Protein efficiency ratios and net protein ratios of selected protein foods

As a part of a cooperative study initiated to assess bothin vitro andin vivo protein quality methods, the protein efficiency ratio (PER) and net protein ratios (NPR) of 15 different protein sources were determined. Male weanling Sprague-Dawley rats were fed a 10% protein diet. Fourteen-day NPR and relative NPR (RNPR) values and 14- and 28-day PER and relative PER (RPER) values were calculated for each protein source. When protein quality values were expressed relative to ANRC casein, the 14- and 28-day PER data ranked the protein sources essentially in the same order. RPER values of nonfat dried skim milk (unheated) and tuna were more than 100% that of casein; nonfat dried skim milk (heated), chickpeas, and breakfast sausage were between 50 and 70% of that of casein; and pinto beans and rice-wheat gluten cereal did not support substantial growth of the rat. The NPR method did not always rank the protein sources in the same order as the PER method. For the poor quality proteins, RNPR values were much higher than the RPER values; however, the RNPR and RPER values agreed closely for high quality protein sources.A preliminary report of this work was given at the Annual Meeting of the Federation of American Societies for Experimental Biology, Washington, D.C., March 29–April 2, 1987. Fed. Proc. 1987; 46: 889.     

Comparative effects of feeding a protease inhibitor-enriched potato protein concentrate and soy flour to rats

Rats were fed casein diets to which had been added a potato protein concentrate (PPC) at a level which provided trypsin- and chymotrypsin-inhibitor activities comparable to that present at the same level (10%) of protein derived from raw soy flour. Control groups consisted of the same diets in which the unheated PPC and raw soy flour were replaced by their heated counterparts in which over 90% of the inhibitor activities had been destroyed. After 5 weeks the following measurements were made: (1) growth, (2) PER, (3) pancreas weight, (4) protein digestibility, (5) a peptide test that reflects pancreatic function, and (6) enzyme activities (trypsin, chymotrypsin, amylase, and lipase) in the pancreas and small intestine. PPC was found to produce the same general pattern of effects as raw soy flour, namely, an inhibition of growth, a decrease in PER and protein digestibility, an increase in the size of the pancreas, an increase in the recovery of p-aminobenzoic acid in the peptide test, and a depletion of enzyme in the pancreas with concomitant increases in the intestines (except for trypsin). PPC was somewhat more effective than raw soy flour in causing an increase in trypsin and chymotrypsin activities in the faces.     

Protein quality of diets based on tuber,legume, and cereal in weanling rats

Weanling male rats (45–55 g) were studied to evaluate the protein quality of diets based on combinations of yam (YA); dehulled brown bean (DBB), dehulled white bean (DWB); and corn flour (PA) that provided 1.6 g N/100 g of diet. Casein served as the reference protein. Rats fed combinations of PA, DBB, and DWB had increases in food intake, weight gain, N intake, digested and retained N, and liver N compared to those of the casein control group and the other test groups (P < 0.05). Supplementation of YA with DBB or DWB reduced weight gain, protein efficiency ratio (PER), N intake, digested and retained N, NPU and liver N values of the animals when compared with those fed the casein and the other diets containing YA. Combinations of DBB or DWB with PA appear to be the best mixtures as shown by food and N intakes, digested and retained N, liver N, and weight gain. These mixtures may possibly be economic sources of N for weaning children where these are staples in the diet.     

The nutritive value of all-vegetable protein diets based on legume,cereal and tuber in weanling rats

Thirty albino weanling male rats (45–55 g) were divided into five groups of six rats each on the basis of body weight and fed combinations of dehulled brown beans (DBB); parboiled rice (R); and cassava meal (G) which provided 10% protein for 35 days. Casein served as the reference protein. Combinations of DBB (50–80%); with R (18–48%); and G (2%) produced varied effects on body weight, nitrogen (N) intake, N digestibility and retention, BV, liver weight and plasma albumin (P<0.05).The DBB:R:G (70:28:2) blend induced decreases in all the parameters tested except for the BV and PER values. The control group produced digested and retained N, protein efficiency ratio (PER), weight gain and liver weight that were significantly higher than for those of the test diets (P<0.05). These results appear to suggest that starchy foods when blended with legumes at low levels produced good quality protein comparable to casein.     

