Study On Quality Changes Of Chopped Peppers Preserving With Low Salt And Temperature

Pepper is the main vegetable for production and consumption in Hunan.Chopped pepper is a special condiment in Hunan.Chopped pepper is loved by the public because of its sour,spicy and crisp taste.At present,the raw material for chopped pepper production is mainly salted pepper with high concentration of salt.The salt content of the billet is as high as 20%-25%,and it needs to be rinsed and desalted before it can be processed into products.The rinsing and desalting of pepper billets leads to a large amount of salt water discharge and the loss of pepper flavor nutrients,resulting in serious environmental pollution and waste of resources.There is an urgent need to study the technology of low-salt preservation of peppers.In this paper,three salt concentrations of 8%(L1),10%(L2),and 12%(L3)combined with0.08% citric acid and 0.03% sodium metabisulfite were used to treat pop pepper,and investigate the changes of physicochemical indexes and volatile substances during its storage at low temperature of 4-6℃ for 10 months,and high-throughput sequencing technology was used to study the bacterial diversity during its billet preservation process,in order to provide technical parameters for the research on the low-salt preservation technology of peppers.The main findings of the study are as follows:1.The total acid content of peppers stored with different salt concentrations showed a trend of first decreasing and then increasing during the refrigeration process.The total acid content of L1 was the highest when stored for 7 months,reaching0.81%;the total acid content of L2 and L3 was stored at 10.The maximum value was reached at 0.79% and 0.75% respectively.The overall trend of p H value was opposite to that of total acid,and the p H value of L1 reached the minimum value of 4.2 at 8months for storage.During refrigeration,the contents of oxalic acid,malic acid and succinic acid in peppers stored with different salt concentrations all showed a trend of first increasing and then decreasing;the overall trend of lactic acid content was that it first increased and then leveled off and all pepper samples reached the maximum lactic acid content at 10 months of storage,which were 4.47g/kg,3.55g/kg and3.3g/kg respectively;the content of tartaric acid and citric acid showed a downward trend,and no formic acid was detected in all samples.During the refrigeration process,the total free amino acid content of all pepper samples showed a trend of increasing first and then decreasing,and all reached the maximum value at 8 months of storage,which were 14.5428mg/g,14.493mg/g and 12.7448mg/g respectively.2.During the refrigeration process,the crispness value of all pepper samples showed a trend of first increasing and then decreasing,and the crispness value reached the maximum value when stored for 4 months,which were 5353.83 g,6443.02 g and 6869.33 g respectively;the brightness values L* were all showing a downward trend,the redness value a* and the yellowness value b* both increased first and then decreased,and the color difference values showed a trend of first decreasing and then increasing.When stored for 10 months,the color difference values were15.54,15.27 and 13.49.The sensory scores of all pepper samples were above 80 when stored for 1-7 months,but L1 dropped sharply at 7 months,L2 at 8 months and L3 at9 months.3.A total of 75 volatile substances were identified during L1 preservation,including 13 alkanes,11 alkenes,13 alcohols,4 aldehydes,22 esters,2 ketones,6acids,and 4 others.The relative contents of alcohols and aldehydes decreased gradually,and the relative content of esters showed a trend of first decreasing and then increasing.A total of 77 volatile substances were identified during L2 storage,including 15 alkanes,11 alkenes,14 alcohols,4 aldehydes,19 esters,5 ketones,5acids,and 4 others.The relative contents of esters,ketones and aldehydes decreased gradually,and the relative contents of alcohols showed a trend of increasing first and then decreasing.A total of 73 volatile substances were identified during the storage of L3,including 14 alkanes,12 alkenes,12 alcohols,4 aldehydes,21 esters,2 ketones,4acids,and 4 others.The relative contents of alkanes,aldehydes,ketones and acids all showed a trend of increasing first and then decreasing,while the relative contents of esters showed a trend of first decreasing and then increasing.4.When peppers with different salt concentrations were stored for 1 month,the indexes of Chao1,Shannon and Simpson all reached the maximum value,and then decreased.The indexes of L1 increased significantly when stored for 8 months.The indexes of L2 and L3 increased significantly when stored for 9 months.5.Proteobacteria and Firmicutes were the dominant phyla in all pepper samples during preservation,followed by Bacteroidetes.Proteobacteria dominated in the early stage of pepper preservation,accounting for 83.35%,96.04% and 83.96% of L1,L2 and L3,respectively.When stored for 4 months,the relative abundance of Firmicutes in L1,L2 and L3 all reached the maximum value,which were 44.65%,39.96%,and43.19%,respectively;when stored for 5-7 months,the relative abundance of Firmicutes in all pepper samples was reduced.The relative abundance of Bacteroidetes and Fusobactecia in all pepper samples increased significantly when stored for 8-10 months.There were 32,33 and 26 bacterial species with relative abundances greater than 2% at the genus level during L1,L2 and L3 preservation respectively.When stored for 1-3 months,the absolute dominant bacteria in all pepper samples were Pseudomonas;when stored for 4-7 months,Lactobacillus,Streptococcus,Bifidobacterium were found in all pepper samples and the relative abundance increased significantly;the relative abundance of Muribaculaceae and Bacteroides also increased in all pepper samples during storage from 8-10 months.