Nitrogen-to-Protein Conversion Factors for Some Common Edible Mushrooms

Mushrooms (13) common to Japan were analyzed for total nitrogen (TN), amino acid nitrogen (AAN), amide-N and nonprotein nitrogen. The distribution of protein nitrogen averaged 67% to TN. Averaged nitrogen-to-protein conversion (N:P) factor was 5.99. Application of the factor for estimation of protein content resulted in a considerable difference from amino acid residue (AAres) levels, due to the high level of nonprotein nitrogen. A net N:P factor, defined as the proportion of AAN to TN, was proposed. The averaged value of 3.99 was derived from analytical TN and AAN data of mushrooms. Calculated protein values using this factor were in good agreement with AAres.     

Effect of source of rumen-degraded protein on production and ruminal metabolism in lactating dairy cows

Twenty-eight (8 with ruminal cannulas) lactating Holstein cows were assigned to seven 4 × 4 Latin squares in a 16-wk trial to study the effects on production and ruminal metabolism of feeding differing proportions of rumen-degraded protein (RDP) from soybean meal and urea. Diets contained [dry matter (DM) basis] 40% corn silage, 15% alfalfa silage, 28 to 30% high-moisture corn, plus varying levels of ground dry shelled corn, solvent- and lignosulfonate-treated soybean meal, and urea. Proportions of the soybean meals, urea, and dry corn were adjusted such that all diets contained 16.1% crude protein and 10.5% RDP, with urea providing 0, 1.2, 2.4, and 3.7% RDP (DM basis). As urea supplied greater proportions of RDP, there were linear decreases in DM intake, yield of milk, 3.5% fat-corrected milk, fat, protein, and solids-not-fat, and of weight gain. Milk contents of fat, protein, and solids-not-fat were not affected by source of RDP. Replacing soybean meal RDP with urea RDP resulted in several linear responses: increased excretion of urinary urea-N and concentration of milk urea-N, blood urea-N, and ruminal ammonia-N and decreased excretion of fecal N; there was also a trend for increased excretion of total urinary N. A linear increase in neutral detergent fiber (NDF) digestibility, probably due to digestion of NDF-N from lignosulfonate-treated soybean meal, was observed with greater urea intake. Omasal sampling revealed small but significant effects of N source on measured RDP supply, which averaged 11.0% (DM basis) across diets. Increasing the proportion of RDP from urea resulted in linear decrease in omasal flow of dietary nonammonia N (NAN) and microbial NAN and in microbial growth efficiency (microbial NAN/unit of organic matter truly digested in the rumen). These changes were paralleled by large linear reductions in omasal flows of essential, nonessential, and total amino acids. Overall, these results indicated that replacing soybean meal RDP with that from urea reduced yield of milk and milk components, largely because of depressed microbial protein formation in the rumen and that RDP from nonprotein-N sources was not as effective as RDP provided by true protein.     

Effects of different protein supplements on omasal nutrient flow and microbial protein synthesis in lactating dairy cows

Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were used in 2 replicated 4 × 4 Latin squares to quantify effects of supplementing protein as urea, solvent soybean meal (SSBM), cottonseed meal (CSM), or canola meal (CM) on omasal nutrient flows and microbial protein synthesis. All diets contained (% of dry matter) 21% alfalfa silage and 35% corn silage plus 1) 2% urea plus 41% high-moisture shelled corn (HMSC), 2) 12% SSBM plus 31% HMSC, 3) 14% CSM plus 29% HMSC, or 4) 16% CM plus 27% HMSC. Crude protein was equal across diets, averaging 16.6%. The CSM diet supplied the least rumen-degraded protein and the most rumen-undegraded protein. Microbial nonammonia N flow was similar among the true protein supplements but was 14% lower in cows fed urea. In vivo ruminal passage rate, degradation rate, and estimated escape for the 3 true proteins were, respectively, 0.044/h, 0.105/h, and 29% for SSBM; 0.051/h, 0.050/h, and 51% for CSM; and 0.039/h, 0.081/h, and 34% for CM. This indicated that CSM protein was less degraded because of both a faster passage rate and slower degradation rate. Omasal flow of individual AA, branched-chain AA, essential AA, nonessential AA, and total AA all were lower in cows fed urea compared with one of the true protein supplements. Among the 3 diets supplemented with true protein, omasal flow of Arg was greatest on CSM, and omasal flow of His was greatest on CSM, intermediate on CM, and lowest on SSBM. Lower flows of AA and microbial nonammonia N explained lower yields of milk yield and milk components observed on the urea diet in the companion lactation trial. These results clearly showed that supplementation with true protein was necessary to obtain sufficient microbial protein and rumen-undegraded protein to meet the metabolizable AA requirements of high-producing dairy cows.     

