Effect of Organic Acids on the Viscosity and Rheological Properties of Basil Seed Mucilage

Background and objectives: Organic acids in foods are exist naturally or added for specific purposes such as reducing pH, chelating metals, increasing antioxidant activity, reducing microorganism activity, and extending shelf life, or they are produced by microorganisms. Mucilages are used as thickening agents, gelling agents, and stabilizers to increase the viscosity and improving the textural and rheological properties of food products. The aim of this research was to investigate the effect of the addition of different organic acids on the viscosity changes of aqueous solution containing basil seed mucilage.
Materials and methods: In this study the effect of four edible organic acids include ascorbic acid, citric acid, malic acid, and tartaric acid, at two concentrations of 0.5, and 1 % (w/v), on the viscosity and rheological behavior of Basil seed mucilage solution was investigated. The Basil seed mucilage solutions were provided by solving the mucilage powder (0.2%, w/v) in distilled water and different concentrations of organic acids using a magnetic stirrer. The rheological parameters of Basil seed mucilage solutions were measured using a viscometer (Brookfield, USA) at 20°C. The shear rate/shear stress data were also fitted using Power law, Bingham, Herschel-Bulkley, and Casson models.
Results: The finding of this study showed that the apparent viscosity of Basil seed mucilage solution reduced when the shear rate increased. Additionally, the apparent viscosity of the Basil seed mucilage solution reduced as the organic acids concentration increased. The highest decrease in viscosity was related to solution containing 1% malic acid and the lowest was related to ascorbic acid with a concentration of 0.5%. The Power law model was the best one for describing the behavior of Basil seed mucilage solutions containing organic acids. The Power law model had a good performance with the highest correlation coefficient (>0.9082) and least sum of squared error (<0.4782) and root mean square error (<0.1996) for all samples. The consistency coefficient of the mucilage solution reduced as the acid concentration was increased. The samples containing 1% malic acid had the lowest consistency coefficient and the samples containing 0.5% citric acid had the highest consistency coefficient. By adding acid to the mucilage solution and reducing its pH, the amount of yield stress of the Bingham and Casson models was decreased. The Casson plastic viscosity value for the control solution prepared from Basil seed mucilage was equal to 0.058 Pa.s. The sample containing 0.5% ascorbic acid had the highest (0.050 Pa.s) and the sample containing 1% tartaric acid had the lowest (0.032 Pa.s) plastic viscosity value.
Conclusion:
By adding acid to the mucilage solution and as a result reducing the pH, the flow behavior index of the samples (Power law and Herschel-Bakli models) increased (reduction in pseudoplastic behavior). Based on the findings of this research, the use of Basil seed mucilage in food products containing high concentration of malic acid is not recommended, and this acid causes a great reduction in the viscosity and consistency of products containing this mucilage.