The effect of infrared heating on the functional and nutritional qualities of green lentil and yellow pea flours
The effect of seed tempering moisture (20 vs. 30%) and infrared heating temperature (120 vs 140oC) on the nutritional and functional properties of the resulting flours from green lentil and yellow pea were evaluated. For both pulses, proximate composition remained unchanged relative to the unprocessed pulses, although seeds became a little darker in colour. The damaged/gelatinized starch content of the control flours steadily increased as both tempering moisture and infrared heat applied to the seeds prior to milling increased. For all processing conditions, surface hydrophobicity (SH) increased relative to the control, whereas surface charge (zeta potential (mV)) remained unchanged. The secondary protein structure of both pulse types transitioned from a more ordered state composed of β-sheet and α-helix structures, to state with a higher relative percentage of random coil structures as processing conditions increased. Functional properties of the flours were mildly affected as a result of tempering and infrared heating, and in most cases were correlated with the SH and damaged/gelatinized starch content of the flours. Protein solubility at pH 5 was unchanged in response to processing, however at pH 7 a slight processing effect was seen, which led to lower solubility. The water and oil holding capacities (WHC, OHC) of the processed flours were improved in comparison to the control group flours, although OHC tended to decline as infrared heat temperatures increased from 120 to 140oC. Poor foaming capacities (FC) and relatively stable foaming stabilities (FS) were observed for both pulse types. Intensifying processing of the pulse seeds improved emulsion activity (EA) and emulsion stability (ES) up until a critical point, where it then significantly declined. The oil emulsion capacity (OEC) declined with processing relative to the control for both pulse types. The peak and final viscosities of the flours decreased, and pasting temperature increased, as processing temperature and moisture increased, relative to the control group flours. In-vitro protein digestibility (IVPD) of processed flours increased relative to the control group flour, with the exception of yellow pea flours, where a slight decrease in IVPD was found for flours tempered to 30% moisture and heated to 140oC. Amino acid contents remained unchanged between control and processed flours in both pulse types, and the limiting amino acid (LAA) was found to be tryptophan in both yellow pea and green lentil flours. The in-vitro protein digestibility corrected amino acid scores (IV-PDCAAS) of the flours were not significantly altered by processing. Rapidly (RDS) and slowly (SDS) digestible starches increased with processing, whereas the amount of resistance starch (RS) declined. RDS and SDS values increased with increased temperature, and with increased moisture when processed. In contrast, RS decreased with increasing temperature and increased moisture. The overall conclusions in this study are that the combined effect of tempering moisture and infrared heat as a pre-milling treatment either did not significantly affect, or slightly reduced, the studied functional properties of the treated flours in comparison to the control group (with the exception of WHC). It was also found that flours that were tempered and infrared heated prior to milling had improved levels of protein and starch digestibility, but not protein quality.
Lentil, Pea, Foaming, Solubility, Protein quality, In vitro protein digestibility-corrected amino acid score, Starch digestibility, Fourier transform infrared spectroscopy
Master of Science (M.Sc.)
Food and Bioproduct Sciences