Use this URL to cite or link to this record in EThOS:
Title: Stability of selected water-soluble vitamins in model systems.
Author: Pacquette, Connie L.
ISNI:       0000 0001 3462 7395
Awarding Body: South Bank University
Current Institution: London South Bank University
Date of Award: 1998
Availability of Full Text:
Access from EThOS:
The potential for regulated additions of L-ascorbic acid, thiamine, and riboflavin to assist in maintaining vitamin stability when each formed part of a multivitamin system was investigated in aqueous solutions. Screening studies were performed to identify major factors that accelerated vitamin loss during aerobic storage at ambient temperature. These showed L-ascorbic acid to be destabilised by cupric ion. Light (at 339 lux) was further shown to affect the influence of cupric ion on Lascorbic acid, whereby the catalytic activity of cupric ion at trace levels (0.5 ppm) appeared to be concealed by the effect of light. Riboflavin degradation, by contrast, resulted directly from the presence of light. Neither cupric ion nor light affected the stability of thiamine. However, a change in pH from acidity (pH 3-6) to neutrality (pH 7) caused a marked decline in thiamine stability. L-Ascorbic acid was more prone to degradation at pH close to its primary pKa value. However, there was no apparent relationship between riboflavin degradation and pH. Investigations of between-vitamin influences showed riboflavin to accelerate Lascorbic acid loss. This effect was apparent whether or not light was present. However, L-ascorbic acid destabilised riboflavin only in the absence of cupric ion and light. To optimise multivitamin stability, study was made under acid conditions in various types of citrate systems with cupric ion and light absent and under reduced levels of oxygen. Input variables included the levels of vitamin additions and pH. Using response-surface methodology, quadratic equations could be fitted adequately to stability data obtained for L-ascorbic acid in citrate-phosphate, citrate-sucrose, and citrate systems and for both thiamine and riboflavin in citrate-phosphate and citrate systems. L-Ascorbic acid and thiamine stability responses (as % residue) were lowered by an increase in pH over the pH 2.6 to 3.0 range in both citrate-phosphate and citrate systems. The stability of riboflavin with pH was maintained solely in the citrate-phosphate system. Within the same system, increased additions of both thiamine and riboflavin improved L-ascorbic acid stability. In citrate, thiamine stability benefited from riboflavin additions only when L-ascorbic acid additions were low. High levels of addition of L-ascorbic acid were also directly responsible for thiamine instability. An improvement in riboflavin stability with L-ascorbic acid additions was observed only with thiamine added at high levels. In citrate-sucrose, L-ascorbic acid was more prone to degradation with an increase in thiamine added level at low pH. Levels of vitamin additions and pH that yield maximum responses in L-ascorbic acid, thiamine, and riboflavin stability have been predicted using the set of conditions given by the quadratic models.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Multivitamins