不同贮藏温度市售热鲜牛肉新鲜度变化研究

为了探究不同贮藏温度对市售热鲜牛肉新鲜度的影响，试验以市售热鲜牛肉为研究对象（采自4头锦江黄牛背最长肌），测定其在不同贮藏温度（5、15、25和35℃）和相对湿度（relative humidity，RH）为80%条件下，pH、L^*、a^*、b^*值、菌落总数、硫代巴比妥酸（thiobarbituric acid reactive substances，TBARS）和挥发性盐基氮（total volatile basic nitrogen，TVB-N）含量随贮藏时间（0、6、12、24、48、72、96和120 h）的变化情况。结果表明，随着贮藏时间延长，不同贮藏温度处理组热鲜牛肉的pH均呈先降低后上升的趋势，L^*、a^*和b^*值呈先上升后降低趋势，菌落总数、TBARS和TVB-N含量呈上升趋势；且贮藏温度越高，各指标随时间变化的趋势加剧。综合分析各指标的变化规律，为了保证热鲜牛肉的新鲜度和食用安全性，在5、15、25和35℃下贮藏的热鲜牛肉，其货架期分别不能超过96、72、24和12 h。     

真空包装冷鲜牛肉品质变化规律研究

为研究真空包装冷鲜牛肉在0~4℃贮藏期间的品质变化规律,对贮藏期间冷鲜牛肉汁液流失、p H值、菌落总数、挥发性盐基氮(TVB-N)、色差值(a*)、蒸煮损失等指标进行定期测定。结果表明:在贮藏期间,冷鲜牛肉失重率增加,p H值呈先上升后下降再上升趋势,菌落总数和TVB-N均呈增加趋势,红度值a*先上升后下降,蒸煮损失增大。结合菌落总数和TVB-N,真空包装冷鲜牛肉的货架期为21d。     

冰温贮藏对冷鲜鸡品质的影响

试验以黄羽肉鸡冷鲜鸡为对象,研究了在-1.5℃(冰温)和4℃(冷藏)环境条件下菌落总数、挥发性盐基氮(TVB-N)、pH值和感官评价等指标变化,比较冰温和冷藏对冷鲜鸡保鲜期的影响。结果显示:冰温保鲜能很好地控制冷鲜鸡肉的菌落总数和TVB-N,延缓pH值的升高。冰温贮藏至10 d时,菌落总数为2.2×10~4cfu/g,TVB-N值为14.93 mg/100 g,pH值为6.51,均符合新鲜肉的要求。结果表明,冰温较冷藏能更好地延缓鸡肉的腐败变质,可将保鲜期延长至10 d。     

混合菌固态发酵制备发酵鱼粉的研究

试验旨在研究不同发酵条件对发酵鱼粉小肽含量和挥发性盐基氮的影响,确定发酵鱼粉生产工艺条件。以嗜酸乳杆菌和枯草芽孢杆菌为发酵菌株,以发酵产物小肽含量和挥发性盐基氮含量为指标,优化了混合菌固态发酵制备发酵鱼粉的生产工艺条件,并对发酵鱼粉的总抗氧化能力和氨基酸组成进行了分析。试验结果表明,适宜的发酵鱼粉生产工艺条件为:菌种接种比(嗜酸乳杆菌枯草芽孢杆菌)12、料水比11、接种量5%、发酵温度35℃、发酵时间24 h。此条件下,发酵鱼粉小肽含量达到24.77%,挥发性盐基氮仅为42.5 mg/100 g,总抗氧化能力提升70%以上,限制性氨基酸的含量提升27.75%以上,发酵鱼粉较传统的普通鱼粉有巨大的优势,应用于饲料中具有广阔的市场前景。     

直接挥发法测定猪肉中的挥发性盐基氮的研究

挥发性盐基氮(TVBN)是肌肉在贮存过程中由于细菌和肌肉自身酶的作用,使氨基酸分解产生的一些碱性易挥发的氨及胺类化合物。新鲜肉TVBN 含量很少,而变质肉 TVBN 含量高。目前,TVBN 是我国食品卫生检验标准中唯一的一项理化检验指标。国家标准 GB2707—81和 GB2727—81规定,一级鲜猪肉 TVBN≤15mg/100g,二级     

