Study On The Freezing And Storage Characteristics Of Jackfruit And Jackfruit Yoghurt

Jackfruit is a combination of edible and medicinal value.It is thick,soft,sweet and delicious,with a strong fragrance.It is very popular with consumers.However,its fruit shape is huge,and its preservation is difficult.It is not suitable for long-distance transportation.Because of the relatively concentrated time of market,most of the products on the market are fresh fruits and primary processed products,and the storage period is short.In order to solve these problems,we studied the law of freezing and storage at medium well different temperatures,so as to achieve long-term storage under the premise of quality assurance.(1)Pretreatment of jackfruit before freezing.The effects of different blanching temperature,blanching time,liquid material ratio and cooling temperature on enzyme activities of polyphenol oxidase(PPO)and peroxidase(POD)were analyzed.Three factors and three superior levels of hot blanching were obtained: Blanching temperature 70 ?,80 ?,90 ?,blanching time1 min,1.5min,2min and liquid material ratio 10:1,15:1,20:1.Using PPO enzyme activity as an index,the response surface test was carried out.The results showed that the best blanching conditions were Blanching 90 ?,blanching time 126 s and material liquid ratio 1:19.8,the predicted value of PPO enzyme activity was 28.919(0.01A/g)/min,the experimental value was 31.31(0.01A/g)/ min,and the coincidence rate between experimental value and predicted value was as high as92.36%.In the single factor experiment,the browning degree and Vc were used as the indexes.The results showed that the concentration of D-was 0.02%,0.04% and0.06% when the concentration of citric acid was 0.4%,0.6% and 0.8% respectively.The phytic acid concentration was 0.1%,0.2% and 0.4%.The concentration of Lcysteine was 0.05%,0.10% and 0.10%.The citric acid,D-isoascorbate sodium and phytic acid which had great influence on the color and browning of the protective coating were optimized.The optimum conditions were determined as follows: citric acid 0.4%,ascorbic acid sodium 0.06% and phytic acid 0.22%,and the browning degree of the predicted pigment was 0.133.The experimental verification shows that the actual value is 0.159,and the coincidence rate between the experimental value and the prediction is 81.76%.The optimum Vc for color retention was 8.47(mg/100g),p H5.17,total soluble sugar 18.92(g/100g),moisture content 81.59%,fat 0.28(mg/100g)and protein 2.05(g/100g).The index is better than blank treatment on the whole.(2)Study on freezingThe freezing curves of different treatments at different freezing temperatures(-20 ?,-30 ?,-40 ?,-50 ?,-60 ?,-70 ?,-80 ?)at different freezing temperatures were measured.In the blank group,the freezing curves of blanching andcolor treatment were consistent with the general law of food freezing,and they all belonged to quick freezing.The lower the freezing temperature is,the shorter the time from 0 ?-18 ? through the maximum ice crystal formation zone and the center temperature is.The time from 0 ?-18 ? through the maximum ice crystal formation zone and the center temperature is shorter than other temperatures,and the change is not significant.Blanching and color treatment had little effect on food freezing curve.The freezing point of the three groups treated at different temperatures was lower than that at-20 ??-30 ??-40 ?,and the supercooling point at-50 ??-60??-70??-80 ? was higher.The lower the temperature,the higher the supercooling point.The freezing point of the blank group is-2.1 ? ?-4.7 ?,the freezing point of the blanching group is-2.5 ? ?-3.8 ?,and the freezing point of the color protecting group is-2.6 ? ?-4.9 ?.The flavor of jackfruit was determined by PEN electronic nose.The flavor of jackfruit in the three groups treated with different treatments decreased with the decrease of freezing temperature.The slower the flavor changes,the closer to the flavor of fresh jackfruit.The flavor was frozen at-80 ? closest to the fresh jackfruit flavor.The blanching treatment had great influence on the flavor of jackfruit.In the analysis of loadings,in the blank group,sulfides,methyls,alcohols,aldehydes and ketones,nitroxides are the major contributors to the first principal component,and sulfides,methyls,alcohols and aldehydes and ketones are the major contributors to the second principal