Effects of phenolics in sorghum grain on its bitterness, astringency and other sensory properties

Abstract

Despite the fact that condensed tannins are potentially important antioxidants, there is a general belief that tannins in sorghum confer objectionable sensory attributes. The objective of this study was to determine differences in the sensory attributes of sorghums containing different levels of total phenolic compounds. A trained sensory panel described and quantified the sensory attributes of different sorghums (condensed-tannin containing and tannin-free). All the sorghum cultivars were perceived as bitter and astringent. Bran infusions of tannin sorghums were perceived as darker, clearer, more bitter and more astringent than those of the tannin-free sorghums, while those of tannin-free sorghums were perceived as sweeter and cloudy. Sorghum whole-grain rice from the tannin sorghums which had relatively soft endosperm texture (PAN 3860 and Ex Nola 97 GH) was perceived as dark, hard, chewy, bitter and astringent, while that from tannin-free sorghums having relatively hard endosperm texture (Segaolane and Phofu) was perceived as soft, sweet and had a maize-flavour. Surprisingly, the bitterness and astringency, as well as other sensory attributes of NS 5511 (tannin sorghum), were perceived as similar to PAN 8564 (tannin-free sorghum) even though NS 5511 had more than twice the total phenol content of PAN 8564. This suggests not all condensed-tannin containing sorghums have objectionable sensory attributes.

Sensory characteristics of wholegrain and bran-rich cereal foods – A review

“…This fraction also contained significant amounts of bioactive compounds, such as alk(en)ylresorcinols and phenolic acids (Heiniö et al, 2008). In sorghum bitterness and astringency are also caused by phenolic compounds, especially by condensed tannins (Kobue-Lekalake, Taylor & De Kock, 2007;Kobue-Lekalake, 2008). …”

“…However, cooked wholegrain kernels from tannin sorghums having a relatively soft endosperm texture were perceived as dark, hard, chewy, bitter and astringent, while tannin-free sorghums having relatively hard endosperm texture were perceived as soft, sweet and having a maize-like flavour (Kobue-Lekalake, Taylor, & De Kock, 2007). KobueLekalake, Taylor, and De Kock (2009) showed that selection of sorghum cultivars containing low concentration of tannins may both promote health and ensure preference by consumers There seems to be tannin-containing sorghums that are palatable, even to bitter-sensitive consumers, because the tannin levels are below a detection threshold.…”

Evaluation of the functional quality of cowpea-fortified traditional African sorghum foods using instrumental and descriptive sensory analysis

“…After 14 h of panel training, the sensory evaluation was done in two sessions. The four types of ugali served in transparent glass ramekins were presented using a protocol similar to that of Kobue-Lekalake, Taylor, & De Kock (2007). The panellists handled the ugali with their fingers, the way ugali is normally eaten.…”

Mashing with unmalted sorghum using a novel low temperature enzyme system: Impacts of sorghum grain composition and microstructure

“…Traditional sorghum beers are usually produced using brown or red skinned 52 sorghum cultivars (Lyumugabe, Gros, Nzungize, Bajyana, & Thonart, 2012). Use of 53 darker skinned, high tannin cultivars in brewing is thought to result in inhibition of 54 mash enzymes and an objectionable increase in product bitterness (Kobue-Lekalake, 55 Taylor, & de Kock, 2007;Novellie, 1981). However, some workers have suggested 56 that the use of high-tannin sorghum cultivars is responsible for only a minor increase 57 in bitterness, not detectable by all panellists (Daiber, 1975).…”