The inhibitory activity and sensory properties of kefir, targeting the low-income African consumer market

[摘要] ENGLISH ABSTRACT:The rapid urbanisation of the African population has led to the establishment of largelow-income communities in and around almost every major town and city in SouthAfrica. Several factors prevent these people from producing or obtaining theirtraditional fermented milk drink, Maas (Amasi), often resulting in the occurrence ofmalnutrition in low-income urban African communities.A product with the potential to satisfy the demand for a fermented milk productis Kefir. Kefir, a self-carbonated fermented milk, is commonly manufactured byfermenting unpasteurised or pasteurised milk with re-usable Kefir grains. These Kefirgrains consist of a combination of mainly lactic acid bacteria and yeasts. NeitherKefir, nor Kefir grains are as yet marketed in South Africa, thus creating an excellentopportunity to launch these products locally.It is often difficult for the low-income communities to obtain high qualityunpasteurised or pasteurised milk, resulting in a serious health risk. The inhibitoryactivity of Kefir towards certain spoilage and pathogenic microorganisms was,therefore, studied. Strains of Escherichia coli, Staphylococcus aureus, Bacilluscereus, Usteria monocytogenes and Clostridium tyrobutyricum were inoculated (10 ³-10 ⁴ cfu.ml⁻¹ ) into pasteurised milk together with Kefir grains (18 gram per litre) andincubated at 25°C. Uninoculated milk samples and milk samples inoculated only withtest organisms served as controls. Growth of all the test organisms were inhibitedsubstantially (>-99.9%) in Kefir over the 30 h incubation period and substantialreductions in microbial log cycles were observed for many of the organisms. Thiscoincided with a steep decrease in pH (6.57 - 4.06) and increase in titratabie acidity(0.20 - 0.72%).If Kefir is eventually marketed to low-income urban African consumers, it willhave to compete with Maas and, therefore, comparative sensory testing of Kefir andMaas was conducted. The differences in the sensory properties of Kefir, 'laboratory'Maas (representing traditional Maas) and commercial Maas (containing thickener,colourants and flavourants) were determined by a trained panel. Thesecharacteristics were identified as yeasty and cowy tastes (p < 0.05),effervescence (p < 0.01), as well as sourness, creaminess and smoothness (p< 0.001). The effect of different incubation temperatures (25°, 30° and 35°C) on theKefir sensory properties was studied to simulate the effect of the large temperaturevariations that would be found in the dwellings of low-income African urbanites. Thesourness and creaminess of the Kefir was found to increase with increase inincubation temperature but no strong off-flavours were found to develop. Sensorypreference testing was conducted by consumer panels consisting of panellists ofdifferent ages and population groups to indicate whether the specific panelssignificantly prefer Kefir, commercial Maas or laboratory Maas. It was found thatcommercial Maas was significantly (p < 0.001) preferred to Kefir by young Africanurbanites. Adult Africans, who presumably still have traditional taste preferences,however, equally (p > 0.05) preferred Kefir and laboratory Maas, identifying thissegment of the African population as the appropriate starting target market for Kefir.Kefir and laboratory Maas were also tested for preference by a wider panelconsisting of people (aged between 18 and 25) representing the different populationgroups in South Africa. Kefir and laboratory Maas were preferred equally (p > 0.05)by all the groups.Several arguments supporting Kefir marketing to the low-income urban Africanpopulation of South Africa have been identified. These include: Kefir's ease ofpreparation; the re-usability of Kefir grains and subsequent affordability; goodpackaging, distribution and storage possibilities; Kefir's acceptability by lactoseintolerantindividuals; high nutritional value; the inhibitory activity of Kefir againstpotential spoilage and pathogenic organisms and subsequent enhanced safety andkeeping ability; and Kefir's acceptable refreshing taste.

[发布机构] Stellenbosch University