The action of endo-xylanase and endo-glucanase on cereal cell wall polysaccharides and its implications for starch digestion kinetics in an in vitro poultry model

Endo-xylanase and endo-glucanase are supplemented to poultry diets in order to improve nutrient digestion and non-starch polysaccharide (NSP) fermentation. Here, the action of these enzymes on alcohol insoluble solids (AIS) from wheat and maize grains as well as its implications for starch digestion in milled grains were evaluated in vitro, under conditions mimicking the poultry digestive tract. For wheat AIS, GH11 endo-xylanase depolymerized soluble arabinoxylan (AX) during the gizzard phase, and proceeded to release insoluble AX under small intestine conditions. At the end of the in vitro digestion (480 min), the endo-xylanase, combined with a GH7 endo-β-1,4-glucanase, released 30.5 % of total AX and 18.1 % of total glucan in the form of arabinoxylo- and gluco-oligosaccharides, as detected by HPAEC-PAD and MALDI-TOF-MS. For maize AIS, the combined enzyme action released 2.2 % and 7.0 % of total AX and glucan, respectively. Analogous in vitro digestion experiments of whole grains demonstrated that the enzymatic release of oligomers coincided with altered grain microstructure, as examined by SEM. In the present study, cell wall hydrolysis did not affect in vitro starch digestion kinetics for cereal grains. This study contributes to understanding the action of feed enzymes on cereal NSP under conditions mimicking the poultry digestive tract.

Understanding how different modification processes affect the physiochemical, functional, thermal, morphological structures and digestibility of cardaba banana starch

In this study, starch was isolated from cardaba banana starch and was subjected to modification by heat-moisture treatment, citric acid, octenyl succinic anhydride, and sodium hexametaphosphate. Both the native and modified cardaba banana starches were examined for chemical, functional, pasting, thermal, morphological, structural, and antioxidant properties, as well as in vitro starch digestibility. Modification significantly influenced the properties of the cardaba banana starch. Cross-linking treatment improved the water, oil absorption, alkaline hydration capacity, swelling power, solubility and paste clarity of the starch. The final viscosity of the banana starch paste was increased alongside succinic anhydride modification which in turn enhanced the suitability of the starch in the production of high viscous products. Both FTIR spectra and X-ray diffractograms confirmed the starch had a C-type starch which was not affected by modification. Modification led to a decrease in relative crystallinity of the starch with succinylation having the maximum effect. The starch fractions; both SDS and RS significantly increased due to modification while the hydrolysis and glycemic index of the starch were significantly decreased by chemical modification. In conclusion, both physical and chemical modification of cardaba banana starch produced a starch that can serve as functional food or functional food ingredients.

Texture and interlinked post-process microstructures determine the in vitro starch digestibility of Bambara groundnuts with distinct hard-to-cook levels

Particular storage conditions are described to promote the development of the hard-to-cook (HTC) phenomenon for most legumes. However, it is not clearly established whether the HTC phenomenon influences starch digestion kinetics. Therefore, this study explored how the HTC phenomenon influences in vitro starch digestion of Bambara groundnuts, taking into account three distinct HTC levels. Stored Bambara groundnuts required prolonged cooking times. Increasing storage time led to a decrease in the rate constant of texture degradation, signifying the development of the HTC phenomenon. For cooking times of 60 min and 120 min, high HTC level samples exhibited higher rate constants and extents of starch digestion compared to the fresh sample. The higher rate of digestion was attributed to the high hardness that resulted in greater cell rupture and faster access of amylase to starch. Adapting cooking times of Bambara groundnuts with distinct HTC levels to obtain equivalent hardness values and microstructures resulted in comparable starch digestion kinetics. Spectrophotometric analysis overestimated the amount of digested starch, in contrast to the more accurate HPLC analysis, which further provided more insight by quantifying multiple digestion products. This work demonstrates that it is the hardness and interlinked pattern of cell failure (microstructure) that determines starch digestion of Bambara groundnuts with distinct HTC levels.