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Antioxidants in chemical terms are electron donors and antioxidants are biologically compounds that can overcome the negative effects of oxidants in the body such as damage to vital cells of the body. The balance between oxidants and antioxidants is very important. Antioxidant from natural sources are safer than synthetic antioxidants. Soybeans are functional food source that contains essential amino acids, vitamin e, saponins and are rich in antioxidants such as flavonoids, isoflavones and anthocyanins. The aim of this research is to investigate antioxidant potential of ethanolic extract of black soybean (EEBS) and its compound daidzein. The phytochemical screening assay evaluated by modified Farnsworth methods and to find out phenolic and flavonoid content, total phenols and flavonoids were tested. DPPH (2,2-diphenyl 1-pichylhydazy), ABTS (2,2’-Azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) reducing activity, FRAP (ferric reducing antioxidant power) activity and H2O2 scavenging activity assay were used to measure antioxidant activity. The analysis of phytochemical of EEBS exhibit the presence of saponins, alkaloids, tannins, steroids and triterpenoids and terpenoids. Total phenol and flavonoid assay showed the presence of phenols and flavonoids. Four assay of antioxidant activity showed that EEBS at highest concentration exhibit higher activity (%), and from three assays EEBS has higher antioxidant activity (expressed as IC50) than daidzein. Overall, three of the four antioxidant tests performed can be concluded that EEBS has better antioxidants activity than daidzein. Further research is needed regarding black soybean as a promising antioxidant resource.

A simple visual ethanol biosensor based on alcohol oxidase (AOX) immobilised onto polyaniline (PANI) film for halal verification of fermented beverage samples is described. This biosensor responds to ethanol via a colour change from green to blue, due to the enzymatic reaction of ethanol that produces acetaldehyde and hydrogen peroxide, when the latter oxidizes the PANI film. The procedure to obtain this biosensor consists of the immobilization of AOX onto PANI film by adsorption. For the immobilisation, an AOX solution is deposited on the PANI film and left at room temperature until dried (30 min). The biosensor was constructed as a dip stick for visual and simple use. The colour changes of the films have been scanned and analysed using image analysis software (i.e., ImageJ) to study the characteristics of the biosensor's response toward ethanol. The biosensor has a linear response in an ethanol concentration range of 0.01%–0.8%, with a correlation coefficient (r) of 0.996. The limit detection of the biosensor was 0.001%, with reproducibility (RSD) of 1.6% and a life time up to seven weeks when stored at 4 °C. The biosensor provides accurate results for ethanol determination in fermented drinks and was in good agreement with the standard method (gas chromatography) results. Thus, the biosensor could be used as a simple visual method for ethanol determination in fermented beverage samples that can be useful for Muslim community for halal verification.

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The stable chromogenic radical 1,1′-diphenyl-2-picrylhydrazyl (DPPH) solution was immobilized on the microwell plate as dry reagent to construct a simple antioxidant sensor. Then, a regular flatbed scanner was used as microplate reader to obtain analytical parameters for antioxidant assay using one-shot optical sensors as scanometry technique. Variables affecting the acquisition of the images were optimized and the analytical parameters are obtained from an area of the sensing zone inside microwell using the average luminosity of the sensing zone captured as the mean of red, green, and blue (RGB) value using ImageJ® program. By using this RGB value as sensor response, it is possible to determine antioxidant capacity in the range 1–25 ppm as gallic acid equivalent (GAE) with the response time of 9 min. The reproducibility of sensor was good (RSD<1%) with recovery at 93%–96%. The antioxidant sensor was applied to the plant extracts, such as sappan wood and Turmeric Rhizome. The results are good when compared to the same procedure using a UV/Vis spectrophotometer.

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