.43%,各营养成分总量均有所上升。在磁场处理时长为3 h和5 h时,出现了磁场促进灰树花生长的"生物学窗效应"。     

磁化处理对脂肪酸精馏过程的影响

在不同磁感应强度的磁场中,研究了磁化处理对脂肪酸精馏过程的影响。研究结果表明,磁场对脂肪酸的精馏过程有一定的影响,脂肪酸经磁化处理后,油酸的含量提高0.41%～0.64%,收率提高0.30%～0.47%;亚油酸的含量提高0.46%～0.69%,收率提高0.37%～0.54%;硬脂酸的含量提高0.44%～0.62%,收率提高0.34%～0.48%。由此可见,磁化处理有利于脂肪酸精馏过程的进行。     

真空杀虫与抑制霉菌的初步研究

以米蛾幼虫和青霉为研究对象,进行真空杀虫与抑制霉菌的初步实验研究。通过真空压力和处理时间对粮食害虫致死率和抑制霉菌生长的影响分析,得出杀虫的最佳真空压力和抑制霉菌生长的最佳真空处理时间。结果表明,随着真空压力的降低和处理时间的增加,真空对粮食杀虫和抑制霉菌的效果会随之增加。真空杀虫达到最佳效果的真空压力在900Pa到1300Pa压力段内,真空抑制霉菌处理时间持续330min以上,可以确保98%的致死率。     

超高压处理对鲜牛奶主要品质影响

为考察超高压处理对鲜牛奶主要品质的影响,在室温条件下对鲜乳施加不同时间以及不同压力的处理,分析测定鲜乳经过超高压作用后其中残留细菌、霉菌和酵母菌的数目,研究了超高压杀菌对鲜乳中这几种微生物致死率的影响和高压对牛奶主要品质的影响。结果表明:压力越高,杀菌效果越好;在同样压力下延长受压时间并不一定能提高灭菌效果。压力处理后牛奶的pH值变化不大,L值会减小。     

低频磁场对紫色红曲菌液态发酵产麦角固醇的影响

探讨低频磁场处理对紫色红曲菌(Monascus purpurcus)发酵产麦角固醇的影响,确定最佳处理条件。分别研究低频磁场强度、处理时间和处理时期对紫色红曲霉液态发酵产麦角固醇的影响规律,探讨在最佳处理条件下,磁场对紫色红曲霉麦角固醇代谢过程的影响和紫色红曲霉的生物量在整个发酵周期的变化,及对紫红曲霉其他主要代谢物的影响。结果表明:低频磁场处理紫色红曲菌的最适条件为磁场强度1.2 mT、处理时间2 d、处理时期在发酵0~2 d,在发酵第12天,麦角固醇产量达到了7.08 mg/g,生物量达到3.2 g/L,比对照组分别增加了62.5%和31.68%。低频磁场是提高紫色红曲菌生产麦角固醇产量的有效手段,研究为低频磁场辅助微生物发酵,提高有益产物的合成提供了数据支持。     

绿色木霉菌抑制芒果炭疽菌特性研究

目的:研究绿色木霉菌抑制芒果炭疽病病菌的特性。方法:采用体外抑菌试验,研究绿色木霉菌最适抑菌温度、pH值以及水杨酸对其抑菌作用的影响。结果:绿色木霉菌抑制炭疽菌的适宜温度是18~28℃;绿色木霉菌抑制炭疽菌生长的pH范围较广,pH 4~8均为其适宜的抑菌pH值;采用1.0 mmol/L水杨酸直接浸泡绿色木霉菌的处理方法,可有效增强绿色木霉菌抑制炭疽菌的效果。结论:绿色木霉菌显著抑制了炭疽病菌的生长,本研究结果为绿色木霉菌抑制芒果采后炭疽菌的控制技术提供了理论参考。     

静磁场对发酵鱼露工艺的影响

为探究鱼露酿造的新工艺,以淡水鱼下脚料为原料,粉碎成鱼糜与80 g/L盐、沪酿3.042米曲霉制成的酱油曲混合后,在静磁场环境下培养发酵生产鱼露.在不同静磁场环境下40℃发酵30 d,通过测定鱼露发酵过程中氨基态氮、总氮、挥发性盐基氮、无盐固形物、总酸、pH值和非酶褐变的变化,分析静磁场环境对鱼露发酵工艺及其品质的影响...     

