The use ofEscherichia coli mutants to measure the bioavailability of essential amino acids in foods

The -galactosidase-based assay for lysine developed by Tuffnell & Payne was used to measure the bioavailabilities of cyst(e)ine, methionine, threonine and tryptophan in pronase digests of 17 foods. The digests were assayed by estimating the -galactosidase synthesis responses of fiveEscherichia coli mutants, each requiring one of the respective amino acids for protein synthesis. Deletion mutants were used whenever possible in order to ensure strain stability. Single digests of each food were assayed with 3 or 4 separate cultures of each mutant and the results were compared with those from the corresponding chemical assay. Omitting the anomalously low values for one food, the rank correlation coefficients of the bio- and chemo-assay values were 0.61 (cysteine), 0.91 (lysine), 0.95 (methionine), 0.64 (threonine) and 0.85 (tryptophan). Mean (± S.D.) relative amino acid bioavailabilities (casein = 100%) for the 17 foods were: cysteine, 53±23; lysine, 90±10; methionine, 95±18; threonine, 89±13; and tryptophan, 89±25. The cysteine mutant appeared to give unusually low bioavailability values except for the milk products. These amino acid mutants afford a rapid method for assaying the bioavailabilities of at least four of the five amino acids studied.     

Chemical and biological characteristics of a West African weaning food supplemented with compea (Vigna unguiculata)

The effects of cowpea and amino acid supplementation on the protein quality and chemical characteristics of a maize-based West African traditional weaning food were studied. Process optimization for improved nutritive value was also determined. Supplementation of the traditional weaning food with cowpea increased the lysine, tryptophan and threonine content while the sulphur-amino acids decreased with increasing levels of cowpea. Further supplementation of 70:30 maize/cowpea blends with lysine, threonine or methionine did not significantly improve (p>0.05) protein quality in terms of the biological value (BV) and net protein utilization (NPU), although significant increases in the protein scores were noted. However, considerable improvements in the BV and NPU were recorded in blends fortified with either tryptophan alone or a combination of lysine, tryptophan, methionine and threonine. Cooking whole cowpea seeds for 45 min before incorporating in the blend formulation also significantly improved (p<0.05) the protein quality of maize/cowpea blends. The BV and NPU of blends containing 30% pre-cooked cowpea increased from 52 to 76% and 50 to 71% respectively compared to pure maize porridge. The protein content increased from 10 to 14% and the utilizable proteins more than doubled. The weight increase of experimental rats fed with these blends was comparable to that of rats on casein diet. A 30% supplementation of the maize-based weaning food with cowpea therefore greatly enhances the nutritive value especially when the cowpea is pre-cooked for 45 min. Use of chemical scores alone for such blends cannot be a reliable index of blend quality.     

Amino acid composition of sainfoin forage

The crude protein concentration, amino acid composition and protein quality of sainfoin (Onobrychis viciifolia) forage was compared to that of lucerne (Medicago sativa). The amino acid analyses showed that sainfoin contained higher amounts of lysine, histidine, proline, cystine, glycine, alanine, valine, leucine, tyrosine, phenylalanine and tryptophan than lucerne, whereas lucerne contained more aspartic acid, methionine and isoleucine than sainfoin; the limiting amino acid in both legumes was methionine. The protein score, an estimation of protein quality for nonruminants, was 68 for sainfoin forage and 71 for lucerne forage compared to 100 for an ‘ideal protein’. The similarity of protein quality of sainfoin forage to that of lucerne indicates that, where conditions permit, sainfoin could be grown for the production of protein as an alternative to other crops.     

Assessment of the Microbiological Safety of Dried Spices and Herbs Commercialized in Spain

Spices and herbs are natural products or their blends that must be free of extraneous matter content. Conventional production of these products implicates a number of hygienic problems so spices and herbs may be exposed to a wide range of microbial contamination during pre- and post-harvest and they can present high microbial counts. In this study, we have analyzed the microbial quality of 53 samples of spices and dry herbs collected from Spanish markets detecting a contamination of samples of spices with mesophilic aerobic counts (10%) and Enterobacteriaceae (20%). The analysis from herbs showed that the percentage of contamination was 26% in both microbiological values. Pathogenic microorganisms like Staphylococcus aureus, Yersinia intermedia, Shigella spp., Enterobacter spp., Acinetobacter calcoaceticus and Hafni alvei were also isolated from spices and herbs. These unsatisfactory results showed a poor microbiological quality. Spices and dry herbs are used as ingredients in a variety of products prepared in different ways, this fact suggests the need to provide a control system to improve the quality of herbs and spices.     

