Abstract

A low-cost lab-on-a-smartphone platform for rapid and on-site assessment of total phenolic content in plant-based milk alternatives has been proposed for the first time. The three main components, including a smartphone, a disposable Eppendorf vial and a specially designed holder with an integrated polychromatic light source, were compactly assembled to enable color-forming reaction, separation and measurement. The method involves the application of the classically used Folin-Ciocalteu reagent to perform a color-forming reaction and the green surfactant alkyl polyglycoside C8-C10 to separate derivatives and impurities of the sample matrix. The coacervation phenomenon proceeding due to the addition of heptanoic acid to a micellar solution facilitates efficient phase separation and overcomes the challenges posed by matrix components such as ash, protein, carbohydrates and crude fibre. It also eliminates the need to use centrifugation and filtration as the matrix components were isolated into the obtained supramolecular solvent. The digital images were captured inside a lab-on-a-smartphone platform with controlled light conditions and analyzed using image processing algorithms. Various types of plant-based milk alternatives, including extracts from cereals, legumes, nuts, seeds and pseudocereals, were analyzed and the total phenolic content was found in the range 34.6 to 2748.7 mg GAE L−1. The results obtained, compared with the reference method, demonstrate significant findings, with a slope of the Passing-Bablok regression equal to 1.0049, indicating results are in good agreement. The linear range for total phenolic content was established as 25–110 mg GAE L−1, with a coefficient of determination of 0.9957. The limit of quantification and limit of detection were determined to be 25 mg GAE L−1 and 15 mg GAE L−1, respectively. Inter-day and intra-day precision, expressed as coefficient of variation (% CV), were 7.28 % and 2.29 %, respectively, while recovery rates ranged from 73 % to 154 %. Additionally, a greenness assessment using the AGREE tool showed an overall score of 0.84, indicating that the proposed smartphone-based method has a low environmental footprint. The total analysis time did not exceed 10 min, which is satisfactory for on-site analysis.

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