Total polyphenol extraction from red sorghum grain and effects on the morphological structure of starch granules

Abstract

Summary The aim of this study was to propose a treatment to reduce the content of total polyphenols (TPP) and to obtain flour without significant morphological changes in the starch granules. The response surface methodology (RSM) was used to predict the influence of temperature and time on TPP extraction. Research work was conducted using the central composite design methodology. Results showed that the effect of temperature was more significant than that of time. A quadratic fit of data regarding temperature and linear data adjustment as to time was obtained. A scanning electron microscopy analysis of starch showed no morphological change in the granules at the temperature studied. Starch granules presented a size distribution ranging from 6 to 25 μm being 35% of granules <15 μm, and 65% of granules >15 μm in size, respectively.

Hydrothermal Treatment to Remove Tannins in Wholegrains Sorghum, Milled Grains and Flour

“…For UMS, extractable polyphenols corresponds to those found in the pericarp. In all the UMS analyzed a second-order polyphenol extraction kinetics could be obtained, which may be modeled with a quadratic polynomial similar to those previously obtained by Acquisgrana et al (2016). This fact suggests that the treatment could continue for longer than the expected 60 minutes, from previous results (Acquisgrana et al, 2016).…”

“…Recent studies provide more evidence on this behavior where a similar relationship between tannins and popyphenols was found (Adetunji et al, 2015). In all cases the tannins values found are much lower than that established in the CAC 0.5% for wholegrains and 0.3% for flours, therefore with the treatment proposed by Acquisgrana et al (2016) it is possible to obtain a flour suitable for human consumption from the varieties of colored sorghum studied and that can be used for the production of gluten-free foods for people with celiac disease.…”

“…In all the UMS analyzed a second-order polyphenol extraction kinetics could be obtained, which may be modeled with a quadratic polynomial similar to those previously obtained by Acquisgrana et al (2016). This fact suggests that the treatment could continue for longer than the expected 60 minutes, from previous results (Acquisgrana et al, 2016). Sorghum with lower tannin content was obtained with longer extraction time, but as it will be seen in the MS and F samples, it would not be necessary since the final concentrations were adequate according to the Codex.…”

“…Previous studies proposed water treatment to reduce the content of polyphenols present in the pericarp of the wholegrain, to take advantage of polyphenols for other uses in food, and to obtain flour with better starch and protein availability (Acquisgrana et al, 2016). After treatment there is still enough polyphenols retaining their antioxidant capacity.…”

“…The samples were washed to eliminate the NaOCl solution and 100 ml of water was added. The preparation was incorporated to a heat bath at 75ºC for 60 min (Acquisgrana et al, 2016), a stage called "annealing" (Singh et al, 2011). Finally, the samples were dried for 12 h at 60º C.…”