分层破胚剥皮玉米不同部位营养成分富集特征

为明确玉米籽粒营养成分的分布差异及不同部位富集特征，应用快速缓苏、微量着水半湿法分层破胚剥皮技术，结合靶向代谢组学方法，对郑单958玉米不同部位的营养成分及基础代谢物质进行分析与比较。结果表明玉米籽粒不同部位的淀粉、脂肪、矿物元素和膳食纤维等营养物质含量存在显著差异（P<0.05）。该研究中的玉米内皮层可能主要由种皮、糊粉层及部分外胚乳构成，该部位营养成分的种类及含量均较为丰富，其中水溶性膳食纤维含量显著高于其他部位（P<0.05），可作为玉米水溶性膳食纤维的提取分离来源。K、P和Mg元素是玉米中含量最高的矿物元素，主要存在于胚芽中，Fe、Zn、Mn和Cu元素在胚芽和玉米皮层中均有较多分布，精制加工会导致这些矿物元素的损失。玉米胚芽中水解氨基酸种类较其他部位丰富且含量较高（P<0.05），甜味氨基酸占总游离氨基酸含量的24.49%，高于玉米皮层部位、显著高于胚乳部位。研究结果为玉米营养健康食品的创制、玉米精深加工及相关专用装备的研发提供参考。

Enrichment characteristics of nutritional components in different parts from corn kernels

Maize (also known as corn) is the third most important food grain after wheat and rice. Corn kernels are the fruits of corn as a vegetable in cooking. This study aims to clarify the distribution patterns and enrichment characteristics of nutritional components in the corn kernels after semi-wet layered milling. Four parts of the Zhengdan 958 corn kernel were collected, named corn bran 1 (CB1), corn bran 2 (CB2), corn germ (CG), and corn endosperm (CE). Standard experiments were used to analyze the chemical contents of the corn kernels. The basic nutritional compositions included the contents of starch, protein, fat, ash, and crude fiber, as well as the content and composition of minerals and dietary fiber. The targeting metabolomics was used to clarify the basic metabolites using the GC-MS detection technique, including free sugar, free and hydrolyzed aminol acids, and fatty acids of the four separated parts, compared with the whole corn kernel (WC). The results showed that the contents of the total starch, protein, fat, ash, and crude fiber were 72.60%, 9.51%, 4.96%, 1.44%, and 7.72%, respectively. Significant differences were observed among these contents in the different parts of the kernel (P<0.05). About 74% starch was found in the CE, while the CG was found rich in protein, fat, and ash, contributing 21.46% of protein, 53.16% of fat, and 57.84% of the ash to the WC. The CB1 and CB2 contained most of the fibers, with the amount of 39.35% and 28.90%, respectively. There were significant differences in the contents of total dietary fiber (TDF), insoluble dietary fiber (IDF), and soluble dietary fiber (SDF) in different parts of corn kernel (P<0.05). The contents of TDF, IDF, and SDF in the CB1 were 43.47%, 36.76%, and 7.54%, respectively, while the IDF content was 4.88 times higher than the SDF. While in the CB2, the contents of TDF, IDF, and SDF were 32.47%, 24.55%, and 8.83%, respectively, while the IDF content was 2.78 times higher than the SDF, indicating a relatively higher ratio of the SDF content in the CB2, compared with the CB1. A total of 10 types of free sugar were detected in the WC, as well as the four separated parts. There was the highest content of free sugars in the CB2, with an amount of 17.47 mg/g, followed by the CB1 with 12.80 mg/g. Glucose, galactose, and fucose were the most abundant free sugar in the corn bran samples. K, P, and Mg were the minerals with the highest contents in corn. Most of the essential trace elements were abundant in germ, whereas, Fe, Zn, Mn, and Cu were also distributed in corn bran. The refined processing of corn led to the loss of these mineral elements. Compared with other parts, the CG contained more abundant hydrolyzed amino acids (P<0.05), while the leucine and glutamic acid were the essential and non-essential amino acids with the highest concentration, respectively. The amino acids for the sweet flavor accounted for 24.49% of the total free amino acids in the CG, which was higher than those in the CB1, CB2, and CE. The total content of free fatty acids in CB2 was also higher than in CB1. The fatty acids constituting triglyceride were linoleic acid (about 40%), oleic acid (37%), and palmitic acid (14%), indicating the rich content of unsaturated fatty acids in corn. Consequently, the CB2 part rich in nutrients can be expected to compose mainly of the seed coat, aleurone layer, and part of the peripheral endosperm. The water-soluble dietary fiber content in this part was significantly higher than the rest (P<0.05), indicating that CB2 was a source of the extraction of SDF. The systematic qualitative and quantitative metabolomics research on the endogenous basic metabolites can also provide new ideas, and then greatly contribute to the improvement of the sensory properties, including the flavor and colors of corn products, as well as the bioprocessing technique and nutritious food development. This finding can provide strong reference data for the enrichment of nutrients and utilization of value-added byproducts during corm processing, particularly for the development of nutritious and healthy corn foods. In addition, it can also offer to optimize and then update the corn layered milling processing.