Ultrasound-assisted extraction of polyphenols from lotus rhizome epidermis by alcohol/salt-based aqueous two-phase system: Optimization, extraction mechanism and antioxidant activities.

In this study, ultrasonic-assisted (UA) alcohol/salt-based aqueous two-phase system (ATPS) method was constructed to extract lotus rhizome epidermis (LRE) polyphenols. The extraction conditions were optimized as salt concentration 26.75 %, ethanol concentration 25.45 %, ultrasonic power 487 W and liquid-solid ratio 35.33 mL/g by comparing response surface methodology (RSM) and artificial neural network (ANN) models. Then, l-dopa (2.35 ± 0.036 mg/g dw), gallocatechin (1.66 ± 0.0035 mg/g dw) and epigallocatechin (1.37 ± 0.0035 mg/g dw) were determined as major polyphenols in LRE by using UA-ATPS method. Moreover, study showed that ultrasound, van der Waals force, hydrogen bond and salting out could accelerate the mass transfer and extraction of polyphenols in LRE cells. The high-pressure cavity and collapse effect of ultrasound could also accelerate the extraction of polyphenols. In vitro antioxidant experiments showed that LRE polyphenols have good antioxidant ability. In sum, this study developed a green and efficient extraction method to enhance the profitability of LRE in food and medicine industries.

Study on the formation mechanism of blackening in damaged lotus rhizome epidermis: Effects of polyphenols and iron.

Lotus rhizome is an important aquatic vegetable, but the blackening of lotus rhizome epidermis (LRE) seriously affects its appearance and quality, which makes lotus rhizome products unmarketable. In this study, the effects of polyphenols and iron on the LRE color were studied to explore the possible mechanism of LRE blackening. Results indicated that the measurable total phenols contents in the mud treatment (MT) group were significantly reduced, and the total iron contents were significantly increased compared with the bruised treatment group (p < 0.05). The high-performance liquid chromatography results showed that the main polyphenols in LRE were dopa, gallocatechin, and catechin, as well as a small amount of catechol, epicatechin, proanthocyanidin B2, and proanthocyanidin C1. Moreover, the results of color difference and ultraviolet adsorption spectroscopy showed that there were obviously black or brown-gray of dopa (525 nm), gallocatechin (504.5 nm), and catechin (550 and 504.5 nm) with FeCl2. The simulated system treatment of LRE further confirmed that the chromaticity effect of dopa and iron in bruised LRE was similar to that of the MT group, whereas 1% (w/w) ascorbic acid, 2% (w/w) EDTA-2Na, or 3% (w/w) citric acid could solely prohibit the blackening. This suggested that the dopa in LRE and FeCl2 in mud may mainly combine into [2(DOPA-2H+)+Fe3+]- through non-covalent interaction, which leads to the blackening of bruised LRE under neutral conditions. These results can guide the storage of lotus rhizomes and improve the development of the lotus rhizome industry.

Effects of different concentrations of ascorbic acid on the stability of (+) - Catechin under enzymatic conditions.

A series of incubation systems of (+) - catechin (Cat), ascorbic acid (AA) and polyphenol oxidase (PPO) of lotus rhizome at 40 °C were performed to investigate the effect and oxidation pathway of AA on the stability of Cat. The results showed that after the enzymatic or non-enzymatic oxidation of Cat, the products of the two reactions were the same, namely epicatechin, catechin dimer and dehydrogenated catechin dimer. After adding AA, the protective effect of AA on catechin increased first and then decreased with the increase of AA concentration. 0.1 mmolL(exp)-1 AA can inhibit PPO activity in a short time. Within 24 h, 1 mmolL(exp)-1 AA can keep Cat content at 87.88 %. At the concentration of 10 mmolL(exp)-1 AA, excessive AA is oxidized to form a large amount of dehydroascorbic acid (DHAA), which forms an adduct with Cat, promoting the consumption of Cat. The effect of AA on the stability of Cat is time-dependent and dose-dependent.

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.

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.

Quartz crystal microbalance for the determination of daminozide using molecularly imprinted polymers as recognition element.

As the daminozide (DM) and its metabolite have been identified to be potentially carcinogenic, rapid detection method for them is necessary for food safety. A type of piezoelectric crystal sensor has been prepared by using a molecularly imprinted polymer (MIP) as recognition element. The molecularly imprinted polymer was prepared by hot-induced precipitation polymerization, and then the polymer particles were fixed on the surface of the electrode. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to evaluate the obtained imprinted polymer particles and the MIP sensitive film coated on the electrode. The results showed that a typical time-response curve of the MIP-coated crystal to the DM solution had been given, frequency shifts versus logarithm changes of DM showed good linear correlation within the concentration range of 1.0x10(-9) to 10(-6) mg/mL (y=11.38 lg x+115.45, r=0.9872) and 1.0x10(-6) to 10(-1) mg/mL (y=25.22lgx+209.44, r=0.9938), respectively. The detection limit was 5.0x10(-8) mg/mL (S/N=3), which is lower than that of conventional methods. Further, computer simulation technology was employed to investigate the interaction between methacrylic acid and DM for elucidating the recognition mechanism. The influencing factor pH has also been investigated. The injection experiments of DM structurally related compounds indicated that the obtained sensor has high sensitivity, excellent selectivity, low cost, good reproducibility, and reusable property by combining with piezoelectric crystal and molecularly imprinted polymer.

[Progress of molecular imprinting technique on the determination of pesticides residues].

People have paid a more attention to the pesticides residues, so the rapid detection method is required. In this paper the application of molecular imprinting technique on the detection of pesticides residues was reviewed, including recognition principles, preparation, current applications, problems and its future.