Preparation and some physicochemical properties of freeze-dried vegetables carving

Freeze-drying is a very gentle dehydration method to preserve the highest quality and give the final product a longer shelf-life, based on the principle of removing the ice by sublimation. This research aimed to study freeze-dried manufacturing processes of vegetable carving for application in the foodservice industry. Plant materials used in this study were pumpkin, carrot and Chinese radish which were carved into a rose shape. To prepare, all carved-rose vegetables were dipped in 1.0% CaCl2 solution as a firming agent for 5 mins before freeze-dried operations at the temperature of –50°C under vacuum (~30 Pa) for 50 hrs. Dyeing operation was conducted specifically in carved-rose Chinese radish using pink (0.05 and 0.1%) and red (0.05 and 0.1%) food-grade colour after pretreatment with CaCl2 . The results showed that dried carved-rose vegetables had low water activity (0.32-0.42) and moisture content (8.01-11.44%). The physical properties of freeze-dried pumpkin and carrot carving were firmed and presented a spongy texture with small bubbles spread continuously throughout the piece which helps protect the structural collapse. However, carved-rose radish had a slight shrinkage but it was restored as fresh after immersing in water. Rehydration time was 5 mins for pumpkin and carrot, and 10 mins for Chinese radish which showed remarkable that firm-liked fresh vegetables. Then, freeze-dried vegetables were packed in an aluminum bag filled with nitrogen gas and kept at 25±1°C for 2-months storage. The sensory characteristics evaluated by specialists were ranged in the medium to very like throughout the storage periods. Thus, freeze-dried carved-rose vegetable seems to be very interesting, moreover, conduction on a larger scale for the foodservice industry was particularly noticeable.