engleski

Influence of enzymatic treatment and cryo- milling of buckwheat hulls on fibre solubility, free phenolic compounds and antioxidant capacity

Buckwheat hulls are a by-product rich in dietary fibre and bioactive compounds. Pre- processing of hulls with techniques such as cryo-milling and enzyme treatment could increase their nutritive value by affecting the content of soluble fibre and free phenolic compounds. Thus, the aim of this study was to determine the effect of different particle size obtained by cryo-milling as well as the enzymatic treatment time and concentration of cellulase and hemicellulase on insoluble and soluble fibre fraction as well as free total phenolic content, flavonoid rutin content, and antioxidant capacity of buckwheat hulls. Buckwheat hulls were cryo-milled for 8 minutes (8’C) in one cycle or in repeated cycles (8’RC), reaching median particle diameter of 50th percentile 93 μm and 61.5 μm, with mean surface weighted mean 13.6 μm and 9.1 μm, respectively (determined with laser diffraction). Enzymatic treatment was performed in 10% hull suspension in water, with the addition of 0.1% or 1% both cellulase (Alphamalt C 21032, Mühlenchemie) and hemicellulase (BIO-CAT) on hull basis, during 1, 4 or 8 hours. Content of insoluble dietary fibre, fibre soluble in water but precipitated in 78% ethanol (SDFP), fibre soluble in water and 78% ethanol (SDFS) was determined according to the AOAC 2011.25 method. Total phenolic content was determined by Folin Ciocalteu method, rutin by HPLC-UV/VIS method, and antioxidant capacity by FRAP and DPPH methods. Obtained results show slightly higher SDFS and SDFP content in 8’RC hulls before and after enzymatic treatment, compared to the 8'C ones. Treatment with a higher enzyme concentration (1%) led to 2- to 3-fold higher increase in the SDFS content compared to the treatment with a lower enzyme dosage (0.1%). Prolongation of enzyme treatment led to reduced content of free total phenolic compounds (up to 26%) and rutin (up to 33%), as well as reduced antioxidant capacity (up to 27- 31%), with higher decrease observed for 8’RC compared with 8’C hulls. Cryo-milling in repeated cycles and enzymatic treatment with the addition of 1% cellulase and hemicellulase for 1 hour was the most successful. The latter enzymatic treatment of 8’RC hulls resulted in 17% higher SDFP content, 4.4-fold higher SDFS content, as well as 16-27% higher antioxidant capacity compared with the non-treated 8’RC hulls.

buckwheat hulls ; cryo-milling ; enzyme treatment ; dietary fibre ; phenolic compounds

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