High nisin Z production by Lactococcus lactis UL719 in whey permeate with aeration

The influence of controlled pH (5.0–6.5) and initial dissolved oxygen level (0–90% air saturation) on nisin Z production in a yeast extract/Tween 80-supplemented whey permeate (SWP) was examined during batch fermentations with citrate positive Lactococcus lactis subsp. lactis UL719. The total activity corresponding to the sum of soluble and cell-bound activities, as measured by a critical dilution method, was more than 50% lower at pH 5.0 than in the range 5.5–6.5, although the specific production decreased as pH increased. A maximum nisin Z activity of 8200 AU/ml (4100IU/ml) was observed in the supernatant after 8h of culture for pH ranging from 5.5 to 6.5. Prolonging the culture beyond 12h decreased this activity at pH 6.0 and 6.5 but not at pH 5.5 or 5.0. A corresponding increase in cell-bound activity was probably due to adsorption of soluble bacteriocin to the cell wall. Aeration increased cell-bound and total activity to maximum values of 32800 and 41000 AU/ml (16400 and 20500IU/ml), respectively, with an initial level of 60% air saturation after 24h of incubation at pH 6.0. The specific production at 60% or 90% initial air saturation was eight-fold higher than at 0%.     

Solubilization of cheese whey protein by trypsin and a process to recover the active enzyme from the digest

Porcine trypsin (EC 3.4.4.4) converted, within approximately 2 hr at 50°C, its 1000-fold weight of water-insoluble, heat-denaturated cheese whey protein into a water-soluble product. In the course of this digestion, the enzyme increased the α-amino nitrogen of the protein by a factor of >20, from 0.40 to 9.40%. After digesting the water-insoluble whey protein, fully active trypsin could be recovered from the soluble digest with the aid of a cellulose-based affinity adsorbent. The enzyme which was eluted from a column of p-aminobenzamidine, bound to succinylated aminododecylcellulose, was fully active and showed essentially unchanged kinetic properties with a synthetic substrate, L -benzoyl-arginine p-nitroanilide. It was possible to perform, with the same amount of trypsin, three subsequent and equally effective solubilizations of whey protein, followed by a fourth digestion which still yielded a soluble product, but was considerably slower and incomplete. During each digestion, an estimated 30% of the trypsin was lost. The was not due to a decreased efficiency of the affinity adsorbent, as its trypsin-binding capacity was essentially unaffected after over 10 cycles of use.     

Production of Fungal Mycelial Protein in Submerged Culture of Soybean Whey

Various soybean whey media were tested as substrate for seven species of fungi in submerged culture. Very little mycelial growth was obtained with Morchella hybrida, Collybia velutipes, Cantharellus cibarius, and Xylaria polymorpha. Agaricus campestris failed to grow. Tricholoma nudum and Boletus indecisus showed the greatest rate of growth and production of mycelial protein and the best utilization of soybean whey solids, with much shorter incubation times compared with those of the other species. T. nudum developed as spheres having diameters of about 5 to 8 mm, instead of the usual slurry or yeastlike form, in the presence of added ammonium acetate. B. indecisus always developed as spheres. Mycelial yields and production of protein by T. nudum greatly decreased with the addition of more than 1% glucose to soybean whey, whereas with B. indecisus the yield of protein almost doubled when up to 3% glucose was added. The effect of minerals on mycelial growth was determined. With soybean whey concentrated to 50%, the rate of mycelial growth of T. nudum was nearly doubled, but protein content of mycelia was greatly reduced. Mycelial growth and yield of protein of B. indecisus grown in concentrated whey were increased greatly. About 4 to 6 g of mycelial protein per liter can be obtained from fermentation in soybean whey, depending upon the medium used. Utilization of soybean whey by fungal fermentation may have economic value in whey disposal and in the production of products of high protein content.     

