Fluidized bed roasting modifying the microstructure of cocoa nibs and improving cocoa butter quality

Abstract

The extraction of butter from cocoa seeds involves various processing steps that weaken the lipid‐storing cell walls of cocoa cotyledons. Roasting is particularly critical, making cocoa nibs porous and brittle. In this study, the degree of disruption of the microstructure of cocoa nibs, and the quality and aroma profile of cocoa butter, were evaluated using two roasting techniques, forced convective oven, and fluidized bed. Fluidized bed roasting, recognized for its energy efficiency and low‐carbon footprint, was 12 times faster than oven roasting. This technique allowed a rapid release of steam when parenchyma cell walls were still in a glassy state, while oven roasting caused gradual physical modification allowing the cell wall to become more elastic. Consequently, small pores expanded and coalesced to produce larger pores. X‐ray tomographic analysis showed a total porosity in unroasted cocoa nibs of 8.5 ± 2.0% (vol/vol), which was doubled upon oven roasting and triplicated upon fluidized bed roasting. The higher porosity in fluidized‐bed‐roasted nibs was reflected in the lowest densities and highest cocoa butter yield. Cocoa butter obtained from fluidized‐bed roasted cocoa showed a higher presence of pyrazines and 3‐methylbutanal, and a lower concentration of hydroperoxides, thus enhancing the chocolate flavor and quality. In this paper, we proved that the pore structure of cocoa nibs is a key quality descriptor of roasting processing, and we concluded by quality considerations that fluidized bed roasting technique should be preferred for cocoa nibs roasting over conventional roasting.

Fluidized-Bed-Roasted Cocoa Has Different Chemical Characteristics than Conventionally Roasted Cocoa

“…In other words, the balance between the release and the degradation of Leu, Phe, and Val was in favor of the degradation under the fluidized bed technique, probably toward the formation of MR products such as volatile organic compounds. This hypothesis is supported by our previous studies, , which reported higher formation of pyrazines by the fluidized bed technique than by traditional oven roasting.…”

“…In contrast, oven roasting is mainly based on conductive heat transfer from the metallic surface of the trays, thus resembling the traditional cocoa roasting. In our previous studies, , we found that the heat transfer efficiency of fluidized bed roasting reduced the roasting time by a factor of 12 compared to traditional roasting. As a consequence, fluidized bed roasting led to (i) a higher porosity, thus suggesting a deeper heat penetration within cocoa nibs and (ii) a lower reduction in water activity, which favored the formation of nitrogen-heterocyclic compounds such as pyrazines.…”

“…The roasting process of sieved cocoa nibs in a fluidized bed roaster and a convective oven was performed as described in our previous study. 23 Briefly, samples of cocoa nibs (70 g) were roasted in a preheated electric fluidized bed coffee roaster (Toper Optical Roaster, Izmir, Turkey) at 120 and 140 °C for 6 min and 27 s, and 3 min and 43 s, respectively. This study refers to this technique as fast roasting or FR.…”

“…A defatting procedure with organic solvent was performed to obtain cocoa powder (CP) (defatted ground cocoa nibs), as described in our previous study. 23 Briefly, cocoa nibs were twice ground using a screw juicer (Vital Max Oscar 900, Hurom, Korea). Ground cocoa (100 g) was defatted with petroleum ether (4 × 200 mL).…”

“…In our previous studies, , we found that the heat transfer efficiency of fluidized bed roasting reduced the roasting time by a factor of 12 compared to traditional roasting. As a consequence, fluidized bed roasting led to (i) a higher porosity, thus suggesting a deeper heat penetration within cocoa nibs and (ii) a lower reduction in water activity, which favored the formation of nitrogen-heterocyclic compounds such as pyrazines. The changes in the chemical composition that fluidized bed roasting causes to the precursors and the MR products in cocoa deserve investigation.…”