Response of tree growth to nutrient addition is size dependent in a subtropical forest.

Understanding how nutrient addition affects the tree growth is critical for assessing forest ecosystem function and processes, especially in the context of increased nitrogen (N) and phosphorus (P) deposition. Subtropical forests are often considered N-rich and P-poor ecosystems, but few existing studies follow the traditional "P limitation" paradigm, possibly due to differences in nutrient requirements among trees of different size classes. We conducted a three-year fertilization experiment with four treatments (Control, N-treatment, P-treatment, and NP-treatment). We measured soil nutrient availability, leaf stoichiometry, and relative growth rate (RGR) of trees across three size classes (small, medium and large) in 64 plots. We found that N and NP-treatments increased the RGR of large trees. P-treatment increased the RGR of small trees. RGR was mainly affected by N addition, the total effect of P addition was only 10 % of that of N addition. The effect of nutrient addition on RGR was mainly regulated by leaf stoichiometry. This study reveals that nutrient limitation is size dependent, indicating that continuous unbalanced N and P deposition will inhibit the growth of small trees and increase the instability of subtropical forest stand structure, but may improve the carbon sink function of large trees.

Identification of calcium chelating peptides from peanut protein hydrolysate and absorption activity of peptide-calcium complex.

BACKGROUND: Peanut peptides have good chelating ability with metal ions. However, there are few studies on the chelation mechanism of peanut peptides with calcium and absorption properties of peptide-calcium complex. RESULTS: Peptides with high calcium chelating rate were isolated and purified from peanut protein hydrolysate (PPH), and the chelation rate of component F21 was higher (81.4 ± 0.8%). Six peptides were identified from component F21 by liquid chromatography-tandem mass spectrometry, and the frequency of acidic amino acids and arginine in the amino acid sequence was higher in all six peptides. Peanut peptide-calcium complex (PPH21-Ca) was prepared by selecting component F21 (PPH21). Ultraviolet analysis indicated that the chelate reaction occurred between peanut peptide and calcium ions. Fourier transform infrared analysis showed that the chelating sites were carboxyl and amino groups on the amino acid residues of peptides. Scanning electron microscopy revealed that the surface of peanut peptide had a smooth block structure, but the surface of the complex had a granular morphology. Caco-2 cell model tests revealed that the bioavailability of PPH21-Ca was 58.4 ± 0.5%, which was significantly higher than that of inorganic calcium at 37.0 ± 0.4%. CONCLUSION: Peanut peptides can chelate calcium ions by carboxyl and amino groups, and the peptide-calcium complex had higher bioavailability. This study provides a theoretical basis for the development of new calcium supplement products that are absorbed easily. © 2024 Society of Chemical Industry.

Assessing the health risks of heavy metals and seasonal minerals fluctuations in Camellia sinensis cultivars during their growth seasons.

The risk assessment of heavy metals in tea is extremely imperative for the health of tea consumers. However, the effects of varietal variations and seasonal fluctuations on heavy metals and minerals in tea plants remain unclear. Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to evaluate the contents of aluminum (Al), manganese (Mn), magnesium (Mg), boron (B), calcium (Ca), copper (Cu), cobalt (Co), iron (Fe), sodium (Na), zinc (Zn), arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), and antimony (Sb) in the two categories of young leaves (YL) and mature leaves (ML) of tea (Camellia sinensis) cultivars throughout the growing seasons. The results showed significant variations in the contents of the investigated nutrients both among the different cultivars and growing seasons as well. Furthermore, the average concentrations of Al, Mn, Mg, B, Ca, Cu, Co, Fe, Na, Zn, As, Cd, Cr, Ni, and Sb in YL ranged, from 671.58-2209.12, 1260.58-1902.21, 2290.56-2995.36, 91.18-164.68, 821.95-5708.20, 2.55-3.80, 3.96-25.22, 37.95-202.84, 81.79-205.05, 27.10-69.67, 0.028-0.053, 0.065-0.127, 2.40-3.73, 10.57-12.64, 0.11-0.14 mg kg-1, respectively. In ML, the concentrations were 2626.41-7834.60, 3980.82-6473.64, 3335.38-4537.48, 327.33-501.70, 9619.89-13153.68, 4.23-8.18, 17.23-34.20, 329.39-567.19, 145.36-248.69, 40.50-81.42, 0.089-0.169, 0.23-0.27, 5.24-7.89, 18.51-23.97, 0.15-0.19 mg kg-1, respectively. The contents of all analyzed nutrients were found to be higher in ML than in YL. Target hazard quotients (THQ) of As, Cd, Cr, Ni, and Sb, as well as the hazard index (HI), were all less than one, suggesting no risk to human health via tea consumption. This research might provide the groundwork for essential minerals recommendations, as well as a better understanding and management of heavy metal risks in tea.