Nutritional properties of nonrice crops in the Asian Rice Farming Systems Network

Six legume crops and three cereal crops in the Asian Rice Farming Systems Network were compared with IR58 brown rice in terms of dry matter, energy and protein yields per hectare. Sorghum was closest to brown rice in dry matter and energy yield but soybean had the highest protein yield. Peanut and soybean had higher crude fat than the other crops which accounted for their high energy content and yield among the legumes. Amino acid analysis showed cowpea, mungbean, pigeonpea, bushsitao, and soybean protein as limiting in sulfur amino acids (cysteine + methionine). Peanut protein was limiting in either lysine or tryptophan + threonine. Corn, sorghum and wheat proteins were limiting in lysine.     

52份波兰小麦种子性状分析

为了解波兰小麦籽粒及其品质性状,对52份波兰小麦品种籽粒性状进行了测定,并对其品质性状间的相关性进行了分析.结果 表明:(1)供试波兰小麦籽粒千粒重变异系数最高为42.27％,其次为粗蛋白、湿面筋含量,变异系数分别为11.47％和11.74％;较高原448,10号的籽粒千粒重提高46.95％,20号的粗蛋白含量提高10...     

A real-time polymerase chain reaction (PCR) method for the identification of Nicotiana tabacum in tobacco products

A simple and specific real-time PCR assay based on TaqMan^® technology has been developed for the identification of cultured tobacco (Nicotiana tabacum) in various commodities such as cigars, cigarettes and reconstituted tobacco. The TaqMan^® assay targets a sequence of the putrescine N-methyltransferase gene family encoding an enzyme that plays a crucial role in the biosynthesis of nicotine. To reduce the possibility of false negatives, universal plant chloroplast primers were also used in a separate real-time PCR reaction to give indication if DNA is amplifiable in the matrix. The TaqMan^® assay successfully identified tobacco in over 40 commercial tobacco products, while negative results were obtained from the assay for DNA extracted from a variety of other botanical products. In our study, two commercial DNA isolation kits were used, namely, the Qiagen DNeasy^® Plant Mini kit and the Qiagen Gentra^® Puregene^® kit. They produced good quality DNAs in sufficient quantities for real-time PCR analysis. In a few cases, an additional purification step with the Promega DNA IQ™ system had to be implemented to obtain amplifiable DNA.     

Nutritive value of soybean protein supplemented with purified amino acids and bread

The nutritive value of soybean alone, supplemented with methionine+tryptophan or with bread was investigated. The results showed high Net Protein Utilization (N.P.U.) values for the autoclaved soybean diet (61.5) compared with that of raw soybean supplemented with methionine+tryptophan (57.7). It was found that rats fed the diets of raw soybean supplemented with methionine and tryptophan survived and the growth was improved to some extent.The N.P.U. values of the autoclaved soybean supplemented with methionine and tryptophan (67.4) was in close for that of casein (70.6).The effectiveness of soybean as a supplement to bread at a protein level of 50% was elucidated. The N.P.U. values of the autoclaved soybean supplemented with bread (65.8) was higher than that of either soybean or bread alone which showed the values of 61.5 and 47.0 respectively.     

人工改造基因Cry1Abm的合成、原核表达及其抗虫鉴定

根据植物密码子的偏好性及使用频率,对苏云金芽孢杆菌Cry1Ab野生型基因的编码区序列进行优化和改造,改造后的Cry1Abm基因序列与原始序列同源性为66.2%,G+C含量由37.3%提高到62.7%。人工合成Cry1Abm基因,并将人工合成的改造后的Cry1Abm基因构建到原核表达载体pET28b中,构建原核表达载体pETAbm。将原核表达载体转入大肠杆菌BL21（DE3）中进行诱导表达,用诱导表达的蛋白进行饲虫（玉米螟）实验。结果表明,该蛋白对幼虫具有很强毒性,幼虫的死亡率高达86.63%,同时,存活幼虫的生长发育也受到明显抑制。该基因可以作为杀虫工程及培育转基因抗虫作物的候选基因。     

Effect of amino acid supplementation on protein quality of soy-based infant formulas fed to rats

