结合低场核磁共振探究浸烫对肉鸡僵直进程和品质的影响

为研究不同浸烫温度和时间下黄羽肉鸡宰后僵直进程和微观结构的变化,实验结合低场核磁共振技术分析了54℃-270 s、58℃-150 s、62℃-120 s、66℃-90 s 4个浸烫处理组中水分的分布、保水性的变化和对食用品质造成的影响。结果表明:高温短时浸烫(66℃-90 s)会引起肉鸡pH值下降速率加快、持水力下降,同时肉鸡的肌肉收缩长度、剪切力和硬度值都在105 min时达到了僵直最大点,比其他3个处理组延缓了30 min,表明不同的浸烫条件会影响肉鸡的僵直进程和肉品质。低场核磁共振结果显示过高的浸烫温度会导致肉鸡表面自由水渗出(比其他3个处理组升高了2.0%~2.8%),肌纤维内不易流动水含量较低(比其他浸烫处理组降低约2%),保水性较差;同时组织学微观结构也揭示了高温浸烫处理组肌细胞较松散、胞外间隙较大,并随着宰后时间的延长出现肌纤维肿胀、细胞膜破裂现象。因此,在肉鸡屠宰过程中,应在温度为58~62℃、时间为120~150 s范围内浸烫,利于提高宰后鸡肉品质。     

AMPK活性对宰后牛肉糖酵解、肌肉内环境及品质的影响

为探究牛肉宰后成熟过程中单磷酸腺苷活化蛋白激酶（adenosine monophosphate-activated protein kinase,AMPK）对糖酵解、肌肉内环境及品质的影响,以0.50 mol/L 5-氨基咪唑-4-甲酰胺核苷（5-amino-4-imidazolecarboxamide,AICAR）处理的西杂牛背最长肌为对象,于4 ℃进行成熟,测定宰后成熟期间肌肉AMPKα基因（PRKAA1、PRKAA2）转录量、P-AMPK表达量、AMPK活性、糖酵解水平及品质指标的变化情况。结果表明：宰后24～120?h,处理组AMPKα基因转录量、P-AMPK表达量及AMPK活力均显著高于对照组（P＜0.05）;72～168?h,处理组pH值和肌糖原含量显著低于对照组（P＜0.05）,乳酸含量显著高于对照组（P＜0.05）;12～168?h,处理组L*、b*值及ATP、ADP、AMP和IMP含量均显著高于对照组（P＜0.05）,a*值显著低于对照组（P＜0.05）;24～120?h,处理组蒸煮损失率和肌原纤维小片化指数显著高于对照组（P＜0.05）,剪切力显著低于对照组（P＜0.05）。AICAR通过激活AMPK并加快宰后糖酵解影响肌肉内环境、肉色、剪切力及肌纤维微观结构变化,加快宰后肌肉成熟进程,说明AMPK活性对宰后肌肉糖酵解及品质变化具有重要影响,且可通过调控宰后肌肉AMPK活性来调节肌肉品质。     

超高压处理对僵直前獭兔肉品质及微观结构的影响

以僵直前獭兔肉为原料,在室温（25 ℃）条件下,分别用100、200、400 MPa超高压处理15 min,－8 ℃贮存24 h,然后对兔肉进行品质分析和超微结构研究。结果表明：随着压力的升高,兔肉亮度（L*）值升高,红度（a*）值降低,兔肉颜色由浅红色逐渐变为灰白;随着压力的升高兔肉蒸煮损失率、滴水损失率呈现先下降后上升的趋势,在200 MPa时兔肉的蒸煮损失率、滴水损失率最低,分别为31.54%和2.61%;超高压对兔肉嫩度影响显著（P＜0.05）,在0.1～200 MPa之间,剪切力随压力增大而降低,而400 MPa处理时,兔肉剪切力急剧升高并显著高于对照组（0.1 MPa）;100 MPa压力处理,兔肉组织结构与对照组相比变化不大,而400 MPa时兔肌肉显微组织结构变化明显：肌节收缩,肌纤维歪曲、片段化,蛋白质发生解聚、三级结构遭到破坏。可见,不同的超高压对僵直前獭兔肉的品质和微观结构有显著影响,且200 MPa是最适于僵直前兔肉处理的超高压条件。     

