Comparison of the Precipitation of Alfalfa Leaf Protein and Bovine Serum Albumin by Tannins in the Radial Diffusion Method

The precipitation of protein by condensed and hydrolysable tannins was evaluated with the radial diffusion method of Hagerman (1987) using bovine serum albumin (BSA) and isolated leaf protein from fresh alfalfa (Medicago sativa). Alfalfa leaf protein (AALP) was included at two concentrations, 25 and 156 mg N litre^-1, at pH 6·8 and 39°C to simulate rumen conditions. The condensed tannins were purified from lyophilised samples of Arachis pintoi, Desmodium ovalifolium, Gliricidia sepium, Manihot esculenta and quebracho (Schinopsis balansae). Hydrolysable tannins from tannic acid (TA) were used as well. There was a significant interaction (P<0·001) between tannin and protein source, and protein level on protein precipitation. Most purified condensed tannins (CTs) precipitated more AALP than BSA when protein was included at the same level. Purified CT from quebracho and hydrolysable tannin from TA failed to precipitate AALP at both protein levels. In a second experiment, tannins from crude plant extracts were studied in the radial diffusion method using BSA and two levels of AALP. The crude plant extracts were obtained from lyophilised plant samples of A pintoi, Centrosema macrocarpum, Clitoria ternatea, D ovalifolium, Erythrina berteroana, E poepigiana, G sepium, M esculenta, Pueraria montana and P phaseoloides. The protein precipitated by soluble tannins in the plant samples was correlated to the total phenolic content and to the soluble CT estimated by the acid butanol assay or by the radial diffusion method. Tannins from different plant species precipitated different amounts of BSA and AALP. Therefore, the measures of the biological activity of tannins based on BSA precipitation may not reflect the ability of tannins to precipitate proteins of plant origin such as those commonly found in the diets of herbivores. The present study offers the possibility of using the radial diffusion method with plant proteins at precipitation conditions similar to those in the rumen. © 1997 SCI.     

Application of flow nephelometry to the analysis of the influence of carbohydrates on protein–tannin interactions

The flow nephelometric technique was recently introduced to study the interaction between tannins and proteins. This technique was employed here to study the ability of the polysaccharides xanthan, dextran and gum arabic to disrupt the interactions between condensed tannin fractions from grape seed and bovine serum albumin (BSA). Xanthan was shown to have a higher ability to inhibit the aggregate formation of tannins and BSA than the other polysaccharides. Xanthan's ability to inhibit protein‐tannin complex formation was higher for condensed tannin fractions of smaller size and lower complexity. Copyright © 2006 Society of Chemical Industry     

In vitro effects of and interactions between tannins and saponins and fate of tannins in the rumen

The rate of fermentation of hay was not affected by purified tannins from Ouercus incana and Dichostachys cinerea at 0.13 mg ml^?1 of the in vitro medium whereas a decrease of 4% in the rate was observed for Acioa barteri tannins at this level. At 0.23 mg and 0.47 mg of tannins per ml, the decrease in rate varied from 4 to 13% and 13 to 20%, respectively. The decrease in in vitro true digestibility of dry matter was 3, 6 and 7% for Q incana, D cinerea and A barteri, respectively, at a tannin concentration of 0.47 mg ml^?1, and 17, 21 and 27%, respectively, at 0.93 mg ml^?1. There was no change in the potential extent of digestion up to 0.47 mg ml^?1 for any of the tannins studied. These results suggested that the rate of digestion is affected to a greater extent than the potential extent of digestion or the in vitro true digestibility and that different tannins even at the same level have different degrees of effect. Tannin-saponin interactions were studied using tannic acid (TA), quebracho tannin (QT) and quillaja saponin (S) at different concentrations (0.2, 0.4 and 0.6 mg ml^?1) alone and in combination with each other. The decrease in the rate of digestion and true digestibility was additive when both the TA and the S were present. Similar results were obtained when TA was replaced by QT except that the effects with QT were more marked as compared to TA at the same concentration. Saponins had little effect on the potential extent of digestion and true digestibility. These tannins also decreased the production of short-chain fatty acid (SCFA) and their molar proportions (acetate decreased whereas propionate increased). Efficiency of microbial protein synthesis, expressed as the ratio of ¹⁵N incorporation per unit of SCFA production, was higher with both S and the tannins studied. A substantial amount (71–93%) of tannins soluble in aqueous acetone was released from leaves of some trees and shrubs on incubation in the in vitro medium for 48 h. The rumen liquor was not capable of degrading oligomeric condensed tannins.     

