Protein extraction from pasture: Effect of crop species,regrowth age and season on the quality of the extracted protein

Leaf protein concentrates (LPC) were prepared from ryegrass (Lolium perenne), white clover (Trifolium repens), lucerne (Medicago sativa cv. Wairau), and from ryegrass/white clover dominant pasture, harvested after a range of regrowth intervals in spring, summer and autumn seasons. Protein quality was measured by rat growth (to give Relative Nutritive Value, RNV) and in-vivo rat true digestibility. RNV for LPC prepared from all crops was about 50% of that for lactalbumin. Results were highest for lucerne and lowest for ryegrass and ryegrass/white clover. When LPC was supplemented with methionine, RNV improved to 80–90% of that for lactalbumin. Quality was highest and similar for white clover and lucerne and lowest and similar for ryegrass and ryegrass/white clover. The true digestibility of protein was highest for lucerne (82%) and lowest for ryegrass and ryegrass/white clover (70%). These variations may be related to the proportions of cytoplasmic and chloroplastic protein in the juice. There was no effect of season (autumn vs spring) or age of herbage at harvest (4, 6, or 8 weeks regrowth) on the quality of protein. Despite standardised procedures for harvesting, processing, and drying the LPC and for assessing protein quality, undefined factors caused variation in methionine-supplemented protein quality.     

Protein extraction from pasture: The nutritional availability of methionine,cystine and lysine in leaf protein concentrates

Leaf protein concentrates (LPC) were prepared from ryegrass (Lolium perenne), white clover (Trifolium repens), mixed ryegrass/white clover and lucerne (Medicago sativa cv. Wairau). Total and nutritionally available levels of methionine and cystine, and nutritionally available levels of lysine were measured. Total and available methionine in LPC averaged 1.94 and 1.60 g 16 g^?1 N respectively. The availability of methionine was increased (from 81% to 85%) when the herbage was treated with sodium metabisulphite before pulping. Total and available cystine in LPC averaged 0.96 and 0.26 g 16 g^?1 N respectively; availability increased (from 27% to 73%) when herbage was treated with metabisulphite. Of the two sulphur amino acids, cystine undergoes the greatest nutritional damage during processing in the absence of reducing agent. Available lysine averaged 5.29 and 5.61 g 16 g^?1 N for control and metabisulphitetreated LPC respectively. Improvements due to metabisulphite were small. Available lysine was higher in LPC from legume herbages (5.9 g 16 g^?1 N) than from ryegrass and ryegrass/white clover herbage (5.0 g 16 g^?1 N).     

Amino acid composition and nutritional value of italian ryegrass,red clover and lucerne as influenced by application and content of nitrogen

In experiments with increasing applications of nitrogen to ryegrass, red clover and lucerne grown in pots, freeze-dried plant material with widely varying N-content was obtained. Increasing N-concentrations were associated with increasing nitrate contents which proportionally decreased the concentrations (g/16 g total-N) of all amino acids. Expressed as g amino acid/16 g total-N minus NO₃-N, concentrations of all amino acids were closely similar at different N-levels. Differences between the three species ' amino acid composition were negligible except for a lower concentration of lysine in the crude protein of ryegrass and of methionine + cystine in the crude protein of clover and lucerne. In feeding experiments with rats increasing total-N concentrations were generally associated with higher true digestibilities of the crude protein of ryegrass, red clover and lucerne, but slightly lower biological values, especially in red clover. Net crude protein utilisation was increased by increasing total-N concentration in ryegrass, decreased in red clover and unchanged in lucerne. When ranked according to the nutritional value of the crude protein, ryegrass comes first, lucerne second and red clover last. Addition of synthetic methionine to ryegrass and lucerne improved their biological values by 30 and 47% respectively.     