生猪宰前不同静养时间和屠宰方式对背长肌肌肉pH值和滴水损失的影响

两个不同的屠宰场分别随机选取50头待宰的商品猪分为两组,分别进行屠宰前禁食6h和12h处理,测定背最长肌pH值和滴水损失率.结果表明,6h和12h不同的静养时间对肌肉滴水损失率没有显著差异,但是升高了屠宰后24h肌肉pH值,表明宰前较长时间的静养有利于提高肌肉品质性能.另外对电击致晕屠宰和活体屠宰方式相比,前者滴水损失率明显低于后者,表明电击致晕的屠宰方式对提升肉品质量来讲是一种更适宜推广的方式.     

宰后浸烫和预冷对白条鸭肉品质的影响

以白条鸭为研究对象,通过响应面法研究宰后因素如浸烫时间(180～220s)、浸烫温度(56～64℃)、预冷时间(40～50min)和预冷温度(10～15℃)对白条鸭肉嫩度的影响,并建立一个高度显著且拟合度良好的二次回归模型。结果表明:当浸烫时间为187s、浸烫温度为64℃、预冷时间为50min、预冷温度为13℃时,白条鸭肉的剪切力为51N。     

电击晕对肉鸭屠宰品质的影响

以肉鸭胸肉和腿肉为研究对象,研究宰前电击晕对肉鸭屠宰品质的影响,以p H值(30 min和24 h)、肉色、加压失水率、蒸煮损失率和剪切力作为评价指标。研究结果表明:电击处理对肉鸭的胸肉影响较大,使胸肉的p H值降低(p0.05),L*值增大(p0.05),加压失水率(p0.05)和蒸煮损失率(p0.05)减小,剪切力值增加(p0.05);电击处理使腿肉的p H值降低(p0.05),对腿肉肉色、加压失水率、蒸煮损失率和剪切力值均无显著影响。     

不同品种羊肉滴水损失与肌肉品质的关系

研究不同滴水损失羊肉的微观结构和理化特性,分析蛋白质降解对羊肉滴水损失的影响,揭示羊肉滴水损失与肌肉品质的关系。选择3个山羊品种(波尔山羊、黄淮山羊、波尔×崂山白山羊)的最高、最低滴水损失的背最长肌样品各3块,分析宰后p H值、肉色、剪切力、微观结构、肌原纤维蛋白降解程度的差异。结果表明,低滴水损失组的宰后45 min样品的p H45 min显著高于高滴水损失组,而L*值与p H45 min相反(P0.05);高滴水损失组的a*、b*、△E、剪切力值、肌节长度和TBARS值与低滴水损失组没有显著差异(P0.05);低滴水损失组的肌节较为完整,肌细胞排列紧密,几乎没有缝隙;而高滴水损失率组部分肌节扭曲、变形,排列错乱,部分Z线偏离或断裂;高滴水损失组的肌节长度均低于低滴水损失组(P0.05);高滴水损失组肌原纤维蛋白发生明显降解,蛋白质变性。总之,羊肉p H值下降导致蛋白质降解,影响蛋白质与水之间的相互作用,引起肌纤维结构的变化,肌肉收缩,造成高的滴水损失。     

不同保水性牦牛肉品质比较及肌原纤维蛋白凝胶特性分析

为探讨宰后不同保水性牦牛肉品质及肌原纤维蛋白凝胶特性变化,本实验利用聚类分析选取低汁液损失率组(n=6)(汁液损失率1.5%)和高汁液损失率组(n=10)(汁液损失率≥1.5%),比较两组品质和蛋白凝胶特性。结果表明:保水性差的牦牛肉宰后p H较低,CIE L*较高,CIE a*较低,总蛋白和肌原纤维蛋白更易变性。牦牛肉肌原纤维蛋白凝胶硬度及保水性在p H7.0,离子强度0.6 mol/L,温度70℃下最优,且保水性好的肌肉凝胶硬度和保水性更佳。总之,水分可显著的改善牦牛肉品质及肉糜蛋白的凝胶特性。     

