菜籽多酚研究进展

Research developments on phenolics of rapeseed

油菜籽富含多酚。菜籽多酚分为酚酸和缩合单宁,其中酚酸包括游离酚酸、酯化酚酸和结合不可溶酚酸,游离酚酸约占总酚的9%~16%,芥子酸是最主要的游离酚酸,占总游离酚酸的70%以上;芥子碱是最主要的酯化酚酸,占总酚的80%以上。多酚的萃取普遍采用有机溶剂萃取法,其中,70%甲醇是最常用的萃取溶剂之一,采用超声波辅助可缩短萃取时间,提高萃取效率;福林酚法、香草醛法和高效液相色谱法是目前国际上普遍采用的总酚、单宁和酚酸测定方法,其中常采用质谱技术对未知多酚成分进行定性。菜籽多酚具有良好的抗氧化活性,一般采用二苯基苦基肼(DPPH)法、铁离子还原抗氧化能力(FRAP)法、氧自由基吸收能力(ORAC)法等方法进行抗氧化活性评价;多酚类化合物的抗氧化活性与羟基和甲氧基的数量及在芳香环上的位置密切相关,羟基肉桂酸衍生物的抗氧化活性优于苯甲酸衍生物。在制油前对油菜籽进行热处理可增加籽和油中多酚含量,并使芥子酸脱羧转化为抗氧化活性更高的canolol,canolol具有脂溶性,压榨制油后,56%~83%的canolol从油菜籽中转移至油中,从而显著改善油的氧化稳定性;脱酸、脱色和脱臭等精炼导致油中多酚和canolol损失严重。未来应进一步采用液相色谱-质谱和核磁共振技术鉴定未知多酚成分的结构并进行定量分析,采用基于细胞模型的生物评价法,系统深入开展菜籽多酚的抗氧化活性研究,为多酚的开发利用提供理论支撑;同时应加强油脂适度精炼技术的研发与推广,尽可能减少精炼过程中多酚的损失,提高油脂营养价值。

Rapeseeds are a rich source of phenolic compounds. The predominant phenolics present in rape- seeds are phenolic acids and condensed tannins. Among them, phenolic acids are present in the free, esterified and insoluble - bound forms and are derivatives of benzoic and cinnamic acids. Free phenolic acids account for 9 - 16% of the total, with sinapic acid being the most important compound of this group （ over 70% of the total free phenolic acids） . The largest fraction of polyphenolic compounds, accounting for about 80% of the total amount, corresponds to esterified phenolic acids, where sinapine, the choline - ester of sinapic acid, is by large the most representative one. Rapeseed phenolic were extracted with different systems. Extraction with organic solvent, spe-cial 70% methanol, is one of the most commonly used. Moreover, ultrasonic assisted extraction can improve effec-tiveness. Folin - Ciocalteus method, vanillin method, and HPLC analysis usually are used to measure total phenol-ics, condensed tannins, and phenolic acids content. Rapeseed phenolic extracts show excellent antioxidant activi-ty, which usually were evaluated by DPPH, FRAP, and ORAC methods. The chemical structures of phenolics play key roles in antioxidant activity, depending on the number and position of free hydroxyl and methoxyl groups atta-ched to the aromatic ring. The derivatives of cinnamic acid show a higher correlation with antioxidant capacity than the derivatives of benzoic acid. Heat treatment of rapeseeds can significantly increase phenolics and canolol content in rapeseeds and oil from them. Canolol can be formed by thermal decarboxylation of sinapic acid occurring natural-ly in rapeseeds. Approximately 56 -8 3% o f canolol are transferred to the oil af ter pressing, due to the strong fat solubility of canolol. Phenolic compounds and canolol are practically completely removed from oil during neutraliza-tion, bleaching, and deodorization steps. Therefore, unknown phenolic compounds would be identified by HPLC - MS/MS and NMR. The antioxidant activity of individual phenolic compound would be evaluated by cellular antioxi-dant activity assay, to provide a basis for the development and utilization of rapeseed polyphenols. Moreover, the moderate refining technology of oil could be developed to reduce the loss of polyphenols in rapeseed oil.