DFD牛肉研究进展

牛肉是主要肉类产品之一,能够为消费者提供丰富的蛋白质。随着社会进步和人们生活水平的提高,人们更加看重肉品质量。但是,目前我国肉牛产业链的各个环节尚不完善,导致了劣质牛肉的产生和较高的DFD（dark,firm and dry）牛肉发生率。本文综述了DFD牛肉的发生机理及其影响因素,同时阐述了恰当的肉牛宰前管理方式和DFD牛肉的控制措施,为我国肉牛产业的发展提供一定参考。     

宰后放置时间对牛肉匀浆物热诱导凝胶特性的影响

通过对宰后1、2、3、4、5d的牛肉匀浆物的可溶性蛋白质浓度、凝胶的保水特性、凝胶强度及质构特性等指标的测定,研究宰后放置不同时间对牛背最长肌匀浆物热诱导凝胶特性的影响。结果表明,匀浆物的蛋白质浓度与凝胶保水性随放置时间呈现相同的先降后升的变化趋势,而凝胶强度、脱水率、硬度、粘性与咀嚼性则呈现相反的先升后降趋势。宰后放置时间较短时(1~3d),凝胶弹性呈现先升后降的显著变化,当放置较长时间(≥4d),弹性值有所回升,但变化并不显著。宰后放置较短时间(1~3d),内聚性随宰后时间的增加显著降低,宰后放置较长时间(≥4d),内聚性增加并趋于稳定。由此可知,宰后放置不同时间对牛肉匀浆物的凝胶特性影响较大,且各指标随宰后时间的变化趋势存在明显的相关性,可为凝胶类肉制品生产的原料选择提供理论依据。      

宰后放置时间对牛肉匀浆物热诱导凝胶特性的影响

通过对宰后1、2、3、4、5d的牛肉匀浆物的可溶性蛋白质浓度、凝胶的保水特性、凝胶强度及质构特性等指标的测定,研究宰后放置不同时间对牛背最长肌匀浆物热诱导凝胶特性的影响。结果表明,匀浆物的蛋白质浓度与凝胶保水性随放置时间呈现相同的先降后升的变化趋势,而凝胶强度、脱水率、硬度、粘性与咀嚼性则呈现相反的先升后降趋势。宰后放置时间较短时(1~3d),凝胶弹性呈现先升后降的显著变化,当放置较长时间(≥4d),弹性值有所回升,但变化并不显著。宰后放置较短时间(1~3d),内聚性随宰后时间的增加显著降低,宰后放置较长时间(≥4d),内聚性增加并趋于稳定。由此可知,宰后放置不同时间对牛肉匀浆物的凝胶特性影响较大,且各指标随宰后时间的变化趋势存在明显的相关性,可为凝胶类肉制品生产的原料选择提供理论依据。     

宰后不同时间冷冻和冻结速率对牛肉食用品质的影响

采用均匀实验设计,以宰后时间和冻结速率为考察因素,以牛背最长肌为原料,探讨宰后放置不同时间进行冷冻和不同冻结速率对解冻后牛肉食用品质的影响规律。结果表明,宰后时间和冻结速率对冻结肉样的蒸煮损失、p H、a*值和剪切力值均有显著影响(p<0.05),但对肉样的L*值、b*值影响不显著(p>0.05)。当保持冻结速率一定时,肉样解冻后的蒸煮损失和p H均随着宰后时间的增加而增加,a*值和剪切力随宰后时间的延长而降低,宰后时间对肉样的解冻汁液流失无显著影响(p>0.05);当保持宰后时间一定时,冻结肉样的解冻汁液流失、蒸煮损失、p H、a*值和剪切力值均随着冻结速率的增大而降低。      

宰后颈臂束缚技术对牛肉品质的影响

颈臂束缚技术是一种在跟腱吊挂基础上,于牛胴体前臂远端与颈前端之间施加一径向外力使之收紧,从而 加快肉牛胴体成熟的技术。为研究该技术对牛肉品质的影响,选取6 头年龄和活体质量相近的新疆褐牛,屠宰后左 半侧胴体采用颈臂束缚技术成熟（实验组）,右半侧胴体采用传统跟腱吊挂方式成熟（对照组）,分别于宰后0、 1、2、3、7、14、21 d测定牛臂三头肌、背最长肌和股二头肌三部位的pH值、失水率、蒸煮损失率、剪切力和肌纤 维超微结构等指标。结果表明：与对照组相比,实验组肉样失水率增加、剪切力降低、肌原纤维小片化指数增大, 且差异显著,肌原纤维结构破坏更为严重。颈臂束缚成熟技术可以缩短牛肉的宰后成熟时间,降低工厂生产成本, 提高生产效率。     

