预冷库内环境温湿度差异对猪胴体品质的影响

通过对猪胴体中心温度、pH值、肉色及菌落总数等指标进行测定,研究二段式预冷工艺条件下0～4 ℃单向风机排布预冷库内不同位置环境温度和环境相对湿度的差异对猪胴体品质的影响。结果表明：预冷库内不同位置环境温度和环境相对湿度之间存在显著差异（P＜0.05）;环境温度低的位置,其猪胴体中心温度下降快;预冷库内不同位置处pH值下降幅度存在差异,位置1、3、6处pH值下降较快,且与同轨道其他位置存在显著性差异（P＜0.05）;不同位置处猪胴体的肉色变化趋势存在显著差异（P＜0.05）,冷库内不同位置环境温度的差异可能是造成猪胴体亮度值和红度值有不同变化趋势的原因之一;不同轨道的猪胴体菌落总数存在显著差异（P＜0.05）,回风口位置处菌落总数最小。     

预冷环境及时间对滩羊胴体品质的影响

通过对滩羊胴体中心温度、干耗率、pH值和肉色等指标进行测定，研究一段式预冷工艺条件下0～4 ℃单向风机排布预冷库内不同预冷环境和预冷时间的差异对滩羊胴体品质的影响。结果表明：预冷库内环境温度从19 ℃左右降至2 ℃左右，环境相对湿度达99.9%以上，保持持续稳定状态；预冷结束后，滩羊胴体中心温度为2.67～3.83 ℃，冷库内6 个不同位置处无显著差异；滩羊胴体干耗率为0.39%～1.05%，预冷时间越长，干耗率越大，靠近墙面且预冷时间越长的位置处与冷库中央位置处存在显著差异（P＜0.05）；预冷后滩羊胴体pH值为5.59～5.74，各位置无显著差异；预冷前，各位置肉色无显著差异，预冷后与预冷前相比，亮度值和红度值均有所提高。     

猪胴体冷却过程中表面微生物的时空分布研究

为了研究在猪胴体冷却过程中风速、温湿度及微生物数量的变化情况,建立猪胴体在冷却期间微生物的时空变化的模型,从而为冷库防治污染提供依据,本文采用热敏式风速仪测量夏季冷库内的风速、温湿度,利用擦拭法测定猪胴体表面微生物菌落总数,最终得到猪胴体冷却过程中微生物的时空变化情况,结果表明:在冷却前期(冷却时间0~8 h),由于冷库门的开启、猪胴体本身散热等原因导致冷库内的风速并非均匀分布,温湿度也逐渐上升,从而导致冷库内不同位置处猪胴体表面微生物的菌落总数均有不同程度的增加,其中冷库中间位置的猪胴体表面菌落总数显著增加(P<0.05),其余位置的猪胴体表面菌落总数增加不显著(P>0.05);在冷却后期(冷却时间8~14 h),冷库门关闭,不再有猪胴体进入冷库,冷库内的温湿度迅速下降,使猪胴体表面微生物的菌落总数显著减少(P<0.05)并趋于稳定;猪胴体迎风面的菌落总数略高于背风面,其中前腿、胸腹腔的微生物较多;相关性分析结果表明猪胴体表面菌落总数与温度、湿度、冷却时间、采样部位有极显著的相关关系(P<0.01),与风速有显著的相关关系(P<0.05)。总之,随着冷却时间的延长,猪胴体表面菌落总数有显著差异(P<0.05),冷库内不同位置的猪胴体表面菌落总数不同,同一猪胴体的不同部位之间也有差异,这为冷库的改进布局和污染控制奠定了基础。     

不同预冷条件下白条损耗及菌落总数变化

以猪胴体为研究对象,研究不同冷却方式、湿度以及贮藏方式对猪胴体损耗的影响。结果表明,猪胴体在预冷库冷却24h,二段式冷却比一段式冷却水分损耗低0.1%~0.2%,菌落总数减少;白条在冷却过程中增加空气湿度,能使白条损耗降低约0.25%,但微生物菌落总数增加;白条套上保鲜袋能使白条水分损耗降低约0.2%,同样微生物菌落总数会增加。     

