Contents of anti-nutritional factors in grains of new sorghum cultivars harvested at two vegetative stages and in two seasons of the year

Contenido de factores antinutricionales de granos de nuevos cultivares de sorgos cosechados en dos estados vegetativos y en dos épocas del año

Janhad L. Rodríguez,^I R., Lima,^I L. I., Marrero,^I,II A. , Castro,^I,II Sandra Hoedtke,^III J. Bindelle,^IV

^IUniversidad Central “Marta Abreu” de Las Villas (UCLV), Departamento de Medicina Veterinaria y Zootecnia, Carretera a Camajuaní, km 5.5. Santa Clara, Villa Clara. Cuba.
^IIUCLV. Centro de Investigaciones Agropecuarias, Santa Clara, Cuba. ]]> ^IIIUniversity of Rostock, Chair of Animal Physiology and Animal Nutrition, Justus-von–Liebig-Weg 8, 18059 Rostock, Germany.
^IVDepartment of Animal Husbandry, Gembloux Agricultural University, 2 Passage des De´ porte´ s, Gembloux 5030, Belgium.

ABSTRACT

Randomly selected grain samples from new sorghum cultivars (CIAP MC-04-12 and CIAP 132-05) harvested in different seasons of the year and at different vegetative stages in 2011 and 2012, were used for determining the contents of phenolic compounds (condensed tannins, total phenols, non-tannin phenols and tannin phenols), β-glucans, phytic acids and cyanogenic glucoside. Results demonstrated that the sorghum cultivar, the vegetative stage and the harvesting season of the grain influenced on the studied concentrations of anti-nutritional factors (ANFs). Tannin phenols in the grains were from 2.6 (CIAP MC-04-12) to 2.8 (CIAP 132R-05) times higher in the dry season regarding the rainy period. Condensed tannin concentrations represented 87 % of the tannin phenols, while the concentrations of β-glucans were from 2.7 to 4.8 times higher (P < 0.001) in the treatments based on CIAP 132R-05 than on those of CIAP MC-04-12.  It is concluded that the two cultivars studied are low in all ANFs.  This suggests a low effect of these ANFs on nutrient digestibility, energetic content and productive performance of monogastric animals receiving diets in which the grains of these cultivars are the main energy source.

Key words: sorghum, anti-nutritional factors, grain vegetative stage.

RESUMEN

A partir de muestras aleatoriamente seleccionadas de granos de nuevos cultivares de sorgo (CIAP MC-04-12 y CIAP 132R-05), cosechados en diferentes épocas del año y a diferentes estados vegetativos, en 2011 y 2012, se determinaron los contenidos de compuestos fenólicos (taninos condensados, fenoles totales, fenoles no taninos y fenoles taninos), β-glucanos, ácido fítico y glucósido cianogénico. Los resultados demostraron que el cultivar de sorgo, el estado vegetativo y la época de cosecha del grano influyeron en las concentraciones de los factores antinutricionales (FANs) estudiados. Los fenoles taninos contenidos en los granos fueron de 2.6 (CIAP MC-04-12) a 2.8 (CIAP 132R-05) veces superiores en la época poco lluviosa con respecto al período lluvioso. Las concentraciones de los taninos condensados representaron 87 % de los fenoles taninos, mientras que las concentraciones de β-glucanos fueron de 2.7 a 4.8 veces superiores (P < 0.001) en los tratamientos de CIAP 132R-05 que en los de CIAP MC-04-12. Se concluye que los dos cultivares estudiados son bajos en todos los FANs. Esto sugiere que sea bajo el efecto de estos FANs en la digestibilidad de nutrientes, el contenido energético y el comportamiento productivo de animales monogástricos que reciban dietas en las que el grano de estos cultivares sea la fuente principal de energía.

Palabras clave: sorgo, factores antinutricionales, estado vegetativo del grano.

