# Optimization of Chinese Chive Juice as a Functional Feed Additive
## 4 Discussion  
Chinese chives are rich in substantial active compounds that provide it with effective antimicrobial and antioxidant activities. In our study, CC displayed broad-spectrum antibacterial activities against 12 pathogenic bacteria responsible for diseases in swine, poultry, horse, and aquaculture. This was consistent with previous studies that have reported the inhibitory effects of CC on a variety of Gram-positive and Gram-negative bacteria [8; 9; 10; 11]. To the best of our knowledge, to date very few studies have explored the use of CC as a functional additive in animal feed. Commercial phytogenic feed additives (PFA) generally need to be in a powder form with stable functional properties. The antibacterial stability of CC was primarily investigated under common drying temperature (60 \({}^{\circ}\)C and 80 \({}^{\circ}\)C) within 3 h. The attenuated antibacterial activity of CC with heat treatment might be attributed to the specific compositional changes. The organosulfur compounds are considered as the main antibacterial agents in CC [26; 27], however they are heat-labile and easily degraded under heating conditions [28]. [PERSON] et al. [9] reported that the antibacterial activity of _Allium_ extracts against _Campylobacter_ species was reduced when subjected to 75 \({}^{\circ}\)C for 30 min. Conversely, [PERSON] et al. [8] reported that CC extracts showed thermal stability with heat pre-processing up to 100-121 \({}^{\circ}\)C for 15 min, and considerable antibacterial activity was retained against diverse food-borne pathogens. Flavonoids are another important compound in CC that are responsible for both antibacterial and antioxidant activities [29]. In line with our TFC result, the flavonoids in kale and raspberry were reported to decrease by 2-92% after air-drying as compared with the fresh products [16]. However, the TPC was not significantly affected by the heating treatments in this study, signifying that the flavonoid constituents are closely related to the antibacterial activity of CC. [PERSON] et al. [30] reported that phenolic acids and flavonoid constituents in garlic (_A. sativum_) varied following different thermal processing conditions, herein, the synthesis and degradation of these compounds in CC during heating displayed relatively constant TPC and reduced TFC. SBM was used as an excipient to solidify the CC juice with optimized drying conditions. The high moisture content (80%) of CC juice may lower shelf-life due to microbial contamination, which may lead to the reduction of biofunctionalities in CC-based products. Low moisture content (<5%) in post-harvest products is desirable as this can extend their shelf life, for example, if an environment that is unsuitable for microbial proliferation is created this prevents deterioration in the product [31]. Hence, the optimal drying conditions are very important in order to make high quality products while simultaneously retaining their biological activities. FFD is widely used to optimize the functional parameters, mass production of end-products, and growth of the target phenotypes [32; 33; 34]. Among the three variable factors, solid content (SBM) ratio was found to be the most critical factor impacting the antibacterial activity of CC against the selected pathogens. Untargeted metabolomics using a UHPLC-LTQ-Orbitrap-MS/MS platform was carried out to analyze the metabolites' disparity in fresh and heated CC samples. Among different flavonoid groups, flavonoids mainly consist of kaempfer, quercetin, and their glycosides derivatives in _Allium_ species with potent antibacterial and antioxidant activities [35; 36]. Quercetin and its glucoside derivatives have been reported to exhibit bacteriostatic effects due to their damage to cell wall and membrane, anti-quorum sensing and anti-biofilm properties [37; 38]. The decreased levels of quercetin and/or kaempfer glycosides in heated CC might have resulted in the reduced antibacterial activity.