冷冻干燥联合膨化干燥工艺优化提高银杏脆粒酥脆质地

Optimization of freeze drying combined with puffing drying process to improve crispy texture of ginkgo crisp granule

为了研究冷冻干燥联合膨化干燥工艺提高银杏脆粒酥脆质地及微观孔隙结构、力学特性对质地形成的影响,采用单因素和响应面试验分析了冷冻-气流干燥、气流-冷冻干燥、冷冻-微波干燥、微波-冷冻干燥4种冷冻干燥联合膨化干燥对银杏脆粒质地的影响及优化冷冻-气流干燥工艺,并研究了冷冻-气流干燥过程中银杏微观结构、孔隙结构及力学特性的变化规律。结果表明:冷冻-气流干燥促使银杏脆粒获得更高的质构特性值,响应面优化获得最佳的干燥工艺为转换点水分35%,膨化温度98℃,膨化压力0.2 MPa,获得的质构特性值为2.25;与蒸煮银杏样品相比,冷冻干燥促使银杏组织形成均匀孔隙结构,孔隙率增加,弹性模量和黏性指数无显著变化(P>0.05),冷冻干燥的银杏样品表现出组织绵软,结构强度不足;进一步的气流膨化干燥瞬间膨化力冲击促使银杏组织出现较大的空洞及水分迁移通道,细胞组织破坏严重,孔隙率继续增加,弹性模量下降,黏性指数增加,这是由于冷冻干燥形成较好的多孔结构,有利于气流膨化干燥时内部水分更易对物料各个部位的膨化动力冲击,促使冷冻-气流干燥银杏脆粒酥脆质地的形成。

The paper was aimed to optimize freeze-drying combined with puffing drying process to improve crispy texture of ginkgo crisp granule and to study the effects of microscopic pore structure and mechanical properties on texture formation.The effects of four freeze-drying processes combined with puffing drying on texture characteristics of ginkgo were analyzed by using the single-factor and response surface experiments,and the changes of microstructure,pore structure and mechanical properties were observed during freezing-explosion puffing drying.The results showed that the freezing-explosion puffing drying promoted ginkgo crisp granule to obtain higher texture characteristics.The optimal drying conditions obtained by response surface optimization were as follows:the moisture content at the transition point was 35%,the puffing temperature was 98℃,the puffing pressure was 0.2 MPa.The texture characteristics were 2.25 under the optimized conditions.Compared with the steamed ginkgo sample,the pore structure of freeze-dried ginkgo sample was more uniform,porosity increased,elastic modulus and viscosity index had no significant difference(P>0.05),and the material tissue performed soft and low intensity.The instant puffing force from explosion puffing drying actuated the emergence of larger cavities and water migration channels,the severe damage of cell issue,increasing of porosity and viscosity index,and decreasing of elastic modulus.Forming the pore structure by freeze drying was conducive to puffing power generated by the internal moisture to impact various parts of the material,and to promote the formation of crispy texture of ginkgo crisp granule submitted to freezing-explosion puffing drying.