Tyrosinase (EC 1.14.18.1), a copper-containing enzyme, can cause enzymatic browning in raw fruits, vegetables, and beverages. Browning is an undesirable reaction that is responsible for less attractive appearance and loss in nutritional quality. These phenomena have encouraged researchers to seek new potent tyrosinase inhibitors for use in the food industry. This article reviews recent studies on tyrosinase inhibitors of natural and synthetic origins. The information offered here should help food industry in developing and using potential tyrosinase inhibitors desirable efficacy and safety, and for improving food quality.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1541-4337.2012.00191.x

Natural and Synthetic Tyrosinase Inhibitors as Antibrowning Agents: An Update

Since the methylenecyclopropane moiety is found in many biologically active natural substances, the synthesis of methylene- and alkylidenecyclopropanes remains a considerable challenge. In addition, an attractive feature is their surprising stability, accompanied by a high level of strain, conferring on them an otherwise unattainable chemical reactivity. The growing interest in the chemistry of these compounds has in its turn stimulated the development of alternative approaches to their skeleton, aimed at selectively introducing structural and chemical diversification. The three principal methods to synthesize these important compounds are based on the formation of the cyclopropane ring, the use of preformed cyclopropanes, and the use of preformed methylene- and alkylidenecyclopropanes.

Synthesis of Methylene‐ and Alkylidenecyclopropane Derivatives

In several years ago, infection with human papillomaviruses (HPVs), have been prevalent in the worlds especially HPV type 18, can lead to cervical cancer. Therefore, rapid, accurate, and early diagnosis of HPV for successful treatment is essential. The present study describes the development of a selective and sensitive electrochemical biosensor base on DNA, for early detection of HPV-18. For this purpose, a nanocomposite of reduced graphene oxide (rGO) and multiwalled carbon nanotubes (MWCNTs) were electrodeposited on a screen-printed carbon electrode (SPCE). Then, Au nanoparticles (AuNPs) were dropped on a modified SPCE. Subsequently, single strand DNA (ssDNA) probe was immobilized on the modified electrode. The link attached between AuNPs and probe ssDNA provided by l-cysteine via functionalizing AuNPs (Cys-AuNPs). The differential pulse voltammetry (DPV) assay was also used to electrochemical measurement. The measurement was based on the oxidation signals of anthraquninone-2-sulfonic acid monohydrate sodium salt (AQMS) before and after hybridization between the probe and target DNA. The calibration curve showed a linear range between 0.01 fM to 0.01 nM with a limit of detection 0.05 fM. The results showed that the optimum concentration for DNA probe was 5 µM. The good performance of the proposed biosensor was achieved through hybridization of DNA probe-modified SPCE with extracted DNA from clinical samples. According to the investigated results, this biosensor can be introduced as a proprietary, accurate, sensitive, and rapid diagnostic method of HPV 18 in the polymerase chain reaction (PCR) of real samples.

/pdf/early-stage-cervical-cancer-diagnosis-based-on-an-ultra-223jhjwgsj.pdf

Early-stage cervical cancer diagnosis based on an ultra-sensitive electrochemical DNA nanobiosensor for HPV-18 detection in real samples

Electrochemical DNA biosensor for human papillomavirus 16 detection in real samples

An electrochemical DNA biosensor for human papillomavirus (HPV) 16 detection has been developed. For this proposed biosensor, L-cysteine was first electrodeposited on the gold electrode surface to form L-cysteine film (CYSFILM). Subsequently, HPV16-specific probe was immobilized on the electrode surface with CYSFILM. Electrochemistry measurement was studied by differential pulse voltammetry method (DPV). The measurement was based on the reduction signals of methylene blue (MB) before and after hybridization either between probe and synthetic target or extracted DNA from clinical samples. The effect of probe concentration was analyzed and the best results were seen at 1000 nM. The hybridization detection presented high sensitivity and broad linear response to the synthetic-target concentration comprised between 18.75 nM and 250 nM as well as to a detection limit of 18.13 nM. The performance of this biosensor was also investigated by checking probe-modified electrode hybridization with extracted DNA from samples. The results showed that the biosensor was successfully developed and exhibited high sensitivity and satisfactory selectivity to HPV16. These results allow for the possibility of developing a new portable detection system for HPVs and for providing help in making an effective diagnosis in the early stages of infection.

Electrochemical DNA biosensor for human papillomavirus 16 detection in real samples.

DNA probes immobilized on a gold electrode (AuE) were employed as the primers of asymmetric PCR on the AuE. In the asymmetric PCR process, the DNA probes extended in the presence of target strands in the PCR solution. After PCR the dsDNAs were denaturalized and the target DNAs were eliminated and only the extended probes maintained on the AuE. At last the electrochemical indicator of methylene blue combined to the extended probes and the electrochemical signal of indicator was measured. This signal was higher than that of the AuE modified only by original probe. When there was no target in the PCR solution, the probe did not extend and the signal did not increase. The specific sequences of chitinase gene were detected successfully from four sorts of target with different length: oligonucleotide acid, PCR products, molecule cloning vector DNA and total genome DNA of transgenic capsicum, and the estimated detection limit were 7.3 × 10 −12 , 3.2 × 10 −11 , 5.4 × 10 −11 and 4.1 × 10 −10  mol l −1 respectively. The regeneration of the biosensor was also tested and the results indicated that its half life was 6 times.

Fabrication and application of a new DNA biosensor based on on-substrate PCR and electrochemistry

5′-Thiol-derivatized specific DNA probes were added to the single primer polymerase chain reaction (asymmetric PCR) solution In the PCR process, the DNA probes extended in the presence of target; the extended probes were then immobilized on a glassy carbon electrode (GCE) via gold nanoparticles Finally, methylene blue and the extended probes were combined and the electrochemical signals were measured This signal was higher than that of the GCE modified only by the original probe When there was no target in PCR solution, the probe did not extend and the signal did not increase The specific sequences of the β-1,3-glucanase gene were detected successfully from three targets with different length: oligonucleotide, molecule clone vector DNA, and total genome DNA of transgenic capsicum The detection limits of 26 × 10−13, 78 × 10−13, and 91 × 10−13 moll−1 for oligonucleotide, molecule clone vector DNA, and total transgenic capsicum genome DNA were estimated

An electrochemical assay of beta-1,3-glucanase gene from transgenic capsicum using asymmetric PCR.

Electrochemical detection of β-1,3-glucanase gene from transgenic capsicums using asymmetric PCR generated by a detecting probe and an anchoring probe

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Fabrication and application of a new DNA biosensor based on on-substrate PCR and electrochemistry

An electrochemical assay of beta-1,3-glucanase gene from transgenic capsicum using asymmetric PCR.

Electrochemical detection of β-1,3-glucanase gene from transgenic capsicums using asymmetric PCR generated by a detecting probe and an anchoring probe