Effects of different protein supplements on milk production and nutrient utilization in lactating dairy cows

Sixteen (8 ruminally cannulated) multiparous and 8 primiparous lactating Holstein cows were used in 6 replicated 4 × 4 Latin squares to test the effects of feeding supplemental protein as urea, solvent soybean meal (SSBM), cottonseed meal (CSM), or canola meal (CM) on milk production, nutrient utilization, and ruminal metabolism. All diets contained (% of DM) 21% alfalfa silage and 35% corn silage plus 1) 2% urea plus 41% high-moisture shelled corn (HMSC), 2) 12% SSBM plus 31% HMSC, 3) 14% CSM plus 29% HMSC, or 4) 16% CM plus 27% HMSC. Crude protein was equal across diets, averaging 16.6%. Intake and production were substantially reduced, and milk urea, blood urea, and ruminal ammonia were increased on urea vs. the diets supplemented with true protein. Although intake was lower in cows fed SSBM compared with CM, no differences were observed for milk yield among SSBM, CSM, and CM. Yields of fat and protein both were lower on CSM than on CM, whereas SSBM was intermediate. Milk urea and milk protein contents also decreased when CSM replaced SSBM or CM. Diet did not affect ruminal volatile fatty acids except that isobutyrate concentration was lowest on urea, intermediate on CSM, and greatest on SSBM and CM. Urinary excretion of urea N and total N was greatest on urea, intermediate on SSBM and CM, and lowest on CSM. Apparent N efficiency (milk N/N intake) was lower on the CSM diet than on the SSBM diet. Overall, production and N utilization were compromised when the diets of high-yielding dairy cows were supplemented with urea rather than true protein and the value of the true proteins, from most to least effective, was in the order CM > SSBM > CSM.     

Effects of feeding formate-treated alfalfa silage or red clover silage on omasal nutrient flow and microbial protein synthesis in lactating dairy cows

Eight ruminally cannulated Holstein cows that were part of a larger lactation trial were blocked by days in milk and randomly assigned to replicated 4 × 4 Latin squares to quantify effects of nonprotein N (NPN) content of alfalfa silage (AS) and red clover silage (RCS) on omasal nutrient flows. Diets, fed as total mixed rations, contained 50% dry matter from control AS (CAS), ammonium tetraformate-treated AS (TAS), late maturity RCS (RCS1), or early maturity RCS (RCS2). Silages differed in NPN and acid detergent insoluble N (% of total N): 50 and 4% (CAS); 45 and 3% (TAS); 27 and 8% (RCS1); 29 and 4% (RCS2). The CAS, TAS, and RCS2 diets had 36% high-moisture shelled corn and 3% soybean meal, and the RCS1 diet had 31% high-moisture shelled corn and 9% soybean meal. All diets contained 10% corn silage, 27% neutral detergent fiber, and 17 to 18% crude protein. Compared with RCS, feeding AS increased the supply of rumen-degraded protein and omasal flows of nonammonia N and microbial protein, which may explain the improved milk yield observed in the companion lactation trial. However, omasal flow of rumen-undegraded protein was 34% greater on RCS. Except for Arg, omasal flows of individual AA, branched-chain AA, nonessential AA, essential AA, and total AA did not differ between cows fed AS vs. RCS. Within AS diets, no differences in omasal AA flows were observed. However, omasal flows of Asp, Ser, Glu, Cys, Val, Ile, Tyr, Lys, total nonessential AA, and total AA all were higher in cows fed RCS1 vs. cows fed RCS2. In this trial, there was no advantage to reducing NPN content of hay-crop silage.     

Contribution of exopeptidases to formation of nonprotein nitrogen during ensiling of alfalfa

The experiment was conducted to investigate the exopeptidase classes in alfalfa (Medicago sativa L.) leaves, and to determine their contribution to the formation of nonprotein nitrogen (NPN) components during ensiling. Six classes of inhibitors that included bestatin (aminopeptidase inhibitor), potato carboxypeptidase inhibitor (PCI, carboxypeptidase inhibitor), 1,10-phenanthroline (dipeptidase inhibitor), diprotin A (dipeptidyl-peptidase inhibitor), butabindide (tripeptidyl-peptidase inhibitor), and dipeptide Phe-Arg (peptidyl-dipeptidase inhibitor) were used. To determine the contribution of each exopeptidase to the formation of NPN products, aqueous extracts of fresh alfalfa were fermented to imitate the proteolytic process of ensiled alfalfa and to ensure that each class of exopeptidase inhibitor would have immediate contact with the proteases in the alfalfa extract. Five classes of exopeptidases; namely, aminopeptidase, carboxypeptidase, dipeptidase, dipeptidyl-peptidase, and tripeptidyl-peptidase, were shown to be present in alfalfa leaves, each playing a different role in alfalfa protein degradation. Aminopeptidase, carboxypeptidase, and dipeptidase were the main exopeptidases contributing to the formation of NH₃-N. Among the 5 exopeptidases, tripeptidyl-peptidase appeared to be the principal exopeptidase in hydrolyzing forage protein into peptides, whereas carboxypeptidase and dipeptidase appeared to be more important in contributing to the formation of amino acid-N. Dipeptidyl-peptidase and tripeptidyl-peptidase did not play a role in the formation of NH₃-N or amino acid-N. Dipeptidase, carboxypeptidase, and tripeptidyl-peptidase were the principal exopeptidases for hydrolyzing forage protein into NPN during ensilage, and treatment with a mixture of the 5 inhibitors reduced the total NPN concentration in the fermented alfalfa extract to about 45% of that in the control after 21 d of fermentation.     

