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Received Jul 30, 2017; Revised Nov 7, 2017; Accepted Dec 13, 2017
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1. Introduction
Lactic acid fermentation is one of the oldest and most economical methods used in food preservation, especially as a “natural” process that enhances the efficacy and quality of foods while improving the organoleptic qualities of the product [1–3]. In fact, at the end of the twentieth century, the Food and Agriculture Organization (FAO) of the United Nations recognized the importance of fermented products, highlighting their economic importance for local communities in developing countries [4]. Probiotic foods are an important and dominating part of the functional food market, accounting for 60% to 70% of the total functional food market [5], with more than 370 products launched worldwide in Japan and Europe in 2005 [6]. A number of studies have reported that the development of fruit juice-based fermented beverages would be the next food category in which health-promoting probiotic bacteria will make their mark [7, 8]. Many countries have conducted extensive research and development on probiotic-fermented fruit and vegetable beverages in recent years, especially in Korea, India, and Brazil. These studies have used watermelons, tomatoes, apples, and so on as raw materials for fermentation by lactic acid bacteria [9–11]. An important aspect of lactic acid bacteria (LAB) fermentation is the production of organic acids, sugar polymers, aromatic compounds, vitamins, polyphenolic compounds, and some useful enzymes, which enrich the human diet [12, 13]. The fermentation products generated by different lactic acid bacteria are not the same. Lee et al. [14] showed variations among the respective LAB strains from kimchi, and Kumar et al. [15] showed that L. plantarum Lp91 has a better effect than Lp21 in the management of hypercholesterolaemia. Thus, significant differences in the antioxidant activity and composition of fermented products can be generated by specific probiotic strains [16].
Papaya (Carica papaya L.), a member of the Caricaceae family, is widely cultivated in tropical and subtropical regions and is marketed around the world for its great taste and nutrients [17, 18]. Papaya has been identified as a valuable source of nutrients...