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Dry desiccants are hygroscopic that can absorb moisture from environment for both physical (for example: Silica Gel) and chemical adsorption (for example: Calcium Chloride). This enable the relative humidity in the headspace of sealed pack to be reduced (Gaikwad et al., 2018). For packaged dried food applications, desiccants are typically placed in tear-resistant permeable plastic sachets. Other than packaged dry food, moisture-drip absorbent pads, sheets and blankets are often used for high water activity (aw) foods such as meats, fish, poultry, fruit and vegetables (Dobrucka & Cierpiszewski, 2014).
These moisture absorbers exist in the forms of powder, granules, beads, blocks that are typically packed in a porous sachet or bag. Silica gel, dry sorbitol, xylitol, sodium chloride, potassium chloride, and calcium chloride are the most common absorbing materials used in the sachets form (Gaikwad et al., 2018). For dual-action devices, sachets also may contain activated carbon for odour adsorption or iron powder for oxygen scavenging (Batt & Tortorello, 2014).
Silica gel is the most commercial and common desiccant used in food and nonfood products. Desiccants made of silica gel can absorb up to 35% of their weight in water. It removes moisture by a physical adsorption mechanism that can be reversible through temperature change (Batt & Tortorello, 2014). Silica gel is used to maintain dry conditions within packages of dry foods, down to below aw of 0.2. Silica gel is inert and is produced in hard forms such as granules which have the specific round shape, transparent and dry structure (Amarakoon & Navaratne, 2017).
There are two types of silica gel: indicating silica gel and non-indicating silica gel.
Non-Indicating Silica Gel
Indicating Silica Gel
Widely used in food industry as a desiccant and is approved safe by USFDA
Contains cobalt chloride as the colour indicator (Salt of the heavy metal Cobalt)
Color changes from blue to pink as the desiccant becomes saturated which is visually warns users of the need for replacement
Not used in contact with food products as it includes heavy metal cobalt
A safe, cobalt chloride free organic indicator which displays an orange/yellow colour when active, and changes to green when the desiccant becomes saturated
Suitable for using with food or pharmaceutical products
Source: Amarakoon & Navaratne, 2017; Humi Pak, n. d.
Silica Gel Sachets Applications
Source: Plastic Bags New Zealand (n. d).
Amarakoon, S., & Navaratne, S. (2017). Evaluation of the Effectiveness of Silica Gel Desiccant in Improving the Keeping Quality of Rice Crackers. International Journal Of Science And Research (IJSR), 6(1), 2163-2168. https://doi.org/10.21275/art2017538
Batt, C., & Tortorello, M. (2014). Encyclopedia of food microbiology (2nd ed., p. 1002). Poland: Academic Press.
Dobrucka, R., & Cierpiszewski, R. (2014). Active and Intelligent Packaging Food – Research and Development – A Review. Polish Journal Of Food And Nutrition Sciences, 64(1), 7-15. https://doi.org/10.2478/v10222-012-0091-3
Gaikwad, K., Singh, S., & Ajji, A. (2018). Moisture absorbers for food packaging applications. Environmental Chemistry Letters. https://doi.org/10.1007/s10311-018-0810-z
Humi Pak. (n. d). Silica Gel.
Plastic Bags New Zealand. (n. d). Silica Gel |Silica Gel Uses | Silica Gel Sachet.