Smart antimicrobial system based on enzyme-responsive high methoxyl pectin-whey protein isolate nanocomplex for fresh-cut apple preservation.

The increase in pectin methylesterase (PME) activity on fresh-cut apple surface can smartly trigger the controlled release of bactericidal agents encapsulated within intelligent responsive Pickering emulsions. In this study, we developed a PME-responsive nanocomplex (W-H-II) to stabilize Pickering emulsion containing thyme essential oil (TEO), preserving fresh-cut apples. W-H-II, formed by heat-induced whey protein isolate (WPI) and high methoxyl pectin (HMP) (pH 4.5, 85 °C, 15 min, WPI:HMP ratio 1:2), exhibited good pH stability due to the stabilizing effects of hydrophobic, hydrogen bonding, and electrostatic interactions. The presence of PME triggered the demethylation of HMP within W-H-II, conferring PME response characteristics. Subsequently, a bacteriostasis experiment with pectinase-producing Bacillus subtilis provided evidence of PME-triggered TEO release from W-H-II-stabilized Pickering emulsion. Furthermore, microscopy techniques were employed to verify the demulsification behavior of the emulsion when PME activity ranged from 0.25 to 2.50 U mL-1. Finally, the PME-responsive TEO Pickering emulsion effectively preserved fresh-cut apples. Stored for 6 days at 5 °C and 10 °C, as the PME activity on the apple surface increased, the decay rate of the coated group was 0 %, with a total colony count below 3.0 log CFU g-1. This study introduces a novel intelligent preservation strategy for storing fresh-cut apples.

Correlationship between self-assembly behavior and emulsion stabilization of pea protein-high methoxyl pectin complexes treated with ultrasound at pH 2.0.

This study investigated the effects of ultrasound on the self-assembly behavior of pea protein (PP)-high methoxyl pectin (HMP) complexes at pH 2.0 through transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and intrinsic fluorescence analysis. The emulsion stabilization mechanism of PP-HMP treated with ultrasound (PP-HMP-US) was also elucidated. The results indicated that ultrasound increased the emulsifying activity index (EAI) and emulsifying stability index (ESI) of PP-HMP. Moreover, PP-HMP-US-based emulsions formed small, dispersed oil drops, which were stable during storage. PP-HMP- and PP-HMP-US-based emulsions did not demonstrate any creaming. The TEM results revealed that ultrasound can regulate the self-assembly behavior of PP and HMP to form spherical particles with a core-shell structure. This structure possessed low turbidity, a small particle size, and high absolute zeta potential values. The FTIR and intrinsic fluorescence spectra demonstrated that ultrasound increased the α-helix and ß-sheet contents and exposed the tryptophan groups to more hydrophilic environments. Ultrasound also promoted the PP-HMP self-assembly through electrostatic interaction and improved its oil-water interfacial behavior, as indicated by the EAI and ESI values of PP-HMP-US-based emulsions. The current results provide a reference for the development of an innovative emulsifier prepared by ultrasound-treated protein-pectin complexes at low pH.

Interaction mechanisms of peanut protein isolate and high methoxyl pectin with ultrasound treatment: The effect of ultrasound parameters, biopolymer ratio, and pH.