Condensed tannins from Lotus corniculatus and Lotus pedunculatus exert different effects on the in vitro rumen degradation of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) protein

Condensed tannins (CT) or proanthocyanidins (PA), which occur in a restricted range of forages, have the ability to interact with proteins and enzymes and can influence the digestion of plant protein in the rumen. We compared the effects of CT extracts from Lotus corniculatus and pedunculatus on degradation of the principal leaf protein, ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), by rumen microorganisms. Total soluble leaf protein extracted from white clover (Trifolium repens ) was incubated with fresh rumen fluid from sheep and a range of concentrations of each CT extract. The rate of degradation of the large (LSU) and small subunit (SSU) of Rubisco was quantified by fractionating the proteins in samples taken from in vitro rumen incubations using sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS‐PAGE) and imaging densitometry. To deduce the effects of the CT extracts, experiments were performed in the presence (CT inactive) and absence (CT active) of polyethylene glycol (PEG; MW 3350). The two CT extracts differed markedly in their effects on the degradation of the LSU and SSU of Rubisco. At concentrations of 0.89 and 1.79 mg CT mg ⁻¹ total soluble leaf protein, the CT extract from L pedunculatus was more effective at preventing the degradation of the LSU and SSU by rumen microorganisms than the CT extract from L corniculatus. At a concentration of 1.79 mg CT mg ⁻¹ total soluble leaf protein, the CT extracts from L corniculatus and pedunculatus prevented about 0.75 and 0.83 of the LSU and about 0.69 and 0.86 of the SSU, respectively, from being degraded. Addition of PEG removed the inhibition and almost complete degradation of these proteins occurred, as was the case in incubations without CT extracts. The results of this study suggest that the concentration of CT in the diet and the chemical structure which affects the activity of the CT needs to be considered when assessing the effects of CT on protein metabolism in ruminants. © 1999 Society of Chemical Industry     

Effect of dietary quebracho tannin extract on milk fatty acid composition in cows

The aim of this study was to examine the capacity of quebracho tannin extract (QTE) to modulate the fatty acid (FA) profile in the milk fat of cows. Fifty Holstein cows yielding 33.2 ± 8.2 kg/d of milk were divided into 2 groups. The cows were fed a basal diet with a forage-concentrate ratio of 66:34 on a dry matter (DM) basis. Diets tested were control (CON, basal diet without QTE) and basal diet plus 15 or 30 g of QTE/kg of DM (QTE₁₅ and QTE₃₀, respectively). Two treatments could be tested simultaneously and were arranged along 6 periods. The milk FA profile was characterized by increments in the proportion of linoleic (LA) and α-linolenic acid (α-LNA) (QTE₁₅ = 10 and 6.1%; QTE₃₀ = 28 and 25%, respectively) compared to CON, which might indicate reduced ruminal biohydrogenation (BH) of both dietary LA and α-LNA. Vaccenic acid (VA) in the milk fat was reduced (QTE₁₅ 8.9% and QTE₃₀ 12%) compared to CON, which may be linked to inhibited BH of LA and α-LNA. Rumenic acid (RA), a conjugated LA (cis-9,trans-11 conjugated linoleic acid) and an important human health promoter, was unfortunately decreased (QTE₁₅ 8.3% and QTE₃₀ 16%) in the milk compared with CON, probably because of inhibited ruminal BH of LA. However, reduced RA in the milk was probably due to reduced availability of VA produced in the rumen and the consequently low VA available to be desaturated to RA in the mammary gland by Δ⁹-desaturase. The proportions of total polyunsaturated FA were increased with QTE₁₅ and QTE₃₀ by 4.7 and 15% compared to CON, respectively, and the long-chain FA proportions were also increased (QTE₁₅ 2.0% and QTE₃₀ 8.2%). Moreover, myristic and palmitic acid were reduced by QTE₃₀ (9.6 and 3.3%, respectively) compared to CON, which also contributed to increasing the nutritional quality of milk because they are recognized to increase high-density lipoprotein in humans. Branched-chain FA in milk was reduced with QTE treatments, which indicates inhibited ruminal BH and microbial activity. In general, our findings suggest that dietary QTE have the potential to modulate FA profile of milk fat, and this effect is dosage dependent. Because QTE influenced the FA profile of milk fat both positively and negatively, further research is needed before concluding that QTE may improve the nutritional quality of cow milk fat in human diets.     

