Microorganisms have been utilized by humans from the ancient time to create various types of flavour for use in foods and drinks. A particular microbiota associated with beer, yoghurt, cheese, sourdough, fruits, etc have been found to be responsible for pleasant flavour generation through fermentation of free fatty acid or other raw materials (Try et al., 2018). To fulfil the demands of the industry, majority of the flavour molecules are produced through chemical synthesis route (Krzyczkowska et al., 2017). However, the chemical synthesis process frequently leads to non-sustainable manufacturing methods and generation of unwanted racemic mixture with low sensory profiles. Additionally, the consumers have developed a "Chemonoia"-attitude towards chemical or synthetic compounds, particularly in regard to food and cosmoceutical applications (Vandamne, 2003). To address the issue, the demand for bioflavors with microbial or biological origin with acceptable sensory value is increasing day by day in food, cosmetics, chemicals, and pharmaceutical industries. The flavour market is predicted to rise from its current value of $15.85 billion in 2020 to $20.27 billion in 2027, escalating at a compound annual growth rate of 4.5% (Alvarez et al., 2022). Certain plant and animal sources continue to be a major source of bioflavours, despite the fact that the bio-active substances they contain are either present only in rare or exotic (plant) species. Further the extraction, isolation, and formulation are prohibitively expensive. Therefore, in order to produce the desired enantiospecific natural flavour compound sustainable and economically viable alternatives are required.

The production of nature-identical molecule is possible by using selected original microbial strains. The microbial bioprocess can produce enantiospecific flavour molecules either de-novo or by converting an additional substrate/precursor compound. The process parameters were optimized for optimal production of the desire and valuable enantiospecific flavour molecules (Kothari et al., 2022). Although, the biochemical pathways involved have been identified in few cases, there is still more to be done in this area. Similarly, many enzymes and their bioconversion pathway mechanism have been established for flavour production (Mikami, 1988). γ-Decalactone (GDL), a peach like flavoured compound is synthesized by microorganisms through its peroxisomal β-oxidation of unsaturated fatty acid i.e., ricinoleic acid (RA). RA is a major component of Castor oil, and it is biotransformed to GDL through 4-steps β-oxidation mechanism followed by lactonization (Braga and Belo, 2015). The graphic description of β-oxidation pathway has been given in Scheme S1 (Supplementary file).

The reaction parameters such as titer, rate, and yield are useful economic metrics in microbial processes. The downstream process associated with running as well as maintenance costs are used to evaluate complex fermentation methods (Singh et al., 2023). Table S1 (supplementary file) lists the yields of GDL production utilising Y. lipolytica and other yeast strains by various researchers at different biotransformation conditions.

Earlier optimization trails were conducted by various researchers such as Gomes et al. (2011a), Warke (2016) and Kothari et al. (2022). Researchers have found that numerous variables affect the yield while studying the parameters of GDL biosynthesis. Major variables such as temperature, pH, media composition, substrate percentage, oxygen concentration and incubation time have substantial impact, along with the nature of the microbial strains (Moradi et al., 2016, Guerreiro et al., 2017). Presence of surfactant, oxidation-reduction potential medium, and biotransformation technology (fed-batch cultures with steps, immobilisation of cells) also played a role in achieving higher lactone production (Braga and Belo, 2015; Darvishi et al., 2021).

In order to choose the optimal condition for maximum product yield, there were only few studies reported (Gomes et al., 2011). Taguchi robust design was used in very few literatures to attempt optimization of GDL production from castor oil biotransformation using yeast strains (Moradi et al., 2016, Małajowicz et al., 2022). On the basis of orthogonal array design, the researchers were able to evaluate how numerous parameters affected the efficiency of a laboratory-scale biotransformation process in shaking flask with a limited number of experiments (Małajowicz et al., 2022, Rahul and Pretesh, 2018). The screening of various microbes isolated from different fruit sources is a crucial step forward in the hunt for novel strains to synthesise valuable compounds. Since it increases the biotechnological efficiency and reduces the detrimental impacts of traditional synthesis on the environment. The current research aimed to examine the isolation, screening and identification of microorganisms involved in the production of GDL from RA through biotransformation method. The best identified microbes were further optimized in different culture conditions to gain higher yield of GDL employing the statistical Taguchi design method. The novelty of the current study is that the isolation of microbes from fruits and novel strains were selected for the production of GDL from RA through biotransformation. Further, the process is optimized using Taguchi model.