Improvement of the Surface Functional Properties of β-Lactoglobulin and α-Lactalbumin by Heating in a Dry State

Controlled heating in a dry state greatly improved the surface functional properties of whey proteins (β-lactoglobulin and α-lactalbumin). Although whey proteins were completely insolubilized by heating at 80°C in an aqueous solution, their solubility was kept even after heating at 80°C in a dry state (7.5% moisture content) for 5 days. The surface hydrophobicity of α-lactalbumin was increased during the dry-heating, while that of β-lactoglobulin was decreased. In addition, the fluorescence spectra excited at 280 nm of dry-heated whey proteins suggested the significant conformational changes. High-performance gel chromatography showed that a considerable amount of soluble aggregates was formed in the dry-heated β-lactoglobulin, while a small amount of soluble aggregate was observed in the dry-heated α-lactalbumin. The foaming properties of dry-heated whey proteins were increased to about 3 times that of untreated proteins. The emulsifying properties of dry-heated whey proteins were also increased, compared to untreated proteins, although a slight decrease in the emulsion stability was observed in dry-heated β-lactoglobulin. The improvement of the surface properties seemed to come from the partial unfolding suitable for the formation of foam film and the entrapment of oil droplets.     

Recovery of residual soluble protein by two-step precipitation process with concomitant COD reduction from the yeast-cultivated cheese whey

The present study was conducted to recover the residual soluble protein after cultivation of yeast (K. marxianus) in cheese whey. Cheese whey continuous fermentation with cell recycle system was carried out at 40 °C and pH 3.5. The yeast biomass was separated from the fermented broth by centrifugation and residual soluble protein from fermented whey supernatant was precipitated by heat treatment (at 100 °C, pH 4.5 and 10 min incubation). The maximum soluble protein recovery up to 53 % was achieved at pH 4.5 with 54 % residual COD removal. However, gravity sedimentable precipitates were obtained at pH 3.5 with 47 % protein recovery. Therefore, the reactor (scale up) study was conducted at pH 3.5 with agitation, which resulted in 68 % of residual soluble protein recovery and simultaneously residual COD removal of 62 %. Further precipitation/coagulation of soluble protein was also evaluated using carboxymethylcellulose (CMC) and then two precipitation (thermal followed by CMC precipitation) processes were combined to increase the protein precipitation, which finally reached up to 81 % of total soluble protein recovery from the supernatant. This optimized process could be applied to recover the residual protein left after fermentation of cheese whey without centrifugation.     

Effect of Water Content on Glass Transition and Protein Aggregation of Whey Protein Powders During Short-Term Storage

The objectives of this study were to investigate the moisture-induced protein aggregation of whey protein powders and to elucidate the relationship of protein stability with respect to water content and glass transition. Three whey protein powder types were studied: whey protein isolate (WPI), whey protein hydrolysates (WPH), and beta-lactoglobulin (BLG). The water sorption isotherms were determined at 23 and 45°C, and they fit the Guggenheim–Andersson–DeBoer (GAB) model well. Glass transition was determined by differential scanning calorimeter (DSC). The heat capacity changes of WPI and BLG during glass transition were small (0.1 to 0.2 Jg⁻¹ °C⁻¹), and the glass transition temperature (T _g) could not be detected for all samples. An increase in water content in the range of 7 to 16% caused a decrease in T _g from 119 down to 75°C for WPI, and a decrease from 93 to 47°C for WPH. Protein aggregation after 2 weeks’ storage was measured by the increase in insoluble aggregates and change in soluble protein fractions. For WPI and BLG, no protein aggregation was observed over the range of 0 to 85% RH, whereas for WPH, ∼50% of proteins became insoluble after storage at 23°C and 85% RH or at 45°C and ≥73% RH, caused mainly by the formation of intermolecular disulfide bonds. This suggests that, at increased water content, a decrease in the T _g of whey protein powders results in a dramatic increase in the mobility of protein molecules, leading to protein aggregation in short-term storage.     

