Development of an ultrasound-assisted pre-treatment strategy for the extraction of d-Limonene toward the production of bioethanol from citrus peel waste (CPW)

Abstract

Citrus is one of the world’s most abundant fruits containing vitamins, pigments, and fragrances, making it vital for several industries. However, these fruits contain about 45–50% residues (peels), which often end up as waste and can be harmful to the environment if not properly treated. Bioethanol production from citrus peel waste offers a potential solution to this problem. Hence, this study explores the potential of using ultrasound-assisted pre-treatment method as a novel strategy to extract d-Limonene (essential oil in the residue), and further demonstrates bioethanol production. This was done by investigating ultrasonication’s optimal effect on pre-treatment of the citrus residue, followed by bioethanol production. The results show that, optimum values for d-Limonene extraction were obtained at a temperature of 14.6 °C and an ultrasound intensity of 25.81 W/cm2 with a validation yield of 134 ± 4.24 mg/100 g dry CPW. With optimal ultrasonic parameters, the study went further to demonstrate the effect of the essential oil on bioethanol production which is hindered by the oils present. Key findings show better bioethanol yield once the essential oil was extracted (treated) from the citrus waste as opposed to it not extracted (untreated), with a 66 and a 29% increase when comparing simultaneous saccharification and fermentation (SSF) and sequential hydrolysis and fermentation (SHF) respectively. Based on this result, ultrasound-assisted extraction as a pretreatment method was found suitable for bioethanol production from citrus residue and could be utilized as a biorefinery pre-treatment approach to scale bioethanol production.

Techno-economic evaluation of soap production from waste cooking oil with additives derived from citrus peel waste.

“…The issues of CPW waste management by disposal are further exuberated by the presence of essential oils, more speci cally limonene which limits biodegradability due to its anti-microbial properties. Therefore, extraction and utilization of limonene not only offer advantages in enhancing soap quality but also aid in the reduction of CPW waste management issues [14].…”

“…Adding D-Limonene could help to enhance the cleansing power and the consumer appeal of the soaps. Nevertheless, the presence of D-Limonene makes the CPW di cult to compost and unsuitable for animal feed or fermentation processes [13,14], as its high acidic content is challenging for biodegradation and fermentation, further exacerbating issues surrounding food waste management [13]. Therefore, extracting D-Limonene from CPW could offer a dual solution, both adding value to soap production technology and mitigating issues in food waste management.…”

Recent advances in the implementation of ultrasound technology for the extraction of essential oils from terrestrial plant materials: A comprehensive review

“…However, two primary physical phenomena commonly observed in the extraction process of EOs are diffusion in cell membranes and walls and cell wall destruction through the cavitation process. It leads to the rinsing of cell contents, resulting in increased mass transfer and enhancing the overall extraction process [63] , [79] , [80] , as shown in Fig. 4 .…”

“… [4] UAP Citrus clementina peel US intensity varied between 1.62 and 49.92 W/cm 2 , time = 60 min and temp = 14.6–––85.4 °C The maximum extraction yield of EOs was 134 mg/100 g at 14.6 °C with 25.81 W/cm 2 US intensity. [79] UAP Tribute citrus peels Time = 0–120 min, frequency = 455 kHz, and sodium chloride concentration 0–3.0 %, solvent to solid ratio was 10:1–24:1. The highest extraction yield of 115.072 mg/g of EOs was obtained through the UAP at 40 min time.…”

“…The primary objective is to prepare the material for more effective extraction during the subsequent steps [10] , [45] . In a study by Teke et al [79] the authors explored the effectiveness of UAP in obtaining EOs from citrus peel. Under extraction conditions with a temperature of 14.6 °C and ultrasound intensity of 25.81 W/cm 2 , a yield of approximately 134 mg/100 g of EOs was obtained.…”