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

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. Copyright © 2007 Society of Chemical Industry     

Influence of sorghum grain type on wort physico‐chemical and sensory quality in a whole‐grain and commercial enzyme mashing process

To determine the most suitable types of sorghum for whole‐grain adjunct in lager beer brewing, 14 cultivars of five different types: white tan‐plant, white non‐tan‐plant, red non‐tannin, white tannin (type II) and red tannin (type III) were evaluated. The effects of grain type on wort physico‐chemical and sensory quality with raw grain and malt plus commercial enzyme mashing were assessed. Tannin content correlated significantly and negatively with wort extract and fermentable sugars (p < 0.001) and free amino nitrogen (FAN; p < 0.1). This is attributable to inactivation of the exogenous enzymes by the tannins during the mashing process. However, the type II tannin sorghums had wort quality attributes closer to the non‐tannin sorghum types, probably owing to their relatively low tannin content (≤1%). Malting gave a great improvement in wort extract, fermentable sugars and FAN, but substantially influenced wort sensory properties in terms of higher sourness, bitterness and astringency, as well as the expected more malty flavour. Worts from raw red non‐tannin sorghums were similar to those of white tan‐plant sorghums in both physico‐chemical and sensory quality. Thus, red non‐tannin sorghums, in view of their better agronomic quality, have considerable potential as a whole‐grain adjunct in lager beer brewing. Copyright © 2013 The Institute of Brewing & Distilling     

Influence of PROP taster status on the consumer acceptability of food made from tannin sorghums

BACKGROUND: Condensed tannins in sorghum are powerful antioxidants, beneficial for health. However, tannin sorghums are believed to be unpalatable. The objective was to determine the influence of 6‐n‐propylthiouracil (PROP) taster status on consumer acceptability of food from tannin sorghums. Consumers (n = 194) classified by PROP taster status (super, medium and non) evaluated the appearance, flavour, overall liking and texture of sorghum rice from two tannin‐free sorghums, PAN 8564 and Phofu, and two tannin sorghums, PAN 3860 (82 g catechin equivalents (CE) kg^?1) and NS 5511 (18 g CE kg^?1), with high antioxidant activity. RESULTS: The PROP tasters could distinguish differences among the sorghum cultivars varying in tannin content levels, finding PAN 3860 less acceptable than the other sorghums. The non tasters preferred all the cultivars equally, presumably because they could not detect taste (bitter and astringent) differences between the sorghums. With the exception of appearance, tannin sorghum NS 5511 was generally equally preferred by PROP tasters to tannin‐free sorghums. CONCLUSION: There appear to some tannin sorghums that are palatable, even to PROP tasters, because the level of tannins is below a sensitivity threshold (ca 20 g CE kg^?1). Hence such tannin sorghums could be used to produce acceptable high‐antioxidant activity foods. Copyright © 2009 Society of Chemical Industry     

125th Anniversary Review: The science of the tropical cereals sorghum,maize and rice in relation to lager beer brewing

Mainstream lager beer brewing using the tropical cereals sorghum, maize and rice, either as malt or as raw grain plus commercial enzymes, is becoming widespread. This review examines the differences in composition between these tropical cereals and barley and their impact on brewing processes and beer quality. All of these cereals have a starch gelatinization temperature some 10 °C higher than barley. The sorghum prolamin proteins are particularly resistant to proteolysis owing to disulphide cross‐linking involving γ‐kafirin. Unlike barley, the major endosperm cell wall components in sorghum and maize are arabinoxylans, which persist during malting. The rice cell walls also seem to contain pectic substances. Notably, certain sorghum varieties, the tannin‐type sorghums, contain considerable levels of condensed tannins (proanthocyanidins), which can substantially inhibit amylases, and probably also other brewing enzymes. Tropical cereal malts exhibit a similar complement of enzymic activities to barley malt, with the notable exception of β‐amylase, which is much lower and essentially is absent in their raw grain. Concerning beer flavour, it is probable that condensed tannins, where present in sorghum, could contribute to bitterness and astringency. The compound 2‐acetyl‐1‐pyrroline, responsible for the popcorn aroma of maize and also the major aroma compound in rice, presumably affects beer flavour. However, much more research is needed into tropical cereals and beer flavour. Other future directions should include improving hydrolysis of prolamins into free amino nitrogen, possibly using prolyl carboxypeptidases and investigating tropical cereal lines with useful novel traits such as high amylopectin, high protein digestibility and low phytate. Copyright © 2013 The Institute of Brewing & Distilling     

