The protein quality of some enteral products is inferior to that of casein as assessed by rat growth methods and digestibility-corrected amino acid scores

The Energy and Nutritional Value of Meat of Broiler Chickens Fed with Various Addition of Wheat Germ Expeller

The study concerns the effect of wheat germ expeller (WGE) as a feed additive given to male Ross-308 broiler chickens on their meat's energy and nutritional value, and coverage of nutrient reference values-requirements (NRV-R) of consumers for particular minerals. The chickens in the control group (CT-Control Treatment) were fed a standard complete mix. The experimental groups (EX5, EX10, EX15) were given a feed in which wheat middling was replaced with 5, 10, and 15% WGE. The breast and thigh muscles of 32 randomly selected chickens (8 in each group) were analyzed. More water, crude protein, P, Mg, Fe, Cu, and Mn were determined in the breast muscles, and more crude fat, crude ash, Ca, and Zn in the thigh muscles. Chickens from the CT group consumed significantly (p ≤ 0.01) less feed per body weight than those from groups EX5 to EX15, but achieved the highest body weight per 100 g of consumed feed. A higher (p ≤ 0.01) feed, energy, crude protein, and crude fat intake was observed in groups EX5 to EX15 compared to CT. The higher (p ≤ 0.01) value of protein efficiency ratios was indicated in the CT group. The WGE additive did not impact the muscles' energy values but affected the nutritional value. The daily consumption of 100 g of breast muscles to a large extent covers the consumer NRV-R for P, Mg Fe, Cu, and Mn. However, thigh muscles cover the NRV-R to a greater extent for Ca and Zn. The EX15, EX5, and EX10 muscles covered most of the NRV-R for P, Ca, and Mg, while the CT muscles did the same for Zn and Mn. Adding 5% WGE to broiler feed is optimal as it does not impair the nutritional value of the muscles.

Natural Fermentation of Cowpea (Vigna unguiculata) Flour Improves the Nutritive Utilization of Indispensable Amino Acids and Phosphorus by Growing Rats

Cowpea (Vigna unguiculata) is among the most cultivated legumes, with interesting agronomic and environmental properties, and great potential as a nutritious food. The nutritional value of cowpea can be improved by technological processing. In this study, we showed that natural fermentation improved bioavailability of protein, amino acids, and dietary essential minerals from cowpea in growing rats, thus strengthening its potential value as functional food or food supplement. Forty Wistar albino rats (48 ± 1.8 g), were fed one of four experimental diets (n = 10 rats per diet): casein, raw cowpea, fermented cowpea or fermented and autoclaved cowpea. Despite lower growth indices of raw and fermented cowpea protein (PER, FTI) than casein, fermentation enhanced apparent digestibility of arginine, leucine, lysine, methionine, phenylalanine, tyrosine, and valine, and true digestibility of essential amino acids, except for tyrosine and valine, compared to raw cowpea. On the other hand, autoclaving of fermented cowpea flour decreased apparent, as did true digestibility of sulfur amino acids. Regarding the nutritive utilization of dietary essential minerals, Vigna unguiculata was a good source of available P, Mg, and K, while fermentation significantly improved the availability of P. Overall, cowpea was a good source of digestible essential amino acids and minerals and fermentation significantly improved its nutritional value that was not further enhanced by autoclaving.

Effects of Industrial Heating Processes of Milk-Based Enteral Formulas on Site-Specific Protein Modifications and Their Relationship to in Vitro and in Vivo Protein Digestibility

Heat treatments are applied to milk and dairy products to ensure their microbiological safety and shelf lives. Types of heating processes may have different effects on protein modifications, leading to different protein digestibility. In this study, milk-based liquid nutritional formulas (simulating enteral formulas) were subjected to steam injection ultra-high-temperature treatment or in-can sterilization, and the formulas were investigated by proteomic methods and in vitro and in vivo digestion assays. Proteomic analyses revealed that in-can sterilization resulted in higher signals for N(ε)-carboxymethyllysine and dephosphorylation of Ser residues in major milk proteins than in steam-injected formula, reflecting the more severe thermal process of in-can sterilization. In vitro and in vivo digestion assays indicated that steam injection improved protein digestibility, supposedly by denaturation, while the improvement seemed to be overwhelmed by formation of aggregates that showed resistance to digestion in in-can sterilized formula. Adverse effects of heat treatment on protein digestibility are more likely to be manifested in milk-based formulas than in cow's milk. Although the differences might be of limited significance in terms of amino acid bioavailability, these results emphasize the importance of protein quality of raw materials and selection of heating processes.

