D-异抗坏血酸抑制鲜切马铃薯褐变的研究

研究了不同褐变抑制剂对鲜切马铃薯褐变和品质的影响.结果表明：4种褐变抑制剂处理均可不同程度地对PPO和POD酶产生抑制作用.硫化物依然是效果最好的护色剂,D-异抗坏血酸的防褐保鲜效果表现较好.马铃薯的PPO、POD活性很高且两者之间具有相关性,与褐变度数值相吻合.经过褐变抑制剂处理的样品之间品质有差异,但不太明显.     

乙醇冷藏处理对鲜切马铃薯酶促褐变的抑制及其机理研究

以鲜切马铃薯为原料,研究了乙醇处理对其多酚氧化酶(PPO)活性、过氧化物酶(POD)活性、褐变指数(BI)和丙二醛(MDA)含量的影响,以及酶促褐变底物L-酪氨酸和L-多巴的紫外和红外光谱图的变化来研究乙醇处理对鲜切马铃薯酶促褐变抑制机理。结果表明,分别用4%、5%、6%体积分数的乙醇溶液处理后的鲜切马铃薯在贮藏过程中,PPO活性、POD活性、BI值和MDA含量均低于对照组,且5%体积分数的乙醇溶液处理对酶促褐变的抑制效果最优;通过酶促褐变底物的紫外及红外光谱图可知,乙醇溶液处理对马铃薯酶促褐变的底物的结构没有产生影响,由此可知,乙醇溶液是通过抑制PPO、POD等相关酶的活性来抑制鲜切马铃薯的酶促褐变。     

鲜切马铃薯复合褐变抑制剂组合的筛选

利用二次旋转组合设计筛选能取代亚硫酸盐的鲜切马铃薯复合褐变抑制剂组合,分析其对鲜切马铃薯贮藏期间PPO活性和褐变度的影响。结果表明,马铃薯切片最佳复合防褐剂配方组合为0.005%曲酸+0.045%异抗坏血酸钠+0.045%半胱氨酸(L-Cys)+0.01%CaCl2+0.2992%EDTA-2Na。该褐变抑制剂能够显著抑制鲜切马铃薯贮藏期间PPO活性,整个贮藏期间推迟PPO活性高峰时间6d以上;对鲜切马铃薯组织的褐变有明显延缓作用,处理组感官效果明显优于亚硝酸盐处理组和蒸馏水对照组,可以替代亚硫酸盐作为防褐剂用于鲜切马铃薯的生产和流通环节。     

热处理对抑制鲜切马蹄褐变效果的研究

研究55℃热处理5 min和100℃热处理1 min 2种热处理方式对鲜切马蹄在4℃贮藏过程中褐变的抑制效果。结果表明:与对照相比,2种热处理方式均能延缓鲜切马蹄褐变度的上升和丙二醛(MDA)、总黄酮含量的上升,其中100℃热处理1 min效果最好。同时,2种热处理方式还抑制了鲜切马蹄褐变相关的多酚氧化酶(PPO)、过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)的酶活性。综合来看,热处理能够抑制鲜切马蹄褐变关键酶的活性,从而减轻褐变的发生,其中100℃热处理1 min效果较好。     

苔干酶促褐变归因分析

为分析苔干酶促褐变的主要影响因素,以"涡青一号"苔干为研究对象,研究了春苔去皮后,苔干三个不同部位(苔头、苔茎、苔根)的褐变度、总酚含量、多酚氧化酶(PPO)活性和过氧化物酶(POD)活性在六个时间点(0、4、8、20、30、48 h)中的大小,褐变度、总酚含量、PPO活性和POD活性在各时间段内的增长速度,以及苔干不同部位、不同时间点的褐变度分别与总酚含量、PPO活性、POD活性的相关性。结果表明:苔干去皮8～30 h内褐变度显著提高(p0.05),30 h后,苔头的褐变情况明显高于苔茎和苔根,是苔干褐变控制的重点部位;总酚含量随时间增加先上升后下降,在20 h达到峰值;PPO、POD活性均随着时间增加而升高,但PPO、POD活性增速分别在8～20 h、20～30 h达到最高水平。在相关性方面,PPO、POD活性与苔头、苔茎和苔根的褐变度均极显著相关(p0.01),总酚含量与苔干去皮0 h内、30 h时的褐变度显著相关(p0.05),PPO、POD活性与苔干去皮48 h时的褐变度极显著相关(p0.01);PPO和POD酶活性是影响苔干酶促褐变的关键因素。     

