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1.
为了了解提高成熟温度对牦牛乳硬质干酪成熟过程中蛋白质降解与苦味程度的影响,本文研究了5、10、15℃成熟牦牛乳硬质干酪在1~6个月成熟过程中p H值4.6可溶性氮含量、12%TCA可溶性氮含量、5%PTA可溶性氮含量、游离氨基酸和苦味程度的变化,并利用RP-HPLC对p H值4.6可溶性氮提取物肽分布进行了分析。结果表明:成熟温度和时间显著影响干酪成熟过程中以p H值4.6可溶性氮含量、12%TCA可溶性氮含量、5%PTA可溶性氮含量、游离氨基酸等所体现的蛋白质降解程度。提高成熟温度导致p H值4.6可溶性氮含量、12%TCA可溶性氮含量、5%PTA可溶性氮含量、游离氨基酸含量等增加,特别是15℃在成熟早期能较快增加干酪12%TCA可溶性氮含量、5%PTA可溶性氮含量。RP-HPLC分析显示从5℃提高到15℃时,干酪p H值4.6可溶性氮提取物亲水性肽含量增加,疏水性肽含量降低。除5、10、15℃成熟2个月干酪具有非常轻微的苦味之外,15℃成熟干酪比5、10℃成熟干酪具有较强苦感,成熟4个月后,10、15℃成熟干酪具有中等较强苦味,且差异不显著(P≥0.05)。该研究为加快牦牛乳硬质干酪成熟提供了试验数据。 相似文献
2.
为阐明酶解前热处理对鸡肉蛋白酶解性质的影响，采用差示扫描量热法分析鸡肉蛋白的热性质，研究热处理温度对鸡肉蛋白巯基(SH)、二硫键(S-S)含量以及碱性蛋白酶(Alcalase)、木瓜蛋白酶(Papain)酶解过程中氨基酸、肽释放的影响。结果表明：鸡肉蛋白有4个吸热峰，对应温度为63.7℃、67.6℃、74.3℃和 77.9℃；热处理温度增加，鸡肉蛋白中SH含量逐渐降低，而S-S含量逐渐增加，游离SH与S-S还原折算的SH量之和在80℃前无明显变化，80℃后下降；酶解前热处理不利于鸡肉蛋白酶解过程中游离氨基酸、小分子量肽的释放和可溶性氮的回收，但有利于大分子量肽的生成，因此可根据酶解产物的应用目的选择热处理参数。 相似文献
3.
利用风味蛋白酶深度酶解蓝园鲹蛋白，通过比较酶解液的水解度曲线和蛋白质利用率曲线之间的差异、对TCA不溶性氮的变化趋势以及不同酶解时间的凝胶过滤图谱进行分析，探讨了深度酶解过程中蛋白质的降解。酶解6h后大部分蛋白质在酶的作用下降解为水溶性多肽，蛋白质利用率达到83。3％；6h以后蛋白质利用率增长速度降低，这可能是由于可被降解的底物含量降低。此后。风味蛋白酶以水溶性多肽为底物将其进一步降解为小分子肽和氨基酸；21h时水解度达到59．7％。21h以后水解度增长速度降低．这可能是由于亮氨酸氨肽酶难于分解氨基末端上带有甘氨酸和酸性氨基酸的肽。21h以后酶解的主要底物分子量范围在6214到10700的多肽。 相似文献
4.
利用风味蛋白酶深度酶解蓝园鱼参蛋白,通过比较酶解液的水解度曲线和蛋白质利用率曲线之间的差异、对TCA不溶性氮的变化趋势以及不同酶解时间的凝胶过滤图谱进行分析,探讨了深度酶解过程中蛋白质的降解。酶解6 h后大部分蛋白质在酶的作用下降解为水溶性多肽,蛋白质利用率达到83.3％;6 h以后蛋白质利用率增长速度降低,这可能是由于可被降解的底物含量降低。此后,风味蛋白酶以水溶性多肽为底物将其进一步降解为小分子肽和氨基酸;21 h时水解度达到59.7％。21 h以后水解度增长速度降低,这可能是由于亮氨酸氨肽酶难于分解氨基末端上带有甘氨酸和酸性氨基酸的肽。21 h以后酶解的主要底物分子量范围在6214到10700的多肽。 相似文献
5.