Effect of high temperature on condensed tannin accumulation in leaf tissues of big trefoil (Lotus uliginosus Schkuhr)

Plants from three clones of big trefoil (Lotus uliginosus Schkuhr) having low, medium and high concentrations of tannin in their leaves were subjected to growing conditions with normal (20°C) and high (30°C) temperature regimes. Plants were tested every 3 weeks for foliar condensed tannin content using the vanillin-HCl and the butanol-HCl assays. Plants from clones growing under high temperatures matured more quickly and by 14 days had condensed tannin levels substantially greater than plants from the same clones grown under normal temperatures. Clones remained consistent with respect to their parental tannin levels throughout two trials. Leaves from high-temperature clones suffering additional nutrient stress symptoms had very low levels of foliar condensed tannins and cross-sections of chlorotic leaves revealed an absence of large tannin vacuoles. It is concluded that high-temperature stress can induce the formation of additional condensed tannin in the leaves of this species.     

Factors affecting the in vitro protein digestibility of chickpea albumins

In vitro protein digestibility (IVPD) of chickpea albumins and its possible relationship to their structure and the presence of trypsin inhibitor activity (TIA) have been studied. Trypsin digestion of the albumin fraction under non‐reducing conditions was incomplete, while the reduction of inter‐ and intramolecular disulphide bonds caused an improvement in the accessibility of sites susceptible to trypsin digestion. Trypsin inhibitor activity in the chickpea albumin fraction was dependent upon both temperature and heating time. Although heating the albumin fraction at 100 °C for 30 min reduced the TIA by more than 50% with respect to the initial activity, an important TIA rate was attributable to heat‐resistant trypsin inhibitor. The TIA decrease was not related to an increase in the rate of IVPD. However, we observed a significant (P ≤ 0.05) increment in IVPD in the presence of β‐ME, confirming the essential role of disulphide bonds in stabilising the protein structure of the albumin fraction. © 2000 Society of Chemical Industry     

蛋白橘皮果胶胶体制备、表征及对红景天苷体外释放研究

以牛血清蛋白与橘皮果胶为原料,采用安全无毒的自组装技术制备缓释水凝胶,并以制备过程中两种原料配比、蛋白浓度与p H进行三因素三水平对凝胶粒径影响的响应面分析。在此基础上,重点研究显著因子添加橘皮果胶比例对蛋白成胶的影响,并结合利用流变、圆二、扫描电镜对其进行表征。以红景天苷为模型检测其包封效果和体外释放,结果表明:橘皮果胶和牛血清蛋白比例为0.5和p H为4.5时加热粒径达到最小259.5 nm,尺寸分布较窄(PDI<0.06),形成良好稳定的三维网络结构水凝胶;红景天苷包封率达到49.88%,在模拟胃肠溶液中具有缓释效果。本研究的水凝胶可作为红景天苷以及其他功能性食品的潜在输送载体。      

Carboxy groups in fatty acids facilitate the formation and thermal stability of starch-fatty acids complexes

