Starch Digestion Kinetics Research Articles

Effects of tea polyphenols and gluten addition on in vitro wheat starch digestion properties

Starch-containing food normally has complex components and structure, which control its digestion kinetic properties and nutritional value. However, interactions among multiple food components and their effects on starch digestion kinetics are rarely reported. Here, we evaluated the influence of tea polyphenols [i.e., (-)-epigallocatechin (EGC) and (-)‑epigallocatechin‑3‑gallate (EGCG)] on the in vitro digestion rate and extent of wheat starch in the presence of gluten under uncooked and cooked conditions. The addition of EGC (20%, starch basis) did not change the starch digestion rate and extent for both uncooked and cooked physical forms in the presence and absence of gluten, whereas EGCG (20%, starch basis) significantly reduced the digestion extent of wheat starch by 25–30% in the absence of gluten and by 6.6–18.5% in the presence of gluten, a phenomenon that was caused by the reduced effective EGCG due to its interaction with gluten.

Amylopectin structure and crystallinity explains variation in digestion kinetics of starches across botanic sources in an in vitro pig model

BackgroundStarch is the main source of energy in commonly used pig diets. Besides effects related to the extent of starch digestion, also several effects related to variation in digestion rate have recently been demonstrated in non-ruminants. Different rates of starch digestion in animals and in in vitro models have been reported, depending on the botanic origin of starch. Starches from different botanic sources differ widely in structural and molecular properties. Predicting the effect of starch properties on in vitro digestion kinetics based on existing literature is hampered by incomplete characterization of the starches, or by a selective choice of starches from a limited number of botanic sources. This research aimed to analyse the relationships between starch properties and in vitro digestion kinetics of pure starches isolated from a broad range of botanic origins, which are used in non-ruminant diets or have a potential to be used in the future. Therefore we studied starch digestion kinetics of potato, pea, corn, rice, barley, and wheat starches, and analysed the granule diameter, number of pores, type and amount of crystalline structure, amylose content and amylopectin side-chain length of all starches.ResultsMultivariate analysis revealed strong correlations among starch properties, leading us to conclude that effects of most starch characteristics are strongly interrelated. Across all analysed botanic sources, crystalline type and amylopectin chain length showed the strongest correlation with in vitro digestion kinetics. Increased percentages of A–type crystalline structure and amylopectin side chains of DP 6–24 both increased the rate of digestion. In addition, within, but not across, (clusters of) botanic sources, a decrease in amylose content and increase in number of pores correlated positively with digestion kinetics.ConclusionThe type of crystalline structure and amylopectin chain length distribution of starch correlate significantly with digestion kinetics of starches across botanic sources in an in vitro pig model. Variation in digestion kinetics across botanic sources is not additively explained by other starch properties measured, but appears to be confined within botanical sources.

Surface structural features control in vitro digestion kinetics of bean starches

Although many studies have investigated the enzyme susceptibility of bean starches, the factors that reduce the lower hydrolysis of bean starch are not well understood. In the present study, we isolated starches from eight commercial bean varieties and established a causal relationship between micro and macro-structure with α-amylase susceptibility. The in vitro starch digestion kinetic profiles were monitored at a fixed enzyme concentration, and the data were fitted into the Logarithm of Slope model to obtain first-order rate coefficients and extent of digestion. Among eight varieties, pinto bean starch showed the lowest digestion rate (0.0013 min−1) and extent (40.7%), whereas red kidney bean starch has the highest rate (0.0042min−1) and extent (69.2%). In order to probe the interdependability of digestion kinetic parameters with starch microstructure, the enzyme binding capacity, molecular size, crystalline structure as well as thermal parameters of eight bean starches were correlated as Pearson's matrix. Whilst, significant correlation was not observed between digestion rate/extent and the structural parameters, the residual enzyme activity after binding with starch granules at non-hydrolyzing condition had significant negative correlation with the digestion rate and extent. Similarly, positive correlation was observed for degree of starch damage and enzyme susceptibility. Thus, it is concluded that for bean starches with similar biological origins, the available sites for initial binding of enzymes predominates the succeeding catalysis rate.

