Crystal size, a key character of lactose crystallization affecting microstructure, surface chemistry and reconstitution of milk powder

Lactose crystallization during storage deteriorates reconstitution performance of milk powders, but the relationship between lactose crystallization and reconstitution is inexplicit. The objective of this study is to characterize crystalline lactose in the context of formulation and elucidate the complex relationship between lactose crystallization and powder functionality. Lactose in Skim Milk Powder (SMP), Whole Milk Powder (WMP) and Fat-Filled Milk Powder (FFMP) stored under 23%, 53% and 75% Relative Humidity (RH) at 25℃ for four months was compared. Lactose, surface chemistry and microstructure of FFMP stored at 25℃ and 40℃ at 23% to 75% RH for four months were also analyzed and interpreted. At the same RH, FFMP crystallized in the same pattern as WMP. At 53% RH, FFMP and WMP differentiated from SMP in terms of lactose morphology as well as the ratio between anhydrous α-lactose and anhydrous β-lactose. Lactose remained amorphous at 23% RH, crystallized predominantly to α/β-lactose (1:4) at 40 to 58% RH and to α-lactose monohydrate at 75% RH. The crystallinity index was similar for all powders containing crystalline lactose. The estimated crystallite size increased from approx. 0.1 to 20 µm with increasing RH and temperature. When amorphous lactose crystallized into crystals below approx. 0.1 µm at 25°C and 43% RH, the microstructure and surface lipid were comparable to that of the reference powder. This powder reconstituted into a stable suspension system comparable to that of reference (well performing) powders. These results demonstrate that crystallite size is the key property linking lactose crystallization and reconstitution. Our finding thus indicates limiting crystallite size is important for maintaining desired product quality

A Complex Dance: The Importance of Glycosaminoglycans and Zinc in the Aggregation of Human Prolactin

The zinc binding hormone pituitary human prolactin (hPRL) is stored in secretory granules of specialized cells in an aggregated form. Glycosaminoglycans (GAGs) are anionic polysaccharides commonly associated with secretory granules, indicating their involvement in granule formation. Here we, for the first time, study the impact of GAGs in combination with Zn²⁺ on the reversible hPRL aggregation across the pH range of 7.4–5.5. Zn²⁺ alone causes hPRL aggregation at pH 7.4, while aggregation between pH 7.4 and 5.5 requires both Zn²⁺ and GAGs. GAGs alone cause hPRL aggregation below pH 5.5. Comprehensive thermal stability investigations show that hPRL is particularly destabilized toward thermal denaturation at pH 5.5 and that GAGs increasingly destabilize hPRL at decreasing pH values. We propose that Zn²⁺ causes hPRL aggregation through low-affinity Zn²⁺ binding sites on hPRL with GAGs facilitating Zn²⁺ binding by neutralizing repulsive positive charges of hPRL in the acidic environments of the TGN and mature secretory granules. In a manner independent of the aggregation-causing agent(s), the different hPRL aggregates show very similar secondary structure and amorphous morphology. We speculate that this may be a recognizable sorting signal in the formation of hPRL granular vesicles

Metabolite Profiling of the Social Spider Stegodyphus dumicola Along a Climate Gradient

Animals experience climatic variation in their natural habitats, which may lead to variation in phenotypic responses among populations through local adaptation or phenotypic plasticity. In ectotherm arthropods, the expression of thermoprotective metabolites such as free amino acids, sugars, and polyols, in response to temperature stress, may facilitate temperature tolerance by regulating cellular homeostasis. If populations experience differences in temperatures, individuals may exhibit population-specific metabolite profiles through differential accumulation of metabolites that facilitate thermal tolerance. Such thermoprotective metabolites may originate from the animals themselves or from their associated microbiome, and hence microbial symbionts may contribute to shape the thermal niche of their host. The social spider Stegodyphus dumicola has extremely low genetic diversity, yet it occupies a relatively broad temperature range occurring across multiple climate zones in Southern Africa. We investigated whether the metabolome, including thermoprotective metabolites, differs between populations, and whether population genetic structure or the spider microbiome may explain potential differences. To address these questions, we assessed metabolite profiles, phylogenetic relationships, and microbiomes in three natural populations along a temperature gradient. The spider microbiomes in three genetically distinct populations of S. dumicola showed no significant population-specific pattern, and none of its dominating genera (Borrelia, Diplorickettsia, and Mycoplasma) are known to facilitate thermal tolerance in hosts. These results do not support a role of the microbiome in shaping the thermal niche of S. dumicola. Metabolite profiles of the three spider populations were significantly different. The variation was driven by multiple metabolites that can be linked to temperature stress (e.g., lactate, succinate, or xanthine) and thermal tolerance (e.g., polyols, trehalose, or glycerol): these metabolites had higher relative abundance in spiders from the hottest geographic region. These distinct metabolite profiles are consistent with a potential role of the metabolome in temperature response

Protein content of model synovial fluid and CoCrMo wear

Wear of cobalt chromium molybdenum alloy in a reciprocating ball-on-plate test was measured for a series of model synovial fluid samples, where the effect of protein and phospholipid content was examined. The protein content (albumin and γ-globulin) was varied to replicate a range of healthy and diseased SF pathologies. The results showed reduced wear was strongly correlated with increasing protein content. The effect of phospholipid addition on wear was more complex. Limited evidence suggested phospholipids reduced wear for a high albumin/γ-globulin ratio (A/G) but increased wear for low A/G ratios. Post-test examination showed thick (~μm) insoluble “gel-like” films were deposited in, and around, the wear scar. Micro Infrared Reflection Absorption Spectroscopy analysis indicated the films were predominately denatured β-sheet proteins although in some cases lipids were also present. Similar films were found in tests with human synovial fluid samples. Scanning Electron Microscopy imaging showed an aggregated fibril “rope” structure typical of non-native β-sheet proteins. The gel film is a protein-rich viscous phase which is entrained intermittently to form a lubrication film which contributes to surface protection and reduction of wear. We also suggest the formation of gel deposits is comparable to the “boosted” lubrication model of proposed by Professor Duncan Dowson for articular cartilage. In the boosted model high-viscosity, concentrated protein films are formed in depressions on the cartilage surface. The tests indicate the chemistry of human synovial fluid, particularly the protein content, could affect CoCrMo wear and therefore the risk of implant failure