Effects of raw soy flour feeding in weanling pigs: comparison with rats and monkeys

Feeding of raw and heated soy flour (RSF & HSF) for 4 or 8 weeks to weanling swine was compared with feeding of casein diets. There was essentially no growth in pigs fed RSF, whereas body weight increased 4.5 fold over 8 weeks with either casein or HSF. No change in pancrease weight as percent body weight was found in any group in either experiment. Both total pancreatic RNA and DNA were decreased in RSF groups, although RNA and DNA/mg pancreas were increased by the RSF diets. Total pancreatic protein, as well as protein/mg, were decreased in RSF-fed pigs compared to casein and HSF. Pancreatic trypsin, chymotrypsin, lipase, and amylase, and fecal trypsin were decreased in RSF-fed pigs to varying degrees compared to either HSF or casein. HSF and casein performance was equivalent in all parameters measured. Results of these experiments are compared with results of feeding similar diets to rats and monkeys.     

Protein quality of some Nigerian traditional diets based on the African yambean (Sphenostylis stenocarpa) and pigeon pea (Cajanus cajan)

The protein quality of Nigerian traditional diets based on the African yambean (AYB) and pigeon pea (PP) were performed by in vivo and in vitro bioassays. The individual foods were processed, cooked, dried and mixed to resemble the traditional diets. Weanling male Wistar rats (45–55 g) were used for the bioassay. The rats were fed ad libitum for 35 days of which 28 days were for growth and 7 days for N-balance. All the eleven diets including casein (control) provided 1.6 g N/100 g diet. The parameters tested include PER, growth, N-balance, BV, NPU and apparent digestibility (AD). The rats fed the AYB diets, except AYB: Agidi (Ag), showed superiority in most of the parameters tested. There were significant positive correlations between PER and NPU (r=0.925;p<0.001); PER and AD (r=0.908;p<0.001); PER and body weight gain (r=0.969;p<0.001). The in vitro protein digestibility of the diets was significantly correlated (r=0.80;p<0.01) with the in vivo apparent digestibility. These parameters were used to rank the various diets. Crayfish protein was a better supplement to legume/cereal or legume starchy staple mixtures than leguminous oil seed. However, supplementation of PP: steamed corn (SC) diet with crayfish did not prove beneficial. The result showed that diets based on the African yambean, an under-exploited legume, are nutritious. The need for its reintroduction into the fare of the populace through increased production and appropriate processing technology is stressed. The results of this study can form a base for the standardization of Nigerian diets based on these legumes.     

Effects of heat treatments on trypsin inhibitor and hemagglutinating activities in winged bean

The effect of different heat treatments on inactivation of trypsin inhibitor and hemagglutinin of winged bean was investigated. Trypsin inhibitor extracted from winged bean meal was stable at 60 °C for 60 min. At 80 °C, the activity of the extracted inhibitor decreased by 25% within 5 min, and continued to decline gradually to a loss of 45% of activity after 30 min. When the extracted inhibitor was incubated at 100 °C, it exhibited a triphasic pattern of inactivation. The winged bean extract incubated at 60 °C lost 60% of its hemaggluinating activity within 30 min. At 80 °C, there was a complete loss of activity within 5 min. The microwave treatment to winged bean meal had no effect on trypsin inhibitor or hemagglutinating activities in the meal. However, infrared treatment to winged bean seeds for 60 seconds was effective in destroying most of the trypsin inhibitor and hemagglutinating activities. Autoclave treatment (120 °C at 15 lb pressure) for 10 min inactivated trypsin inhibitor and hemagglutinin in winged bean meal almost completely. Cooking of presoaked beans in boiling water for 30 min was effective in destroying most of the trypsin inhibitor and hemagglutinating activities.     