柿子醋贮藏期间褐变及其抑制方法

研究柿子醋褐变原因及抑制其褐变方法。利用分光光度计和色差法分析柿子醋在贮藏期间总酚含量、多酚氧化酶(polyphenol oxidase,PPO)和过氧化物酶(peroxidase,POD)活性以及褐变度的变化,并研究几种抑制剂(NaCl、柠檬酸和L-抗坏血酸)对其褐变抑制的影响。结果表明:柿子醋贮藏期间发生的褐变主要是由于PPO和POD催化氧化总酚类物质引起的酶促褐变。不同质量浓度的褐变抑制剂NaCl、柠檬酸和L-抗坏血酸均显著维持醋液中较高的总酚含量,抑制PPO和POD活性,从而降低褐变度,减缓褐变发生,其中以0.24g/100mL NaCl、溶液1.2g/100mL柠檬酸和0.48g/100mL L-抗坏血酸对柿子醋抑制效果较好。     

鸡腿菇的酶促褐变机理及其抑制研究

采用SPSS软件分析鸡腿菇贮藏过程中褐变与多酚氧化酶(PPO)、过氧化物酶(POD)活性变化的关系.用抗坏血酸(Vc)、亚硫酸钠和柠檬酸分别处理鸡腿菇,试图找到减轻鸡腿菇褐变的方法.结果表明:鸡腿菇在贮藏过程中褐变度逐渐增大,POD活性呈先上升后下降的趋势,其褐变度与PPO活性显著相关,均趋于上升,PPO活性的变化是引起鸡腿菇酶促褐变的主要原因;Vc、亚硫酸钠和柠檬酸三种处理均可不同程度地减轻鸡腿菇的褐变度,其中0.15-0.2mmol/L的柠檬酸处理效果最好,其次是亚硫酸钠和Vc.     

稳定态二氧化氯对鲜切马铃薯贮藏性及酶褐变的初步研究

本文对不同浓度二氧化氯（ClO2）对鲜切马铃薯褐变和贮藏性的影响进行了研究。实验结果表明ClO2处理时间越长效果越好，浓度却不一定越大越好。不同浓度二氧化氯（ClO2）处理均对PPO和POD酶产生抑制作用，其中二氧化氯240mol／L处理10min、360mol／L处理5min和360m01／L处理10min处理效果最好；马铃薯的PPO、POD活性很高且两者之间具有相关性，与褐变度数值相吻合：经过不同浓度二氧化氯（ClO2）处理的样品之间蛋白质含量有差异，但不太明显。     

影响鲜切马铃薯褐变相关酶及底物的研究

本文通过对克新4号和克新13号马铃薯鲜切贮藏期间,褐变相关酶活性、相关底物的比较研究,探讨鲜切马铃薯褐变机理。结果表明:鲜切后1 h,克新4号即出现轻微褐变,4 h后褐变明显,而克新13号鲜切后12 h仍具有较好颜色,2 d后出现轻微褐变。两个品种马铃薯汁液颜色在初始时比较接近,而25 min后汁液颜色差异明显,克新4号褐变程度明显重于克新13号。褐变重的马铃薯,PPO活性高。切割后贮藏期间,克新4号PPO活性始终高于克新13号。克新4号酪氨酸酶活性高于克新13号,POD活性始终低于克新13号,两个品种的PAL活性差异不显著(p0.05)。褐变相关的主要底物可能是原儿茶酸,不是绿原酸。机械伤害增加了膜脂过氧化作用,导致了丙二醛含量的升高。     

不同抗褐变剂处理对鲜切慈姑褐变的影响

以慈姑为研究材料,研究1%抗坏血酸和0.2 g/L阿魏酸2个抗褐变剂处理对鲜切慈姑冷藏(4±1℃)过程中褐变的影响。通过测定贮藏过程中鲜切慈姑褐变度、可溶性固形物含量(TSS)、总酚、类黄酮含量、多酚氧化酶(PPO)、过氧化物酶(POD)和苯丙氨酸解氨酶(PAL)活性等各项指标的变化,确定抗褐变剂对鲜切慈姑褐变的影响。结果发现, 2种抗褐变剂均能有效抑制鲜切慈姑的褐变,较好维持鲜切慈姑TSS含量,降低鲜切慈姑贮藏过程中总酚、类黄酮含量的上升,有效抑制褐变关键酶PPO、POD和PAL活性,不同抗褐变剂抑制效果不同,但是从褐变度和营养品质上看0.2 g/L阿魏酸处理效果较好。     