INTRODUCTION

Sorghum (Sorghum bicolor L. Moench) is one of the cereals showing higher adaptability in areas where the climate is not favorable. Therefore, it represents a good energy source for pigs (Mushandu et al. 2005). The ICRISAT reports that the sorghum guinea breed has a great tolerance to rainfall shortage or abundance, with high grain yields, resistance to bird attack, as well as adaptation characteristics (flexible panicles and glumes) and acceptable nutritive value making these properties a viable alternative for producing grains in tropical systems.  The sorghum cultivar CIAP MC-04-12 is a new cultivar of the guinea breed obtained by selection at the Agricultural Research Center (CIAP, Santa Clara, Cuba).  However, it is known that cereals and its by-products have in its composition a group of substances that affects the bioproductive performance and animal health (Castro et al. 2002). Consequently, the content of the main anti-nutritional factors present in grains of new sorghum cultivars harvested at two vegetative stages and in two seasons of the year in the central region of Cuba was established.

MATERIALS AND METHODS

From randomly selected grain samples of the sorghum cultivars CIAP MC-04-12 and CIAP 132R-05, harvested in two seasons of the year and at different vegetative stages in 2011 and 2012, the anti-nutritional factors (ANFs) were determined by standardized methods at the universities of Hohenheim, in Germany and Lieja, in Belgium. The protocols described by Makkar et al. (2007) were used for the phenolic compounds (condensed tannins, total phenols, non-tannin phenols and tannin phenols), phytic acid and cyanogenic glucoside.

Phenols and tannins. The method used assumes the determination of four fractions: condensed tannins, total phenols, non-phenol tannins and phenol tannins. These essays are based on the oxidation-reduction principle and the utilization of the Folin-Ciocalteu reagent. Tannins are distinguished from non-tannins by the use of a solid matrix, polyvinyl polypirolidose (PVPP).  Total phenols are measured in a plant extract using the Folin-Ciocalteu methods, before and after the PVPP treatment.  For condensed tannins the methods of butanol-HCl-Fe was used that shows anthocyanidines of pink color when the oxidative breaking off of the condensed tannins interflavones links occurs in the presence of acid minerals in alcoholic solutions at 95º C.

Phytic acid. Phytates were extracted with trichloroacetic acid and precipitated with ferric salt. The iron contents of the precipitate was spectrophotometrically determined and the phosphorus phytate content from this value. A constant in the molecular relationship of 4 Fe/6 P was assumed in the precipitate.

Cyanogenic glucoside. The method was based on the reaction of the hydrocyanic acid with potassium hydroxide for forming potassium cyanide reacting with the sodium picrate developing a red color compound.  Color intensity is measured at 520 nm.

Results from the chemical analyses were statistically processed in the general linear model (GLM) of SPSS 21.0 for assessing the effects of the sorghum cultivar, the vegetative stage of the grain and the harvesting season of the grain on the variables studied following the model:

Y_ijk = μ + SC_i=1-2 + HS_j=1-2+ GVS_k=1-2 + SC×HS + SC×GVS + HS×GVS + SC×HS×GVS + ε_ijk

with SC_i=1-2,

The sorghum cultivar (CIAP MC-04-12 vs. CIAP 132R-05)

HS_{l = 1-2}

The harvesting season (rainy vs. dry)

GVS_{k =l-2}

The vegetative stage of grain at harvesting time (soft paste vs hard paste) SC x HS + SC x GVS + HS x GVS + SC x HS x GVS

The interaction between the different factors and ε_ijk, the experimental error.

RESULTS AND DISCUSSION

The contents of phenolic compounds shows great variation, depending on the harvesting time (table 1), in which stress situations as the dry period (Makkar et al. 2007) make the concentrations of these compounds (e.g. tannin phenols increase 2.66 (CIAP MC-04-12) or 2.87 (CIAP 132R-05) times more in the dry period than in the rainy period).  Tannin contents evidenced that the two cultivars studied can be classified as low in tannins (Osuntogun et al. 1989) and show similar or lower levels than other Cuban sorghum cultivars (Castro et al. 2002). These results suggest that the effect of these is low (Duodu et al. 2003 and Mushandu et al. 2005) on nutrient digestibility, energetic contents and the productive performance of monogastric animals receiving diets in which the grain of these cultivars is the main energy source.