不同解冻方法对鹅腿肉理化特性和品质的影响

为探究快速微波解冻与传统低温和流水解冻相比,对鹅腿肉品质是否存在不利影响,本实验研究了低温、流水和微波(微波解冻1:45℃、1 800 kW、2 min;微波解冻2:45℃、1 800 kW、6 min)3种解冻方法对鹅腿肉解冻过程中的色差、硫代巴比妥酸值、高铁肌红蛋白含量、蒸煮损失率、滴水损失率、pH值、剪切力值以及蛋白质构象变化的影响。结果表明:低温解冻较微波解冻1处理组能更好地维持鹅肉滴水损失率、蒸煮损失率和剪切力值;而微波解冻1处理组的鹅肉滴水损失率和蒸煮损失率优于流水解冻;微波解冻2处理组鹅肉蒸煮损失率、滴水损失率、剪切力值及硫代巴比妥酸值相比其他组较高,品质最不理想;4 种解冻方式的p H值没有显著性差异(P0.05);拉曼光谱分析显示,流水解冻对蛋白质二级结构的影响大于微波解冻,而低温解冻的影响最小。与生产中常规解冻方法即低温解冻和流水解冻相比,微波解冻鹅肉的品质不如低温解冻鹅肉理想,但短时间微波解冻可以显著改善流水解冻过程中鹅肉品质劣变,提高解冻效果。3种解冻方法中,低温解冻和微波短时间解冻能较好地保持解冻鹅腿肉的品质。     

宰后成熟过程中猪肉保水性的变化

以三元猪背最长肌为研究对象,在第4、8、12、16、20、24、28、32和36 h分别检测蒸煮损失率、滴水损失率、贮藏损失率、剪切力值和pH值的变化情况,研究宰后成熟过程中猪肉保水性的变化规律。结果表明,蒸煮损失率呈先升高后降低的趋势,在第20 h蒸煮损失率达到最大值32.80%;贮藏损失率和滴水损失率呈先下降后上升再下降的趋势;剪切力值在4~12 h内显著性上升（p<0.05）,且在12 h达到最大62.29 N;pH值呈整体先下降后上升再下降最后趋于稳定的变化趋势;其中,成熟时间与剪切力值呈显著负相关（p<0.01）,pH值与蒸煮损失率呈极显著负相关（p<0.01）,滴水损失率与贮藏损失率呈较高的相关性（p<0.01）。综合指标,猪肉在宰后成熟36 h内保水性有先变弱后增强的趋势,在12~16 h内进入僵直高峰点,随后进入解僵成熟期。该研究结果可为后续深入研究宰后成熟过程中猪肉嫩度变化规律及机理提供基础指标和参考依据。     

超声波与氯化钙对鸭肉嫩化的协同作用

以肌原纤维小片化指数和剪切力为考察指标,利用超声波与钙离子协同对淘汰蛋鸭肌肉进行嫩化研究,确定超声波与钙离子协同嫩化淘汰蛋鸭肌肉的最佳工艺条件,并分析肌原纤维小化片指数和剪切力之间的关系。结果表明:超声波与钙离子协同嫩化鸭肉的最适条件为超声波功率300 W、钙离子浓度200mmol/L、超声波处理时间15min、超声波处理温度40℃。超声波/钙离子协同嫩化鸭肉的肌原纤维小片化指数与剪切力之间存在着显著的相关性。     

