Witthuhn R Corli, Cilliers Annamie, Britz Trevor J
Department of Food Science, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa.
J Dairy Res. 2005 Feb;72(1):125-8. doi: 10.1017/s0022029904000652.
Kefir is an acidic, mildly alcoholic dairy beverage produced by the fermentation of milk with a grain-like starter culture (Koroleva, 1988). These grains usually contain a relatively stable and specific balance of microbes that exist in a complex symbiotic relationship (Obermann & Libudzisz, 1998; Witthuhn et al. 2004). The different groups of microbes present in the grains are active at different stages of the fermentation (Koroleva, 1982). The lactococci, including Lactococcus lactis subsp. lactis, Lc. lactis subsp. cremoris and Lc. lactis subsp. diacetilactis provide rapid acid development during the first hours of the fermentation (Litopoulou-Tzanetaki & Tzanetakis, 2000). As the acidity of the milk increases it provides favourable conditions for the growth of the lactobacilli (Rea et al. 1996). The yeasts, acetic acid bacteria and the aroma-producing microbes, mainly leuconostocs, have a much slower growth rate than the lactic acid producers, resulting in the slow production of the aroma compounds and the gradual increase in the concentration of these substances in the later stages of the fermentation (Koroleva, 1982). In the past the preservation of the microbial populations present in the traditional Kefir grains was achieved by methods including freezing (Garrote et al. 1997), lyophilisation (Oberman & Libudzisz, 1998), air-drying (Kroger, 1993) and refrigeration (Marshall, 1993). Research has shown that traditional Kefir grains preserved by air-drying and lyophilisation retain their activity for up to 12-18 months (Oberman & Libudzisz, 1998). Frozen grains stored at -20 degrees C were found to maintain the microbial activity for up to 7-8 months, whereas grains stored at refrigerated temperatures showed a decreased activity after about 10 d (Oberman & Libudzisz, 1998). The aim of this study was to evaluate the impact of four different preservation techniques on the activity of mass cultured Kefir grains (Schoevers & Britz, 2003). The activity of the grains was evaluated at different time intervals using four activity measurements, including changes in substrate pH, titratable acidity (TA), lactose and lactic acid levels of the final Kefir beverage.
开菲尔是一种酸性、微含酒精的乳制饮品，由牛奶与一种类似谷物的发酵剂发酵制成（科罗列娃，1988年）。这些谷物通常含有相对稳定且特定的微生物平衡，它们以复杂的共生关系存在（奥伯曼和利布齐希，1998年；维图恩等人，2004年）。谷物中存在的不同微生物群在发酵的不同阶段发挥作用（科罗列娃，1982年）。乳球菌，包括乳酸乳球菌乳酸亚种、乳酸乳球菌乳脂亚种和乳酸乳球菌双乙酰亚种，在发酵的最初几个小时能快速产酸（利托普洛乌-察内塔基斯和察内塔基斯，2000年）。随着牛奶酸度的增加，它为乳酸菌的生长提供了有利条件（雷亚等人，1996年）。酵母、醋酸菌和产生香气的微生物，主要是明串珠菌，其生长速度比产乳酸的微生物慢得多，导致香气化合物产生缓慢，且在发酵后期这些物质的浓度逐渐增加（科罗列娃，1982年）。过去，传统开菲尔谷物中微生物种群的保存方法包括冷冻（加罗特等人，1997年）、冻干（奥伯曼和利布齐希，1998年）、风干（克罗格，1993年）和冷藏（马歇尔，1993年）。研究表明，通过风干和冻干保存的传统开菲尔谷物可保持活性长达12至18个月（奥伯曼和利布齐希，1998年）。发现储存在-20摄氏度的冷冻谷物可保持微生物活性长达7至8个月，而储存在冷藏温度下的谷物在大约10天后活性下降（奥伯曼和利布齐希，1998年）。本研究的目的是评估四种不同保存技术对大规模培养的开菲尔谷物活性的影响（朔弗斯和布里茨，2003年）。使用四种活性测量方法在不同时间间隔评估谷物的活性，包括最终开菲尔饮品的底物pH值、可滴定酸度（TA）、乳糖和乳酸水平的变化。