In addition, results show that condensed tannins represent 87 % of the tannin phenols.  The sorghum cultivar as the grain vegetative stage affected (P < 0.001) the condensed tannin levels and other phenolic fractions. However, interdependence is evidenced between the harvesting season of the grain and its vegetative stage, as well as between the sorghum cultivar and the grain harvesting season in all the phenolic compounds.

The β-glucans of the sorghum cultivars studied regarding other cereals (Castro et al. 2002) allow its classification as of low in β-glucans (table 2).  In view of the low contents of these substances, there must be no negative effect on the digestive nutrient utilization and on the productive performance of monogastric animals receiving diets in which the grain of these cultivars is the main energy source.  Nonetheless, in spite of these low concentrations in both cultivars, the concentrations of β-glucans were from 2.7 to 4.8 times higher in the treatments based on CIAP 132-05 than in those of CIAP MC-04-12.

The contents of phytic acid are very variable in the sorghum and depend on the type of cultivar (Doudu et al. 2003). In our study the CIAP MC-04-12 cultivar showed 1.3-1.7 times less phytic acids regarding the CIAP 132R-05 cultivar. Also, there was effect (P < 0.001) of the grain vegetative stage and the grain harvesting season on the phytic acid contents (table 2).  The concentrations of these substances in the studied cultivars classify them as cultivars low in phytic acid, though the highest part of the phosphorus contained in these grains will be more assimilable by the animals and its effect on protein digestibility and the immobilization of trace minerals will be minimum (Duodu et al. 2003).

The cyanogenic glucoside content is very variable in sorghum cultivars.  Osuntogun et al. (1989) studying 15 sorghum cultivars used in human feeding found values between 8 and 38 mg/kg DM. The concentrations of cyanogenic glucoside in the studied cultivars (table 2) are within this range and present values far lower than the permissible limits in the diets (500 mg of cyanogenic glucoside/kg DM).

It is concluded that the two cultivars are low in all the ANFs studied, which allows suggesting a low effect of these ANFs on nutrient digestibility, energetic contents and the productive performance of monogastric animals receiving diets in which the grain of these cultivars is the main energy source.  Nonetheless, there are differences between both cultivars regarding the ANFs concentrations and in the way in which the vegetative stage and the harvesting season act in these cultivars.

REFERENCES

Duodu, K. G., Taylor, J. R. N., Belton, P. S. & Hamaker, B. R. 2003. “Factors affecting sorghum protein digestibility”. Journal of Cereal Science, 38 (2): 117–131.

Makkar, H. P. S., Siddhuraju, P. & Becker, K. 2007. Methods in molecular biology ‘Plant secondary metabolites’. Totowa, New Jersey: Humana Press, 47-49 p.

Megazyme 2011. Mixed-Linkage β-glucan assay procedure (K-BGL 07/145). Wicklow, Irlanda: Megazyme International Ireland, 15 p.

Mushandu, J., Chimonyo, M., Dzama, K., Makuza, S. M. & Mhlanga, F. N. 2005. “Influence of sorghum inclusion level on performance of growing local Mukota, Large White and their F 1 crossbred pigs in Zimbabwe”. Animal feed science and technology, 122 (3): 321–329.

Osuntogun, B. A., Adewusi, S. R. A., Ogundiwin, J. O. & Nwasike, C. C. 1989. “Effect of cultivar, steeping, and malting on tannin, total polyphenol, and cyanide content of Nigerian sorghum”. Cereal chemistry, 66 (2): 87–89.

Received: November 25, 2015
Accepted: January 10, 2016

Janhad L. Rodríguez, Universidad Central “Marta Abreu” de Las Villas (UCLV), Departamento de Medicina Veterinaria y Zootecnia, Carretera a Camajuaní, km 5.5. Santa Clara, Villa Clara. Cuba. Email: raciello@uclv.edu.cu