Evaluation of atmospheric pressure plasma to improve the safety of sliced cheese and ham inoculated by 3-strain cocktail Listeria monocytogenes

The objective of this study was to evaluate the efficacy of atmospheric pressure plasma (APP), which is capable of operating at atmospheric pressure in air, in sliced cheese and ham inoculated by 3-strain cocktail of Listeria monocytogenes (ATCC 19114, 19115, and 19111, LMC). The process parameters considered were input power (75, 100, 125, and 150 W) and plasma exposure time (60, 90, and 120 s). Microbial log reduction increased with increases of input power and plasma exposure time. After 120 s APP treatments at 75, 100, and 125 W, the viable cells of LMC were reduced by 1.70, 2.78, and 5.82 log in sliced cheese, respectively. More than 8 log reductions can be achieved in 120 s at 150 W. In contrast, reductions after 120 s ranged from 0.25 to 1.73 log CFU/g in sliced ham. Calculated D values, the exposure time required to inactivate 90% of a population, from the survival curves of 75, 100, 125, and 150 W of APP treatments were 71.43, 62.50, 19.65, and 17.27 s for LMC in sliced cheese, respectively, and those in sliced ham were 476.19, 87.72, 70.92, and 63.69 s. No viable cells were detected at 125 and 150 W of APP treatment in sliced cheese, irrespective of plasma exposure time, after 1 week at a detection limit of 10¹ CFU/g. These results indicate that the inactivation effects of APP on L. monocytogenes are strongly dependent on the type of food.     

Effects of illumination and packaging on non-heme iron and color attributes of sliced ham

This study was designed to investigate effects of illumination and packaging on color of cooked cured sliced ham during refrigeration, and the possibility of decomposition of nitrosylheme under light and oxygen exposure. Three illumination levels and three packaging films with different oxygen transmission rates (OTRs) were used in two separate experiments during 35 days storage, and pH value, a* value, nitrosylheme, residual nitrite and non-heme iron were evaluated. Packaging OTRs had significant effects (P<0.01) on a* value, but illumination level and packaging OTR did not affect (P>0.05) nitrosylheme concentration during storage. For both groups, storage time had a significant effect (P<0.01) on a* value and nitrosylheme. Negative relationships between nitrosylheme and nitrite in the illumination group, and between nitrosylheme and non-heme iron in the packaging group were observed. Therefore, illumination level and packaging OTR had limited effects on overall pigment stability, but more discoloration and loss of redness occurred on the surface of products.     

Inactivation kinetics of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni in ready-to-eat sliced ham using UV-C irradiation

To investigate the applicability of UV-C irradiation on the inactivation of foodborne pathogenic bacteria in ready-to-eat sliced ham, UV-C treatment was evaluated. Irradiation dose required for 90% reduction of the populations of Listeria monocytogenes, Salmonella enterica serovar Typhimurium, and Campylobacter jejuni were determined to be 2.48, 2.39, and 2.18 J/m². Ready-to-eat sliced hams were inoculated with the pathogens and irradiated with UV-C light of 1000, 2000, 4000, 6000, and 8000 J/m². Microbiological data indicated that foodborne pathogen populations significantly (p < 0.05) decreased with increasing UV-C irradiation. In particular, UV-C irradiation at 8000 J/m² reduced the populations of L. monocytogenes, S. Typhimurium, and C. jejuni in the ham by 2.74, 2.02, and 1.72 log CFU/g. The results indicate that UV-C irradiation can be used as a microbial inactivation method for ready-to-eat sliced ham, and inactivation kinetics of the foodborne pathogens fit the Weibull model better than the first-order kinetics model.     

