Methoxyamine hydrochloride

Extraction and quantification of sugars were followed as described by Raviv et al. (2020 (link)). Briefly, two grains were ground using Multi-beads Shocker MB2000. The samples were extracted in 1.4 mL of 100% methanol with ribitol (12 μg) supplemented as an internal standard. The samples were homogenized and incubated at 70 °C with shaking for 10 min. The samples were centrifuged for 10 min at 12,000 × g. The supernatant was taken and vigorously mixed with 0.7 mL chloroform and 1.5 mL ice-cold water. The phases were separated by centrifugation at 2000 × g for 15 min, and 150 μL of the upper polar phase was sampled and dried in a vacuum concentrator. The dried samples were sequentially derivatized with methoxyamine hydrochloride and N-methyl-N-trimethylsilyl-trifluoroacetamide (Tokyo Chemical Industry). The derivatized samples were diluted by ten times with dichloromethane (FUJIFILM, Japan), and metabolites were analyzed with an Agilent 7890A-GC/240-MS instrument (Agilent Technologies). Mass spectra data were collected in full scan mode in mass range m/z 40–750. Metabolites were identified by comparing their fragmentation patterns with Mass Spectral Library (National Institute of Standards and Technology).

In Tongwei (Hainan) Aquatic Food Co., Ltd., the skins with scales of Genetic Improvement of Farmed tilapia after fillet processing were frozen and then the frozen skins with scales were shipped by cold chain and stored at −18 °C in our laboratory. The used chemicals in this work were: methanol (high-performance liquid chromatography (HPLC) grade, CNW Technologies GmbH, Düsseldorf, Germany), acetonitrile (HPLC grade, CNW Technologies), chloroform (HPLC grade, Adamas-beta Reagent Co., Ltd., Shanghai, China), pyridine (HPLC grade, Adamas-beta), methoxyamine hydrochloride (analytical grade (AR), Tokyo Chemical Industry Co., Ltd., Tokyo, Japan), adonitol (purity ≥ 99%, Sigma-Aldrich, Shanghai, China), ammonium acetate (HPLC grade, Sigma-Aldrich), ammonium hydroxide (HPLC grade, Fisher Chemical, Fair Lawn, NJ, USA), Bis(trimethylsilyl)trifluoroacetamide with 1% (v/v) trimethylsilyl chloride (REGIS Technologies Inc., Chicago, IL, USA), and fatty acid methyl esters (Dr. Ehrenstorfer Gmbh, Augsburg, Germany).