速冻保鲜过程中冰晶生长形态研究

冷冻是保藏食品常用且有效的方法之一。但在传统冷冻过程中,生成的大冰晶会破坏食品组织,导致品质劣变,因此如何利用新型冷冻技术改善冷冻食品的品质成为研究的热点。磁场辅助冷冻技术是一种新型的调控冰晶成核技术。本文综述了磁场调控冰晶成核的机制,重点阐述了磁场冷冻在果蔬、畜禽肉、谷物等食品领域的应用。综述结果发现,虽然磁场冷冻技术在多种食品领域有所应用,但目前研究主要集中于磁场对冷冻食品品质及冷冻参数的影响,而磁场辅助冷冻调控冰晶成核的机制目前尚无统一结论,仍需科研者进一步系统地研究揭示磁场冷冻的作用机制,推动磁场辅助冷冻技术在食品领域的应用,促进冷冻食品品质的提升。

     

磁场辅助冻结对马铃薯块冻结及贮藏特性影响

为确定马铃薯块在冻结过程中施加不同强度直流磁场对其冻结特性以及后期贮藏品质影响,在冻结实验中分别施加0、4.6、9.2、18、36 Gs的磁场强度,然后在-18 ℃下贮藏70 d,定期测定产品汁液流失率、细胞膜透性、硬度和咀嚼度。结果表明,磁场可增加马铃薯块过冷度,缩短冻结时间,减少细胞汁液流失,能更好地保持马铃薯块品质。当磁场强度在18 Gs时,马铃薯块通过最大冰晶生成带的速率最快,在贮藏末期(第70 d)时马铃薯块的各项品质指标均优于其他组,更利于马铃薯块的贮藏。     

超声波辅助冷冻技术及其在食品中的应用

冷冻是实现食品长期贮藏保鲜的主要手段,冷冻过程中水分的成核与结晶决定着食品冷冻效率和冷冻食品的质量。超声波辅助冷冻作为一种新型的冷冻技术,能在食品冷冻过程中有效地诱导成核并控制结晶过程,提高冷冻食品质量,引起研究者的广泛关注。该文介绍超声波辅助冷冻机制、冷冻效果的影响因素,总结超声波辅助冷冻技术在水产品、果蔬、肉类等食品冷冻加工中的应用研究进展,为超声波辅助冷冻技术在食品领域的深入研究和推广应用提供参考和借鉴。     

离子迁移谱及其在食品监测中的应用

离子迁移谱(ion mobility spectrometry,IMS)是近年来快速发展起来的一项检测技术。由于其操作简便、检测快速、灵敏度高、体积小等明显优势,现已被应用到危险品检测、医药、环保、食品安全、过程控制等诸多领域的研究中。本文简要地介绍了其结构和工作原理,重点阐述其在国内外食品监测领域中的最新进展。目前在食品工业中的应用研究包括:食品与农产品中农药、兽药等的残留检测,食品生产加工储蓄保鲜等过程中的质量控制如控制啤酒发酵程度、储藏保鲜过程监测,食品原产地及真实性的快速检验如橄榄油和葡萄酒等级鉴定、原产地鉴定等。在此基础上也与现行的常规检测技术(高效液相色谱、气相色谱)进行了比较。简要讨论了其在食品安全和质量检测中的可能应用前景,认为IMS具有提高食品质量、优化生产过程、规范市场行为的巨大潜力。     

STORAGE DETERIORATION OF FREEZE-DRIED AVOCADO PUREE AND GUACAMOLE

SUMMARY— The effect of storage temperature, time and atmosphere on the chemical and organo-leptic characteristics of freeze-dried avocado puree and guacamole was studied using Waldin, Lula and Booth-8 varieties of avocado. Oxidation rates were slower at 21°C than at 38°% storage and nitrogen atmospheres reduced the peroxide formation. Significant differences existed in oxidation rates between avocado varieties and also between guacamole and avocado puree in some instances. A logarithmic relationship was found between peroxide values and storage time in air. Guacamole made with Lula avocados was unacceptable after 3 weeks of storage in air at 38°C. Samples stored in nitrogen at 38°C ware unacceptable at the end of 7 weeks. Samples stored in air at 21°Cwere acceptable after 12 weeks and those stored in nitrogen at 2l°C after 15 weeks. A commercial BHA antioxidant reduced the oxidation rate of Lula puree but did not increase shelf life in air storage at 38°C. Peroxide values were of no use in predicting acceptability, since organoleptic deterioration could occur without any peroxide increase.     

