发芽燕麦淀粉的热特性

Thermal Properties of the Starch from Germinated Oat

摘要:

发芽是进一步提升谷物种子营养价值的重要手段，已经成为当前谷物研究的新热点。本文以晋燕八号燕麦为原料，通过在16 ℃浸泡并避光发芽，分别提取不同时间段的燕麦淀粉，用差示扫描量热（differential scanning calorimetry，DSC）和热重分析（thermogravimetric analysis，TGA）两种手段对原燕麦和发芽后燕麦淀粉的热特性进行表征。结果发现，发芽对燕麦中淀粉的起始糊化温度影响不大，在发芽144 h内，平均起始糊化温度为57.44±0.48 ℃，但发芽72 h以后的燕麦中淀粉糊化温度范围扩大，以发芽72 h为界，前后两段的糊化焓都是逐渐增加的，这可能提示发芽期间淀粉结构存在由无序到有序的交替变化过程；氮气氛围下，淀粉的分解温度在275~363 ℃之间，此温度区间内淀粉的质量损失为65%~73%；发芽淀粉热分解反应活化能比原燕麦淀粉均有降低，其中原燕麦淀粉的热分解活化能为219.44±14.46 kJ/mol，活化能最小的为发芽144 h的淀粉，其值为157.75±5.58 kJ/mol，各发芽阶段淀粉热分解反应级数均为一级。

Abstract:

Germination is an important method to enhance grain seed value. In this research, Jinyan Ⅷ oat was soaked and geminated at 16℃ in the dark, then starches were extracted from raw and germinated oat at different time. Their thermal properties of starches were characterized by differential scanning calorimetry and thermogravimetric analysis. The results showed that germination had little effect on start gelatinization temperature, the average temperature was 57.44 ℃ within 144 h germination, but the range of gelatinization temperature expanded when germinating was beyond 72 h. Moreover, all the gelatinization enthalpies before and after 72 h germination period increased with time increasing, which suggested that there was an alternating change of the starch structure from disorder to order during germination. Under nitrogen atmosphere, the decomposition temperature of starch was within 275-363℃ and mass loss of starch was 65~73% among the temperature range. Decomposition activation energy of the raw oat starch was higher than that of soaked and germinated samples. And the minimum activation energy presented in 144 h sample was 157.75 kJ/mol while the value of raw starch was 219.44 kJ/mol. In addition, reaction orders of all samples were of the first reaction level.