Modification of Immobead 150 support for protein immobilization: Effects on the properties of immobilized Aspergillus oryzae β‐galactosidase

We studied the modification of Immobead 150 support by either introducing aldehyde groups using glutaraldehyde (Immobead‐Glu) or carboxyl groups through acid solution (Immobead‐Ac) for enzyme immobilization by covalent attachment or ion exchange, respectively. These two types of immobilization were compared with the use of epoxy groups that are now provided on a commercial support. We used Aspergillus oryzae β‐galactosidase (Gal) as a model protein, immobilizing it on unmodified (epoxy groups, Immobead‐Epx) and modified supports. Immobilization yield and efficiency were tested as a function of protein loading (10–500 mg g^?1 support). Gal was efficiently immobilized on the Immobeads with an immobilization efficiency higher than 75% for almost all supports and protein loads. Immobilization yields significantly decreased when protein loadings were higher than 100 mg g^?1 support. Gal immobilized on Immobead‐Glu and Immobead‐Ac retained approximately 60% of its initial activity after 90 days of storage at 4°C. The three immobilized Gal derivatives presented higher half‐lifes than the soluble enzyme, where the half‐lifes were twice higher than the free Gal at 73°C. All the preparations were moderately operationally stable when tested in lactose solution, whey permeate, cheese whey, and skim milk, and retained approximately 50% of their initial activity after 20 cycles of hydrolyzing lactose solution. The modification of the support with glutaraldehyde provided the most stable derivative during cycling in cheese whey hydrolysis. Our results suggest that the Immobead 150 is a promising support for Gal immobilization. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:934–943, 2018     

Production of β-carotene from deproteinized waste whey filtrate using Mucor azygosporus MTCC 414 in submerged fermentation

The cheese whey, a by-product of dairy industry proved to be an attractive substrate for production of β-carotene. The β-carotene production from Mucor azygosporus MTCC 414 by using deproteinized waste whey filtrate under submerged fermentation was investigated. Various fermentation variables, such as lactose content in whey, initial pH, production temperature, incubation time, and carbon and nitrogen sources played significant role on β-carotene production. Maximum β-carotene production (385 μg/g dcw) was obtained with the whey (pH 5.5) containing 3.5% (w/v) lactose supplemented with soluble starch at (1.0%, w/v) at 30°C after a 5 days incubation. Moreover, unlike other microorganisms which utilize pre-hydrolyzed lactose, this Mucor azygosporus MTCC 414 was found to be capable of utilizing unhydrolyzed lactose present in the whey.     

Improved purification of beta-lactoglobulin from acid whey by means of ceramic hydroxyapatite chromatography with sodium fluoride as a displacer

The successful separation of beta-lactoglobulin from other bovine whey proteins was performed by ceramic hydroxyapatite chromatography with a fluoride ion gradient in phosphate buffer as displacement agent. The method was applied to acid whey originating from milk of healthy as well as of mastitic cows. beta-Lactoglobulin was completely eluted in one peak at a fluoride concentration of about 0.6 mol/l. The purity of beta-lactoglobulin in this fraction was at least 96% if whey from healthy milk was processed. Co-eluted contaminants are traces of immunoglobulin G, serum albumin and lactoferrin. In case of mastitic whey the proportion of beta-lactoglobulin is diminished as the amounts of immunglobulin G, serum albumin and lactoferrin are increased within this fraction. Size exclusion chromatography on Superdex 75 pg effectively removed contaminants resulting in a purity for beta-lactoglobulin from normal whey of approximately 99%. The yield of beta-lactoglobulin from physiological whey was 50-55% referring to the fraction highly enriched with beta-lactoglobulin by hydroxyapatite chromatography. In case of mastitic milk the higher amounts of contaminants were also removed successfully by size exclusion chromatography.     