Bitterness and astringency of flavan‐3‐ol monomers,dimers and trimers

Intensity of astringency and bitterness of seven flavonoid compounds was evaluated by a time‐intensity (TI) procedure. Eighteen trained judges rated intensity continuously from ingestion, through expectoration at 10 s until extinction of the sensation. The seven stimuli included two flavan‐3‐ol monomers, (+)‐catechin and (−)‐epicatechin, three dimers and two trimers synthesised from catechin or epicatechin by condensation with (+)‐dihydroquercitin. As the degree of polymerisation increased, maximum bitterness intensity (I_max) and total duration (T_tot) decreased whereas astringency I_max increased. The monomers were significantly higher in bitterness at I_max than the dimers, which were significantly higher than the trimers. Astringency I_max of the monomers was lower than the dimers or trimers, although no significant difference was found in T_tot among the polymer classes. The bond linking the monomeric units had an influence on both sensory properties. The catechin‐catechin dimer linked by a 4→6 bond was more bitter than both catechin‐(4→8)‐catechin and catechin‐(4→8)‐epicatechin. Astringency was affected by both the specific linkage and the identity of the monomeric units with the dimer, catechin‐(4→8)‐catechin, being lower in astringency than either catechin‐(4→6)‐catechin or catechin‐(4→8)‐epicatechin. © 1999 Society of Chemical Industry     

感官评定方法确定麻竹笋苦涩味物质成分及与口感的关系

通过分析测定麻竹笋苦涩味物质含量与感官评定方法确定竹笋苦涩味物质成分及与口感的关系。麻竹鲜笋在100℃纯净水中分别进行0、30、90、150 s和420 s 5个时间梯度水煮处理,并测定煮后笋汤、笋渣的可溶性单宁、草酸和游离苦味氨基酸(Phe、Val、Arg、Met和Leu)含量,感官评定小组对其涩味、苦味强度评定,并通过对食品级草酸、单宁标准样品配制的不同质量浓度溶液进行苦涩味感官评定,建立单宁、草酸、单宁和草酸混合液的质量浓度与滋味强度的特征曲线函数。结果表明,影响麻竹笋苦涩味的主要物质是可溶性单宁,竹笋苦味和涩味均与单宁含量呈极显著关系,相关系数分别达0.896和0.867;竹笋涩味与草酸含量呈显著关系,相关系数为0.448,而竹笋苦味与草酸含量无显著关系;竹笋苦涩味与游离苦味氨基酸含量均无显著关系。利用单宁特征曲线函数对竹笋苦涩味偏重的成因进行了分析,对9个笋渣、笋汤的分析结果表明,单宁特征曲线函数对竹笋涩味的解释程度达60.6%~136.4%,对竹笋苦味的解释程度达63.4%~132.0%,较高的可溶性单宁含量是引起麻竹笋苦涩味偏重的主要原因。     

Improving the quality of sorghum injera by decortication and compositing with tef

