Molecular rearrangement of Laird lentil (Lens culinaris Medikus) starch during different processing treatments of the seeds

Abstract

The molecular structural changes of the starch isolated from untreated (ULS), roasted (RLS), germinated (GLS), fermented (FLS), microwave cooked (MLS), conventional cooked (CLS), and autoclaved (ALS) lentil seeds were investigated. All starch samples obtained were categorized by size exclusion chromatography with multi-angle laser scattering into two groups, i.e., Group A with two population of peaks appeared for samples including ULS, RLS, and GLS; and Group B with three population of peaks shown in samples including FLS, MLS, CLS and ALS. A noticeable decrease in relative crystallinity by XRD was found for all starch from the processed seeds (11.41–3.24%) compared with starch isolated from untreated seeds (15.90%), especially that a greater extent of such decreasing was observed for FLS, MLS, CLS, and ALS (Group B samples). The intensity of the absorptions related to hydrogen bonding by FT-IR (3000-3600 cm−1, and ∼1000 cm−1) were markedly decreased for lentil starch isolated from processed seeds compared with native starch, and, especially for treated samples of Group B, which also exhibited the significantly higher degree of double helix and lower value of degree of order. Small angle X-ray scattering data manifested that the typical ∼9–10 nm semi-crystalline structure was disappeared for the Group B samples which were characterized with the relatively higher values of d, da, and dc. The results suggested that the densely packed crystalline structure could be shifted within the crystallites and tended to result small new crystal structure during the processing of lentil seeds, and such effect was particularly obvious for starch samples including FLS, CLS, MLS, and ALS.