The powder forms of soy-based infant formulas obtained from four manufacturers were fed to weanling rats for two weeks, as the sole source of protein in diets containing 8% protein, 20% fat, and adequate amounts of minerals and vitamins. The relative protein efficiency ratio (RPER) and the relative net protein ratio (RNPR) values (casein + methionine=100) of diets containing unsupplemented formulas were 71–81 and 78–85, respectively. Supplementation of the formula diets with lysine (0.2%), methionine (0.2%), threonine (0.1%) or tryptophan (0.05%) increased the level of the supplemental amino acid in rat serum but generally failed to improve the RPER or RNPR values. Addition of all four essential amino acids to the formula diets, however, caused a marked improvement in their protein quality (RPER or RNPR values=100). The data suggested that proteins in soy-based formulas could be marginally co-limiting in several indispensable amino acids.Presented in part at the 202nd annual meeting of the American Chemical Society, New York City, 25–30 August 1991.     

Nutritional quality of a spun soya-bean protein: Comparison of biological and microbiological tests

A commercial spun soya-bean protein that had been subjected to mild alkali treatment in its manufacture, and the protein isolate from which it had been made, were evaluated in biological and microbiological tests. When diets were givenad lib. in tests with rats, growth was better on the parent protein; but with equal, restricted dietary intakes there was no difference between the two protein sources. The kidneys of all the rats appeared normal on histological examination and showed no signs of nephrocytomegalia, which has been found in the kidneys of rats given soya protein subjected to severe alkali treatment. Similarly in growth tests with chicks, there was no difference between the two proteins and it was concluded that the manufacturing process did not impair the nutritional quality of the spun protein. In microbiological assay tests withStreptococcus zymogenes, the available methionine of the alkali-treated material was consistently lower by about 20%. But when pronase was substituted for the papain normally used in the assay procedure there was no difference between the preparations; the methionine appeared fully available. The lower values following papain predigestion probably indicated a real though small difference in rate of proteolysis but this was clearly not significant in relation to biological availability for rats and chicks.     

Digestibility of protein and amino acids in selected foods as determined by a rat balance method

Values (%) for true digestibility of crude protein and individual amino acids in 20 selected foods were determined by the rat balance (fecal) method. The products were fed as the sole source of protein in diets containing 8% crude protein (N × 6.25). Lowest true protein digestibility values (79–84) were obtained for pinto beans, kidney beans and lentils; intermediate values (89–92) were obtained for chick peas, beef stew, skim milk (over heated), rolled oats, whole wheat cereal, and pea protein concentrate; and highest values (94–100) were obtained for sausage, macaroni-cheese, rice-wheat gluten cereal, skim milk, tuna, soy isolate, peanut butter, chicken frankfurters, beef salami, casein and casein + methionine. In animal foods, peanut butter and soy isolate, the differences between true digestibility of crude protein and most individual amino acids were less than 5%. However, the values for true digestibility of methionine and cystine were up to 44% lower than those of crude protein in pinto beans, kidney beans, lentils, chick peas and pea concentrate. In these legumes, digestibility of crude protein was not a good predictor of digestibility of the limiting amino acids.     

Chemical composition and nutritional quality of five peanut cultivars grown in Pakistan

Four high yielding imported and one local peanut cultivar, grown under local soil and climatic conditions, were compared for their chemical composition and nutritional quality. The local cultivar Kurram contained the maximum protein (28.3%) and the imported cultivar No. 45 contained the maximum oil content (49.5%). K, Mg, P, Fe, Zn, Cu and Mn were present in nutritionally significant and comparable amounts in all the cultivars. Lysine was the first limiting amino acid in all the cultivars. The chemical scores and net protein utilization (operative) values were higher for the imported than local cultivar while net dietary protein calories percent (NDP Cal%) values showed only minor variations among the five cultivars. Significant differences (P<0.05) were observed for protein, oil, Na, K, Ca, P and Zn contents of all the cultivars. Roasting (150°C, 1/2 h) decreased the lysine, threonine, methionine, cystine, arginine, tryptophan and tyrosine contents but increased the protein, oil, ash, fiber, mineral elements (except Na and C1), aspartic acid, serine, glutamic acid, proline and phenylalanine contents.     

