Abstract
The effect of pressure-assisted thermal processing (PATP) in combination with seven synthetic antioxidants was evaluated on the retention of conjugated linoleic acid (CLA) in enriched milk. Milk rich in CLA was first saturated with oxygen, followed by the addition of either catechin, cysteine, ascorbic acid, tannic acid, gallic acid, caffeic acid or p-coumaric acid (500 mg kg−1 untreated milk). Samples were treated at 600 MPa and 120 °C up to 15 min of holding time. During PATP, CLA not only oxidized at a slower rate, but also less oxygen was consumed compared to the control (0.1 MPa and 120 °C). In addition, phenolic antioxidants were able to quench dissolved oxygen in samples treated with PATP. For those samples added with gallic acid and catechin, 85% and 75% of the CLA was retained after 15 min of holding time at 600 MPa and 120 °C, respectively. The retention of CLA was enhanced by the application of PATP in combination with gallic acid.
Highlights
Pressure-assisted thermal processing (PATP) has become a valuable alternative to traditional thermal treatments
conjugated linoleic acid (CLA) was retained up to 90% when catechin, a potent antioxidant, was added at 1 g per kg of milk, regardless of the processing conditions used (60–120 °C and 100–600 MPa) [17]. These findings suggest that the use of antioxidants can enhance the retention of CLA in milk
In the presence of oxygen, CLA was remarkably stable in samples treated with PATP compared to the control
Summary
Pressure-assisted thermal processing (PATP) has become a valuable alternative to traditional thermal treatments. Pressure reduces interatomic distance, affecting interactions, the bond energy which is distance dependent Such interactions are van der Waals forces, electrostatic forces, hydrogen bonding and hydrophobic interactions of proteins. Covalent bonds are unlikely to be affected by pressure, because the bonding distance can be hardly further compressed [3]. This has been the main hypothesis in preserving the biological activity of functional compounds, such as ascorbic acid [4,5], folates [6,7], anthocyanins [8], lycopene [9] and conjugated linoleic acid [10]. The effect of pressure favours those reactions with a negative reaction volume and those reaction pathways with a negative activation volume [3]
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