Storage stability of spray-dried Lacticaseibacilleus rhamnosus GG microcapsules coated by wood hemicelluloses

Lacticaseibacilleus rhamnosus GG (LGG), a type of probiotic strain mainly used in dairy products, is recognized for its health benefits when consumed. Storage stability, an important determinant of LGG viability, is mainly influenced by external conditions such as relative humidity (RH), water activity (aw), and temperature. In the previous study conducted by Suutari (unpublished), the applicability of wood hemicelluloses as wall materials to protect LGG from heat-induced stress during spray drying was investigated, yielding a survival rate and probiotic count higher than 90% and 106 cfu/g, respectively. High moisture content observed in the LGG microcapsules after spray drying would serve as a limiting factor, hence the need for the investigation of storage stability for LGG microcapsules. In this research, the storage stability of LGG microcapsule powders coated by glucuronoxylan (GX) and galactoglucomannans (GGM) at 22 oC (11, 33, 55, and 75% RH) and 4 oC were assessed and compared to that of gum arabic (GA) over a period of two months. The moisture sorption of the spray-dried microcapsules was determined, followed by the viability of the stored microcapsules, which was evaluated during each storage period in addition to the powder properties, such as particle size, aw, and morphology. The results indicated that GGM and GX exhibited higher equilibrium moisture content than GA. Storage viability results of the LGG microcapsules showed that all LGG microcapsules stored at 11% RH exhibited the highest viability (>106 cfu/g) and were the most stable out of all the storage conditions, followed by those stored at 4 oC. GX exhibited the most viability during storage, even at 55 and 75% RH, which were regarded as harsh storage conditions. The aw levels in the LGG microcapsules displayed an inverse relationship with storage viability; as aw increased, the viability of the microcapsules decreased. Physical characterization of all LGG microcapsules stored at 22 oC (11, 33, and 55% RH) and 4 oC showed no significant difference in terms of particle sizes and morphology, while the LGG microcapsules stored at 22 oC (75% RH) displayed distinct differences, yielding multiple peaks in their particle size distributions, large particle size, and agglomerations during storage. All LGG microcapsules remained amorphous throughout the storage period.