# The Impact of Different Cooking Methods on the Flavor Profile of Fermented Chinese Spicy Cabbage
## 1 Introduction  
Chinese spicy cabbage (CSC, also known as \"Chinese cabbage kimchi\") is a traditional fermented vegetable in northeast China and Korea. CSC is usually made from cabbage, scallion, ginger, garlic, red pepper, salt, and other ingredients, and fermented by various microorganisms present in the raw materials [1]. Among these microorganisms, lactic acid bacteria (LAB) played a dominant role in the fermentation process, producing organic acids, amino acids, sugars, and other metabolites including volatile flavor compounds (VFCs), thereby improving the nutritional and sensory properties of vegetables [2]. The CSC is usually eaten directly and served as a side dish or appetizer. Due to continuous fermentation, microbial metabolism and enzyme activity continued after optimal ripening, leading to over-ripening or deterioration mainly manifested as peculiar smell, over-acidity, increased bitterness, softening texture, and packaging expansion during marketing and storage [2, 3]. In particular, CSC packaged in sealed pouches produces carbon dioxide and pressure, resulting in volume expansion, package leaking, and breakage [4, 5]. Boiling or stir-frying are the most common processing methods for daily consumption of CSC besides direct eating. After heat treatment, the number of microorganisms in CSCdecrease significantly, delaying the changes in pH, acidity, organic acid, microbial population, and carbon dioxide, which could stabilize the quality of CSC and effectively maintain its shelf life [5; 6]. Therefore, CSC boiled or stir-fried is also the product most frequently sold packaged in sealed pouches on the market. Boiling and stir-frying are two common processing methods in Chinese cuisine, which could affect the nutrition and sensory characteristics, aroma components, and levels of bioactive compounds of vegetables by changing the chemical composition [7; 8]. A previous study showed that the content of flavonoids and hydroxycinnamic acid decreased in boiled kale [9]. Most phenolic compounds (gallic acid, 3,4-dihydroxybenzoic acid, 1,2-dihydroxybenzene, syringe, caffeic, rutin trihydrate, p-coumaric acid, apigenin-7-glucoside, quercetin, trans-cinnamic acid, and naringenin) in celery root were reduced after boiling [10]. [PERSON], et al. [11] showed that the content of glutamic acid, arginine, proline, alanine, valine, serine, and glycine in mushroom were significantly reduced after boiling. Boiling resulted in significant loss of ascorbic acid, soluble proteins, and soluble sugars in broccoli [12]. After boiling, cauliflower had an astringent taste, and watermelon juice had a cooking and sulfur odor [13; 14]. Stir-frying could also change the nutrition and flavor of foods. The contents of ascorbic acid and chlorophyll in broccoli decreased after stir-frying with soybean oil for 5 min [12]. Dimethyl sulfide, allyl alcohol, diallyl sulfide, methyl allyl disulfide, and diallyl disulfide were identified as the major volatile compounds in stir-fried garlic. Increasing the frying temperature and time lowered the contents of these sulfur compounds [15]. After frying, the content of volatile compounds in adzuki beans increased, and the odorants changed from \"green\" and \"grassy\" to \"roasted\" and \"nutty\" [16]. Alcohols, aldehydes, ketones, acids, and esters were the main sources of characteristic flavors of stir-frying muton \"sao zi\", generated by lipid hydrolysis and oxidation [17]. Different cooking methods could produce different flavors, which directly affect consumer choice and food industrialization [18]. However, there have been few studies on the flavor profile changes in fermented vegetables after heat processing, and the difference in flavor between boiled and stir-fried CSC was unclear. In this study, gas chromatography-mass spectrometry (GC-MS), principal component analysis (PCA), odor activity value (OAV), and fold change (FC \(>\) 2 or \(<\)0.5) were used to investigate the key aroma compounds (KACs) causing flavor differences in CSC after boiling or stir-frying.