Improvement of the nutritive value of cereals by leaf protein supplementation

The gross composition and amino acid content of the proteins of barley, corn, rye and wheat grains were determined. Leaf protein concentrates (LPC) were produced from the green matter of clover, lucerne, barley and ryegrass using standard methods and analysed as for the cereal grains. Each cereal was mixed with each concentrate at a protein ratio of 2:1, respectively. The chemical score (CS) and essential amino acid index (EAAI) of the cereals, the protein concentrates and their mixtures were calculated. The biological value (BV) and true digestibility (TD) of all proteins were determined on rats using the Thomas-Mitchell balance method. LPC proteins contained more lysine (4.6–6.0%) but less cystine than cereal proteins (2.8–3.8 and 2.3–2.7 g per 16 g N, respectively). The CS and BV of LPC proteins were low (30–40 and 44–58, respectively) because of the low cystine content. Mixing cereals with LPC improved the CS, EAAI and BV of their proteins. The BV of the protein mixtures was in almost every case higher than that of either protein alone, but the digestibility of the cereal proteins was reduced as a result of admixture with LPC, especially with clover LPC.     

The in-vitro digestibility and chemical composition of plant parts in white clover,red clover and lucerne during primary growth

White clover (cv. Grasslands Huia), red clover (cv. Norseman) and lucerne (cv. Sabilt) were sampled during primary growth at the flower bud, near full flowering and seeds formed stages in each of 2 years. Each sample was separated into 2–11 plant parts, depending on species and stage of growth, and for each part the in-vitro true dry matter digestibility, digestibility of cell wall and percentages of cell content, nitrogen, water-soluble carbohydrate and lignin were determined. Green leaflets of all three species were consistently high in digestibility. The cell wall fraction of green leaflets was less digestible in red clover than in white clover and lucerne. The digestibility of the upper part of the stem of lucerne and red clover was high at the flower bud stage but declined considerably thereafter, whereas the digestibility of the lower part of the stem was much lower at the flower bud stage and declined relatively little. The green leaf stalks and inflorescences were generally rather less digestible than green leaflets and, in lucerne and red clover, more digestible than stems. In white clover the inflorescence stalks were less digestible than the leaf stalks. The digestibility of plant parts was strongly correlated with the proportion of cell content, and less strongly with the digestibility of cell wall. The proportion of cell content was positively correlated with N%, and the digestibility of cell wall was negatively correlated with the proportion of lignin in cell wall.     

Digestive utilisation of protein and amino acids from raw and heated lentils by growing rats

The effect of autoclave treatment on the digestive utilisation of protein and amino acids from lentils was studied in growing rats. Twenty 3‐week‐old Wistar rats (mean live weight 59 ± 4.8 g) were fed two experimental diets (n = 10 rats per diet) consisting of raw lentils (Lens culinaris M, var vulgaris, cv magda‐20) (diet RL) or lentils autoclaved at 120 °C and 1 atm for 30 min (diet AL). An additional group of 10 animals was fed a low‐protein (4%) diet and used to estimate metabolic nitrogen and amino acid excretion. Autoclaving caused a 76% reduction in the levels of trypsin inhibitor activity, but failed to improve the faecal digestive utilisation of protein or total amino acids. Lowest essential amino acid true digestibility in diets RL and AL was found for cysteine (60.2 vs 60.1%) and methionine (68.9 vs 66.6%). The protein digestibility‐corrected amino acid score was 71.2 and 66.4% and the availability of sulphur amino acid‐corrected amino acid score was 57.1 and 52.1% for diets RL and AL respectively. Sulphur amino acids were the first limiting ones. Overall, autoclave treatment did not improve protein or total amino acid digestibility from lentils, but caused a significant improvement in leucine and lysine digestibility and a significant decrease in the digestive utilisation of tyrosine and methionine. © 2002 Society of Chemical Industry     

Nutritional quality of the blue-green alga Spirulina platensis geitler

The nutritional quality of the blue-green alga Spirulina platensis has been evaluated on the basis of its chemical and amino acid compositions and feeding trials with rats. The protein content of the alga was 58.5%, lysine 4.34 g 100 g^?1 protein, sulphurcontaining amino acids (methionine and cystine) 2.77 g 100 g^?1 protein, and nucleic acids 4%. The true protein digestibility of the alga was found to be 75.5 and its biological value (BV) 68. Supplementation of the alga with methionine (0.2%) resulted in a significant improvement in the BV and net protein utilisation (NPU), but had no effect on true digestibility (TD). TD, BV and NPU were significantly improved when the alga was supplemented with barley (50% nitrogen from both). In Chad and Mexico the alga has been used for centuries as a food. This together with its low cost of production, makes it a suitable source of high quality protein for use as a feed supplement.     