畜禽血经微生物蛋白酶水解，脱除血红素等工艺生产出的酶化脱血红素饲料蛋白，具有感观良好，气味清香，适口性强，消化率高等特点，粗蛋白含量在８２％－８６％，血红素脱除率在８０％以上，消除了血醒味。经酶化使大分子不易消化的蛋白质水解为小分子溶性的腙、胨；肽以及游离氨基酸。经测定可溶性氮达到８．２１％，占总氮的６１％，并含有较多的钙，磷以及其它矿物营养素，经科学配比可制成含蛋白质６０％左右的动物蛋白饲料，测 相似文献
6.
近年来,我国的干酪消费量迅速增加。小规模牧场的手工挤奶方式可能会导致体细胞混入原料奶中,从而影响终产品干酪的品质。但是,体细胞组成及相应酶的活力对干酪品质的影响尚未阐明。该研究分别从牛乳房表面、乳房炎牛乳和正常牛乳收集体细胞。通过将体细胞分离再与脱脂乳混合,原料乳质量的一致性得到保证。将含不同体细胞组成的牛乳用于Cheddar干酪制作,分别为干酪A,B和C。3种干酪的原料乳中,上皮细胞质量分数最高组为干酪A的原料乳（65.41%）,巨噬细胞和淋巴细胞质量分数最高组为干酪B的原料乳（分别为78.15% 和12.15%）,而多核中性粒细胞在干酪C的原料乳中质量分数最高（34.23%）。结果表明,成熟过程中各干酪的蛋白酶活性和蛋白水解程度差异显著（P < 0.05）。成熟90d后,干酪C中的血纤维蛋白溶酶和组织蛋白酶B活性显著高于其他组。此外,在整个成熟过程中,干酪中αs1-, αs2-和β-酪蛋白的存留率,以及pH 值4.6的可溶性氮和12%三氯醋酸可溶性氮的质量分数均为C组< B 组< A组。另外,3组试验干酪中干酪A的硬度最高,B和C之间无显著性差异。综上所述,体细胞对干酪品质的影响与体细胞的类型有关。体细胞中上皮细胞的增加对干酪品质的影响较小,而多核中性粒细胞的增加对干酪品质有显著影响。 相似文献
7.
近年来,我国的干酪消费量迅速增加。小规模牧场的手工挤奶方式可能会导致体细胞混入原料奶中,从而影响终产品干酪的品质。但是,体细胞组成及相应酶的活力对干酪品质的影响尚未阐明。该研究分别从牛乳房表面、乳房炎牛乳和正常牛乳收集体细胞。通过将体细胞分离再与脱脂乳混合,原料乳质量的一致性得到保证。将含不同体细胞组成的牛乳用于Cheddar干酪制作,分别为干酪A,B和C。3种干酪的原料乳中,上皮细胞质量分数最高组为干酪A的原料乳(65.41%),巨噬细胞和淋巴细胞质量分数最高组为干酪B的原料乳(分别为78.15%和12.15%),而多核中性粒细胞在干酪C的原料乳中质量分数最高(34.23%)。结果表明,成熟过程中各干酪的蛋白酶活性和蛋白水解程度差异显著(P0.05)。成熟90d后,干酪C中的血纤维蛋白溶酶和组织蛋白酶B活性显著高于其他组。此外,在整个成熟过程中,干酪中α_s1-,α_s2-和β-酪蛋白的存留率,以及pH值4.6的可溶性氮和12%三氯醋酸可溶性氮的质量分数均为C组B组A组。另外,3组试验干酪中干酪A的硬度最高,B和C之间无显著性差异。综上所述,体细胞对干酪品质的影响与体细胞的类型有关。体细胞中上皮细胞的增加对干酪品质的影响较小,而多核中性粒细胞的增加对干酪品质有显著影响。 相似文献
8.
钼、氮肥配合施用对冬小麦子粒蛋白质及其氨基酸组成的影响 总被引：7，自引：1，他引：7
盆栽试验结果表明 ,施钼和缺钼时 ,氮肥对冬小麦的增产率分别为 319.9%和 174.0% ;冬小麦子粒中蛋白氮、清蛋白氮、醇溶蛋白氮含量 ,面粉蛋白质氨基酸总量及其氨基酸组分的含量以及谷氨酸、脯氨酸的比例等随氮肥水平提高而增加 ;但冬小麦面粉中游离天门冬氨酸和苏氨酸的含量和比例降低 ,游离氨基酸含量在缺钼时提高了 38.3% ,施钼时则下降了 37.1%。在高、低氮肥水平下施钼 ,冬小麦子粒中蛋白质含量没有明显影响 ,但分子量小的蛋白质含量及其占总量的比例下降 ,清蛋白比例分别下降 14.5、6.6个百分点 ;而大分子量蛋白质含量和比例均提高。在不同施氮水平下缺钼冬小麦子粒中游离氨基酸含量比施钼分别高 48.0%和 15.26% ,且亲水性氨基酸比例增加。缺钼冬小麦子粒中低分子量蛋白质、游离氨基酸以及亲水性氨基酸的增加 ,可能是诱发缺钼冬小麦子粒低休眠度以及出现收获前萌芽的重要原因。 相似文献
9.
