Effect of fermentation on water mobility and distribution in fermented cornmeal using LF-NMR and its correlation with substrate

Abstract

Cordyceps militaris (C. militaris) was utilized to ferment cornmeal by solid state fermentation. The main objective of this study was to investigate effect of fermentation on the dynamic state of water and microstructure distribution of water within cornmeal with Low-field nuclear magnetic resonance, as well as the effect on composition and microstructure properties. The spin-spin relaxation time (T₂) showed significant changes in solid-state fermented cornmeal. Principal component analysis further revealed that the variations within different fermentation stage could be discriminated by the T₂ parameters. Bulk water (T₂₂) was the main form of water present and lost in substrates. The weights of different indicators, as assessed by multiple regression analysis, demonstrated that there was a strong correlation between starch and T₂ relaxation. Scanning electron microscopy demonstrated that fermentation can cause the appearance of micropores. The longer relaxation time of T₂₂ during logarithmic period can be interpreted as a loosening of the structure at the starch hydrolysis, introducing more water into the structure. Thus, the differences in composition and structure of the substrate at different fermentation time produce different T₂ values.

Keywords: Cordyceps militaris; Cornmeal; LF-NMR; Solid-state fermentation.

Fig. 1

Variations of traditional parameters during SSF: a total starch, b acid-soluble protein, c moisture content, d biomass content

Fig. 2

LF-NMR T₂ relaxation time distribution curves of unfermented samples (a) and fermented samples (b)

Fig. 3

PCA plot obtained using distributed NMR T₂ relaxation data of different fermentation time

Fig. 4

Scanning electron micrographs of unfermented sample (a), fermented sample at 1 days (b), fermented sample at 2 days (c), fermented sample at 3 days (d), fermented sample at 4 days (e), fermented sample at 5 days (f), fermented sample at 6 days (g), fermented sample at 7 days (h), fermented sample at 8 days (i), fermented sample at 9 days (j), fermented sample at 10 days (k)