菜籽微波过程中挥发性硫苷降解产物的形成途径研究

Cold pressing technology is a new oil producing process. It has been developed gradually and recognized in recent years. This technology has a advantage for the retention of trace nutrients. However, the content of glucosinolate in rapeseed material was remained at a high level. This technology development is limited because the pungent spicy flavor derived from glucosinolate which is different to accept by customers. From the previous studies, rapeseed microwave pretreatment will be a good way which was not only can ease the off-flavor, but also can enhance oil yield and quality. However, the degradation path of glucosinolate is not clear because rapeseed microwave is a complex process. The following work is to make a accurate identification of volatile glucosinolate degradation products use GC×GC-TOF MS and find out off-flavors with GC/O methods. In this study, it is very important to make sure the influence of five aspects on glucosinolate degradation pathway including moisture, structure, myrosinase and system temperature. We build enzymatic degradation and thermal degradation system using different single glucosinolate as precursor substances. Based on the above results, we can infer the formation path of volatile glucosinolate degradation theoretically. The final purpose was to make a control of off-flavor and improve the flavor of cold-pressed rapeseed oil. This study will provide the guiding significance to high quality cold pressing technology development.

低温压榨制油技术是近年来逐步发展并被认可的新型制油工艺，能最大限度保留油脂中微量营养成分。然而我国商品菜籽硫苷含量偏高，低温压榨后产生的硫苷降解产物使菜籽油具有辛辣风味，不易为消费者接受，制约了菜籽低温压榨技术的推广应用。研究表明对菜籽进行微波预处理可降低压榨油辛辣味、提高出油率和改善油脂品质。但微波过程复杂多变，油中挥发性硫苷降解产物的形成途径、产物结构和含量及对菜籽油风味的影响尚不清楚。本项目拟采用全二维-飞行时间质谱对菜籽油中挥发性降解产物结构进行准确鉴定，利用嗅觉检测器明确其中具有不良风味的产物，综合分析原料水分、微波条件、微观结构、芥子酶活性和体系温度对这些产物的影响规律，构建硫苷单体的酶促降解和热降解模拟体系，推导出微波过程中挥发性硫苷降解产物的形成途径，实现对不良风味的调控，改善低温压榨菜籽油风味。本项目的研究成果对推动高品质、清洁高效的低温压榨制油技术发展具有重要意义。

硫苷是油菜籽中重要的次生代谢产物，加工后产生的降解产物对菜籽油风味具有重要影响。本项目利用顶空固相微萃取-全二维气相色谱/飞行时间质谱建立挥发性硫苷降解产物的分析方法，在不同基因型（甘蓝、白菜、芥菜）微波低温压榨油中共鉴定出20种硫苷降解产物；利用GC/O对硫苷降解产物的风味进行嗅闻，锁定具有特征气味的关键硫甙降解产物包括3-丁烯基异硫氰酸酯、异硫氰酸丁酯、异硫氰酸烯丙酯。3种不同品种低温压榨油中甘蓝型菜籽油中的辛辣味最弱，卷心菜味最强，白菜型菜籽油中青草味最明显，芥菜型中的酸味最明显，辛辣风味强度与前体物质中硫苷含量成正相关关系。经微波预处理后，菜籽油中3种关键辛辣风味的稀释因子显著降低。对不同初始水分的菜籽中硫苷挥发性硫苷降解产物的形成规律进行系统研究，3种基因型菜籽中硫苷呈现相似的降解规律，初始水分为9%时，硫苷总量和关键分量（2-羟基3-丁烯基硫苷、3-丁烯基硫苷、4-羟基-3-吲哚基硫苷、丙烯基硫苷）的降解速度最快。微波6min时，芥子酶已完全失活，体系温度升高，菜籽油中异硫氰酸酯的含量和辛辣风味强度最低，同时焙烤风味增加，有利于改善菜籽油的整体风味。利用半制备型液相从菜籽中分离得到丙烯基硫苷、2-羟基-3-丁烯基硫苷、3-丁烯基硫苷的单体，通过脱脂粕-硫苷-芥子酶降解体系的构建，初步推测菜籽微波过程中硫苷降解途径为：微波0-3min时同时存在酶促降解和热降解，微波后期（3min后）则以热降解为主。该研究结果将有利于通过微波处理技术改善菜籽油的风味，为低温压榨菜籽油的推广和应用提供指导。

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