宰后成熟对牛肉品质的影响

本文通过对牛肉中粗钙激活因子（依钙蛋白酶CAF）的活性及肌原纤维小片化指数、胶原含量的测定,说明牛肉中依钙蛋白酶的活性随宰后时间的延长面下降,直影响到肉嫩度的变化、成熟时间越长,肌原纤维小片化程度越高,肌原纤维结构破坏越来在重,越有利于提高肉的嫩度。     

热鲜牛肉适宜冷藏时间的研究

试验将屠宰后8h牛肉置于0～4℃的冰箱内分别贮藏1d、3d、5d、7d,通过对其进行剪切力、煮熟率的测定,以及对其颜色和风味的评定,以研究热鲜牛肉的适宜冷藏时间。结果表明:随冷藏时间的延长,牛肉嫩度和系水力得到改善,但是5d色泽变暗、7d后风味变差。由试验结果看,在0～4℃下热鲜牛肉的冷藏期最多不超过5d。     

宰后成熟对牛肉品质的影响

文章通过对牛肉中粗钙激活因子的活性及肌原纤维小片化指数、胶原含量的测定。说明牛肉中依钙蛋白酶的活性随宰后时间的延长而下降,直接影响到肉嫩度的变化,成熟时间越长、肌原纤维小片化程度越高,肌原纤维结构破坏越严重,越有利于提高肉的嫩度。     

去除牛肉膻味的研究

新鲜牛肉经过腌制,添加枸杞、芹菜、β－环状糊精等物质,可有效地去除令人不悦的膻味,制成口味良好的肉丸、牛肉肠等产品。     

宰后成熟过程中冷却牛肉、猪肉色泽和嫩度的变化

本实验比较研究了冷却牛肉和猪肉在宰后120h内色泽和剪切力的变化.分别从牛屠宰厂和猪屠宰厂选取牛、猪各4头,按规范工艺屠宰后取背最长肌,分切成8个肉块,经简易包装后在0～4℃下18、48、96、120h,之后测定肉色、剪切力值及其他相关指标.结果表明,牛肉和猪肉的pH值、肉色(L*、a*、b*)、水分含量、剪切力值等指标存在显著差异(p<0.05).随着成熟时间延长,亮度增加、红度下降、剪切力下降;宰后120h内,猪肉嫩度的变化比牛肉更明显.     

A practical method to prevent dark-cutting (DFD) in beef

A method for the prevention of dark-cutting in beef, based on recognition of social relationships within groups of bulls, was tested on 2234 bulls slaughtered under commercial conditions. When the influence of time between loading the animals and slaughter was eliminated statistically, the bulls of the socially stablized group showed the lowest pH₂₄ values, whereas those of the socially unstable group showed the highest ones. When the type of social group was eliminated statistically, the earlier slaughtered animals had lower pH₂₄ values than those slaughtered later. When the two major factors were integrated, there was no statistically significant difference in the pH₂₄ values in bulls of the socially stabilized group whether they were slaughtered immediately after transport or during the following day. In contrast, in bulls from the socially unstable group, the pH₂₄ values increased substantially after overnight lairage at the abattoir. In conclusion, for longer transportion, bulls from loose housing with stable social relationships should be used. It is necessary to keep the same social groups from loading to slaughter, strictly avoiding any mixing of strange bulls. Bulls from tethered stalls should be transported and slaughtered within as short a time after regrouping as possible.     

Prevention of dark-cutting (DFD) beef in penned bulls at the abattoir

There is a large body of evidence indicating that activities associated with regrouping of bulls before slaughter, which leads to physical exhaustion mainly from mounting, are primary factors inducing dark-cutting (DFD) in beef. The aim of this study was to test several methods to control activity when regrouping cannot be avoided. Fifty bulls previously individually tied for at least 16 months were drafted into groups of five animals and released in a pen at the abattoir. After 18 to 22 h they were slaughtered. According to environmental conditions in the pen, the bulls were divided into four groups: Control group (n = 10, no experimentation); Electricity group (n = 10, an electric fence was constructed above the pen so that a mounting bull would receive an electric shock); Darkness group (n = 10, the whole stall was in darkness); and Combination group (n = 20, both treatments, of the electricity and darkness groups were applied). During the first hour of penning the behaviour of the bulls was videorecorded. After slaughter meat quality characteristics were measured. Dark-cutting was found in Control (70%), Electricity (30%) and Darkness (70%) groups, but not in the Combination group (0%). No treatment altered the repertoire of agonistic activity, but under the combined treatments the number of agonistic interactions was significantly lower than in any other group.     

