Interactions oftrans-cinnamic acid,its related phenolic allelochemicals,and abscisic acid in seedling growth and seed germination of lettuce

Phenolic compounds have been identified as the most common allelochemicals produced by higher plants. Inhibitions of cinnamic acid, its related phenolic derivatives, and abscisic acid (ABA) on seedling growth and seed germination of lettuce were studied.trans-Cinnamic acid, ando-,m-, andp-coumaric acids inhibited the growth of etiolated seedlings of lettuce at concentrations higher than 10^–4 M and seed germination above 10^–3 M. Coumarin inhibited seedling growth and seed germination at 10^–5 M or above. Chlorogenic acid inhibited seedling growth above 10^–4 M, but did not inhibit seed germination at 10^–5–5×10^–3 M. Low concentrations (below 10^–3 M) of caffeic and ferulic acids promoted the elongation of hypocotyls, but higher concentrations (over 10^–3 M) inhibited seedling growth and seed germination. These phenolic compounds and abscisic acid had additive inhibitory effects both on seedling growth and seed germination. The inhibition on lettuce was reversed by caffeic and ferulic acids at concentrations lower than 10^–3 M except for the inhibition of germination by coumarin. These results suggest that in naturetrans-cinnamic acid,o-, m-, p-coumaric acids, coumarin, and chlorogenic acid inhibit plant growth regardless of their concentration. However, caffeic and ferulic acids can either promote or inhibit plant growth according to their concentration.     

Effects of Quillaja saponaria extract and Nα-lauroyl-l-arginine ethyl ester on reducing selected foodborne pathogens in vitro and maintaining quality of fresh-cut endive (Cichorium endivia L.) at pilot plant scale

The aim of the present study was to evaluate the applicability of Quillaja saponaria extract (QSE) and N^α-lauroyl-l-arginine ethyl ester (LAE) as antimicrobial wash water additives in fresh-cut lettuce processing. Antibacterial activities of LAE and QSE against selected strains of the foodborne pathogens Salmonella enterica, Bacillus cereus, Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes were examined in vitro. Minimum inhibitory concentrations determined by broth microdilution assay demonstrated that LAE exhibited a strong antimicrobial activity with MICs between 4 and 32 μg/mL against all tested strains, whereas QSE showed a weaker antimicrobial activity with MICs >512 μg/mL. On a pilot-plant scale, the effects of warm water washing at 45 °C for 120 s with and without 40 mg/L QSE or 100 mg/L LAE as well as cold water washing at 4 °C for 120 s with QSE or LAE, respectively, of shredded endive (Cichorium endivia L.) were investigated regarding microbiological and sensory quality as well as physiological properties. Samples were analyzed for headspace O₂ and CO₂ levels, phenylalanine-ammonia-lyase activity and contents of nitrite and nitrate during nine days of cold storage at 4 °C. By analogy to its antimicrobial effect against the foodborne pathogens in vitro, LAE allowed up to 4 log₁₀ cfu/mL reduction of the microbial load in the washing water of the pilot plant, and might therefore reduce cross-contamination while saving water. The addition of LAE to warm washing water impaired sensory properties of fresh-cut endive during storage, which was predicted by chlorophyll fluorescence imaging analyses. QSE treatment combined with warm water washing best retained sensory appearance throughout our study, being possibly suitable for the production of premium products.     

Arsenic uptake potential of water lettuce (Pistia Stratiotes L.)

Arsenate uptake by aquatic plant water lettuce (Pistia stratiotes L.) was studied in the laboratory condition to investigate a low cost natural aquatic treatment system for pollutant removal. The plants were harvested from a local pollution‐free pond in young condition and hydroponically cultured in the laboratory. Bio‐accumulation was noticed to be both concentration and duration dependent. The results show that the plant could effectively absorb arsenic between a range of 0.25 to 5.0 mg/l to the extent of 82.0 to 22.8% for a biomass of 20 g/l at pH 7.0 after 144 h. The results were also plotted in Langmuir and Freundlich isotherms and the data were well fitted. The sorption capacity was evaluated as 1.43 mg/g for the Langmuir isotherm and 1.01 mg/g for the Freundlich isotherm. The removal efficiency was, however, noted to be maximum (87.5%) at pH 6.5. The effect of biomass quantity has also been investigated along with some metabolic parameters.     

冷配送莴笋菜肴的货架期预测模型建立与评价

本文以真空冷却后的热烫莴笋菜肴为对象,研究在0℃、4℃、10℃下冷藏的莴笋菜肴的品质变化规律,并建立冷配送莴笋菜肴在0℃~10℃冷藏温度下的货架期预测模型。结果表明:随着冷藏时间的延长,菌落总数、亚硝酸盐含量、色差a*值呈上升趋势,而硬度呈下降趋势。冷藏温度越高,其品质变化程度越大。亚硝酸盐含量与菌落总数密切相关,但其货架期终点比菌落总数的滞后,而冷藏温度和时间对硬度影响不大,两者均不适合作为冷配送莴笋菜肴货架期评定指标。以色差a*值为指标得到的一级反应动力学方程和Arrhenius方程拟合度较高(R20.97),而Logistic模型能很好拟合莴笋菜肴在0℃~10℃冷藏温度下的菌落总数生长动态(R20.99)。建立的色差和菌落总数货架期模型的预测值与实测值之间相对误差均小于10%。其中,以色差a*值为指标的货架期要求最高,若对莴笋菜肴进行护色处理,可提高其色差货架期。     