Injera is an Ethiopian fermented pancake‐like bread made from cereals, with tef being preferred. Decortication and compositing with tef were evaluated as methods to improve the injera‐making quality of red tannin‐free and tannin‐containing sorghums. Both decortication and compositing improved sorghum injera quality. Concerning decortication, mechanical abrasion was found to be more effective than hand pounding because acceptable injera was obtained with lower milling loss. Good quality injera was produced at an extraction rate of 540 g kg^?1 for tannin‐containing and 830 g kg^?1 for tannin‐free sorghum. With compositing, good quality injera was produced with a 50:50 (w/w) composite of whole tannin‐containing sorghum and tef. Both processes reduced the tannin content of the flours, which appeared to relieve the inhibiting effects of tannins on the fermentation. Decortication also seemed to improve sorghum flour injera‐making quality by improving flour pasting as a result of reducing the level of interfering substances such as lipids and proteins. In contrast, the improvement brought about by compositing with tef seemed to be due to inherent differences between tef and sorghum starch granules and an increase in the water solubility index of the flour. Compositing seems to be a more useful method of improving sorghum injera quality than decorticating as it avoids the grain loss associated with decortication. Copyright © 2005 Society of Chemical Industry     

Effects of viscosity on the bitterness and astringency of grape seed tannin

To examine the separate effects of viscosity and sweetness on astringency, aqueous solutions of grape seed tannin (GST) were thickened with carboxymethyl cellulose (CMC) from 2 to 45 cP (experiment 1) or sweetened with 0 to 1.8 g/L aspartame (experiment 2). Trained subjects continuously rated astringency and bitterness in duplicate. Subjects were categorized by the salivary flow induced by citric acid and ability to taste n-propyl thiouracil (PROP). In experiment 1, maximum intensity and total duration of astringency were significantly decreased as viscosity rose, although time to maximum intensity of astringency was not affected. Maximum intensity and total duration of bitterness were not significantly affected by increasing viscosity; however, the onset of bitterness was significantly delayed. In experiment 2, increasing sweetness had no affect on any astringency parameter, although maximum intensity of bitterness was significantly decreased. Neither PROP nor salivary flow-status had any effect on perception of bitterness or astringency in either experiment.     

Effect of extrusion cooking and simulated in vitro gastrointestinal digestion on condensed tannins and radical scavenging activity of type II and type III whole grain sorghum

The effect of extrusion cooking and simulated in vitro gastrointestinal digestion on proanthocyanidins in type II and III tannin sorghums was studied. Extrusion cooking was performed at different feed moisture levels (2 L h^?1, 3 L h^?1, 5 L h^?1 and 8 L h^?1), with a barrel temperature of 150 °C followed by in vitro gastrointestinal digestion. Extrusion cooked samples had lower total phenols, tannin content and radical scavenging properties than unprocessed tannin sorghum flour. For extrudates, there was progressive increase in total phenols and tannin content with increase in feed moisture. Extrusion cooked samples had increased proportion of dimers and decreased oligomers in the two tannin sorghums. Gastric and duodenal digests of the extrudates contained high proportions of monomers and dimers and some oligomeric proanthocyanidin species. Undigested porridges, gastric and duodenal digests inhibited radical‐induced oxidative DNA damage. Extruded tannin sorghum may have health‐promoting potential in relation to combating chronic diseases associated with oxidative stress.     

Optimizing the orosensory properties of model functional beverages: the influence of novel sweeteners, odorants, bitter blockers, and their mixtures on (+)-catechin

This paper is dedicated to the memory of colleague and friend, Dr. Samson Agboola, who recently passed away. Abstract: The use of flavor‐modifying strategies are important to improving the sensory profile of some excessively bitter and astringent functional ingredients, such as (+)‐catechin (CAT). Two bitter blockers (ß‐cyclodextrin [CYCLO], homoeriodictyol sodium salt [HED]), two sweeteners (sucrose [SUC], rebaudioside A [REB]), and two odorants (vanillin [VAN], black tea aroma [TEA]) were assessed for their efficacy at modifying the bitterness and astringency of CAT in model aqueous solutions. The intensity of oral sensations elicited by CAT was determined in duplicate in binary, ternary, and quaternary mixtures of these stimuli by a trained panel (n= 15) using a 15 cm visual analogue scale. Overall, bitterness and astringency were most effectively reduced by ternary solutions containing CYCLO + REB or CYCLO + SUC (68%, 60%, and 45%, 43% for bitterness and astringency, respectively). Odorants were not effective at modifying the bitterness or astringency of CAT. We conclude that the use of select bitter blockers and sweeteners may be of value in optimizing the flavor and acceptance of functional food and beverages fortified with phenolic compounds. Practical Application: (+)‐Catechin is a bitter‐tasting plant‐derived health‐promoting phenolic compound of interest to functional food and beverage manufacturers. We investigated the efficacy of bitter blockers, plant‐based sweeteners, and odorants in decreasing the bitterness and astringency elicited by (+)‐catechin. Some of these additives, both alone and in combination, reduced bitterness and astringency, and may therefore assist in optimizing the flavor and consumer acceptance of some phenolic‐based functional foods and beverages.     

