| Author: | Li, Zhen Yan |
| Title: | Investigation of arsenic accumulation in deep-frying oil |
| Advisors: | Yao, Zhongping (ABCT) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Arsenic -- Toxicology Deep frying Rape oil Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | xix, 131, h pages : color illustrations |
| Language: | English |
| Abstract: | Deep-frying is a popularly used cooking method, and the deterioration of deep-frying oil has been a topic of concern and has been extensively studied. However, the transfer and accumulation of heavy metals from the food being deep-fried to the deep-frying oil has not been well studied although it has been proven possible and poses high risk due to their highly toxic nature. This study aims to address this issue by a series of deep-frying experiments by repeatedly using rapeseed oil, a commonly used frying oil, and settings that mimicked the typical food trade practice. Oyster was the first type of food to be tested due to its being commonly deep-fried and high heavy metal levels. The results showed that arsenic could accumulate to over 0.1 ppm, a limit established by the Hong Kong government in edible oil, after 16 deep-frying cycles and could reach as high as over 0.5 ppm with more frying cycles. Further study revealed that the residues in the frying oil contained high concentrations of arsenic (could reach over 6 ppm) and were the major cause of high arsenic concentrations of the deep-frying oil. It was found that the residues were formed from liquid leached from the oysters during the deep-frying. The study also demonstrated that arsenic could be transferred from the deep-frying oil to the food being deep-fried by adherence of the residues onto the food. Deep-frying of grouper fish fillets yielded deep-frying oil with arsenic concentrations similar to that of the oysters, while the colours of the oil and the residues were significantly lighter compared to those of the oysters. The lighter colour and the slower deterioration rate of the deep-frying oil would likely lead to delayed replacement of oil, leading to higher food safety risks as oil with high arsenic content would not be replaced in time. In addition, the results demonstrated that heavy metal accumulation in deep-frying oil was not limited to oysters but also other types of deep-fried food, leading to wider implications. Arsenic speciation analysis was performed to evaluate the potential food risks associated with consumption of deep-frying oil and deep-fried food of high arsenic levels. The preliminary results showed the potential food safety concerns since the levels of dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), both carcinogenic, increased in the deep-fried food, the residues and the deep-frying oil, and deep-frying might cause demethylation of organic arsenic species, transforming them into more toxic forms. Further studies are needed to completely understand the conversion of the arsenic species during deep-frying. In summary, our results revealed that arsenic could be accumulated to very high concentrations in repeatedly used deep-frying oil when frying foods such as oysters and grouper fish fillets, posing risk to the consumers. Replacing deep-frying oil based on oil colours and deterioration may not be suitable in such cases, and new guidelines and quality indicators for heavy metal contaminations in deep-frying oil should be considered. Our study also indicated that removing residues from the frying oil and using batter to mask the food before the frying could help to reduce accumulation of heavy metals in deep-frying oil, which should also be recommended to the food trade. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/13117