Stage of lactation and corresponding diets affect in situ protein degradation by dairy cows.

The influence of stage of lactation and corresponding diets on rates of protein degradation (kd) is largely unstudied. Study objectives were to measure and compare in situ ruminal kd of crude protein (CP) and estimate rumen CP escape (rumen-undegradable protein; RUP) of selected feeds by cows at 3 stages of lactation fed corresponding diets, and to determine the incubation times needed in an enzymatic in vitro procedure, using 0.2 units of Streptomyces griseus protease per percent of true CP, that predicted in situ RUP. Residue CP was measured after in situ fermentation for 4, 8, 12, 24, 36, 48, and 72 h of 5 protein sources and 3 total mixed rations, which were fed to the in situ cows. Two nonlactating (dry) cows and 2 cows each at 190 (mid) and 90 (peak) days of lactation were used. Each pair of cows was offered free-choice diets that differed in composition to meet their corresponding nutrient requirements. Diets had decreasing proportions of forages and contained (dry matter basis) 11.9, 15.1 and 16.4% CP and 54.3, 40.3 and 35.3% neutral detergent fiber, for dry, mid, and peak TMR (TMR1, TMR2, and TMR3), respectively. Intakes were 10.3, 21.4, and 23.8kg of dry matter/d, respectively. Kinetic CP fractions (extractable, potentially degradable, undegradable, or slowly degradable) were unaffected by treatment. Lag time and kd varied among feeds. The kd was faster for all feeds (0.136/h) when incubated in dry-TMR1 cows compared with mid-TMR2 (0.097/h) or peak-TMR3 (0.098/h) cows, and no differences in lag time were detected. Calculated RUP, using estimated passage rates for each cow based on intake, differed between dry-TMR1 (0.382) and mid-TMR2 (0.559) or peak-TMR3 (0.626) cows, with a tendency for mid-TMR2 to be different from peak-TMR3. Using the average kd and lag time obtained from dry-TMR1 to calculate RUP for mid-TMR2 and peak-TMR3 cows using their passage rates reduced RUP values by 6.3 and 9.5 percentage units, respectively. Except for that of herring meal, in vitro residue CP at 6, 12, and 48h of enzymatic hydrolysis was correlated (r=0.90) with in situ RUP of peak-TMR3, mid-TMR2, and dry-TMR1, respectively. Although confounded within treatments, stage of lactation, diet, and intake appeared to affect CP degradation parameters and RUP. Using kd from nonlactating cows, or the RUP calculated from them, may bias diet evaluation or ration formulation for lactating cows. In addition, enzymatic in vitro predictions of RUP should be measured using incubation times that are appropriate for lactating cows.

Composition and aroma compounds of Ragusano cheese: native pasture and total mixed rations.

Raw milk from 13 cows fed TMR supplemented with native pasture and from 13 cows fed only TMR on one farm was collected separately 4 times with an interval of 15 d between collections. Two blocks (14 kg each) of cheese were made from each milk. The objective was to determine the influence of consumption of native plants in Sicilian pastures on the aroma compounds present in Ragusano cheese. Milk from cows that consumed native pasture plants produced cheeses with more odor-active compounds. In 4-mo-old cheese made from milk of pasture-fed cows, 27 odor-active compounds were identified, whereas only 13 were detected in cheese made from milk of total mixed ration-fed cows. The pasture cheeses were much more rich in odor-active aldehyde, ester, and terpenoid compounds than cheeses from cows fed only total mixed ration. A total of 8 unique aroma-active compounds (i.e., not reported in other cheeses evaluated by gas chromatography olfactory) were detected in Ragusano cheese made from milk from cows consuming native Sicilian pasture plants. These compounds were 2 aldehydes ([E,E]-2,4-octadienal and dodecanal), 2 esters (geranyl acetate and [E]-methyl jasmonate), 1 sulfur compound (methionol), and 3 terpenoid compounds (1-carvone, L(-) carvone, and citronellol). Geranyl acetate and (E)-methyl jasmonate were particularly interesting because these compounds are released from fresh plants as they are being damaged and are part of a possible plant defense mechanism against damage from insects. Most of the odor-active compounds that were unique in Ragusano cheese from pasture-fed cows appeared to be compounds created by oxidation processes in the plants that may have occurred during foraging and ingestion by the cow. Some odor-active compounds were consistently present in pasture cheeses that were not detected in the total mixed ration cheeses or in the 14 species of pasture plants analyzed. Either these compounds were present in other plants not analyzed, created in the rumen or in cheese after the pasture-plant material had been consumed, or the compounds were lost in the method of sample extraction used for the plant analysis (i.e., steam distillation) versus the solid-phase microextraction method used for the cheeses. This research has demonstrated clearly that some unique odor-active compounds found in pasture plants can be transferred to the cheese.

