The fabrication of a novel polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal-organic framework electrospun nanofiber adsorbent for the ultrasonic-assisted thin-film microextraction of fatty acid methyl esters in dairy products with gas chromatography-flame ionization detection.

R Mirzajani,F Kardani,Z Ramezani

doi:10.1039/d0ra07674k

Abstract

In this work, electrospun polyacrylonitrile/reduced graphene oxide-amino-halloysite/bimetallic metal–organic framework (PAN/rGO-amino-HNT/Co0.5Zn0.5(MeIm)2) nanofiber film was synthesized and investigated as a novel adsorbent for the ultrasonic-assisted thin-film microextraction (UA-TFME) of fatty acid methyl esters (FAMEs), including palmitic methyl ester (PAME), oleic methyl ester (OAME), stearic methyl ester (SAME), and linoleic methyl ester (LAME), from dairy products. The hybrid nanocomposite was obtained via bonding halloysite nanotubes to reduced graphene oxide, followed by loading with bimetallic metal–organic frameworks. The determination of FAMEs with nanofiber film was performed in two stages of desorption and absorption where, initially, the analytes were adsorbed onto the nanofiber film and then desorbed with organic solvent. In this study, ultrasound was used for both the adsorption and desorption stages. The advantages of ultrasonication are extensive, overcoming the shortcomings of conventional techniques in terms of energy consumption and solvent use, allowing a shorter treatment time with a low cost of implementation. Based on PAN/rGO-amino-HNT/Co0.5Zn0.5(MeIm)2 thin film, a microextraction-gas chromatography-flame ionization detection (TFME-GC-FID) method was developed. Experimental parameters affecting the extraction and desorption steps were optimized. The desorption parameters, including desorption time and the properties of the desorption solvent, were investigated one factor at a time. Then, effective parameters in the adsorption step were optimized using a Box–Behnken design and Design-Expert 7 software. Under the optimal conditions, the method detection limits (S/N = 3) were in the range of 0.03–0.06 μg L−1 and the limits of quantification (S/N = 10) were within 0.11–0.23 μg L−1. The relative standard deviations for intra-day and inter-day precision were 2.4–4.7% and 2.6–3.4%, respectively. In the present work, the UA-TFME method was successfully applied for the quantification of fatty acid methyl esters in dairy products (milk, yogurt, cheese, yogurt soda and butter samples) for the first time. The fatty acids were transesterified using standard procedures and were subjected to UA-TFME treatment prior to GC-FID determination. The developed method possesses the advantages of simplicity, rapidity, cost-effectiveness, sensitivity, and non-invasiveness.

Highlights

IntroductionDairy products are milk and any of the foods made from milk, including butter, cheese, ice cream, yogurt, and condensed and 14686 | RSC Adv., 2021, 11, 14686–14699Paper products is important due to their (fatty acids') impact on the avour and texture of dairy products and because of their potential impact on nutrition and health, as well as for their anti-microbial properties
Dairy products are milk and any of the foods made from milk, including butter, cheese, ice cream, yogurt, and condensed and 14686 | RSC Adv., 2021, 11, 14686–14699Paper products is important due to their impact on the avour and texture of dairy products and because of their potential impact on nutrition and health, as well as for their anti-microbial properties
Scanning electron microscopy (SEM) observations of GO, reduced graphene oxide (rGO), rGO-amino-Halloysite nanotubes (HNT), and rGO-amino-HNT/Co0.5ZnO0.5(MeIm)[2] Metal–organic frameworks (MOFs), as well as nano bers prepared by electrospinning are shown in Fig. 4a–f, respectively

Summary

Introduction

Dairy products are milk and any of the foods made from milk, including butter, cheese, ice cream, yogurt, and condensed and 14686 | RSC Adv., 2021, 11, 14686–14699Paper products is important due to their (fatty acids') impact on the avour and texture of dairy products and because of their potential impact on nutrition and health, as well as for their anti-microbial properties. While milk and dairy foods are generally supposed to be healthy foods, milk fat comprises around 70% of saturated fatty acids (SFA). These fatty acids (mostly myristic and palmitic acids) may increase total and low-density lipoprotein (LDL) cholesterol, raising the possibility of cardiovascular disease (CVD), and the consumption of milk fat should be limited.[1,2,3]. Palmitic and stearic acids are other important PUFAs which exist in the lipids of most organisms.[4,5,6,7] an essential step in the detection and control of the fatty acids of dairy products in human life is to employ a simple, accurate, and practicable method. The derivatization procedure (especially for the longer chain FAs) is mandatory for enhancing the volatility and overcoming the adsorption of the polar functional groups onto the GC column.[10,11] Thermally labile FAs can be separated using high performance liquid chromatography (HPLC), capillary electrophoresis, and supercritical uid chromatography.[12]

Methods

Results

Conclusion