Improved methodology for analyzing relations between starch digestion kinetics and molecular structure

A new combined methodology for obtaining relations between starch molecular structure and digestion kinetics of starch-based foods is illustrated using published data on cooked rice. Digestibility data are treated with the logarithm of slopes method, giving region(s) where first-order loss kinetics are applicable; accurate values for the rate parameters are obtained by non-linear least-squares. A new method is developed to find independent structural variables for whole and enzymatically-debranched starches. Chain-length distributions of amylose and amylopectin are fitted with models using biologically-meaningful parameters, including accounting for SEC band broadening. While slower digestion rate usually means higher residual starch, this is not always so; both digestion parameters must be considered separately. The treatment shows that digestion kinetics depend on amylose content and also amylose molecular fine structure: the amount of shorter amylose chains and total amylose molecular size. The new combined data-treatment methodology is applicable to a wide range of food systems.

Modulation of Carbohydrate Digestibility of North Indian Parotta Using Protein and Dietary Fiber Based Functional Ingredients

Diet is the cornerstone in the management of hyperglycemia. Indian diets are predominantly cereal based providing a higher proportion of carbohydrate. Hence whole wheat flour (staple cereal) is substituted with a blend of 20–30% of chickpea flour, psyllium husk, fenugreek seed powder (CPF) for increasing the protein and dietary fiber contents. The effects of CPF on the rheological characteristics of whole wheat flour; physico‐chemical, sensory characteristics, and carbohydrate digestive profile of north Indian parotta (NIP) are studied. The results show an increase in the farinograph water absorption; extensograph resistance to extension; amylograph pasting temperature, peak viscosity, and a decrease in the extensograph extensibility. The overall quality score of NIP increases from 50 to 54, from a maximum score of 60 with an addition of 25% CPF of and decreased to 40 for 30% CPF content. Hence NIP with 25% CPF is selected for determinations of protein, dietary fiber, carbohydrate digestibility, kinetics of starch digestion in comparison with control NIP. The NIP with 25% CPF shows higher protein, dietary fiber, slowly available glucose, resistant starch, and lower rapidly available glucose than the control NIP. The differences in the digestibility profile are found to be statistically significant. The rate of starch hydrolysis and kinetics further confirmed the reduced glucose release of the NIP with 25% CPF. The predicted glycemic index of the NIP with 25% CPF is found to be “low.”

In vitro digestion properties of native isolated starches from Mexican blue maize (Zea mays L.) landrace

Mexican blue maize (Zea mays L.) grains have been scantily appraised concerning their impact on human health, as dietary carbohydrates. The purpose of this study was to investigate the in-vitro digestion properties of wet-milled blue native maize starches obtained from an array of fifteen Mexican genotypes Elotero Sinaloa landrace. The total starch, amylose content and resistant starch in the blue raw maize starches varied from 99.32 to 99.60%, 16.49–26.50% and 0.44–2.85%, respectively. The modified first-order model adequately predicted the kinetics of starch digestion. Although native starches from blue maize were digested almost entirely (>97%), considerable variability was observed in the rates of hydrolysis (K), which ranged from 0.0020 to 0.0047 min−1. The blue raw maize starches had low hydrolysis index (HI) and average glycemic index (GHAVG), which varied from 13.84 to 20.29% and 48.00–52.36%, respectively. Overall, the results suggest that native starches of the collection of Mexican blue maize could be valuable information for the development of functional food, particularly when slow or minimum starch digestion is highly desired.

Process-induced cell wall permeability modulates the in vitro starch digestion kinetics of common bean cotyledon cells.