Nutritive value of meat meals. II. Influence of raw materials and processing on protein quality

Commercial meat meals have shown low net protein utilisation values with rats of about 32, which is only 40% of the corresponding value for freeze-dried meat or gut. Biological assays for methionine and tryptophan, based on the weight gains of chicks, have shown a similar inferiority of meat meals despite 81–87% digestibility of their N. It is concluded that the lysine, methionine and tryptophan of the meat meals are approximately 80% available and that dilution of muscle protein with tendon and ossein in the raw material is at least as important as processing damage in reducing the quality of the products. It is argued that previous estimates of only 30% availability of methionine in meat meals are erroneous. Further problems in the use of values for fluorodinitrobenzene-available lysine and Streptococcus zymogenes-ayailable trytophan are discussed.     

The nutritional quality of some Pakistani wheat varieties.

The nutritional quality of some improved wheat varieties grown in pakistan was measured chemically (including amino acid analyses) and biologically in n-balance experiments with growing rats. the protein content ranged from 12.3 to 16.7%. lysine per 100 g protein varied between 2.46 and 2.90%. the protein of chenab-70, punjab-76 and barani-70 contained 16-18 % more lysine than the sa-75 having highest content of protein. iron content was highest in pari-73. the true protein digestibility (td), biological value (bv), net protein utilisation (npu) and net dietary protein calorie percent (ndp cal %) varied between 91-94 %, 58-69 %, 54-63 % and 7.4-8.8 %, respectively. available carbohydrate, lysine and biological value were lowered in varieties with a higher content of protein.     

Effect of cooking on protein quality of chickpea (Cicer arietinum) seeds

Amino acid composition and in vitro protein digestibility of cooked chickpea were determined and compared to raw chickpea seeds. Heat treatment produced a decrease of methionine, cysteine, lysine, arginine, tyrosine and leucine, the highest reductions being in cysteine (15%) and lysine (13.2%). Protein content declined by 3.4% and in vitro protein digestibility improved significantly from 71.8 to 83.5% after cooking. The decrease of lysine was higher in the cooked chickpea seeds than in the heated protein fractions, globulins and albumins. The structural modification in globulins during heat treatment seems to be the reason for the increase in protein digestibility, although the activity of proteolytic inhibitors in the albumin fraction was not reduced. Results suggest that appropriate heat treatment may improve the bioavailability of chickpea proteins.     

Protein quality and energy density of green peas as influenced by seed size and time of harvest

Green peas (Pisum sativum L) were harvested at three different time points—3 days apart—and subsequently sorted into four fractions according to seed size (diameter > 10.2 mm; 10.2–8.75 mm; 8.75–8.2 mm and 8.2–6.0 mm). Three varieties from two years were investigated. The study comprised a total of 31 green pea samples. The average protein content of the samples was 276 g kg^?1 DM with relatively low variation (SE = 5.7). Protein content was highest in the smallest seeds. The average energy content was 18.6 MJ kg^?1DM. Dietary fibre content was 226 g kg^?1 DM, the major part (77%) as insoluble fibre. Seeds of early harvest and seeds with the smallest diameter had the lowest fibre (IDF and TDF) content and at the same time the highest energy digestibility. The average energy digestibility was 83.2%. Protein digestibility was relatively high (average 92.1%), while biological value (BV) and net protein utilisation (NPU) were moderate to low (60.6% and 55.8% respectively) due to low contents of the essential amino acids (g per 16 g N), especially tryptophan, methionine + cystine and lysine. Contents of lysine, tryptophan and methionine + cystine were more than 20% higher in the smallest seeds compared to the larger seeds. Similar differences were observed in seeds of late harvest as compared with seeds of early harvest. Correlation coefficients revealed a strong positive correlation between lysine, tryptophan and methionine + cystine content and the biological value of green pea protein. The three varieties investigated showed no differences in the chemical parameters although small differences in BV and NPU were observed.     

