Effects of compound additives on the physicochemical properties oflow-temperature spray drying Lonicera edulis powder

This study aims to improve the quality of spray-drying Lonicera edulis powder. Maltodextrin, β-cyclodextrin and whey protein were used as the compound additives. A systematic investigation was implemented to clarify the effects of compound additives on the physicochemical properties of spray-drying Lonicera edulis powder. The golden split formulation test was designed as a single-factor test. An analysis was made on the effects of low-temperature air inlet temperature (50-90 °C) on anthocyanin retention rate, powder collection rate, and water content of Lonicera edulis powder. The results show that the powder collection rate was as high as 37.96% in the first golden split formulation test, when the mass ratios of maltodextrin and β-cyclodextrin were 85.4% and 14.6% (test point T₄), respectively. There was an increasing trend in the glass transition temperature (T_g), water solubility index, bulk density, L* value, a* value, and color difference ΔE of Lonicera edulis powder, with the increase in the mass ratio of maltodextrin in the feed solution, while the water content, anthocyanin content, and b* value showed a decreasing trend. A comparison was then made on the physicochemical index of each test point in the first golden split. The test point T₄ was selected for the second golden split formulation test; The highest powder collection rate (40.11%) was achieved, when the ratios of maltodextrin, β-cyclodextrin and whey protein were 72.9%, 12.5%, and 14.6% (test point E₄), respectively. The contents of water and anthocyanin tended to increase in the prepared Lonicera edulis powder, with an increase in the proportion of whey protein in the feed solution, while there was a decrease in the glass transition temperature (T_g), water solubility index, L* value, a* value, b* value and color difference ΔE. A comparison was also made on the physicochemical indexes of single additive T₆ (maltodextrin mass ratio of 100%), T₇ (β-cyclodextrin mass ratio of 100%), E₇ (whey protein mass ratio of 100%), the best composite additives T₄ (in the first golden section), and E₄ (in the second golden section) test points. The composite additives significantly improved the powder collection rate of Lonicera edulis powder via a synergistic effect (P<0.05). The physical and chemical indexes (such as water content, water solubility index, and bulk density) were all close to the optimum level, indicating that the composite additives improved the comprehensive quality of Lonicera edulis powder better than that of a single additive. The additives in the feed solution shared their physical and chemical properties during spray drying and then interacted with each other with the biological activity. The low-temperature spray drying test showed that the powder collection rate and water content were negatively correlated with the increase in inlet air temperature. The test site E₄ presented a high anthocyanin retention rate (89.94%) while maintaining a high powder collection rate at 90^oC. The spectral and proton density images were captured in the Lonicera edulis stock and sample solution at each test site. Additives were added to increase the content of strong bound water, weak bound water and immobile water in the feed and liquid. The freedom of free water was also reduced for the stable hydrate, in order to improve the droplet coalescence resistance, the overall T_g of feed and liquid, and the powder collection rate. The water distribution of the sample solution was much more uniform, while the whole solution was more stable after pretreatment with compound and single additive, which was conducive to the preparation of blue Lonicera edulis powder by spray drying. Fourier transform infrared spectroscopy (FTIR) analysis showed that the compound additives formed the intermolecular hydrogen bonds in Lonicera edulis powder, thus protecting the anthocyanins and other active substances. The findings can provide theoretical support and reference for the production of Lonicera edulis spray drying.