- Title
- Probiotic application in the development of goat's milk products with special reference to Propionibacterium jensenii 702: effects on viability and functionality
- Creator
- Ranadheera, Chaminda Senaka
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2011
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Goat's milk and goat's milk products are widely consumed in developing countries, and are attractive to many consumers in developed countries due to their therapeutic and nutritional value. Although an increasing global demand exists, the variety of commercially available goat's milk products is currently limited. Goat's milk itself may be a suitable vehicle for delivering probiotics to humans, and the addition of probiotics to goat's milk may further enhance its health promoting value. This thesis examines the feasibility of using the novel probiotic Propionibacterium jensenii 702 in co-culture with established probiotic organisms (lactobacilli and bifidobacteria) in the manufacture of goat's milk products such as fermented milk, yogurt, ice cream and spray dried powder. To provide beneficial health effects probiotic bacteria must survive passage through the gastrointestinal tract, then adhere to and colonise the gut epithelium. As these functional properties can be influenced by the food carriers used in probiotic delivery, a series of in vitro studies were performed to investigate the effect of goat's milk carrier foods on these functional aspects of probiotic efficacy. The viability of the probiotics during product shelf life, and the physico-chemical characteristics and sensory attributes of these products, were also analysed in order to assess both their general quality and appeal. The first of the studies presented involved the examination of different mono-culture and co-culture combinations of P. jensenii 702 in fermented goat's milk with respect to viability during storage, physico-chemical and sensory attributes of the milk, and in vitro gastrointestinal tolerance and adhesion ability. Co-cultivation of P. jensenii 702 with L. acidophilus LA-5 and B. animalis subsp. lactis BB-12 in goat's milk was not found to impact adversely on either the physico-chemical properties or sensory characteristics of the fermented milk preparations, or the functional properties of these bacteria. Thus it was found that combining P. jensenii 702 with lactobacilli and bifidobacteria could be effectively utilised in the development of probiotic goat's milk products. Based on these findings, a triple co-culture of these three organisms was utilised in all subsequent studies. In the second study, plain and stirred fruit yogurts were developed. P. jensenii 702 demonstrated high viability (108cfu/g) in all types of yogurt throughout storage, while the viability of the bifidobacteria also remained above the minimum recommended level (106 cfu/g). However, the results indicated that yogurt starter culture bacteria may have had an adverse effect on L. acidophilus LA-5 viability during the shelf life of the products, resulting in low viable counts in both types of yogurts (<105 cfu/g). In general the physico-chemical properties of the yogurts were within acceptable ranges and sensory tests revealed that the addition of fruit juice improved consumer acceptability of the yogurt. The third study involved development of a chocolate flavoured probiotic ice cream using goat's milk. In addition to the performance of P. jensenii 702, the effect of packaging materials on both probiotic viability, and the physico-chemical and sensory properties of the product were also evaluated. Regardless of packaging type (glass, polyethylene or polypropylene) all three probiotics were able to maintain high viability (107-108 cfu/g) in the ice cream during 52 weeks of storage at -20°C. While no significant effect on the sensory properties of the ice cream could be associated with the packaging materials, product stored for 12 weeks was more highly ranked for all sensory attributes than that stored for one week. The relative influence of different food matrices on the gastrointestinal tolerance and adhesion of probiotics was examined in vitro using goat's milk ice cream, plain and 10% stirred fruit yogurts. In relation to the different food types, significant variation in the viability of all three probiotics was observed when exposed to simulated gastro-intestinal conditions of either low pH (2.0) or 0.3% bile. In general, ice cream was found to improve the acid and bile tolerance of the probiotics compared to plain and stirred fruit yogurts. In contrast, the fruit yogurt appeared to be the most favourable carrier in terms of in vitro adhesion of the probiotics to human Caco-2 intestinal cells, although a substantial number of viable bacteria (105-106 cfu/g) were found to be adherent in all cases. The effects of micro-encapsulation and subsequent storage on the viability of the three probiotics was examined after spray drying the triple combination in reconstituted goat's milk. Although spray drying resulted in an initial reduction in the number of viable cells, the viability of all three probiotics remained unaffected (~106 cfu/g) under refrigerated storage for 24 weeks. Rehydration of spray dried probiotics in coffee and black tea at 85°C lowered viable cell numbers, however, both P. jensenii 702 and L. acidophilus LA-5 retained satisfactory viability (~106 cfu/g) even after rehydration at this temperature. This thesis provides evidence to suggest that the novel probiotic P. jensenii 702 may be successfully utilised in probiotic co-culture for the manufacturing of functional goat's milk products such as ice cream and yogurts. The findings also reveal the importance of careful selection of both the species to be used in co-cultured probiotic preparations, and a suitable carrier food matrix, in order to assure maximum benefit to consumers.
- Subject
- probiotics; goat's milk; milk products; viability; functional properties
- Identifier
- http://hdl.handle.net/1959.13/927942
- Identifier
- uon:10296
- Rights
- Copyright 2011 Chaminda Senaka Ranadheera
- Language
- eng
- Full Text
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