速冻建莲加工与贮藏过程中多酚氧化酶活性抑制的研究

为提高速冻建莲的品质,本文研究了不同的抑制剂组合对建莲多酚氧化酶(PPO)活性的抑制效果,并观察了速冻建莲贮藏期间PP0活性的变化。结果表明:0.025％EDTA-Na_2+0.1％抗坏血酸+0.1％柠檬酸能最大限度地抑制建莲的多酚氧化褐变,以此应用于速冻建莲的生产,能有效抑制冻藏过程中建莲的多酚氧化酶活性,褐变程度明显降低。     

Microwave processing of avocado: Volatile flavor profiling and olfactometry

The aim of this research was to evaluate the effect of microwave time, pH and avocado leaves on the volatile profile of avocado using response surface methodology, and aroma extract dilution analysis (AEDA) was employed to evaluate changes in the odorant composition. Response surface analyses showed maximum values for volatiles derived from lipid oxidation at high levels of microwave time and low values of pH. The presence of terpenoids, estragole, hexanal and 2-hexenal [E] was enhanced with the addition of avocado leaves. The optimum condition to prepare avocado puree was 30 s heating time, pH 5.5 and 1% of leaves. Comparative AEDA analysis for microwaved avocado puree added with and without avocado leaves showed changes in the FD of compounds derived from lipids. In addition, AEDA suggests that the addition of avocado leaves to microwaved avocado is related to the presence of important odorants such α-pinene, estragole and 2-hexenal [E].

Industrial relevance

Several attempts have been made to process avocados as purée or “guacamole”. Microwave treatment offers an alternative for the blanching of fruits and vegetables, since the application of high temperatures for short times often results in minimum damage. Furthermore, previous studies have shown that better retention of color and lightness is obtained when avocado purée is processed in a microwave oven. However, a great loss of flavor takes place when this commodity is treated by heat. The application of a combined treatment consisting of microwaves, pH and the addition of avocado leaves to the purée minimizes flavor loss and results in a product with the characteristic flavor of avocado.     

超高压处理对芒果泥品质的影响

为了提升芒果泥的品质,本研究采用了超高压、辐照和低温等离子三种非热加工手段对芒果泥进行处理,并对不同方法的杀菌效果进行分析比较。选取其中较优的方法（超高压）,进一步研究其对芒果泥的色度、感官、可溶性固形物含量以及储藏稳定性的影响。结果表明,超高压（≥200 MPa）和辐照（≥3 kGy）处理均对芒果泥有良好的杀菌效果,果泥的菌落总数均≤2 lg(CFU/g),达到商业无菌标准。但低温等离子处理效果不理想,当处理时间≤6 min时,果泥中的菌落总数均未达到商业无菌标准。超高压处理后芒果泥的口感与对照样品较为接近。大于500 MPa的压力处理后,芒果泥的储存期稳定性较好,特别是用600 MPa处理后的样品,其储存期至少可以达到9个月。这一结果表明,超高压可以在杀灭芒果泥中有害微生物提高芒果泥稳定性的同时,最大限度地保持芒果泥的原有品质。本研究为超高压技术在食品加工中的应用提供了一定的理论依据和方法指导。     

Biochemical Changes during the Storage of High Hydrostatic Pressure Processed Avocado Paste