Ultrasound could effectively change molecular structure of proteins, polysaccharides, and their interactions, and was used to treat the peanut protein isolate-high methoxy pectin (PPI-HMP) complexes in this study. Effects of different ultrasound parameters, PPI-HMP mixing ratio (40:1-5:2), and pH (2.0-8.0) on the PPI-HMP interactions were investigated. Turbidity, solution appearance, and Zeta-potential analysis revealed an electrostatic interaction between PPI and HMP from pH 2.0 to pH 6.0. Ultrasound changed the tertiary structure conformation of PPI according to the surface hydrophobicity analysis. Increased ultrasound power density and pH broke the hydrogen bonds between the complexes according to Fourier transform infrared spectroscopy analysis. Apparent viscosity and confocal laser scanning microscopy analysis showed that appropriate ultrasound treatment (5.43 W/cm3, 25 min, 25 °C) reduced the viscosity of the complexes, and enhanced the electrostatic and hydrophobic interactions between PPI and HMP. These findings will contribute to the application of PPI-HMP complexes in the food industry.

Spontaneous gelation behaviors and mechanism of Ficus awkeotsang Makino pectin.

Ficus awkeotsang Makino (jelly fig) can produce edible gels by rubbing its seeds in water at room temperature in which pectin is considered as the main gelling component. However, the spontaneous gelation mechanism of Ficus awkeotsang Makino (jelly fig) pectin (JFSP) is still unclear. This study aimed to reveal the structure, physicochemical properties, and spontaneous gelation behaviors and mechanism of JFSP. JFSP was first obtained by water extraction and alcohol precipitation method, with a pectin yield of 13.25 ± 0.42 % (w/w), weight-average molar mass (Mw) of 111.26 kDa, and methoxylation degree (DM) of 26.8 %. Analysis of monosaccharide compositions showed that JFSP was composed of 87.8 % galactose acid, indicating a high percentage of galacturonic acid blocks. Measurement on the gelling capacity suggested that JFSP gels can be easily formed by simply dispersing the pectin in water at room temperature without adding any co-solutes or metal ions. Gelation force analysis indicated that hydrogen bonding, hydrophobic interactions, and electrostatic interactions were the main factors contributing to gel formation. At 1.0 % (w/v) of pectin concentration, JFSP gels exhibited relatively high gel hardness (72.75 ± 1.15 g) and good thermal and freeze-thawing stability. Overall, these findings highlight the potential application of JFSP as a promising commercial pectin resource.

The droplet breakup model and characteristics of pH-shifted peanut protein isolate-high methoxyl pectin stabilised emulsions under ultrasound.

The effect of pH on the occurrence states of peanut protein isolate (PPI) and high methoxyl pectin (HMP), and droplet breakup model of the emulsions under ultrasound were studied. Particle size distribution and scanning electron microscopy results showed that PPI-HMP existed a soluble complex at pH 5.0, had no interaction at pH 7.0, and was co-soluble at pH 9.0. Droplet breakup model results revealed that the characteristics of emulsion stabilised by PPI-HMP treated at pH 5.0 was different from that at pH 7.0 and 9.0. The average diameter of the droplet well satisfied the model. According to rheological properties, interface tension, and microstructure, the formation mechanism and characteristics of emulsion stabilised by PPI-HMP treated at pH 5.0 was different from that at pH 7.0 and pH 9.0. The research provided a reference for constructing emulsions using pH-shifted PPI-HMP under ultrasound.

Phosphorus addition regulates the growth of Chinese fir by changing needle nitrogen fractions in growing and dormant seasons.

Forest productivity is generally limited by nutrient scarcity. This study aims to reveal seasonal interactions among leaf carbon (C), nitrogen (N) fractions and tree growth driven by nutrient addition in a subtropical forest. Here, a field nutrient addition experiment was conducted with six treatments, namely, +N5 (5 g N m-2 yr-1), +N10 (10 g N m-2 yr-1), +P5 (5 g P m-2 yr-1), +N5 + P5, +N10 + P5, and control (N0 + P0). C fractions (structural and non-structural carbohydrates) and N fractions (soluble N, nucleic N and protein N) in needles as well as tree growth indicated by basal area increment (BAI) were measured in growing and dormant seasons. Total N and protein N in old needles were significantly increased by P addition, while no significant differences of non-structural carbohydrates in young (<1-year old) and old needles (>1-year old) were detected among the treatments in both seasons. N and P addition increased the structural carbohydrates of old needles in dormant season. P addition decreased and increased tree growth in growing and dormant seasons, respectively. The variation of BAI was explained 18.3 % by total N and 17.8 % by protein N in growing season, and was explained 33.9 % by total N and 34.2 % by protein N in dormant season. Our study suggested that the P addition effect on Chinese fir growth mostly depends on needle N fractions. This study highlights tree seasonal growth driven by nutrient alteration might be characterized by leaf N fractions rather than C fractions in subtropical forests.