为探究凋落物对森林土壤氮的影响及氮沉降的调节,本研究以亚热带天然阔叶林(罗浮栲林)和人工针叶林(杉木林)2种林型土壤和凋落物为对象,分别设置土壤(对照)、土壤+凋落物(3倍添加)、土壤+氮(120 mg/kg)、土壤+凋落物(3倍添加)+氮(120 mg/kg) 4种处理,每种处理设置3个重复,进行为期一年的室内模拟淋溶试验,分析土壤可溶性氮和物理分级后各粒径土壤水解氨基酸变化。结果表明：与对照比较,阔叶林土壤添加凋落物处理增加土壤铵态氮和游离氨基酸,而降低硝态氮含量;氮添加降低针叶林土壤氨态氮,增加硝态氮含量,但是增加阔叶林土壤铵态氮和游离氨基酸;凋落物添加的情况下,氮添加显著增加阔叶林土壤硝态氮含量。土壤的各粒径组分分布比例差异显著,氮添加倾向于降低针叶林土壤大粒径、增加小粒径分配比例,而阔叶林相反。针叶林土壤添加凋落物显著增加土壤粒径组分2 000～250μm、20～2μm、<2μm水解氨基酸含量;氮添加增加针叶林全土、2 000～250μm和20～2μm粒径水解氨基酸含量;在凋落物添加或氮添加情况下,氮添加或凋落物显著降低全土、250～53μm、53～20μm粒径水解氨基... 相似文献
10.
黄土区人工牧草地有机氮组分变化研究 总被引：7，自引：0，他引：7
黄土区人工牧草地18年苜蓿连作对土壤耕层水解总氮，氨态氮，氨基酸氮及氨基糖氮含量有很大影响，不施肥条件下苜蓿连作能明显增加土壤耕层水解总氮，氨基酸氮和氨基糖氮含量，连续施P处理根层水解总氮，氨态氮，氨基酸氮和氨基糖氮含量分别比对照增加413.55mg/kg,58.39mg/kg,169.83mg/kg和107.01mg/kg;NPM处理土壤耕层水解总氮与对照相比增加192.58mg/kg，氨基酸氮增加223.44mg/kg，氨基糖氮增加25.66mg/kg，而氨态氮含量则大幅度降低，在60－10cm不同处理的各种形态氮含量接近且随土层加深逐渐减少，粮草轮作系统中不同苜蓿生长年限对土壤的水解总氮和氨基酸氮含量有增加的作用。 相似文献
11.
Fernández-Salguero J Prados F Calixto F Vioque M Sampaio P Tejada L 《Journal of agricultural and food chemistry》2003,51(25):7426-7430
A recombinant cyprosin from the cardoon (Cynara cardunculus L.) was assayed and compared with calf rennet in batches of ewes' milk cheese by determining different chemical, biochemical, and microbiological parameters over 4 months of ripening. There were no differences between the two types of coagulants in most chemical parameters, a(w), and pH. Proteolysis was more marked and rapid in cheese containing recombinant cyprosin as coagulant, the soluble nitrogen content of which was significantly higher (p < 0.01) than that of the cheese obtained with animal rennet; at the end of ripening the nonprotein nitrogen of cheese produced with recombinant cyprosin was slightly higher (p > 0.05) as compared with that in cheeses obtained with animal rennet. Microbial counts in the milk used for making cheese were high in most of the groups analyzed. Despite slight differences in counts, the main microbial groups analyzed were similar in cheese produced with both types of coagulants throughout ripening. 相似文献
12.
