HAVE YOU TRIED COATING ON FREEZE-DRIED PRODUCTS ?

Researchers and food industries are in search of methods to preserve their nutritional qualities and organoleptic properties and dehydrating foods through freeze-drying results in high-value products [1]. Nowadays, food industries use pre-treatments to enhance the quality of dried food products. Many of the fruits that are freeze-dried retain their flavor and color excellently and also have a high capacity for rehydration such as strawberries [2]. But this high capacity of rehydration can limit their use in liquid carriers because of the texture collapse.  

Therefore, in such circumstances, freeze-dried products need to be coated with suitable material to decrease the rate of rehydration to preserve the good taste of products. Consequently, there has been a continuous development of edible coating applications used as pre-treatment for freeze-drying vegetables and fruits.

HOW DO THE EDIBLE COATINGS WORK?

Edible coatings are usually applied as thin layers on the surface of the product that effectively blocks the solute from entering the food. The fine layer provides an excellent barrier protecting the product from the effects of the environment. The edible coating reduces the diffusion of oxygen into the food resulting in improved nutritional and physicochemical properties [3-5]. Accordingly, the loss of color, aroma, antioxidant and nutritional substances decreases during the process of drying [6].

AGENTS USED AS COATING MATERIAL

Agents used as edible coating are either based on polysaccharides (maltodextrin, modified starch, gums, carboxymethyl cellulose, etc.) and/or proteins (whey, sodium caseinate, gluten, protein isolates, gelatin, etc.). The mechanical strength of edible coating should be good, its sensory properties satisfying, water diffusivity high and its solute diffusivity should be low [7]. According to past research, generally, polysaccharides meet these criteria in a better way than lipid or protein coatings and films alone [8].

EFFECTS OF EDIBLE COATING ON FREEZE-DRIED PRODUCTS

The safety and appearance of freeze-dried foods are improved with the help of edible coating because of their environment-friendly nature. The coatings provide a barrier against gases and moisture that can act on food substances during handling, processing, and storage. It protects freeze-dried food against the atmospheric effects due to moisture and oxygen, abrasion and fragmentation, and microorganisms by incorporating antimicrobial substances.

Other advantages include stabilization of freeze-dried products thereby increasing the shelf life, decreasing packaging waste, and protection from harmful effects of the environment by maintaining food system transfer of carbon dioxide, oxygen, aroma, moisture, and taste compounds. Additionally, some functional ingredients may also be present in coatings such as flavors and nutrients, antioxidants that help to increase the quality, safety, stability, and functionality of freeze-dried food products. The coating material is generally applied either by dipping the vegetables or fruits into it, or spraying or brushing the coating material onto the food substance forming a thin and semi-permeable membrane on the food’s surface. The thin layer helps to the control loss of moisture, suppresses the rate of respiration, and provides other necessary functions.

Coating on freeze-dried products is usually applied in a commercial setting. However, as freeze dryers become affordable for domestic use, you can freeze dry food in the kitchen and try the coating trick mentioned in this article.

References

1. Huang L lue, Zhang M, Mujumdar AS, Sun D feng, Tan G wei, Tang S. Studies on Decreasing Energy Consumption for a Freeze-Drying Process of Apple Slices. Dry Technol. 2009 Aug 18;27(9):938–46.
2. Shishehgarha F, Makhlouf J, Ratti C. Freeze-Drying Characteristics of Strawberries. Dry Technol. 2002 Nov 1;20(1):131–45.
3. Nottagh S, Hesari J, Peighambardoust SH, Rezaei Mokarram R, Jafarizadeh H. Effectiveness of edible coating based on chitosan and Natamycin on biological, physico-chemical and organoleptic attributes of Iranian ultra-filtrated cheese. Biologia (Bratisl). 2019 Nov 1;75:1–7.
4. Sakooei-Vayghan R, Peighambardoust SH, Hesari J, Peressini D. Effects of osmotic dehydration (with and without sonication) and pectin-based coating pretreatments on functional properties and color of hot-air dried apricot cubes. Food Chem. 2020 May 1;311:125978.
5. Silva K de, Garcia C, Amado L, Mauro M. Effects of Edible Coatings on Convective Drying and Characteristics of the Dried Pineapple. Food Bioprocess Technol. 2015 Jul 1;8.
6. Lago-Vanzela ES, do Nascimento P, Fontes EAF, Mauro MA, Kimura M. Edible coatings from native and modified starches retain carotenoids in pumpkin during drying. LWT - Food Sci Technol. 2013 Mar 1;50(2):420–5.
7. Dhall RK. Advances in edible coatings for fresh fruits and vegetables: a review. Crit Rev Food Sci Nutr. 2013;53(5):435–50.
8. Khin M, Zhou W, Perera C. A study of the mass transfer in osmotic dehydration of coated potato cubes. J Food Eng. 2006 Nov 1;77:84–95.