Effects of different industrial heating processes of milk on site-specific protein modifications and their relationship to in vitro and in vivo digestibility

Heating processes are applied to milk and dairy products to ensure their microbiological safety and shelf lives. However, how differences in "industrial" thermal treatments affect protein digestibility is still equivocal. In this study, raw milk was subjected to pasteurization, three kinds of ultra-high-temperature (UHT) treatment, and in-can sterilization and was investigated by in vitro and in vivo digestion and proteomic methods. In-can sterilized milk, followed by UHT milk samples, showed a rapid decrease in protein bands during the course of digestion. However, protein digestibility determined by a Kjeldahl procedure showed insignificant differences. Proteomic analysis revealed that lactulosyllysine, which reflects a decrease in protein digestibility, in α-lactalbumin, β-lactoglobulin, and caseins was higher in in-can sterilized milk, followed by UHT milk samples. Thus, industrial heating may improve the digestibility of milk proteins by denaturation, but the improvement is likely to be offset by heat-derived modifications involved in decreased protein digestibility.

Impact of antinutritional factors in food proteins on the digestibility of protein and the bioavailability of amino acids and on protein quality

Dietary antinutritional factors have been reported to adversely affect the digestibility of protein, bioavailability of amino acids and protein quality of foods. Published data on these negative effects of major dietary antinutritional factors are summarized in this manuscript. Digestibility and the quality of mixed diets in developing countries are considerably lower than of those in developed regions. For example, the digestibility of protein in traditional diets from developing countries such as India, Guatemala and Brazil is considerably lower compared to that of protein in typical North American diets (54-78 versus 88-94 %). Poor digestibility of protein in the diets of developing countries, which are based on less refined cereals and grain legumes as major sources of protein, is due to the presence of less digestible protein fractions, high levels of insoluble fibre, and/or high concentrations of antinutritional factors present endogenously or formed during processing. Examples of naturally occurring antinutritional factors include glucosinolates in mustard and canola protein products, trypsin inhibitors and haemagglutinins in legumes, tannins in legumes and cereals, gossypol in cottonseed protein products, and uricogenic nucleobases in yeast protein products. Heat/alkaline treatments of protein products may yield Maillard reaction compounds, oxidized forms of sulphur amino acids, D-amino acids and lysinoalanine (LAL, an unnatural nephrotoxic amino acid derivative). Among common food and feed protein products, soyabeans are the most concentrated source of trypsin inhibitors. The presence of high levels of dietary trypsin inhibitors from soyabeans, kidney beans or other grain legumes have been reported to cause substantial reductions in protein and amino acid digestibility (up to 50 %) and protein quality (up to 100 %) in rats and/or pigs. Similarly, the presence of high levels of tannins in sorghum and other cereals, fababean and other grain legumes can cause significant reductions (up to 23 %) in protein and amino acid digestibility in rats, poultry, and pigs. Normally encountered levels of phytates in cereals and legumes can reduce protein and amino acid digestibility by up to 10 %. D-amino acids and LAL formed during alkaline/heat treatment of lactalbumin, casein, soya protein or wheat protein are poorly digestible (less than 40 %), and their presence can reduce protein digestibility by up to 28 % in rats and pigs, and can cause a drastic reduction (100 %) in protein quality, as measured by rat growth methods. The adverse effects of antinutritional factors on protein digestibility and protein quality have been reported to be more pronounced in elderly rats (20-months old) compared to young (5-weeks old) rats, suggesting the use of old rats as a model for assessing the protein digestibility of products intended for the elderly.

Effects of supplemental cystine or methionine on growth and lifespan of stroke-prone spontaneously hypertensive rats

Stroke-prone spontaneously hypertensive (SHRSP) rats are considered a suitable model for studying the effects of dietary and other environmental factors on human essential hypertension and haemorrhagic stroke. To investigate the suitability of a control diet for this strain of rats, we studied the effects of supplementing casein and soya protein isolate (SPI) with two sulphur amino acids (methionine and cystine) on the growth and lifespan of SHRSP rats. The source of dietary protein and the type of supplemental sulphur amino acid had significant (P<0·05) effects on food intake and weight gain measured after 31d of the feeding study, while only the type of supplemental sulphur amino acid had significant effects on mean survival times and the survival rates. On average, the casein groups had higher food intake and weight gain compared with the SPI groups. The methionine-supplemented groups had lower food intake but higher weight gain than the cystine-supplemented groups. Similarly, the methionine-supplemented groups had higher mean survival times and survival rates compared with the cystine-supplemented groups. The data would suggest that a control diet based on cystine-supplemented casein (as recommended for normal healthy rats by the American Institute of Nutrition), may not meet the sulphur amino acid requirements for SHRSP rats, and that the methionine-supplemented casein would be an appropriate control diet for this animal model.