Gagnaire V Carpino S Pediliggieri C Jardin J Lortal S Licitra G 《Journal of agricultural and food chemistry》2011,59(23):12443-12452
Ragusano is a pasta filata cheese produced from raw milk in Sicily. The proteolysis was extensively analyzed after stretching (day 0), at 4 and 7 months of ripening through soluble nitrogen, urea-PAGE, and peptide identification by tandem mass spectrometry. After stretching, 123 peptides were identified: 72 arising from β-casein, 34 from α(s1)-casein, and 17 from α(s2)-casein. The main protein splitting corresponded to the action of plasmin, chymosin, cathepsin D, cell envelope proteinase, and peptidase activities of lactic acid bacteria. Unlike other types of cheeses, <10% residual β- and α(s)-caseins remained intact at 7 months, indicating original network organization based on large casein fragments. The number of identified soluble peptides also dramatically decreased after 4 and 7 months of ripening, to 47 and 25, respectively. Among them, bioactive peptides were found, that is, mineral carrier, antihypertensive, and immunomodulating peptides and phosphopeptides. 相似文献
13.
Syed Masood Hasan Rizvi Aaron D. Beattie Brian Rossnagel Graham Scoles 《Cereal Chemistry》2011,88(6):609-613
During the malting process, barley is germinated via a carefully controlled procedure so that its components are degraded to sugars, amino acids, and other low molecular weight compounds that can be used for subsequent fermentation. One of the most important of these processes is the hydrolysis of proteins into peptides and amino acids. During seed germination, proteases hydrolyze insoluble reserve proteins into soluble peptides that are subsequently hydrolyzed into free amino acids. During kilning, green malt is initially air dried at 40–60°C, and then the temperature is gradually increased to 85–95°C. Although most proteases are denatured during kilning, the malt contains a small proportion of heat‐stable protease enzymes able to further break down protein in the subsequent mashing process. In this study, protocols were developed and standardized to measure the activity of different proteases. These protocols were then used to study protease thermostability in Canadian two‐row spring malting barley lines. We found a wide range in protease activity under controlled conditions. Upon heat treatment, several lines exhibited significant protease thermostability. These thermostable enzymes were purified by ammonium sulfate precipitation and Sephadex columns for further study. 相似文献
14.
E Engel C Tournier C Salles J L Le Quéré 《Journal of agricultural and food chemistry》2001,49(6):2940-2947
The aim of this study was to add to the understanding of changes in taste that occur during the ripening of a bitter Camembert cheese by the evolution of its composition. Physicochemical analyses were performed on rind, under-rind, and center portions of a Camembert cheese selected for its intense bitterness. At each of the six steps of ripening studied organic acids, sugars, total nitrogen, soluble nitrogen, phosphotungstic acid soluble nitrogen, non-protein nitrogen, Na, K, Ca, Mg, Pi, Cl, and biogenic amines were quantified in each portion. Changes in cheese composition seemed to mainly result from the development of Penicillium camemberti on the cheese outer layer. Migration phenomena and the release of potentially taste-active compounds allowed for the evolution of saltiness, sourness, and bitterness throughout ripening to be better understood. Apart from taste-active compounds, the impact of the cheese matrix on its taste development is discussed. 相似文献
15.
The squid (Loligo pealei) byproduct composed of heads, viscera, skin, fins, and small tubes was subjected to hydrolysis at 55 degrees C and natural pH (6.8) using endogenous proteases. Squid hydrolysate was characterized during the course of hydrolysis for changes in the degree of hydrolysis, viscosity, electrophoretic pattern of proteins and peptides, and amino acid and fatty acid profiles. The change in viscosity can be used to monitor the progress of protein hydrolysis up to the molecular mass of 26.63 kDa. The 2 h hydrolysis resulted in a 2-fold increase in the total free amino acids and yielded hydrolysate with protein molecular mass of < or =45 kDa having feed attractability and good amino acid and fatty acid profiles with high contents of essential amino acids and fatty acids. Such hydrolysis-induced changes can make squid byproduct hydrolysate a good source of aquaculture feed ingredient, especially for a starter diet for larval fish. 相似文献
16.
凝乳是干酪加工的关键环节,对奶油干酪的品质具有重要影响。通过对奶油干酪理化成分、产率、涂抹性的测定,比较了酶凝、酸凝、酸-酶互作凝乳3种方式对奶油干酪涂抹性的影响。结果表明,随着酸化程度的加深,奶油干酪的脂肪含量和蛋白质含量逐渐减少,含水率显著增加,校正产率、脂肪回收率和酪蛋白回收率降低。有酶高酸组(RHA)涂抹性最佳,其剪切功、屈服应力都分别为最小(19.23N·s、195.67Pa),与传统酸凝型奶油干酪(NR)相比,RHA的剪切功和屈服应力分别降低了17.04%和27.88%,干酪涂抹性得到明显改善。这为涂抹型奶油干酪的研发提供了技术基础。 相似文献
17.