Hydrolysis of lactose in whey permeate by immobilized β-galactosidase from Penicillium notatum

A new low-cost β-galactosidase (lactase) preparation for whey permeate saccharification was developed and characterized. A biocatalyst with a lactase activity of 10 U/mg, a low transgalactosylase activity and a protein content of 0.22 mg protein/mg was obtained from a fermenter culture of the fungus Penicillium notatum. Factors influencing the enzymatic hydrolysis of lactose, such as reaction time, pH, temperature and enzyme and substrate concentration were standardized to maximize sugar yield from whey permeate. Thus, a 98.1% conversion of 5% lactose in whey permeate to sweet (glucose-galactose) syrup was reached in 48 h using 650 β-galactosidase units/g hydrolyzed substrate. After the immobilization of the acid β-galactosidase from Penicillium notatum on silanized porous glass modified by glutaraldehyde binding, more than 90% of the activity was retained. The marked shifts in the pH value (from 4.0 to 5.0) and optimum temperatures (from 50°C to 60°C) of the solid-phase enzyme were observed and discussed. The immobilized preparation showed high catalytic activity and stability at wider pH and temperature ranges than those of the free enzyme, and under the best operating conditions (lactose, 5%; β-galactosidase, 610–650 U/g lactose; pH 5.0; temperature 55°C), a high efficiency of lactose saccharification (84–88%) in whey permeate was achieved when lactolysis was performed both in a batch process and in a recycling packed-bed bioreactor. It seems that the promising results obtained during the assays performed on a laboratory scale make this immobilizate a new and very viable preparation of β-galactosidase for application in the processing of whey and whey permeates.     

Influence of temperature and pH on the nonenzymatic reduction of triphenyltetrazolium chloride

The effects of temperature and pH on the nonenzymatic (chemical) reduction of triphenyltetrazolium chloride (TTC) to triphenyl formazan (TF) in cheese whey and municipal solid waste compost samples were studied. Ten different incubation temperatures and 13 pH levels were tested. The study showed that the TTC could be reduced nonenzymatically at high temperatures and/or under alkaline pH conditions. The nonenzymatic TTC reduction was observed at pH values greater than 9.5 and 11.0 for the cheese whey and compost, respectively. The TTC chemical reduction rate followed the same trend in both media. The TF content increased with increasing the pH value, reaching its maximum at a pH of 12, then decreased and was not detected at a pH of 13. The TTC was also reduced nonenzymatically at temperatures higher than 70 and 85 degrees C for cheese whey and compost, respectively. Evaporation did not seem to have any significant effect on the TTC chemical reduction since less than 3% of water content was lost at a temperature of 100 degrees C. It was noticed that the TF yield in cheese whey samples was higher than that in compost samples. This was due to the higher moisture content of cheese whey and the presence of copper in the compost samples, which reacted chemically with the TF causing reduction in the red color. For a given incubation period, the effect of pH on the TTC chemical reduction was more significant than the effect of incubation temperature (at a 2 h incubation period, 57.5% and 17.9% of the TTC were chemically reduced at a pH of 12 compared to 10.9% and 7.7% at an incubation temperature of 100 degrees C, for cheese whey and compost, respectively). Among the six metals tested (Ca, Cu, K, Na, Ni, and Zn) only Cu affected the color intensity of the TF. The activation energy of the TTC chemical reduction was 168,808 and 239,102 J/mol in cheese whey and municipal solid compost, respectively. For dehydrogenase activity measurement, the pH of the samples and the incubation temperature should not be higher than 9 and 60 degrees C in order to ensure that the TTC reduction is caused only by the biochemical reaction. Measuring the color intensity of TF in waste samples that contain copper could give misleading results as a result of the formation of formazan copper complex, which reduces the red color.     

