Methodological challenges in carbohydrate analyses

Abstract

Carbohydrates can provide up to 80% of the dry matter in animal diets, yet their specific evaluation for research and diet formulation is only now becoming a focus in the animal sciences. Partitioning of dietary carbohydrates for nutritional purposes should reflect differences in digestion and fermentation characteristics and effects on animal performance. Key challenges to designating nutritionally important carbohydrate fractions include classifying the carbohydrates in terms of nutritional characteristics, and selecting analytical methods that describe the desired fraction. The relative lack of information on digestion characteristics of various carbohydrates and their interactions with other fractions in diets means that fractions will not soon be perfectly established. Developing a system of carbohydrate analysis that could be used across animal species could enhance the utility of analyses and amount of data we can obtain on dietary effects of carbohydrates. Based on quantities present in diets and apparent effects on animal performance, some nutritionally important classes of carbohydrates that may be valuable to measure include sugars, starch, fructans, insoluble fiber, and soluble fiber. Essential to selection of methods for these fractions is agreement on precisely what carbohydrates should be included in each. Each of these fractions has analyses that could potentially be used to measure them, but most of the available methods have weaknesses that must be evaluated to see if they are fatal and the assay is unusable, or if the assay still may be made workable. Factors we must consider as we seek to analyze carbohydrates to describe diets: Does the assay accurately measure the desired fraction? Is the assay for research, regulatory, or field use (affects considerations of acceptable costs and throughput)? What are acceptable accuracy and variability of measures? Is the assay robust (enhances accuracy of values)? For some carbohydrates, we may have to accept that there are currently no acceptable, widely applicable analyses that meet these criteria, and seek to fill this analytical gap. Overall, there are good possibilities for accomplishing the nutritional partitioning of carbohydrates. But to ensure that this is done well, as a discipline, we need to continue our discussions on the basis for partitioning, on what fractions are actually significant, and rigorously evaluate proposed analyses to verify that they are analytically sound

Simulation of variations in the composition of samples in the evaluation of neutral detergent fiber contents by using cellulose standard in filter bags made from different textiles

“…The positive biases of NDF are explained by the fact that starch can gelatinize when exposed to temperatures of 90 to 100ºC (Hall, 2007), which hampers its removal during (Mertens, 2002) and avoids overestimation of NDF content (Faithfull, 2002). It was not observed effects of pectin levels or interaction of pectin levels and textiles on recovery bias of NDF (P>0.01) in the second experiment.…”

Utilização de enzimas industriais na avaliação da fibra insolúvel em detergente neutro em amostras com alto teor de amido

“…Por outro lado, nas análises empíricas o método empregado define o material medido, que é o caso da FDN. Para adoção das análises empíricas é essencial que o método estabelecido seja seguido precisamente ou os resultados não descreverão o que se pretende medir (HALL, 2007).…”

“…A contaminação por amido ocorre devido à sua gelatinização em meio neutro em temperaturas de 90 a 100°C (HALL, 2007), as quais são atingidas na avaliação de FDN. Com a gelatinização, o amido precipita em conjunto com os componentes da FDN, sendo erroneamente contabilizado como fibra ROBERTSON;LEWIS, 1991;VALENTE et al, 2011a).…”

“…Entretanto, a sua aplicação a outros tipos de matrizes orgânicas não fibrosas está associada a alguns problemas analíticos. De forma particular, a limitação do sistema detergente na avaliação da fibra insolúvel em detergente neutro (FDN) em alimentos com elevado teor de amido está associada à dificuldade de filtração devido à concentração de amido em si, o qual pode se exceder em relação à capacidade do detergente em solubilizar a amostra (MASCARENHAS-FERREIRA; KERTENS; GAST, 1983) ou precipitar por gelatinização, promovendo superestimação da concentração de fibra insolúvel (HALL, 2007;VALENTE et al, 2011a).…”

Fractions of carbohydrates and of nitrogenous compounds of tropical grasses at different cutting ages

“…Recently, in addition to the values of chemical composition, it has been used the proportions of the fractions potentially digestible of carbohydrates and the nitrogenous compounds (Hall, 2007).…”