Responses of microbial function, biomass and heterotrophic respiration, and organic carbon in fir plantation soil to successive nitrogen and phosphorus fertilization.

Carbon dioxide (CO2) emissions from forest ecosystems originate largely from soil respiration, and microbial heterotrophic respiration plays a critical role in determining organic carbon (C) stock. This study investigated the impacts of successive nitrogen (N) and phosphorus (P) fertilization after 9 years on soil organic C stock; CO2 emission; and microbial biomass, community, and function in a Chinese fir plantation. The annual fertilization rates were (1) CK, control without N or P fertilization; (2) N50, 50 kg N ha-1; (3) N100, 100 kg N ha-1; (4) P50, 50 kg P ha-1; (5) N50P50, 50 kg N ha-1 + 50 kg P ha-1; and (6) N100P50, 100 kg N ha-1 + 50 kg P ha-1. The N100P50 treatment had the highest cumulative soil CO2 emissions, but the CK treatment had the lowest cumulative soil CO2 emissions among all treatments. The declines of soil organic C (SOC) after successive 9-year fertilization were in the order of 100 kg N ha-1 year-1 > 50 kg N ha-1 year-1 > CK. Compared to the CK treatment, successive N fertilization significantly changed soil microbial communities at different application rates and increased the relative gene abundances of glycoside hydrolases, glycosyl transferases, carbohydrate-binding modules, and polysaccharide lyases at 100 kg N ha-1 year-1. Relative to P fertilization alone (50 kg P ha-1 year-1), combined N and P fertilization significantly altered the soil microbial community structure and favored more active soil microbial metabolism. Microbial community and metabolism changes caused by N fertilization could have enhanced CO2 emission from heterotrophic respiration and eventually led to the decrease in organic C stock in the forest plantation soil. KEY POINTS: • N fertilization, alone or with P, favored more active microbial metabolism genes. • 100 kg N ha-1 fertilization significantly changed microbial community and function. • N fertilization led to a "domino effect" on the decrease of soil C stock.

Effect of soybean oil content on textural, rheological, and microstructural properties of WBAXs-SPI emulsion-filled gels.

This study aimed to prepare wheat bran arabinoxylans-soy protein isolate (WBAXs-SPI) emulsion-filled gels with different oil contents and investigate their rheological, textural, water-holding capacity (WHC), and microstructural properties. The rheological analysis results showed that the maximum correlation interaction occurs when the soybean oil concentration was 10%, and the elastic modulus (G') reaches the highest value of 13,562 Pa. Interestingly, the WHC and texture change trend of WBAXs-SPI emulsion-filled gel were consistent with rheology. Meanwhile, confocal laser scanning microscopy (CLSM) observation indicated that the emulsion-filled gels formed an interpenetrating polysaccharide-protein complex network system. Therefore, the filling emulsion performance could be adjusted by changing the concentration of oil droplets as the active filler. This provides the possibility of developing new food materials encapsulating fat-soluble substances with a low oil rate and more stable structure.

The Mechanism of Extraction of Peanut Protein and Oil Bodies by Enzymatic Hydrolysis of the Cell Wall.

