| Fresh chestnuts contain a lot of water and are prone to decay and deterioration,which are not suitable for storage and transportation and may cause a substantial waste.The deep processing of chestnut into chestnut powder to prolong the storage period of chestnut is in accordance with the demand of consumers for diversified products and is conducive to improving the added value of chestnut.However,nowadays,the commercially available chestnut flour is mostly applied as semi-finished products added to bread and cakes,also its processing mostly develops from small-scale farmers.These are accompanied by high price,unstable quality,and poor color and flavor for brewing.Based on the screening of chestnut flour process,the key factors affecting the color of chestnut flour were found through correlation analysis,and the free amino acid content was analyzed by principal component analysis to investigate the mechanism of color formation of chestnut flour.A green and healthy instant chestnut paste with good color and flavor was formulated through amylase compound hydrolysis to provide a reference and theoretical basis for the deep processing of chestnut.The main research results are as follows.(1)Three ripening treatment methods of steaming ripening,boiling ripening and baking ripening,as well as the two drying methods of hot air drying and vacuum freeze drying were compared.Temperature and time gradient were set,then the color value and sensory evaluation of chestnut powder were applied as evaluation indexes.The best consistency under hot air drying conditions(60℃,1.5 h)and the best color and flavor under hot air drying conditions(100℃,3.5 h)were obtained through screening after roasting and maturing(200℃,25 min).(2)Nutritional indexes such as total free amino acids,soluble protein,reducing sugar and soluble solids of the products were determined under different treatment conditions,the color difference values of the samples were measured and the comprehensive analysis was combined with sensory evaluation.The contents of each free amino acid,glucose,fructose,sucrose and maltose in the samples under different treatment conditions were obtained by HPLC.The measurements showed that the main free amino acid species in chestnut powder were: proline,threonine,aspartic acid,glutamic acid and serine;the main watersoluble sugar was sucrose,whose content could reach to 220.887±5.659 mg/g after baking and maturation and hot air drying treatment,and the highest content in the control group was 165.639±5.909 mg/g;The indexes and the color difference value of chestnut flour were under correlation analysis and results showed that there was a highly significant correlation(P < 0.01)between various sugar substances,amino acids and soluble proteins,which indicated that the color change of chestnut flour was closely related to the melad reaction;the results of the principal component analysis of each free amino acid showed that contents of leucine,proline,lysine,tyrosine,phenylalanine,methionine,histidine,glycine,threonine,and sulphuric acid affected the color change of chestnut flour.The changes in the content of leucine,proline,lysine,tyrosine,phenylalanine,methionine,histidine,glycine and threonine affected the L* value of chestnut flour;the changes in the content of alanine and aspartic acid affected the b*,ΔE* and a* values of chestnut flour,which further verified that a large number of free amino acids were involved in the color change of chestnut flour.(3)To solve the problem of insufficient sweetness of chestnut flour,the conditions ofα-amylase,β-amylase and saccharase saccharification parameters(temperature,time,p H,addition amount),different combinations and saccharification methods were screened,and the experimental results showed that the addition amount of α-amylase(as a percentage of chestnut mass)was 0.2%,the addition amount of saccharase(as a percentage of chestnut mass)was 0.9%,the temperature was 62℃,p H 6.0,time 0.5 h,the one-step saccharification method had the best saccharification effect,with reducing sugar content of16.205±0.478% and soluble solids content of 17.833±1.041%,compared with0.266±0.074% and 4.667±0.289% in the control group.The formulation design was carried out with the pre-screened optimal group and optimized as(color and flavor optimal group)A:(viscosity optimal group)B:(saccharification group)C(mass ratio)= 5:1:4;to further optimize the chestnut paste and increase the flavor diversity of chestnut paste,the optimal amount of addition(to the mass ratio of chestnut paste)was determined by single-factor experiment as: red date powder 10%,corn flour 20%.It could be applied in practice to provide a feasible novel approach and theoretical basis for deep processing of chestnut.(4)The quality analysis of the blended and commercially available products was compared,and the sensory evaluation of each product was performed;physical properties such as color difference,viscosity and particle size;nutritional indicators such as total free amino acids,soluble protein,reducing sugars and starch were determined;microbiological indicators such as total colony count and fungal count were determined.Combined with the sensory evaluation of the raw soy milk powder flavor and the abnormal peaks in the HPLC chromatogram of the commercially available finished product 1,it might be speculated that the purity of chestnut powder in the commercially available finished product 1 was not sufficient.In summary,through the screening of maturation and drying methods,the color and flavor of chestnut flour was optimized by baking maturation combined with hot air drying;the sweetness of chestnut flour was improved by enzymatic saccharification,and the optimal formulation of chestnut paste was obtained by compounding with auxiliary ingredients.The correlation analysis showed that there was a highly significant correlation between sugar substance,amino acid,soluble protein and color difference value,indicating that the color change of chestnut flour was closely related to the melad reaction;the principal component analysis further verified that a large amount of free amino acid was involved in the color change of chestnut flour. |
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