Pulse electric fields and ultrasound technologies for extracting phenolic compounds from avocado by-products

Avocado (Persea americana Mill) is a tropical fruit wide consumed which production was 8.69 million metric tons of avocado in 2021. After food processing, around 40% of the whole fruit is discarded as by-products (peels and seeds). These by-products are a source of phenolic compounds, specially procyanidins. Thus, this study focuses on optimizing the conditions for pulsed electric field (PEF) technology as a pretreatment to obtain extracts rich in phenolic compounds from the avocado peel and seed. Two Box-Behnken designs of 15 experiments with three levels (-1, 0, 1) were carried out. The independent factors in the case of avocado peel were frequency (1, 50, 100 Hz), voltage (1500, 2250, 3000 V) and number of pulses (100, 150, 200), and for the avocado seed frequency (50, 100, 150 Hz), total operating time (1, 5, 10 s) and electric field (0.6, 0.7, 0.8 kV/cm), established based on preliminary experiments. The dependent variable in both models was the procyanidins content in the extracts obtained by ultrasound technology via sonotrode and analyzed by HPLC-FLD. The models were confirmed and validated by ANOVA. The optimized parameters chosen for the avocado peel model included a frequency of 50 Hz, 2625 V, and 175 pulses, resulting in a desirability value of 0.9468. This configuration predicted a procyanidin content of 9845.41 ± 222.60 µg CE/g d.w. On the other hand, for the avocado seed model, the selected conditions involved a frequency of 100 Hz, a field strength of 0.75 kV/cm, and a total operating time of 5.5 s, yielding a 163 desirability value of 1 and a predicted procyanidin content of 20955.06 ± 452.35 µg/g d.w. They were achieved significant (p < 0.05) increases of 9.5 and 31.5% in the procyanidin content in avocado seed and peel, respectively, compared to only using ultrasound extraction. The combination of optimized PEF pretreatment with ultrasound extraction has to obtain avocado byproducts enriched extracts in procyanidins that could be used for food, nutraceutical, and cosmeceutical scopes.