Development of a novel tomato (Solanum lycopersicum ) peeling process using power ultrasound technology

Peeling is one of the most important unit operations in tomato processing. Steam/hot water and lye peeling have been the most commercialized methods in the U.S. However, lye peeling is more preferred among processors due to its association with higher product yields and better product quality. In the recent years, tomato-processing industry is facing ever-toughening environmental regulations, which call for chemical-free alternatives to replace lye peeling. In this study, the development of power ultrasound (PU) as a novel alternative chemical-free method was investigated. Tomatoes were treated with lye (10%) and PU (20 kHz, 1500 W) and steam for 45, 60 and 120s at 97 +/- 3°C, respectively, and peeling losses (%) in addition to peeling performance based on a subjective ease of peel score (from 1-difficult to peel to 5-very easy to peel) after treatments was determined. Effects of PU peeling on the quality parameters (firmness, pH, soluble solids (SS), titratable acidity (TA), color) were also evaluated. Results showed no significant differences (P < 0.05) in ease of peeling scores of lye compared to PU. Peeling losses were significantly (P < 0.05) lower in tomatoes treated with PU compared to and steam. The firmness (N) of PU (15.4 +/- 7.3; 18.2 +/- 2.8) treated samples was significantly (P < 0.05) higher than lye (12.9 +/- 6.1; 12.8 +/- 3.5) and steam (2.62 +/- 0.83; 2.94 +/- 0.47; 3.44 +/- 1.03) at 45 and 60 s, respectively. Although there was some variability in the pH, SS, TA and color, the processing quality of the tomatoes were preserved with the exception of lycopene and color in steam peeled tomatoes. In conclusion, PU may be a promising alternative to lye and steam for tomato peeling and its technological advancement in the tomato-processing industry. Additionally from this study, it can be suggested that PU technology as an alternative peeling technology for the conventional (lye and steam) is economically and financially feasible. Empirically, it was found that a tomato cannery plant potentially installed with PU as a peeling technology may be 10 and 12 K...