A mechanistic model for predicting the nutrient requirements and feed biological values for sheep.

The Cornell Net Carbohydrate and Protein System (CNCPS), a mechanistic model that predicts nutrient requirements and biological values of feeds for cattle, was modified for use with sheep. Published equations were added for predicting the energy and protein requirements of sheep, with a special emphasis on dairy sheep, whose specific needs are not considered by most sheep-feeding systems. The CNCPS for cattle equations that are used to predict the supply of nutrients from each feed were modified to include new solid and liquid ruminal passage rates for sheep, and revised equations were inserted to predict metabolic fecal N. Equations were added to predict fluxes in body energy and protein reserves from BW and condition score. When evaluated with data from seven published studies (19 treatments), for which the CNCPS for sheep predicted positive ruminal N balance, the CNCPS for sheep predicted OM digestibility, which is used to predict feed ME values, with no mean bias (1.1 g/100 g of OM; P > 0.10) and a low root mean squared prediction error (RMSPE; 3.6 g/100 g of OM). Crude protein digestibility, which is used to predict N excretion, was evaluated with eight published studies (23 treatments). The model predicted CP digestibility with no mean bias (-1.9 g/100 g of CP; P > 0.10) but with a large RMSPE (7.2 g/100 g of CP). Evaluation with a data set of published studies in which the CNCPS for sheep predicted negative ruminal N balance indicated that the model tended to underpredict OM digestibility (mean bias of -3.3 g/100 g of OM, P > 0.10; RMSPE = 6.5 g/100 g of OM; n = 12) and to overpredict CP digestibility (mean bias of 2.7 g/100 g of CP, P > 0.10; RMSPE = 12.8 g/100 g of CP; n = 7). The ability of the CNCPS for sheep to predict gains and losses in shrunk BW was evaluated using data from six studies with adult sheep (13 treatments with lactating ewes and 16 with dry ewes). It accurately predicted variations in shrunk BW when diets had positive N balance (mean bias of 5.8 g/d; P > 0.10; RMSPE of 30.0 g/d; n = 15), whereas it markedly overpredicted the variations in shrunk BW when ruminal balance was negative (mean bias of 53.4 g/d, P < 0.05; RMSPE = 84.1 g/d; n = 14). These evaluations indicated that the Cornell Net Carbohydrate and Protein System for Sheep can be used to predict energy and protein requirements, feed biological values, and BW gains and losses in adult sheep.

Contribution of native pasture to the sensory properties of Ragusano cheese.

Ragusano is a Protected Denomination of Origin cheese produced in the Hyblean area of Sicily. Sixteen samples of Ragusano cheese from two different treatments [pasture and total mixed ration (TMR)] were evaluated after 4 and 7 mo of aging. The color of the cheeses produced from milk of cows consuming fresh native pasture plants was much more yellow than cheeses from TMR fed cows (i.e., higher Hunter b value). This was due to transfer of beta-carotene and related compounds from the diet and demonstrated that compounds from native pasture plants changed the sensory characteristics of Ragusano cheese. To avoid a "halo" effect in a trained panel, quantitative descriptive analysis sensory evaluation of these cheeses for odor, taste, consistency, and mouth structure, color differences among cheeses were masked. A unique approach in sensory analysis was developed using sunglasses with lenses designed to block light at the specific wavelengths at which panelists would detect differences in color among samples. Testing was conducted every 2-wk period (15-d increments) with two tests per week using 11 trained panelists. All the panelists tasted all the products. Panelists were able to detect significant differences in the sensory characteristics of cheeses produced from milk of cows consuming native pastures versus TMR even when the color difference was masked.

