Exploiting microdistillation and smartphone-based digital-image colorimetry for determination of protein in foods

Author(s)

Goncalves, Isabela Camargo ; Soares, Samara ; Rocha, Fabio R. P.

• Document type: Journal article
• Source: Microchemical Journal; v. 188, p. 6-pg., 2023-01-30.

Abstract

Because of their nutritional importance and industrial interest, determination of proteins is usual in food quality control. The Kjeldahl method, the most usual for protein determination and a reference to other indirect methods, is time-consuming and generates significant amounts of waste. Aiming to circumvent these drawbacks, this work proposes a simple, cost-effective, and more environmental friendly procedure based on micro- distillation of the ammonium from Kjeldahl digests, absorption on an acid-base indicator solution, and digital - image colorimetry for protein determination in food. Microdistillation was carried out in a simple and inex- pensive lab-made apparatus. The digital images were acquired by a smartphone camera under controlled illu- mination and the intensity of the reflected radiation was converted to the RGB color system using a free app (PhotoMetrix (R)). Measurements were based on the color change of phenol red from yellow to pink and the G channel (corresponding to the complementary color of the dissociated indicator) was taken as analytical response. A linear response was achieved within 5.0-50.0 mg/L ammonium, equivalent to 0.003-0.03 % protein (r=0.996), as confirmed by the lack-of-fit test at the 95 % confidence level. Coefficient of variation (n=10) and limit of detection (99.7 % confidence level) were estimated at 2.3 % and 2 mg kg-1 protein, respectively. A sample throughput of 12 h-1 was achieved with simultaneous sample processing. Protein amounts determined in foods of animal (milk) and vegetal (beans and lentils) origin yielded results in agreement with the micro-Kjeldahl reference procedure at the 95 % confidence level. (AU)

• FAPESP's process: 21/02590-6 - Development of green analytical strategies for the determination of protein and urea in foods
• Grantee: Isabela Camargo Gonçalves
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 18/07687-5 - Exploitation of novel calibration strategies, digital images and flow analysis for biodiesel quality control
• Grantee: Samara Soares
• Support Opportunities: Scholarships in Brazil - Doctorate