Dr Sean Hogan is a research officer at Teagasc Food Research Centre, Moorepark. He has a PhD in Food Chemistry from University College Dublin. He was employed as a Post-Doctoral Researcher in University College Cork before joining Teagasc in 2007. His research interests include ingredient interactions, spray drying, powder technology and rheology.
Development of high-protein bars as vehicles for delivery of functional ingredients
Hogan, S.A.1, Hunt, K2. Potes, N.1, Rosberg-Cody, E.2 and Kelly, P.M.1
1Food Chemistry & Technology Department, Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland. 2Food Safety Department, Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland.
The intermediate water activity (aw) typical of high-protein bars precludes bacterial growth but should allow their survival and removes the need for refrigerated storage. Time-dependent hardening, however, represents a major deteriorative factor. This work seeks to produce texturally-stable, high-protein bars as vehicles for delivery of functional ingredients, namely galactooligosaccharides (GOS) and probiotic bacteria. A range of whey protein isolate (WPI), hydrolysed whey protein (WPH) and soy protein isolate (SPI)-based bar formulations were compared. Bars containing WPI were softer during storage compared to SPI and were enhanced by addition of lower melting-point oils. Addition of WPH to WPI further improved the textural stability of model bars as did control of glycerol/water ratio. The maximum acceptable level of protein inclusion was established at 35% (w/w). With the exception of galactose, significant losses of GOS fractions occurred in bars stored at 37 oC. Such losses, however, were less extensive in the presence of glycerol. Viability of commercial freeze-dried, probiotic bacteria (L. casei 431 and Bifidobacterium BB-12®) remained stable in low aw bar ingredients but decreased as a function of storage temperature (4, 20 and 37 oC) when added to bars (108 cfu/g). Inoculation of probiotic cultures via the oil phase enhanced viability, which was also extended by pre-suspension of cell cultures in a skim milk/prebiotic mixture prior to freeze-drying. Encapsulation of probiotics in molten chocolate also improved bacterial stability during storage. Migration of moisture from the sugar phase (high aw) to freeze-dried probiotics (low aw) was considered the driving force for loss of microbial stability. Although survival of probiotic bacteria in protein-bar matrices was temperature sensitive, control of aw along with the provision of barriers to moisture migration can provide the means by which the efficacy of protein bars as vehicles for delivery of sensitive, functional ingredients can be improved.