低压静电场下不同隔距冻结-解冻对牛肉品质的影响

Effects of different gauges under low voltage electrostatic field assisting thawing-freezing on beef quality

为研究低压静电场(low voltage electrostatic field,LVEF)辅助冻结-解冻对牛肉品质的影响,采用牛背最长肌作为试验材料,探究与静电场发生板隔距分别为15、30、45、60 cm处(试验组,冻结温度为?18℃,解冻温度为4℃)和自然冻结-解冻(未施加静电场,对照组,条件同上)肉样冻结-解冻过程中的品质变化。对比分析了温度曲线、色泽、解冻汁液流失、汁液中蛋白含量、蒸煮损失及质构特性等指标变化,显微观察肌肉纤维组织中的冰晶形态和肌肉微观结构。结果表明:与对照相比,试验组牛肉在冻结过程中通过最大冰晶生成带时间较短,组织中的冰晶较对照组体积小、数目多、分布均匀;肉样解冻速度较快,解冻后肉色更新鲜,咀嚼性、嫩度较高,解冻汁液流失率、汁液中蛋白含量及蒸煮损失率均显著降低(P<0.05);扫描、透射电镜结果表明,试验组肉样解冻后肌肉微观结构遭破坏程度较轻,肌纤维束排列相对紧密。其中,与静电板隔距为30 cm处冻结-解冻的肉样亮度值、红度值和色彩饱和度值分别为39.47、21.77和23.71,显著高于对照组的31.74、17.76和20.73(P<0.05);解冻汁液流失率、蒸煮损失率及解冻汁液中蛋白质量分数较对照分别降低4.18、8.28、0.7个百分点,咀嚼性增加32.68 N,差异显著(P<0.05)。试验结果表明低压静电场辅助能显著缓解牛肉在冻结和解冻过程中的品质劣变,提高解冻牛肉品质,肉样在与静电板隔距为30 cm处冻结-解冻较为适宜。

To research the effect of low voltage electrostatic field （LVEF） assisted freezing-thawing on beef quality, using bovine longissimus dorsi as experimental materials, the beef quality of samples at the distance of 15, 30, 45 and 60 cm away from the electrostatic field generating plate （test group） and without LVEF treatment （control group） was studied during freezing-thawing process. The test group and the control group had the same freezing temperature of-18 ℃ and thawing temperature of 4 ℃. The indices including freezing-thawing temperature curve, color, thawing loss, protein content of thawing drip, cooking loss, texture profiles were compared and analyzed. Scanning electron micrograph （SEM） and transmission electron microscope （TEM） were used to observe the microstructure of muscle, and the ice crystal morphology in muscle fiber tissue was observed under light microscope. During the process of freezing, the temperature curve showed that LVEF had accelerated the freezing process of beef samples, and the time used in the zone of the maximum ice crystal formation was shorter compared to the control group. Accordingly, the ice crystals in muscle fiber tissue were smaller and uniformly distributed under LVEF. From the thawing temperature curve, it was found that the thawing speed of treatment group was faster. After the process of thawing, several indices were determined. The result showed that LVEF could significantly increase lightness （L^＊） value, redness （a^＊） value, chroma （C） value, tenderness and chewiness （P〈0.05）. In addition, cooking loss, thawing loss and protein content of thawing drip were significantly decreased by LVEF （P〈0.05）. SEM and TEM showed that the muscle microstructures of control group and treatment group were both damaged after freezing-thawing process. The microstructure of muscle fiber bundles of control group was damaged more seriously, and more muscle fiber bundles were torn and a visibly larger gap was exhibited between muscle fibers, while the muscle microstructure of treatment sample was less damaged and the fiber bundles were relatively tight. Particularly, the samples at the distance of 30 cm away from the electrostatic field generating plate （LVEF30） required the shortest time to finish the process of freezing and thawing, and the time used in the zone of the maximum ice crystal formation was only 290 min, which was shortened by 66% compared with the control group. LVEF30 formed the smallest and most uniform ice crystals, and the muscle fiber tissue was less damaged by ice crystals. SEM showed that LVEF30 maintained the structure of muscle fibers and perimysium effectively, and the gap between muscle fibers had no obvious expansion. TEM showed that Z-disc and M-disc remained relatively intact and A-band and I-band were still clear and legible, which indicated that LVEF30 maintained the integrity of the myofibrillar structure effectively. The L^＊ value, a^＊ value and C value of LVEF30 were 39.47, 21.77 and 23.71 respectively, which were significantly higher than 31.74, 17.76 and 20.73 of the control group （P〈0.05）, and had no significant differences with the fresh meat （P〉0.05）. Thawing loss, protein content of thawing drip and cooking loss of LVEF30 were reduced 4.18, 8.28 and 0.7 percent points, respectively, compared to the control group, and the difference was also significant （P〈0.05）. The experimental results show that LVEF is able to alleviate the deterioration of beef quality during the freezing-thawing process and improve the quality of the thawed beef significantly, and the most suitable gauge for treatment group is 30 cm.