Influence of cryogenic treatment on micro-structural characteristics of some Indian spices: X-ray micro-tomography investigation

Spices are ground cryogenically to retain their thermo-sensitive flavoring compounds, thereby producing a high-quality powder. In the cryogenic grinding process, spices are initially precooled with a cryogen (Liquid nitrogen; LN2) followed by grinding. To simulate and model breakage, fluid, and heat transport phenomena during cryo-grinding an insight of spices micro-structure is required. Thus, the article aims to investigate the effect of cryogenic treatment on micro-structural characteristics of some Indian spices namely black pepper, cinnamon, king chili, and fenugreek. X-ray micro-computed tomography (X-ray μCT) coupled with image analysis was used to observe quantitative parameters along with two- and three-dimensional images of micro-structure of the spices. Dimensional details, color, moisture level, and volatile oil content of the samples were also elaborated in line. The micro-structural changes of cryogenically treated (LN2 dipped) spices were compared with respect to their untreated counterparts. In the treated samples, total pore volume (except for king chili), total sample volume, and total solid volume were relatively higher by 100-526.83%, 5.83-120.90%, and 4.41-120.12%, respectively, along with prominent size distribution of pores. This increase in micro-structural properties of spices has resulted in 2.31-10.45% higher volatile oil extraction yield. Three-dimensional images of micro-structure also supported the inference drawn from the quantitative results. Concurrently, the results confirm the applicability of X-ray μCT as a useful tool to observe micro-structural changes in spices.