Sensory evaluation of bitterness and astringency of 3R(−)-epicatechin and 3S(+)-catechin

Bitterness and astringency of the monomeric flavan-3-o!s ( + )-catechin and (?)-epicatechin were rated using time-intensity (T-I) methodology. Three concentration levels (0.5. 0.9 and 1.2 g liter^?1) oi each compound were assessed, and the parameters time to maximum intensity (TMAX), intensity at the maximum (IMAX) and total duration (TTOT) were extracted from the T-I curves. No differences in TMAX for either bitterness or astringency were found between these chiral isomers or as a function of concentration within a compound. Epicatechin had a significantly higher bitter IMAX than catechin at all three concentration levels, and had a significantly longer TTOT at the two higher concentrations. Epicatechin was more astringent than catechin. but this was only significant at one concentration. Astringency TTOT was longer for epicatechin, although this was nonsignificant at the lowest concentration. The three concentrations of catechin were significantly different for both bitterness and astringency IMAX and TTOT. Epicatechin showed evidence for the astringency response plateauing above the 0.9 g litre^?1 level. n-Propylthiouracil status had no effect on perception of either bitterness or astringency.     

酿酒高粱籽粒微观形态分析及其果皮厚度和单宁含量的相关性

该研究对全国已推广的19份酿酒高粱的果皮（果皮层和种皮层）厚度及淀粉粒径长度进行统计分析,并初步总结了高粱籽粒单宁含量与果皮厚度间的关系。结果表明,酿酒高粱的果皮厚度并不呈单峰分布,西南糯高粱的果皮厚度与其他地区高粱差异显著（P＜0.05）,其中红缨子高粱果皮厚度在＜100 μm范围内平均值为（59.74±9.87） μm。不同酿酒高粱淀粉粒径长度差异也比较明显,说明高粱原料酿造性状的优劣要综合考虑其性状表现。单宁含量和果皮厚度间具有较好的直线相关关系（R=0.501 4）,果皮厚度每增加1 μm,籽粒的单宁含量则增高0.014 7%。     

Kinetics of Tannin Deactivation during Anaerobic Storage and Boiling Treatments of High Tannin Sorghums

Grain from three high tannin sorghums had their moisture contents raised by adding distilled water at 15, 20 and 25% W/W, respectively, and were stored under CO₂ atmosphere at 25, 35 and 45°C respectively, for 1–20 days. In another trial, grain from the same high tannin sorghum sources was boiled in water at a ratio of 1g to 3 mL for periods of 10–60 min. Both anaerobic storage and boiling treatments deactivated the tannins with time. Moisture content and temperature levels influenced the rate of tannin deactivation during anaerobic storage. The process of tannin deactivation for both anaerobic storage and boiling treatments followed first order kinetics.     