The protein quality of lupins (Lupinus mutabilis) alone and in combination with other protein sources

The chemical compositions, of raw and treated lupine flour were determined and compared with other plant protein sources. The protein content in the dry matter was 47.7% in untreated seeds ofLupinus mutabilis and about 56% in debittered seeds. The oil-cake contained 65.3% protein. The amino acid analysis showed that lupine protein is characterized by a low level of S-amino acids, the content of which amounts to only 50% of that of the FAO standard reference pattern. The protein quality was measured using the biological tests PER (Protein Efficiency Ratio), NPU (net protein utilization), and BV (biological value) in rats on diets with and without DL-methionine supplementation. PER determinations gave low values for the non-supplemented lupine proteins (1.34, semi-sweet variety; 1.53, water-extracted seeds; 1.19, oil-cake; 3.09, casein), but the PER's were improved by the addition of 0.2% DL-methionine to the diets (3.05, 2.69, 2.81, respectively). Raw as well as processed lupine protein showed an excellent apparent digestibility (80.0–85.8%; casein, 87.1%). The observed NPU and BV values confirmed the importance of methionine supplementation. The true digestibility of 92% was equivalent to that of casein. The complementation effects of mixing lupine protein with proteins from wheat, oat, barley, rice, maize, potato, quinua or fish were investigated by determination of the PER values of the respective mixtures. Feeding lupine protein with cereal proteins resulted in PER values that exceeded by far those of the proteins fed separately (true complementation). This result was not observed for the mixture of potato and lupine. High quality proteins like quinua and fish protein also showed no complementation effect with lupine protein but did improve the quality of the lupine protein to a great extent. The best results could be obtained with combinations of three different plant proteins, in which lupine protein always contributed one third of total protein. These mixtures resulted in PER values equal to those for casein or other animal proteins and may be applied as an economical way to prevent and combat malnutrition.     

Nutrient composition and biological evaluation of mesta (Hibiscus sabdariffa) seeds

Two varieties of mesta (Hibiscus sabdariffa) seeds were analysed for their proximate composition. Their protein (18.8–22.3%), fat (19.1–22.8%) and dietary fiber (39.5–42.6%) contents were found to be high. The seeds were found to be a good source of minerals like phosphorus, magnesium and calcium. Their lysine and tryptophan contents were also high. Sulphur containing amino acids were limiting in this seed protein and the chemical score of mesta seed protein was 40 and 57 for AMV-2 and Bhimili-1 varieties respectively. Mesta seed oil is rich in unsaturated fatty acids (70%), of which linoleic acid constituted 44%. Weanling rats were fed with 10% mesta seed protein before and after cooking for 4 weeks. Food intake of animals receiving raw mesta seed diets was significantly lower than those receiving cooked mesta seed diets as well as the casein control diet. Protein and dry matter digestibilities of raw and cooked mesta seed diets were lower than that of casein control diet. Cooking improved the food intake, gain in body weight, dry matter and protein digestibility of mesta seed diets. PER and NPU of cooked mesta seed diets were significantly higher than the corresponding raw diets. These results indicate that cooked mesta seed protein is of relatively good quality.     

The USDA trypsin inhibitor study. IV. The chronic effects of soy flour and soy protein isolate on the pancreas in rats after two years

In two year feeding trials, histologic changes in the pancreas of the Wistar rat were evaluated after chronic dietary exposure to raw and heated, dehulled, defatted soy flour and soy protein isolates which provided a range of trypsin inhibitor (TI) concentrations from 93 to 1271 mg/100 g diet. Also investigated was the nutritional interaction of level of dietary protein with the development of pancreatic pathology. Graded levels of TI were achieved from mixtures of raw and heated soy flour or protein isolate. Dietary protein levels were 10%, 20%, and 30%; the two higher levels obtained in some diets through casein supplementation. A total of 26 diets, including casein controls, were fed to groups of 40 male rats. Growth rates with these diets were commensurate with protein quality and level. Mortality rates tended to be slightly greater in the higher protein diets, and rats fed only raw soy as a source of protein survived well.Two lesions, nodular hyperplasia (NH) and acinar adenoma (AA) constituted the major pathological findings in the pancreas, and the incidence rates of both were positively associated with the concentration of dietary TI. The incidences of pancreatic NH and AA compared to those of the corresponding casein control were significantly elevated in rats fed heated soy flour supplying 10% protein and the lowest level of TI investigated (93 mg/100 g diet). At low levels of TI (215 mg/100 g diet), supplementation by casein to raise the concentration of protein from 10% to 20% and 30% reduced the frequency of NH and AA. When the dose-response data for NH and AA was linearized by plotting the probit of percent incidence against log of TI concentration per gram of dietary protein, the response to soy flour and soy protein isolate was not significantly different. Numerous lesions commonly found in the aging rat were diagnosed, and modulation of their rate of occurrence by nutritional factors associated with the diets was apparent in some instances.Reference to a company and/or product named by the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.     