Trypsin inhibitors in leaf protein concentrate

A study has been made of the tryptic inhibitory activity of leaf protein concentrate (LPC) prepared from several crops. The highest level of inhibition was found in LPC extracted from lucerne (50%), compared with that from fescue, Italian ryegrass and quinoa, which contained about 20% tryptic inhibitory activity. No inhibitory activity was found in kale LPC when measured under the defined conditions. Aqueous extraction of LPC decreased inhibitory activity, but solvents (propan-2-ol and acetone) were ineffective. The inhibitory activity in lucerne LPC was reduced by autoclaving, but the inhibitors in fescue, Italian ryegrass and quinoa were heat stable. Phenolic compounds were implicated in the inhibitory activity of fescue and Italian ryegrass LPC. Kinetic studies of the inhibitory activity of standard LPC samples prepared from Italian ryegrass, fescue and quinoa indicated that, in each instance, there was mixed inhibition.     

Solvent fractionation of leaf juice to prepare green and white protein products

The effectiveness of organic solvents in the separation of pigmented protein from leaf juice was studied, thus permitting the recovery of a non-pigmented protein suitable for use in human foods. Juices extracted from lucerne (Medicago sativa L.), tall fescue (Festuca arundinacea L. var. Alta) and Italian ryegrass (Lolium multiflorum L. var. RVP) were studied. The yield of ?white’? protein from lucerne was double that from the grasses and it was lighter in colour. Of 20 solvents tested, 13 promoted the separation of chloroplastic material. These were in two categories: solvents with limited water solubility which were effective at a 3-4% (w/w) concentration and highly polar solvents which were effective at a 10-12% (w/w) concentration. Solvents of high specific gravity were not effective. Various conditions of solvent concentration, temperature and pH were studied with representatives of both groups of solvents in order to optimise the yield of ?white’? protein. Solvent fractionation, as a method of preparing a non-pigmented protein concentrate, is discussed in relation to differential heat treatment of leaf juice and solvent extraction of whole leaf protein concentrate. The potentials of these concentrates in human foodstuffs is compared.     

In-vitro protein and sulphur amino acid availability as a measure of bean protein quality

The total and ‘available’ cystine and methionine, and the in-vitro and in-vivo protein digestibilities were determined in six varieties of Phaseolus vulgaris with different seed coat colours. Reactive cystine and methionine, evaluated by chemical methods after in-vitro enzymic digestion, were taken as a measure of the availability of sulphur amino acids. Cystine ‘availability’ ranged from 43 to 51% and from 31 to 58% in raw and cooked samples, respectively, while methionine ‘availability’ was over 90%, except for the two red varieties (55% and 74%). No correlation was found between cystine and methionine ‘availability’ and in-vitro protein digestibility. In-vitro protein digestibility (76.6-80.7%) showed a good correlation (r = 0.857; P < 0.05) with in-vivo values (72.0-80.9%). Amino acid score corrected for protein digestibility and for sulphur amino acids availability, as suggested by the Codex Committee on Vegetable Proteins, seems to predict accurately the biological quality of bean protein, as was shown when in-vitro indices were compared with net protein utilisation and relative protein value.     

Use of leaf enriching harvesting methods to increase the yield of leaf protein concentrate from lucerne

A prototype leaf stripping machine and a conventional forage harvester with a raised header were used to obtain high protein lucerne (alfalfa) fractions. The stripped lucerne leaves and lucerne tops contained 26.2 and 27.2% protein, respectively. Pilot-scale extraction of the ground leaves and the ground tops resulted in leaf protein concentrate (LPC) yields of 18.8 and 20.0%, respectively, compared with 12.8 and 15.7% for the appropriate whole lucerne control. LPC yields as high as 27.4% were obtained by the addition of lucerne solubles to the lucerne tops prior to grinding. Low LPC yields (4.0–8.0%) were obtained from the lucerne stem fraction. After processing, the press cake fraction from the leaf-enriched feed materials still contained over 17% protein.     