Propionic acid fermentation of ultra-high-temperature sterilized whey using mono-and mixed-cultures

Summary Unlike sterilization by autoclave (Anderson et al. 1986) high concentrations of cheese whey sterilized by ultra high temperature (UHT) resulted in a medium conducive to microbial growth and propionic acid production. Propionibacterium freudenreichii ss. shermanii, grown with pH control in 12% whey solids and 1% yeast extract sterilized by UHT, produced about 1.9% propionic acid within 70 h; more than 50% of the lactose was not used. Under similar conditions, mixed cultures of P. shermanii and Lactobacillus casei produced more than 3.0% propionic acid. Acclimating the mixed culture to the whey medium resulted in 4.5% propionic acid. The amount of propionic acid produced was further increased to about 6.5% by raising the concentration of whey solids to about 18%. Using the mixed culture, all the lactose was consumed and lactic acid did not accumulate.     

Simultaneous single-cell protein production and COD removal with characterization of residual protein and intermediate metabolites during whey fermentation by K. marxianus

Cheese whey fermentation with Kluyveromyces marxianus was carried out at 40 °C and pH 3.5 to examine simultaneous single-cell protein production and chemical oxygen demand (COD) removal, determine the fate of soluble whey protein and characterize intermediate metabolites. After 36 h of batch fermentation, the biomass concentration increased from 2.0 to 6.0 g/L with 55 % COD reduction (including protein), whereas soluble whey protein concentration decreased from 5.6 to 4.1 g/L. It was confirmed through electrophoresis (SDS-PAGE) that the fermented whey protein was different from native whey protein. HPLC and GC–MS analysis revealed a change in composition of organic compounds post-fermentation. High inoculum concentration in batch fermentation resulted in an increase in biomass concentration from 10.3 to 15.9 g/L with 80 % COD reduction (including protein) within 36 h with residual protein concentration of 4.5 g/L. In third batch fermentation, the biomass concentration increased from 7.3 to 12.4 g/L with 71 % of COD removal and residual protein concentration of 4.3 g/L after 22 h. After 22 h, the batch process was shifted to a continuous process with cell recycle, and the steady state was achieved after another 60 h with biomass yield of 0.19 g biomass/g lactose and productivity of 0.26 g/L h. COD removal efficiency was 78–79 % with residual protein concentration of 3.8–4.2 g/L. The aerobic continuous fermentation process with cell recycle could be applied to single-cell protein production with substantial COD removal at low pH and high temperature from cheese whey.     

A Sensitive Radial Diffusion Method for Detection of Esterolytic Activities of Proteases

The influence of under-nutrition (sub-maintenance feeding) and ad libitum feeding on the deposition of proteins in different subcellular sarcoplasmic fractions of red (tonic) and white (phasic) muscles of growing broilers was investigated. The relative concentration of overall sarcoplasmic proteins was lesser in red than in white muscles from ad libitum fed broilers. The content of mitochondrial proteins was slightly more and that of lysosomal and microsomal proteins and of true soluble proteins was lesser in red than in white muscles. Besides, the relative amount of some specific molecular weight proteins in each subcellular fractions differed by more than 50% between red and white muscle.

There was also conspicuous differences in the influence of under-nutrition on the proteins in red and white muscles. Some reduction in mitochondrial, lysosomal, microsomal, and soluble protein content occurred only in white muscle, whereas little change was found in subcellular fractions in red muscle from underfed broilers. The relative amount of some proteins in each subcellular fraction of both muscles remained unaffected, and that of others either decreased or increased more than 20 to 50% due to nutritional stress.     