Abstract: High hydrostatic pressure (HHP) processing improves the shelf life of avocado paste without a significant impact on flavor; however, scarce information is available on biochemical modifications during its extended storage period. The present study focused on the changes in oxidative enzyme activities of pressurized avocado paste (600 MPa for 3 min) during refrigerated storage (45 d at 4 °C). Aerobic plate counts (APC), lactic acid bacteria counts (LAB), pH, and instrumental color were also evaluated during storage. Processing with HHP caused a decrease in polyphenol oxidase (PPO) and lipoxygenase (LOX) activities, resulting in residual enzyme levels of 50.72% and 55.16%, respectively. Although instrumental color values didn't change significantly during the evaluated storage period, both enzymes (PPO and LOX) recuperated their activities at 10 to 15 d of storage, reached the original values observed in the fresh paste, and then started a declining phase until the end of the storage period. Pulp pH presented a consistent decline during the first 20 d of storage. LAB counts were very low during storage, discarding lactic acid production as responsible for the observed pH decline. Enzyme reactivation, cell disruption, and a gradual migration of intracellular components such as organic acids are herein proposed as the main mechanisms for the deterioration of HHP treated avocado paste during its refrigerated storage. Practical Application: At the present, HHP is the most effective commercial nonthermal technology to process avocado paste when compared to thermal and chemical alternatives. Although it has proven to be an excellent product-technology match, little information is known on the biochemical changes that take place in the product during its refrigerated shelf life. Biochemical reactions during storage are important, since they can influence avocado paste nutritional and flavor qualities at the time of product consumption. The present study reports for the first time the re-activation of PPO and LOX during storage of avocado paste under commercial and economically feasible processing conditions (600 MPa and 3 min). The reactivation of oxidative enzymes observed in the present study is relevant for future studies on the HHP stability of food systems in general, and it is considered an important finding for the food industry and researchers seeking to deliver products with superior nutritional and flavor characteristics.     

冻结速率对苹果片多酚氧化酶和过氧化物酶活性影响的研究

低温断裂是果蔬超速冻过程中常见的问题。本文初步研究了速冻过程对苹果片生化特性的影响,发现不同的冻结速率会引起可溶性过氧化物酶(POD)的活性较大幅度变化,而可溶性多酚氧化酶(PPO)活性变化较小。通过对实验结果的初步分析,指出速冻过程与冻藏食品的保存质量有密切关系     

感应电场处理后蓝莓泥酶活性及总花青素含量变化

为了避免食品电场加工中因电极使用而产生电化学反应造成食品污染和电极腐蚀的问题,采用交变磁通代替电极作为激励源,在果泥料液中诱导形成感应电场(induced electric field,IEF),实现对蓝莓果泥的IEF处理:分析激励电压、温度和时间对蓝莓果泥多酚氧化酶(polyphenol oxidase,PPO)和过氧化物酶(peroxidase,POD)活性及总花青素含量的影响。结果表明,100 V激励电压产生的IEF可减缓PPO和POD酶活的受热损失。150和250 V激励电压下,IEF与高温钝化PPO和POD具有协同作用。IEF可提高花青素分子的热稳定性且电场强度越高稳定作用越强。与未处理果泥相比,经85℃、250 V激励电压的IEF处理30 min的果泥总花青素含量得到最大提升(12. 55%),PPO和POD可被完全灭活。该条件下获得的蓝莓果泥表观黏度与鲜榨果泥更为接近,且储藏期内(4℃,8周)的菌落总数维持在1 lg(CFU/mL)以下,显著低于常规热处理(0 V)和未经热处理的果泥。研究为蓝莓果泥的IEF处理提供了数据参考。     

Effect of zinc and copper chloride on the color of avocado puree heated with microwaves

The effect of microwave heating, and zinc and copper chloride addition on the color of avocado puree was studied. Rates of color variation at different temperatures were determined by plotting a*/b* vs. time of storage. Results showed that the color was best preserved when avocado purees either with or without zinc and copper salts were microwave treated for 30 s, due to inhibition of enzymatic browning. Samples with copper chloride added showed a better color than samples with zinc chloride added, both showing a better color than the blank. This effect is attributed to the formation of chlorophyll complexes with copper and zinc cations. Also the combined effect of different concentrations of zinc and copper salts along with various pH values was evaluated through a response surface analysis. The best response was obtained in the following conditions: zinc chloride 120 ppm, copper chloride 12 ppm, and pH 5.5.     

