## 1 Introduction  
Peppers (_Capsicum_ spp.) are economically important agricultural and horticultural crops. They are of great economical value because of their outstanding contributions as important sources of spices and high antioxidants [1, 2]. The _Capsicum_ genus comprises more than 30 described species, and the fruits of that exhibit variability widely with respect to shape, size, color, and sensory attributes [3]. Among these species, five are considered to be domesticated: _Capsicum annuum_ (sweet or bell pepper), _Capsicum frutscens_ (chili pepper), _Capsicum chinense_ (Scotch pepper chili), _Capsicum huccatum_ (aji amarillo chili), and _Capsicum pubescens_ (apple chili) [4]. The general nutrient compounds of pepper, with its array of vitamins, phenolic, carotenoids, and capsaicinids, have beneficial effects for humans, including antioxidant and antibacterial properties [2, 5].  
The main quality features of pepper fruits are color and spice level [6]. The pungency of the ripe fruits in peppers is due to the presence of capsaicinoids, which is a group of many different alkaloids. Capsaicin and dihydrocapsaicin are the major alkaloids which account for 90% of the total capsaicinoids in chili peppers [7; 8]. Twenty-three capsaicinoids have been reported up to now, and the pungency level of fruit is related with their molecular structure and concentrations [9; 10]. The fruit of pepper contains 46-243 mg/100 g ascorbic acid (vitamin C) by fresh weight, which depend on different species and cultivars as well as degree of ripeness [4; 11]. Ascorbic acid is an antioxidant that plays a vital role in human nutrition and body function, being actively involved in neutralizing free radicals, iron assimilation, the wound healing process, and protecting the skin from viral and bacterial infection by building collagen in the skin [12].  
The ripe fruits of pepper varieties display a wide range of colors, which have been traditionally generated by the accumulation of different carotenoids and flavonoids in the pericarp [13]. Carotenoids are naturally occurring pigments found in plants and responsible for different colors of peel, with covering red, brown, orange, salmon-pink, and yellow [13; 14]. In recent years, carotenoids have attracted widespread attention because of their higher antioxidant activity and positive health benefits for preventing cardiovascular diseases [15; 16]. Particularly, carotenoids containing k-terminal have been proved to be one of the characteristics of peppers [17]. Anthocyanins, as the final products of the flavonoid biosynthesis pathway, mainly accumulate in the outer epidermis of pepper fruit [18]. However, the major components are delphinidin, cyanidin and malvidin derivatives therein, and that is why some pepper fruits appear with purple or black colors, which are related to the concentrations and proportions of various anthocyanins in fruits at different development stages or genotypes [13; 18].  
The nutritional value of the fatty acids profile depends on their ratio and constitutes. A reasonable fatty acid composition should include low saturated fatty acid, high monoun-saturated fatty acid, balanced omega-6 and omega-3 fatty acids, and a large number of vitamin E and phytosterols. The lipids of pepper fruits are vital quality features as they play an important role in preparation for attractive spice. Fatty acids accumulate both in the peel and seeds of pepper fruits [19].  
It is obvious that the discrepancy of capsaicinoids and metabolites in different varieties may be helpful for further pepper breeding programs. Thus, the present study was designed to evaluate the diversity of traits involving fruit morphology, the concentrations of capsaicinoids and other metabolites in 75 different _Capsicum_ genotypes mainly collected from Yunnan Province, China. Integrating the biochemical and molecular mechanisms underlying this variation could be instructive for developing new commercial hybrid cultivars with fruits rich in health-related compounds.