A study of variables affecting carbonyl retention in model systems and bermuda onion juice during lyophilization

Abstract

Information leading to the improvement and understanding of volatile retention during lyophilization was developed. This was accomplished by studying the effects of selected process variables on retention of carbonyl components in model carbohydrate-pyruvic acid systems and in Bermuda onion juice. Variables studied were carbohydrate type, concentration, and mixtures. Other variables considered were freezing temperature and sample thickness. Data were interpreted by theoretical predictions of freezing rate, drying rate, and ice cell diameter. The validity and usefulness of current volatile retention theories was explored. The effect of concentration of sucrose, lactose, and glucose on carbonyl retention during freeze-drying was studied. Increases in carbohydrate concentration increased retention both in model systems and onion juice. Increases in retention were greater at low carbohydrate concentration (5 to 10%) than at high concentrations (15 to 20%). Differences in retention between carbohydrates were found in model systems but not in onion juice. In model systems, sucrose retained more pyruvic acid than lactose. Glucose retained the least carbonyl. The same trend was apparent at low carbohydrate levels in onion juice (5 to 10%) but not at high concentrations (15 to 20%). ...