Year: 2024
Type: dissertation
Abstract: Concerns regarding the safety of food are growing due to contamination by small plastic wastes called microplastics (MPs). MP is defined by the European Food Safety Authority (EFSA) as small plastic debris ranging from 0.1 – 5,000 μm. They enter the environment either as large portions of plastic that break down into smaller pieces, or as already micro-sized debris. The potential of MPs to bioaccumulate in the marine environment and move up the food chain consequently leads to human exposure. A growing body of evidence also shows that MPs not only occur in seafood, but also in other food items (e.g., water, fruits, and vegetables) which further increases human exposure through diet. This raises the question; how many MPs are we exposed to from the diet and how do MPs affect our health? This dissertation contributes to addressing this question by focusing on dietary exposure through the consumption of clams, improved means of MP detection, and their potential impacts on human digestive health. The comparative profiling of MPs from small and large Manila clams (R. philippinarum) from South Korea, using both Nile red staining and μFTIR imaging, showed that the concentration of MPs is similar despite the substantial differences in size, weight, and age of shellfish. According to μFTIR imaging, 2.70 ± 1.66 MP/g and 3.65 ± 1.59 MP/g were detected from the small and large clams, respectively. Particle diameters of 20–100 μm were the most dominant while polystyrene (PS) accounted for at least 50% of total MPs. This gives an estimated dietary intake (EDI) of 1232 MP/person/year via small clams, 1663 MP/person/year via large clams, and 1489 MP/person/year via clams independent of size. Half of the EDI from small clams accounts for PS intake while 46% is due to polyethylene terephthalate (PET). On the other hand, 65% of the EDI from large clams is also due to PS while 20% comes from polypropylene (PP). The measurement of MPs from the clams through Nile red staining proved to be challenging due to the lack of tools that accurately detect MPs from digital images. Currently existing tools for image segmentation (e.g., MP-VAT, MP-VAT 2.0, and C-VAT) overestimated MP quantities up to 168%. An alternative deep-learning based image segmentation called MP-Net was developed to overcome the drawbacks of already existing image processing tools. MP-Net was trained using digital images of Nile redstained MPs obtained from Manila clams. Through a series of pre-training, fine-tuning, and validation, MP-Net performed better in quantifying fluorescent MPs in digital images, giving a percentage recovery of 101-123%. With MP-Net, the number of false positive detections were significantly reduced, thereby providing a relatively more accurate measure of MP quantity. Lastly, the most abundant polymer in clams, PS, was found to interfere with the gastric digestion of proteins by interacting with pepsin, the major proteolytic enzyme in the stomach. Using static in vitro simulated human gastric digestion model, pepsin was exposed to increasing concentrations of 10 μm PS and 100 μm PS. The 2-hour exposure to high concentration of the small, low zeta-potential PS led to preferential binding of pepsin which caused structural changes to the protein, resulting in reduced enzymatic activity. The kinetics of cow’s milk digestion in the presence of 10 μm PS showed transient accumulation of larger peptides (10–35 kDa) and reduced bioaccumulation of short peptides (2–9 kDa) in the gastric phase. Formation of a hard protein corona, mainly composed of casein fragments, was also observed on the surface of small PS particles. This reduced protein breakdown and availability potentially limits downstream nutrient assimilation which may be harmful to humans in the long run. Overall, this dissertation demonstrated the high exposure of the Korean population to MPs, especially PS MPs, through consumption of clams. The larger and older clams did not accumulate more MPs as initially postulated which shows that the potential hazard of their consumption is similar to that of other sizes. The hazard associated with the intake of PS MPs was also established in relation to gastric protein digestion. To the best of our knowledge, this is the only study so far that reveals the kinetics of in vitro gastric digestion of actual food proteins in the presence of PS MPs. Finally, a new and more accurate tool for MP detection was developed which provides an alternative and free means for automated MP quantification in digital images.
Author: de Guzman, Maria Krishna
Language: English
Subfield: Pollution
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
Awards: AN INNOVATIVE ANALYTICAL PLATFORM TO INVESTIGATE THE EFFECT AND TOXICITY OF MICRO AND NANO PLASTICS COMBINED WITH ENVIRONMENTAL CONTAMINANTS ON THE RISK OF ALLERGIC DISEASE IN PRECLINICAL AND CLINICAL, G434337789, G4424559298, G5134074893, Twinning of research activities for the frontier research in the fields of food, nutrition and environmental ‘omics
OpenAlex ID: W7011402002