The mechanism of interaction between lotus rhizome polyphenol oxidase and ascorbic acid: Inhibitory activity, thermodynamics, and conformation analysis.

In this study, the interaction between lotus rhizome polyphenol oxidase (PPO) and ascorbic acid (AA) was discussed from the aspects of inhibitory activity, thermodynamics, and conformation. Results showed that PPO was purified from lotus rhizome by DEAE-52 anion exchange chromatography and Sephadex G-100 gel filtration chromatography, with its optimum substrate being determined as pyrogallic acid. Spectrophotometric and polarographic assays demonstrated that AA exhibited strong inhibitory activity against PPO. Thermodynamics, fluorescence, and circular dichroism spectral analysis showed that hydrophobic interactions caused the formation of AA-PPO complex, leading to the remarkable fluorescence quenching and conformational change of PPO. Atomic force microscopic analysis revealed that binding to AA induced significant changes in the surface morphology and molecular aggregation of PPO molecules. In this study, the interaction mechanism between PPO and AA was proposed for the first time, which provided a theoretical basis for AA to inhibit lotus rhizome browning. PRACTICAL APPLICATIONS: Lotus rhizome, an aquatic vegetable, is prone to enzymatic browning in processing operations, which leads to a decrease in market value and economic loss. At present, ascorbic acid (AA) is widely used in industries as an excellent antioxidant because of its good antibrowning effect and relatively low cost. However, the interaction between the enzymatic browning-related polyphenol oxidase (PPO) from lotus rhizome and ascorbic acid has not been clearly studied. Understanding the mechanism of inhibiting PPO will help to prevent vegetable browning, especially fresh-cut products. The inhibitory effect of AA on PPO in lotus rhizome favors simultaneous use with other types of PPO inhibitors because of their likely synergistic effects.

Effects of air discharge on surface charges and cell walls of Fusarium oxysporum.

Air discharge showed significant inhibition on mycelial growth and spore germination of Fusarium oxysporum, one of the main spoilage fungi in post-harvest lotus roots which is an important economic aquatic vegetable in China. However, the antimicrobial mechanism of air discharge is not clear yet. In the present study, the effects of air discharge on F. oxysporum separated from post-harvest rotten lotus roots were characterized by analyzing surface charges, cell wall permeability, and changes in chitin and chitosan including surface morphology, functional groups, degree of deacetylation, crystallinity, and C/N ratio. After air discharge treatments, alkaline phosphatase leak assay revealed that cell wall permeability of F. oxysporum was magnified. What's more, zeta potentials of F. oxysporum increased and negative charges on cell surfaces decreased. The ordered and compact molecular arrangements of chitin and chitosan in cell walls of F. oxysporum were reduced. The deacetylation degree of chitin and chitosan increased, and the C/N ratios of chitin and chitosan decreased. It was concluded from these results that air discharge caused the transformation in structures of chitin and chitosan, resulting in the exposure of positively charged amino groups and decrease of negative charges on cell surfaces which brought damage to the structure and function of F. oxysporum's cell walls.

Elevated expression of ASF1B correlates with poor prognosis in human lung adenocarcinoma.

Aim: ASF1 is involved in tumorigenesis. However, its possible role in lung adenocarcinoma (LUAD) is unclear. This study thus explored the role of ASF1A and ASF1B in LUAD. Materials & methods: Data from The Cancer Genome Atlas and Gene Expression Omnibus were employed to investigate ASF1A and ASF1B expression and its roles in LUAD prognosis. Immunohistochemistry was applied to determine the protein expression of ASF1B of 30 LUAD patients. Results: The upregulation of ASF1B in tumor tissues is associated with worse overall survival and progress-free survival and is correlated with advanced tumor stage and tumor development. However, aberrant expression of ASF1A was not found in LUAD and ASF1A was not related to patients' overall survival and progress-free survival. Conclusion:ASF1B could be a promising prognostic and therapeutic biomarker in LUAD.

Mechanism of lipid metabolism regulation by soluble dietary fibre from micronized and non-micronized powders of lotus root nodes as revealed by their adsorption and activity inhibition of pancreatic lipase.

Soluble dietary fibre (SDF) of micronized and non-micronized powders of lotus root nodes were investigated based on its adsorption and activity inhibition of pancreatic lipase (PL) by using circular dichroism, fluorescence spectroscopy and modification. Results showed that SDF2 (SDF from micronized powders of lotus root nodes) had stronger PL adsorption and enzyme activity inhibition than SDF1 (SDF from non-micronized powders of lotus root nodes). Specifically, SDF2 showed more binding sites than SDF1 in PL. There were hydrogen bonds and van der Waals interactions between SDF and PL, with Trp on PL probably serving as the main binding site. Carboxyl groups exhibited a stronger inhibition on PL by carboxymethyl and hydroxypropyl modification. The common mechanisms between SDF1 and SDF2 can be attributed to the combination between Trp and carboxyl groups, while the differences may be generated by the variations in structures or chemical groups induced by micronization.