Effects of Storage on Protein Nutritional Quality of Grain Legumes

The effect of storage under moderate conditions (12% relative humidity and 20°C) on protein nutritional quality of legumes grown in Canada (faba bean, lentil, seafarer, pinto and black beans and trapper and century peas) was determined. Little change in legume amino acid contents and only slight changes in relative net protein ratio (RNPR) and true crude protein digestibility occurred over the three years. No consistent changes were seen in plasma amino acids of rats fed the stored legumes, although plasma methionine and tryptophan were lower compared to casein-fed rats, reflecting dietary deficiencies in these amino acids. Amino acid scores indicated that tryptophan and sulfur amino acids were first and second limiting, respectively, in most of the legumes. Correction of amino acid scores for true digestibility of protein in the legumes greatly improved correlation coefficients between scores and RNPR.     

Nutritional quality evaluation of newly developed high-protein genotypes of pigeonpea (Cajanus cajan)

Two high-protein genotypes of pigeonpea (Cajanus cajan L), HPL 8 and HPL 40, were analysed for their nutritional quality characteristics, and the results were compared with those of normal-protein genotypes (C 11 and ICPL 211). The protein content of the high-protein genotypes was higher on average by nearly 20% but their starch content, the principal constituent of the seed, was lower by about 8%. The higher fraction (about 7%) of globulin, the major storage protein, was associated with a lower glutelin fraction in the high-protein genotypes. The amino acid composition (g per 100 g protein) of the high-protein genotypes was comparable with those of the normal-protein genotypes. However, the sulphur-containing amino acids methionine and cystine were noticeably higher (about 25%) in high-protein genotypes when results were expressed in g per 100 g sample. No large differences in true protein digestibility, biological value and net protein utilisation were observed between HP and NP genotypes. True protein digestibility was significantly increased by cooking in both whole-seed and dhal samples. The values for utilisable protein were considerably higher in high-protein genotypes, suggesting their superiority from the nutritional point of view.     

Effect of Heat Treatments on In Vitro Digestibility of Delactosed Whey Protein as Determined by the Digestion Cell Technique

Diafiltered whey protein concentrates (WPC) were heated, in liquid form, under various conditions of time and temperature. Protein and amino acid digestibilities were determined by in vitro pepsin and pan-creatin digestion with continuous dialysis. Whey nitrogen digestibility decreased (P < 0.05) after heating at 121°C for 5000 sec. Heating WPC for 5000 set at temperatures below 121°C increased the digestibility of all amino acids except alanine and lysine at 75°C, and methionine and lysine at 100°C. In general, the longer was the heating period at 100°C or 121°C the lower was the amino acid digestibility. These results emphasized the importance of structural modifications brought about by heat treatments on protein digestibility.     

Rapeseed meal. II. Chemical composition and biological quality of the protein

The chemical composition (moisture, ash, protein, amino acids, ether extract, crude fibre, Ca, P, Fe, thioglucosides, isothiocyanates and oxazolidinethiones) and biological quality (net protein utilisation, available lysine and digestibility) were investigated in 12 samples of presscake meal of rapeseed (Brassica napus) collected from local factories. Crude fibre and mineral contents were comparatively high. Thioglucosides and their hydrolysis products (isothiocyanates and oxazolidinethiones, which are toxic) were found in high concentrations. All samples showed a high protein content and their amino acid patterns corresponded to a good-quality protein with a score of 80, and an adequate level of available lysine. Nevertheless, the biological quality measured as net protein utilisation and digestibility gave low values, which could be explained on the basis of the presence of the toxic factors and the high level of crude fibre, respectively.     

Lysine in cassava based diets: I. A note on the effect of heat on digestibility and available lysine

Heating Conophor seeds and Amaranthus leaf protein concentrate (LPC) for 24 h at 121°C reduced the digestibility of their crude protein contents.Loss in available lysine was moderate in LPC alone and cassava-LPC mixtures heated for 24 h at 121°C (≤45% loss) but high in Conophor seeds and glucose-LPC mixtures (72 and 80% loss respectively).