EFFECT OF HEAT TREATMENTS ON THE CONTROL OF DISEASE INCIDENCE AND CHEMICAL COMPOSITION OF STORED CARROT (Daucus carota L.) SAMPLES

Abstract

This study was carried out to investigate the effect of hot water and steam treatment on disease incidence, chemical composition and weight loss of carrots after storage for 35 days. Mature and healthy carrots of imperator variety were disinfected with 10% sodium hypochlorite solution for 10 minutes. The disinfected carrots were treated separately with hot water (HW) and steam (ST) at 45, 50, 55 and 60ºC for 2, 4, 6 and 8 minutes respectively while the untreated carrots served as control. The treated and untreated carrots samples were then stored in sterile plastic containers at 26 ± 2ᵒC and 90 – 95% relative humidity (RH) for 35 days. The stored samples were been observed daily for disease incidence. At day 35 of storage, carrots treated with HW at 45ºC for 2minutes and ST treated carrots at 60ºC for 4 and 8 minutes recorded 20% disease incidence while steam treated carrots at 50ºC for 8 minutes had no observable disease incidence. Reduction in nutritional parameters (Vitamin A, C and β- carotene) and weight loss was observed in the treated carrot samples stored at 45ᵒC for 2 minutes, 50ᵒC for 8 minutes, 60ᵒC for 4 and 8 minutes respectively. Steam treated carrot samples at 50ᵒC for 8 minutes, at 60ᵒC for 4 minutes,and 60ᵒC for 8 minutes had the highest loss of Vitamin A (943.14μg/g), Vitamin C (0.91mg/g) and β- carotene ( 269μg/100g) respectively, compared with the control with 10551μg/100g (Vitamin A), 0.57mg/g (Vitamin C) and 336.67μg/g (β- carotene). Untreated carrot samples had the highest weight loss (42.71%) compared with the weight of carrot samples treated at 60ºC for 4 minutes (6.56%). Hot water treatment at 45ᵒC for 2 minutes, and steam treatment at 60ᵒC for 8 minutes proved to be most effective and could be applied for non- chemical prestorage treatment of carrots. In conclusion, Hot water and steam treatment had profound effect on reduction of disease incidence, and nutritional composition of carrot samples during and after storage.