不同预冷方式对肉鸡胴体肉品质和货架期的影响

为比较风冷、浸没式预冷(水冷)和先水冷后风冷的混合式预冷对鸡胴体胸肉品质和保质期的影响,随机选取54只60日龄的肉鸡,经过3种预冷方式处理后,在屠宰后的第1、3、5天分别测定胸肉的各项理化指标.结果:预冷后,水冷组胴体重增加最多(+3.18％),混合预冷组次之(+1.61％),而风冷组胴体重下降了1.53％;屠宰后24 h,混合预冷和水冷组的L*值高于风冷组(P＜0.05);但风冷和混合预冷组的剪切力低于水冷组(P＜0.05),剪切力随着储存时间的延长而明显下降;3种预冷方式胸肉的加压失水率和pH值均无显著差异(P＞0.05),pH值与保存时间成正相关;不同预冷方式的TVB-N(挥发性盐基氮)含量无显著差异(P＞0.05),随着储存时间的延长,TVB-N含量明显上升,在宰后的第7天达到或超过15 mg/100 g.试验表明:在无抑菌剂条件下,肉鸡胴体的保质期为5d;混合预冷充分结合了风冷和水冷的优势,是较为理想的冷却方式.     

不同贮藏温度市售热鲜牛肉新鲜度变化研究

为了探究不同贮藏温度对市售热鲜牛肉新鲜度的影响,试验以市售热鲜牛肉为研究对象(采自4头锦江黄牛背最长肌),测定其在不同贮藏温度(5、15、25和35℃)和相对湿度(relative humidity,RH)为80%条件下,pH、L*、a*、b*值、菌落总数、硫代巴比妥酸(thiobarbituric acid reactive substances,TBARS)和挥发性盐基氮(total volatile basic nitrogen,TVB-N)含量随贮藏时间(0、6、12、24、48、72、96和120h)的变化情况。结果表明,随着贮藏时间延长,不同贮藏温度处理组热鲜牛肉的pH均呈先降低后上升的趋势,L*、a*和b*值呈先上升后降低趋势,菌落总数、TBARS和TVB-N含量呈上升趋势;且贮藏温度越高,各指标随时间变化的趋势加剧。综合分析各指标的变化规律,为了保证热鲜牛肉的新鲜度和食用安全性,在5、15、25和35℃下贮藏的热鲜牛肉,其货架期分别不能超过96、72、24和12h。     

猪鲜肉中细菌学指标和重金属、兽药残留分析

本实验测定了绿洲灌区规模养猪场中三元(杜长大)和四元(皮杜长大)杂交商品猪鲜肉中的细菌菌落总数、大肠杆菌群、沙门氏菌微生物指标,挥发性盐基氮含量,汞、铅、砷、镉、铬等重金属残留以及金霉素、土霉素、磺胺类药物、伊维菌素、喹乙醇、盐酸克伦特罗和莱克多巴胺等兽药残留理化指标。结果显示,在被检的120份新鲜肉样中,所有肉样均检出细菌菌落、大肠杆菌、挥发性盐基氮及汞、铅、无机砷、镉和铬等重金属,未检出沙门氏菌与金霉素、土霉素、磺胺类药物、伊维菌素、喹乙醇、盐酸克伦特罗和莱克多巴胺等兽药残留。在检出的指标中,细菌菌落总数平均值为8.4×104 cfu/g,大肠杆菌群为4.5×103 mpn/100g,挥发性盐基氮为6.01mg/100g,总汞为0.007mg/kg,铅为0.018mg/kg,无机砷为0.006mg/kg,镉为0.026mg/kg,铬为0.031mg/kg,各项指标合格率均达100%。表明张掖市市售新鲜猪肉安全良好,可放心食用。     

竹醋液、壳聚糖和茶多酚对冷却猪肉的复合保鲜研究

为研究竹醋液、壳聚糖及茶多酚作为保鲜剂保存冷却猪肉的复合保鲜效果,试验先通过单因素试验对单一保鲜剂进行了筛选,在此基础上采用L_9(3~3)正交试验进行了竹醋液、壳聚糖及茶多酚的最优组合筛选。结果表明:最佳复合保鲜剂组合为壳聚糖0.9 g/100 mL、茶多酚0.9 g/100 mL、竹醋液2%(V/V),在最优条件下冷却猪肉的菌落总数对数值、pH值、挥发性盐基氮(TVB-N)值均显著低于对照组。说明竹醋液、壳聚糖和苯多酚复合保鲜剂;货架期能够有效地延长冷却猪肉的贮藏期。     