Nutritional responses of rats fed mixtures of plant and animal proteins

Twenty four male rats (45–65 g) were used to determine the nutritional responses to mixed plant and animal protein diets. Rats were fed various mixtures of sorghum (S), pigeon pea (PP), bread fruit (TAP) plus crayfish (CR) to provide 1.6 g N/100g of daily diet for a 35-day study period. Three different diets were fed to 6 rats assigned to each diet on the basis of body weight. Combination of PP:CR caused increases in N intake and retention, weight gain, and PER higher than for those of the other test groups. Its values for N intake and retention, and BV were higher than for those of the control except for food intake, NPU, weight gain and PER. Substitution of CR (20%) with TAP and PP as supplements to S decreased food intake, weight gain and PER and increased N intake, digested and retained N, NPU and BV. The results appear to indicate that (a) PP:CR blend was better than other blends as judged by the parameters, and (b) TAP and PP were superior to CR alone as supplement to S.     

The USDA trypsin inhibitor study. III. Sequential development of pancreatic pathology in rats

Weanling male, Wistar rats (40 per diet) were maintained on 15 diets which provided 4 graded trypsin inhibitor (TI) levels (93, 215, 337, and 577 mg/100g diet) repeated at 3 levels of protein (10%, 20%, and 30%). Raw and heated (toasted) soy flour provided 10% protein in the diet, while casein was added to increase the protein level to 20% and 30%. Three diets containing only casein as the protein source, at 10%, 20%, and 30% were included. Histologic changes occurring in the pancreas were evaluated in approximately 5 rats from each diet at 3 month intervals, beginning at 6 months, for 22 months. Criteria for the diagnosis of the observed histologic changes in the pancreas are discussed. Ultrastructure of the endocrine cells in the gastrointestinal mucosa was also examined.Pancreatic acinar cell density, as determined morphometrically, was reduced throughout the study in rats fed the 577 mg TI/100 g diet, indicating hypertrophy at the cellular level. Nodular hyperplasia was observed in the first sacrifice group at 6 months. Incidence of the lesion was positively related to both time of exposure and level of dietary TI. Acinar adenoma was first observed at 18 months and was most prevalent in rats fed the highest concentration of TI.Endocrine cells of the duodenal mucosa which contain cholecystokinin (so-called I cells) contained a denser population of secretory granules in animals fed the high TI diet compared with I cells from control animals, leading to the speculation that production and secretion of cytoplasmic hormones was increased in TI treated rats.Reference to a company and/or product named by the Department is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others which may also be suitable.     

Cereal and nut bars,nutritional quality and storage stability

Six snack-type bars were manufactured, to contain oat and wheat germ and two different walnut levels, agglutinated with natural sweeteners and fats. Two bars also contained toasted amaranth with brown sugar cover and wheat extrudate, while two others, contained puffed instead of toasted amaranth. Water activity (Aw) and moisture were determined in the manufactured products. Quality and sensory evaluation and proximate analysis were carried out on the bars containing highest levels of walnuts (18%). The caloric contribution of the bars was computed by Atwater methods. The nutritional quality of the bars was determined by means of the Protein Efficiency Ratio (PER) and Net Protein Ratio (NPR), and the results were used to obtain relative PER and relative NPR. Samples of the latter bars were kept under accelerated storage for 15 days at 37 °C and analyzed every 5 days to determine their Aw, moisture, peroxide and sensory acceptability. The drying time for the cereal — and walnut — based bars was 45 min at 120 °C. All bars presented a good fiber supply and the CN₁ bar, containing only oat, wheat germ and walnut, had the greatest protein content. In the sensory evaluation, the walnut level with the greatest preference was 18%. PER and NPR values of the bars did not differ significantly showing values approximately 86% that of the casein value. During storage, the moisture and Aw decreased in all the bars. Peroxides remained within the acceptable ranges; acceptability based on sensory evaluation remained best in the bar with toasted amaranth. Walnuts can successfully be used in the manufacture of snack bars as these offer good nutritional and sensory quality and remain stable in storage.     