Acute versus chronic effects of whey proteins on calcium absorption in growing rats

The acute and chronic effects of whey proteins on calcium metabolism and bone were evaluated. In acute studies, 8-week-old male rats were gavaged with 50 mg whey protein concentrate (WPC) and 25 mg calcium. 45Ca was administered intravenously or orally. Kinetic studies were performed, and femurs were harvested. Four of seven WPCs significantly increased femur uptake of 45Ca compared with controls. One WPC at 50 mg enhanced calcium absorption over a range of calcium intakes from 35.1 +/- 9.4% to 42.4 +/- 14.0% (P < 0.01). Three of the most effective WPCs were tested further in a chronic feeding study. One hundred 3-week-old rats were randomly divided into four adequate dietary calcium (ADC; 0.4% Ca) groups (control of 20% casein and three WPC groups with 1% substitution of casein with each of three WPCs) and two low calcium (LC; 0.2% Ca) groups (control of 20% casein and one WPC group with 1% substitution of casein with one WPC). After 8 weeks, there was no effect of WPCs on femur uptake of 45Ca among ADC groups and there was no effect of WPCs on calcium retention, femur breaking force, femur bone mineral density, or total femur calcium at either dietary calcium intake. However, whole body bone mineral content (BMC) was significantly higher (P < 0.05) in the three whey protein concentrate ADC groups compared with the ADC control group. Total BMC at the proximal tibia in whey protein ADC groups was increased, as shown by peripheral quantitative computed tomography. Our results indicate that the acute calcium absorption-enhancing effect of whey proteins did not persist through long-term feeding in rats. However, the initial enhancement of calcium absorption by whey protein was sufficient to increase BMC.     

Temporary immersion bioreactors (TIB) provide a versatile,cost-effective and reproducible in vitro analysis of the response of pineapple shoots to salinity and drought

Effects of salinity (NaCl) and the carbon source mannitol (0–200 mM) on micropropagation of pineapple cv. MD2 were analyzed in temporary immersion bioreactors (TIBs). Shoot multiplication rate, shoot cluster fresh weight and levels of aldehydes, chlorophylls, carotenoids and phenolics were determined in the plant material. The content of soluble phenolics in the culture medium was also evaluated. NaCl or mannitol above concentrations of 50 mM decreased pineapple shoot multiplication and fresh weight significantly. Two hundred mM NaCl decreased multiplication rate by 71.5% and cluster fresh weight by 40.0%. NaCl increased 2.4 times the levels of other aldehydes; 1.4 times the soluble phenolics in shoots; and 1.4 times the phenolics excreted to the culture medium. On the other hand, mannitol decreased the multiplication rate and cluster fresh weight by about 60%. Mannitol increased the contents of chlorophyll b 1.4 times and soluble phenolics 2.1 times. Results indicated that pineapple cv. MD2 is more sensitive to NaCl than to mannitol. Multiplication rates indicate that a 50% reduction was obtained with 37.4 mM NaCl and 66.5 mM mannitol. These concentrations can be used to stress shoots during micropropagation in TIBs and screen for/detect somaclonal variants with an increased salinity or drought tolerance.     

Purification of glycomacropeptide from dialyzed and non-dialyzed sweet whey by anion-exchange chromatography at different pH values

Glycomacropeptide (GMP) was purified from sweet whey dialyzed in water by anion-exchange chromatography on DEAE-Sephacel at pH 2.0–4.5. The optimum pH range was 2.5–4.0. The yield of purified GMP increased and its sialic acid concentration decreased with increasing pH value. The GMP had an apparent isoelectric point <3.8. Dialysis of sweet whey was shown to be important to maximize the yield of GMP adsorbed to the anion-exchanger. Only highly sialylated GMP, accounting for approximately 55% of total sialic acid content, was adsorbed on the anion-exchanger from non-dialyzed sweet whey.     

Calmodulin antagonists inhibit germination of Bacillus cereus T spores

M. RACINE, J. DUMONT, C.P. CHAMPAGNE AND A. MORIN. 1991. The effects of lactose, ammonium and phosphate on the production of extracellular polysaccharide from Propionibacterium acidi-propionici VM-25 were studied in whey-based media. The polysaccharide was composed of a water-soluble fraction (15% w/w), a water-insoluble fraction (27% w/w) and ca 65% (w/w) of ash. Up to 15 g/l of polysaccharide was produced during growth on partially deproteinated whey, supplemented with lactose, NH₄ Cl and KH₂ PO₄, after incubation at pH 7.0 and 25.C for 90 h. The final viscosity of the medium remained under 20 centipoises at the end of the fermentation (100–140 h). The fermentation of whey enabled a reduction of the lactose content up to 50%. The polysaccharide-containing fractions were composed of glucose, galactose, mannose, rhamnose and fucose and had M, < 5800. The polysaccharide may have applications as a low viscosity stabilizing agent.     

