Experimental Characterization of the Drying of Kampot Red Pepper (Piper nigrum L.)

Abstract

The objective of this work is to provide new insights into the mechanisms taking place during the drying of the mature grains of Kampot pepper, a cultivar of pepper (Piper nigrum L.), which is produced in the Kampot Province, Cambodia. Indeed, even if the Kampot pepper is recognized for its organoleptic qualities, no research works were dedicated to the drying of its mature grains, in order to yield red pepper. Experiments with different pretreatment and drying conditions were performed. The results of these experiments were analyzed, regarding the drying kinetics, the color of the dry product, and the degradation of the bioactive compounds during the drying. Regarding these bioactive compounds, several parameters were considered: the total phenolic content, the total flavonoid content, and the piperine content. The results show that the Kampot mature pepper is prone to alterations when dried at a temperature of 55∘C or 65∘C: the color, the total phenolic content, and the flavonoid content are significantly altered, while the piperine content, important for the pungency of this spice, seems unaltered. Raising the temperature leads to more important degradations. However, performing a pretreatment by dipping the pepper grains into boiling water appears to significantly reduce these alterations and, concomitantly, to accelerate the drying. As a conclusion of the analysis of the results, it can be stated that, to increase the product quality, it is recommended to pretreat the pepper by dipping it into boiling water during 5 min., before drying at 55∘C.

Keywords: Piper nigrum L.; boiling pretreatment; drying; kampot pepper; piperine; total phenolic content.

Figure A1

HPLC-UV chromatogram of the piperine standard.

Figure A2

HPLC-UV chromatogram of an extract from the fresh mature pepper.

Figure A3

HPLC-UV chromatogram of an extract from dry red pepper.

Figure A4

Ratio of the piperine content of dry grains to the piperine content of fresh grains, as a function of the boiling time, for two drying temperatures: $55{}^{°}$C and $65{}^{°}$C. The error bars are standard deviations.

Figure A5

Ratios of the TPC and TFC of dry grains to the TPC and TFC of fresh grains, as functions of the boiling time, for two drying temperatures: $55{}^{°}$C and $65{}^{°}$C. The error bars are standard deviations.

Figure 1

Left: pepper grains showing different level of maturity. Right: harvested mature pepper grains. Pictures taken by the authors.

Figure 2

Time evolution of the moisture content of the grains during their drying, at $55{}^{°}$C (black symbols) and $65{}^{°}$C (gray symbols), and for various boiling times. The error bars are the standard deviations.

Figure 3

Kinetic constant of the drying k as a function of the boiling time (0 = no boiling), for the two drying temperatures: $55{}^{°}$C (black symbols) and $65{}^{°}$C (gray symbols). The error bars are the standard deviations.

Figure 4

Ratios of the values of the parameters $L^{*}$, $a^{*}$ and $b^{*}$ for the grains after drying to the values of these parameters for the fresh grains (i.e., unboiled and undried), $L_0^{*}$, $a_0^{*}$ and $b_0^{*}$, as functions of the boiling time and for the two drying temperatures: $55{}^{°}$C and $65{}^{°}$C. The error bars are the standard deviations.

Figure 5

$\Delta E$ as a function of the boiling time, for the two drying temperatures: $55{}^{°}$C (black symbols) and $65{}^{°}$C (gray symbols). The error bars are standard deviations.