Study On The Quality Evaluation System Of Dried Persimmon And The Influence Of Drying On Its Texture

Dried persimmon is a kind of dried fruit products,with soft,fragrant,sweet quality.At present,the research on dried persimmon by hot air mainly focuses on the removal of its moisture and astringent,and there are few researches on the evaluation and influencing factors of its texture.However,the soft texture is the characteristic of dried persimmon,which is also the key factor to evaluate its quality.Therefore,this paper evaluates the quality of the commercially available dried persimmon,establishes the chemical data model of the quality evaluation,and compares the quality difference between the hot air-dried persimmon and the traditional dried persimmon,and discuss the factors affecting the texture of dried persimmon during hot air drying,and clarify the formation mechanism of texture,which provided a theoretical basis for further optimization of hot air drying process.The experimental results obtained in this paper were as follows:（1）The quality evaluation indexes of the commercially available dried persimmon were analyzed,and the evaluation model of dried persimmon grade is established by using PLS regression analysis:Y=0.848-0.074X₁-0.091X₂+0.001X₃+0.039X₄-0.959X₅+0.756X₆+9.540X₇+0.644X₈+10.463X₉+0.058X₁₀-0.056X₁₁-0.851X₁₂(Among them,X₁～X₁₂ are soluble solids,fructose,glucose,sucrose,soluble pectin,protopectin,soluble tannin,total acid,cellulose,bound water,immobilized water and free water respectively),determined that the first-class dried persimmon Y is 0.6 to 1.4,the second-class Y is 1.6 to 2.4,and the third-class Y is 2.6 to 3.4.The six indexes of cellulose,soluble pectin,protopectin,free water,bound water and immobilized water were the main factors influencing the classification of dried persimmon.（2）The quality of the traditional dried persimmon and the hot air dried persimmon was compared and analyzed.The results showed that the quality of the 50℃hot air dried persimmon could meet the requirements of the local standard.However,compared with the traditional dried persimmon,there is still a large gap,which is mainly reflected in the sensory indexes such as skin,tissue structure,hardness,elasticity and viscosity,reflected in the chemical indicators are mainly pectin,cellulose,bound water,immobilized water and free water.The content of WSP（47.79～87.88 mg/g AIR）,the relative content of immobilized water and free water（1.09～2.11%和0.12～0.37%）and the degradation rate of cellulose（28.59～49.32%）of 50℃hot air dried persimmon with 30-40%water content were lower than those of traditional dried persimmon（94.74～116.96 mg/g AIR,1.78～7.53%,0.40～1.12%and35.63～61.67%respectively）,and the content of CSP and NSP（29.89～58.79mg/g AIR and 149.40～208.64 mg/g AIR）and the relative content of bound water（97.56～98.77%）were higher than those of traditional dried persimmon（22.75～44.31 mg/g AIR,73.44～139.72 mg/g AIR and 91.38～97.59%respectively）.Correlation analysis showed that the texture parameters were closely related to pectin,cellulose and water state,indicating that the changes of these indexes could reflect the changes of texture.In addition,texture parameters were significantly correlated with all sensory indexes,so texture parameters could be used to replace sensory indexes.（3）We characterized the water state,cell wall components and related modifying enzymes involved in the development of persimmon texture during the drying process of persimmon were characterized,and the formation mechanism of persimmon texture was clarified:During the drying process,temperature will affect the activity of pectinase and physiological respiration,which will lead to changes in pectin composition and moisture status.As a result,persimmon has formed a texture with low hardness and high viscosity in the simulation of traditional drying,and a texture with high hardness and low viscosity in hot air drying.In the early stage of drying,the increased activity of PME promoted pectin solubility,which increased the relative content of WSP and immobilized water,and caused persimmon softening.Within a certain range,increasing the drying temperature can improve the PME activity and increase the accumulation of WSP,but it is easy to form hard shells on the surface of persimmon,leading to weakened physiological respiration and reduced the contact between enzyme and substrate,thus reducing the softening degree of persimmon.In the late drying stage,the enhanced action of PG leads to the degradation of pectin,and the relative content of immobilized water decreased,thus leading to the increase of hardness,elasticity and viscosity of persimmon.Correlation analysis showed that the texture of persimmon was closely related to pectin content and water state during drying.