Assessment of the dairy production needs of cattle owners in southeastern Sicily.

This study was undertaken to investigate research and outreach priorities for Progetto Ibleo (Project Ibleo), a center created in 1990 with tripartite government funding to serve dairy producers in the Hyblean region of Sicily. Data comprised values for production and composition of milk from 1984 to 1989 from 35 herds of Modicana cows on a system based on pasture and that from 69 input-intensive herds of Holstein cows, associated lactation and reproduction measures, and yield and composition of forages from 4 of these farms in 1988. Season had a large effect on the neutral detergent fiber and crude protein composition of forages, production and composition of milk, and predicted yield of fresh Ragusano cheese manufactured from the milk of these cows. The poorest forage quality and the poorest cow performance were observed in summer and fall months (May to October). Lactation curves that were flat, without a discernible peak, or convex were observed for both systems, especially for cows calving in spring and in the dry summer seasons (March to July). These abnormalities, signifying substantial sacrifices in production potential, probably had a complex etiology that stemmed from low nutrient intake and high neutral detergent fiber and low crude protein composition of the grazed and preserved forages. Research and outreach priorities to support the Hyblean dairy industry should include chemical evaluation of forages and other feedstuffs, low moisture ensiling of high quality winter forages, better formulation of diets that are dense with nutrients, and the shifting of calving patterns to better exploit high quality winter forages.

Predicting forage indigestible NDF from lignin concentration.

We used chemical composition and in vitro digestibility data from temperate and tropical forages to develop relationships between indices of lignification and forage indigestible NDF. Neutral detergent fiber indigestibility increased nonlinearly as the lignin concentration of the NDF increased. Differences in estimated indigestible NDF using equations developed for a specific forage class (C3 and C4 grasses and legumes) were small and are probably not biologically significant when compared to those estimated from a common equation. Selected equations were compared with the Cornell Net Carbohydrate and Protein System (CNCPS) for the prediction of ADG. The linear equation (2.4 times NDF lignin content) used by the CNCPS and the Beef NRC had some of the largest errors due to mean bias. A log-log model [4.37 x (lignin/NDF)(.84)] provided the best combination of low total prediction error, low mean bias, and minimal error due to regression bias when permanganate lignin was used. A similar equation based on sulfuric acid lignin [6.17 x (lignin/NDF)(.77)] also met the above criteria. These equations then were evaluated with the CNCPS model against animal growth data from diets ranging in forage quality. Regardless of the equation used for predicting unavailable fiber, the CNCPS underpredicted daily gain, with mean biases ranging from -.10 to -.22 kg/d. Regression bias ranged from .13 to .14 kg/d and the coefficients differed from unity (P = .0001). The new equations gave numerically lower energy allowable ADG by steers compared to the linear equation currently used by the CNCPS model. The estimates were lower due to a higher predicted indigestible NDF, which resulted in a lower estimated forage energy value.

Studies on the effects of selenium on rumen microbial fermentation in vitro.

