The uptake of na and its redistribution between leaves during the development and alleviation of K deficiency

Changes in the concentration of Na in the shoot dry matter and in the petiole sap of individual leaves of lettuce were measured in order to determine the extent to which Na was able to replace K within the plants during K deficiency. The results were used to estimate changes in the distribution of the total ionic concentration between leaves and to make deductions about likely variations in osmotic potential within the shoots and their effect on plant growth. Measurements of Na concentration revealed both a pronounced delay in the uptake of additional amounts of Na and in its translocation within the K-deficient plants. Sodium concentrations increased most rapidly in the young expanding leaves during the onset of K deficiency but the changes in its concentration were ultimately larger in the middle to older ones. Elevated Na concentrations in the younger leaves of K-deficient plants also declined more rapidly than those in any of the other leaves following reintroduction of the K supply. Although the pattern of these changes broadly mirrored the corresponding changes in K concentration within the shoots there were significant reductions in the combined K+Na concentrations during the onset and development of K deficiency. The deficit in K+Na was initially greatest in the young leaves but subsequently disappeared more quickly when either the uptake of Na was increased or the K supply was resumed. Since the combined concentrations of K+Na were directly related to the changes in total ionic concentrations within the shoots, the results suggest that during K deficiency, plants adopt a strategy which reduces the effects of a decline in ionic strength at the most actively growing sites in order to minimise the damage to normal growth processes from changes in the internal osmotic pressure.     

Inhibition of Browning of Harvested Head Lettuce

Treatments to control browning of lettuce stem discs (cv Iceberg) were evaluated by measuring changes in the L*, a* and b* parameters as well as Hue angle values. Cysteine, resorcinol, EDTA and citric acid prevented discoloration. Different concentrations of organic acids (citric, acetic and gluconic), vinegar and lemon juice were also tested. The best results were obtained when the discs were treated with 10 mL/L and 50 mL/L acetic acid solutions and vinegar. These treatments were then applied to head lettuces and browning was measured during 7 days storage at 2°C plus an additional commercialization of 3 days at 13°C. Vinegar and 50 mL/L acetic acid solution inhibited browning on lettuce stem cuttings and could be used to prevent lettuce butt discoloration during cold storage and commercial handling.     

Some observations on the oxygen changes in a lake covered with Pistia stratiotes L.

A study has been made on the dissolved oxygen levels and pH changes in a polluted lake covered with Pistia stratiotes L. (water lettuce). The lake generally showed low levels of dissolved oxygen and low pH values. These could be attributed to the incoming organically rich water, coverage of the surface by Pistia plants and to the decomposition of these plants resulting in the formation of sludge at the bottom of the lake.     

结球生菜二氧化碳伤害预警指标的初步筛选

目的 研究结球生菜在不同浓度二氧化碳中挥发性成分含量的变化情况,有助于筛选结球生菜二氧化碳伤害预警的特征性成分。方法 将结球生菜放置于动态气调环境中,通过气相色谱-质谱分析其挥发性成分。结果 实验结果表明,结球生菜在0℃、氧气的体积分数为3%条件下贮藏时,当环境中二氧化碳的体积分数大于6%时会受到伤害。在伤害和非伤害条件下,氯代十八烷、4-丙基甲苯、4-乙基甲苯、1,2,4-三甲基苯、乙酸十一酯、丁酸癸酯、己二酸单乙酯、己酸己酯、二苯乙烯、二烯丙基二硫醚的变化趋势显著不同,这些成分的变化可能与二氧化碳伤害有关。结论 十四烷、乙酸十一酯和丁酸己酯的浓度在结球生菜开始受到伤害时出现了拐点式变化,这可作为结球生菜受到二氧化碳伤害的候选预警指标。     

鲜切莴苣护色处理的试验研究

研究贮藏条件及抗坏血酸、植酸和柠檬酸等护色剂对鲜切莴苣色泽变化的影响。结果表明,真空冷藏可较好地抑制酶促褐变,把鲜切莴苣片置入0.05%抗坏血酸、0.25%植酸、0.05%柠檬酸和0.5%氯化钙组成的复合护色液中,浸泡5min可有效护色,护色时间可达5d。     