Effect of magnetic field with different dimensions on quality of avocado puree during frozen storage

The magnetic field-assisted freezing (MFAF) has been identified as an emerging physical method used for food preservation, characterised by its high penetrability in food materials. However, effects of magnetic fields in different dimensions on food freezing process and its products quality have not been previously compared. Thus, the alternating magnetic fields (4 mT and 50 Hz) were applied in different directions and its impact on the physiochemical properties of frozen avocado puree during the storage were investigated. In comparison with the conventional freezing process, the application of MFAF could reduce the weight loss and soluble solids rise. The transformation between different types of water and their corresponding redistribution were also limited under MFAF. The decrease of total polyphenol content with extended storage time was reduced due to the inhibitory effect of MFAF on the polyphenol oxidase activity. In general, the MFAF of avocado purees presented better texture characteristics and higher sensory qualities than the controls. The more directions the magnetic field was applied, the better it performed in maintaining the quality of avocado puree. This study provides a reference for the application of the MFAF on food cryopreservation.     

4D打印技术在食品加工领域的研究进展

4D打印技术作为3D打印技术的延伸,可以促使打印材料的结构、形状以及功能随时间的变化而发生改变,从而实现打印材料由静态结构向动态结构的转变。4D打印技术作为新兴的数字化生产技术,其早期主要应用于医学和工业领域。近几年,4D打印技术逐渐在食品领域得到了一定的应用。通过4D打印可以设计并生产出营养价值更高、感官品质更佳的新型食品。本文综述4D打印食品技术的原理、影响因素以及打印设备,并进一步地论述4D打印技术在食品加工领域的国内外研究进展及其优势,最后展望4D打印食品技术的发展前景,以期为4D打印技术在食品领域的应用研究提供参考。     

Emerging technologies: chemical aspects

Consumer demands for high-quality foods with “fresh-like” characteristics that require only a minimum amount of effort and time for preparation has led to the introduction of convenience foods preserved by mild treatments. Non-thermal methods allow the processing of foods below temperatures used during thermal pasteurisation, so flavours, essential nutrients, and vitamins undergo minimal or no changes. Foods can be non-thermally processed by irradiation, high hydrostatic pressure, antimicrobials, ultrasound, filtration, and electrical methods such as pulsed electric fields, light pulses, and oscillating magnetic fields. Due to technological developments, high pressure processing and high electric field pulse processing have received increased attention during the last decade. This paper focuses on high pressure treatment of foods, a process which is also used to create food and food ingredients with new sensory and functional properties including also physiological functionality. Effects of high pressure on chemical and sensory changes in foods are discussed.     

INACTIVATION of SACCHAROMYCES CEREVISIAE IN APPLE JUICE BY SQUARE-WAVE and EXPONENTIAL-DECAY PULSED ELECTRIC FIELDS

With equivalent electrical energy input, inactivation of microorganisms by pulsed electric fields depends on pulse waveform. Exponential-decay and square-wave pulsed electric fields were selected to treat Saccharomyces cerevisiae suspended in apple juice. A parallel-plate static treatment chamber with 25 ml volume and 0.95 cm electrode gap was used. Peak electric field and pulse electric energy input were 12 kV/cm and 260 Joules per pulse for both waveforms. Both waveforms were found effective in the microbial inactivation. However, inactivation of S. cerevisiae treated with square-wave pulses was greater than yeast treated with exponential-decay pulses. For the purpose of food pasteurization, square-wave pulsed electric fields may result in significant energy savings compared to exponential-decay pulses.     