Influence of the time of year on the incidence of PSE and DFD in Irish pigmeat

The conditions of PSE (pale, soft, exudative) and DFD (dark, firm, and dry) are significant causes for downgrading of pigmeat resulting in financial loss to the slaughter plant. The objective of this study was to document the variation in quality of pigmeat from one slaughter plant over a 15-month period, based on colour, appearance and pH. During 4 days of most weeks, 30 pigs were randomly selected from the slaughter line, resulting in a total number of 4560 pigs. Muscle pH between the third and fourth rib was measured 45 min, 90 min and 24 h after slaughter. Using a Minolta colorimeter (Hunter L, a, b scale), colour of the longissimus dorsi muscle was measured 24 h after slaughter. Muscle colour was also visually scored on a scale of 1-6. Carcass pH at 24 h post-mortem varied significantly with month of slaughter (P<0.04) as did colour (Hunter L, P<0.001; Hunter a, P<0.001; Hunter b, P<0.001). It was concluded that meat quality as measured by 24 h pH and colour was poorest during the months of November and December. While this may be at least partly related to weather, it is probable that the increased slaughtering rates at this time and variable resting period before slaughter had the biggest impact.     

The incidence of dark cutting beef in Sweden

The incidence of DFD (Dark, Firm, Dry) in Swedish cattle was studied at four abattoirs and the influence of some parameters of special interest for the development of DFD were evaluated. The pH was measured in a total of 2686 carcasses of different categories. Carcasses with a pH(24) ≥ 6·2 were classified as being DFD. Only for electrically stimulated carcasses could the pH(24) be considered to be the ultimate pH value. DFD incidences of 3·4% and 13·2% were recorded as overall means for electrically stimulated and non-stimulated carcasses, respectively. The highest incidence was found in young bull carcasses having almost twice as high an incidence of DFD compared with the other categories. Considering seasonal variations, the highest incidence of DFD was found in the period May to August but significant differences in pH were found only for short lairage times. Overnight lairaging increased the incidence of DFD. However, the influence of the lairage time is closely related to the lairage conditions and needs further study.     

Dissimilarity scaling and INDSCAL analysis in the study of flavour differences between normal pHu and DFD beef

Overall dissimilarity measurement of paired stimuli followed by Individual Differences Scaling (INDSCAL) analysis was used to study flavour perception in a set of beef extracts. The experiment was designed to determine whether pH contributed to flavour difference between beef of “normal” ultimate pH (pHu5.8) and “dark-cutting” (DFD) beef (pHu6.2). Assessors distinguished the flavour of “normal” pHu and DFD beef both by a combination of pH and titratable acidity, and a second dimension independent of pH. The chemicals added to adjust pH independently of the original muscle composition contributed a third flavour dimension. Substantial assessor variation was observed in the relative weight given to the three flavour dimensions, and this is discussed in relation to the task of judging overall dissimilarity.     

Consumer acceptability of dark, firm and dry (DFD) and normal pH beef steaks

The sensory attributes of dark, firm and dry (DFD) and normal pH beef, both raw and fried, were evaluated and compared by a consumer panel (n=64). Consumer sensory evaluations indicated that the general appearance (P<0.05), colour (P<0.001) and acceptability (P<0.01) of raw normal pH steaks were preferred to those of raw DFD steaks. Twice as many panellists preferred the raw normal pH than raw DFD steaks because of the more attractive red colour, compared to the almost black colour of raw DFD steaks. No significant differences were found between the hedonic ratings of the sensory attributes of fried normal pH and fried DFD steaks. It was expected but not confirmed that consumers would find the tenderness of the DFD steaks more acceptable compared to the normal pH steaks. However, when forced to choose, female consumers significantly preferred fried normal pH steaks to fried DFD steaks, presumably because of a better flavour and more acceptable colour.     