The effects of selenium (Se) on ruminant microbial fermentation were investigated in vitro using rumen microflora collected from a rumen-fistulated dairy cow. First, the effects of L-selenomethionine (SeMet; at 0.2 or 2 ppm Se) in the presence or absence of wheat bran (WB, 500 mg per incubation flask) were evaluated. Second, the effects of several forms of Se (elemental Se: 50 ppm Se; sodium selenite: 2 ppm Se; SeMet: 2 ppm Se) were compared. Results showed that the amounts of short-chain fatty acids (SCFAs) tended to be increased by SeMet treatment, whereas SeMet in the presence of WB transiently suppressed fermentation. The addition of SeMet tended to increase the production of acetate while reducing the production of butyrate with the without WB supplementation. Among the different Se compounds tested, the amounts of SCFAs were greater with SeMet treatment, which yielded a higher proportion of acetate compared to other treatments. Selenite did not influence the total SCFAs concentrations; however, it increased the relative proportion of butyrate at the expense of acetate. Elemental Se did not significantly affect fermentation. Higher bacterial Se concentrations were observed for selenite than for SeMet. It was concluded that Se supplementation can influence rumen microbial fermentation and that Se compounds differ in this regard.

Prediction of ruminal volatile fatty acids and pH within the net carbohydrate and protein system.

A steady-state model of the production, absorption, passage, and concentration of ruminal VFA and pH is developed from published literature data and is structured to use the feed descriptions and inputs from the net carbohydrate and protein system. Included are the effects of pH on growth rate and yield of structural and non-structural carbohydrate-fermenting bacteria; production of acetate, propionate, butyrate, lactate, and methane; conversion of lactate to VFA; ruminal absorption of acids; and prediction of ruminal pH from dietary measures and from ruminal buffering and acidity. The root mean square error of predicted total VFA concentration was 12 mM. Individual VFA fractions were inadequately predicted. In a review of literature data, effective NDF (eNDF) provided a better correlation with ruminal pH than forage or NDF. Digestion rate of NDF remained at normal levels above pH 6.2, which corresponds to a minimum eNDF of 20% of dietary DM. Further research is needed to determine the individual VFA produced from carbohydrate fractions at various pH, the appropriateness of partitioning the starch and pectin carbohydrate pool into slowly and rapidly degraded fractions, and the effect on microbial yield, total tract digestibility, and predicted energy values of feeds.

Comparison of Landim and Africander cattle in southern Mozambique: I. Body weights and growth.

The growth performance of Landim and Africander breeds was compared using data collected from 1968 to 1981 at the Chobela Research Station in Mozambique. Animals from both breeds were managed together in groups by age and sex, except when separated for breeding. Growth traits were body weights at birth, weaning at 7 mo, 18 mo, and first calving, and pre- and postweaning daily growth rates. These traits were analyzed using a mixed-effects least squares model containing breed, year-season of birth, sex, the nested effect of parity within breed, a linear regression on dam's age, and the random effect of sire within breed. Africander calves were 16, 9, and 7% heavier (P < .01) than Landim calves at birth, weaning, and 18 mo (18 +/- 6 kg heavier than the 237-kg Landim average). However, there was no detectable difference for age-adjusted weight at first calving and postweaning daily growth rate. Diminishing weight and growth differences with advancing age may indicate adaptation by the Landim to the prevailing environmental limitations in southern Mozambique, especially through younger ages at puberty and at first calving.

Comparison of Landim and Africander cattle in southern Mozambique: II. Female fertility, reproduction, and beef offtake.

Fertility and reproductive performance of Landim and Africander females were compared using data collected from 1968 to 1981 at the Chobela Research Station in Mozambique. Breeds were managed together and grouped by age and sex, except when separated for breeding. Traits were relative fertility (probability of fertile females calving from the first breeding season), age at first calving, first calving interval, and subsequent calving intervals. calving rates were tested by x2 procedures with equal expected frequencies in each subclass. The statistical model included breed, the random effect of sire within breed, year-season of birth or calving, and calving group within breed. Landim survivors were more fertile (P < .05) than the Africander ones throughout their recorded lifetimes. Landim females were 1.32 +/- .21 mo (or 3%) younger at first calving and had a 48 +/- 12 d (or 11%) shorter interval between first and second calving than the Africander average of 473 d. When reproductive and growth information were combined to compute an annual index of beef offtake expressed as 18-mo calf yield per unit of dam's weight at first calving, Landim cows annually yielded 30% more calf weight (P < .001) than Africander cows per kilogram of their own body maintenance despite lighter body weights at 18 mo. Superior fertility of Landim females led to greater beef offtake from higher calving rates. Greater fertility and relatively less feed to maintain the reproducing herd are probable mechanisms for a population to adapt to nutrient-limiting environments such as the one in southern Mozambique.