延迟冷却对牛肉品质及超微结构影响的研究

本文研究了常规冷却与延迟冷却对中国杂交黄牛(鲁西黄牛×西门塔尔)宰后冷却过程中牛胴体pH值、温度变化、胴体冷却失重、肉色及成熟过程中剪切力值、背最长肌汁液损失、蒸煮损失、保水性、肌原纤维结构变化的影响.结果表明延迟冷却能减缓牛胴体温度的下降速率(P＜0.05),加快牛胴体pH值的降低(P＜0.05),提高牛背最长肌的嫩化速率,改善肉色(P＜0.05),但加剧了汁液损失、蒸煮损失,降低了保水性(P＜0.05).延迟冷却对成熟0d、3d时的肌原纤维结构影响显著(P＜0.05),延迟冷却组的肌节长度明显长于对照组的肌节长度.     

不同预冷方式对甜玉米储藏品质的影响

为探究不同预冷方式对甜玉米储藏品质的影响,本研究采用3 种预冷方式（冷库预冷、压差预冷和流态冰预冷）处理甜玉米,测定其预冷过程中的温度变化,预冷后将甜玉米储藏于0 ℃冷库,测定其储藏期间感官品质、色泽、呼吸速率、乙烯产生速率、可溶性固形物（total soluble solid,TSS）质量分数以及可溶性淀粉、可溶性糖、葡萄糖、果糖、蔗糖含量的变化。结果表明,流态冰预冷在储藏期间保鲜效果最佳,其次是压差预冷。流态冰预冷可快速降低甜玉米内部温度,延缓苞叶黄化,保持籽粒色泽,维持其感官品质,抑制甜玉米呼吸和乙烯释放速率;此外,流态冰预冷可以较好地维持甜玉米籽粒TSS质量分数及可溶性淀粉、可溶性糖、葡萄糖、果糖和蔗糖的含量。在储藏第28天时,流态冰预冷组TSS质量分数为13.8%,压差预冷组为13.4%,冷库预冷组为13.1%,流态冰预冷组显著高于其他组（P＜0.05）,而压差预冷组和冷库预冷组差异不显著（P＞0.05）;同时,流态冰预冷组的蔗糖含量为120.4 mg/g,压差预冷组为118.0 mg/g,而冷库预冷组仅为92.3 mg/g,流态冰预冷处理甜玉米蔗糖含量高于其他两种处理,压差预冷次之,冷库预冷处理蔗糖含量在储藏末期较低,由此可见,流态冰预冷处理可以明显延缓甜玉米储藏品质劣变。综上,本研究为甜玉米预冷方式的选择提供了理论依据。     

猪胴体预冷过程中雾化增湿与喷淋对干耗的影响差异性研究

本研究对比了雾化增湿与雾化喷淋两种方式对猪胴体预冷干耗的影响。采用超声雾化加湿器来增加预冷环境湿度方式以及气液两相流间歇雾化喷淋的方式分别对猪胴体样品进行预冷处理,以直接冷却猪胴体样品为对照组。实验结果表明:雾化增湿组样品最终平均干耗为1.442%,经14 h雾化喷淋处理的各样品继续冷却至24 h后测得最终平均干耗为1.066%,对照组实验样品最终平均干耗为2.914%。雾化喷淋冷却处理与雾化增湿冷却处理均可使猪胴体冷却速度加快(p0.05)。雾化喷淋冷却处理与雾化增湿冷却处理均可有效缩短样品干耗达到峰值的时间(p0.05),其达到峰值时间关系为:雾化喷淋组雾化增湿组对照组。雾化喷淋冷却处理与雾化增湿冷却处理均可显著降低猪胴体预冷干耗(p0.05);雾化喷淋冷却处理比雾化增湿冷却处理降低干耗效果更为理想(p0.05)。     

