Sprouting of Sorghum (Sorghum bicolor [L.] Moench): Effect of Drying Treatment on Protein and Starch Features

Abstract

The nutritional and physicochemical properties of sorghum proteins and starch make the use of this cereal for food production challenging. Sprouting is a cost-effective technology to improve the nutritional and functional profile of grains. Two drying treatments were used after sorghum sprouting to investigate whether the drying phase could improve the protein and starch functionalities. Results showed that the drying treatment at lower temperature/longer time (40 °C for 12 h) extended the enzymatic activity that started during sprouting compared to the one performed at higher temperature/shorter time (50 °C for 6 h). An increased protein hydrolysis and water- and oil-holding capacity were found in the flour obtained by the former treatment. Higher protein matrix hydrolysis caused high exposure of starch to enzymes, thus increasing its digestibility, while worsening the technological functionality. Overall, modulating drying conditions could represent a further way, in addition to sprouting, to improve sorghum flour's nutritional profile.

Keywords: drying; functionality; kafirins; nutritional profile; physicochemical properties; sorghum; sprouting; starch.

Figure 1

Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of kafirin (a) and non-kafirin (b) fractions of sorghum flours. US, unsprouted sorghum flour; SSD50, flour from sprouted sorghum dried at 50 °C for 6 h; SSD40, flour from sprouted sorghum dried at 40 °C for 12 h.

Figure 2

Pasting properties of sorghum flour samples measured by means of a Micro-Visco Amylograph. US, unsprouted sorghum flour; SSD50, flour from sprouted sorghum dried at 50 °C for 6 h; SSD40, flour from sprouted sorghum dried at 40 °C for 12 h.

Figure 3

Representative differential scanning calorimeter (DSC) thermograms of US, SSD50 and SSD40 flours in the range 50–110 °C. US, unsprouted sorghum flour; SSD50, flour from sprouted sorghum dried at 50 °C for 6 h; SSD40, flour from sprouted sorghum dried at 40 °C for 12 h.

Figure 4

Morphological observations of sorghum flours acquired with environmental scanning electron microscopy (ESEM). Micrographs of US, SSD50 and SSD40 flours were acquired with a magnification of 3000× (a,c,e) and 6000× (b,d,f). US, unsprouted sorghum flour; SSD50, flour from sprouted sorghum dried at 50 °C for 6 h; SSD40, flour from sprouted sorghum dried at 40 °C for 12 h; S, starch granule; PB, protein body; PHS, partially hydrolyzed starch; PM, protein matrix.