Browsing by Subject "VOC"

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Process development for spray drying of aroma rich herbs and spices : challenges, strategies and experimental results
(2025) Heimbach, Julia; Kohlus, Reinhard
Conventional air drying of herbs and spices is associated with a loss of quality due to degradation reactions that occur during the process. Spray drying was introduced to the processing of herbs and spices to evaluate the suitability of this method in an attempt to create a dried product of improved quality. Basil and ginger were used as model systems. Different options for the conversion of the frozen raw material into an atomisable feed liquid were reviewed. For basil, milling with a mincer with subsequent particle removal by a screw press gave the best results. Rapid and oxygen-free processing was crucial to prevent the development of bitterness. Ginger was juiced and subjected to a split-stream process, where the ginger fibres were dried and milled separately before being reintroduced to the juice as drying aid to prevent stickiness. The resulting feed material was dried in a pilot plant spray dryer and the effect of process parameters on volatile retention was investigated. Increasing air inlet temperature and decreasing air outlet temperature enhanced essential oil retention for both systems. In addition, large particle sizes and short residence times improved retention when drying basil. The dry matter content of the feed material was identified as key factor for volatile retention in all systems studied. Additional approaches to improve volatile retention were explored using a maltodextrin-linalool model system. The aim was to reduce the volatile partial pressure gradient between the atmosphere and the droplet in order to reduce volatile transition. While the use of zeolite for selective dehumidification and volatile enrichment did not show the desired effect, elevating the condenser temperature and increasing linalool loading of the feed proved to be effective. A relationship was found between volatile organic compound content in the atmosphere and volatile retention in the powder. The experimental results obtained were used to assess the accuracy of a retention prediction model based on the selective diffusion theory. Good estimates were obtained for linalool- and methanol-maltodextrin systems. The linalool model was transferred to basil material to test the prediction quality in a highly heterogeneous food material, which was successfully represented. Analysis of the influence of process parameters on the retention model emphasized the significance of particle size in maximising retention. This work highlights the challenges of processing and spray drying aromatic herbs and spices. While the process without carrier it is not an alternative to conventional drying, the addition of encapsulation material significantly improves the result.