The presence of cell walls entrapping starch granules in common bean cotyledons, prevailing after thermal processing and mechanical disintegration, has been identified as the main reason for their (s)low in vitro starch digestibility. Nevertheless, it is unknown if the role of cell walls on starch digestion changes as processing conditions (e.g. time) are modified. In this study, it was hypothesised that cell wall permeability would be differently affected depending on thermal process intensity, giving origin to distinct in vitro starch digestion kinetic profiles. Cotyledon cells were isolated from common beans by applying processing conditions normally found at the household level (95 °C and times between 30 and 180 min (palatable range)). Isolated cells were characterised and subsequently subjected to in vitro simulated digestion. Microstructural properties, the starch gelatinisation degree, and the total starch content were similar among samples. In contrast, a higher diffusion of fluorescently labelled pancreatic α-amylase inside the cells was evident as processing time increased. From the kinetic analysis of digestion products, it was determined that longer lag phases and slower reaction rate constants were present in samples with a lower degree of process-induced cell wall permeability. The qualitative analysis of the remaining pellets showed that cellular integrity was maintained throughout in vitro digestion. A mechanism for the in vitro starch digestion of isolated common bean cotyledon cells as well as an alternative kinetic model to describe this process were proposed. Overall, our work demonstrated that the in vitro starch digestion kinetics of common bean cotyledon cells can be modulated by influencing cell wall permeability through thermal processing time.

A comparison of the kinetics of in vitro starch digestion in smooth and wrinkled peas by porcine pancreatic alpha-amylase

This study describes the impact of crop genetics and processing in two pea lines (Pisum sativum L.) on starch digestion kinetics. Mutation at the rugosus (r) locus leads to wrinkled pea seeds, a reduction in starch content and a lower extent of in vitro starch digestibility. The Logarithm of Slope (LOS) kinetic model was used to analyse digestion curves obtained using porcine pancreatic α-amylase for a range of particle size fractions. Changes in starch structure induced by the r mutation led to clear differences in starch digestion kinetics for purified starches and pea flours. Larger particle size fractions showed slower starch digestion relative to the purified starch, but significant differences still existed between r and wild type pea lines. It is expected that this work will help inform the design of future studies where both starch structure and food structure are important determinants of digestion behaviour.

Impact of resistant vs. digested starch on starch energy value in the pig gut

A major energy substrate for monogastric species such as humans and swine is starch from cereal grains, pulses and tubers. The rate, site and extent of starch digestion in the gastro-intestinal tract are dependent on the intrinsic factors of starch origin and the extrinsic factors such as applied processing methods. In monogastric species, starch escaping small intestinal digestion becomes readily available for microbial fermentation in the hindgut and has been coined resistant starch (RS) accordingly. Host physiological and metabolic responses differ according to the site and rate of starch digestion; however, the quantity of energy derived to the host from fermented vs. digested starch remains debated. A detailed understanding of the underlying mechanisms that cause nutrient flow and substrate availability in the hindgut to alter host energy metabolism and growth potential is lacking. Dietary RS may in fact have nearly equal energetic efficiency as digested starch due adequate provision of short chain fatty acids (SCFAs) and decreased energy loss due to decreased activity. Thus, proper characterization of the energetic efficiency of purified and whole grain starch sources is required for accurate diet formulation. This review will focus on how various methodologies can be used to quantify site, extent and kinetics of starch digestion, illustrating the differences in energetic efficiency between RS vs. digested starch.

Technological properties, in vitro starch digestibility and in vivo glycaemic index of bread containing crude malva nut gum

SummaryThe effects of crude malva nut gum (CMG) on the texture, digestion and the glycaemic index (GI) of white bread were investigated. Different CMG levels (0%, 2.5%, 5%, 7.5% and 10% w/w based on weight of flour) were added into a bread formula. The lightness (L*) and loaf‐specific volumes of the bread decreased with increased CMG levels. Firmness of the bread increased with increased CMG content. The in vitro starch digestion kinetics showed that bread containing CMG had generally lower predicted GI (74–81 vs. the control). In vivo human testing showed that increasing the CMG reduced the GI of the bread. The GI values of bread containing CMG ranged from 73 to 98 of the control. Overall liking scores of consumers ranged between ‘like slightly’ and ‘like moderately’ (6.1–7.1) compared to 7.1 for the control. Thus, the addition of CMG in carbohydrate‐based foods may lower the GI.

