3种超声方式对蓝莓蜡质层和细胞结构及真空冷冻干燥特性的影响

Effect of Three Ultrasonic Methods on Wax Layer,Cell Structure and Vacuum Freeze-Dried Properties of Blueberry

蓝莓表皮蜡质成分严重阻碍其真空冷冻干燥过程中的水分扩散。以新鲜蓝莓为原料,分析3种超声方式对蓝莓蜡质层和内部细胞结构的影响,结合蓝莓脆品质特性和干燥特性,探究适宜蓝莓真空冷冻干燥的超声预处理方式。气相色谱-质谱联用结果表明:不同超声处理对蓝莓表皮蜡质组成和含量影响不同,其中间歇式超声处理后蓝莓表皮蜡质组成和总相对含量变化最大,与对照组相比总相对含量减少了35%。微观结构分析结果表明:探头式和间歇式超声处理后蓝莓表皮的蜡质分布疏松,表皮裸露;连续式超声处理后蓝莓表皮蜡质晶体结构由管状变为片状。探头式和间歇式超声处理对蓝莓内部细胞结构破坏较大,使其形成大尺寸微通道,并且探头式超声处理后,蓝莓细胞膜渗透率显著高于其他处理方式(P<0.05)。不同超声处理后蓝莓的T 2弛豫曲线均整体向左移动,峰面积和信号幅值减小;3种超声处理方式明显改善了真空冷冻干燥蓝莓干燥速率,连续式和探头式超声处理显著改善了真空冷冻干燥蓝莓的脆性,分别提高了38.25%、40.09%。连续式超声处理获得的真空冷冻干燥蓝莓维生素C和花青素保留率显著提高,分别为86.17%±0.18%和71.30%±1.88%。综合比较,连续式超声处理是较优的蓝莓真空冷冻干燥预处理方式。

The waxy composition of blueberry epidermis seriously hinders the diffusion of water during its vacuum freeze-drying(VFD)process.Fresh blueberries were used as raw materials to investigate the effects of three ultrasonic methods on the wax layer and cell structure of blueberries.Combining the crisp quality and drying characteristics of blueberries,the suitable ultrasonic pretreatment methods for vacuum freeze-drying of blueberries was explored in the study.The results of gas chromatography-mass spectrometry analysis showed that three ultrasonic treatments had different effects on the wax composition and content of blueberry epidermis.The wax composition and total relative content of intermittent ultrasonic treatment showed the greatest changes,with a 35%decrease in total relative content compared to the control group.The results of microstructure analysis indicated that,after probe and intermittent ultrasonic treatment,the wax distribution on the blueberry epidermis was loose,and the skin was exposed.After continuous ultrasonic treatment,the wax crystal structure of blueberry epidermis changed from tubular to flaky.Probe and intermittent ultrasonic treatment had significant damage to the internal cellular structure of blueberries,forming large-sized micro-channels.Moreover,after probe ultrasonic treatment,the cell membrane permeability of blueberries was significantly higher than that of other treatment methods(P<0.05).After different ultrasonic treatments,the T 2 relaxation spectra of blueberries shifted to the left as a whole,and the peak area and signal amplitude decreased.Three ultrasonic treatment methods significantly improved the drying rate of VFD blueberries,and the continuous and probe ultrasonic treatment significantly improved the brittleness of VFD blueberries,increasing by 40.12%and 38.27%,respectively.After the continuous ultrasonic pretreatment,the retention rates of vitamin C and anthocyanins in VFD blueberries were significantly increased,reaching 86.17%±0.18%and 71.30%±1.88%,respectively.By comprehensive comparison,the continuous ultrasonic treatment was an optimal pre-treatment for VFD blueberries.