Protein quality of peas as influenced by location,nitrogen application and seed inoculation

A study was conducted to evaluate the contribution of location, N application andRhizobium seed inoculation to variations in seed protein content and amino acid (AA) composition of field peas. The magnitude of AA variations with protein level and the nature of the relationships that are involved were determined. Regression equations to predict AAs from protein were developed for the cultivar Bohatyr. The experiments were carried out at two locations in southern Manitoba in 1994. The levels of N fertilization investigated were: 56, 75, 100, 125, 150, 200, 250 and 300 kg/ha. At each level of N application, seeds planted were eitherRhizobium inoculated or not inoculated. The combination of location, fertilizer treatments and inoculation yielded 192 samples for chemical analyses. The samples were analyzed for dry matter (DM), N and AA contents. Location and N fertilization had significant (p0.001) effects on seed protein content and AA composition. Seed protein content increased with increasing levels of N application. The response of protein to fertilization was not the same in both locations as evidenced from the presence of interaction (p0.01) between location and N application. Except for methionine and cystine, percent AAs in DM increased with increasing levels of N application. The effects of N application on the concentrations of methionine and cystine were not consistent. On protein basis, the concentrations of AAs decreased with increasing levels of N application. The only exception was arginine which strongly increased in concentration. There was no effect (p0.05) of seed inoculation observed in this study. Strong positive correlations (r>0.80) between seed protein content and AA concentrations expressed as percent of DM were found for all AAs except for methionine (r=0.76) and cystine (r=0.51). When AA concentrations are expressed as g per 16 g N, 15 of the 17 AAs were negatively correlated to seed protein content. Only arginine (r=0.78) and aspartic acid (r=0.17) had positive correlations. The regression equations developed from this study could be used to predict the concentrations of AAs except methionine and cystine for the cultivar Bohatyr once the protein content is known.     

Effect of selected Egyptian cooking methods on faba bean nutritive value and dietary protein utilization 2: Ability of faba bean products to support hemoglobin response in rats

To evaluate the dietary protein utilization and iron deficiency anemia as affected by the faba bean nutrient intake, a bioassay with rats was carried out with different experimental diets containing four faba bean products (stewed beans ‘Medammis’, deep fried dough ‘Falafel’, boiled germinated beans ‘Nabet Soup’ and poured paste ‘Bissara’) widely consumed in the Middle East. Amino acid composition of all faba bean products was determined and compared to raw beans. Severe heat-processing markedly decreased some essential amino acids, especially phenylalanine, cystine, methionine and tryptophan. Protein scores were 24.6, 19.5, 29.2, 28.2 and 35.6 for raw faba beans, ‘Medammis’, ‘Falafel’, ‘Nabet Soup’ and ‘Bissara’, respectively. ‘Bissara’ possessed the highest nutritional value, since it had the lowest GDR value [Grams consumed of product to cover the daily requirements for adult man in protein (63 g) and in energy (2900 kcal)] for the limiting amino acids (L A A). As indicated by P S/150 values [Satisfaction of the daily requirements of the adult man when 150 g (one can content) are consumed of product] for L A A, i.e. methionine+cystine (lowest P S/150 value), the above-mentioned faba bean products cover about 53, 77, 77 and 97% of the daily requirements of adult man in L A A, respectively. Fecal nitrogen excretion increased and true nitrogen digestibility decreased significantly (p<0.01) with the inclusion of ‘Medammis’ in the diet. ‘Nabet Soup’ exhibited the highest true nitrogen digestibility. In contrast, the biological value of nitrogen was apparently unaffected. Highest blood hemoglobin level was found in rats fed diets containing ‘Bissara’, ‘Falafel’ and ‘Nabet Soup’, whereas the addition of ‘Medammis’ in the diet induced a significant (p<0.05) reduction in blood hemoglobin level of fed rats.     

Effects of roasting and storage on proteins and oil in peanut kernels

Peanut kernels, untreated or soaked in salt solution, were roasted at 160°C for 30 min in a hot air oven or oil roasted at 147°C for 2 min and, stored at 27°C and 5°C up to 150 days. The heat treatments significantly decreased methionine, tryptophan and in vitro protein digestibility (IVPD) and, increased the soluble proteins and acid value of kernel oil. Storage of heated peanuts caused an increase in water-soluble proteins, IVPD, acid value and saponification value and a decrease in methionine, tryptophan and iodine value. The oil roasting was found to be more detrimental to nutritional quality and storage stability of peanuts as compared to dry roasting. The storage of heated peanuts at 5°C was found to be beneficial in lowering the undesirable nutritional changes in the peanut kernels.     

