You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Health-related lipids components of sardine muscle as affected by photooxidation. The aim of this study was to evaluate the oxidative stability of sardine muscle lipids as related to the storage conditions. Whole sardines were stored at 4°C for 4h under light exposure and at dark. The lowest levels of peroxide value (PV), thiobarbituric acid reactive substances (TBARs), cholesterol oxidation products (COPs) and the highest level of polyunsaturated fatty acids (PUFAs) content, especially PUFA n-3, were found in the untreated sardines (time zero). After light exposure, PUFA dramatically dropped (up to a 19% decrease) and a marked increase of PV (11.8meq O2/kg fat), TBARs (3.7mg MDA/kg meat) and COPs (3.7μg/g muscle) was observed; under darkness, the values of the oxidation parameters were similar to those found in untreated sardines. Although cholesterol oxidation rate did not exceed 0.9%, further research is required about toxicity levels of the single COPs, to better understand if the COPs levels found in untreated and photoxidized muscle (0.62-3.72μg/g of muscle) do not represent a risk for human health.
{"Chemical": ["PUFA n-3", "thiobarbituric acid", "O2", "cholesterol", "PUFAs", "polyunsaturated fatty acids", "peroxide", "PUFA"]}