The effects of Curcuma longa L. leaf extracts on the prevention of oxidation in soybean oil

Abstract

Background. The use of natural plant antioxidants has been an alternative approach to synthetic antioxidants for food applications. This study investigated the antioxidant properties of the leaves of Curcuma longa L. against the oxidation of soybean oil using leaf extracts obtained from seven different types of organic solvents and compared to the action of efficient synthetic antioxidants which are widely used and low cost but with toxicity risk. The application of natural alternatives from sources still little studied is a proposal and the extraction of compounds with high antioxidant capacity may vary according to the type of solvent, its mixture, its polarity and other factors that burden or harm the health of the consumer. Materials and methods. The leaf extracts were sanitized, dried, and obtained for solvent selection. The quantification of total phenolic compounds (TPC) and antioxidants was performed by using different combinations and proportions of solvents: water (100%), ethanol (100%), methanol (100%), ethanol/water (70%:30%), methanol/water (70%:30%), methanol/acetic acid (99.5%:0.5%), and acetone/water/acetic acid (70%:28:2%). The solvent selected was the one that extracted the highest content of phenolic and antioxidant compounds (using the free radical DPPH scavenging method and FRAP assay). It used an accelerated storage test and experimental design to assess oxidative stability (using peroxide index (PI), thiobarbituric acid reactive substances (TBARS), dienes (DC) and triple conjugates (TC) and statistical analysis). Results. The ethanol/water solvent was efficient in the extraction of TPC (2422 mg GAE 100 g -1 ). The mixture of solvents extracted an average of 23.65% more TPC when compared to the single solvents. Regarding the antioxidant capacity, the ethanol/water solvent showed 1847 mg TE 100 g -1 using the DPPH and 217 µmol of FeSO 4 100 g -1 using the FRAP assays. In addition, the oxidation of soybean oil was delayed by the accelerated storage test showing equivalent results to BHT at 0.02% for the values of PI, TBARS and DC/TC. Conclusion.The E/W extract showed the highest yield in the extraction of phenolic compounds and is a safe solvent for food. The addition of Curcuma longa L. leaf extract to soybean oil caused reductions in PI, TBARS, CD and CT values. The leaf extract of C. longa L. is considered to be a good alternative to synthetic antioxidants against the oxidative degradation of soybean oil.

Headspace GC/MS for identification of bioactive compounds of Curcuma longa L. leaf extract: Industrial application as antioxidant for soybean oil

“…In this study, 1.5% C. longa L. leaf extract showed higher inhibitory activity than synthetic antioxidant BHT in preserving soybean oil, which was inferred from the decrease in the TBARS and peroxide index values. Alves et al (2021) reported that the TBARS values in soybean oil with 1.5% extract at 70 °C were lower than that in soybean oil with synthetic antioxidant BHT throughout the study period. The lower TBARS values in the 1.50% extract were also shown by the results obtained in this study.…”