Effect of interactions between starch and chitosan on waxy maize starch physicochemical and digestion properties

ABSTRACTPhysicochemical and digestion properties of chitosan modified starch prepared by dry heat treatment were investigated. Starch granule aggregation occurred following the addition of chitosan and this trend was enhanced with increasing chitosan concentration. The size of chitosan modified starch particles was about six times of that of the native starch granules. Interactions between the hydroxyl groups of starch and the amino groups of chitosan was confirmed by Fourier transform infrared spectroscopy analysis. The disappearance of the trough in the Rapid Visco Analyzer profile indicated that the cross-links increased the starch shear resistance. The cross-links between starch and chitosan also reduced starch digestion rate compared to the control (p < 0.001), and this reduction was further enhanced with an increasing chitosan concentration. Additionally, the addition of chitosan altered starch digestion kinetics from one phase to two phases, implying that chitosan modification changed both starch structure and its digestion behaviors.

Effect of starch content and processing method on in situ ruminal and in vitro intestinal digestion of barley grain in beef heifers

Rate of barley starch digestion in the rumen is critical issue in high-grain fed beef cattle because it is associated with growth performance and health. The digestion rate of starch varies with variety, grain processing or starch content. The objectives of this study were to evaluate the effect of starch content and processing method of barley grain on in situ ruminal dry matter (DM) and starch digestion kinetics, and to develop a model to predict the rate of DM digestion of barley grain. The study was a 2×2 factorial arrangement of treatments: starch content (low vs. high) and processing method (PM; grinding vs. dry rolling). Ten barley samples with 5 low (571±17g/kg) and 5 high (660±7g/kg DM) starch were either ground 2mm or dry-rolled with processing index (PI) of 0.75 (PI=bulk density processed/bulk density whole). Three beef heifers (650kg body weight) fitted with rumen cannulas and fed diet consisting (g/kg DM) of 700 barley silage and 300 barley grain were used for in situ incubation. In situ degradation kinetics of DM, starch, neutral detergent fibre (NDF) and crude protein (CP) were estimated after 0, 2, 4, 8, 12, 24, and 48h of ruminal incubation. Data from DM, starch, NDF and CP degradation at different times of incubation were fitted to a model y=a+b(1−e−c(t−L)). In vitro intestinal disappearances of DM, starch, NDF and CP of ruminal residue after 12h of incubation were determined using a modified three-step procedure. Interactions between starch content and PM on the degradation kinetic parameters of DM, starch, NDF and CP were seldom observed. High starch barley had greater (P<0.01) a and effective degradability (ED) of DM and starch, but it had less (P=0.03) b of starch versus low starch barley. Ground barley had greater (P<0.01) a, c and ED of DM and starch, and lower (P<0.01) b compared with dry-rolled barley. Intestinal disappearance DM and starch of rumen residues were affected by both starch content and PM. Starch content of barley grain and manipulating processing method could effectively alter rumen digestion of barley grain.

In vitro starch digestion kinetics of diets varying in resistant starch and arabinoxylan compared with in vivo portal appearance of glucose in pigs

The current study was undertaken to investigate the relationship between the in vitro starch digestion kinetics and the in vivo portal glucose appearance in pigs used as models for humans. In vivo data were obtained from a previous study where the portal glucose appearance was obtained from six catheterised pigs equipped with permanent catheters in an artery and the portal vein and with a flow probe attached to the portal vein for monitoring the blood flow rate. Three experimental diets were studied — a low dietary fibre (DF), western-style diet (WSD) and two high-DF diets containing resistant starch (RSD) or arabinoxylan (AXD). A modified Englyst-assay involving gradual glucose hydrolysis over a time frame of 6h was used in vitro. The in vitro starch digestion kinetics was modelled using a mechanistic growth model (R2>0.995), whereas the in vivo data were better described by a sigmoid Gompertz model (R2>0.997). The estimated plateau values were higher in vitro than in vivo but the diets were similarly ranked; ~95% for AXD and WSD and 81.8% for RSD in vitro and ~86% and 76.6% for the same diets in vivo. The rate of glucose release in vitro was much faster than the portal glucose appearance in vivo (0.0347–0.0705 versus 0.0136–0.0197%starch/min) with the starch in RSD being the most slowly degradable. This difference was most likely an effect of gastric retention. In conclusion, the in vitro method ranked the three diets in a similar relative manner as in vivo but the rate of glucose release was much faster in vitro than in vivo. It was only when the starch structure set the limit for the starch hydrolysis, however, that similar relative results were obtained.

