乳熟期甜玉米汁鲜嫩风味的化学基础研究

Sweet corn juice，as a Chinese-charactered food, is developed from the culture crossing of traditional conjee made by grain and the modern customarily consumed fruit and vegetable juice. Sweet corn is the result of a naturally occurring recessive mutation in the genes which control conversion of sugar to starchinside in the endosperm of the corn kernel. Sweet corn is picked when immature (milk stage) and prepared and eaten as a vegetable, rather than a grain. As part of the plant developing tissue, "fresh, delicious" would be the key quality characteristic of it. In this study, we divided this character as "fresh, not stale" and "umami". Firstly,the sensory attributes would be analyzed and quantified using reference samples,and then establish the relationship between sensory attributes and chemical molecules by volatile and umami components determination. Since former researches of "fresh" in fruit and vegetables and "stale" in grain were both focused on the lipoxygenase pathway, this study aimed at the effect of lipoxygenase pathway on sweet corn. we construct the sweet corn juice system with different lipoxygenase activity, and then from tracking the change of fatty acid oxidation products, olfactory active components, umami substances, and sensory characteristics, the correlation of lipoxygenase pathway and sweet corn juice would be clarified. Results of this study would make a better explanation of the "fresh" and "umami" note according to sweet corn juice, and would be benefit for the quality control and authentic identify of sweet corn juice.

甜玉米汁衍生于传统谷物粥饮文化，融汇现代果蔬汁消费理念，成为一种独具中国特色的饮品。甜玉米是糖转化为淀粉的基因发生隐性突变的特殊类型，因乳熟期采收的特性而不同于谷物，往往以蔬菜的形式食用。作为幼嫩的植物组织，甜玉米清新鲜嫩的风味是其关键品质之一。为更好的诠释乳熟期甜玉米汁特有的"鲜嫩"风味，本项目将"鲜嫩"分解为"新鲜"及"鲜味"两个角度进行研究。首先通过建立参比样等方法实现对"鲜嫩"风味感官属性的解析、量化,然后通过挥发性成分及鲜味成分的测定，建立感官属性与化学分子的对应关系，实现 "鲜嫩"风味的化学表征；鉴于以往研究中果蔬"新鲜"风味与谷物"陈化"均与脂氧合酶（LOX）途径密切相关，本项目通过构建不同LOX活力的玉米汁体系，研究LOX途径、嗅感成分、鲜味物质以及感官属性的关联性，并进一步明确脂LOX途径对甜玉米风味的作用。研究结果将为甜玉米汁的风味调控、品质提升、鉴伪辨优提供理论基础。

我国玉米饮品长期以来广受消费者喜爱，但是加工制作中原料、工艺、配方千差万别，产品质量不一，“原料靠随机、风味靠调配”的现象阻碍了产业的良好发展。本项目围绕乳熟期甜玉米特有的“新”与”鲜“的风味特点开展，以其他发育期及类型的玉米为对照，探讨加工前原料的生化特点、加工过程中挥发性和非挥发性风味成分变化与香气滋味变化的关系。研究发现通过匀浆制作的生鲜甜玉米汁挥发性成分中己醛和己醇含量可达68.81%，通过调节pH值以及加热抑制LOX活力可使己醛和己醇含量显著降低，同时气味也由刺激生味、陈味转为清新的青叶香或嫩玉米香。另外，更为幼嫩的玉米中亚油酸的相对含量越高，可生成的己醛和己醇越多，二者呈显著的正相关关系，但与LOX的活力相关性不显著。另一方面，对甜玉米中4种游离糖和18种游离氨基酸进行了定量分析，结果显示乳熟期甜玉米具有高于其他发育期的蔗糖、丙氨酸及谷氨酸含量，但是缺失试验和三角试验对滋味差异的感官分析结果显示，丙氨酸的加入不能增强糖溶液的甜味，而谷氨酸与天冬氨酸对鲜味有显著作用。本项目从制汁的角度，综合原料和工艺影响，确定了甜玉米汁香气与滋味形成的化学基础，明确了LOX途径在玉米汁香气中的作用，研究结果将有助于玉米汁加工的原料选择和工艺优化。