Validation of a microscopic method and mathematical model for the detection of corn and wheat starch in adulterated ground black pepper

Adulteration of spices may negatively impact food quality and safety. The addition of starch is a fraud unlikely to be detected by consumers. Therefore, this study was developed in order to quantify, by optical microscopy, the presence of corn and wheat starch in ground black pepper and to validate equations for estimating starch percentage to identify adulteration. Black pepper grain samples were ground and intentionally adulterated with 3%, 5%, 10%, 15%, and 20% corn starch and wheat flour, separately, and subsequently analyzed by optical microscopy. A linear regression model was adjusted to estimate the percentage of adulterant starch. A spreadsheet was developed to calculate the estimated mean starch percentage and its lower and upper limits. The model was validated by means of a blind test (samples adulterated at unknown levels to the analyst). Additionally, three commercial samples and three suppliers were evaluated. Structural differences were observed between corn and wheat starch granules, enabling their identification and quantification. The blind test confirmed the effectiveness of the method in identifying and counting starch granules, validated the adjusted mathematical model, and enabled satisfactory quantification of the adulteration percentage, reinforcing the reliability of the results. Wheat starch was detected in all three commercial samples and in two of the three supplier samples. Therefore, optical microscopy may be highlighted as a practical tool for the food industry, contributing significantly to fraud detection, quality assurance, and authentication of spices.