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China is the world’s largest walnut producer, with an annual output of 4.795 9 million tons. Walnut kernels have high nutritional value, containing 65%−69% of oil and 15%−20% of protein. Walnut meal, an abundant byproduct of walnut oil production, is mainly used in animal feed and fertilizers with low processing efficiency, whose potential for high-value utilization is far from being excavated. Studies have found that walnut meal contains a large amount of protein (42%−54%), its amino acid composition is rich, and the proportion of amino acids in walnut meal is suitable for human absorption. Walnut meal is a source of high-quality plant protein with a true protein digestibility score of 86.22%, and a biological valence of 98.77%. Therefore, high-efficiency utilization of walnut meal proteins is an important pathway for the high-value utilization of walnut meal. In this article, the composition, structure, and nutritional value of walnut proteins are reviewed. The extraction methods and functional characteristics of walnut proteins are summarized. The effect of modification on their functionalities and digestibility is also summarized. Finally, the application potential of walnut protein in foods is discussed.

In this study, the flavor components of double-low fragrant rapeseed oils (cv. “Zhongyouza 19”) from nine different planting areas were qualitatively and quantitatively analyzed by headspace solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry coupled with olfactometry (GC-MS-O). The results showed that a total of 63 aroma-active compounds were identified using two columns (polar and non-polar) at a total concentration of 222.0 to 468.9 mg/kg. The total concentration of aroma compounds was highest in the Hunan sample and lowest in the Jiangxi sample. Out of the identified flavor substances, 38 had odor activity value (OAV) greater than 10. The results of partial least squares-discriminant analysis (PLS-DA) and sensory evaluation showed that 2-methylpyrazine, 2,3,5-trimethylpyrazine, and 2-methyl-3,5-diethylpyrazine were the main contributors to roasted aroma notes, 3-butenylisothiocyanate provided spicy notes, and 5-hexenenitrile and 4-methylthionitrile led to green notes. Based on variable important in the projection (VIP) values, nine key differential substances were selected, namely, methanthiol, 2-methylpyrazine, 2,3-diethyl-5-methylpyrazine, dimethyl disulfide, 5-methylthiopentonitrile, 5-hexenenitrile, (E,Z)-2,4-pentadienonitrile, hexanal and dimethyl trisulfide. They could be considered as potential flavor markers for the discrimination of double-low fragrant rapeseed oils from different planting areas. This research can provide a theoretical guide for the screening of raw materials for fragrant rapeseed oils.

Three kinds of silicon dioxide including S655, R92 and R40F were characterized, and their application in low-temperature adsorption refining of fragrant rapeseed oil was studied. The results showed that all three kinds of silicon dioxide had a loose porous structure, but the particle size distribution, specific surface area, pore volume and pore size were obviously different. After being treated with 1.0% silicon dioxide at 45 ℃ for 30 min, the dephosphorization rates of rapeseed oil by S655, R92 and R40F were 90.3%, 99.6% and 88.5%, the lightness increased by 49.9%, 52.5% and 53.9%, the redness decreased by 31.5%, 23.4% and 37.8%, the yellowness increased by 17.3%, 20.0% and 20.6%, respectively. Meanwhile, the retention rate of sterols (above 97.1%) was high, and there were no significant differences in deacidification rate, fatty acid composition or tocopherol retention rate among the three treatment groups. The highest retention rates of total phenol and canolol (98.1% and 99.4%) were found in the samples treated with R92. The contents of glucosinolate degradation products, pyrazines, aldehydes and ketones in fragrant rapeseed oil all increased significantly after refining with the three kinds of silicon dioxide.

The major route of rapeseed utilization is by the preparation of rapeseed oil. Different oil preparation technologies have a significant influence on lipid concomitants (including polyphenols, phytosterols, tocopherols, and β-carotene) in rapeseed oil. Lipid concomitants are an important part in rapeseed oil quality, so it is crucial to understand the changes of lipid concomitants during rapeseed oil production. The aim of this review is to summarize the major outcomes of recent research on the influence of different oil preparation technologies on lipid concomitants in rapeseed oil with a focus on pretreatment technologies (including pulsed electric field, microwave, and roasting/steaming), oil extraction technologies (including supercritical carbon dioxide extraction, aqueous enzymatic extraction, and solvent extraction) and refining processes (including degumming, deacidification, decolorization, and deodorization). We hope that this review will provide a theoretical basis for the development of green and efficient technology for rapeseed processing.