Kiwifruit peeling by infrared heating technology: Effects of operational parameters on peeling performance

The commercial lye peeling method used in kiwifruit processing industry is water and energy intensive process and has negative impact on the environment. Infrared (IR) technology has been proposed as an alternative to food processing technologies with attractive merits such as uniform heating, high heat transfer rate, reduced processing time and energy consumption, and improved product quality and safety. However, no previous reports were found on the feasibility of kiwifruit peeling using IR heating technology. Therefore, the goal of this research was to develop a new and sustainable peeling technology for kiwifruit using IR radiation heating.
A lab scale IR dry-peeling system for kiwifruit was designed and constructed. The system consisted of two major sections including the IR heating and rotating rollers. The rotating kiwifruits (Actinidia deliciosa cv Hayvard) were heated using a ceramic IR element. The effects of IR radiation power (250-850 W), distance between IR emitter and sample (10-70 mm) and heating time (45-125 s) on the peeling performance of kiwifruit were investigated. The lye peeling method including 15% NaOH solution at 95 ͦC for 4 min was selected as a control treatment. The operating parameters of IR peeling were optimized using RSM.
The second-order polynomial models predicted by RSM showed a significant fitting (p 0.1105). The validation experiments were in good agreement with the predicted values by the fitted models. The heating with a power of 446 W at the distance of 70 mm for 125 s were found as the optimum operating conditions for kiwifruit IR peeling. The comparison of the peeling performance of kiwifruit peeled by IR and by lye peeling showed that both the IR and lye peeling could produce a satisfactory peelability (> 90%) and ease of peeling (> 4.5) for kiwifruit. The IR peeled kiwi had significantly low weight loss (4.5% vs. 11.7%), surface temperature (64.1 ͦC vs. 95 ͦC) and color difference (2.4 vs. 11.4) and high firmness (57.5 N vs. 40 N) compared to lye peeled treatment. Because the dry-peeling is a chemical- and water- free process, residuals of kiwifruit skins after IR peeling could be easily utilized as value-added by products. Based on the research results, it is concluded that IR dry-peeling has a promising potential for commercialization. This investigation should also help kiwifruit processing industry in developing the environmentally safe IR peeling technique to produce high quality products from kiwifruit.