Cellulose Surface Nanoengineering for Visualizing Food Safety
A recent article published by The Guardian newspaper offers an overview of a new research article published in July regarding food safety, that reports on testing methods used to detect amounts of pesticides on produce, and further, how far into the fruit or vegetable the chemical penetrated.
There is a reason that news aggregators are a popular way to learn about advances in science: site science writers read and paraphrase papers like Cellulose Surface Nanoengineering for Visualizing Food Safety by Zewan, Xiaotong, Ke, Shaobo, Chaoji, and Dongdong, in order to interpret texts that are dense with scientific jargon and acronyms. This one is no exception; the paper's abstract spells out the scope and conclusions of the study, but the rest of the paper is quite dense. A link to the paper is posted at the bottom of this topic. A term throughout this paper is SERS - "Surface-enhanced Raman scattering (SERS)2 is the most common method" used for this kind of testing. From the report: "The findings of this study provide new concepts for designing cellulose nanostructures and broaden the use of cellulose nanomaterials in SERS applications." These are used when testing contamination levels in foods.
From The Guardian:
The central aim of the new paper is to share the technical details of a process the authors developed for enhanced trace detection of pesticides in foods. But the underlying finding about the ineffectiveness of washing fruit is important for consumers who may be relying on food safety practices that are insufficient, the authors said. . . . When using the technique to examine an apple, for instance, the researchers said the “imaging results prove that the pesticides penetrate the peel layer into the pulp layer”.
Apples are used for the example tested. The penetration of the pesticides in use, in this case, Thiram and CBZ tested at specific recommended rates, went deeper than just onto or even into the skin of the apple, they penetrated slightly into the pulp. The membrane being used for testing is a proxy for the apple skin and "showed that the characteristic Raman spectrum enhanced by the composite membrane could still distinguish the distinct peaks of pesticides even at a thiram concentration as low as 10−9 M demonstrating the membrane’s high sensitivity and SERS effect in practical applications." This means the composite new nanomembrane (proxy) is very sensitive to spread out particles of pesticides and those that lodged deeper into the fruit. And this means that while the levels of pesticides are acceptable to the USDA they are still there and you may want to peel your apples.
For the consumer, the upshot is that some processes we use for cleaning fruit and vegetables aren't enough due to the permeability of pesticides to be more than skin deep. Some fruits and vegetables should washed but then also should be peeled. Additionally, the Guardian article discusses reports from Consumer Reports and the USDA regarding their testing of produce for contamination by pesticides.
Abstract
Food safety is vital to human health, necessitating the development of nondestructive, convenient, and highly sensitive methods for detecting harmful substances. This study integrates cellulose dissolution, aligned regeneration, in situ nanoparticle synthesis, and structural reconstitution to create flexible, transparent, customizable, and nanowrinkled cellulose/Ag nanoparticle membranes (NWCM-Ag). These three-dimensional nanowrinkled structures considerably improve the spatial-electromagnetic-coupling effect of metal nanoparticles on the membrane surface, providing a 2.3 × 108 enhancement factor for the surface-enhanced Raman scattering (SERS) effect for trace detection of pesticides in foods. Notably, the distribution of pesticides in the apple peel and pulp layers is visualized through Raman imaging, confirming that the pesticides penetrate the peel layer into the pulp layer (∼30 μm depth). Thus, the risk of pesticide ingestion from fruits cannot be avoided by simple washing other than peeling. This study provides a new idea for designing nanowrinkled structures and broadening cellulose utilization in food safety.
Keywords: cellulose membrane, aligned nanostructure, nanoengineering, Raman imaging, food safety