| Summary: | Retentate obtained from ultrafiltration was used as a substitute for skim milk powder, in the manufacture of ice cream and cajeta (Mexican dairy spread). The products were assessed by chemical, physical, sensory and structural analysis. Ice creams made using ultrafiltered retentate had increased ash, protein, calcium, phosphorus and magnesium, but reduced lactose, potassium and sodium contents. Physical evaluation showed that UF-products were harder, more viscous and had better melting resistance, but had lower overrun and extrusion temperature than control ice cream. In Sensory analysis UF-products scored better for iciness, sandiness and fluffiness, and resisted heat shock treatment better. No consumer preference for UF-based ice cream or control ice cream was found. The UF-ice cream took longer to soften to eating consistency. Structural examination of ice cream products by various microscopy techniques revealed air cell, ice crystal and fat droplet structures within a sugar and protein matrix. Freeze substitution was applied to ice cream for Transmission Electron Microscopy to produce unique thin sectioned samples. This showed a more agglomerated casein structure than UF-based ice cream. Heat shock changed ice cream structure. Ice crystal size increased and crystals fused into a network. Air cells could be distorted into a modified channel shape. Chemical, physical, microbiological and sensorial analysis of cajeta were carried out. UF-cajeta had slightly higher protein calcium and phosphorous contents and lower lactose, potassium and sodium contents. UF-cajeta showed better sensory attributes after storage than the control, however as shelf life was extended yeast and mould growth was possible. Structural examination of cajeta showed ultrafiltered retentate in cajeta manufacture prevented the formation of larger crystals and prevented sandiness that developed in the control product.
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