Potential of Industrial Pineapple (_Ananas comosus_ ([PERSON]) By-Products as Aromatic and Antioxidant Sources  
Analytical Chemistry, Nutrition and Food Science Department, University of Alicante, P.O. Box 99,  
E-03080 Alicante, Spain, [EMAIL_ADDRESS] (A.V.G. ); [EMAIL_ADDRESS] (M.L.D.M. ); [EMAIL_ADDRESS] (M.P.L. ); [EMAIL_ADDRESS] (M.S.P.M.) 50-80% of the total volatile compounds identified and being related to the quality of the flavor of different pineapple parts [6]. Apart from esters, other volatile compounds present in pineapple are terpen (2-30%), alcohols (16%), acids (7-14%), aldehydes (10-13%), lactones (2-13%), phenolic compounds (6-12%), and ketones (7-10%) [7; 8]. This fruit can be consumed fresh, processed into juice, or packaged in different formats such as pineapple in its juice, slices, natural, etc. [5]. In 2016, 1.45 million tons of pineapple were imported into Europe, of which 50% was treated [1]. During the processing steps, around 60 wt.% of by-products (435,000 tons) such as the crown, peeled skin, and core were generated, which represented around EUR 360,000,000 of economic losses. Traditionally, trying to avoid a negative impact of residues on the environment, these pineapple by-products are usually used for animal feed, disposed of as waste in landfills, or burned for energy production [9]. Nonetheless, the mentioned by-products constitute a potential source of high-added valuable substances, such as volatile compounds, antioxidants, organic acids, sugars, bromelain, and phenolic compounds [5]. However, most of the research related to their revalorization has been focused on the reuse of proteolytic enzymes such as bromelain [10], the extraction of pectin from the peel [11], or the use of juice to produce vinegar [12]. One additional promising possibility is the extraction of the antioxidant compounds from the pineapple by-products to use in the pharmaceutical industry as natural sources of bioactive substances. The potential source of antioxidants and alfa-glucosidase inhibitors in pineapple subproducts was recently verified by [PERSON] and coworkers in ethanolic extracts [13]. To characterize the volatiles, present in pineapple by-products, Headspace Solid Phase Microextraction (SPME) coupled with Gas Chromatography-Mass Spectrometry (GC-MS) is a relatively inexpensive, easy-to-use analytical technique that is widely applied to volatile compound profile analysis. This technique has also been used to characterize the aroma of pineapples combining extraction and preconcentration in a single step [6; 7; 8]. Some parameters, such as the extraction temperature and time, salinity of the medium, pH, amount of solvent, and the sample amount and/or volume, among others, directly influence the extraction process using HS-SPME [14]. In this sense, previous studies have described the effect of the addition of a saline solution on the efficiency of the extraction of volatile aromatic compounds in pineapple at different concentration levels [15]. Regarding the extraction temperature in pineapple samples, the reported values of this parameter in studies carried out are between 25-40 \({}^{\circ}\)C, while the most suitable extraction time is around 40 and 60 min, depending on the study [6; 7; 8]. However, optimal operating conditions related to the extraction process of volatile compounds can be obtained using more complex experimental designs, such as the Doehlert matrix (DM), the central compound design (CCD), and three-level designs, such as the Box-Behnken (BBD) design. Focusing on the BBD-type experimental design, it has been used in the extraction of volatile compounds present in fruits such as raspberry [16] or pineapple [17], among others. However, no studies have been found in the literature in which this type of design has been used to optimize the extraction process of volatile compounds present in pineapple by-products, as is shown in this work. Total Phenolic Content (TPC) can be used as a preliminary screening test of the antioxidant potential of a fruit subproduct.