Low intensity pulsed electric fields as an alternative to scalding in the curing of Vanilla planifolia beans

Abstract

Vanilla bean curing remains a highly manual and traditional procedure that requires long periods of time and reduces the level of activity of endogenous enzymes related to the production of vanillin and other aromatic compounds due to heat application in the killing step. Pulsed electric fields (PEF) are a non-thermal technology that acts by generating pores in the membrane and cell wall, and it has also been observed that it can modify enzyme activity and increase the content of metabolites such as phenolic compounds. PEF could be an alternative to high-temperature blanching during vanilla curing to improve vanillin content and accelerate the curing process. This work evaluated the effect of low field strength PEF (~1.2 kV/cm, 100 Hz) at different energy density inputs (kJ/kg) as a killing method for curing. Its effect was compared against blanched (control) pods on moisture loss rate, phenolic compounds content and the activity of β-D-glucosidase (BGLU) and phenylalanine ammonia lyase (PAL) enzymes during specific sweating/drying cycles. PEF (100P and 250P) reached a maximum vanillin content at cycle 5, exceeding scalded pods by 60%. They also hydrolyze glucovanillin a 54% (k=0.463 day-1) and 26% ( k=0.376 day-1) faster than blanching. PEF condition 750P can reduce drying time by 6.2%. BGLU activity was reduced <95% after blanching, whereas using PEF preserved or even increased activity by 24% and 11% (20P and 100P). PEF (100P) increased PAL activity (200%) at cycle 0 and maintained residual activity until cycle 3 (2%). PEF (4.5-32.7 kJ/kg) better preserves enzyme activity increases vanillin accumulation, and can reduce drying time; thus, accelerating the beneficiation process or increasing vanillin yield.