多酚复合材料的种类及应用研究进展

多酚复合材料是多酚与某种配合物通过共价键或非共价键相互作用合成的新型复合体。与多酚结合的配合物种类多样，尤以多糖、蛋白质、磷脂等生物大分子以及金属元素居多。通过合成多酚复合材料可显著改善某些天然多酚水溶性差、稳定性差、生物利用率低等问题，不仅可以增强多酚作为口服营养素或药物的靶向释放，还可以用作体外植物源抑菌剂，很大程度上扩大了多酚在食品、药品、农产品质量安全等领域的应用范围。本文在总结近年来多酚复合材料最新研究结果的基础上，综述了多酚复合材料的不同类型、结构表征和功能性质以及应用现状，最后针对多酚复合材料在目前研究中存在的问题以及今后的重点研究方向提出了合理建议。     

Use of hydrocolloids as cryoprotectant for frozen foods

Freezing is one of the widely used preservation methods to preserve the quality of food products but it also results in deteriorative changes in textural properties of food which in turn affects its marketability. Different foodstuffs undergo different types of changes in texture, taste and overall acceptability upon freezing and subsequent frozen storage. Freezing and thawing of pre-cut or whole fruits and vegetables causes many deleterious effects including texture and drip losses. The major problem in stability of ice-cream is re-crystallization phenomena which happens due to temperature fluctuations during storage and finally impairs the quality of ice-cream. Frozen storage for longer periods causes rubbery texture in meat and fish products. To overcome these problems, hydrocolloids which are polysaccharides of high molecular weight, are used in numerous food applications involving gelling, thickening, stabilizing, emulsifying etc. They could improve the rheological and textural characteristics of food systems by changing the viscosity. They play a major role in retaining texture of fruits and vegetables after freezing. They provide thermodynamic stability to ice cream to control the process of re-crystallization. Hydrocolloids find application in frozen surimi, minced fish, and meat products due to their water-binding ability. They are also added to frozen bakery products to improve shelf-stability by retaining sufficient moisture and retarding staling. Various hydrocolloids impart different cryoprotective effects to food products depending upon their solubility, water-holding capacity, rheological properties, and synergistic effect with other ingredients during freezing and frozen storage.     

超高压对菠菜浆贮藏期间颜色变化的影响

为探究超高压技术（HHP）处理菠菜浆的颜色品质在不同贮藏条件下的变化规律,对HHP处理样品的CIEL’a’6’颜色进行测定。结果表明,HHP处理菠菜浆在处理后和贮藏期与传统热处理菠菜浆相比其颜色品质更好。在4~C下进行贮藏,HHP处理样品的一a‘值和h。值均显著高于热处理样品,并且在贮藏期阀基本保持不变;￡_’值在HHP处理后显著增加,在贮藏过程中亦基本保持不变,色泽更为明亮。在27。C下进行贮藏,HHP处理样品的一a’值和h。值均显著高于热处理和未处理样品,并在贮藏期间呈下降趋势;上’值在贮藏过程中呈现曲折上升的趋势。因此,HHP处理菠菜浆的表观绿色在冷藏和室温贮藏条件下均要好于传统热处理。HHP处理可以在一定程度上保持绿色菠菜浆的颜色品质,减缓其颜色品质的劣变。     

Novel assistive technologies for efficient freezing of pork based on high voltage electric field and static magnetic field: A comparative study

To enhance the freezing rate and thawed product quality of pork tenderloin, an experimental study was conducted using the high voltage electric field and static magnetic field separately during freezing. Pork tenderloin pieces were frozen at −20 °C under several high voltage electric fields (10 kV/m (HVEF1), 30 kV/m (HVEF3), 50 kV/m (HVEF5)) and magnetic fields of 2 mT (MF2), 4 mT (MF4), 6 mT (MF6) and 8 mT (MF8). The effects of different methods on freezing rate, ice crystal size as well as the distribution, and product quality after thawing were investigated. The freezing time of pork tenderloin was reduced by 40.04% and 37.81% respectively, under the optimal electric and magnetic field conditions tested. The thawing loss decreased from 5.7% of conventional freezing to 1.7% of HVEF1 and 2.4% of MF2, respectively. In addition, both high-voltage electric field freezing and magnetic field freezing can better maintain the moisture state in the sample. The results for color and pH confirmed that the thawed product quality using HVEF1 and MF2 was superior to that obtained under other conditions. The myofibrillar protein in the thawed products obtained from HVEF1 and MF2 treatments was also found to be thermally more stable. It is noteworthy that the HVEF1 treated sample has the highest umami signal and the lowest salty signal. Considering the enhanced freezing efficiency and improved quality, application of HVEF1 is recommended as a viable strategy to produce high-quality frozen pork tenderloin.Industrial relevanceThe slow freezing rate of frozen meat products and serious deterioration of product quality are the key problems. Therefore, improving the efficiency of freezing is desirable. This study provides ideas for pork preservation. It caters to the need of industrial production of meat product where better efficiency freezing process is highly desirable, and the findings of this study is beneficial to the meat processing industry.     