The nutritional quality of potato protein from intraspecific hybrids

The nutritional value of potato hybrids with Groups Andigena, Phureja, and Tuberosum parentage was measured by protein efficiency ratio (PER). Three diets at 6.0%, 7.75%, and 9.0% crude protein in potato flakes were fed to rats; 18 genotypes were analyzed and the hybrids had higher PER values than Group Tuberosum varieties, but increased tuber protein did not influence the PER values. The overall mean PER was 2.3, and 12 of the potato-flake diets were not different from the casein controls. Fortification with isoleucine did not improve the nutritional quality of the potato flakes. One diet was improved with the addition of both isoleucine and methionine. The influence of sulfur-containing amino acids in potato protein quality among these hybrids is not clear. It is suggested there may be two types of hybrids, one with dependence on these amino acids and a second type with a different protein factor(s) affecting the nutritional quality of the protein. Protein from these potato hybrids, as measured by PER, is among the highest in biological quality when compared with other proteins in plant foods.     

Evaluation of the protein quality of rice supplemented with bean or crayfish in rats

Weanling male rats (45–60 g) were used to compare the supplemental effects to rice protein of bean or crayfish protein. Rats were fed various combinations of rice plus bean (B) or crayfish (C) to provide 1.6 g N/100 g of the daily diet for 28-day growth studies and a 7-day N balance period. Five different diets were fed. Six rats were assigned to each diet on the basis of body weight. Combinations of R:B of 80:20 and of R:C of 80:20 produced food intake, weight gain, PER, N intake, digested and retained N; and liver weight values that were comparable. However, increasing C to 30% of the dietary protein led to reduced value for food intake, weight gain, PER, N intake, digested and retained N, BV, NPU, and liver weight when compared with values obtained when B was increased to 30% (P<0.05). The results appear to indicate that, above a certain level of supplementation, brown bean protein is superior to crayfish as a supplement to rice protein.     

Influence of dietary soybean trypsin inhibitors and DL-ethionine on sulfur amino acid adequacy of diets for young rats

Weanling male Wistar rats were fed 20% protein diets based on casein or either of two combinations of soy protein isolate and ground raw soy providing three levels of soybean trypsin inhibitors (SBTI; 0,448 and 808 mg of trypsin inhibited per 100g of diet respectively). DL-ethionine was included at three levels (0,0.05% and 0.10%) with each level of SBTI. After 4, 8 and 12 weeks ofad libitum feeding, diets containing SBTI without DL-ethionine were associated with decreases in weight gain, feed efficiency, serum cholesterol and serum urea nitrogen. Higher levels of triglycerides, glutamate pyruvate transaminase (SGPT) and altered serum free amino acid levels were also found. Increased dietary levels of DL-ethionine also resulted in deficits in growth and feed efficiency, decreased serum cholesterol, increased SGPT and similar alterations in serum free amino acids. Combination of dietary SBTI with DL-ethionine resulted in even greater growth deficits and serum cholesterol decreases as well as increases in SGPT and serum triglycerides and changes in serum free amino acid levels. Methionine deficiency in the young rats fed SBTI and DL-ethionine was indicated by the changes in serum amino acids and growth deficits. Moderation of some effects over the 12 week test period suggested decreased methionine requirements in the older rats.     

Nutritive value of soybean,rapeseed and wheat proteins,and various blends of these vegetable proteins and their fractions in rats

