## 1 Introduction  
Watermelon (_Cittullus lantus_) is an essential and globally popular fruit; it constitutes 7% of the agricultural space dedicated to fruit and vegetable production [1]. In 2017, the global watermelon production was 118 million tonnes [2], with an estimated value of $60 billion. Watermelon fruit consists of peel/skin, rind (approximately 40% of total fruit weight), flesh (approximately 60% of total fruit weight), and seeds [2]. Despite being edible, the rind is often discarded before serving/processing, causing biomass loss [3]. The waste is currently sent to landfills, incinerated, used for animal feed, or composed, all of which are low value, costly, or have additional negative environmental effects [4]. The rind waste could be redirected to commercial use in the food industry considering its potential.  
The potential value of watermelon rind has been recognized and explored. Approaches include converting rind polysaccharides into other products like bioethanol [3], biosorbent [5], and biochar [6]. Rind is also a food ingredient source for pectin [7, 8] and citruline [9, 10, 11]. Rind has been directly processed by pickling [12], as well as being incorporated into jams [13]. Watermelon rind in powder form has been applied in cakes [14, 15], cookies [16, 17], noodles [18, 19], beef patties [20], and pork patties [21]. In addition, a few studies have investigated the use of whole watermelon rind as medium for microbials [22, 23, 24]. Overall, it was determined that incorporating rind into foods added value such as with pectin and specific amino acids.  
In recent years, recycling valuable components from agro-food byproducts back into the food chain has gained great attention. Watermelon is a natural source of citruline, a neutral non-essential \(\alpha\)-amino acid and a precursor of L-arginine in the urea cycle [25]. Arginine is an essential amino acid which regulates blood flow and nitric oxide levels. Extensive studies have focused on citruline in both watermelon flesh and rind [25; 26]; however, fewer studies have investigated watermelon rind full amino acid profiles.  
In addition to the mentioned food applications, the application of fresh rind in a food product has also been performed in our lab. Our previous consumer tests indicated that fresh rind's sweet, sour taste and watermelon-like aroma is very different compared to the flesh [27]. Aroma, along with sweet (sugars) and sour (acids) tastes, is essential for fresh and processed fruit products. Flavor (aroma and taste) is gaining consideration as the major quality attribute. Although qualitative volatile characterization of watermelon flesh is well-documented [26; 28], few studies have analyzed watermelon rind's volatile compounds [29]. Quantitative volatile studies for rind and flesh are limited. Chemical and sensory analysis of the rind flavor profile would assist with the determination of the scope and suitable applications for rind usage in the food industry.  
The present study aimed to address the potential application of watermelon rind in watermelon rind-flesh juices by evaluating the amino acid profiles and volatile aroma composition using instrumental analysis and quantification. Five samples were formulated for comparison: rind alone, flesh alone, and rind-flesh blends with rind portions of 10%, 20%, and 30%. The 20% rind sample was selected for this study based on the previously determined consumer acceptable level of 20% rind [27]. The 10% and 30% rind samples were included to monitor ratio changes which could potentially alter flavor perception.