Use of a time-to-failure model to evaluate the shelf-life of freeze-dried, carrot juice-fortified apples stored under controlled conditions

The consumption of β-carotene has been shown to offer several health benefits, including a reduced risk of diseases such as cancer, a bolstered immune system, and protection against age-related eye degeneration. However, modern lifestyles often hinder the intake of this essential nutrient due to the increasing consumption of processed foods for convenience. Dehydrated foods provide an alternative option as they are convenient, possess a long shelf-life, and retain many of their nutrients. The aim of this study was to enhance the total carotenoid (TC) content in Pink Lady apples through vacuum-impregnation with carrot juice at various concentrations (20, 30, 40, and 50° Brix) and to determine the shelf-life of the treated apples after freeze-drying. The highest TC concentration (12.30±0.48 mg β-carotene/100 g) and minimal shrinkage were achieved using 20° Brix juice (20BJ). The freeze-drying of vacuum-impregnated apples with 20BJ reduced the time to reach equilibrium compared to fresh apples. The shelf-life of the freeze-dried impregnated samples was examined using time-to-fail (TTF) models under various conditions, including package permeability (P=2.17×10^-15 and 1.04×10^-6 g / s Pa m), temperature (T=15, 25, and 35 °C), and relative humidity (H=0, 35, and 75%). The TTF predictions indicate a shelf-life exceeding 105 days for P=1.04×10^-6 g/ s Pa m evaluated at H<35%. Consumers preferred the impregnated freeze-dried apples with intermediate hardness textures (above 18.14N) and TC>0.81 mg β-carotene/100 g when stored at H=35% and T=15°C. The model predicts the time when the TC value of 100 g of the sample does not provide the minimum recommended daily intake of β-carotene for an adult. Optimal storage conditions were at intermediate H and low temperatures. These findings demonstrate the effectiveness of vacuum impregnation with carrot juice and freeze-drying as methods to enhance the nutritional value and shelf-life of apples.