New application of Hehner's test with modification for detection of formalin in cheeses and fish

The modified Hehner's test (MHT) was applied to detect the formalin in experimentally contaminated and collected commercial cheeses and fish. The spectrophotometric method was adapted to determine the formalin in cheeses and fish samples. The principle of test modification was a complete homogenization and dilution of the examined cheeses and fish samples. By two methods, the incidences of formalin in the market soft and Ras cheeses samples were 31.66 and 3.33%, respectively. Formalin was not detected in the examined market fish samples by MHT, and its concentration by the spectrophotometric method was less than 1 µg/g. The findings of the study indicated that the results obtained by both MHT and spectrophotometric methods were comparable. The applicability of the MHT in different food matrices might mean it has potential as a standard technique with high sensitivity up to 0.001%. Graphical abstract (A): Prepared Ras cheese homogenate; (B): Positive and negative modified Hehner's test in the examined Ras cheese samples with different formalin concentrations; (C): Positive and negative modified Hehner's test in the examined soft cheese samples with different formalin concentrations; (D): Negative modified Hehner's test in the examined fish flesh samples with 0.001% formalin concentration; (E): Positive modified Hehner's test in the examined fish flesh samples with 0.1% formalin concentration; (F): Positive modified Hehner's test in the examined fish wash samples with 0.01% formalin concentration