Journal of Food Science and Engineering 10 (2020) 83-102 doi: 10.17265/2159-5828/2020.03.001 Mathematical Modeling and Optimization of the Microwave Assisted Extraction of the Natural Polyphenols and Flavonoids from the Raw Solid Waste of the Orange Juice Industry Konstantinos Petrotos 1 , Ioannis Giavasis 2 , Konstantinos Gerasopoulos 1 , Chrysanthi Mitsagga 2 , Chryssoula Papaioannou 1 and Paschalis Gkoutsidis 1 1. Department of Agrotechnology, School of Agricultural Sciences, University of Thessaly, Geopolis Campus, Periferiaki Odos Larisas Trikalon, Larisa 41500, Greece 2. Department of Food Science and Nutrition, School of Agricultural Sciences, University of Thessaly, Karditsa Campus, End of N. Temponera Street, Karditsa 43100, Greece Abstract: Orange pomace is the solid waste of the orange juice industry which accounts for approximately 50% of the quantity of the fruits processed into juice and is a good raw material for production of high added value products with diverse uses. Orange pomace is rich in polyphenols and flavonoids which can substitute the potentially hazardous or less desirable chemical antioxidants/antimicrobials used in agro-food and cosmetics industry. In this work, an eco-friendly aqueous microwave assisted extraction of orange pomace was investigated and optimized in order to produce aqueous bioactive antioxidant/antimicrobial extracts. A three factorial Response Surface Optimization methodology with centered Box & Behnken experimental design was used to obtain optimum values of total polyphenols and total flavonoids and build predictive models for their optimal extraction conditions. The three optimization factors in terms of applied process parameters were (a) water/solid ratio, (b) extraction temperature and (c) extraction time. The effectiveness and statistical soundness of the two corresponding models regarding optimal total polyphenols and flavonoids were verified by Analysis of Variance (ANOVA). Key words: Orange pomace, microwave assisted extraction, response surface optimization, Box & Behnken, polyphenols, flavonoids. 1. Introduction Orange fruit belongs to the species Citrus sinensis and in the family Rutacae and it originates from China. It is designated as sweet orange in order to be discriminated from the bitter orange which is known as Citrus aurantium [1] and it is cultivated in tropical and subtropical regions. In 2017, the global production of fresh orange fruits was 73 million MT, from which Brazil has the largest share of 24%, followed by China and India. According to Lohrasbi et al. [2], 33% of the global orange fruits production is Corresponding author: Konstantinos Petrotos, PhD, professor, research field: food process engineering. industrially processed and 15 million MT of solid orange fruit waste, known as raw orange pomace is produced, which roughly represents the 50% of the total orange fruits which are processed [3]. The orange pomace consists of peels, seeds, pulp, and segment residue [4]. In an investigation carried out by Sharma et al. [5] it was found out that the orange peel could be a valuable raw material for production of a variety of high added value products as it contains substantial quantities of flavonoids, carotenoids, edible fibers, polyphenols, essential oils and ascorbic acid as well as sugars that could be a good substrate of various D DAVID PUBLISHING