Effect of increasing work rate on metabolic responses of the donkey (Equus asinus).

Oxygen consumption (VO2) and concentration of venous blood metabolites were measured in donkeys trained to run and to pull loads on a treadmill. VO2 in two donkeys running at maximal speed on a 9.8% slope was 110 +/- 2 ml.min-1.kg-1, approximately 22 times preexercise VO2. Average heart rate at maximal VO2 (VO2max) was 223 +/- 2 beats/min, five times the preexercise heart rate. Blood lactate increased 14-fold, and blood glucose did not change (P > 0.05). Animals running up a 4% incline and incremental draft loading of five donkeys walking on the level were also studied. The total energy cost of walking unloaded was 2.86 +/- 0.06 J.m-1.kg live wt-1. During low- to medium-intensity draft work for 25 min, glucose fell below preexercise values (P < 0.05), whereas plasma hematocrit and cortisol increased (P < 0.05). Blood lactate remained unchanged up to approximately 40% VO2 max but increased 170% at approximately 60% VO2max. The responses in donkeys are similar to those of exercising horses except for the rapid decline in blood glucose observed during low-intensity exercise and the lower lactate levels at both the high-intensity exercise and the apparent anaerobic threshold.

Economic comparison of nutritional management strategies for Venezuelan dual-purpose cattle systems.

Objectives of this study were to compare three nutritional management strategies for dual-purpose herds in Venezuela in 1987 using a deterministic, multiperiod linear programming model of a representative farm. The model maximized discounted net margin (total revenues minus variable costs) from the herd for a 3-yr cow replacement cycle partitioned into six periods. The periods accounted for seasonal variation in forage availability and quality, and the model provided information about optimal animal inventories, animal sales, land in forage, and feed supplements. We compared current nutritional management practices and alternatives allowing optimal supplementation with commercial concentrate, molasses, cassava root, and urea. Iteration between the programming model and results from the Cornell Net Carbohydrate and Protein System assured technical coefficients consistent with predicted animal performance. Compared with management practices relying on commercial concentrate, optimal use of molasses and urea permitted increases in the stocking rate. Productivity and profit were restricted primarily by energy intake, which was constrained by intakes of NDF and DM. Alternative management strategies changed the relative importance of nutrient requirements and feed intake constraints. Thus, optimal interventions to alleviate nutritional constraints will vary with current management. Mobilizing adipose and protein tissues during lactation was optimal for most strategies. Supplementing with molasses and urea instead of commercial concentrate was the most profitable strategy, increasing herd net margin by 16% compared to the predominant feeding strategy in the late 1980s.

A net carbohydrate and protein system for evaluating cattle diets: III. Cattle requirements and diet adequacy.

The Cornell Net Carbohydrate and Protein System (CNCPS) has equations for predicting nutrient requirements, feed intake, and feed utilization over wide variations in cattle (frame size, body condition, and stage of growth), feed carbohydrate and protein fractions and their digestion and passage rates, and environmental conditions. Independent data were used to validate the ability of the CNCPS to predict responses compared to National Research Council (NRC) systems. With DMI in steers, the CNCPS had a 12% lower standard error of the Y estimate (Sy.x) and three percentage units less bias than the NRC system. For DMI in heifers, both systems had a similar Sy.x but the NRC had four percentage units less bias. With lactating dairy cows' DMI, the CNCPS had a 12% lower Sy.x. Observed NEm requirement averaged 5% under NRC and 6% under CNCPS predicted values at temperatures above 9 degrees C but were 18% over NRC and 9% under CNCPS at temperatures under 9 degrees C. Energy retained was predicted with an R2 of .80 and .95 and a bias of 8 and 4% for the NRC and CNCPS, respectively. Protein retained was predicted with an R2 of .75 and .85 with a bias of 0 and -1% for NRC and CNCPS, respectively. Biases due to frame size, implant, or NEg were small. Body condition scores predicted body fat percentage in dairy cows with an R2 of .93 and a Sy.x of 2.35% body fat. The CNCPS predicted metabolizable protein allowable ADG with a bias of 1.6% with a Sy.x of .07 kg compared to values of -30% and .10 kg, respectively for the NRC system.