山东省玉米真菌毒素污染状况调查及分析

为掌握山东省玉米的真菌毒素污染状况,评估污染带来的安全风险,为加强真菌毒素污染防控提供依据,采集了山东省玉米主产县2013年~2014年收获和储藏的玉米样品共520批次,采用液相色谱—飞行时间质谱联用仪(UPLC-Q-TOF)方法检测了玉米中黄曲霉毒素(AFB_1、AFB_2、AFG_1、AFG_2)、伏马毒素(FB_1、FB_2、FB_3)、呕吐毒素(DON)和玉米赤霉烯酮(ZEN)的污染水平。结果表明,AFB1、AFB2、AFG1在玉米中检出率分别为18.08%、7.88%、0.77%,平均含量分别为7.62、0.60、0.05μg/kg;FB1、FB2、FB3检出率分别为92.50%、88.08%、83.85%,平均含量分别为1 798.69、531.83、197.71μg/kg;DON检出率为26.35%,平均含量为240.44μg/kg;ZEN检出率为14.62%,平均含量为74.90μg/kg;AFG2未检出。调查结果还表明,伏马毒素在所测样品中污染最为严重,超标率达33.46%;单一样品受多种毒素混合污染的情况较严重。     

山东地区饲料原料真菌污染状况调查

目的调查山东地区饲料原料真菌污染状况。方法从山东地区代表性饲料生产企业采集豆粕、棉籽粕、麦麸、可溶性干酒糟(distillers dried grains with soluble,DDGS)和玉米粉5种饲料原料样品,密封送至实验室采用平板稀释法接种分离,并对不同样品的真菌进行鉴定。结果 5种饲料原料的真菌检出率分别为豆粕(76.19%)、棉籽粕(68.75%)、麦麸(85.71%)、DDGS(21.62%)和玉米粉(100%)。玉米粉带菌量最高,达4.75×105 cfu/g;豆粕带菌量最低,均小于103 cfu/g。污染真菌种类多样,共检出曲霉属8种、镰刀菌属3种、青霉属7种、其他真菌19种,其中以黄曲霉、串珠镰刀菌和串珠镰刀菌胶孢变种最为常见。结论山东地区饲料原料受真菌污染较普遍,不同种类饲料原料受真菌污染水平不同。污染的黄曲霉和镰刀菌可能含产毒菌株,值得关注。     

山东烟区烟草农机专业合作社现状分析

为考察烟草农机专业合作社服务烟农和现代烟草农业的现状和能力,采用实地调查和问卷调查相结合的方法,对山东烟区烟草农机专业合作社的发展情况进行了详细调研.调查表明,烟草农机专业合作社具有发展快,建立基础好,领办主体多元等特点,在提高劳动生产效率、保障烟叶质量、促进烟草专业化和标准生产等方面发挥了重要作用.同时也存在治理结构不健全、规章制度不完善、盈余分配不规范、财务管理较混乱、经营服务不到位等问题,需要从增强烟农合作意识,完善治理结构,实行科学管理,增强服务效能等方面对合作社运营进行完善,同时也需要烟草公司和政府提供政策与资金支持.     

山东仓储片烟表面微生物区系研究

对山东不同产地库存正常和霉变片烟表面微生物区系进行了系统研究。从正常和霉变片烟表面分离鉴定了17属51个真菌菌株,3属8个细菌菌株和4属10个放线菌菌株。正常和霉变片烟表面真菌类群以曲霉、青霉、根霉、毛霉相对分离频率较高,且多数真菌可致使烟叶霉变,以黑曲霉、黄曲霉、总状毛霉、匍枝根霉、黄柄曲霉等致霉力较强。诱致山东仓储片烟霉变的主要霉菌类群为黄柄曲霉、黑曲霉、黄曲霉、桔青霉、纯绿青霉、产黄青霉、总状毛霉、匍枝根霉。正常片烟表面微生物数量为细菌放线菌真菌,霉变片烟表面微生物数量为真菌细菌放线菌。与正常片烟相比,霉变片烟表面真菌菌相单一,真菌菌落密度大幅增加,细菌与放线菌菌落密度相对变化较小。正常片烟真菌带菌量约在80～1100cfu/g,平均为400cfu/g。霉变片烟真菌带菌量最低5000.0cfu/g,平均达1.3×107cfu/g,是正常片烟平均真菌带菌量的3302.5倍。真菌带菌量的增加是片烟霉变的显著特征之一。