小麦粉特性对刀削面品质的影响

为了研究小麦粉性能指标对刀削面品质的影响并优选刀削面适用的小麦品种,测定了国内外41个不同品种小麦粉的品质和制成刀削面的相关性能,采用相关分析、通径分析方法对小麦粉品质指标与刀削面品质之间的关系进行分析。结果表明:小麦粉中湿面筋含量、吸水率、稳定时间、弱化度、拉伸阻力、最大拉伸阻力、拉伸面积等指标与刀削面的黏性、适口性、硬度等相关性显著(P0.05)或极显著(P0.01);再结合通径分析得出小麦籽粒硬度、灰分含量、湿面筋含量、总蛋白含量、稳定时间、弱化度、拉伸阻力、拉伸面积为影响刀削面品质的主要因素;优选出了12种最适宜制作刀削面的小麦品种;确定了优质刀削面用小麦及小麦粉关键指标范围:灰分小于0.55%、籽粒硬度指数45.0~62.0 H、湿面筋含量27.8%~32.5%、总蛋白质量分数12.7%~15.9%、稳定时间3.9~6.7 min、弱化度67.7~108.3 FU、拉伸阻力222.6~303.0 BU、拉伸面积65.9~99.1 cm2。     

Formation of biogenic amines and relation to microbial flora and sensory changes in smoked turkey breast fillets stored under various packaging conditions at 4 degrees C

The present study evaluated: (1) the formation of biogenic amines (BAs) in smoked turkey fillets during storage under aerobic and modified atmosphere packaging (MAP) conditions at 4 degrees C, (2) the relation of BAs to microbial and sensory changes in turkey meat and (3) the possible role of BAs as indicators of poultry meat spoilage. Smoked sliced turkey fillets were stored in air and under vacuum, skin and two modified atmospheres (MAP), M1 (30% CO(2)/70% N(2)) and M2 (50% CO(2)/50% N(2)), at 4+/-0.5 degrees C, for a period of 30 days. The BAs determined were: tryptamine, tyramine, histamine, putrescine, cadaverine, spermidine and spermine. Low levels of BAs were observed throughout the entire storage period, with the exception of histamine, tyramine and tryptamine, for which higher concentrations were recorded. Values for these three BAs were the highest for air-packaged samples (32.9, 25.0 and 4.1mg/kg, respectively) and the lowest for skin-packaged samples (11.9, 4.3 and 2.8 mg/kg, respectively) after 30 days of storage. All microorganism populations increased throughout the storage period, except for Pseudomonas spp. and Enterobacteriaceae, in skin-packaged fillets and modified atmosphere M2, which remained under the method detection limit (<1logCFU/g) until day 30 of storage. Pseudomonas spp. and Enterobacteriaceae for the rest of the packaging treatments remained below 5logCFU/g throughout storage. On the other hand, lactic acid bacteria were dominant throughout the storage period, regardless of the packaging conditions reaching 8.9logCFU/g on day 30 of storage. Mesophiles reached 7logCFU/g after ca. 19-20 days for the air and skin packed samples, 22-23 days for the M2 and vacuum packed samples and 25-26 days for the M1 packed samples. BA values for tryptamine, histamine and tyramine correlated well with both microbiological and sensory analyses data. Tryptamine, histamine and tyramine may be used as chemical indicators of turkey meat spoilage.     

Effect of modified atmosphere packaging on the shelf-life of coated, whole and sliced mushrooms

Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl₂ and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms.     

Chemical, sensory and shelf life evaluation of sliced salmon treated with salts of organic acids

This study was carried out to evaluate the shelf life, chemical quality and sensory attributes of salmon slices treated by dipping in 2.5% aqueous solution of sodium acetate (NaA), sodium lactate (NaL), or sodium citrate (NaC) during refrigerated storage at 1 degrees C. The chemical analyses demonstrated significant reduction in K value, hypoxanthine (Hx) concentration, total volatile base nitrogen (TVB-N), and trimethylamine (TMA) in treated salmon slices when compared with the control. Sensory scores of treated salmon were in a typical category for appearance, juiciness and tenderness compared with the control. Only minor changes in the sensory attributes were recognized by few panellists in NaA- and NaL-treated samples. A shelf life of 12, 12 and 15 days has been estimated for salmon treated with NaL, NaC, and NaA, respectively, versus 8 days for control. The salts of organic acids can therefore be used as safe preservatives for fish under refrigerated storage.     

