Water-soluble pectin films prepared with extracts from Citrus maxima wastes under acidic conditions and their moisturizing characteristics

Waste peel of Citrus maxima was used as raw material to extract pectins with varying degrees of methyl esterification (DM) using aqueous acetic acid (AA) or hydrochloric acid (HCl) at 40 °C and 100 °C. The resulting pectins had DM% values ranging from 39 to 78%. Pectins dissolved in 3% water were cast into a mold, then dried in an oven at 50 °C for a day to make pectin films. These yellowish transparent films had varying crystallinity, which was higher when extracted at 100 °C and lower when extracted at 40 °C. The tensile strength of the films tended to increase with the degree of crystallinity of the pectin film. Water accessibility results showed that higher DM% pectin films had higher contact angle values than lower DM% films, indicating lower water accessibility. The water solubility of the pectin films was determined in water by monitoring changes in the storage modulus ( G ′) of the dynamic viscoelasticity in water over time. As the immersion time increased, G ′ values decreased due to increased solubility. The solubility of the films was determined by measuring the film modulus in water. It was found that films with low crystallinity dissolved in a few seconds, while the dissolution time was longer for films with high crystallinity. In addition, the skin moisturizing properties of the pectin film solution were evaluated by assessing skin cell proliferation and moisturization. All pectins demonstrated good cell affinity, but the pectin with a DM% of 70% exhibited particularly high levels of skin cell proliferation.