A net carbohydrate and protein system for evaluating cattle diets: I. Ruminal fermentation.

The Cornell Net Carbohydrate and Protein System (CNCPS) has a kinetic submodel that predicts ruminal fermentation. The ruminal microbial population is divided into bacteria that ferment structural carbohydrate (SC) and those that ferment nonstructural carbohydrate (NSC). Protozoa are accommodated by a decrease in the theoretical maximum growth yield (.50 vs .40 g of cells per gram of carbohydrate fermented), and the yields are adjusted for maintenance requirements (.05 vs .150 g of cell dry weight per gram of carbohydrate fermented per hour for SC and NSC bacteria, respectively). Bacterial yield is decreased when forage NDF is < 20% (2.5% for every 1% decrease in NDF). The SC bacteria utilize only ammonia as a N source, but the NSC bacteria can utilize either ammonia or peptides. The yield of NSC bacteria is enhanced by as much as 18.7% when proteins or peptides are available. The NSC bacteria produce less ammonia when the carbohydrate fermentation (growth) rate is rapid, but 34% of the ammonia production is insensitive to the rate of carbohydrate fermentation. Ammonia production rates are moderated by the rate of peptide and amino acid uptake (.07 g of peptide per gram of cells per hour), and peptides and amino acids can pass out of the rumen if the rate of proteolysis is faster than the rate of peptide utilization. The protein-sparing effect of ionophores is accommodated by decreasing the rate of peptide uptake by 34%. Validation with published data of microbial flow from the rumen gave a regression with a slope of .94 and an r2 of .88.

A net carbohydrate and protein system for evaluating cattle diets: II. Carbohydrate and protein availability.

The Cornell Net Carbohydrate and Protein System (CNCPS) has a submodel that predicts rates of feedstuff degradation in the rumen, the passage of undegraded feed to the lower gut, and the amount of ME and protein that is available to the animal. In the CNCPS, structural carbohydrate (SC) and nonstructural carbohydrate (NSC) are estimated from sequential NDF analyses of the feed. Data from the literature are used to predict fractional rates of SC and NSC degradation. Crude protein is partitioned into five fractions. Fraction A is NPN, which is trichloroacetic (TCA) acid-soluble N. Unavailable or protein bound to cell wall (Fraction C) is derived from acid detergent insoluble nitrogen (ADIP), and slowly degraded true protein (Fraction B3) is neutral detergent insoluble nitrogen (NDIP) minus Fraction C. Rapidly degraded true protein (Fraction B1) is TCA-precipitable protein from the buffer-soluble protein minus NPN. True protein with an intermediate degradation rate (Fraction B2) is the remaining N. Protein degradation rates are estimated by an in vitro procedure that uses Streptomyces griseus protease, and a curve-peeling technique is used to identify rates for each fraction. The amount of carbohydrate or N that is digested in the rumen is determined by the relative rates of degradation and passage. Ruminal passage rates are a function of DMI, particle size, bulk density, and the type of feed that is consumed (e.g., forage vs cereal grain).

Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition.