德国优质牛肉的介绍(下)

三）什么是排酸？为了达到最佳的适口性，牛肉必须经过排酸处理，即指牛肉经过悬挂后变得酥软可口。随着排酸时间的增长，一是牛肉的切力值降低；二是牛肉变得嫩些，味道也好些。剖边牛肉或分割牛肉在排酸时，（１）胴体重下降；（２）在较长时间的悬挂贮藏后（超过１０天...     

Determination of biogenic amines in aerobically stored beef using high-performance thin-layer chromatography densitometry

The aim of this study was to develop a high-performance thin-layer chromatography densitometry method to simultaneously evaluate levels of different biogenic amines (BAs) in beef stored aerobically at 4°C. Steaks from M. longissimus thoracis et lumborum muscles were overwrapped with polyvinyl chloride film and stored for 0, 4, 7, and 10 days. For this purpose, the solvent system and pH for the derivatization of BAs with dansyl chloride were optimized. Moreover, this method was also validated for linearity, limits of detection and quantification, precision, and recovery. As found using this method in beef samples, spermine content decreased significantly after 7 days of storage, and tyramine and cadaverine were not detected until day 10.     

Growth Model of a Plasmid‐Bearing Virulent Strain of Yersinia pseudotuberculosis in Raw Ground Beef

The growth kinetics of virulence plasmid‐bearing Yersinia pseudotuberculosis (YPST) in sterile ground beef were studied at temperatures ranging from 0 to 30°C. In irradiated sterile ground beef, YPST replicated from 0 to 30°C, with corresponding growth rates (GR) ranging from 0.023 to 0.622 log CFU/h at 0–25°C, and the GR was 0.236 log CFU/h at 30°C. The maximum population densities (MPD) ranged from 8.7 to 11.0 log CFU/g. The growth and MPD of YPST were reduced significantly at 30°C. Models for GR and MPD of YPST in raw ground beef (RGB) as a function of storage temperatures were produced and displayed acceptable bias and accuracy. The models were validated with rifampicin‐resistant YPST (rif‐YPST) in sterile ground beef stored at 4, 10 and 25°C. The observed GR and MPD were within 95% of the predicted values. When compared to non‐sterile retail ground beef, the growth of rif‐YPST was not inhibited and displayed similar GR at 0, 10 and 25°C and MPDs as sterile ground beef at 10 and 25°C. Moreover, there was no loss of virulence plasmid in YPST during its growth in ground beef indicating that RGB contaminated with virulence plasmid‐bearing YPST could cause disease due to refrigeration failure, temperature (10–25°C) abuse, and if the meat was not properly cooked.     

不同品种牛背最长肌抗氧化性能的研究

本试验旨在研究不同品种牛肌肉的抗氧化特性,为优质牛肉的生产提供试验数据。选用5个品种牛(利木赞牛、中国西门塔尔牛、鲁西牛、秦川牛、晋南牛)的背最长肌,测定肌内脂肪含量、24小时的滴水损失以及在0～4℃下肉色、过氧化物值(PV)及硫代巴比妥酸反应物(TBARS)在72h内的变化动态。结果表明,背最长肌的肌内脂肪含量与24小时滴水损失率在不同品种牛肌肉之间没有显著差异(P>0.05);在整个储存时期(0～72h),5个品种牛肌肉的a*、b*值均呈下降趋势;4～72h内,利木赞牛肌肉的a*值均是最高的,且在冷藏8、12h时,利木赞牛肌肉的a*值显著大于鲁西牛肉和秦川牛(P<0.05),24h后利木赞牛的a*值显著大于西门塔尔牛(P<0.05);随着储存时间的延长,5个品种牛背最长肌的PV和TBARS值均有不同程度的增加,利木赞牛肌肉的PV和TBARS值增加最慢,秦川牛和鲁西牛肌肉的PV和TBARS值增加较快。结果表明,5个品种牛的肌内脂肪含量和滴水损失差异不显著,利木赞牛肌肉能够较长时间保持肉色和抗氧化特性。     