Significance of thermal transitions on starch digestibility and firming kinetics of restricted water mixed flour bread matrices

The impact of wheat (WT) flour replacement up to 45% (weight basis) by incorporation of ternary blends of teff (T), green pea (GP) and buckwheat (BW) flours on the thermal profiles of quaternary blended dough matrices have been investigated by simulating baking, cooling, and storage in differential scanning calorimeter (DSC) pans. Endothermal transitions related to suitable patterns for low and slow starch hydrolysis, softer crumb and retarded firming kinetics in blended breads include delayed temperatures for starch gelatinization, and for the dissociation of amylose–lipid complex. In addition, (a) higher stability for the amylose–lipid inclusion complex, (b) lower energy for starch gelatinization, (c) lower limiting melting enthalpy and (d) slower rate for amylopectin retrogradation meet thermal requirements for achieving suitable textural and starch digestibility features in blended breads, fulfilled by adding T/GP/BW to replace 45% of WT flour in blended dough formulations.

Influence of maize particle size on the kinetics of starch digestion in the small intestine of growing pigs

The kinetics of starch digestion in the small intestine, nutrient utilisation and the performance of growing pigs that were fed diets containing maize of different particle sizes were evaluated. For the performance evaluation, 42 barrows and females (initial weight: 30.5 ± 1.78 kg) were used in a randomised block design with three treatments [maize with different geometric mean diameters (GMD) of 550, 700 and 850 μm] and seven replications. To evaluate the kinetics of starch digestion, one animal from each experimental trial was sacrificed. The small intestine was removed and separated into five equal parts. The starch digestibility in each segment was determined. To determine the total digestibility and nitrogen balance, 24 barrows (initial weight: 41.3 ± 4.72 kg) were housed in metabolism cages in a randomised block design with three treatments and eight repetitions. The animals that were fed diets containing maize of 550-μm GMD exhibited better (P = 0.008) feed conversion. However, the digestion of starch was gradual and variable among the degrees of grinding that were tested. There were higher (P = 0.008; 0.005 and 0.009) digestible energy, dry matter digestibility and nitrogen uptake in diets containing the maize ground to 550 and 700 μm in GMD. Thus, the smallest GMD of maize (550 μm) that was used in diets for growing pigs improves feed conversion. GMD of 550, 700 and 850 μm of maize were associated with rapid, intermediate and slow starch digestion, respectively.

Graded inclusions of sodium metabisulphite in sorghum-based diets: II. Modification of starch pasting properties in vitro and beneficial impacts on starch digestion dynamics in broiler chickens

