香蕉果酒接种发酵和自然发酵过程中乳酸菌菌落变化及有机酸代谢特征

香蕉营养丰富、活性物质含量高，可作为深加工产品的优质原料。香蕉果酒是香蕉精深加工产品中的重要一类。由于香蕉果浆碳水化合物含量较高、酸度低、糖分高，其酿造过程中适宜各种微生物的生长繁殖，特别是乳酸菌数量的变化与酸类物质的产生密切相关。乳酸菌群落的变化容易增加发酵过程的风险，造成香蕉酒挥发酸含量超标、品质低下等不良结果。因此明确香蕉果酒发酵过程中自然存在的乳酸菌的生长繁殖规律及其对有机酸代谢的影响，可为精准调控发酵过程、提高产品质量提供理论依据。试验设置商业酵母Lalvin K1^TM接种发酵过程（K1）与香蕉果汁自然发酵过程（SF）2组对比，采用实时定量PCR方法和高效液相色谱法对香蕉汁接种发酵（K1）与自然发酵过程（SF）中酵母菌、乳酸菌的生长规律以及有机酸的含量变化进行监测。结果表明：2种发酵处理下，酵母菌和乳酸菌的生长规律有差异；K1酵母菌主导的发酵过程中，乳酸菌的生长受到显著抑制，最大生长量仅为4.0×10⁶ CFU/mL，而酵母菌生物量为1.2×10⁷ CFU/mL；在自然发酵过程中，乳酸菌与酵母菌的生长周期完全错开，但对乳酸菌的生物量无显著影响，乳酸菌与酵母菌的生长量分别达到1.0×10⁷ CFU/mL和1.6×10⁷ CFU/mL。2种发酵过程均表明，酵母菌和乳酸菌的生长存在竞争与抑制关系；有机酸代谢主要与乳酸菌菌落数量相关，不同有机酸的总体变化趋势一致；在发酵过程中，乳酸含量逐渐增加，乙酸含量呈先增后降的趋势，二者在自然发酵样品中的累积量均高于接种发酵；柠檬酸、苹果酸、酒石酸含量整体呈下降趋势。

Characteristics of Lactic Acid Bacteria Colony Change and Organic Acid Metabolism During Inoculation and Spontaneous Fermentation of Banana Fruit Wine

Bananas, rich in nutritional and bioactive ingredients, can be used as remarkable raw materials for deep processing products in food industry. Banana wine is one of the important deep-processing products. During the fermentation process, high sugar and low acidity of banana juice is suitable for microorganisms growth, especially for lactic acid bacteria (LAB) growth which is closely related to the production of organic acids. The change of LAB community easily produces excessive volatile acid content during the fermentation process, leading to low-quality banana wine. Therefore, this study was to investigate the growth and reproduction pattern of naturally existing LAB, as well as to evaluate the effect of LAB on the organic acid metabolism during banana wine fermentation. The findings of this research could provide theoretical references for accurately managing fermentation process to promote banana wine quality. In this study, the commercial yeast K1 inoculated fermentation and the banana juice spontaneous fermentation (SF) were used as the fermentation processes. The colony changes of yeast and LAB in the fermentation processes were monitored by real-time PCR, and the changes of organic acid content in fermentation processes were also detected by high performance liquid chromatography (HPLC). The organic acid metabolism characteristics of LAB in the processes were comparatively studied as well. The results showed that the growth of yeast and LAB differed significantly in the fermentation processes. In the fermentation process using K1 yeast, the number of LAB community was significantly inhibited, and the maximum growth amount of LAB was only 4.0×10⁶ CFU/mL and the biomass of yeast was 1.2×10⁷ CFU/mL. In the banana juice spontaneous fermentation process, the growth cycles of LAB and yeast were not affected mutually, and the biomass of LAB and yeast was 1.0×10⁷ CFU/mL and 1.6×10⁷ CFU/mL, respectively. Both fermentation processes demonstrated that there was a competitive relationship between yeast and LAB in banana wine fermentation. Additionally, organic acid metabolism was mainly related to the number of LAB community, and the contents of different organic acids had the similar change trends in this study. During the fermentation processes, lactic acid content was increased, and acetic acid content was increased firstly and then decreased. However, the total lactic acid and acetic acid contents in the spontaneous fermentation were higher than those in the yeast K1 inoculated fermentation. The citric acid, malic acid and tartaric acid contents showed a decreasing trend during the two kinds of fermentation process.