Effects of rate of pH fall, time of deboning, aging period, and their interaction on veal quality characteristics

Three groups of veal carcasses were selected on the basis of their pH in the longissimus lumborum muscle at 3 h postmortem (pH3) to study the effects and interaction with time of deboning on quality characteristics of veal. The following groups of 10 calves each were selected: 1) fast pH fall, pH3 < 6.2; 2) intermediate pH fall, 6.2 < pH3 < 6.7; and 3) slow pH fall, pH3 > 6.7. Longissimus thoracis et lumborum (LTL) muscles of sides of the selected carcasses were randomly assigned to be excised at either 24 or 48 h postmortem. Color, water-holding capacity, and shear force measurements were determined after an aging period of 2, 3, 4, 7, and 14 d, respectively. Color of longissimus muscle samples from veal calves with similar preslaughter blood hemoglobin values becomes significantly lighter with a faster pH fall. Muscle color was not affected by time of deboning and overall color of all longissimus samples remained stable during storage and was not affected by rate of pH fall and time of deboning. Cooking losses increased with both a faster rate of pH fall and by deboning at 24 h postmortem. Drip losses during vacuum storage were higher for muscles excised at 24 rather than 48 h postmortem. Both when deboned at 24 and 48 h, postmortem veal carcasses with a lower rate of pH fall had higher shear force (SF) values than did carcasses with a higher rate of pH fall. Deboning at 24 h postmortem resulted in higher SF values than deboning at 48 h postmortem. Differences in SF between 24- and 48-h deboning were larger in slower glycolyzing carcasses. Aging improved tenderness but did not fully reduce the difference in SF values between 24- and 48-h deboning. The results suggest that deboning of veal carcasses before the ultimate pH has been reached may result in muscle contraction, which may exert negative effects on tenderness and water-holding capacity of veal. Effects of time of deboning can, at least partly, be explained by differential effects on shortening of the muscle fibers.     

Developmental competence of cat oocytes from ovaries stored at various temperature for 24 h

We conducted two experiments to investigate the effects of storage temperature and period for cat ovaries on the meiotic and developmental competence of oocytes collected from the ovaries. In Experiment 1, ovaries were stored in physiological saline for 24 h at 4 C, 23-25 C, or 38 C (cold, room, and incubator temperature groups, respectively), and then oocytes were collected from the ovaries in each group. Morphologically intact oocytes were then selected and cultured in maturation medium for 24 h. Significantly more oocytes reached metaphase II (MII) in the cold temperature group (53.4%) than in the room and incubator temperature groups (20.0 and 2.4%, respectively). In Experiment 2, ovaries were stored in physiological saline at room temperature for 0, 6, 12 or 18 h, and then they were stored at 4 C (cold storage) until reaching a total storage period of 24 h. After storage of the ovaries, morphologically intact oocytes were matured, fertilized with frozen-thawed spermatozoa, and cultured in vitro. The rates of morphologically intact oocytes obtained from the ovaries stored at room temperature for 0, 6, 12 or 18 h were 35.3, 30.0, 26.4 and 14.7%, respectively, and the rates of intact oocytes that reached MII were 63.2, 36.4, 26.5 and 11.9%, respectively. The results suggested that the numbers of morphologically intact oocytes and intact oocytes that reached MII after in vitro maturation decrease gradually as the period of storage at room temperature before cold storage increases. Only oocytes from ovaries stored for 6 h developed to the blastocyst stage after in vitro maturation and fertilization when ovaries were stored at room temperature before cold storage. These results indicate that 24 h storage of ovaries at high temperatures (>23 C) decreases the meiotic competence of oocytes. The quality and developmental competence of oocytes are influenced by the length of storage at room temperature before cold storage.     

