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    Multi-well plate as headspaces for paper-based colorimetric detection of sulfur dioxide gas: An alternative method of sulfite titration for determination of formaldehyde
    (2023-01-25)
    Yodpach, Nattapon
    ;
    Chantiwas, Rattikan
    ;
    Wilairat, Prapin
    ;
    Choengchan, Nathawut
    ;
    Praditweangkum, Wiboon
    This work describes the analysis of formaldehyde using a 96-well microplate as multiple headspaces for the separation of sulfur dioxide gas generated from the sulfite remaining after its reaction with the formaldehyde in the sample. The quantitation of the gas is by colorimetric detection of an indicator paper placed over the microplate. The samples are aqueous extracts of various foods that are possibly adulterated with formaldehyde. A known excess amount of sulfite is added to the extract solution aliquoted in the well. The remaining sulfite is acidified with hydrochloric acid to generate sulfur dioxide gas which diffuses through the headspace above the solution to be absorbed at the moist strip of the indicator paper placed over the mouth of the wells. Anthocyanins extracted from the butterfly pea flower is used as the pH indicator giving a color change from the increase of hydrogen ions by hydrolysis of the absorbed sulfur dioxide gas. The exposed paper strip is scanned, and the digital images of the colored region analyzed using ImageJ software. The optimized method has a linear range of 200–1000 mg L<sup>−1</sup> formaldehyde with limit of detection ((2.57*SD of intercept)/(slope of calibration line)) of the aqueous extract of 40 mg L<sup>−1</sup> and coefficient of determination (r<sup>2</sup>) > 0.9979. Samples of fresh produce, such as seafood, meat, and vegetables, and various processed food were analyzed for their possible formaldehyde content. The results obtained from the headspace paper-based colorimetric detection are not statistically different from the values obtained from the titration method by paired t-tests.
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    Application of butterfly pea flower extract in processing some Vietnamese traditional foods
    (2022-09-01)
    Thuy, Nguyen Minh
    ;
    Ben, Tran Chi
    ;
    Ngoc, Pham Thi Be
    ;
    Tai, Ngo Van
    Butterfly pea flower (BPF) extract was applied to the processing of traditional Vietnamese food products to bring attractiveness and safety. Different cooking techniques as steaming, boiling, frying, baking, and sterilization were used and controlled. All products were analyzed for total anthocyanin content remaining after processing conditions. The selected percentage of extract and treatment time (minutes) in different processing methods were obtained: Bloating fern-shaped cake/thin cakes (bánh bèo) (10% extract – steaming time 7 min); Rice ball sweet soup – chè ỉ) (15% extract – boiling time 6 min), fried Meat stuffed rice ball – viên thịt) (10% extract (v/w) – frying time 4 min), and bread (15% extract – baking temperature 160°C). Half-life values of anthocyanin degradation at different temperatures (through cooking methods) were observed. A case study was performed with BPF drink, this product had high quality when adding 5% BPF extract (v/v), sterilized at 125°C for 3 min with extended storage time (more than 4 months). The degradation of anthocyanin during storage was modeled according to the first-order kinetics. The half-life values were calculated as 38 and 46 weeks, respectively, at ambient (28 ± 2°C) and low temperature (6 ± 2°C) storage.