component.In scalding group,sulfide,nitrogen oxides,methyl group,aromatic group,alcohol group and aldehyde ketone group contributed more to the first principal component,while sulfide,nitrogen oxides and aromatic group contributed more to the second principal component.For the color protection group,methyl,sulfide,aromatic,organic sulfide,alcohol and aldehyde ketone contribute more to the first principal component,while sulfide,aromatic,organic sulfide and nitrogen oxide contribute more to the second principal component.The fresh cells are intact.Low temperature can destroy cells to a certain extent,but with the decrease of freezing temperature,the degree of cell damage is getting lower and lower,and cells can better maintain their morphology.The blank group was frozen at-10 ? ?-40 ?,without intact cells.The cells frozen at-50 ? ?-80 ?were tightly connected and close to the fresh cells.Blanching has a very significant effect on the cells,and cell collapse is not formed.In the color protection group,intact cells were frozen at temperatures below-30 ?,and proper coloring treatment helped to maintain the original morphology of the cells.With the decrease of freezing temperature,p H,electrical conductivity and malondialdehyde content decreased,hardness increased,moisture content and chromatic aberration L fluctuated,and sensory scores were good.Hot blanching is conducive to moisture content,electrical conductivity and malondialdehyde maintenance.Color protection helps to maintain hardness,delay softening,blanching and color protection.Considering the cost,combined with sensory score,-30 ? is the best.At this time,the moisture content of jackfruit was 80.94%,p H was 5.21,hardness was 10.7N,conductivity was 725 ?s/cm,malondialdehyde(MDA)was 1.27?mol/g,the color difference before thawing was 65.92,the color difference L valueafter thawing was 63.22,and the sensory score was 95.(3)Changes in quality of jackfruit during storageThe quality of storage at different storage temperatures(-10 ?,-20 ?,-30 ? and-80 ?)at different storage temperatures was measured.MDA,dry consumption,juice loss rate and electrical conductivity increased with the prolonging of storage time.PH decreased with the prolongation of storage time,and these indexes all changed slowly with decreasing storage temperature.With the increase of storage time,the difference between flavor and freshness was more and more serious,but the flavor changed slowly.The slower the storage temperature,the slower the change.Among them,blanching had a great influence on flavor,and the difference between hot and fresh flavors was significant.However,the change of flavor after blanching was more obvious,and the flavor change was slower than that of blank group and color protecting group.The major components of jackfruit's main flavoring components were sulfides,nitrogen oxides,aromatic compounds,organic sulfides,methyl compounds,alcohols and aldehydes and ketones.Combined with sensory score,storage time of three groups can reach 180 days when stored at-30? and-80?.-80? can store longer time.After blanching treatment,storage at-10? and-20?can reach 160 days,while blank and color protecting groups are stored at 80-10 for80 days,and stored at-20?.All indexes indicated that-80? was the best storage temperature.But considering the quality change of jackfruit and equipment investment and operation cost,the best production temperature is-30?.That is to say,the best process is to remove the kernel of Hainan jackfruit honey and cut the flesh of half cut jackfruit.The weight of each jackfruit meat is about 11.5?12.5 g,which is blanched at 90 ? and blanching time 126 s,the material liquid ratio is 1:19.8,and the storage time is up to 180 days after blanching at-30 ?.(4)Process optimization of sour yogurtBy analyzing the effect of single factor experiment on sensory score and DPPH clearance ability of jackfruit yogurt,a better single factor was obtained.Then the orthogonal test of six factors and three levels was carried out.Orthogonal experiments showed that the influence of jackfruit yogurt on the quantity of jackfruit yogurt,fermentation temperature,inoculation amount,sucrose,gelatin and fermentation time were optimized.The optimized formula of jackfruit yogurt was 16% jackfruit,11%sucrose,0.6% gelatin,0.004 g inoculation,6 hours and 44 degree temperature,and the DPPH clearance rate was 83.10%.