Citation: Sadiq, U.; Gill, H.; Chandrapala, J. Ultrasound-Assisted Encapsulation of Anthraquinones Extracted from Aloe-Vera Plant into Casein Micelles. Gels 2022, 8, 597. https://doi.org/10.3390/ gels8090597 Academic Editor: Xiufang Xia Received: 14 August 2022 Accepted: 13 September 2022 Published: 17 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). gels Article Ultrasound-Assisted Encapsulation of Anthraquinones Extracted from Aloe-Vera Plant into Casein Micelles Uzma Sadiq * , Harsharn Gill and Jayani Chandrapala School of Science, RMIT University, Bundoora, Melbourne, VIC 3083, Australia * Correspondence: uzma.sadiq@student.rmit.edu.au Abstract: Aloe-vera extracted anthraquinones (aloin, aloe-emodin, rhein) possess a wide range of biological activities, have poor solubility and are sensitive to processing conditions. This work investigated the ultrasound-assisted encapsulation of these extracted anthraquinones (AQ) into casein micelles (CM). The particle size and zeta potential of casein micelles loaded with aloin (CMA), aloe-emodin (CMAE), rhein (CMR) and anthraquinone powder (CMAQ) ranged between 171–179 nm and −23 to −17 mV. The AQ powder had the maximum encapsulation efficiency (EE%) (aloin 99%, aloe-emodin 98% and rhein 100%) and encapsulation yield, while the whole leaf Aloe vera gel (WLAG) had the least encapsulation efficiency. Spray-dried powder (SDP) and freeze-dried powder (FDP) of Aloe vera showed a significant increase in size and zeta potential related to superficial coating instead of encapsulation. The significant variability in size, zeta potential and EE% were related to anthraquinone type, its binding affinity, and its ratio to CM. FTIR spectra confirmed that the structure of the casein micelle remained unchanged with the binding of anthraquinones except in casein micelles loaded with whole-leaf aloe vera gel (CMWLAG), where the structure was deformed. Based on our findings, Aloe vera extracted anthraquinones powder (AQ) possessed the best encapsulation efficiency within casein micelles without affecting its structure. Overall, this study provides new insights into developing new product formulations through better utilization of exceptional properties of casein micelles. Keywords: casein micelles; ultrasonication; nanoencapsulation; Aloe vera extracted anthraquinones; spray dried powder; freeze-dried powder; aloin; aloe-emodin; rhein 1. Introduction Identification and extraction of biologically active components from plants have led to the discovery of a range of nutraceuticals, pharmaceuticals and functional foods for health improvement [1]. There are a total of 21,000 plants used for medicinal purposes through- out the world, out of which <200 have been used commercially by biopharmaceutical companies [2]. Aloe vera is a magical plant in Ayurveda that contains plenty of secondary metabolites [3]. Secondary metabolites of Aloe vera are the anthraquinones, including aloin, aloe-emodin and rhein, that are tricyclic aromatic quinones produced through a plant-specific type III polyketide biosynthesis pathway [4]. These anthraquinones possess a wide range of biological and pharmacological activities. These include laxatives [5], anti- cancer [6–9], antibacterial [10,11], anti-inflammation, homeostatic and antispasmodic [12]. Although Aloe vera has been used in many food systems such as ready-to-serve drinks, soft drinks, yoghurt, sports drinks, laxative drinks, whisky and white bread [13] for decades, the available information concerning the effect of food processing on the degradation of anthraquinones during preparation is limited. In our previous study, it was reported that the degradation of these anthraquinones starts right after harvesting the Aloe vera leaves and continues to decompose during pro- cessing and storage [14]. So, encapsulating these anthraquinones seems to be an efficient method for food formulators while developing traditional medicines, functional foods, Gels 2022, 8, 597. https://doi.org/10.3390/gels8090597 https://www.mdpi.com/journal/gels