Degradation of the peanut cell wall is a critical step in the aqueous enzymatic extraction process to extract proteins and oil bodies. Viscozyme® L, a compound cell wall degrading enzyme, has been applied as an alternative to protease in the process of aqueous enzymatic extraction, but the mechanism of cell wall enzymolysis remains unclear. The present study aims to investigate the changes in cellulose, hemicellulose, and pectin content of the peanut cell wall hydrolyzed by Viscozyme® L. The degree to which the main components of the peanut cell wall, such as trans-1, 2-cyclohexanediamine-N,N,N',N'-acetic acid-soluble pectin (CDTA-soluble pectin), Na2CO3-soluble pectin, cellulose, and hemicellulose, are degraded is closely related to the extraction of oil bodies and peanut protein at different solid-liquid ratio of powered peanut seed in distilled water, enzyme concentration, enzyme hydrolysis temperature, and enzyme hydrolysis time. The key sites of Viscozyme® L activity on cell wall polysaccharides were explored by comparing the changes in chemical bonds under different extraction conditions using Fourier-transform infrared spectroscopy (FT-IR) absorption bands and principal component analysis (PCA). Viscozyme® L acted on the C-O stretching, C-C stretching, and CH2 symmetrical bending of cellulose, the C-O stretching and O-C-O asymmetrical bending of hemicellulose, and the C-O stretching and C-C stretching of pectin.

Carboxymethyl chitosan-decorated proliposomes as carriers for improved stability and sustained release of flaxseed oil.

A flaxseed oil carboxymethyl chitosan-decorated proliposome system was fabricated in this research. The physicochemical characteristics, stability, and in vitro release behaviors of flaxseed oil were studied and compared with that of flaxseed oil-loaded liposomes. The results of dynamic light scattering, transmission electron microscopy, and oxidation stability indicated that the storage stability of proliposomes was better. After 28 days of storage, the peroxide value of flaxseed oil-loaded liposomes (20.1 meq/kg) was significantly (P < 0.05) higher than that of flaxseed oil-loaded proliposomes (9.0 meq/kg); the thiobarbituric acid reactive substances in the former (0.53 mmol/kg) was also higher than that in the latter (0.27 mmol/kg). The in vitro release behavior of flaxseed oil indicated the proliposomes were more stable in the simulated gastrointestinal fluids. Therefore, the flaxseed oil-loaded proliposome system could be a promising vehicle for delivery flaxseed oil in food industry. PRACTICAL APPLICATION: A flaxseed oil-loaded proliposome delivery system was fabricated in this research. Their physical and oxidation stability of flaxseed oil were improved, and the in vitro cumulative release of flaxseed oil was delayed compared with flaxseed oil liposomes. This system may provide an effective strategy for the flaxseed oil encapsulation in the food industry.

Successive mineral nitrogen or phosphorus fertilization alone significantly altered bacterial community rather than bacterial biomass in plantation soil.

Bacteria play determining roles in forest soil environment and contribute to essential functions in the cycling of nitrogen (N) and phosphorus (P). Understanding the effects of different fertilizer applications, especially successive fertilization, on soil properties and bacterial community could reveal the impacts of fertilization on forest soil ecology and shed light on the nutrient cycling in forest system. This study aimed to evaluate the impacts of successive mineral N (NH4NO3) and P (NaH2PO4) fertilization at different rates, alone or together, on soil bacterial biomass and communities at 0-5, 5-10, and 10-20 cm. Compared with the control, N fertilization decreased soil pH, but P alone or with N fertilization had negligibly negative impacts on soil pH. Different mineral fertilizer applications, alone or together, showed no significant effects on soil organic matter contents, relative to the control treatment. Bacterial biomass remained stable to different fertilizations but decreased with sampling depths. Sole N or P fertilization, rather than combined fertilizations, significantly changed soil bacterial community structures. Our results demonstrated that mineral N or P fertilization alone significantly affected bacterial community structures rather than biomass in the plantation soils. KEY POINTS: • Impacts of successive mineral fertilization on soil bacteria were determined. • Mineral fertilization showed negligible impacts on bacterial biomass. • N additions stimulated Chloroflexi relative abundances. • Mineral N or P fertilization significantly altered bacterial community structure.

Effect of chitosan coatings on the evolution of sodium carbonate-soluble pectin during sweet cherry softening under non-isothermal conditions.

The inhibiting effect of chitosan coating (2%) on the softening and sodium carbonate-soluble pectin (SSP) evolution of sweet cherries during non-isothermal storage was investigated. Chitosan coating significantly extend the softening (6.4% greater than the control group), maintained the SSP content (6.6% greater than the control group), and reduced the degradation of SSP by inhibiting the expression of the paPME1-5 genes, which regulating pectin methylesterase activity of sweet cherries under temperature variation. In addition, the results of methylation and monosaccharide composition indicated that the chitosan coating reduced demethylation of SSP and the loss of RG-I main and side chain neutral sugars. Atomic force microscopy images revealed that the coated sweet cherries contained more linked, branched, and long SSP chains and maintained the width of the pectin backbone (>140 nm). These results indicated that a chitosan coating is feasible to preserve postharvest fruit under non-isothermal conditions.

