Clustering function and minimum change in spreading pressure as key factor to predict storage conditions for black pepper oleoresin encapsulated by spray drying

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Black pepper oleoresin was encapsulated by spray drying using gum arabic (GA) and whey protein concentrate (WPC) as wall materials. The physical surface features were examined using low-temperature adsorption of nitrogen at 77 K. Clustering function and spreading pressure were evaluated to predict optimal storage conditions of the microcapsules, through analyzing the data from the water adsorption isotherms determined using a gravimetric method at 25, 35, and 45 °C. Kinetic studies of the color changes and loss of piperine of the microcapsules stored at different water activities at 35 °C were carried out. It was found that the GAB, BET and Condon models adequately describe the sorption characteristics. The monolayers calculated with the clustering function and minimum change in spreading pressure (MCSP) were close to those obtained by the adsorption models. The isotherms local from the Condon model coincided with the levels of stability of the microcapsules. Two local isotherms were found for GA microcapsules, which exhibited two regions of chemical stability during storage. One region with high stability in the range of 0.108–0.515 aw, and the other with poor stability of 0.515–0.821 aw. Conversely, WPC microcapsules showed one isotherm local, which had high stability in the entire water activity range studied. For both microcapsules, the lowest values of color changes were of 1.5–4, while the degradation rate constants were −0.017 day−1 and -0.002 day−1 for GA and WPC, respectively. The water activities where occurred the optimal stability fall within of the MCSP zone.