Effect of muscle restraint on sheep meat tenderness with rigor mortis at 18°C

The effect on shear force of skeletal restraint and removing muscles from lamb m. longissimus thoracis et lumborum (LT) immediately after slaughter and electrical stimulation was undertaken at a rigor temperature of 18°C (n=15). The temperature of 18°C was achieved through chilling of electrically stimulated sheep carcasses in air at 12°C, air flow 1-1.5 ms(-2). In other groups, the muscle was removed at 2.5 h post-mortem and either wrapped or left non-wrapped before being placed back on the carcass to follow carcass cooling regimes. Following rigor mortis, the meat was aged for 0, 16, 40 and 65 h at 15°C and frozen. For the non-stimulated samples, the meat was aged for 0, 12, 36 and 60 h before being frozen. The frozen meat was cooked to 75°C in an 85°C water bath and shear force values obtained from a 1 × 1 cm cross-section. Commencement of ageing was considered to take place at rigor mortis and this was taken as zero aged meat. There were no significant differences in the rate of tenderisation and initial shear force for all treatments. The 23% cook loss was similar for all wrapped and non-wrapped situations and the values decreased slightly with longer ageing durations. Wrapping was shown to mimic meat left intact on the carcass, as it prevented significant prerigor shortening. Such techniques allows muscles to be removed and placed in a controlled temperature environment to enable precise studies of ageing processes.     

Investigation on CAST, CAPN1 and CAPN3 porcine gene polymorphisms and expression in relation to post-mortem calpain activity in muscle and meat quality

This study aimed to detect variability in CAST, CAPN1 and CAPN3 porcine genes and to investigate the effect of CAST and CAPN1 polymorphisms on the activity of native and autolyzed μ-calpain and m-calpain, measured from 1 to 72 h post-mortem in Longissimus dorsi (LD) muscle of 30 pigs. Effects of polymorphisms on meat quality parameter such as pH, color and drip loss were also evaluated. Samples carrying CAST EU137105:g.76,872AA genotype showed higher autolyzed μ-calpain activity 24 and 72 h post-mortem, as well as lower drip loss values. Expression of CAST, CAPN1 and CAPN3 was assessed in LD muscles divergent for shear force. Higher CAST and CAPN3 expression was found in LD with high shear force (P<0.2), confirming a direct role for calpastatin but not for calpain 3 in meat tenderization. In conclusion, CAST gene affected post-mortem activation time of calpain and drip loss.     

High pre rigor temperature limits the ageing potential of beef that is not completely overcome by electrical stimulation and muscle restraining

Two simultaneous trials were conducted to determine the effects of electrical input [electrical stunning and stimulation (ES)], wrapping, pre rigor temperature (15 °C and 38 °C) and different post rigor chilling rates on beef quality using M. longissimus lumborum (n=100). The high pre rigor temperature induced a faster pH decline than ES. The loins at 38 °C had significantly greater protein denaturation, more purge and drip loss, higher shear force values and less desmin degradation compared with the loins at 15 °C. No difference in sarcomere length was determined between the pre rigor temperatures regardless of ES and wrapping. Different post rigor chilling rates did not play a substantial role in water-holding capacity, proteolysis, or shear force values during ageing. These results suggest that high pre rigor temperature induces temperature-related toughness of muscle due to protein denaturation with subsequent limitation of proteolysis by μ-calpain, regardless of ES and wrapping treatments.     

Effects of rigor temperature and electrical stimulation on venison quality

The effects of rigor temperature and electrical stimulation on venison quality were assessed using venison longissimus dorsi muscle. In the first trial, effect of rigor temperature (0, 15, 25, 30, 35 and 42 °C) and time post-mortem (at rigor, 3, 7 and 14 days) on drip and cooking losses, % expressible water (water holding capacity, WHC), sarcomere length, protein solubility, meat tenderness and colour were investigated. In the second trial, the effects of rigor temperature (15 and 35 °C), electric stimulation (stimulated or not stimulated) and time (at rigor, 3 and 6 weeks post-mortem) on tenderness and colour were further investigated. Results of the first trial showed no clearly established trends of the effect of rigor temperature and time on the cooking and drip losses and protein solubility except venison muscles that went into rigor at 42 °C tended to have higher drip loss and lower protein solubilities compared to muscles that went into rigor at the other temperatures. Venison water holding capacity (WHC) decreased with the increase in rigor temperature (P < 0.001) and venison became more tender with time post-mortem. Venison colour improved with increasing rigor temperature. During display, samples that went into rigor at 15, 25 and 35 °C had the lowest and those at 0 and 42 °C had the highest rate of change of redness (a^*) value with time. In the second trial, tenderness was improved by stimulation (P = 0.01). Redness (a^*) values were affected by rigor temperature (P < 0.01) and post-mortem time (P < 0.001) but not by electrical stimulation. It is concluded that venison tenderness can be improved via the manipulation of rigor temperature to obtain acceptable level of tenderness early post-mortem with less damaging effect on colour stability.     