[Responses of seedling growth in subtropical secondary broad-leaved forest to nitrogen and phosphorus addition in Jiulian Mountain, China]. / ä¹è¿žå±±æ¬¡ç”Ÿé˜”å¶æž—å¹¼è‹—ç”Ÿé•¿å¯¹æ°®ç£·æ·»åŠ çš„å“åº”.

An experiment with four treatments of control (CK), N addition (100 kg N·hm-2·a-1), P addition (50 kg P·hm-2·a-1) and N + P (100 kg N·hm-2·a-1 + 50 kg P·hm-2·a-1) were conducted to examine the responses of plant height, ground diameter, crown width, specific leaf area, and mortality of seedlings to N and P addition. Under P addition, growth rates of plant height and ground diameter of seedlings decreased significantly by 45.1% and 30.3%, respectively. Fertilization affected the mortality of main constructive tree species. N addition significantly increased seedling mortality of Castanopsis carlesii to 25.1%. Fertilization treatment significantly increased mortality of Castanopsis fargesii to 25.1%-31.3%, while N addition and P addition signi-ficantly reduced mortality of Schima superba and Machilus nanmu. Fertilization significantly decreased the importance value of S. superba and C. fargesii in the seedling community. N addition and P addition significantly increased the importance value of M. nanmu seedling. The combined N and P addition significantly decreased Shannon index and Simpson index of the seedling community. Seedling growth was mainly affected by soil ammonium, available phosphorus, total nitrogen, canopy openness, and specific leaf area. Seedling mortality was mainly affected by soil ammonium, available phosphorus and canopy openness. Synthetically, N and P addition affected seedling growth mainly by regulating soil nitrogen and phosphorus availability and changing leaf functional trait. It accelerated the death of ectomycorrhizal tree species (C. carlesii and C. fargesii), changed the importance value of constructive species in seedling community, reduced species diversity, and ultimately changed community structure of adult trees in subtropical secondary broad-leaved forest.

Bacterial Acid Resistance Toward Organic Weak Acid Revealed by RNA-Seq Transcriptomic Analysis in Acetobacter pasteurianus.

Under extreme acidic environments, bacteria exploit several acid resistance (AR) mechanisms for enhancing their survival, which is concerned with several aspects, such as issues in human health and fermentation for acidic products. Currently, knowledge of bacterial AR mainly comes from the strong acid (such as hydrochloric acid) stresses, whereas AR mechanisms against organic weak acids (such as acetic acid), which are indeed encountered by bacteria, are less understood. Acetic acid bacteria (AAB), with the ability to produce acetic acid up to 20 g/100 mL, possess outstanding acetic acid tolerance, which is conferred by their unique AR mechanisms, including pyrroloquinoline quinine-dependent alcohol dehydrogenase, acetic acid assimilation and molecular chaperons. The distinguished AR of AAB toward acetic acid may provide a paradigm for research in bacterial AR against weak organic acids. In order to understand AAB's AR mechanism more holistically, omics approaches have been employed in the corresponding field. However, the currently reported transcriptomic study was processed under a low-acidity (1 g/100 mL) environment, which could not reflect the general conditions that AAB are usually faced with. This study performed RNA-Seq transcriptomic analysis investigating AR mechanisms in Acetobacter pasteurianus CGMCC 1.41, a widely used vinegar-brewing AAB strain, at different stages of fermentation, namely, under different acetic acid concentrations (from 0.6 to 6.03 g/100 mL). The results demonstrated the even and clustered genomic distribution of up- and down-regulated genes, respectively. Difference in AR between AAB and other microorganisms was supported by the down-regulation of urea degradation and trehalose synthesis-related genes in response to acetic acid. Detailed analysis reflected the role of ethanol respiration as the main energy source and the limited effect of acetic acid assimilation on AR during fermentation as well as the competition between ethanol respiratory chain and NADH, succinate dehydrogenase-based common respiratory chain. Molecular chaperons contribute to AR, too, but their regulatory mechanisms require further investigation. Moreover, pathways of glucose catabolism and fatty acid biosynthesis are also related to AR. Finally, 2-methylcitrate cycle was proposed as an AR mechanism in AAB for the first time. This study provides new insight into AR mechanisms of AAB, and it also indicates the existence of numerous undiscovered AR mechanisms.