甘薯泥作为吞咽障碍食品的研究进展

质构改良食品作为吞咽障碍患者的安全食品,具有质地柔软、吞咽安全及满足患者营养需求的特点,不同国家对吞咽障碍食品的分级各不相同,大多都聚焦于食品本身的质构特性。近些年,吞咽障碍患者的饮食安全备受关注,开发吞咽障碍食品的研究逐渐增加。甘薯泥是新鲜甘薯经过一系列加工制成的泥状食品,保留了甘薯中绝大多数营养物质,具有柔软、营养成分高的特点,是适合吞咽障碍患者食用的质构改良食品的优质原料。但甘薯泥的质构特性受到多方面因素的影响,例如加工原料、加工工艺以及贮藏条件等,限制甘薯泥作为吞咽障碍食品在食品领域的应用。该文将对质构改良食品的分类、甘薯泥加工工艺及影响甘薯泥质构特性的研究进行综述,旨在为适合吞咽障碍患者食用的甘薯泥产品的研发及应用提供理论依据。     

Recent developments in smart freezing technology applied to fresh foods

Due to the increased awareness of consumers in sensorial and nutritional quality of frozen foods, the freezing technology has to seek new and innovative technologies for better retaining the fresh like quality of foods. In this article, we review the recent developments in smart freezing technology applied to fresh foods. The application of these intelligent technologies and the associated underpinning concepts have greatly improved the quality of frozen foods and the freezing efficiency. These technologies are able to automatically collect the information in-line during freezing and help control the freezing process better. Smart freezing technology includes new and intelligent technologies and concepts applied to the pretreatment of the frozen product, freezing processes, cold chain logistics as well as warehouse management. These technologies enable real-time monitoring of quality during the freezing process and help improve product quality and freezing efficiency. We also provide a brief overview of several sensing technologies used to achieve automatic control of individual steps of freezing process. These sensing technologies include computer vision, electronic nose, electronic tongue, digital simulation, confocal laser, near infrared spectroscopy, nuclear magnetic resonance technology and ultrasound. Understanding of the mechanism of these new technologies will be helpful for applying them to improve the quality of frozen foods.     

超声辅助冷冻技术的作用机制及其对食品品质影响的研究进展

冷冻是一种重要的食品保藏技术,但冻结也会引起食品品质的变化。作为一项高新加工技术,超声辅助冷 冻技术可以加快冷冻速率,减小冰晶的尺寸,进而改善冷冻食品的品质。本文主要论述了超声辅助冷冻技术的作用 机制及对冰结晶形成的影响,同时综述了超声辅助冷冻技术对食品品质的影响及食品冷冻中常用的工艺参数。最 后,展望了超声辅助冷冻技术的发展方向,为超声辅助冷冻技术在食品中的应用提供理论支持。     

食品的低温高压处理技术及其研究进展

文中介绍了低温高压处理技术的基本原理、应用范围和研究进展。在 0～ 6 32 4MPa范围内 ,高压下水的冻结点均较常压下的低 ,并在低于 0℃的温度下形成一个水的不冻结区域。高压还使水的体积收缩、温度升高。低温高压处理技术可应用于食品杀菌和抑酶、高压冻结和高压解冻、低温高压不冻结贮藏。低温高压具有比常温高压更好的杀菌效果 ;高压冻结和高压解冻可缩短食品冻结和解冻的时间、改善冻藏食品的品质 ;低温高压下的不冻结贮藏能更好地保持食品原有的风味和质地