Fast and selective determination of total protein in milk powder via titration of moving reaction boundary electrophoresis

Abstract

In this paper, moving reaction boundary titration (MRBT) was developed for rapid and accurate quantification of total protein in infant milk powder, from the concept of moving reaction boundary (MRB) electrophoresis. In the method, the MRB was formed by the hydroxide ions and the acidic residues of milk proteins immobilized via cross-linked polyacrylamide gel (PAG), an acid-base indicator was used to denote the boundary motion. As a proof of concept, we chose five brands of infant milk powders to study the feasibility of MRBT method. The calibration curve of MRB velocity versus logarithmic total protein content of infant milk powder sample was established based on the visual signal of MRB motion as a function of logarithmic milk protein content. Weak influence of nonprotein nitrogen (NPN) reagents (e.g., melamine and urea) on MRBT method was observed, due to the fact that MRB was formed with hydroxide ions and the acidic residues of captured milk proteins, rather than the alkaline residues or the NPN reagents added. The total protein contents in infant milk powder samples detected via the MRBT method were in good agreement with those achieved by the classic Kjeldahl method. In addition, the developed method had much faster measuring speed compared with the Kjeldahl method.

Undergraduate laboratory experiment on determination of total protein content in milk powder by moving reaction boundary titration

“… and Guo et al . advanced the MRBT technique for determination of total protein content in milk. In this MRBT system, the MRB is formed by hydroxide ions in the catholyte and acidic residues of milk proteins immobilized in highly cross‐linked polyacrylamide gel, and an acid–base indicator is used to denote the boundary movement.…”

“…Based on these concepts, Yang et al [22] and Wang et al [23] developed the MRBT method and designed the relevant device for acid-base titration analysis. Then in 2013, Wang et al [24] and Guo et al [25] advanced the MRBT technique for determination of total protein content in milk. In this MRBT system, the MRB is formed by hydroxide ions in the catholyte and acidic residues of milk proteins immobilized in highly cross-linked polyacrylamide gel, and an acid-base indicator is used to denote the boundary movement.…”

A stable and convenient protein electrophoresis titration device with bubble removing system

“…To address the issue of NPN adulteration in milk products, the concept of moving reaction boundary titration (MRBT) was proposed, based on the moving reaction boundary (MRB) electrophoresis . In the MRBT analysis, samples or milk proteins were immobilized in highly cross‐linked polyacrylamide gel and hydrogen or hydroxide ions could migrate into the gel and neutralized the alkaline or acidic groups of proteins under electric field .…”

Estratégias para aumento de sensibilidade e seletividade de separações cromatográficas em sistemas de análises em fluxo

“…Ela também tem sido utilizada na adulteração de alimentos, especialmente de leite, devido o seu alto teor de nitrogênio, o qual corresponde a 66,7 % da massa total e também ao seu baixo custo [106]. A adição de 1% (m/m) de melamina ao leite eleva o conteúdo aparente de proteínas em 4% [112]. Melamina apresenta baixa toxicidade por via oral, mas a exposição prolongada a esta substância causa a formação de cristais nos rins e na bexiga, sendo as crianças mais afetadas devido à imaturidade de seus órgãos [109].…”

“…Outros procedimentos empregando eletroforese capilar [112,119], cromatografia de íons [125], cromatografia a gás acoplada a espectrometria de massas [113], voltametria [117], espectrometria de massas MALDI-TOF [126], quimiluminescência [127,128], imunoensaios [129] e espectrometrias Ramam [110] e por fluorescência [130] foram desenvolvidos. Estes procedimentos geralmente envolvem preparo de amostra demorado [126], incluindo etapas de extração e pré-concentração e em alguns casos, alto consumo de solventes orgânicos [120][121][122][123][124].…”