Protein digestibility and quality in products containing antinutritional factors are adversely affected by old age in rats

The protein digestibility-corrected amino acid score (PDCAAS) has been recommended to be the most suitable method for routine evaluation of protein quality of foods by FAO/WHO. The PDCAAS method includes the use of young rats for predicting protein digestibility of foods for all ages including the elderly. To assess the usefulness of protein digestibility in old rats in the calculation of PDCAAS for the elderly, the influence of age on the digestibility of protein in 5-wk-old and 20-mo-old rats by the balance method was studied. Fifteen protein products were tested. Each protein product was fed as the sole source of 10% dietary protein. A protein-free diet was also included to obtain an estimate of metabolic fecal protein. Protein digestibility values (corrected for metabolic fecal protein loss) in old rats were significantly (P < 0.05) lower than in young rats for most products; however, these differences were small (up to 3%) for properly processed animal products (casein, whey protein concentrate, whey protein hydrolysate, lactalbumin and skim milk powder). Similarly, the differences attributed to age were not large (up to 5%) for properly processed vegetable protein products (soy protein isolate and autoclaved soybean meal, black beans and fava beans). However, digestibility values in old rats were considerably lower (7-17%) than in young rats when fed products containing antinutritional factors, that is, mustard flour containing glucosinolates; alkaline/heat-treated soy protein isolate and lactalbumin-containing lysinoalanine; raw soybean meal and black beans containing trypsin inhibitors; and heated skim milk powder containing Maillard compounds. Therefore, the inclusion of protein digestibility data obtained using young rats in the calculations of PDCAAS may overestimate protein digestibility and quality of these products for the elderly. For products specifically intended for the elderly, protein digestibility should be determined using old rats.

Infusion of soy and casein protein meals affects interorgan amino acid metabolism and urea kinetics differently in pigs

For routine evaluation of the quality of dietary protein, amino acid scoring patterns were used. Evaluation of this pattern for soy and casein revealed that these proteins are of almost equal quality. However, in vivo studies showed a large difference. To study the biological effects of meals with casein and soy protein, the contributions of individual amino acids to net protein retention and amino acid kinetics in gut, liver and muscle in healthy pigs were investigated. Isonitrogenous enteral nutrition, infused at a rate of 10 mL. kg body wt-1. h-1 and consisting of maltodextrin (137 g/L) with added casein (53 g/L) or soy protein (68 g/L), was given to conscious, healthy female multicathetized pigs (20-22 kg, n = 12). A primed-constant infusion protocol with L-[ring-2,6-3H]phenylalanine, L-[3,4-3H]valine and [15N-15N]urea was used to measure amino acid and urea kinetics in gut, liver and muscle. Measurements were done postabsorptively and 2-6 h after initiation of the enteral nutrition. During the meal, appearance of amino acids into the portal vein and the uptake by the liver was lower with casein infusion. Muscle uptake did not differ. Gut protein synthesis tended to be lower with soy infusion (P = 0.1). Liver protein synthesis and degradation were higher with casein infusion (P < 0.05), while in muscle, soy infusion stimulated protein turnover (P < 0.05). In comparison to the postabsorptive condition, liver urea production was unchanged after casein infusion, while it was significantly increased after soy infusion. These results suggest that the quality of soy protein is inferior to that of casein protein.

The protein digestibility-corrected amino acid score method overestimates quality of proteins containing antinutritional factors and of poorly digestible proteins supplemented with limiting amino acids in rats

The validity of the protein digestibility-corrected amino acid score (PDCAAS) method in predicting the quality of fourteen protein products was compared with the commonly used protein quality methods, protein efficiency ratio (RER) and net protein ratio (NPR). A rat growth and balance study was conducted to determine protein digestibility and quality of the animal and vegetable protein products by the PER and NPR methods. Amino acid compositions of the products were also determined, and PDCAAS were calculated using a rat and a human pattern of amino acid requirements. Compared to the biological methods, the scoring method overestimated protein quality of mustard flour [PDCAAS of 84-92% vs. relative PER (RPER) or relative NPR (RNPR) of 0], raw black beans (PDCAAS of 45-72% vs. RPER or RNPR of 0), alkaline-treated lactalbumin and soybean protein isolate (PDCAAS of 44-67% vs. RPER or RNPR of 0) and heated skim milk (PDCAAS of 29-31% vs. RPER and RNPR of 0-5%). The scoring method also overestimated the protein quality of zein (true protein digestibility of 63%) supplemented with Lys, Met, Thr and Trp (PDCAAS of 63-71% vs. RPER and RNPR of 3-44%). These data demonstrate that the PDCAAS method is inappropriate for predicting protein quality of those protein sources which may contain naturally occurring growth-depressing factors or antinutritional factors formed during alkaline and/or heat processing.