低温低气流冷却对冷鲜鸡品质的影响

为研究低温低气流对冷鲜鸡肉品质的影响，将日龄90 d笼养肉鸡宰后立即置于不同温度（-10、-15、-20℃）进行冷却，并控制空气流速为0.1 m/s。以4℃冰水浴冷却为对照，测定肉鸡胴体冷却速率，分析胴体冷却后及4℃冷藏24 h后的胴体质量变化、色泽、保水性、可溶性蛋白含量、肌原纤维小片化指数（myofibril fragmentationindex,MFI）及剪切力等品质指标。结果表明：气冷组可以在60 min内将肉鸡胴体中心温度降低到4℃，蒸煮损失率、离心损失率和MFI等指标显著优于冰水组（P<0.05）；不同气冷组间，-15℃气冷组胴体质量损失、蒸煮损失率、离心损失率和剪切力等指标显著优于-10℃气冷组（P<0.05），红度值、蒸煮损失率、离心损失率等指标显著优于-20℃气冷组（P<0.05）。综上，在温度为-15℃、气流为0.1 m/s条件下将肉鸡胴体冷却60 min，可以满足胴体快速冷却要求，并且能够改善肉鸡在冷却及贮藏过程中的品质劣变，使鸡肉具有较好的品质。     

快速冷却对山单背最长肌肉品质的影响

6头云南地方云岭黑山羊(羯羊)屠宰、劈半后,左半胴体进行常规冷却(0～4℃冷却24h,相对湿度90～95%),右半胴体进行快速冷却(-20℃,冷却1.0 h后,转入0～4℃冷却23h,相对湿度90～95%),取背最长肌,测定相关肉品质指标.结果显示,样品经3d成熟,快速冷却的羊肉剪切力显著低于常规冷却(P＜0.05),快速冷却的羊肉嫩度的感官评分显著高于常规冷却(P＜0.05),而P H、肉色,蒸煮损失等指标两种冷却方式无显著差异.研究表明,本试验采用的快速冷却方式对山羊肉的嫩度有显著改善效果.     

预冷却温度对冰藏大黄鱼品质变化的影响

本研究模拟大黄鱼实际生产中的操作方式,通过分析不同预冷却温度(2℃、10℃和18℃)下冰藏大黄鱼的感官品质、细菌学和生化指标的变化,比较不同预冷却温度对冰藏期间大黄鱼品质变化和货架期的影响程度.感官评分表明不同预冷却温度(2、10、18℃)的大黄鱼冰藏货架期不同,分别为23、20、17d.贮藏过程中,预冷却温度为2℃和10℃的大黄鱼感官品质差别不大,细菌数和TVB-N值变化差异也不显著(P＞0.05),而预冷却温度为18℃的大黄鱼感官品质较前两组差,细菌数与TVB-N值增速比另外两组快,变化差异显著(P＜0.05).因此,在大黄鱼生产流通过程中充分低温预冷却(＜10℃)对于保持大黄鱼品质及延长产品货架期具有很重要的意义.     

低场核磁共振技术研究猪肉冷却过程中水分迁移规律

目的:采用低场核磁弛豫时间和低场核磁成像技术,研究在模拟冷库环境条件下,风循环冷却和雾化喷淋冷却过程中猪肉水分迁移规律。方法:选择宰后2 h内的整条带皮猪背最长肌(通脊)10条,沿肌肉走向垂直方向分切成4份14 cm×10 cm×6 cm的肉块,其中2份保留猪皮及皮下脂肪(带皮组),另2份则去除猪皮及皮下脂肪(不带皮组),带皮组和不带皮组肉块分别放入风循环冷却和雾化喷淋冷却的模拟冷库中进行冷却,并于0.0、1.5、3.0、4.5、6.0 h和7.5 h进行低场核磁共振横向弛豫时间(T_2)和低场核磁成像测定,同时记录肉块质量变化。结果:风循环冷却过程中猪肉中结合水峰面积A_(2b)和结合水占猪肉中总水分的百分比P_(2b)变化差异不显著(P0.05)、不易流动水t_(21)显著降低(P0.05),自由水A_(22)、P_(22)也显著降低(P0.05);而在雾化喷淋冷却过程中,结合水A_(2b)、P_(2b)和不易流动水t_(21)、A_(21)、P_(21)变化差异不显著(P0.05),自由水A_(22)、P_(22)则显著降低(P0.05)。带皮猪肉和不带皮猪肉在冷却过程中水分迁移的变化过程相同,但水分损耗存在差异。结合图像分析,在冷却过程初期,猪肉干耗主要是自由水的损失;而冷却后期,猪肉干耗则主要是部分不易流动水的损失。雾化喷淋冷却通过补充外源水,来减小猪肉内部和外表的水势差而抑制不易流动水由内向外迁移,可有效降低冷却干耗。     