Molecular dynamics study of the effects of static and oscillating electric fields in ovalbumin

Understand the conformational changes caused by emergent technologies in nutrients is important to assess the total impact of these processes in foodstuff. In this study, molecular dynamics simulations were used to analyze the effects of static and oscillating electric fields in ovalbumin at different temperatures. The results indicate that the protein secondary structure is more thermally stable under electric processing. While molecular size, dipole moment and surface area increased, number of hydrogen bonds decreased under field application. The results agree with experimental observations and were used to discuss the mechanisms of some already reported non-thermal effects of ovalbumin. This paper helps to shed some light on the influence of electric fields in proteins structures and may contribute to the creation of peptides with improved technological properties by alternative processing.Industrial relevance text: Molecular dynamics simulations were used to study the conformational changes caused by continuous and oscillating electric fields in ovalbumin at four temperatures (300, 320, 340 and 360 K), representative of different food processing scenarios. Our results can be used to understand the consequences of electric field treatments in a large peptide and may help to improve functional properties of this protein. The analyzed variables at molecular level can be correlated to experimental observations, helping to explain some of the mechanisms responsible for non-thermal effects in ovalbumin.     

A review on effect of DC voltage on crystallization process in food systems

Crystallization of water and food systems may be affected by electric and magnetic fields. In this review paper, the crystallization of water and food systems assisted by DC voltage (DC-V) is compiled based on existing literature. Two ways of applying DC-V during electrocrystallization can be identified, namely charge flow (CF) conditions with electrical charges flowing through the matrix and static electric field (SEF) conditions. Both processes have shown to interact with nucleation mechanism by reducing supercooling and favouring a higher nucleation rate. The theoretical calculations show that the application of SEF can modify the free energy of formation of ice nuclei in the water phase. Moreover, SEF application can also enhance heat and mass transfer during crystallization process. Various molecular simulations and experimental studies have shown that SEF aligns the water molecules in its direction by the phenomenon of dielectric polarization, and thus, reduces the degree of supercooling (∆T). The freezing process under SEF produces smaller ice crystals in the food products, resulting in less freeze damage; it is thus expected to minimize cell disruption, to reduce the drip loss, to lessen the protein denaturation, and finally to preserve the texture of the fresh food after thawing. Furthermore, freezing under SEF may help to use less energy intensive freezing conditions (higher set point temperature, low air velocity). As a conclusion, the use of DC-V in the case of crystallization of food systems (especially freezing) offers a new perspective to the food industry.     

Pectin methyl esterase and natural microflora of fresh mixed orange and carrot juice treated with pulsed electric fields

The effects of pulsed electric fields (PEFs) on pectin methyl esterase (PME), molds and yeast, and total flora in fresh (nonpasteurized) mixed orange and carrot juice were studied. The PEF effect was more extensive when juices with high levels of initial PME activity were subjected to treatment and when PEF treatment (at 25 kV/cm for 340 micros) was combined with a moderate temperature (63 degrees C), with the maximum level of PME inactivation being 81.4%. These conditions produced 3.7 decimal reductions in molds and yeast and 2.4 decimal reductions in total flora. Experimental inactivation data for PME, molds and yeast, and total flora were fitted to Bigelow, Hülsheger, and Weibull inactivation models by nonlinear regression. The best fit (lowest mean square error) was obtained with the Weibull model.     

强脉冲磁场对草莓过氧化物酶的钝化及对草莓汁的杀菌效果研究

以冷冻丙酮法制备草莓过氧化物酶粗酶液。以愈创木酚、双氧水为底物,用分光光度法测定氧化产物的方法测过氧化物酶活性;以草莓汁为原料,施加强脉冲磁场进行杀菌实验。研究了磁感应强度、脉冲数对过氧化物酶活性、草莓汁中菌落总数、霉菌和酵母菌的杀灭效果。结果表明:在室温(28±1℃)下,当磁感应强度为18.9T,脉冲数为9个时,就可以把草莓过氧化物酶活性钝化到处理前的8%;当磁感应强度达到17.3T以上,脉冲数达到12个以上时,菌落总数可以降低到100cfu/mL以下,霉菌、酵母菌可以被全部杀灭,可以达到商业无菌的要求。