Kimia pangan dan Hasil. Pertanian

Summary

This presentation by Professor Brutarin from the University Science, Malaysia explores the chemical properties and reactions of fats and oils, focusing on palm oil. It discusses key reactions such as hydrolysis, oxidation, polymerization, and their impacts during deep fat frying and oil modification. Hydrolysis leads to free fatty acid accumulation, affecting oil quality. Oxidation accelerates rancidity, while polymerization increases viscosity, resulting in foaming. The presentation highlights how frying conditions, food moisture, and oil reuse influence these reactions. Preventive measures like antioxidants and anti-foaming agents are also discussed to maintain oil quality.

Takeaways

• 😀 Fats and oils are primarily composed of triglycerides, which can undergo various chemical reactions such as hydrolysis, oxidation, hydrogenation, polymerization, interesterification, and isomerization.
• 😀 Hydrolysis (lipolysis) is the breakdown of triglycerides into free fatty acids (FFAs) through enzymes or heat. It occurs during frying and refining processes.
• 😀 Free fatty acids in the oil can lower its smoking point, making it more prone to producing smoke when used for frying.
• 😀 Oxidation of fats, especially those with unsaturated bonds, leads to rancidity and the formation of undesirable compounds like aldehydes and ketones. This reaction accelerates in the presence of high temperature, oxygen, and metals.
• 😀 High amounts of free fatty acids in fats increase their susceptibility to oxidation, leading to the formation of harmful compounds and rancidity.
• 😀 Hydrolysis is beneficial in cheese production, where enzymes like lipase break down fats to impart characteristic flavors, but generally, hydrolysis is undesirable in cooking oils.
• 😀 Polymerization of oils can occur during deep-fat frying, where smaller molecules combine to form larger polymers, increasing the oil’s viscosity and potentially causing foam formation.
• 😀 The deep-fat frying process involves a series of chemical reactions, including hydrolysis, oxidation, and polymerization, which are influenced by factors like moisture content, temperature, and frying time.
• 😀 During deep-fat frying, water in the food causes hydrolysis in the oil, producing free fatty acids, which, in turn, affects the oil's quality and contributes to foaming.
• 😀 To improve oil quality during deep-fat frying, antioxidants such as BHA or BHT can be added to minimize oxidation, while anti-foaming agents like metal silicones help reduce foam formation.

Q & A

What are the main chemical reactions that fats and oils can undergo?

Fats and oils, primarily composed of triglycerides, can undergo hydrolysis, oxidation, hydrogenation, polymerization, interesterification, and isomerization.

How does hydrolysis (lipolysis) occur in fats and oils?

Hydrolysis occurs when triglycerides are broken down into glycerol and free fatty acids (FFA) by the action of water, heat, or enzymes such as lipase. It is accelerated by high temperature, pressure, and the presence of water.

Why is hydrolysis generally undesirable in crude oils?

Excessive hydrolysis increases free fatty acid content, which lowers the smoke point of the oil and requires additional refining, increasing processing costs.

In what cases is hydrolysis desirable?

Hydrolysis is desirable in the production of cheese and some yogurts, where lipase enzymes produce characteristic flavors, and in the soap and oleochemical industries, where complete hydrolysis provides free fatty acids for production.

What factors accelerate oxidation in fats and oils?

Oxidation is accelerated by high temperature, exposure to light, the presence of trace metals like copper and iron, and the presence of oxygen. Unsaturated fatty acids and free fatty acids are more susceptible.

What is autooxidation and how does it affect fats?

Autooxidation is the oxidation of fats at room temperature induced by air, occurring as a free radical chain reaction. It leads to the formation of peroxides, which decompose into aldehydes, ketones, alcohols, acids, and hydrocarbons, causing rancidity.

How does polymerization occur during deep fat frying?

During extended frying at high temperatures, small molecules like aldehydes and ketones formed through oxidation combine to form high-molecular-weight polymers. This increases oil viscosity and can cause foaming.

What are the main physical and chemical changes in oil during deep fat frying?

Deep fat frying causes hydrolysis (FFA formation), oxidation (peroxide and radical formation), polymerization (large molecules increasing viscosity), non-enzymatic browning (Maillard reaction producing color), and absorption or solubilization of food components into the oil.

How does the moisture content of the food being fried affect FFA formation?

Higher moisture content in food, such as potatoes, accelerates hydrolysis in the oil, producing more free fatty acids. The rate of FFA accumulation increases with higher moisture, higher frying temperature, and larger food loads.

What happens to the quality of oil when it is reused multiple times for frying?

Repeated use of oil increases free fatty acids, polymeric compounds, and solubilized food components. This reduces the smoke point, increases foaming, and generally decreases the oil's quality.

What measures can be used to minimize oil degradation during frying?

Antioxidants like BHA or BHT can slow oxidation, while anti-foaming agents such as metal silicates (0.5–2 ppm) reduce foaming. Regular oil turnover and filtration also help maintain quality.

How does oxygen get incorporated into frying oil, and what is its effect?

Vigorous boiling of food in hot oil introduces oxygen from the atmosphere into the oil. This accelerates oxidation, forming peroxides and unstable radicals, which further degrade the oil and contribute to polymerization.