This study aimed to investigate the effect of the number of carboxy group on the formation of complexes between starch and fatty acids using different dicarboxylic acids and monobasic acids as ligand. The complexing index (CI) indicated that dicarboxylic acids could form complexes with starch and show stronger complexing ability than corresponding monobasic acids. Results from differential scanning calorimetry also displayed that starch-dicarboxylic acids complexes presented higher onset temperature, narrow transition peaks and higher enthalpy change, indicating the higher thermal stability and uniform and homogenous crystal of starch-dicarboxylic acids complexes. X-ray diffraction, Fourier transform infrared and Raman spectroscopy showed that the long-range and short-range order of starch-dicarboxylic acids complexes was better than that of starch-monobasic acids. According to above results, fatty acid with two carboxyl groups could form larger amount and more stability complexes than it is with one carboxyl group.     

Controlling the formation of indole and skatole in in vitro rumen fermentations using condensed tannin

Indole and skatole are formed in the rumen from the fermentation of tryptophan and have been correlated to the presence of undesirable pastoral flavours in meat from grazing ruminants. A series of four in vitro rumen fermentation experiments was carried out to determine the effectiveness of condensed tannin (CT) for reducing the formation of indole and skatole. Experiment 1 utilised fresh white clover (WC; Trifolium repens) in ratios with the CT‐containing forage Lotus pedunculatus (LP; 97 g CT kg^?1 dry matter (DM)). Increasing the ratio of LP to WC decreased the formation of indole and skatole. Experiments 2 and 3 used extracts of CT from LP and grape seed added to incubations of fresh non‐CT‐containing WC or perennial ryegrass (PRG; Lolium perenne). Including the CT extracts in incubations at 40 and 80 g kg^?1 DM was more effective at reducing indole and skatole formation than lower concentrations of CT extract (P < 0.05). Including fresh LP in ratios with WC gave a linear decrease in indole and skatole concentration (indicating dilution), while including a CT extract in the incubations gave an exponential decrease in indole and skatole concentration (suggesting binding). Experiment 4 elucidated the mechanisms behind the action of CT by delayed addition of tryptophan and polyethylene glycol (PEG) to incubations of LP. Rumen microbes that were exposed to CT of LP in planta for up to 6 h and then provided with tryptophan were still able to convert tryptophan to indole and skatole. Adding PEG to incubations of LP after 6 h inhibited the activity of plant CT and increased the availability of substrate for indole and skatole formation. These studies have shown that a higher concentration of CT is more efficient for reducing indole and skatole formation and that CT contained within plants acts differently in in vitro rumen fermentations than additions of extracted CT. Under the conditions of these experiments, there was no evidence that CT contained in LP affected the protein present in WC in a mixed fermentation. Copyright © 2007 Society of Chemical Industry     

Factors affecting the concentration of sphingomyelin in bovine milk

Sphingomyelin is a phospholipid located in the outer leaflet of the plasma membrane of most cells and is a component of the milk fat globule membrane. Sphingomyelin and its digestion products participate in several antiproliferative pathways that may suppress oncogenesis. Although milk and dairy products are important sources of sphingomyelin in the human diet, little is known about factors that influence sphingomyelin concentrations in milk fat or whether concentrations can be modified via the nutrition of cows. Sphingomyelin concentrations were determined in milk from Holstein and Jersey cows matched for parity and stage of lactation. Sphingomyelin was more concentrated in milk fat from Holstein cows than in milk fat from Jersey cows (1,044 vs. 839 μg/g of fat). Concentrations in whole milk did not differ because of greater milk fat content for milk from Jerseys. Differences between breeds may be related to the greater fat globule size in milk from Jerseys. Sphingomyelin content in whole milk increased with increasing days in milk because of associated increases in milk fat content. Regardless of breed, primiparous cows had greater amounts of stearic acid and less palmitic acid in sphingomyelin than did older cows. The sphingomyelin concentration in milk fat of cows in a commercial Jersey herd was lower for cows in their fourth or greater parity. Sphingomyelin content in whole milk was greater for cows in late lactation because of greater milk fat content. Feed restriction of multiparous Holstein cows to 37% of ad libitum dry matter intake increased milk fat content but did not affect milk sphingomyelin content or milk fat globule size. Supplementation of the diet with 4% soybean oil did not affect milk composition, sphingomyelin content, or milk fat globule size. Milk was sampled seasonally from 7 herds throughout Illinois during a 2-yr period. Sphingomyelin concentration in milk fat was greatest during summer and least during winter, but whole milk concentrations did not vary across seasons. We conclude that 1) sphingomyelin content of milk fat is greater in milk from Holsteins than that from Jerseys, 2) sphingomyelin content in whole milk increases with stage of lactation, and 3) sphingomyelin content of milk fat is greater during summer. However, efforts to produce milk with a greater sphingomyelin content through altering management and nutrition are unlikely to be successful.     