Acetic acid pretreatment improves the hardness of cooked potato slices.

The effects of acetic acid pretreatment on the texture of cooked potato slices were investigated in this work. Potato slices were pretreated with acetic acid immersion (AAI), distilled water immersion (DWI), or no immersion (NI). Subsequently, the cell wall material of the pretreated samples was isolated and fractioned to evaluate changes in the monosaccharide content and molar mass (MM), and the hardness and microscopic structure of the potato slices in different pretreatments before and after cooking were determined. The results showed that the highest firmness was obtained with more intact structure of the cell wall for cooked potato slices with AAI pretreatment. Furthermore, the MM and sugar ratio demonstrated that the AAI pretreated potato slices contained a higher content of the small molecular polysaccharides of cell walls, especially in the hemicellulose fraction. This work may provide a reference for potato processing.

Changes in physicochemical properties related to the texture of lotus rhizomes subjected to heat blanching and calcium immersion.

Pretreatments such as low temperature blanching and/or calcium soaking affect the cooked texture of vegetal food. In the work, lotus rhizomes (Nelumbo nucifera Gaertn.) were pretreated using the following 4 treatments, blanching at 40°C, blanching at 90°C, soaking in 0.5% CaCl2, and blanching at 40°C followed by immersion in 0.5% CaCl2. Subsequently, the cell wall material of pretreated samples was isolated and fractioned to identify changes in the degree of esterification (DE) and monosaccharide content of each section, and the texture of the lotus rhizomes in different pre-treatments was determined after thermal processing with different time. The results showed that the greatest hardness was obtained after blanching at 40°C in CaCl2, possibly attributing to the formation of a pectate calcium network, which maintains the integrity of cell walls. Furthermore, the content of galactose, rhamnose and arabinose decreased due to the breakage of sugar backbones and subsequent damage to cell walls. Our results may provide a reference for lotus rhizome processing.

ATP bioluminescence rapid detection of total viable count in soy sauce.

The adenosine triphosphate (ATP) bioluminescence rapid determination method may be useful for enumerating the total viable count (TVC) in soy sauce, as it has been previously used in food and beverages for sanitation with good precision. However, many factors interfere with the correlation between total aerobic plate counts and ATP bioluminescence. This study investigated these interfering factors, including ingredients of soy sauce and bacteria at different physiological stages. Using the ATP bioluminescence method, TVC was obtained within 4 h, compared to 48 h required for the conventional aerobic plate count (APC) method. Our results also indicated a high correlation coefficient (r = 0.90) between total aerobic plate counts and ATP bioluminescence after filtration and resuscitation with special medium. The limit of quantification of the novel detection method is 100 CFU/mL; there is a good linear correlation between the bioluminescence intensity and TVC in soy sauce in the range 1 × 10(2) -3 × 10(4) CFU/mL and even wider. The method employed a luminescence recorder (Tristar LB-941) and 96-well plates and could analyse 50-100 samples simultaneously at low cost. In this study, we evaluated and eliminated the interfering factors and made the ATP bioluminescence rapid method available for enumerating TVC in soy sauce.

Determination of catechin in lotus rhizomes by high-performance liquid chromatography.

A novel method was developed to analyze lotus rhizome polyphenolic catechin using high-performance liquid chromatography (HPLC). The retain time of catechin was 14.72 min under the optimized condition. Mass spectrometry was further employed to qualify and quantify the purity of the catechin peak. Good linearity (R=0.9997) was obtained within the range of 50-1,000 ng. The coefficient of variance was determined as 5.2%, with a recovery rate of 97%. The detection and quantification limitations of catechin were 23 ng and 50 ng, respectively. The catechin level was 0.0025% in the lotus rhizome, and 0.011% in the knot of the lotus rhizome (Nelumbo nucifera cv. 'damao jie'). The optimized conditions of HPLC for catechin detection in the lotus rhizome matrix were as follows: the SuperlcosIL™ LC-18 analytical column (150 mm×4.6 mm, 5 µm), methanol-water-acetic acid (10:90:1, volume ratio) as the mobile phase, an UV detector at 280 nm, a flow rate of 0.8 ml/min, column temperature at 30°C, and an injection volume of 10 µl.