Heat and Fermentation Effects on Total Nonprotein Nitrogen and Urea in Milk

Kinetic analysis was applied to the increase of NPN and the decrease in urea when milk was heated at 80, 100 and 120°C. NPN increase with heat followed zero-order kinetics with an energy of activation of 17 kcal/mole. Urea losses with heating followed pseudo first-order kinetics with an energy of activation of 20 kcal/mole. Commercial yogurt and leben fermentation processes were used to determine the effects of fermentation on NPN and urea. Yogurt and leben fermentations increased NPN by 150 mg/kg and 208 mg/L, respectively, but had no effect on urea.     

Protein quality of parched immature durum wheat (Frekeh)

The protein quality of parched immature Durum wheat (frekeh) produced from Deir Alla-2 variety was evaluated. Frekeh from two maturity stages was used: one at the end of the milk stage (F1) and the other at the end of the dough stage (F6). Two animal experiments were carried out in which net protein utilisation (NPU) was determined for the two samples and for mature wheat using Sprague Dawley rats, the first for 12 and the second for 11 days. Additionally, the chemical scores for these cereals were calculated. The results indicated that the protein of F1 was of higher quality than that of F6 or mature wheat; the protein efficiency ratio adjusted values for F1, F6 and wheat were respectively 2.70, 1.93 and 1.45, and the NPU_op values were 53, 46 and 44 respectively. There was agreement between these results and the chemical score values as they were 54, 41 and 42 for F1, F6 and wheat respectively. There was a significantly higher voluntary intake of cereal-based diets in comparison with the casein-based diet (P <0.05). Thus it is shown that frekeh produced from wheat harvested at an early stage of maturity was of higher protein quality than that produced at a late stage of maturity or mature wheat.     

Nonprotein nitrogen content of defatted jojoba meals

Extraction of defatted jojoba meals with 0–5 M triehloroacetic acid solutions revealed a minimum solubility of nitrogenous compounds in the range of 0.5–2 M . This minimum was assumed to correspond to the nonprotein nitrogen (NPN) fraction. Trichloroacetic acid concentrations of 0.8–1.0 M were found to be optimal for NPN determination. NPN values for laboratory-prepared meals ranged from 21 to 29% of the total nitrogen for undecorticated (with seed coat) meals and from 21 to 30% for decorticated (without seed coat) meals. Commercial presscakes and presscake fines ranged from 15 to 20% of total nitrogen as NPN. These lower values apparently reflect heat treatments received by the presscakes during commercial expelling of the jojoba liquid wax esters, In aqueous dispersions of unheated jojoba meals, nitrogenous compounds exhibited a minimum solubility of 23–45% of total nitrogen at pH 3–4, the apparent isoelectric region of the storage proteins. In some meals NPN comprised up to 100% of the nitrogen soluble at this minimum; thus, low yields of recoverable meal nitrogen in the form of protein isolates are predicted. The NPN fraction was characterized by amino acid analysis and gel electrophoresis and found to contain free amino adds, peptides, and polypeptides of 6–10 kDa. Simmondsin and its derivatives are estimated to make up about one-third of the NPN.     

Screening for mutagens in norwegian foods by the ames test

Twelve Norwegian food products prepared in an ordinary domestic manner, were screened for mutagenic activity towards Salmonella typhimurium strains. Mutagenic activity towards the frameshift mutations strains (TA1538 and TA98) was observed in the basic organic extracts from fried fish cakes and fish pudding. Metabolic activation with rat liver homogenate (S9) was required. The ten other food items studied were found to be devoid of mutagenic activity.     

大米蛋白制备研究进展

大米蛋白是一种优质谷物蛋白,是目前稻米深加工研究热点。该文介绍制备大米蛋白常用方法,如溶剂提取、酶法提取、碱法提取、物理分离和复合提取等方法,并探讨各方法特点。     

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谷物食品是人类能量摄入的主要来源之一,随着人们生活水平的提高,谷物食品的营养价值和食用品质受到了广泛关注。发酵是改善食品性质、功能及营养缺陷的重要方法,也是谷物加工的重要手段。乳酸菌能够利用碳水化合物进行生长代谢,在食品工业中被广泛应用于各种发酵制品,其发酵产生的代谢产物有许多重要的生理功能,包括调节肠道菌群平衡、提高免疫力、抗菌和抗肿瘤等。因此,乳酸菌发酵在谷物食品中的研究与应用,对提升食品品质具有重要意义。本文综述了乳酸菌发酵对谷物营养成分、生物功能和结构、理化性质的影响,总结了乳酸菌发酵谷物产品的优势以及乳酸菌发酵在多种谷物产品中的应用,分析了乳酸菌发酵谷物食品目前研究的不足及可能的发展方向, 拟为乳酸菌发酵在谷物中的研究与开发提供参考。     

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本文综述谷物蛋白组成特性、应用和改性方面最新研究概况。开发利用谷物蛋白，已成为谷物科学领域研究热点。