Factors affecting ANKOM™ fiber analysis of forage and browse varying in condensed tannin concentration

BACKGROUND: Browse species containing condensed tannins (CTs) are an important source of nutrition for grazing/browsing livestock and wildlife in many parts of the world, but information on fiber concentration and CT–fiber interactions for these plants is lacking. RESULTS: Ten forage or browse species with a range of CT concentrations were oven dried and freeze dried and then analyzed for ash‐corrected neutral detergent fiber (NDFom) and corrected acid detergent fiber (ADFom) using separate samples (ADFSEP) and sequential NDF‐ADF analysis (ADFSEQ) with the ANKOM^? fiber analysis system. The ADFSEP and ADFSEQ residues were then analyzed for nitrogen (N) concentration. Oven drying increased (P < 0.05) fiber concentrations with some species, but not with others. For high‐CT forage and browse species, ADFSEP concentrations were greater (P < 0.05) than NDFom values and approximately double the ADFSEQ values. Nitrogen concentration was greater (P < 0.05) in ADFSEP than ADFSEQ residues, likely due to precipitation with CTs. CONCLUSION: Sequential NDF‐ADF analysis gave more realistic values and appeared to remove most of the fiber residue contaminants in CT forage samples. Freeze drying samples with sequential NDF‐ADF analysis is recommended in the ANKOM^? fiber analysis system with CT‐containing forage and browse species. Copyright © 2010 Society of Chemical Industry     

Sources of variation in rates of in vitro ruminal protein degradation

Rates and extents of ruminal protein degradation for casein, solvent soybean meal (SSBM), expeller soybean meal (ESBM), and alfalfa hay were estimated from net appearance of NH3 and total amino acids in in vitro media containing 1 mM hydrazine and 30 mg/L of chloramphenicol. Protein was added at 0.13 mg of N/mL of medium, and incubations were conducted for 4 to 6 h, usually with hourly sampling. Inocula were obtained from ruminally cannulated donor cows fed diets of grass silage or alfalfa and corn silages plus concentrates. Preincubation or dialysis of inocula was used to suppress background NH3 and total amino acids; however, preincubation yielded more rapid degradation rates for casein and SSBM and was used in subsequent incubations. Preincubation with added vitamins, VFA, hemin, or N did not alter protein degradation. Protein degradation rates estimated for SSBM, ESBM, and alfalfa were not different when computed from total N release or N release in NH3 plus total amino acids, regardless of whether amino acids were quantified using ninhydrin colorimetry or o-phthalaldehyde fluorescence. Accounting for the release of peptide-N also did not affect estimated degradation. However, casein degradation rates were more rapid when using total N release or accounting for peptide-N, indicating significant accumulation of small peptides during its breakdown. Rates also were more rapid with inocula from lactating cows versus nonlactating cows with lower feed intake. Protein degradation rates were different due to time after feeding: casein rate was more rapid, but SSBM and ESBM rates were slower with inocula obtained after feeding. Several characteristics of ruminal inoculum that influenced breakdown of the rapidly degraded protein casein did not appear to have direct effects on degradation of protein in soybean meal.     

