Effect Of Lactobcillus Fermentation On The Quality Of Pickled Baby-ginger

As a Chinese pickle,pickled baby-ginger has agreeable flavor,good texture,and health function,and is consumed by more and more people in the world.However,technical level of ginger processing is very low,and quality standardization of pickled baby-ginger has not been realized.Firstly,fermentation characteristics of 8 ginger brine samples were analyzed.The dominant strains were identified and isolated from the ginger brine sample with better fermentation characteristics.Then,effects of different fermentation modes on the quality(such as sensory quality and basic physical-chemical indicators)of pickled baby-ginger were analyzed.At last,aroma composition,organic acids and amino acids of baby ginger pickled by the better fermentation mode were detected,and their dynamic changes were analyzed.Through experimental investigations,the following results are obtained.(1)The difference of acidity among the 8 ginger brine samples was obvious.So was the difference in salinity or pH value.Their salinity values ranged from 3.65%to 13.16%,and their pH values ranged from 0.43 to 0.83 g/100g.Baby ginger pickled by PJS7 ginger brine sample(it was sampled from a pickle production enterprise in Leshan city)had better quality than others.Three dominant strains were isolated from the PJS7 ginger brine sample.After identification,the three strains were Lactococcus raffinolactis,Lactobacillus coryniformis and Leuconostoc pseudomesenteroides respectively.(2)The sensory score of pickled baby-ginger inoculated with Lactococcus raffinolactis,Lactobacillus coryniformis or Leuconostoc pseudomesenteroides,reached the maximum on the 4^th,6^th or 6^th day,their maximum values were 6.33±0.26,6.50±0.18 and 6.18±0.20respectively.The sensory score of pickled baby-ginger fermented by co-inoculation of the three strains reached the maximum(6.78±0.13)on the 4th day.When baby-ginger was soaked in old brine and fermented,its sensory score reached the maximum(6.79±0.14)on the 2nd day.Pickled baby-ginger fermented by co-inoculation had sensory quality similar to that fermented in old brine,and their quality were more better than that of the fermentation with single lactic acid bacteria inoculation.The two pickled baby-ginger had strong characteristic aroma and excellent characteristic taste quality(such as salty,sour taste,spicy),crisp and tender texture,strong overall acceptability.With the increase of fermentation time,the pH value decreased gradually until it became stable,while the total acid content increased gradually.The total acid content of the samples treated with ginger brine was the highest(it was as high as 0.935 g/100g on the 8^th day),while that of the samples inoculated with Leuconostoc pseudointestinalis was the lowest(it was 0.376g/100g on the 8^th day).Brightness(L*)of pickled baby-ginger was lower than that of fresh ginger,and color difference ranged from 15.3 to 21.Brittleness of pickled baby-ginger varied slightly while hardness decreased gradually.spicy degree decrease gradually,and it decreased to about 0.17%on the 8th day.Salinity increased gradually until it stabilized.Change rate of hardness,salinity or spicy degree was less affected by fermentation mode.Reducing sugar contents and amino acid nitrogen contents decreased gradually.Reducing sugar content didn't change significantly from the 6^th to 8^th day(ranging from 0.1%to0.2%),and amino acid nitrogen content didn't change significantly from the 6^th to 8^th day(ranging from 0.02%to 0.04%).Nitrite content peak appeared on the 2^nd day during fermentation by inoculating single lactic acid bacteria,while there was no nitrite content peak in the fermentation by co-inoculation or the old brine.Among the five fermentation methods,the fermentation by co-inoculation of the three strains was the best way to produce pickled baby-ginger.(3)High throughput sequencing method was used to analyze bacterial community in the fermentation process under co-inoculation.Sequencing results showed that Lactococcus raffinolactis or Lactobacillus coryniformis had strong growth activity during the fermentation.At the initial point of fermentation,inoculum concentration of three strains was equal.On the 1^st day,relative abundance of Lactococcus raffinolactis was27.18%,while that of Lactobacillus coryniformis was 2.49%.Relative abundance of Lactococcus raffinolactis reached its maximum(38.76%)on the 4^th day,while that of Lactobacillus coryniformis reached its maximum(46.97%)on the 6^th day.However,the relative abundance of Leuconostoc pseudomesenteroides was merely 0.22%on the 1^st day,it decreased gradually with the increase of fermentation time.(4)The volatile compounds of pickled baby-ginger largely were terpenoids or their derivatives.Total content of all volatile compounds of pickled baby ginger was significantly reduced with the increase of fermentation time.The relative and absolute content of some volatile compound(such as?-Farnesene and?-Sesquiphellandrene)decreased gradually,while absolute content of some compound(such as Geranyl acetate)increased gradually and then stabilized at a certain level.some volatile compound(such as decanal)was produced by the metabolic action of lactic acid bacteria.?-Myrcene,Eucalyptol,trans-?-Ocimene,cis-?-Ocimene,Linalool,Decanal,?-Citral,Geraniol,Geranyl acetate,?-Curcumene and?-Bisabolene were the most important aroma-active components in pickled baby-ginger.(5)During the fermentation process,the content of oxalic acid or Vc decreased,while the content of lactic acid or acetic acid increased gradually.Oxalic acid content of baby-ginger fermented for 8 days was only 160.76±4.01 mg/100g,while that of fresh baby-ginger was as high as 1728±9.14 mg/100g.Vc content of the baby-ginger fermented for 8 days was 1.19±0.03 mg/100g(it was one third of the Vc content of fresh baby-ginger).Lactic acid content and acetic acid content of the baby-ginger fermented for 8 days were57.70±2.16 and 44.43±0.03 mg/100g,while those of the fresh baby-ginger were 2.32±0.08and 0.65±0.12 mg/100g respectively.Change in the content of formic acid,malic acid,citric acid,fumaric acid or succinic acid showed a trend of first increasing and then decreasing.The total amount of free amino acids of pickled baby ginger decreased gradually.The content of delicious amino acid was the highest in pickled baby-ginger,while that of bitter amino acid was the lowest.Aspartic acid was higher than the other free amino acid in ginger.The content of serine was second only to that of aspartic acid.Free amino acids which contributed more to the taste quality mainly included aspartic acid,histidine,glutamic acid,serine and alanine(Flavor intensity of these five amino acids in baby-ginger fermented for 4 days was 0.72,0.60,0.43,0.29 and 0.15,respectively).6-gingerol,8-gingerol and 6-shogaol were characteristic spicy ingredients,their contents decreased to 425.61±12.16 mg/kg(it was 78.27%of that of fresh baby-ginger),403.58±16.56 mg/kg(it was 83.64%of that of fresh baby-ginger)and 469.26±13.52 mg/kg(it was 85.52%of that of fresh baby-ginger)respectively.The content of glucose and fructose showed a trend of first increasing and then decreasing.The content of glucose or fructose in pickled baby-ginger was less than 0.1%.