Monitoring of changes in physical and microbiological properties of a Chernozem amended with different organic substrates

A soil microcosm study was made to monitor changes in soil physical and microbiological properties of a Chernozem during a period of up to 126 or 252 days following the addition of whey, straw or vegetable oil. In the whey treatment soil maximum water-holding capacity (MWHC) had decreased after seven and 28 days of incubation. At both dates, the differences to the untreated control were significant. Straw was able to increase MWHC of soil during incubation and after 42 and 126 days values differed significantly from those of the control. Compared with the control, whey, oil and straw treatments had higher meanweight diameter of dry aggregates. The differences were significant after seven, 28 and 126 days with whey, after 42, 126 and 252 days with oil, and after 126 days with straw. The sensitivity of dry aggregates to abrasion (SAA), representing a negative index of dry aggregate stability, was lower in the whey treatment than in the control after three and seven days incubation. In the later phase of incubation, whey tended to increase SAA. A trend to increase SAA also was observed with straw and after 126 days a significantly higher SAA for the straw than for the oil treatment was determined. This trend still was to observe after 252 days incubation. An increase in SAA observed for the oil treatment after 42 days was followed by a decrease till the end of incubation. Aggregates of organic treatments were more resistant to the dispersive effect of water than those of the control. Microbial biomass-C contents were high in the whey treatment, ranging between 1931 and 754 g g^–1 soil dry mass during incubation. With whey, fungal contributions to biomass-C increased from 40.5% after three to 76.5% after 126 days incubation. Addition of straw or oil stimulated biomass synthesis less than whey. High fungal contributions to biomass-C, approx. 70%, were sustained by straw during incubation. With oil, fungal contributions were 20.5% after three, 76% after 42 and less than 20% after 126 and 252 days incubation. Fungal contributions to biomass-C correlated positively with SAA. High sensitivity of the fungal biomass to mechanical stress is discussed as a cause for the low dry aggregate stability of soils amended with organic substrates encouraging fungal biomass development.     

海水胁迫对苦荬菜幼苗生长及生理特性的影响

抗盐耐海水植物的种植是有效利用和开发滩涂资源的措施之一。采用温室砂培方式, 研究了不同稀释配比的海水处理8天对苦荬菜(Lactuca indica)幼苗生物量、根冠比、叶绿素含量、离子含量、可溶性蛋白和可溶性糖含量的影响。结果表明: 苦荬菜幼苗地上部受海水胁迫较为显著, 而根在海水浓度小于30%时与对照相比没有显著差异; 根冠比随着海水浓度的增加而不断提高; 在10%和20%海水浓度处理下, 叶绿素含量与对照相比差异不显著, 但随着海水浓度的进一步增加,叶绿素含量显著下降; 在10%海水浓度处理下, 苦荬菜地上部分及根部的K⁺含量与对照相比差异不显著, 而海水浓度高于10%时, 随着海水浓度的增加地上部和根部的K⁺含量均逐渐降低; 海水处理下, 苦荬菜体内Na⁺和Cl^–含量逐渐增加; 地上部可溶性糖含量逐渐增加, 而可溶性蛋白含量先升后降。海水胁迫下, 苦荬菜幼苗维持一定的K⁺选择性吸收是其一定程度上盐适应的重要原因。同时, 积累的可溶性糖和可溶性蛋白是苦荬菜幼苗在盐胁迫下的重要渗透调节物质, 可作为其抗盐性的生理参数。