Effects of replacing soybean meal with canola meal differing in rumen-undegradable protein content on ruminal fermentation and gas production kinetics using 2 in vitro systems

Previous research indicated that there were significant differences in rumen-undegradable protein (RUP) among canola meals (CM), which could influence the nutritional value of CM. The objectives of this study were to (1) evaluate the effects of feeding CM with different RUP contents on ruminal fermentation, nutrient digestion, and microbial growth using a dual-flow continuous culture system (experiment 1) and (2) evaluate ruminal gas production kinetics, in vitro organic matter (OM) digestibility, and methane (CH₄) production of soybean meal (SBM) and CM with low or high RUP in the diet or as a sole ingredient using a gas production system (experiments 2 and 3). In experiment 1, diets were randomly assigned to 6 fermentors in a replicated 3 × 3 Latin square. The only ingredient that differed among diets was the protein supplement. The treatments were (1) solvent-extracted SBM, (2) low-RUP solvent-extracted CM (38% RUP as a percentage of crude protein), and (3) high-RUP solvent-extracted CM (50% RUP). Diets were prepared as 3 concentrate mixtures that were combined with 25% orchardgrass hay and 15% wheat straw (dry matter basis). Experiments 2 and 3 had the same design with 24 bottles incubated 3 times for 48 h each. During the 48-h incubation, the cumulative pressure was recorded to determine gas production kinetics, in vitro OM digestibility, and CH₄ production. In experiment 1, N flow (g/d), efficiency of N use, efficiency of bacterial N synthesis, total volatile fatty acids (mM), and molar proportion of acetate, propionate, and isobutyrate were not affected by treatments. There were tendencies for a decrease in ruminal NH₃-N and an increase in molar proportion of butyrate for the SBM diet compared with both CM diets. The molar proportion of valerate was greater in both CM diets, whereas the molar proportion of isovalerate and total branched-chain volatile fatty acids was lower for the CM diets compared with the SBM diet. In experiments 2 and 3, the SBM diet had a greater gas pool size than both CM diets. The SBM diet increased in vitro OM digestibility; however, it also tended to increase CH₄ production (mM and g/kg of DM) compared with both CM diets. Based on the results of this study, CM with RUP varying from 38 to 50% of crude protein does not affect ruminal fermentation, nutrient digestion, and microbial growth when CM is included at up to 34% of the diet.     

Effects of fatty acid and emulsifier on the complex formation and in vitro digestibility of gelatinized potato starch

The effects of fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with varying chain length in their acyl chains on the extent of complex formation (complex index) and in vitro enzymatic digestibility of gelatinized potato starch were investigated. The complex index increased with increase in the concentration of the ligands (fatty acid, monoacylglycerol, and polyglycerol fatty acid ester), with the plateau in the complex index value depending on the type of ligands. In comparison of complex index among fatty acid-samples, the complex index maximum increased as the chain length increased up to octanoic acid and then decreased. In comparison of complex index among fatty acid-, monoacylglycerol-, and polyglycerol fatty acid ester-samples at each acyl chain, the complex index maximum followed the order polyglycerol fatty acid ester > monoacylglycerol > fatty acid. Fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with long acyl chains greatly reduced the enzymatic hydrolysis of starch. Polyglycerol fatty acid ester with palmitic acid chains was the strongest inhibitor of starch hydrolysis, suggesting that further complex formation may occur during the hydrolysis of gelatinized starch (enzyme-annealing).     

The passage of lactic acid bacteria from silage into rumen fluid, in vitro studies