Seven sorghum-based broiler diets containing the reducing agent, sodium metabisulphite (SMBS) at levels of 0, 1.50, 2.25, 3.00, 3.75, 4.50 and 5.25g/kg were prepared. The in vitro starch pasting properties of the sorghum-based diets and starch extracted from the diets were assessed by rapid viscosity analysis (RVA). The seven dietary treatments were offered to 294 male Ross 308 chicks from 10 to 24 days post-hatch to determine SMBS effects on starch and nitrogen digestion dynamics. Digesta samples were collected, freeze-dried and weighed for determination of digestibility coefficients and mean retention times in the proximal jejunum, distal jejunum, proximal ileum and distal ileum. The digestion kinetics of starch and nitrogen (N) were determined using an exponential mathematical model to relate digestibility coefficients to mean retention times in each small intestinal segment. SMBS inclusions linearly reduced apparent starch digestibility coefficients in the proximal jejunum (r=−0.444, P<0.01), distal jejunum (r=−0.371, P=0.010) and predicted glycaemic responses (r=−0.474; P<0.001). SMBS linearly decreased (r=−0.413; P<0.01) starch disappearance from the proximal jejunum (abruptly digestible starch) and increased (r=0.483; P<0.001) starch disappearance from the three caudal small intestinal segments (gradually digestible starch). SMBS significantly (P<0.001) reduced final starch viscosity in diets from 2567 to 1935 cp and final extracted starch viscosity from 1035 to 441 cp. The SMBS-induced reductions in final viscosity of extracted starch were correlated with apparent metabolisable energy (AME) (r=−0.347; P<0.05), N-corrected AME (AMEn) (r=−0.376; P<0.01) and feed conversion ratio (FCR) (r=0.337; P<0.05). Also, gradually digestible starch was correlated (r=−0.291, P<0.05) with FCR improvements and abruptly digestible starch was negatively correlated (r=−0.282; P<0.05) with AMEn. It appears that the previously reported positive responses in AME, AMEn and FCR generated by SMBS stem from reductions in final starch viscosity that are probably attributable to SMBS-induced oxidative–reductive depolymerisation of starch polysaccharides. The small intestinal sites of starch digestion (and glucose absorption) were altered with higher levels of gradually digestible starch disappearing from the distal jejunum, proximal and distal ileum. Consideration is given to the possible mechanisms whereby SMBS generated more gradually digestible starch and how gradually digestible starch enhanced energy utilisation and efficiency of feed conversion.

Esterification of high amylose starch with short chain fatty acids modulates degradation by Bifidobacterium spp.

Large bowel luminal short chain fatty acids (SCFA) are protective against gut diseases such as colorectal cancer, Crohn’s disease and ulcerative colitis. High amylose maize starches acylated with acetic, propionic or butyric were previously shown to deliver SCFA to the gut and increase gut SCFA. This study examines the ability of five Bifidobacterium spp. (B. longum, B. breve, B. infantis, B. adolescentis and B. bifidum), Ruminococcus bromii and Faecalibacterium prausnitzii to degrade starches acylated with SCFA. Release of SCFA from modified starches was not observed, suggesting no preferential hydrolysis of the SCFA ester bond over the glycosidic bond. Acetylated and propionated starches are more readily degraded than either the base or butyrated starches in tested cultures. These observed differences may depend on modification to the starch structure. These structural differences alter the kinetics of starch digestion, irrespective of bacterial type, which may impact current approaches of prebiotic selection.

Influence of white- and red-sorghum varieties and hydrothermal component of steam-pelleting on digestibility coefficients of amino acids and kinetics of amino acids, nitrogen and starch digestion in diets for broiler chickens

