Lookup NU author(s): Dr Gerry O'Brien
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Background Kefir yoghurt is produced from milk that is fermented using kefir grains, and contains several different microorganisms including Lactobacillus, Lactococcus and yeast spp. Several alleged health benefits have been associated with kefir consumption1, 2, 3, and benefits to public health might be envisaged if kefir were incorporated into more ‘mainstream’ food products. In this study, the abilities of kefir organisms raised in two different climates (one cool, the other tropical) to thrive under / withstand different food-relevant treatment régimes were compared. Objectives The objectives were: (1) to characterise the growth of two kefir cultures (from Singapore and Ireland respectively) at different incubation temperatures and using milks of differing fat content; (2) to explore the effects of freeze-thaw and mild cooking treatments upon the viability of kefir microorganisms from the two cultures. Methods Biomass (grain weight) of Irish-origin kefir in pasteurised full-fat (4%) and low-fat (1.5%) cow’s milk, at both 25ºC and 30ºC, was observed over a 21-day period. Biomass of Singapore-origin kefir (in full-fat milk only) was observed under the same conditions. In separate trials, samples of strained kefir yoghurt taken from the different incubation régimes were subjected to, respectively: freeze-thaw treatment; heating to 50ºC; and heating to 60ºC. Before and after each treatment, enumeration of Lactobacillus, Lactococcus and yeasts was carried out, and respective survival rates were subsequently estimated. Sample replication in these exploratory trials was limited, and therefore estimates of significance of effects are not provided Results Cultivation of kefir grains under constant-temperature conditions led to biomass increasing by 4.6 – 5.6 times, with highest growth observed in Irish-origin kefir in high-fat milk at 25ºC. Freeze-thaw treatment led to major losses (92.7 – 99.7%) of yeasts in all yoghurts tested, while losses of lactic acid bacteria (LAB) varied between 67.0 – 93.6%. With heating to 50ºC, losses of yeasts ranged from 59-92%, while LAB losses were lower (0 – 59.6%), particularly in high-fat milk yoghurts. Heating to 60ºC resulted in total elimination of yeasts, and 78.9 – 99.3% losses of LAB. Conclusions Kefir biomass grew at a satisfactory rate during incubation at 25 and 30ºC, regardless of origin and whether full-fat or low-fat milk was used. Despite major losses of yeasts as a result of the thermal treatments of kefir yoghurt, LAB survival rates were more encouraging: after freeze-thaw and 50oC treatments, LAB levels were compatible with food industry probiotic requirements4. There was also some evidence of a possible LAB-protective effect in mildly-heated full-fat yoghurt. 1. Guzel-Seydim KT, Greene AK & Seydim A C (2011) Crit Reviews in Food Sci Nutr 51, 261-268. 2. Hertzler SR & Clancy SM (2003) J American Dietetic Assoc 103, 582-587. 3. Otles S & Cagindi OE (2003) Pakistan J Nutrition 2, 54-59. 4. Vinderola G, Binetti A, Burns P & Reinheimer J (2011) Frontiers in Microbiology 2, 1-6.
Author(s): Tee M, O'Brien GM
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: The Gut, its Microbes and Health
Year of Conference: 2014
Online publication date: 08/10/2014
Acceptance date: 01/01/1900
Publisher: International Life Sciences Institute (ILSI) - SE Asia Region