莴笋渗透脱水有效扩散系数研究

以葡萄糖溶液浓度(10%～40%)和温度(35～65℃)为影响因素,研究了莴笋渗透脱水的动力学过程。分别使用Azuara模型和Fick第二扩散定律计算出了平衡时刻的失水率、固形物增加率以及相应的水分和固形物有效扩散系数。设计了均匀实验,通过曲面拟合的方法得到了水分、固形物有效扩散系数与因素的回归方程。结果表明:失水率随着葡萄糖溶液浓度增加而增大,但随着温度的升高而降低;固形物增加率随着溶液浓度和温度的增加而增加。Azuara模型可用来预测失水率和固形物增加率,通过曲面拟合得到的有效扩散系数回归方程拟合性较高。有效扩散系数反映了失水率和固形物增加率达到平衡时刻的快慢程度。     

Ultrasonication and Fresh Produce (Cos lettuce) Preservation

Washing Cos lettuce in various sanitizers at different concentrations with and without ultrasonication (40 KHz) reduced the microbiological counts by 1 to 2.5 log colony‐forming units (CFU)/g immediately after washing. Ultrasonication of Cos lettuce in water, chlorinated water, peracetic acid, hydrogen peroxide, and their combinations at various temperatures (4 °C, 20 °C, 35 °C, 47 °C, and 50 °C) had no significant effects (P > 0.05) on the total or the psychrophilic counts during storage at 10 °C. The total count in Cos lettuce reached 9.74 ± 0.035 log CFU/g after ultrasonication (2 min at 50 °C) in chlorinated water (100 mg/L) and storage for 6 d at 10 °C. Extending the ultrasonication (40 kHz) of Cos lettuce for up to 20 min did not improve the bactericidal effect of ultrasonication. However, long‐time ultrasonication (20 min) caused significant (P < 0.05) damage to the quality of Cos lettuce tissues.     

Influence of Green,Red and Blue Light Emitting Diodes on Multiprotein Complex Proteins and Photosynthetic Activity under Different Light Intensities in Lettuce Leaves (Lactuca sativa L.)

The objective of this study was to investigate the response of light emitting diodes (LEDs) at different light intensities (70 and 80 for green LEDs, 88 and 238 for red LEDs and 80 and 238 μmol m⁻² s⁻¹ for blue LEDs) at three wavelengths in lettuce leaves. Lettuce leaves were exposed to (522 nm), red (639 nm) and blue (470 nm) LEDs of different light intensities. Thylakoid multiprotein complex proteins and photosynthetic metabolism were then investigated. Biomass and photosynthetic parameters increased with an increasing light intensity under blue LED illumination and decreased when illuminated with red and green LEDs with decreased light intensity. The expression of multiprotein complex proteins including PSII-core dimer and PSII-core monomer using blue LEDs illumination was higher at higher light intensity (238 μmol m⁻² s⁻¹) and was lowered with decreased light intensity (70–80 μmol m⁻² s⁻¹). The responses of chloroplast sub-compartment proteins, including those active in stomatal opening and closing, and leaf physiological responses at different light intensities, indicated induced growth enhancement upon illumination with blue LEDs. High intensity blue LEDs promote plant growth by controlling the integrity of chloroplast proteins that optimize photosynthetic performance in the natural environment.     

NaClO处理鲜切生菜中大肠菌群数的预测模型研究

NaClO是一种在食品消毒方面普遍使用的消毒剂。本文主要研究了NaClO处理对鲜切生菜中大肠菌群数的影响。运用中心复合设计(CentralCompositeDesign,CCD)的响应曲面(ResponseSurfaceMethod)试验,建立以NaClO浓度、浸泡时间、和水菜比三个因素为自变量,以大肠菌群减少百分率值为响应值的预测模型,通过统计学分析(线性相关系数r=0.9707,p值=0.0044)表明所建立的模型预测能够有效的预测NaClO处理后鲜切生菜中的大肠菌群数。     

壳聚糖降解液对鲜切莴笋的防腐保鲜效果

用常温水解壳聚糖得到的粘均相对分子质量Mv在1500～2000的降解液、结合热处理对鲜切莴笋进行保鲜试验。结果表明,采用质量分数50%的壳聚糖降解液、45℃浸泡2min的处理方法,鲜切莴笋的微生物生长以及褐变被明显抑制,在贮藏期9d内,细菌总数在106cfu/g左右,PPO活性峰值比对照降低46%,Vc含量高于对照56%,感官品质保持良好。