This study was carried out to determine the cholesterol removal rate and resulting changes in flavor, fatty acid and bitter amino acid production in reduced-cholesterol Cheddar cheese, made by cream separation followed by 10% beta-cyclodextrin (beta-CD) treatment. The cholesterol removal from the cheese was 92.1%. The production of short-chain free fatty acids (FFAs) increased the ripening time in control and cream-treated cheeses. The quantity of short-chain FFAs released between treatments during ripening was different, while not much difference was found in the production of neutral volatile compounds in the samples. Reduced-cholesterol cheese produced much higher levels of bitter amino acids than the control. In sensory analysis, the texture score of control Cheddar cheese increased significantly with ripening time; however, that of the cream treatment group decreased dramatically with ripening time. On the basis of our results, we conclude that the cheese made from beta-CD-treated cream had a higher rate of cholesterol removal and ripened rapidly. 相似文献
18.
The coagulant retained in cheese curd is a major contributor to proteolysis during ripening. The objective of this study was to quantify the effects of several milk-related factors and parameters during cheese manufacture on the retention of coagulant in cheese curd. The amount of coagulant retained in curd was determined by its activity on a synthetic heptapeptide (Pro-Thr-Glu-Phe-[NO2-Phe]-Arg-Leu) using reversed-phase HPLC. The retention of chymosin in cheese curd increased significantly when the pH of milk was reduced at rennet addition below pH 6.1, the pH at whey drainage below pH 5.7, or the average casein micelle size in milk and when the ionic strength of milk was increased. The casein content of milk and the quantity of chymosin added to milk had no significant effect on the retention of chymosin in curd; the quantity of coagulant bound per gram of casein remained unchanged. 相似文献
19.
Lopez C Maillard MB Briard-Bion V Camier B Hannon JA 《Journal of agricultural and food chemistry》2006,54(16):5855-5867
This study followed the progression of lipolysis in Emmental cheese by quantifying the concentrations of individual free fatty acids (FFA) released during ripening in each of the different rooms: 12 days at 12 degrees C, 28 days at 21 degrees C, and 8 days at 4 degrees C. Lipolysis, which corresponded to 1.56% of fat, mainly occurred in the 21 and 4 degrees C rooms, with 68 and 16.5% of total FFA, respectively. The nonselectivity of lipolytic enzymes was evidenced: all fatty acids were released with level of > or =1%. Differential scanning calorimetry experiments showed that the thermal properties of cheese were affected by (i) lipolysis of fat, that is, the monoacylglycerols, diacylglycerols, and FFA that may be localized at the fat/whey interface, and/or by (ii) hydrolysis of high-melting-point triacylglycerols constituted mainly by long-chain saturated fatty acids (e.g., palmitic acid). Analysis of the cheese microstructure was performed using confocal laser scanning microscopy. Fat globules were mainly disrupted after pressing of curd grains, leading to the release of the milk fat globule membrane (MFGM); fat inclusions were surrounded by pockets of whey, delimited by casein strands. Moreover, colonies of bacteria were preferentially localized in situ at the fat/protein interface. This study showed that both the localization of bacteria and the supramolecular organization of fat which was not protected by the MFGM can help the accessibility of milk fat to lipolytic enzymes and then contribute to the quality of cheese. 相似文献
20.
Taborda G Molina E Martínez-Castro I Ramos M Amigo L 《Journal of agricultural and food chemistry》2003,51(1):270-276
Volatile and nonvolatile compounds present in the water-soluble fraction (WSF) and water-soluble fraction with molecular weight lower than 1000 Da (WSF < 1000 Da) of six Spanish cheeses, Cabrales, Idiazábal, Mahón, Manchego, Roncal, and a goat's milk cheese, were analyzed. Different nitrogen fractions (determined by Kjeldahl method), caseins (by capillary electrophoresis), peptides and amino acids (by HPLC), and volatile components (by dynamic headspace coupled to GC-MS) as well as mineral content in the cheese fractions were analyzed and compared. The different nitrogen and volatile compounds identified in the WSF were characteristic of each cheese variety. Cabrales cheese displayed the highest content of free amino acids and the highest quantity and variety of volatile compounds. The WSF < 1000 Da fraction was less representative, especially for volatile compounds, as some of the components were lost in the ultrafiltration. Alcohols were better recovered than ketones and esters. 相似文献