| Malolactic fermentation (MLF) is one of indispensable process in cidermaking, which carried out the conversion of malic acid to lactic acid and released CO2. Malolactic fermentation is desirable because it can enhance the organoleptic characteristic of cider. Furthermore, it also could decrease the acidity and increase the microbiological stability of cider.In this research, considering the final contribution to cider aroma, the selecting criterions including malolactic activity, sensory analysis, softness index and the productivity of acetate of each strain were studied respectively. The malolactic activities of various LAB (Lactic Acid Bacteria) were compared. It was found that Oenococcus oeni L5 presented the highest malolactic activity at 215.19u among these seven strains. After sensory analysis to each sample produced by different LAB fermentation, the consequence indicated that the flavor of various cider samples was greatly distinct with each other. Among the microorganisms studied, only three strains (O.oeni L2, O.oeni L3, and O.oeni L4) performed good organoleptic quality, and the softness indexes of these three samples were all above 3.5. In addition, the amounts of acetic acid produced by the three microorganisms during MLF were all below 250mg/L, which could not make negative effects on the organoleptic characteristic of cider. By using Primary Component Analysis for screening efficient strains in cidermaking, it was found that O.oeni L2, O.oeni L3, and O.oeni L4 process positive brewing properties.For the growth of LAB could be inhibited by SO2, ethanol, T, and pH, an excellent malolactic strain should adapt to the cidermaking conditions well. Further researches on the effects of several restrictive factors on cell growth were also carried out in this paper. It was observed that O.oeni L4 represented good resistance to severe cidermaking conditions and could remain growth under the conditions as pH3.2, the concentration of SO2 and ethanol were 50mg/L and 6% (v/v), respectively. Consequently, O.oeni L4 was selected as the profitable malolactic strain for cidermaking.The technology of malolactic fermentation for cidermaking was also investigated. In our research, it was indicated that a successful MLF carried on with the conditions as sequential fermentation at 20, and inoculated with 106 cfu/mL. Furthermore, acetic acid with small amount was produced during the fermentation and malolactic fermentation could still complete even with a high concentration of malic acid of 6676.95mg/L. Corresponding with the technology above, cider was made with softer mouth-feel and tasted better than the cider samples without malolactic fermentation.After analyzing the components of cider samples, it was suggested that the aroma of cider was enhanced by malolactic fermentation. Total esters and total alcohols were 3.98 folds and 8.25 folds more than that without MLF, respectively. Among such esters and alcohols, the contents of ethyl lactate, ethyl acetate, isoamyl acetate, isobutyl alcohol, isoamyl alcohol and 4-penten-2-ol increasedin a large level, and the concentration of these alcohols and esters were found to be greatly influenced by the volume of ammo acids. It was also proposed that acetic acid contained in cider was produced through heterofermentation pathway by LAB and the content of diacetyl could not increase with MLF.
|
PDF Full Text Request