快速冷却对山羊背最长肌肉品质的影响

6头云南地方云岭黑山羊(羯羊)屠宰、劈半后,左半胴体进行常规冷却(0～4℃冷却24h,相对湿度90～95%),右半胴体进行快速冷却(-20℃,冷却1.0h后,转入0～4℃冷却23h,相对湿度90～95%),取背最长肌,测定相关肉品质指标。结果显示,样品经3d成熟,快速冷却的羊肉剪切力显著低于常规冷却(P<0.05),快速冷却的羊肉嫩度的感官评分显著高于常规冷却(P<0.05),而pH、肉色、蒸煮损失等指标两种冷却方式无显著差异。研究表明,本试验采用的快速冷却方式对山羊肉的嫩度有显著改善效果。     

延迟冷却对牛肉品质影响的研究

研究了常规冷却和延迟冷却对中国杂交黄牛(鲁西黄牛×西门塔尔)宰后冷却过程中牛胴体pH、温度的变化、胴体冷却失重、背最长肌汁液损失、蒸煮损失、保水性、肉色及成熟过程中剪切力值的变化。结果表明:延迟冷却减缓了牛胴体温度的降低速率(P<0.05),加快了牛胴体pH的降低(P<0.05);延迟冷却提高了牛背最长肌的嫩化速度,改善了肉色(P<0.05),但增加了汁液损失和蒸煮损失,降低了保水性(P<0.05)。因此,优化延迟冷却程序是必要的。     

The ultra rapid chilling of pork

Pork carcasses and sides were ultra rapidly chilled in air at -30°C and 1 m/s for 4 h and compared with controls chilled in air at 0°C and 0·5 m/s for 24 h. All the required heat was removed during the 4-h process, there was a 1% saving in evaporative weight loss, the pork could be cut and packed immediately and there were no important differences in appearance and bacteriological quality. The loin from sides, but not carcasses, froze during chilling and showed a fourfold increase in drip loss. Loins from both sides and carcasses were tougher than the controls.     

EFFECTS OF PROCESS PARAMETERS ON BEEF CARCASS CHILLING TIME AND MASS LOSS PREDICTIONS USING A FINITE ELEMENT HEAT AND MASS TRANSFER MODEL

The effects of model and process parameters on the predicted chilling time and mass loss of a beef carcass during chilling were studied by validated computer simulation. The effects of surface heat transfer coefficient, and thermal diffusivities of fat and muscle on the chilling time were significant as well as the effects of surface heat transfer and mass transfer coefficients on mass loss. However, the effects of moisture diffusivities on the chilling time and mass loss were insignificant. All of the process parameters significantly affected mass loss and chilling time. A decrease in relative humidity or an increase in air velocity or ambient temperature increased mass loss. An increase in air velocity or a decrease in ambient temperature decreased the chilling time. Based on the parametric analysis of the process parameters, air velocity in the chiller should be less than 1 m/s and the relative humidity of the chiller should be more than 80%.     

Chilling pig carcasses: Effects on temperature, weight loss and ultimate meat quality

Effects of conventional (4°C, air velocity 0·5 m/s) and forced chilling at -5°C (120 min) or -30°C (30 min) with air velocities of 1, 2 or 4 m/s, followed by conventional chilling till 24 h post mortem on temperatures, meat quality and weight losses, were studied. Experiments were carried out in six batches of six slaughter pigs each (crossbred gilts, weighing 105-110 kg. The subcutaneous temperature decreased very rapidly to values below 0°C when 'ultra' rapid chilling (-30°C) at high air velocities (4 m/s was used. Immediately after rapid chilling, when the carcasses were railed into a conventional chiller, the subcutaneous temperature increased above the air temperature, after which the decline in temperature was continued. Temperature inside the biceps femoris muscle decreased from the start of chilling rather slowly according to an asymptotic curve until ultimate values of 4°C were reached. Theoretically calculated temperatures during slaughter and chilling were comparable with the measured values; indicating that a finite-element calculation method in combination with a cylindrical model for heat transport can be used to predict muscle temperatures for various chilling regimes. Losses in carcass weight, 24 h after conventional and forced chilling at -5°C, were about 2%. After 'ultra' rapid chilling (-30°C) the losses were reduced to 1·3% when air velocity was increased to 4 m/s. Meat quality of the longissimus lumborum muscle was not significantly affected by the various chilling regimes except for the variables related to tenderness. The Warner-Bratzler shear forces were higher (P < 0·05) together with shorter sarcomere lengths (P < 0·10) after 'ultra' rapid chilling at a high (4 m/s) air velocity, indicating an increased risk of cold shortening.     

