Modern Extraction and Purification Techniques for Obtaining High Purity Food-Grade Bioactive Compounds and Value-Added Co-Products from Citrus Wastes

Abstract

Citrus contains a range of highly beneficial bioactive compounds, such as polyphenols, carotenoids, and vitamins that show antimicrobial and antioxidant properties and help in building the body's immune system. On consumption or processing, approximately 50% of the fruit remains as inedible waste, which includes peels, seeds, pulp, and segment residues. This waste still consists of substantial quantities of bioactive compounds that cause environmental pollution and are harmful to the ecosystem because of their high biological oxygen demand. In recent years, citrus cultivation and the production of processed foods have become a major agricultural industry. In addition to being a substantial source of economy, it is an ideal and sustainable and renewable resource for obtaining bioactive compounds and co-products for food and pharmaceutical industries. In the present article, the various methods of extraction, conventional and modern, as well as separation and isolation of individual bioactive compounds from the extraction mixture and their determination have been reviewed. This article presents both aspects of extraction methods, i.e., on a small laboratory scale and on an industrial mass scale. These methods and techniques have been extensively and critically reviewed with anticipated future perspectives towards the maximum utilization of the citrus waste.

Keywords: citric acid; citrus byproducts; citrus waste; environment friendly extraction; essential oils; flavonoids; limonene; phenolics; phytochemical extraction and purification; waste management.

Figure 1

Climate sustainability and the annual production of citrus fruits in different geographical regions across the globe [3,4,15].

Figure 2

The main citrus varieties and its physical composition in terms of edible juice and inedible waste part, which consists of peel (flavedo and albedo), rags (pith, pulp residue, and segment membrane), and seeds [10,13,21].

Figure 3

(a) The composition of typical citrus waste (peel and rag); (b) the composition of dried citrus pulp [9,22,23,24,25,26,27].

Figure 4

Schematic diagram illustrating the risks and potential threat of damage to soil and aquatic ecosystems and the overall environment by the disposal of untreated citrus wastes.

Figure 5

The steps involved in the extraction, separation, isolation, and purification of important compounds from citrus waste and techniques employed for determination and structural elucidation.

Figure 6

Effect of the nature of solvents on the yield of total phenolics by the solvent extraction process [58].

Figure 7

Classification of citrus polyphenols [11].

Figure 8

(a) Extraction of pigments in different solvents, (b) pigment composition, and (c) stability of the extracted pigments at different pH [122].

Figure 9

Stages of typical citrus waste processing to generate molasses [22].

Figure 10

(a) Composition of citrus molasses; (b) mineral composition of citrus molasses [9,22,23,24,25,26,27].

Figure 11

Steps involved in the different extraction methods for obtaining pectin from citrus waste [65,155,156]

Figure 12

Byproducts obtained from citrus waste processing are utilized in manufacturing various types of commercial products. The photographs were collected from a local supermarket and have been used for academic purposes only and not for any advertising purposes.