Inoculated silages sometimes improve cattle performance, possibly because of probiotic effects of lactic acid bacteria (LAB) silage inoculants. The cause of improved animal performance following feeding with inoculated silage is unclear. One issue in studying this phenomenon is to find out whether LAB pass from silage into the rumen fluid and survive in it. The purpose of the present study was to determine whether LAB from inoculated and uninoculated silages pass into the rumen fluid in vitro. Wheat and corn silages, uninoculated or inoculated with 1 of 10 commercial silage inoculant LAB, were prepared in glass jars. After ensiling, a 2.5-g silage sample was added to 25 mL of heat-sterilized or strained rumen fluid together with 5 g/L glucose, and incubated for 48 h at 39 degrees C. Analysis of the incubated rumen fluid included pH measurement, enumeration of LAB, and determination of lactic acid and volatile fatty acids (VFA). The pH of the rumen fluid decreased during incubation; both heat-sterilized and strained rumen fluid contained large numbers of LAB. The heat-sterilized rumen fluid contained lactic acid in addition to VFA, whereas the strained rumen fluid contained only VFA. The results indicate that LAB pass from silage samples into the rumen fluid in vitro and survive there. Their interactions with rumen microorganisms should be studied further to understand how some silage inoculant LAB exhibit probiotic effects in dairy cattle.     

Effects of caffeic acid and bovine serum albumin in reducing the rate of development of rancidity in oil-in-water and water-in-oil emulsions

The antioxidant properties of caffeic acid and bovine serum albumin in oil-in-water and water-in-oil emulsions were studied. Caffeic acid (5 mmol/kg emulsion) showed good antioxidant properties in both 30% sunflower oil-in-water (OW) and 20% water-in-sunflower oil emulsions (WO), pH 5.4, during storage at 50 °C. Although bovine serum albumin (BSA) (0.2%) had a slight antioxidant effect, the combination of caffeic acid and BSA showed a synergistic reduction in the rate of development of rancidity, with significant reductions in concentration of total volatiles, peroxide value (PV) and p-anisidine value (PA) for both emulsion types. The synergistic increase in stability of the OW and WO emulsions containing BSA and caffeic acid was 102.9% and 50.4% respectively based on total oxidation (TOTOX) values, which are calculated as 2PV + PA, with greater synergy calculated if based on formation of headspace volatiles. The OW emulsion was more susceptible to the development of headspace volatiles by oxidation than the WO emulsion, even though the degree of oxidation assessed by the TOTOX value was similar.     

采用牛血清白蛋白/果糖体系研究荧光性AGEs生成的动力学

为分析荧光性晚期糖基化末端产物(advanced glycation end products,AGEs)生成的动力学,采用牛血清白蛋白(bovine serum albumin,BSA)/果糖模拟反应体系,荧光光谱法测定荧光强度来衡量荧光性AGEs生成量,分别考察了不同BSA质量浓度、果糖浓度、温度及p H值对荧光性AGEs生成量的影响,探究荧光性AGEs生成和底物消耗的反应动力学。结果表明:随着BSA质量浓度、果糖浓度、温度及p H值的增加,荧光性AGEs生成量均呈现增加的趋势。体系反应24 min后,果糖和氨基酸浓度分别减少了1.25×10-2、1.92×10-4 mol/L,果糖消耗量要高于氨基酸消耗量。在此基础上,运用最小二乘法拟合,得出在各反应条件下,荧光性AGEs的生成符合0级反应动力学,最大速率常数为31.57 AU/min,反应活化能为70.58 k J/mol;底物消耗符合1级反应动力学。     

不同预处理对家庭制豆浆抗营养因子含量的影响

目的:研究不同预处理对家庭制豆浆中抗营养因子含量的影响。方法:对大豆在室温和冷藏条件浸泡、干炒及发芽2d处理后制成豆浆,以与干豆制浆为对照,比较其单宁、植酸、皂苷和胰蛋白酶抑制剂的保存率。结果:发芽处理豆浆组分的单宁、植酸、皂苷、胰蛋白酶抑制剂的保存率分别为31.83%、27.28%,20.19%、12.89%;室温浸泡处理12h分别为34.56%、43.72%、32.10%和9.91%;干炒处理消除抗营养因子的效率不及发芽和浸泡处理,但与干豆制浆处理差异显著,各抗营养因子的保存率分别为64.05%、54.59%、28.78%、10.88%。结论:与干豆制浆相比,各处理均显著降低了豆浆中抗营养因素的保存率。其中发芽处理对于降低单宁和植酸的效果最显著,12h浸泡处理对降低胰蛋白酶抑制剂最为有效。