Two experiments were conducted to examine the influence of sorghum variety and the hydrothermal component of steam-pelleting diets on apparent amino acid digestibility coefficients and digestion kinetics of amino acids, nitrogen and starch in broiler chickens. In experiment one, 84 male Ross 308 chicks were offered steam-pelleted diets based on white (Liberty) and red (Buster) sorghum from 7 to 28 days post-hatch. In experiment two, the same red sorghum-based diets were offered to chicks from 7 to 28 days post-hatch as either unprocessed raw mash or reground mash following steam-pelleting at 95°C. In both experiments, digesta samples from proximal jejunum, distal jejunum, proximal ileum and distal ileum were collected in their entirety at day 28. The samples were then freeze-dried and weighed for determination of mean retention time in each small intestinal segment. The digestion kinetics of amino acids, nitrogen and starch were determined using an exponential mathematical model to relate apparent digestibility coefficients with mean retention times in each small intestinal segment. In experiment one, white sorghum-based diets had significantly higher average amino acid digestibility coefficients than red sorghum in the proximal ileum and distal ileum (P<0.05). Nine from sixteen amino acids in white sorghum-based diets had significantly higher apparent digestibility coefficients in the proximal ileum and distal ileum. The potential digestible fraction of starch and rate of starch digestion in white sorghum-based diet were significantly higher than red sorghum (P<0.05). However, there were no significant differences in digestion rates of nitrogen and amino acids. However, pre-determined feed conversion ratios were strongly correlated with potential digestible starch (r=−0.840, P<0.001). The differences in white and red sorghum-based diets were more pronounced in starch digestion than nitrogen digestion and further research is required to identify the precise causes of deficient starch digestion in red sorghum. In experiment two, the hydrothermal component of the steam-pelleting process had a negligible impact on digestion of amino acids as there were no significant differences in the extent or rate of amino acid digestion in raw mash and reground mash diets. Therefore, the linear increases of amino acid digestibilities with increased conditioning temperatures observed in a previous study may be attributed to the feed form effect of intact pellets generating heavier relative gizzard weights; thereby enhancing the overall protein digestive process.

In vitro Starch Digestibility and Nutritional Composition of Improved Rice Varieties from Cameroun

Aims: Resistant starch (RS), kinetics of starch digestion, predicted glycemic index (pGI) and nutritional composition were determined in two improved rice varieties from Cameroun. Place and Duration of Study: Department of Bioresource Engineering, McGill University, Canada between December 2012 and March 2013. Methodology: Non-parboiled and parboiled samples of TOX 3145 and NERICA-3 varieties were involved in this study. An in vitro enzymatic starch digestion method was applied to measure starch digestibility parameters. Standardized methods were adopted for proximate and mineral contents evaluation. Results: The parboiled samples had significantly higher (P<0.05) resistant starch (8.35 11.07%) than the non-parboiled samples (3.81 4.84%). The values for pGI among Original Research Article European Journal of Nutrition & Food Safety, 3(4): 134-145,, 2013 135 samples ranged from 57.57 to 67.78%. Significantly higher values for protein, phosphorus and potassium were found among the parboiled samples (P<0.05). Nutritional composition was positively related to RS while pGI had inverse relationship with protein, ash, fat, phosphorus, potassium and RS. Conclusion: Starch digestibility of these rice varieties was associated to their nutritional composition.

The kinetics of starch and nitrogen digestion regulate growth performance and nutrient utilisation of broilers fed coarsely ground, sorghum-based diets

A study was conducted to examine the effect of starch and nitrogen digestion kinetics on broiler performance using sorghum-based diets as a model. Three sorghum varieties with red, white and yellow pericarps and three feed forms, mash, intact pellets and reground pellets, constituted a 3 × 3 factorial array of dietary treatments. Starch and nitrogen digestion kinetics were determined using an exponential mathematical model to relate digestion coefficients in the proximal jejunum, proximal ileum and distal ileum with mean retention times in each segment. There were interactions between sorghum variety and feed form for starch and nitrogen digestion kinetics. Steam-pelleting at a conditioning temperature of 90°C (unprocessed mash versus reground pellets) substantially influenced starch digestion rate in red and yellow sorghum-based diets, but not in white sorghum-based diets. Alternatively, with nitrogen digestion rate, there were no significant differences in yellow sorghum-based diets between feed forms but there were in red and white sorghum-based diets. The digestion rate of starch was more rapid than nitrogen, especially in the proximal jejunum. Starch digestion rates were significantly correlated with nitrogen retention but this was not the case with nitrogen digestion rates. The rate of glucose absorption from predicted glycaemic indices was highly correlated with enhanced feed efficiency. Thus this study demonstrates that even under ad libitum feeding regimes, kinetics of starch and protein digestion regulated feed efficiency and nitrogen retention in broiler chickens. The dynamics of starch and protein digestion were more accurate indicators of feed efficiency and nitrogen retention than apparent ileal starch and nitrogen digestibility.