酸奶发酵菌的研究及其风味化合物的鉴定

酸奶是一种营养价值很高,又富有良好风味的广为消费者喜爱的传统发酵乳制品。本文对酸奶发酵菌的研究和酸奶中主要风味化合物的分析鉴定进行了初步探讨。在发酵菌方面,选择了本所保藏的6038号(str. thermophilus)和6047号(Lb. bulgaricus)两支较好的乳酸菌为本实验的出发菌株。按1∶1的配合比,保温在43℃下进行牛乳发酵,凝结后立即放在4～7℃下保持24小时左右,可以获得较为满意的发酵乳风味。在挥发性风味化合物的分析鉴定方面,采用了真空蒸馏、溶剂提取和调节pH分离的方法,将风味组分分为酸类和非酸类两部分,经浓缩后使用气相色谱(GC)分析技术、气相色谱—质谱(GC—MS)联用技术和离子色谱(IC)分析技术,分析鉴定了酸奶中主要风味化合物;并定性定量分析了不同发酵和低温保持阶段上重要香气成份——双乙酰的生物合成水平。由此得到结论。发酵培养完成后,于低温保持24小时,酸奶中双乙酰的生成量最高可达到10.34ppm。该水平双乙酰含量可以赋与酸奶特有的香气和良好的风味。进而推论,此含量范围的双乙酰应为酸奶中的较适水平;酸奶发酵进行后,低温保持阶段的初期对酸奶风味的形成有十分重要的意义。

Studies on the Selection of Starter and Identification of the Flavor Compounds of Yogurt (sour milk)

A traditional fermented dairy product-yogurt with high nutrition value and pleas ant flavor has a great marketing. This paper was dealing with the selection of starter and identification of volatile flavor compounds of it. Both Streptococcus thermophilus 6038 and lactobacillus bulgaricus 6047 were selected as the best cultures among more than ten cultures which were collected from IFFI. The sterilized milk incubated with 1:1 of 6038 and 6047 mixed starter at 43℃ for 5 hrs.first until coagulation,then aged it in refrigerator at 4-7℃ for one day. Finally, the yogurt came out very tasty and high aroma. The volatile compounds involved were isolated by a special method including vaccum disstillation, extraction with solvent, seperating into acidic fraction and non-acidic fraction, dehydration and concentration etc. The primary fractionation were perfermenced by GC and IC and the second fractionation were idenrified by GC-MS. Several flavor compounds were identified in the investigation. Diacetyl which was recognized the aromotic key compounds for yogurt was analysed qualitatively and quanti-tively during fermentation and cold storage interval. It is found that the highest level of the diacetyl can be up to 10. 34ppm after 24 hrs.cold storage and the product reached the best aroma and flavor at the sometime. It suggested that the storage in refrigerator played a very important role for this sort of fermented milk product.