| Lotus root(Nelumbo nucifera Gaertn.)is one of the most important aquatic vegetables in China,combining nutritional and economic values,and due to its diverse cultivars,there are many kinds of root products,among which lotus root juice is widely welcomed by consumers because of its unique fragrance,but the quality of lotus root juice is the main factor for its limited market share.In this study,eight cultivars of lotus root with large planting area and high yield were used as experimental materials to study the basic components of lotus root raw materials and their differences in color,physical and chemical and processing quality indexes for juice production.The basic components of lotus root raw materials of different cultivars and maturity levels as well as the differences in color,physicochemical and processing quality indexes of freshly squeezed juice were investigated to screen out the cultivars and maturity levels of lotus root suitable for juice production,and correlation analysis was used to determine the common physicochemical and processing characteristics of lotus root raw materials suitable for juice production.In order to improve and enhance the quality of lotus root freshly squeezed juice,the enzymatic process conditions of compound enzyme were optimized by using lotus root cultivars and maturity with lower juice making quality as the research subject,and using juice yield,clarity and brightness L~*values as reference indicators.The nutritional and physicochemical qualities of lotus root freshly extracted juice and enzymatic juice were also compared and analyzed,and the volatile flavor substances of lotus root juice were investigated by using electronic nose and Headspace Solid-Phase Micro-Extraction coupled with gas chromatography-mass spectrometry(HS-SPME-GC-MS),and the results were as follow:1.Analysis of the basic composition of different cultivars of lotus roots at different maturity levelsThe results of the analysis of the basic composition of lotus root raw materials show that the brightness of lotus root flesh of different cultivars would show different trends with their own growth and development.With the increase of maturity,the degree of greenish flesh of lotus root decreases,and in December,it was inclined to red.The hardness of three Farinose lotus roots,Elian No.5,Miancheng lotus root and Elian No.9,gradually increased with maturity.With the increase of maturity,the water content of lotus root gradually decreased,starch and crude fiber content showed an increasing trend,while pectin content increased and then decreased.2.Evaluation of the suitability of different cultivars and maturity of lotus root for juice productionThe color quality,physicochemical quality and processing quality of freshly squeezed juice of lotus root of different cultivars and maturity were significantly different(P<0.05),and the quality indexes of freshly squeezed juice of lotus root were evaluated by principal component analysis to obtain a comprehensive score F.A total of 24 lotus root juice samples of 8 cultivars and 3 maturity levels were clustered into 5 categories using cluster analysis,and the top 8 lotus root cultivars and maturity levels in terms of overall score were clustered into Class I.The results showed that the overall quality of lotus root juice from this cluster was superior and more suitable as cultivars for processing juice production.The correlation analysis of the quality indicators of lotus root juice with the raw materials of the lotus root showed that the characteristics of lotus root cultivars suitable for processing juice are small brightness of the flesh,high juice yield,low starch and crude fibre content.3.Optimization of enzymatic process of lotus root freshly squeezed juice compound enzymeTaking Elian No.5-12 as the research object,the appropriate amount of amylase addition was determined with reducing sugar and soluble solids content as indicators,and the juice yield,clarity and brightness L~*values of lotus root juice were measured on the basis of single-factor and response surface experiments to study the optimization of enzymatic process for the compound enzyme of lotus root freshly squeezed juice.The results showed that the optimal addition of pectinase,cellulase and xylanase were 605U/g,346 U/g and 5056 U/g,respectively,and under these process conditions obtained:the juice yield was 85.05%,the clarification was 97.27%and the brightness L~*was 28.58.4.Quality and flavor characteristics analysis of lotus root freshly squeezed juice before and after enzymaticThe freshly squeezed juice and enzymatic juice were prepared by using Elian No.5-12 as the research object.By comparing the quality indexes of lotus root freshly squeezed juice,CK group and enzymatic juice,the results showed that the juice yield of enzymatic juice increased by 52.07%compared to freshly squeezed juice,the reducing sugar,soluble solids,protein and total amino acid contents in enzymatic juice were significantly(P<0.05)higher than that of freshly squeezed juice.The total phenolic content in enzymatic juice increased by 6.95%,the total flavonoid content increased by 44.93%,the browning degree reduced by 50%and the clarification degree increased by 168.18%compared with that of freshly squeezed juice.The comprehensive evaluation showed that the compound enzymatic digestion not only increased the content of nutrients and effective active ingredients in the lotus root juice,but also inhibited the browning of the lotus root juice during the preparation process and improved the clarification.The radar map of the electronic nose sensor showed that the electronic nose could rapidly detect the aroma components in lotus root juice,and its principal component analysis could clearly distinguish the three lotus root juice samples.The volatile flavor substances in the three lotus root juice samples were detected by headspace solid-phase microextraction-gas chromatography,and a total of 72 substances were obtained,with the highest content and rich variety of aldehydes contributing to the overall flavor of lotus root juice,followed by esters,aromatics and ketones.The types and contents of volatile flavor substances in lotus root juice varied greatly,among which the enzymatic juice had relatively high types and contents,containing 7 aldehydes,9 esters,9 aromatics,5 ketones,1 alcohol,5 acids,2 olefins,1 amine,5 pyrazines and 2 other categories,indicating that the enzymatic treatment with compound enzyme could increase the types and contents of volatile flavor substances in the freshly squeezed juice,making the overall flavor of lotus root juice richer and more concentrated,and played a role in natural aroma enhancement.In summary,the results showed that the comprehensive quality and flavor characteristics of lotus root enzymatic juice were better than those of freshly squeezed juice. |
PDF Full Text Request