Evaluation of beef tallow as a natural source of conjugated linoleic acid

Cis‐9, trans‐11 conjugated linoleic acid (9c, 11t CLA) is a potential anticarcinogen that is found in higher concentrations in beef lipids. However, the effect of CLA on lipid peroxidation, which is closely related to carcinogenesis, is controversial. In this study, we determined the levels of 9c, 11t CLA contents and thiobarbituric acid reactive substances (TBARS) in the tissues of rats fed beef lipid. Sprague‐Dawley rats (male, 8 weeks old) were fed experimental diets containing 20% lyophilized beef, and 12% beef tallow or vegetable oils, for 56 days. With the exception of the brain, the tissues from the rats fed the experimental diets accumulated 9c, 11t CLA, depending on the levels of CLA in the diets. The beef tallow group showed significantly higher 9c, 11t CLA contents in all tissues examined than the other diet groups. The intake of beef lipid did not affect the TBARS levels in the rat tissues. The hepatic lipid content from the beef tallow group was lower than that from the group fed vegetable oils. These results suggest that beef is a good source of 9c, 11t CLA, and that the intake of an appropriate level of beef lipid is not hazardous to health.     

亚麻籽对育肥牛肉品质及脂肪酸的影响

本试验旨在研究亚麻籽对育肥牛肉品质及脂肪酸的影响。选择体重接近的西门塔尔杂交牛32头,采用单因素试验设计,随机分为4组,每组8头,其中试验Ⅰ组(对照组)、Ⅱ组、Ⅲ组和Ⅳ组牛饲喂亚麻籽的比例分别占精料0%,5%,10%和15%。结果表明,1)各试验组屠宰率,净肉率与对照组比较无显著差异(P>0.05),背膘厚度显著提高(P＜0.05),试验Ⅳ组的背膘厚度比对照组显著提高了57.75%,牛肉中脂肪含量显著提高(P＜0.05); 2)日粮中添加亚麻籽显著降低育肥牛宰后24和48 h剪切力(P＜0.01)和pH(P＜0.01);3)日粮中添加亚麻籽使肉牛背最长肌中多不饱和脂肪酸(PUFA)显著提高(P＜0.01)。日粮中添加亚麻籽可以改善胴体品质,优化了肉牛肌肉的脂肪酸组成,特别是显著增加了PUFA含量。综合分析,亚麻籽在育肥牛日粮中的适宜饲喂比例为精料的10%～15%。     

安格斯牛和荷斯坦牛热鲜牛肉、冷鲜牛肉和冷冻牛肉的品质测定分析

[方法]以安格斯牛和中国荷斯坦奶牛为研究对象,比较分析同一品种内热鲜肉、冷鲜肉、冷冻肉3种形态牛肉的营养品质、理化特性和微观结构。[结果]结果表明,3种形态牛肉的营养成分和肉品质存在一定差异。冷冻肉水分和蛋白质含量最低(P<0.05);安格斯牛热鲜肉和冷鲜肉的甜味和芳香味氨基酸含量最高(P<0.05),荷斯坦牛热鲜肉的苦味氨基酸含量最高(P<0.05);荷斯坦牛热鲜肉、冷鲜肉的十三碳酸、花生四烯酸含量最高(P<0.05),热鲜肉、冷冻肉的花生二烯酸和二十碳三烯酸含量最高(P<0.05)。热鲜肉肉色深红,冷鲜肉和冷冻肉色泽稍亮偏黄(P<0.05)。安格斯牛热鲜肉最嫩,荷斯坦牛冷鲜肉最嫩(P<0.05);冷冻肉保水性最差(P<0.05)。热鲜肉肌肉横断面排列紧密,冷鲜肉和冷冻肉排列疏松呈蜂窝状,冷鲜肉肌节长度最大(P<0.05),冷冻肉肌纤维呈蜂窝状。[结论]本研究显示,同一品种不同形态牛肉的品质存在一定的差异,热鲜肉和冷鲜肉营养成分保存较完整、食用品质较好,可为牛肉产品的消费选择和优质生鲜肉加工提供理论参考。     

青海牦牛与日本牛动物性食品脂肪酸含量比较分析

采用气相色谱法，对牦牛与日本牛肉、酥油及奶酪中的脂肪酸成分进行比较分析，牦牛脂肪酸与日本牛含量相同，C18：1n-7日本牛肉含量只有1.32％，而牦牛肉为8．69％；牦牛肉的脂肪平均含量4．5％，日本牛肉平均脂肪含量8.81％。牦牛产奶酪中的平均脂肪含量为3％，日本牛产奶酪中的平均脂肪含量为24％，差异较大。牦牛和日本牛产酥油中的平均脂肪含量差别不大。