Effects of the Addition of Beetroot Juice and Simulated In-Vitro Digestion on the Chemical, Physicochemical, Antioxidant and Hypoglycemic Properties of Carrageenan and Oligo-Carrageenan Gels

Yap, Yi Xuen (2025) Effects of the Addition of Beetroot Juice and Simulated In-Vitro Digestion on the Chemical, Physicochemical, Antioxidant and Hypoglycemic Properties of Carrageenan and Oligo-Carrageenan Gels. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Beetroot is recognized as a 'superfood' due to its potential to lower diabetes risk, provide antioxidants and enhance athletic performance. Oligo-carrageenan, a partially hydrolysed product of carrageenan also exhibits various beneficial activities. This study investigates the effects of beetroot juice and simulated in-vitro digestion on the physicochemical, chemical, antioxidant and hypoglycemic properties of carrageenan and oligo-carrageenan gels. Carrageenan and oligo-carrageenan gels were prepared by dissolving 1% carrageenan/oligo-carrageenan in beetroot juice and half-diluted beetroot juice, respectively. 1% carrageenan and oligo-carrageenan prepared in distilled water served as control. The pH, viscosity and gel strength of all gels were measured and compared. Next, all gels were digested through simulated in-vitro digestion, and the total phenolic content (TPC), total flavonoid content (TFC), nitrate content, total betalain content, antioxidant activity (DPPH, ABTS and FRAP) and alpha-amylase inhibition activity were determined. Results showed oligo-carrageenan had significantly lower (p < 0.05) viscosity and gel strength than carrageenan. Additionally, the addition of beetroot juice significantly increased (p < 0.05) viscosity and gel strength but significantly reduced (p < 0.05) pH of all gels. Simulated digestion caused a significant reduction (p < 0.05) of TPC, TFC, nitrate, betalain contents, FRAP and alpha-amylase inhibition activity. DPPH and ABTS of the gels increased significantly (p < 0.05) after digestion. Compared with oligo-carrageenan, TPC, TFC, betalain content, DPPH, ABTS, FRAP and alpha-amylase inhibition activity were retained better in carrageenan after digestion, except nitrate content. The nitrate content of beetroot juice was better retained in oligo-carrageenan. Although beetroot juice and all gels showed alpha-amylase inhibition activity, the activity was lost to below 20% after digestion. This study proved that additional beetroot in carrageenan gels effectively improved the antioxidant activity of carrageenan and oligo-carrageenan gels. The nitrate content of beetroot juice can be protected against digestive loss in the oligo-carrageenan matrix. A future study is proposed to prepare beetroot juice concentrate for incorporation into carrageenan and oligo-carrageenan gels to further enhance the bioactivity of the gels.