Effects of calcium and pectin methylesterase on quality attributes and pectin morphology of jujube fruit under vacuum impregnation during storage.

Calcium chloride (1% w/w, CaCl2) and pectin methylesterase (PME) (15 U/mL) were vacuum impregnated (VI) into jujubes to preserve their quality. The nanostructure of jujube pectin was investigated using atomic force microscopy (AFM) to determine the degradation mechanism of pectin. CaCl2 with PME under VI treatment (VI + Ca + PME) maintained jujubes' quality. Weight loss in VI + Ca + PME group at day 56 was only 60.36% of that in control group (CK). Firmness, soluble solids content, and ascorbic acid content of jujubes in VI + Ca + PME group were higher than those in CK. Firmness was highly positively correlated with sodium carbonate-soluble pectin (SSP) content. According to AFM results, frequencies of molecules with a width ≥60 nm of water-soluble pectin (WSP), chelate-soluble pectin (CSP), and SSP were the highest in VI + Ca + PME group at the end of storage. WSP, CSP, and SSP degradation was delayed by VI + Ca + PME treatment. The quality of jujubes was effectively maintained by VI + Ca + PME treatment.

The effects of simulated acid rain on internal nutrient cycling and the ratios of Mg, Al, Ca, N, and P in tea plants of a subtropical plantation.

Acid rain alters nutrient cycling in tea plantations. However, the acquisition of Mg and Ca by plants and their nutrient interactions with Al, N, and P in response to acid rain are poorly understood. Experimental treatments simulating acid rain at various acidities (pH 4.5, 3.5, and 2.5) were performed within a red soil tea plantation in China. The available Mg, Al, Ca, N, and P were analyzed in the rhizosphere and bulk soils. Further, these elements were measured in absorptive, transportive, and storative roots in addition to twigs, tea, and mature leaves. Available soil Mg and Ca exhibited negative and positive rhizosphere effects, respectively, but the levels of both decreased due to acid rain treatment. In addition, average Mg and Ca concentrations generally decreased in plant tissues with increasing acidity. In contrast, average Al concentration increased across all plant tissues with increasing acidity treatment. Meanwhile, the ratios of Al/Mg and Al/Ca increased with increasing acidity but that of N/Al decreased in twigs and roots. Lastly, the ratios of N/Al, P/Ca, and N/P were all altered by acid treatment in tea and/or mature leaves. Taken together, these results indicated that elevated acidity increased the internal cycling of Al in plants but decreased Mg and Ca fluxes between soils and roots. Further, the response of interactions among the five measured elements to different acidities varied with tea plant tissue. Our findings may advance our understanding of plant adaptation to increasing soil acidification and atmospheric acid deposition around the world.

Combined effects of ultrasound and calcium on the chelate-soluble pectin and quality of strawberries during storage.

The combined effects of ultrasound and calcium on the water migration, quality, and chelate-soluble pectin (CSP) properties of strawberries were investigated using nuclear magnetic resonance (NMR), high-performance liquid chromatography (HPLC), and atomic force microscopy (AFM). The relationship among water migration, firmness, and CSP properties was also determined. Treatment with ultrasound and calcium (U + Ca) prevented the decrease in firmness of strawberries during storage (17 days). Measurements of physicochemical parameters (titratable acidity (TA), soluble solid content (SSC), CSP and Ca content) showed that U + Ca treatment maintained better fruit quality. AFM showed a larger percentage of wider and longer CSP molecules in the U + Ca group (width ≥90 nm; length ≥800 nm). These results, together with the HPLC results, confirmed that U + Ca treatment effectively inhibits CSP degradation. This study revealed that the application of ultrasound and calcium could preserve the quality of stored strawberries.