Effects of major drying methods on the stability and retention of vitamin C, B group vitamins, fat-soluble vitamins, and carotenoids in kiwifruits

This study investigates the effects of five drying methods—freeze, vacuum, microwave, convective, and natural—on the nutritional and visual quality of kiwifruit, focusing on the vitamin C, B-group vitamins, fat-soluble vitamins, and carotenoids. Fresh samples contained 5.57 mg/g ascorbic acid, and freeze drying retained the highest level (3.13 mg/g), followed by vacuum drying (2.63 mg/g), while natural and convective drying resulted in severe reductions (1.06 and 1.21 mg/g). Riboflavin, initially 1.59 μg/g, decreased to 0.91 μg/g after freeze drying, 0.82 μg/g after vacuum drying, and 0.54 μg/g under natural drying. Carotenoids followed similar trends, with β-carotene declining from 2.88 μg/g in fresh samples to 2.24 μg/g after freeze drying and below 1 μg/g with natural drying. Freeze and vacuum drying best preserved vitamin content and color by minimizing oxidation and thermal damage, whereas natural and convective drying led to greater losses due to prolonged heat exposure and oxidative stress. Color changes strongly correlated with nutrient degradation. Notably, ΔE was negatively associated with ascorbic acid (−0.96) and thiamine (−0.95), while hue angle correlated positively with carotenoids and fat-soluble vitamins. These results show that color parameters reliably indicate nutritional retention, offering a practical approach for quality assessment in dried fruits.