Amorphous Ascorbic Acid Degradation in PVP Solid Dispersions and the Effects of Water and Pre-Lyophilization Solution pH on its Chemical Stability
Abstract
Ascorbic acid (vitamin C) is an essential micronutrient found both naturally in foods as well as supplemented in fortified foods and dietary supplements. In foods, ascorbic acid typically exists in the aqueous or crystalline solid state, but the lyophilization of ascorbic acid polymer solutions has been proven to render ascorbic acid into the amorphous solid state. This study investigated the importance of two matrix effects – the weight ratio of ascorbic acid to PVP and the pre-lyophilization solution pH – on the chemical degradation of ascorbic acid in the amorphous solid state. Amorphous ascorbic acid was generated via lyophilization with PVP and stored at several controlled temperature conditions and 11% relative humidity. Low pH lyophiles (pH 3.0 and pH 3.5) displayed strongly non-additive moisture sorption behavior while higher pH lyophiles (pH 4.0 and pH 4.5) displayed additive moisture sorption. Changes in the pre-lyophilization solution pH caused up to four-fold increases in the extent of ascorbic acid degradation in lyophiles in spite of similar glass transition temperatures and equal relative humidity storage conditions. Modification of the weight ratio of ascorbic acid to PVP caused over six-fold increases in loss of ascorbic acid during storage. Recrystallized ascorbic acid dispersions showed no significant differences in loss during storage regardless of weight ratio, supporting the importance of the physical state of small molecules on their chemical stability. Given the large differences in chemical stability caused by ascorbic acid to PVP weight ratio and pre-lyophilization solution pH, these two matrix effects should be considered important factors in the chemical stability of small molecules in amorphous solid dispersions.
Degree
M.S.
Advisors
Mauer, Purdue University.
Subject Area
Food Science|Chemistry|Materials science
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