Antilisterial activity of carrots: Effect of temperature and properties of different carrot fractions

Physiological or microbiological factors associated to carrot tissue were responsible for a lethal or otherwise inhibitory effect on Listeria monocytogenes, depending on culture conditions and carrot preparation. The fate of L. monocytogenes on sliced carrots subjected to different attachment and incubation temperatures has been analyzed in this work, as well as the effect of the carrot temperature itself. The maximum antilisterial activity was achieved under the lowest assayed values of attachment and incubation temperatures (10 and 4 °C, respectively), whereas an inhibitory but not lethal effect was observed under higher values. Carrot temperature itself interfered with the antilisterial activity, since, as the pre-warming length increased, carrot lethality against Listeria decreased, although its proliferation was inhibited in all cases. Additionally, the antilisterial activity of two different carrot fractions, the alcohol-insoluble carrot extract (AICE) and carrot juice, has been analyzed. The AICE did not exert any lethal effect on Listeria, although microbial growth was not detected either. Reductions in Listeria population below the detection limit were achieved later on carrot disks (50 h) than in juice (24 h), which suggested higher availability of the antilisterial compound in the juice and maybe an antagonistic action of the indigenous microflora, present in the juice but not in the sterile disks.     

Comparison of primary predictive models to study the growth of Listeria monocytogenes at low temperatures in liquid cultures and selection of fastest growing ribotypes in meat and turkey product slurries

This study compared the performance of four primary mathematical models to study the growth kinetics of Listeria monocytogenes ribotypes grown at low temperature so as to identify the best predictive model. The parameters of the best-fitting model were used to select the fastest growing strains with the shortest lag time and greatest growth rate. Nineteen food, human and animal L. monocytogenes isolates with distinct ribotype were grown at 4, 8, and 12 degrees C in tryptic soy broth and slurries prepared from cooked uncured sliced turkey breasts (with or without potassium lactate and sodium diacetate, PL/SD) and cooked cured frankfurters (with or without PL/SD). Separate regressions were performed on semi-logarithm growth curves to fit linear (based on Monod) and non-linear (Gompertz, Baranyi-Roberts, and Logistic) equations and performance of each model was evaluated using an F-test. No significant differences were found in the performance of linear and non-linear models, but the Baranyi model had the best fit for most growth curves. The maximum growth rate (MGR) of Listeria strains increased with the temperature. Similarly MGR was found significantly greater when no antimicrobials were present in the formulation of turkey or frankfurter products. The variability in lag times and MGRs in all media as determined by the Baranyi model was not consistent among strains. No single strain consistently had the fastest growth (shortest lag time, fastest MGR, or shortest time to increase 100-fold), but nine strains were identified as fastest growing strains under most growth conditions. The lack of association between serotype and fastest strain was also observed in the slurry media study. The fastest growing strains resulting from this study can be recommended for future use in L. monocytogenes challenge studies in delicatessen meat and poultry food matrices, so as to develop conservative pathogen growth predictions.     

Inhibition of Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus on sliced roast beef by cetylpyridinium chloride and acidified sodium chlorite

The effects of 0.5% cetylpyridinium chloride (CPC), 0.12% acidified sodium chlorite (ASC) and a mix of equal volume of the two (0.25% CPC-0.06% ASC) on Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus were evaluated on inoculated sliced roast beef. The antimicrobial agents were, respectively, sprayed on the beef surfaces and tray absorbent pads, and samples were stored at 4 degrees C for 10 days (d). At 0 d, L. monocytogenes and S. aureus were reduced to undetectable levels in 2 h after spraying with CPC. CPC-ASC treatment reduced E. coli O157:H7, L. monocytogenes and S. aureus by 4.07, 6.37 and 4.32 log cfu/cm2, respectively, at 0 d. ASC treatment reduced the population of E. coli O157:H7 by 6.09 log cfu/cm2 at 10 d. CPC treatment caused a slight discoloration and ASC-treated beef surfaces demonstrated the lowest redness and highest lightness. The grey colour and off-odour were significant in the ASC-treated beef samples, while CPC-treated samples demonstrated less off-odor and brown colour from 0 to 4 d. Based on our results, it appears that the application of CPC on sliced roast beef can extend the shelf-life of the product without impairing its quality.