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Influence of experimental conditions on the yield of phenols and flavonoids obtained from tomato peel waste by microwave-assisted extraction

Industrial processing of tomatoes generates a considerable amount of waste, such as peels and seeds. These residues are an environmental problem, so their reuse would bring several benefits. They are used to extract pectin, polyphenols and fatty acids, which are a valuable source of additives, natural antioxidants and edible oils, respectively. To maximize the extraction of polyphenols from tomato waste, different extraction techniques and operating conditions can be used. One of the innovative techniques is microwave-assisted extraction (MAE), which allows higher extraction efficiency in less time and at lower temperature. In this work, MAE was applied as an environmentally friendly technique for the extraction of total phenols (TP) and flavonoids (TF) from tomato peels with respect to the solvents used, i.e., water and aqueous solution of HCl (1%, v/v), methanol (50 and 70%, v/v), with or without addition of 1% HCl and ethanol (50 and 70%, v/v), temperatures (25, 55, and 90 °C), and times (5 and 10 min). The results showed that all samples contained high mass fractions of TP (53.12 g/kg) and TF (50.36 g/kg), which varied as a function of extraction time, temperature, and solvent. Increasing the temperature significantly improved the solubility of TP and TF, and the highest value was obtained for samples extracted at 55 and 90 °C. In contrast to the effects of temperature, increasing the extraction time from 5 to 10 min did not significantly affect the recovery of TP (p = 0.333826) and TF (p = 0.519694). As for the solvents used in MAE, the addition of HCl to 50 and 70% methanol had no significant effect (p > 0.05) on the amounts of TP and TF. Better extraction of flavonoids was ensured with 70% methanol and ethanol, especially at higher temperatures. However, better extraction of TP was obtained with 50% methanol and ethanol. In conclusion, tomato peel waste contains remarkable amounts of phenols and flavonoids. Of the parameters evaluated, temperature had the greatest effect on their extraction. However, the yield of TP and TF also depended on the choice of the appropriate solvent and its combination with the extraction temperature.

tomato peel waste ; microwave-assisted extraction ; phenols ; flavonoids

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