Possible mechanism for the effect of the RN(-) allele on pork tenderness

The effect of the dominant RN⁻ allele on rigor development, ageing and tenderness was studied in M. longissimus dorsi (LD) from 11 heterozygous carriers and five non-carriers of the RN⁻ allele. Rigor development was followed by measurements of muscle shortening, isometric tension, pH and FOP. During ageing the myofibrillar length and Warner–Bratzler shear force were measured in the meat. Sensory analysis was performed at 4 days post-mortem using a trained expert panel. It was found that the decrease in pH was faster for RN⁻ carriers than non-carriers during the first 5 h post-mortem, after which the pH-time slope was similar for the two groups. This resulted in a significantly lower mean ultimate pH in LD from RN⁻ carriers than non-carriers. During rigor development the isometric tension was lower in RN⁻ carriers than in non-carriers, while contraction (shortening and sarcomere length) did not differ significantly between the two genotypes. The myofibrillar length, which is an indirect measure of the proteolytic activity that has occurred in the meat, was shorter for the RN⁻ carriers than for the non-carriers. The difference in myofibrillar lengths between the genotypes was significant at 1 and 4 days post-mortem but not at 7 days post-mortem, which indicates that the RN⁻ carriers have a higher proteolytic activity earlier post-mortem. The results from the Warner–Bratzler shear force measurements showed that the meat from the RN⁻ carriers was significantly more tender, 1 and 4 days post-mortem, than the meat from the non-carriers. The meat from non-carriers needed 7 days to reach the tenderness attained by that from the RN⁻ carriers 4 days post-mortem. The greater tenderness in LD from RN⁻ carriers than that from non-carriers was also confirmed by a sensory panel at 4 days post-mortem. In conclusion, differences observed in the course of rigor and ageing in muscle from carriers and non-carriers of the RN⁻ allele suggest that proteolytic action, as initiated by a more rapid fall in pH, is the most important factor governing the variation in tenderness of the two genotypes.     

The effect of exercise stress, adrenaline injection and electrical stimulation on changes in quality attributes and proteins in Semimembranosus muscle of lamb

Exercise pre-slaughter has previously been shown to increase drip loss and tenderness in the longissimus muscle of lambs. The mechanism causing higher water loss in post-mortem muscle of lambs is not well understood. This experiment examines the effects of exercise stress, adrenaline injection and electrical stimulation (ES) on meat tenderness and water holding capacity. Forty crossbred lambs (20±2 kg live weight) were used in this study. Meat quality measurements were carried out on the Semimembranosus muscle (SM). The ultimate pH was higher with exercise stress (pH 5.93) compared to controls (pH 5.55; P<0.01). As expected the glycogen levels 30 min and 24 h post-mortem in the exercise stressed (P<0.01) muscle were lower. Lactate concentration at 30 min post-mortem in the electrical stimulation (ES: P<0.05) treated muscle was higher than all other treatment combinations. Myofibrillar protein denaturation, measured by protein solubility, was higher (P<0.05) and the rate of proteolysis of muscle proteins titin and troponin-T, as observed with western blots, increased with exercise stress. However, there were no treatment effects on Warner-Braztler shear force (WBSF). Exercise stress and an interaction with adrenaline caused increased drip loss (P<0.05) and purge (P<0.01) from the muscle. Muscle drip from the exercise stress treatment group had lower Mg(2+) (P<0.01) and K(+) (P<0.01) than controls. The main findings were that exercise stress pre-slaughter increased water loss and the rate of titin breakdown but had no effect on tenderness measured by WBSF. Together the different rates of proteolysis, protein denaturation and ionic conditions may have caused the reduced capacity of the muscle proteins to hold water, despite their relatively high ultimate pH.