莴笋泡菜护绿护脆工艺研究

实验对莴笋泡莱护绿护脆工艺进行研究,通过正交试验确定最佳工艺条件:护脆处理:低温漂烫时间20 min,温度55℃,乳酸钙添加量为20 g/L;护绿处理:铜离子浓度为500μg/mL,锌离子浓度为500μg/mL,温度为80℃,浸泡时间为3 h.     

一株莴苣内生产香酵母菌的分离、鉴定及挥发性香气成分分析

通过平板划线分离法,从茎用莴苣中分离出一株酵母样真菌,命名为G0901。形态学特征、生理实验以及26S rDNA D1/D2区序列分析表明,该菌株属于Wickerhamomyces属的Wickerhamomyces anomalus。采用GC-MS方法,对该菌株麦芽汁发酵产生的挥发性香气成分进行检测,结果表明：该酵母菌发酵产生的香气组分主要为烯类和醇类,包括柠檬烯、月桂烯、香桧烯、α-蒎烯、罗勒烯、3-甲基-1-丁醇、苯乙醇和2-辛醇等,其中,柠檬烯的相对含量高达20%,这在发酵产香的微生物当中较少存在。因此,G0901菌株的分离为利用微生物高效生产柠檬烯提供了较好的研究材料。     

椰壳粉与腐植酸混合基质在生菜育苗上应用初探

研究了椰壳配制的基质对生菜幼苗生长发育的影响。结果表明,基质的配比椰壳∶蛭石∶腐植酸为4∶1∶1时,生菜幼苗的叶面积、株高、茎粗、根冠比、壮苗指数均显著优于其他比例的基质。该基质培育的生菜幼苗的干重也较其他处理呈明显差异(P<0.05),生物量增加效果显著。在实际生产中建议采用该比例的育苗基质进行生菜育苗。     

Prediction Equations for Gases in Flexible Modified-Atmosphere Packages of Respiring Produce are Different Than Those for Rigid Packages

Total pressure generally decreases in a sealed rigid package containing respiring produce, whereas total pressure is essentially constant and free volume decreases in a flexible package. We found that predicted O₂, CO₂, and N₂ partial pressures were different for similarly designed (same surface area, thickness, film permeabilities and produce mass) flexible and rigid packages at “quasi steady state” and steady state, respectively. Predicted O₂ and CO₂ partial pressures were slightly higher in a flexible package than in a rigid package and were a function of the film permeability ratio of N₂ to O₂ and of CO₂ to O₂. They also related to the ratio of product CO₂ production rate to O₂ uptake rate, target steady-state O₂ partial pressure, and respiration characteristics. Differences were slight for films such as low-density polyethylene.     

Dynamics of Indigenous Microbial Populations of Butter Head Lettuce Grown in Mulch and on Bare Soil

ABSTRACT:  The native microflora of lettuce cultivated in mulch and on bare soil and its evolution during storage at optimal condition were evaluated. Inner, mid, and outer leaves of the lettuce heads were analyzed separately and the evolution of the microbial populations were fitted to Gompertz and logistic models. The cultivation method (bare soil and mulch) introduced differences in the initial counts, evolution, and tolerance to refrigeration temperatures for some of the microbial populations under study. Most microbial populations from mulch lettuce presented a decline or little growth under refrigerated storage. However, populations from bare soil lettuce presented some growth phase during storage. Lactic acid bacteria from bare soil lettuce presented significant growth after 8 d of storage while LAB from mulch grown lettuce did not. Concurrently with the LAB growth, there was a decline in the coliform counts in bare soil grown lettuce. At the end of storage, the inner and mid leaves of mulch lettuce presented lower counts of psychrotrophic bacteria, LAB, and yeast and molds.     

Comparison of calcium lactate with chlorine as a washing treatment for fresh‐cut lettuce and carrots: quality and nutritional parameters

The efficacies of calcium lactate and chlorine washing treatments of fresh‐cut lettuce and carrots were compared during storage at 4 °C over 10 days. The gas composition of packages, colour, enzyme activity, texture, sensory attributes, microflora and levels of ascorbic acid and carotenoids were evaluated at 1, 3, 7 and 10 days. Calcium lactate treatment was not significantly different to chlorine treatment (p < 0.05) in terms of maintaining colour, texture and acceptability of fresh‐cut lettuce and carrots during the entire storage period. The washing treatments did not affect levels of ascorbic acid of fresh‐cut lettuce or carrots. Carotenoid levels were higher in calcium lactate‐treated carrots than chlorine‐treated samples at the end of storage. Mesophilic, psychrotrophic and lactic acid bacteria counts were not significantly different between treatments for both vegetables. Copyright © 2005 Society of Chemical Industry