Influence of the heat treatment of sugarcane juice on the fermentative process and chemical composition of cane spirit

Abstract The introduction of different strains of microorganism in the fermentations destined for the production of cane spirit, due to successive broth feeds, may contribute to the development of different classes of microorganism, compromising the metabolic activity of the yeasts and hence the direction of the fermentative process. Thus the present study aimed to evaluate the influence of the heat treatment of the sugarcane juice on the technological and microbiological characteristics of the substrate and their effects on the direction of the fermentative process and the chemical quality of the cane spirit. The juice was treated at 90 °C for 5 minutes and the concentrations of lactic bacteria, total yeasts and non-Saccharomyces yeasts then quantified. Five fermentative cycles were carried out using heat treated and untreated sugarcane juice musts. The process was monitored via cell viability and bud production and determination of the budding index, and the total and non-Saccharomyces yeast populations quantified in the recycled yeast. At the end of the fermentations, the pH, total titratable acidity, alcohol content by volume and total residual reducing sugars of the wines were determined, these being distilled in a copper still for quantification of the chemical composition of the cane spirit. The heat treatment allowed for inactivation of the microorganisms in the juice without compromising their physicochemical characteristics. The cell viability was reduced when the fermentations were carried out with untreated juice, although the physicochemical characteristics of the wines were not affected. The distillates from fermentations carried out with untreated juice showed higher levels of volatile acidity and esters at the end of the 5th cycle. The concentrations of higher alcohols and furfural were elevated for both treatments in the 1st and 5th cycles, respectively.

摘要：在甘蔗烈酒生产的发酵过程中，因连续补料而引入的不同微生物菌株，可能会促进各类微生物的增殖，削弱酵母菌的代谢活性，进而改变发酵进程的方向。因此，本研究旨在评估甘蔗汁热处理对发酵底物的工艺学与微生物学特性的影响，及其对发酵进程走向和甘蔗烈酒化学品质的作用。实验将甘蔗汁置于90℃下热处理5分钟，随后定量检测其中乳酸菌、总酵母菌及非酿酒酵母菌（non-Saccharomyces yeasts）的浓度。分别采用经热处理与未经热处理的甘蔗汁醪开展5轮发酵批次。通过细胞存活率、出芽率与出芽指数的测定，以及对回收酵母中总酵母菌与非酿酒酵母菌种群数量的定量分析，对发酵过程进行监测。发酵结束后，测定发酵液的pH值、总滴定酸度、体积酒精含量与总残留还原糖，随后将其置于铜质蒸馏器中蒸馏，以定量分析甘蔗烈酒的化学成分。热处理可使甘蔗汁中的微生物失活，且不会损害其理化特性。采用未经热处理的甘蔗汁开展发酵时，酵母菌细胞存活率有所降低，但发酵液的理化特性未受影响。在第5轮发酵批次结束后，采用未经热处理的甘蔗汁所制得的蒸馏产物，其挥发性酸度与酯类含量均更高。两种处理方式的蒸馏产物中，高级醇的浓度在第1轮发酵批次中处于较高水平，糠醛（furfural）的浓度则在第5轮发酵批次中升高。