Traditional methods for the extraction of essential oils are often inefficient, resulting in lower yield and quality. Therefore it is a need to achieve the best extraction parameters for highest yield of essential oils while enhancing the quality. Superheated steam extraction is emerging as a promising technique to improve both yield and quality, particularly for citrus peels like those of Citrus limetta, which have significant applications in the food and cosmetic industries. Citrus peel, accounting for approximately 40–50 % of the fruit's weight, is a substantial byproduct of the citrus processing industry, particularly during juicing and packing. This waste is a valuable source of bioactive substances such as carotenoids, ascorbic acids, phenolic compounds, and essential oil (EO). The treatment of citrus peel is a big issue for the citrus processing industry, as the majority of citrus peel waste is currently being buried or burned, causing environmental pollution. Citrus peel is a useful source of EO production (with up to 0.5-3 kg/ton of citrus fruits currently being processed)(Shan, 2016; Singh et al., 2021). Extracting essential oils from citrus peel is more beneficial than the fruit because it is less labor-intensive, more cost-effective, and better for the environment. Citrus peel EO (CPEO) is used as a cough suppressant, enhances the secretion of digestive juices and gastrointestinal motility, reduces inflammation, and dissolves gallstones. Moreover, CPEOs are a great source of fragrance for perfumes and flavoring for the food industry (Bustamante et al., 2016; Nair et al., 2018).

EOs from citrus fruit mainly comprise terpenes, oxygenated terpenes and low concentrations of various volatile components. Citrus EO (CEO) contains up to 90 % monoterpenes, 5 % oxygenated monoterpenes, and around 1 % nonvolatile components. The main bioactive monoterpene is limonene (around 90 % of the total composition). While oxygenated monoterpenes were also present in lower amounts. Limonene in citrus EO is known to have antifungal properties (Colecio-Juárez et al., 2012).

EOs contain compounds with antioxidant and antimicrobial activity, making them valuable to pharmaceuticals, food, agriculture, cosmetics, and healthcare industries (Bolouri et al., 2022). As public awareness of the health impacts of different food components grows, food safety has emerged as a top priority for both public health and the food industry. Natural and organic ingredients have gained popularity over inorganic ones in the food industry because of their health benefits, fewer side effects, and environmental sustainability. For example, antifungal agents produced from plants have replaced artificial preservatives to improve food safety and quality (Velázquez-Nuñez et al., 2013). CEOs have become increasingly popular among plant essential oils (EOs) due to their broad-spectrum insecticidal, antifungal, and antibacterial properties, as well as their high yields, appealing fragrances, and flavours (Chanthaphon et al., 2008; Souza et al., 2005). CEOs play a significant role in ensuring food quality and safety through their involvement in the preparation, packaging, and preservation of food products (Calo et al., 2015).

Citrus limetta, commonly known as sweet lime, is an aromatic plant belonging to the citrus genus, species limetta and botanical family Rutaceae (Nicolosi, 2007). The citrus genus consists of trees, herbs and shrubs of different sizes. Citrus fruits belong to six different genera, which are Eremocitrus, Fortunella, Clymendia, Microcitrus, Poncirus, and Citrus, encompassing several species within each. These plants are found in tropic and sub-tropic regions of Asia and Pakistan. The Citrus genus includes ten species, one of which is the sweet lime, or Citrus limetta, primarily found in Pakistan. Known for its cooling and therapeutic properties, Citrus limetta juice is commonly used to treat jaundice, malaria, and fever (Cowan, 1999). Citrus species also have applications in cosmetics and aromatherapy. Essential oils extracted from citrus fruits are utilized by the pharmaceutical industry and also hold nutritional importance. Essential oils from sweet lime are valued for their antioxidant, anti-inflammatory, antifungal, antibacterial, anti-infection, and allelopathic properties (Derwich et al., 2010). Citrus EOs are primarily used in perfumery and the food industry, and they also exhibit anticancer and antioxidant properties (Norajit et al., 2007). The demand for plant essential oils is growing due to their rising popularity among consumers, recognized safety, and versatile applications across various fields (Javed et al., 2013).

