Mechanisms of isomerization and oxidation in heated trilinolein by DFT method

Total fat and fatty acid profile including TFA content of Indian fried foods versus the oils used for frying

Due to deleterious health effects, consumption of trans fat containing fried foods is a major concern. The present study has assessed total fat, SFA, cis-UFA and TFA content of Indian fried foods-French fries, Poori, Potato chips, Bread Pakora and Mathri (on dry weight basis), at varying number of frying cycles/temperatures as well as composition of the oils extracted from the foods and the oils used for frying. Total fat in the food items was significantly higher at 32nd (x̄27.4%) versus the 1st frying cycle (x̄22.5%; p < 0.05). Progressive frying cycles (1st vs. 32nd)/temperatures demonstrated declining levels of cis-UFAs (at 180 °C: x̄16.33% vs. x̄11.29%; at 160 °C: x̄19.54% vs. x̄13.81%) with concomitant increase in SFA (at 180 °C: x̄4.97% vs. x̄14.97%; at 160 °C: x̄5.19% vs. x̄13.79%) and TFA content (at 180 °C: x̄0.05% vs. x̄0.89%; at 160 °C: x̄0.04% vs. x̄0.17%). Compared to the unheated oil, at 32nd frying cycle (irrespective of the frying temperatures), oils extracted from fried foods registered a significant decrease in cis-UFA (x̄17.41%) coupled with an increase in SFA (x̄63.74%) and an exponential increase in TFA (39-301 folds); however, the change was slightly lesser in oils used for frying (cis-UFA: x̄15.06%; SFA: x̄53.75%; TFA: 20-264 folds). To curb TFA in fried foods, necessary regulations are needed for restricting the number of frying cycles as well as the frying temperatures along with awareness generation regarding appropriate frying practices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-024-05989-z.

Thermal oxidation mechanism of palmitic aicd

The oxidation and degradation of fats lead to a decrease in the nutritional value of food and pose safety concerns. Saturated fatty acids also hold a significant position in the field of lipid oxidation. In this study, the oxidation products of methyl palmitate were investigated by using gas chromatography mass spectrometry (GC-MS). Seven monohydroperoxides and 72 secondary oxidation products were detected. Combined with density functional theory (DFT) calculations, the formation mechanisms of oxidation products can be summarized into four stages. The initial stage involved the formation of monohydroperoxides and alkanes, followed by the subsequent stage involving methyl x-oxo(hydroxy)hexadecanoates. The third stage involved the formation of methyl ketones, carboxylic acids, and aldehydes, while the final stage involved lactones. Meanwhile, methyl ketones were the most abundant oxidation product, approximately 25 times more abundant than aldehydes; the calculated results agreed well with the experimental results. The establishment of a comprehensive thermal oxidation mechanism for palmitic acid provided a new foundation for future lipid oxidation analyses.

Mechanisms of the Formation of Nonvolatile and Volatile Oxidation Products from Methyl Linoleic Acid at High Temperatures

The impact of the oxidation of linoleic acid cannot be overlooked in daily food consumption. This study used gas chromatography-mass spectrometry (GC-MS) to identify both nonvolatile oxidation products and volatile oxidation products of methyl linoleic acid at 180 °C and density function theory to investigate oxidation mechanisms. An analysis of nonvolatile oxidation products revealed the presence of three primary oxidation products. The three primary oxidation products were identified as hydroperoxides, peroxide-linked dimers, and heterocyclic compounds in a ratio of 2.70:1:3.69 (mmol/mmol/mmol). The volatile components of secondary oxidation products were found including aldehydes (40.77%), alkanes (19.89%), alcohols (9.02%), furans (6.11%), epoxides (0.46%), and acids (2.50%). DFT calculation proved that the secondary oxidation products mainly came from peroxides (77%). Finally, we look forward to our research contributing positively to lipid autoxidation and human health.

Mechanism of the initial oxidation of monounsaturated fatty acids

The development of detection technology prompts the need to elaborate on the theory behind the oxidation of unsaturated fatty acids. This study integrates the detection of monounsaturated fatty acid oxidation at 60 °C with computational simulations to provide an advanced theoretical basis for the formation of hydroperoxides and allyl. The results indicate that oxidation reaction led to increases of 3.4 mg/g for 8-hydroperoxy-trans-9-octadecenoate (trans8) and 2.7 mg/g for 9-hydroperoxy-trans-10-octadecenoate (trans9) and 10-hydroperoxy-trans-8-octadecenoate (trans10) despite low temperatures. The energy of peroxyl radical production was 0.36 kcal/mol and that of allylic isomerization was 78.52 kcal/mol, indicating the existence of two pathways for hydroperoxides formation: β-fragmentation and the allylic isomerization. Structural equation modeling (SEM) verified the multistep competitive side reactions that occurred during oxidation. This finding provides a new basis for future analysis of lipid oxidation.

Oxidative Stability of Vegetal Oil-Based Lubricants

Lipids are widely distributed in nature and are one of the most important components of natural foods, synthetic compounds, and emulsions. To date, there is a strong social demand in the industrial sector for the use of sustainable products with a minimal environmental impact. Depending on their origin and composition, lipids can be employed as a plausible alternative as biodegradable lubricants in order to reduce the use of conventional mineral oil lubricants and mitigate their environmental impact. This perspective provides an overview of the advantages and constrains of vegetal oils under different lubrication regimes and the tribochemical reactions that can take place. Also, the different factors and pathways that influence their oxidation, the key role of moisture, and the changes of physical properties under pressure and temperature are reviewed. Special emphasis is devoted to the oxidation instability of fatty acids and vegetal oils and the physical and chemical approaches to improve oxidative and thermal stability are described in detail.