Enzymatic peelingof citrus fruits
From the molecular point of view, pectin, cellulose, and hemicellulose are responsible for the adherence of the skin to the fruit (Whitaker, 1984). Therefore, both pectinases and cellulases are needed for the enzymatic peeling. The cellulases are probably needed for the release of the pectins in the albedo, and the pectinases contribute to the hydrolysis of the polysaccharides of the cell wall (Ben-Shalom et al., 1986; Coll, 1996). Bruemmer et al. (1978) were the rst authors employing this enzymatic method in the peeling of grapefruits by vacuum infusion of commercial pectolytic preparations, showing that the obtained sections maintained their original taste and texture with higher efciency and quality than those obtained by conventional peeling processes. They also observed how the commercial pectinases considerably differ on their peeling efciency. Likewise, Berry et al. (1988) showed that the loss of juice in both enzymatically peeled entire grapefruits and segments by the method developed by Bruemmer et al. (1978), was lower than in fruits obtained by conventional chemical or manual methods. To obtain a better knowledge of the enzymatic degradation, Ben Shalom et al. (1986) stated the importance of evaluating the effect of commercial enzymes on the substrates to be degraded. This fact was later conrmed by other authors (Rouhana and Mannheim, 1994; Soffer and Mannheim, 1994; Baker and Wicker, 1996; Pretel et al., 2005; Pinnavaia et al., 2006). However, not only the enzymatic preparation is critical for obtaining a good peeling efciency; there are many other determining parameters. For instance, the adherence of the peel to the fruit and its thickness are different according to the species or the citrus varieties, and the design of the cuts, the vacuum conditions, temperature, and pH also affect the peeling (Berry et al., 1988; Adams and Kirk, 1991; McArdle and Culver, 1994; Pretel et al., 1997; Pretel et al., 1998a,b; Prakash et al., 2001; Suutarinen et al., 2003; Liu et al., 2004; Pagán et al., 2005; Pretel et al., 2007a,b). On the other side, the reuse of the enzymatic solution has been studied by different authors since, from the economical point of view, this is one of the important factors when using the operation at industrial level (Pretel et al., 1997; Rouhana and Mannheim, 1994; Pagán et al., 2006; Pretel et al., 2007b).