Effect of production site, storage duration, and hot water and molybdenum dips on bioactive compounds with antioxidant properties in lemon flavedo during cold storage

Abstract

Certain bioactive compounds, such as vitamin E (α-tocopherol), vitamin C (ascorbic acid), β-carotene, polyphenols (e.g. flavonoids and flavonones, viz. hesperidin and naringin) have antioxidant properties and their presence in the citrus flavedo plays a significant role in mitigating oxidative stress, which could possibly result in chilling injury during cold storage. The purpose of this investigation was, therefore, to alter the concentration of these bioactive compounds in lemon flavedo using hot water and molybdenum (Mo) treatments prior to cold storage to allow fruit to withstand such storage, and avoid the occurrence of chilling injury. Fruit from three sources (Ukulinga Farm, Sun Valley and Eston Estates) were treated for 2 min with hot water dips (HWD) (at 47 °C or 53 °C) with or without a subsequent soaking in 1 or 10 μM Na₂MoO₄ for 30 min. Fruit were then stored at −0.5 °C for up to 7, 14, 21 or 28 d and thereafter moved to room temperature (±21 °C and ±68% RH) for 7 d. Lemon fruit from Sun Valley Estates were chilling-susceptible and had the lowest concentration of bioactive compounds, significantly lower than chilling-resistant fruit from Ukulinga Farm. Application of HWD at 53 °C, as well as 1 μM Mo in combination with HWD at 53 °C, enhanced the flavedo concentration of bioactive compounds. Furthermore, storage duration seemed to induce an increase or decrease in flavedo bioactive compounds concentration. In general, HWD and Mo dips enhance the rind concentration of phenolics and ascorbic acid at specific storage times.

Keywords: β-carotene, chilling injury, Citrus limon, phytosanitary requirement, polyphenols, vitamin C, vitamin E

South African Journal of Plant and Soil 2014, 31(4): 203–212