Chemical Reactions of Fat and oils

Summary

This presentation by Professor Caron from Universe Assigns Malaysia discusses the chemical properties and reactions of fats and oils, with a focus on palm oil. It explores important reactions such as hydrolysis, oxidation, hydrogenation, polymerization, and interesterification, particularly during deep-fat frying. The lecture highlights how these reactions affect oil quality, including the generation of free fatty acids, the formation of polymers, and oxidation processes. Additionally, it explains the implications of using oil repeatedly in cooking, such as reduced smoke points and increased oil viscosity, and methods to mitigate these effects.

Takeaways

• 🛢️ The presentation focuses on the properties and chemical reactions of palm oil, especially during deep fat frying.
• 🧪 Triglycerides, or triacylglycerols, are the primary components of fats and oils, and they undergo chemical reactions such as hydrolysis, oxidation, hydrogenation, polymerization, and interesterification.
• 🔥 Hydrolysis occurs during frying, breaking down ester bonds and producing free fatty acids, which can be undesirable in crude oil but beneficial in products like cheese.
• 🚫 Oxidation is an undesirable reaction in fats, causing rancidity due to the reaction of unsaturated double bonds with oxygen, especially in the presence of heat, light, or metals.
• 🌀 Polymerization can occur during deep fat frying at high temperatures, leading to the formation of larger molecules, which increases oil viscosity and can result in foaming.
• 🍟 The frying process leads to various chemical changes, including the production of volatile and non-volatile decomposition products and the solubilization of colored compounds.
• 💧 Foods with high moisture content, such as potatoes, can accelerate the hydrolysis of fats during frying, leading to more free fatty acid production and reduced oil quality over time.
• 🌬️ Aeration during frying incorporates oxygen into the oil, increasing oxidation and the formation of hydroperoxides, which then decompose into smaller reactive compounds.
• 🧴 Antioxidants like BHA and BHT can be added to minimize oxidation during frying, and defoaming agents like methyl silicon help reduce foaming in the oil.
• ⏳ Repeated use of frying oil results in more free fatty acids, polymers, and solubilized compounds, leading to reduced oil quality, increased viscosity, and lower smoke points.

Q & A

What are triacylglycerols, and why are they important in the study of fats and oils?

Triacylglycerols, also known as triglycerides, are the main components of fats and oils. They consist of glycerol bonded to three fatty acids. Understanding their chemical reactions, such as hydrolysis, oxidation, and hydrogenation, is essential for modifying fats and oils to produce high-value products and for managing chemical changes during processes like deep fat frying.

What is hydrolysis, and how does it affect edible oils during deep fat frying?

Hydrolysis is the breakdown of ester bonds in triglycerides, releasing free fatty acids (FFAs). This process can occur due to heat, moisture, or enzymes such as lipase. During deep fat frying, high moisture content in foods accelerates hydrolysis, leading to the accumulation of FFAs, which reduce the oil's smoke point and stability.

Why is hydrolysis undesirable in crude palm oil production, and how is it controlled?

Hydrolysis in crude palm oil production is undesirable because it increases the free fatty acid content, requiring more refining. To minimize hydrolysis, oil producers control factors like temperature and moisture content during processing.

What role does hydrolysis play in food products like cheese and yogurt?

In certain food products like cheese and yogurt, controlled hydrolysis is desirable. It helps develop characteristic flavors during processes like cheese ripening or yogurt fermentation by breaking down fats into fatty acids, which contribute to the food’s taste.

What is oxidation in the context of fats and oils, and why is it considered undesirable?

Oxidation occurs when the unsaturated bonds in fats react with oxygen, forming compounds like hydroperoxides. This reaction can cause rancidity, affecting the taste and quality of the oil. Oxidation is undesirable because it degrades the oil and reduces its shelf life.

How does polymerization occur during deep fat frying, and what are its effects?

Polymerization occurs when smaller molecules, like aldehydes and ketones, combine to form larger polymers, often preceded by oxidation. This reaction increases the viscosity of the oil and can result in the formation of foam, which decreases the oil's quality and performance during frying.

What physical and chemical changes occur in oil during deep fat frying?

During deep fat frying, the oil undergoes physical changes such as browning due to the Maillard reaction, and chemical changes like hydrolysis, oxidation, and polymerization. These changes lead to the formation of free fatty acids, volatile compounds, and polymers, which degrade the oil’s quality.

How does deep fat frying increase the risk of oxidation in oils?

Deep fat frying accelerates oxidation because the process involves high temperatures and aeration, which introduces oxygen into the oil. This leads to faster breakdown of unsaturated fatty acids, forming free radicals and rancid compounds, especially in oils with high levels of free fatty acids.

What strategies can be used to reduce oxidation and polymerization during deep fat frying?

To reduce oxidation and polymerization, antioxidants like BHA and BHT can be added to oils. Antifoaming agents like methyl silicon can also be used to minimize foaming. Additionally, using fresh oil regularly and maintaining the frying temperature at optimal levels can help limit these chemical reactions.

What are the long-term effects of repeatedly using the same oil for frying?

Repeatedly using the same oil for frying leads to the accumulation of free fatty acids, polymers, and solubilized compounds. This degrades the oil's quality, reducing its smoke point and causing it to foam or smoke at lower temperatures. Prolonged use of degraded oil can affect the taste and safety of fried foods.