Nutritional improvement of lentils,chick pea,rice and wheat by natural fermentation

Effect of natural fermentation process (4 days) on the non-protein nitrogen, crude and true protein, amino acids content and in vitro digestibility of two kinds of legumes (lentils and chick pea) and two kinds of cereals (rice and wheat) was investigated. Non-protein nitrogen increased significantly (p<0.001) in the fermented products. Little increase has occured in the crude protein while no significant change was observed in the fermented true protein samples. It was observed that methionine and cystine which are considered the limiting amino acids in legume seeds were close to those of FAO/WHO patterns. Also, lysine content (the first limiting amino acid in cereals was higher in fermented rice than that of FAO/WHO pattern. Moreover, fermentation process improved significantly, the in vitro digestibility of both legume and cereal products.     

Influence of tryptophan supplementation of soy-based infant formulas on protein quality and on blood and brain tryptophan and brain serotonin in the rat model

A 2-wk feeding study with weanling rats was conducted to investigate theeffects of tryptophan supplementation of soy-based infant formulas on proteinquality and on the levels of blood and brain tryptophan and brain serotoninand 5-HIAA (5-hydroxyindole-3-acetic acid), a metabolite of serotonin. Thepowder and liquid concentrate forms of soy-based infant formulas obtainedfrom four manufacturers were tested. The tryptophan contents of the testsoy-based formulas (10.0–12.3 mg/g protein) were considerably lower comparedto those of human milk (17–19 mg/g protein). The infant formulas were fedas the sole source of protein in diets containing 8% protein, 20% fat, 5%cellulose and adequate amounts of minerals and vitamins. In general, supplementation of the diets containing test formulas with graded levels ofL-tryptophan (0.1 or 0.2%) had no effect on protein quality indices basedon rat growth such as PER (protein efficiency ratio), NPR (net protein ratio)and relative NPR (RNPR), but resulted in significant (p<;0.05) increases inthe concentrations of tryptophan in the plasma and brain, and serotonin and5-HIAA in brain of rats. The increased concentrations of brain tryptophan and5-hydroxyindoles (serotonin + 5-HIAA) in rats fed tryptophan-supplementedformulas compared to those fed unsupplemented formulas support the need forfurther research to investigate the influence of tryptophan supplementationof soy-based infant formulas on tryptophan metabolites and their potentialrelated effects on sleep latency and neurobehavioral developments in infants.     

Methionine-containing proteins in twoPhaseolus vulgaris cultivars with different methionine bioavailabilities

The full utilization of legumes as human food is limited by a deficiency of sulfur amino acids, low protein digestibility, low methionine bioavailability and the presence of anti-nutritional factors. A new cultivar ofPhaseolus vulgaris (Carioca 80) has 56.8% available methionine, compared with 29.3% availability in the parent cultivar Carioca. The total methionine content, denaturing gel electrophoretic patterns of methionine-containing proteins, and the percentage of phaseolins (the major storage proteins in Phaseolus) relative to the total protein are similar in the two cultivars. Although the digestibility of the two cultivars is similar, the increased biological value of Carioca 80 may indicate that there are differences in overall bean composition that affect protein hydrolysis and utilization. We suggest the tentative explanation that this is due to differences in the distribution of methionine in the methionine-containing proteins of the two cultivars.     

野生一粒小麦根干旱响应蛋白的筛选与鉴定

为解析野生一粒小麦根响应干旱胁迫的调控网络,用20%(w/v)PEG6000处理两叶一心期野生一粒小麦,通过对小麦根蛋白质的分离和鉴定,分析了干旱胁迫下野生一粒小麦根中的蛋白质变化。结果共分离、鉴定得到85个表达差异倍数在1.5以上的蛋白质。这些差异蛋白主要涉及碳代谢(27%)、氨基酸代谢(15%)、解毒与防御(11%)、分子伴侣(8%)、能量代谢(8%)、信号传导(6%)、蛋白质代谢(5%)、脂代谢(4%)、转录与翻译(4%)、核苷酸代谢(2%)以及骨架蛋白(1%)。对这些表达差异蛋白进行进一步的功能分析,发现大部分信号传导相关蛋白上调表达;碳代谢途径中的糖酵解相关蛋白下调表达,而磷酸戊糖途径相关蛋白上调表达。同时下调表达的还包括蛋白质代谢相关蛋白。大部分氨基酸代谢相关蛋白质下调表达,但是谷氨酸脱羧酶及甲硫氨酸合酶含量上升。结果表明,干旱胁迫增强了野生一粒小麦根中信号传导与磷酸戊糖途径代谢,促进了谷氨酸与甲硫氨酸的生物合成,降低了糖酵解与蛋白质代谢等过程。研究结果丰富了野生一粒小麦根响应干旱胁迫机制信息。