چكيده لاتين
In this study, an integrated biorefinery approach was developed to valorize lemon waste and assess its potential for the simultaneous production of high-value compounds, including pectin, limonene, fermentable sugars, and xanthan gum. Lemon residues were first subjected to basic preparation steps and then pretreated using dilute sulfuric acid (1% w/v) at four temperatures (100, 120, 140, and 160 °C) and three residence times (15, 30, and 60 min). The effects of temperature, reaction time, and prior Soxhlet extraction on the lignocellulosic structure and extractable components were thoroughly evaluated. Results indicated that increasing temperature reduced the recovered solid fraction, accelerated hemicellulose degradation, and enriched glucan content in the solid phase. At 160 °C for 60 minutes, the lowest xylan and the highest glucan percentages were obtained. Performing Soxhlet extraction before pretreatment effectively removed lipidic and phenolic compounds, thereby improving glucan accessibility and enhancing the processability of the biomass.
The highest pectin extraction yield was achieved under mild conditions 100 °C for 60 minutes in the Soxhlet-treated sample—reaching 18.13%. In contrast, higher temperatures (140 and 160 °C) caused severe reductions in pectin yield due to depolymerization and thermal degradation. Limonene extraction results showed that Soxhlet extraction with n-hexane enabled more selective recovery of limonene due to its nonpolar nature, yielding the highest limonene concentration (7.54 g/L). Although Soxhlet extraction with ethanol produced lower limonene concentrations, it resulted in a higher overall extraction yield because of its deeper penetration into the biomass. Total phenolic content increased consistently with temperature and residence time, with non-Soxhlet samples releasing significantly higher phenolic levels.
The hydrolysate obtained from pretreatment was used as the carbon source for fermentation by Xanthomonas campestris ATCC 33913. The highest xanthan gum production was observed under the pretreatment condition of 140 °C and 30 minutes (Soxhlet-treated sample), yielding 8.99 g/L, which is comparable to yields obtained from pure glucose media. Antimicrobial assays demonstrated that extracted limonene exhibited inhibitory effects against X. campestris in a concentration-dependent manner, emphasizing the importance of limonene removal or control in fermentation processes.
Overall, the findings of this study demonstrate that lemon waste, as an abundant and low-cost biomass, holds considerable potential for the simultaneous production of valuable bioproducts such as pectin, limonene, and xanthan gum.