The effect of pre-slaughter showering and post-slaughter rapid chilling on meat quality in intact pork sides

Thirty pairs of Landrace or Large White pigs were used to determine the effects of pre- and post-slaughter cooling treatments on pork quality and yield. One animal from each pair was showered in cold water and after slaughter one side from each carcass was rapidly chilled and the other side was conventionally chilled. Two experiments were carried out in winter: they examined different times of exposure to cooling treatments; a further experiment was carried out in summer time. Showering caused a reduction in the temperature of the deep loin at 40 min post mortem (P < 0·01). Rapid chilling caused a further reduction in carcass temperature and the rate of pH fall was lower (P < 0·05) in the rapidly chilled sides. There was a strong indication that showering in the winter time lowered drip loss in slices of Longissimus dorsi muscle (P = 0·077) whereas showering in the summer time was not effective. Shower water temperature may have been important in this regard. Showering did not lower drip loss in intact pork legs. Rapid chilling was not effective in lowering drip loss in either slices of Longissimus dorsi or intact pork legs. Rapid chilling at -20°C for 3 h without an air blast lowered evaporative chill losses in sides of pork by 27-29% (P < 0·1) compared to normal chilling. Reduced treatments gave reduced effects. Neither treatment had any significant effect on cooking loss or toughness in broiled slices of pork Longissimus dorsi muscle.     

Extending the potential of evaporative cooling for heat-stress relief

Factors were analyzed that limit the range of environmental conditions in which stress from heat may be relieved by evaporative cooling in shaded animals. Evaporative cooling reduces air temperature (Ta), but increases humidity. Equations were developed to predict Ta reduction as a function of ambient temperature and humidity and of humidity in cooled air. Predictions indicated that a reduction of Ta becomes marginal at humidities beyond 45%. A reduction of Ta lessens with rising ambient Ta. The impact of increasing humidity on respiratory heat loss (Hre) was estimated from existing data published on Holstein cattle. Respiratory heat loss is reduced by increased humidity up to 45%, but is not affected by higher humidity. Skin evaporative and sensible heat losses are determined not only by the humidity and temperature gradient, but also by air velocity close to the body surface. At higher Ta, the reduction in sensible heat loss is compensated for by an increased demand for Hre. High Hre may become a stressor when panting interferes with resting and rumination. Effects of temperature, humidity, air velocity, and body surface exposure to free air on Hre were estimated by a thermal balance model for lactating Holstein cows yielding 35 kg/d. The predictions of the simulations were supported by respiratory rate observations. The Hre was assumed to act as a stressor when exceeding 50% of the maximal capacity. When the full body surface was exposed to a 1.5 m/s air velocity, humidity (15 to 75%) had no significant predicted effect on Hre. For an air velocity of 0.3 m/s, Hre at 50% of the maximum rate was predicted at 34, 32.5, and 31.5° C for relative humidities of 55, 65, and 75%, respectively. Similar results were predicted for an animal with two-thirds of its body surface exposed to 1.5 m/s air velocity. If air velocity was reduced for such animals to 0.3 m/s, the rise in Hre was expected to occur at approximately 25° C and 50% relative humidity. Maximal rates of Hre were estimated at 27 to 30° C when ambient humidity was 55% relative humidity and higher. High humidity may stress animals in evaporative cooling systems. Humidity stress may be prevented by a higher air velocity on the body surface of the animal, particularly in sheltered areas in which the exposed body surface is reduced, such as mangers and stalls. This may extend the use of evaporative cooling to less dry environments.