Blends of vegetable proteins were prepared to improve the nutritive value of these proteins. Soybean flour, rapeseed protein concentrate, whole wheat flour, soybean 2S+11S extract, wheat albumin-globulin + glutenin (AG+G) functions, and some of their blends were compared to casein for protein efficiency ratio (PER) and apparent digestibility coefficient (ADC). Autoclaving (1 h) soybean proteins was also studied. Casein and rapeseed protein concentrate gave the highest weight gains and PER. Other protein sources gave lower values for both PER (P<0.05) and weight gain. The digestibility of all vegetable proteins was lower (P<0.05) than that of casein. PER of soybean 2S+11S extract was significantly lower (P<0.05) than that of soybean flour. Autoclaving significantly (P<0.05) improved the PER of both soybean flour and 2S+11S extract. The ADC of autoclaved 2S+11S extract was similar (P<0.05) to that of autoclaved soybean flour and significantly higher (P<0.05) than that of 2S+11S extract. Soybean flour had the lowest (P<0.05) ADC. Heat treatment destroyed antinutritional factors, probably trypsin inhibitors and/or haemagglutinins of soybean. This was accompanied by improvement in the nutritional value of protein. The four blends were chosen on the basis of amino acid composition, chromatography of proteolyzates and nutritive value of each fraction. The PER of wheat albumin-globulin and glutenin (AG+G) blend was similar (P<0.05) to that of wheat flour and lower (P<0.05) than that of all other blends used. Wheat AG+G+rapeseed protein concentrate and wheat AG+G+soybean flour blends gave the highest (P<0.05) PER. Wheat AG+G improved the PER of 2S+11S extract and of soybean flour but decreased the PER of rapeseed protein concentrate. Wheat AG+G and wheat AG+G+rapeseed protein concentrate blends gave an ADC significantly higher (P<0.05) than that of wheat AG+G blend containing soybean flour of 2S+11S extract. However, blending wheat AG+G with either 2S+11S extract of soybean flour improved ADC.     

The effect of algal protein diets on the regeneration of serum and liver proteins in protein depleted rats

The protein quality of algaeSpirulina platensis was evaluated biochemically in adult albino rats by serum protein regeneration studies. Rats depleted for 12 days were repleted for 15 days with diets containing 10% protein derived from algae, methionine supplemented algae, or casein. On protein depletion, the activity of the hepatic enzymes, succinic dehydrogenase and alanine aminotransferase, were lowered while the activity of alkaline phosphatase increased. Protein repletion with algal and casein diets resulted in an increased activity of succinic dehydrogenase and alanine amino transferase and a decrease in alkaline phosphatase activity. However, the levels of these three enzymes were lower with the algal than with the casein diets. Algal diets regenerated serum protein effectively though to a slightly lesser extent than casein.     

Interaction of Dietary Fat and Soybean Isolate (SBI) on Azaserine-induced Pancreatic Carcinogenesis

Raw soybean flour contains high levels of both soybean trypsin inhibitor and unsaturated fat. The chronic ingestion of this flour enhances pancreatic carcinogenesis in rats that have been treated with pancreatic carcinogens. In these studies we have examined the separate and combined effects of trypsin inhibitor in purified soybean isolate (SBI) and a high level of unsaturated fat fed during the postinitiation phase of pancreatic carcinogenesis. Male Wistar rats were injected with the known pancreatic carcinogen azaserine (30 mg/kg, ip) 14 days after birth and were weaned to the test diets. No further exposure to carcinogen occurred. Dietary composition (% by weight) of fat (corn oil) was either 5%, or for the high fat group 20%. Dietary protein (20% in all diets) was supplied as either casein, or heated or raw SBI. All diets were fedad libitum for the postinitiation phase. The number and size of transections of azaserine-induced putative, preneoplastic foci and the volume of pancreas occupied by these foci were determined by light microscopy. High fat diet increased the number and transectional size of the azaserine-induced foci as compared to the control (5% corn oil) group. The volume of pancreas occupied by foci doubled. Heated SBI had no effect upon the foci. Raw SBI, however, significantly increased the number and size of foci. The combination of raw SBI plus the high fat diet elicited an increase in focal growth that was greater than that produced by either component alone. These observations indicated that both trypsin inhibitor and the high unsaturated fat content of raw soy flour contribute to the enhancement or promotion of pancreatic carcinogenesis.     

Effect of supplementation of blue green alga (Spirulina) on outcome of pregnancy in rats

To study the supplementary effect of Spirulina, pregnant rats were fed 5 different kinds of diets (casein, Spirulina, wheat gluten, Spirulina + wheat gluten, Spirulina-without additional vitamins and minerals), each providing 22% protein during the period of pregnancy. The outcome of pregnancy was assessed from litter and dams' weight and litter size. Maternal weight gain was found to be maximum with Spirulina + wheat gluten and least with the wheat gluten diet. Rats receiving Spirulina containing diets produced significantly (p<0.05) higher litter size than those receiving casein and wheat gluten. In spite of having higher litter size, Spirulina containing diet groups produced pups with birth weights comparable to those of casein. Spirulina appears to be a good dietary supplement during pregnancy.