Effects of glutinous and nonglutinous sorghums on Saccharomyces cerevisiae fermentation for Chinese liquor making

This work investigated the effect of sorghum, including Chinese glutinous (S1 and S2) and nonglutinous (S3 and S4), Canadian nonglutinous cultivars (S5 and S6), on fermentation of Saccharomyces cerevisiae MT and FJ, the representative strains for Chinese liquor fermentation with glutinous and nonglutinous sorghums as materials, respectively. S. cerevisiae MT and FJ exhibited a longer stationary phase in glutinous and nonglutinous cultivars, respectively. Fat and tannin contents in sorghums were, respectively, negatively related with ethanol and esters production by both MT and FJ. FJ produced the most amount of flavour compounds in nonglutinous cultivars, while MT showed no preference on sorghum cultivars, as it produced most flavour compounds in both S1 and S3. Moreover, sorghums showed different characteristics on flavour production. The nonglutinous cultivars S3 and S4 were correlated with most of the acids, aromatic compounds and terpenoids, while S5 and S6 were correlated with most of the esters.     

Chemical and sensory evaluation of Bordeaux wines (Cabernet-Sauvignon and Merlot) and correlation with wine age

Wine quality study was carried out with 24 vintages of Cabernet-Sauvignon (CS) and 7 vintages of Merlot (M) produced by two different Bordeaux wine-growing areas. Proanthocyanidin monomers and oligomers were identified and quantified by HPLC-UV-Fluo. Percentage of galloylation (%G), of prodelphinidins (%P) as well as mean degree of polymerisation (mDP) were also determined. Total phenolic compounds, total anthocyanins, total tannins, hue, CI (colour intensity), titratable acidity, ethanol level and pH were evaluated. Sensory analysis concerning astringency and bitterness intensity was also performed. Total phenolic compounds, total anthocyanins, total tannins, tannin monomers, hue, CI, % G, % P, mDP and astringency intensity differentiate both wines (M and CS) according to vintage. Correlations between wine age and: mDP, hue, astringency and tannin monomers (C + EC) are obtained. Qualitative tannin characterisation is established by correlation between astringency and mDP (R² = 0.509, p = 0.051, CS; R² = 0.780, p = 0.000 M). In addition, mDP decreases significantly during ageing (R² = 0.796, p = 0.000; CS and R² = 0.946, p = 0.000; M). Scale patterns between wine mDP and tannin perception (astringency) are proposed.     

基于电子舌的氯吡脲对草莓风味影响的研究

在草莓“甜查理”盛花后一周,喷施清水及4个浓度（2.5、5.0、10、20 mg/L）的氯吡脲,检测由此产生的草莓果实可溶性固形物、总酸、游离氨基酸、单宁等风味营养品质含量,电子舌分析技术检测酸、甜、苦、鲜、咸、涩味、苦味回味、涩味回味等味觉指标,评价氯吡脲的使用及浓度水平对草莓风味营养品质和滋味的影响,并分析电子舌在检测氯吡脲对草莓滋味影响方面运用的优势。结果表明：氯吡脲能够提高草莓果实的可溶性固形物的含量,降低总酸含量,提高固酸比值,降低游离氨基酸种类和游离氨基酸总量;低浓度（2.5、5.0 mg/L）的氯吡脲处理能降低草莓单宁含量,而高浓度（10、20 mg/L）处理会使单宁含量显著升高;电子舌味觉分析结果表明低浓度氯吡脲处理可使草莓甜味增加,酸味降低,但是咸味和鲜味及与其高度相关（相关系数均为0.99）的苦味也相应降低;游离氨基酸总量与鲜味值、单宁含量与涩味回味值、总酸含量与酸味值、固酸比与甜味值均呈正相关性。低浓度氯吡脲使用对草莓的甜味、酸味等滋味和风味组成具有正面影响,而无论氯吡脲浓度使用高低对咸味和鲜味等滋味和风味组成均有负面影响。     