Hydro-distillation (HD) and steam distillation (SD) are the most commonly used extraction methods for extracting EOs. The first plant extracted through HD was rose. The Clevenger apparatus is mostly used for HD. Plant material is placed in water, thus allowing great interaction of plant material with the boiling water, leading to better extraction. Hydrodistillation typically extracts essential oils at temperatures close to, but not exceeding, 100 °C, generally around 95 to 98 °C, depending on altitude and atmospheric pressure. This temperature range is crucial as it allows for efficient extraction while minimizing the degradation of thermolabile compounds (El Asbahani et al., 2015). However, improvements have been made to conventional HD techniques to improve both the quality and yield of the EO. Microwave-assisted hydro distillation (MAHD) and ohmic-assisted hydro distillation (OAHD) are more advanced forms of HD, achieving higher yields of EO. Moreover, the extraction time required for these innovative techniques is less (Gavahian et al., 2012). Steam distillation is the most frequently used method for EO extraction. The yield of EO is determined by the amount of steam that contacts the plant material. Using this method, the production of EO can be increased while reducing water waste (Masango, 2005). Moreover, EO extracted by SD possess higher antioxidant activity than EOs extracted via HD (Babu & Kaul, 2005). Steam distillation (SD) typically operates at higher temperatures and uses steam, which facilitates rapid rupture of oil glands and more efficient release of intracellular compounds such as limonene oxide, trans-carveol, carvone oxide, and limonene key contributors to antioxidant activity due to their free radical scavenging potential (Bakkali et al., 2008). Furthermore, SD minimizes prolonged contact of plant material with boiling water, reducing the likelihood of thermal degradation or transformation of heat-sensitive antioxidant compounds. In contrast, hydro distillation (HD) involves direct boiling of the plant material in water, which can lead to degradation of some bioactive constituents due to extended thermal exposure (El Kharraf et al., 2021; Vahidi et al., 2019). Traditional extraction methods, such as hydrodistillation, often involve prolonged extraction times, high energy input, and may lead to loss or transformation of sensitive volatile compounds. Consequently, novel approaches have been introduced to enhance both the yield and the quality of essential oils. (El Asbahani et al., 2015). SHSE is a novel technique for the extraction of EOs from plant material. In SHSE, steam is produced at a higher temperature than used for normal steam extraction. Superheated steam ruptures the oil glands, resulting in quicker evaporation (Ayub, Choobkar, et al., 2023). The temperatures used in SHSE depend on the pressure and type of container used. Reports indicate that the lower polarity, higher dielectric constant, lower viscosity, and higher thermal conductivity of superheated steam contribute to improved yields of essential oils (Ayub, Goksen, et al., 2023). The temperature of superheated steam greatly affects the solvation capacity of steam, thus affecting the EO yield obtained. Some other factors, including flow rate and extraction time along with temperature, influence the extraction process and EO yield (Plaza & Turner, 2015).

The response surface methodology (RSM) of extraction is an empirical modeling approach that employs a collection of mathematical and statistical techniques to evaluate the effects of variables on an outcome. Response surface methodology offers a graphical representation of how factors influence the response. The model's significance is determined through variance analysis (ANOVA). The regression model compares predicted results with experimental values to calculate their accuracy (Eikani et al., 2013).

The literature study has shown that hydro-distillation and steam distillation have been employed to extract EO from the Citrus limetta peel. However, the optimization of experimental conditions for optimum extraction of EO from Citrus limetta peel by SHSE has not yet been reported. To address this, the current study applied RSM with a central composite design to optimize extraction conditions, including temperature, flow rate, and extraction time, to maximize the yield of Citrus limetta essential oil (CLEO). Additionally, GC–MS was employed for the qualitative and quantitative analysis of the chemical constituents present in the CLEO.