There is a need to standardize the NDF procedure. Procedures have varied because of the use of different amylases in attempts to remove starch interference. The original Bacillus subtilis enzyme Type IIIA (XIA) no longer is available and has been replaced by a less effective enzyme. For fiber work, a new enzyme has received AOAC approval and is rapidly displacing other amylases in analytical work. This enzyme is available from Sigma (Number A3306; Sigma Chemical Co., St. Louis, MO). The original publications for NDF and ADF (43, 53) and the Agricultural Handbook 379 (14) are obsolete and of historical interest only. Up to date procedures should be followed. Triethylene glycol has replaced 2-ethoxyethanol because of reported toxicity. Considerable development in regard to fiber methods has occurred over the past 5 yr because of a redefinition of dietary fiber for man and monogastric animals that includes lignin and all polysaccharides resistant to mammalian digestive enzymes. In addition to NDF, new improved methods for total dietary fiber and nonstarch polysaccharides including pectin and beta-glucans now are available. The latter are also of interest in rumen fermentation. Unlike starch, their fermentations are like that of cellulose but faster and yield no lactic acid. Physical and biological properties of carbohydrate fractions are more important than their intrinsic composition.

On the two-compartment model for estimating the rate and extent of feed degradation in the rumen.

An analysis of the compartmental scheme used to determine the rate and extent of ruminal degradation of feeds is presented. Attention is given to the kinetic representation of the degradation of the potentially degradable fraction. Changing the kinetic order of the rate, and introducing indigestible substrate inhibition and microbial activity into its representation, are investigated. This leads to response functions such as the Gompertz and logistic for describing the cumulative disappearance of potentially degradable substrate during in-sacco and in-vitro incubation.

Improved methods for analysis and biological characterization of fiber.

Dietary fibers are not uniform, chemically or in their nutritive and biological properties, the only common ground being their resistance to mammalian digestive enzymes. The AOAC method for total fiber is subject to inferences from ash, protein, tannins and resistant starches. These interferences can be reduced by urea enzymatic dialysis. The measurement of soluble and insoluble fiber is nutritionally relevant, since physical properties greatly modify dietary effects of fiber. Insoluble fiber is conveniently measured as neutral-detergent fiber. This procedure has been improved by reducing the starch interference and the time of analysis. Physical and biological properties of dietary fiber can be measured by using relevant procedures for hydration capacity, metal ion exchange capacity and rate of fermentation. The lignin and tannin content modify the characteristics of dietary fiber.

Analysis of foodstuffs for dietary fiber by the urea enzymatic dialysis method.

Total dietary fiber (TDF) values for cereal grains, fruits, vegetables, processed foods, and purified or semi-purified dietary fiber products were determined by a new method using 8M urea and enzymes (urea enzymatic dialysis, UED, method). The results are compared with the official AOAC procedure. Soluble and insoluble dietary fiber were determined for several of these foodstuffs and compared with the NDF values. Crude protein and ash contamination was usually lower with the UED method compared with the AOAC method, particularly for samples that formed gels during ethanol precipitation. Urea and the heat stable amylase were effective in removing starch even at relatively low temperatures of the assay (50 degrees C). The new assay is relatively economical in use of equipment, enzymes, and reagents. Studies are currently in progress to minimize the assay time for the UED method while further improving its flexibility and robustness. The results of the studies will be discussed.

Urea enzymatic dialysis procedure for determination of total dietary fiber.

A method that uses urea and enzymes for determination of total dietary fiber (TDF) in foods has been developed and compared with the AOAC enzymatic-gravimetric method (43.A14-43.A20). In the evaluation, results for crude protein and ash contamination were higher by the AOAC method, particularly for samples that form gels during ethanol precipitation. The new urea enzymatic dialysis (UED) method quantitatively recovered, with less variation, more of the purified and semipurified dietary fiber products. TDF recoveries for carboxymethylcellulose and locust bean gum were 98% (SD 3.3) and 95% (SD 6.1) by the AOAC method and 99% (SD 1.0) and 100% (SD 0.6) by the UED method, respectively. The UED method was the more effective in removing starch. For kale samples, starch recovery was 3.5 and 0.2% from TDF residues obtained using the AOAC and UED methods, respectively. Differences were not significant among replicate values for determination of TDF in foods by the UED method (P greater than 0.01). Preliminary studies suggest that the new method can separately determine soluble and insoluble dietary fiber. The data indicate that the UED method is more precise and accurate than the AOAC method.