Starch properties as affected by sorghum grain chemistry

To determine the relationship between sorghum grain polyphenol content, grain structure, and starch properties, starch was isolated from 10 sorghum varieties using an alkali steep and wet‐milling procedure. SV2, a tannin‐free variety with white pericarp, gave a white starch. Varieties having red or white pericarp and higher polyphenol levels gave pink starches. Hunter colour values (L, a, b) of starches were not correlated with grain polyphenol content. Grain appearance in terms of pericarp colour, or presence or absence of pigmented testa, did not relate to the intense pink colouration of sorghum starches. Starch amylose content was significantly negatively correlated (r = −0.88, p < 0.001) to grain floury endosperm texture. Sorghum starches had higher peak viscosity (PV) in pasting than commercial maize starch. The time taken to reach peak viscosity from the initial viscosity rise was less for sorghum starches than maize starch. However, sorghum starches had a higher rate of shear thinning (R_st) than maize starch. There was a significant positive correlation between grain polyphenol content and starch PV (r = 0.75, p < 0.05). Starch gel hardness was negatively correlated to pasting properties of R_st and paste breakdown (r = −0.78 and −0.77 respectively) at p < 0.01. Peak gelatinisation temperature (T_p) occurred over a narrow range from 66 to 69 °C. T_p was negatively correlated to the floury endosperm portion of the grain (r = −0.77) at p < 0.01. It is concluded that sorghum grain polyphenol content and grain characteristics influence its starch properties. © 2000 Society of Chemical Industry     

Red Wine and Model Wine Astringency as Affected by Malic and Lactic Acid

Red wines and model solutions containing grape seed phenols were assessed for perceived astringency, bitterness and sourness by a panel of trained assessors using time-intensity (T–I) methodology. The effect of lactic and malic acid on perception of these attributes was evaluated at two pH values, by adding different amounts of acids. Maximum intensity (I_max) and total duration (T_tot) of astringency increased with decreasing pH in model solutions and red wine, but no differences were found between malic and lactic acid on perception of astringency. The pH and the acid type did not affect any of the bitterness T-I parameters. However, sourness showed an increase in 1_max and T_tot with decreasing pH.     

Bitterness and astringency of grape and wine polyphenols

Extracts containing anthocyanins (ACN), and skin tannins (SKIN) and seed tannins (SEED) were prepared from Vitis vinifera cv. Cabernet Franc grapes grown in the Loire Valley, and characterised. Phenolic fractions from Cabernet Franc wines made from three Loire Valley locations were also isolated and characterised. Bitterness and astringency of ACN, SEED and SKIN as well as the wine extracts were evaluated by time intensity procedures in citric acid solution and in a base white wine. SEED and SKIN were equally astringent when tasted at the same concentration in spite of differences in tannin composition. The lower molecular weight (MW) of SEED was equal in astringency to larger MW SKIN which had a lower percentage of galloylation. The SEED fraction was slightly more bitter than the SKIN fraction in the citric acid solution, although no difference could be detected between samples in base white wine. Astringency of ACN alone was much lower than either SKIN or SEED. Addition of ACN to either tannin fraction produced very small sensory effects in citric acid. In wine, addition of ACN to either SEED or SKIN increased astringency significantly over either fraction alone, but had no effect on bitterness. The wine fractions differed only in astringency, which was correlated with tannin units as determined by thiolysis.     

Effect of malt pretreatment on phytate and tannin level of two sorghum (Sorghum bicolor) cultivars

The seeds of two cultivars of Sudanese sorghum (Sorghum bicolor), namely Wad Ahmed and Tabat, were germinated for 4 days to obtain 1‐, 2‐ and 4‐day‐old malts. Sorghum malt (5% and 10%) was added to sorghum flour. The mixtures were incubated at 30 °C with shaking for 30, 60, 90 and 120 min. Malting loss was very slight for both cultivars and for all incubation periods. Phytic acid and tannin contents were assayed for all treatments. The results revealed that phytate and tannin contents were significantly (P ≤ 0.05) reduced when sorghum flour was pretreated with malt. When a mixture containing 10%, 4‐day‐old malt and sorghum flour was incubated for 120 min, it significantly (P ≤ 0.05) reduced phytate and tannin contents by 92% and 98%, respectively, for Wad Ahmed cultivar, while for Tabat they were reduced by 93% and 96%, respectively. The rate of reduction of phytate and tannin content increased with incubation time and malt age and concentration.