A Preliminary Study on the Effect of the Instant Controlled Pressure Drop Technology (DIC) on Drying and Rehydration Kinetics of Maize Kernels (Zea mays L.)

Abstract

Maize is one of the three worldwide cereal crops with the most outstanding production; however, its postharvest losses range from 2 to 40% due to inadequate harvesting, drying, and storage technologies. This study focuses on the Instant Controlled Pressure Drop technology (DIC) effect on maize kernels' drying and rehydration kinetics. In total, 19 different DIC treatments were carried out on maize kernels (~25% d.b.). The DIC parameters studied were steam pressure (0.1 to 0.4 MPa) and treatment time (10 to 90 s). After DIC treatment, drying kinetics were carried out by Convective Air Drying (CAD) at 50 °C and 0.4 ms^-1 airflow. Rehydration kinetics and Water Holding Capacity (WHC) were evaluated at 20 °C. In comparison to CAD samples, DIC (0.4 MPa and 90 s) reduced the drying time from 180 min to ~108 min. Additionally, regarding the rehydration and WHC results, DIC achieved the same moisture content in only 3.5 min that controls achieved after 1 h of rehydration (0.40 g H₂O/g dry matter). Moreover, DIC (0.4 MPa and nine cycles of 10 s) increased the WHC 2.3 times compared to the control. In this way, DIC could be a postharvest technology to improve maize kernels' drying operations and functional properties.

Keywords: Instant Controlled Pressure Drop technology (DIC); drying kinetics; maize kernel; rehydration kinetics; water holding capacity.

Figure 1

(A) Schematic of the time-temperature-pressure profile of a DIC processing cycle. (1) Establishment of the vacuum within the processing reactor; (2) injection of steam at the selected pressure; (3) maintenance of treatment pressure during selected time; (4) instant controlled pressure drop towards vacuum; and (5) establishment of the atmospheric pressure within the processing reactor. (B) Laboratory DIC reactor (LABIC0.1, ABCAR-DIC Process; La Rochelle, France).

Figure 2

Pareto chart: effects of steam pressure (MPa) and treatment time (s) of DIC treatment on the thousand kernel weight (g) of maize kernels.

Figure 3

Drying curves of maize kernels W = f(t): Control and DIC-CAD (P = 0.14 MPa and t = 22 s; P = 0.4 MPa and t = 90 s and P = 0.4 MPa and t = 90 s divided into nine cycles of 10 s).

Figure 4

Pareto chart: the effects of steam pressure (MPa) and time (s) of DIC treatment on the apparent drying coefficient (10⁻¹⁰ m²/s) of maize kernels.

Figure 5

Rehydration curves of maize kernels: Control and DIC-CAD (P = 0.14 MPa, t = 22 s; P = 0.4 MPa, t = 90 s and P = 0.4 MPa, t = 90 s divided into nine cycles of 10 s).

Figure 6

Dried and rehydrated maize kernels: (A) Dried control, (B) Dried DIC 14 (P = 0.4 MPa, t = 90 s), (C) Dried DIC 18 (P = 0.4 MPa, t = 90 s divided into nine cycles of 10 s), (D) Rehydrated Control, (E) Rehydrated DIC 14, and (F) Rehydrated DIC 18.

Figure 7

Effects of Pressure (MPa) and time (s) of DIC treatment on the rehydration effective diffusivity (10⁻¹⁰ m²/s) in maize kernels. (A) Pareto Chart and (B) surface response and fitting model. D_eff-rehy = 0.0202 − 0.230P + 0.664P² + 0.00071t − 0.0000037t² − 0.001509P × t.

Figure 8

Effects of Pressure (MPa) and time (s) of DIC treatment on (A) starting accessibility of maize kernels during rehydration, and (B) water content of maize kernels after 2 h of rehydration.

Figure 9

Effects of Pressure (MPa) and time (s) of DIC treatment on the water holding capacity (WHC) of maize kernels. (A) Pareto Chart and (B) surface response and fitting model. WHC = 1.146 − 1.114P + 3.306P² − 0.0034t + 0.000023t² + 0.0147P × t.