Paula Allan-Wojtas

Microscopy and other imaging techniques in food structure analysis

Abstract Microscopy and imaging techniques are the most appropriate techniques for evaluating food structure because they are the only analytical methods that produce results in the form of images rather than numbers. However, images may now also be converted into numerical data to allow for statistical evaluation. Advances in microscopy and imaging techniques are made, for the most part, outside the field of food science, drawing from the fields of materials science, biology and medicine. Such techniques cannot, in most cases, be directly applied to study food structure. They must be adapted because the processing conditions that turn biological raw materials into food cause structural and textural changes which, in turn, change the innate properties and behaviour of the foods. This necessitates the development of appropriate methods and also the specialization of researchers. Future developments in this field can be divided into the use of new equipment developed for use in other fields, and the application of techniques modified to solve specific food science problems, such as the development of new foods with particular properties and texture or the detection of defects in foods.

Lipophilic components of the brown seaweed, Ascophyllum nodosum, enhance freezing tolerance in Arabidopsis thaliana

Extracts of the brown seaweed Ascophyllum nodosum enhance plant tolerance against environmental stresses such as drought, salinity, and frost. However, the molecular mechanisms underlying this improved stress tolerance and the nature of the bioactive compounds present in the seaweed extracts that elicits stress tolerance remain largely unknown. We investigated the effect of A. nodosum extracts and its organic sub-fractions on freezing tolerance of Arabidopsis thaliana. Ascophyllum nodosum extracts and its lipophilic fraction significantly increased tolerance to freezing temperatures in in vitro and in vivo assays. Untreated plants exhibited severe chlorosis, tissue damage, and failed to recover from freezing treatments while the extract-treated plants recovered from freezing temperature of −7.5°C in in vitro and −5.5°C in in vivo assays. Electrolyte leakage measurements revealed that the LT50 value was lowered by 3°C while cell viability staining demonstrated a 30–40% reduction in area of damaged tissue in extract treated plants as compared to water controls. Moreover, histological observations of leaf sections revealed that extracts have a significant effect on maintaining membrane integrity during freezing stress. Treated plants exhibited 70% less chlorophyll damage during freezing recovery as compared to the controls, and this correlated with reduced expression of the chlorphyllase genes AtCHL1 and AtCHL2. Further, the A. nodosum extract treatment modulated the expression of the cold response genes, COR15A, RD29A, and CBF3, resulting in enhanced tolerance to freezing temperatures. More than 2.6-fold increase in expression of RD29A, 1.8-fold increase of CBF3 and two-fold increase in the transcript level of COR15A was observed in plants treated with lipophilic fraction of A. nodosum at −2°C. Taken together, the results suggest that chemical components in A. nodosum extracts protect membrane integrity and affect the expression of stress response genes leading to freezing stress tolerance in A. thaliana.

Effect of process variables on particle size and viability of Bifidobacterium lactis Bb-12 in genipin-gelatin microspheres

Gelatin microspheres cross-linked with genipin were developed to encapsulate the probiotic Bifidobacterium lactis Bb-12 The effects of different gelatin concentrations (10–19% w/v), bloom strengths (175 and 300), surfactants, stirring rates during emulsion formation and genipin concentrations (0–10 mM) on the microsphere sizes and viability of bacterial cells were investigated. Principal Component Analysis revealed microsphere size distribution differed depending on the presence or absence of surfactants as well as a trend of increasing micropshere size with increasing gelatin concentration and bloom strength. Lower stirring rates resulted in larger microspheres with higher encapsulation yields of bifidobacteria Microsphere size and cell viability were not significantly (p < 0.05) influenced by increasing genipin concentrations up to 10 mM whereas microsphere stability in simulated gastric juice increased with increasing genipin concentration. The encapsulation yields were higher in 175 bloom strength gelatin microspheres than in 300. Cold-stage scanning electron microscopy showed encapsulated bacteria distributed throughout the genipin cross-linked gelatin matrix.

Microencapsulation in genipin cross-linked gelatine-maltodextrin improves survival of Bifidobacterium adolescentis during exposure to in vitro gastrointestinal conditions

To improve survival during exposure to adverse conditions, probiotic Bifidobacterium adolescentis 15703T cells were encapsulated in novel mono-core and multi-core phase-separated gelatine-maltodextrin (GMD) microspheres where the gelatine (G) phase was cross-linked with genipin (GP). Microscopy showed that encapsulated cells were exclusively associated with maltodextrin (MD) core(s). Small (average diameter 37 µm) and large (70 µm) GMD and G microspheres were produced by modulating factors (e.g. mixing speed, surfactant, GP and G concentrations) affecting the size, structural stability and phase-separation. In vitro sequential gastro-intestinal (GI) juice challenge experiments revealed increased survival of cells encapsulated in GMD (∼106–7 cfu mL−1) and G (∼105 cfu mL−1) microspheres as compared to free cells (∼104 cfu mL−1). In GMD microspheres, the bacteria derive energy from MD to survive during exposure to acid and bile salts. In conclusion, the novel food grade GMD microencapsulation formulation was shown to protect probiotic bifidobacteria from adverse conditions.